basler sr8a

Basler SR8A Voltage Regulators forEmergency Diesel Generators

Technical Report

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WARNING:Please read the License Agreementon the back cover before removingthe wrapping material.

Equipment

Reliability

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Maintenance

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Cost

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

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EPRI Project Manager J. Sharkey

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA 800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Basler SR8A Voltage Regulators for Emergency Diesel Generators 1011109

Final Report, December 2004

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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IMPORTANT NOTICE

USE OF THIS DOCUMENT IS VOLUNTARY. IT IS NOT INTENDED FOR REGULATORY OR ENFORCEMENT PURPOSES. IT IS OFFERED FOR CONSIDERATION AND USE BY MEMBERS OF NMAC. USE OF THIS DOCUMENT AND ITS CONTENTS BY ANYONE OTHER THAN THOSE FOR WHOM IT IS INTENDED IS NOT AUTHORIZED. THIS DOCUMENT IS BASED ON CONSENSUS OF UTILITY PERSONNEL, WITH INPUT FROM THE MANUFACTURER AND OTHER CONTRIBUTORS. THERE MAY BE OTHER TECHNIQUES OR MEANS OF PERFORMING THE WORK OR ACTIVITIES DESCRIBED IN THIS DOCUMENT. QUESTIONS CONCERNING USE OF THIS MATERIAL SHOULD BE DIRECTED TO EPRI’S NUCLEAR MAINTENANCE APPLICATIONS CENTER (NMAC).

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CITATIONS

This report was prepared by

Nuclear Maintenance Applications Center (NMAC) EPRI 1300 W.T. Harris Boulevard Charlotte, NC 28262

Principal Investigator J. Sharkey

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Basler SR8A Voltage Regulators for Emergency Diesel Generators, EPRI, Palo Alto, CA: 2004. 1011109.

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REPORT SUMMARY

This report contains information to help utilities address emergency diesel generator voltage regulator issues.

Background Over 40% of domestic U.S. nuclear power plant emergency diesel generator (EDG) voltage regulators are obsolete. EDG voltage regulators, typically of 1950–60 vintage, have recently experienced aging and obsolescence issues that have created a heightened awareness among nuclear utilities because of the threat to overall EDG performance. The industry’s situation is complicated by parts shortages and limited or nonexistent manufacturer support. It is noted that all Basler Model voltage regulators are not obsolete at this time (other than the systems provided by Basler to support the EMD Mag Amp design), and their line is currently supported by nuclear EDG manufacturers or distributors and a Basler teaming arrangement with a third-party company.

Objectives • To provide guidance on maintenance and maintenance-related issues of Basler SR8A voltage

regulators in nuclear EDG service

• To provide maintenance guidance, including a description of specific voltage regulator systems; a review of failure history, tuning, troubleshooting, routine preventive maintenance tasks; and discussions of special maintenance tasks

Approach The project team’s approach focused on addressing (1) industry-wide voltage regulator maintenance issues (provided under separate cover) and (2) specific issues relating to specific models of voltage regulators.

The project team reviewed industry databases for EDG voltage regulator failure information and analyzed these data to identify common industry maintenance issues. The resultant maintenance issues were combined with the project team’s own expertise in maintenance, training, and troubleshooting to develop discussions on voltage regulator failures/problems, testing, obsolescence, and good practices. Tuning and troubleshooting information was added based on the project team’s extensive experience.

Original equipment manufacturer (OEM) materials and existing training materials were used to develop the voltage regulator descriptions. This document was then reviewed by consultants and utility personnel responsible for EDG system and voltage regulator maintenance.

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Results This report is one of a series of reports (each under separate cover) that provides component-specific information for five voltage regulators. This report provides information for the Basler SR8A voltage regulator; other reports provide information for the Portec (NEI Peebles) (EPRI product number 1011108), the Basler SBSR (EPRI product number 1011110), the EMD Mag Amp (EPRI product number 1011111), and the Basler SER-CB Voltage Regulators (EPRI report number 1011218). These reports describe each voltage regulator and its functional and support circuits. Details on tuning and guidance on bench testing are provided. Failures and problems, their respective solutions, and troubleshooting information are also provided along with guidance on specific obsolescence issues and preventive maintenance.

An additional report, Emergency Diesel Generator Voltage Regulator Maintenance Issues (EPRI product number 1011232), provides generic guidance applicable to all nine models of voltage regulators in service at domestic U.S. nuclear plants. A review and analysis of industry failure data is provided. EDG testing practices are discussed along with their impact on voltage regulators, including post-maintenance testing, power factor testing, and droop operation. Information on obsolescence and vendor support is provided as well as specific information relating to voltage regulator systems that are obsolete, and actions that station personnel can take to address obsolescence. The report also discusses some general industry good practices.

EPRI Perspective This series of reports provides users with several tools that they can use to cost-effectively address voltage regulator maintenance. Stations can use the provided troubleshooting guides, specific problems and solutions, tuning procedures, maintenance recommendations, and post-maintenance testing guidance to improve their EDG maintenance programs.

Keywords Voltage regulator Static exciter Emergency diesel generator Diesel engine Electrical maintenance

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EPRI Licensed Material

ACKNOWLEDGMENTS

Various individuals and organizations provided substantive contributions to this report. NMAC would like to recognize the following for their contributions, reviews, and support of this document. The time and consideration of each are greatly appreciated.

NMAC would especially like to recognize the technical contributions of Kevin Nichols and Robert Sawyers of ProTec, Inc., and Ted Bronson of Power Equipment Associates.

Paul Banaszak Turkey Point

David Blackwell Dresden

Branko Boži Krško, Slovenija

Ted Bronson Power Equipment Associates

Alan DeGracia Fitzpatrick

Clayton Erickson Kewaunee

Harry Epstein IEN Engineering

Erban Green Diablo Canyon

Rick Hermann Columbia Generating Station

Bill Hill Comanche Peak

Arvin Ho Exelon

Jeff Keene Pilgrim

Steve Kowalski Clinton Station

Roger Kulavich St. Lucie

Steve Laughlin Quad Cities

Skip Lehman Consultant

Kevin Nichols ProTec, Inc.

David Pederson Point Beach

Wayne Reynolds St. Lucie

John Rosenberger Surry

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Todd Sarver McGuire

Robert Sawyers ProTec, Inc.

Alan Smith Millstone

Jeff Warren Robinson

Don Willis Sequoyah

Laurentius Wyngaard Koeberg Nuclear Power Station

Gary Yezefski Comanche Peak

Basler Electric

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CONTENTS

1 INTRODUCTION ....................................................................................................................1-1 1.1 Background..................................................................................................................1-1 1.2 Contents ......................................................................................................................1-2 1.3 Highlighting of Key Points............................................................................................1-3

2 BASLER SR8A.......................................................................................................................2-1 2.1 Overview of the Basler SR8A Voltage Regulator.........................................................2-1

2.1.1 Ratings and Features..........................................................................................2-2

3 FUNCTIONAL CIRCUITS.......................................................................................................3-1 3.1 Sensing Circuit.............................................................................................................3-2 3.2 Error Detector ..............................................................................................................3-2 3.3 Error Amplifier ..............................................................................................................3-3 3.4 Power Controller ..........................................................................................................3-4 3.5 Stabilization Network ...................................................................................................3-5 3.6 Automatic Voltage Buildup...........................................................................................3-6 3.7 Operational Description ...............................................................................................3-7

4 SUPPORT CIRCUITS.............................................................................................................4-1 4.1 Droop ...........................................................................................................................4-1 4.2 Excitation Support: Series Boost Option......................................................................4-4 4.3 Motor-Operated Potentiometer ....................................................................................4-7 4.4 Manual Voltage Control ...............................................................................................4-8 4.5 Field-Conditioning Relay..............................................................................................4-9 4.6 Under-Frequency/Overvoltage Module (UFOV) ..........................................................4-9

4.6.1 Under-Frequency Circuit .....................................................................................4-9 4.6.2 Overvoltage Circuit............................................................................................4-10

4.7 Voltage Shutdown......................................................................................................4-11 4.8 Field Flash .................................................................................................................4-12

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5 CONNECTIONS .....................................................................................................................5-1 5.1 Sensing Terminals .......................................................................................................5-1 5.2 Field Power Terminals F+ and F- ................................................................................5-2 5.3 Terminal A- ..................................................................................................................5-2 5.4 Input Power (Terminals 3 and 4)..................................................................................5-2 5.5 Droop Input Terminals 1 and 2 ....................................................................................5-2

6 TUNING ..................................................................................................................................6-1 6.1 Range Adjustment (R3 Potentiometer) ........................................................................6-3 6.2 Stability Adjustment (R4 Potentiometer) ......................................................................6-5 6.3 Droop Adjustment (R25 Slide Wire Resistor)...............................................................6-6

7 BENCH TEST .........................................................................................................................7-1

8 FAILURES AND PROBLEMS................................................................................................8-1 8.1 Erratic R3 Potentiometer..............................................................................................8-2 8.2 Erratic R1 Potentiometer..............................................................................................8-2 8.3 Erratic R4 Potentiometer..............................................................................................8-2 8.4 Failure of the SR8A Electronics...................................................................................8-2 8.5 Failure of the MOP Diode Bridge.................................................................................8-2 8.6 Voltage Droop in Isochronous Mode............................................................................8-2 8.7 Poor or Open Connection at Sensing PTs...................................................................8-3

9 TROUBLESHOOTING ...........................................................................................................9-1

10 OBSOLESCENCE..............................................................................................................10-1 10.1 Obsolescence .......................................................................................................10-1 10.2 Other Parts Issues ................................................................................................10-1

11 PREVENTIVE MAINTENANCE..........................................................................................11-1 11.1 Thermography.......................................................................................................11-2

12 REFERENCES ...................................................................................................................12-1

A LISTING OF KEY INFORMATION ....................................................................................... A-1

B U.S. PLANTS AND THEIR RESPECTIVE DIESEL MANUFACTURERS AND VOLTAGE REGULATOR MODELS ........................................................................................ B-1

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C TRANSLATED TABLE OF CONTENTS .............................................................................. C-1 Français (French) ................................................................................................................. C-2

日本語 (Japanese) ............................................................................................................... C-7

Español (Spanish).............................................................................................................. C-14

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LIST OF FIGURES

Figure 2-1 Brushless Exciter......................................................................................................2-2 Figure 2-2 Typical Model Number..............................................................................................2-4 Figure 3-1 Block Diagram ..........................................................................................................3-1 Figure 3-2 Sensing Circuit .........................................................................................................3-2 Figure 3-3 Error Detector ...........................................................................................................3-3 Figure 3-4 Error Amplifier...........................................................................................................3-4 Figure 3-5 Power Controller.......................................................................................................3-5 Figure 3-6 Stabilization Network ................................................................................................3-6 Figure 3-7 Voltage Buildup Circuit .............................................................................................3-7 Figure 3-8 Lower Signal.............................................................................................................3-8 Figure 3-9 Raise Signal .............................................................................................................3-9 Figure 4-1 Quadrature Connection ............................................................................................4-2 Figure 4-2 Unity Power Factor ...................................................................................................4-3 Figure 4-3 Lagging Power Factor ..............................................................................................4-4 Figure 4-4 SBO Internal Diagram ..............................................................................................4-5 Figure 4-5 SBO Internal Diagram ..............................................................................................4-5 Figure 4-6 SBO Connections to CTs .........................................................................................4-6 Figure 4-7 Motor-Operated Potentiometer Internals ..................................................................4-7 Figure 4-8 Manual Voltage Control Connections .......................................................................4-8 Figure 4-9 Under-Frequency Characteristic.............................................................................4-10 Figure 4-10 UFOV Connection Diagram..................................................................................4-11 Figure 5-1 Brushless Exciter Connections.................................................................................5-1 Figure 5-2 CT Connections to the Droop Circuit ........................................................................5-3 Figure 6-1 Wiring Diagram.........................................................................................................6-2 Figure 6-2 Component Location ................................................................................................6-3 Figure 7-1 Bench Test ...............................................................................................................7-2

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LIST OF TABLES

Table 8-1 Summary of Basler SR8A Voltage Regulator Experiences .......................................8-1 Table 9-1 Symptoms, Possible Causes, and Solutions to Problems with SR8A Voltage

Regulators..........................................................................................................................9-1 Table B-1 U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator

Models............................................................................................................................... B-1

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1 INTRODUCTION

1.1 Background

Emergency diesel generators (EDGs) have been a key industry issue since the early 1980s due to their importance to plant safety. Industry initiatives from the U.S. Nuclear Regulatory Commission (NRC), Institute of Nuclear Power Operations (INPO), Nuclear Energy Institute (NEI), EPRI, and the EDG owners groups have helped the industry to improve EDG system performance over the past 20 years.

Industry initiatives that have had a significant impact on EDG system performance include the establishment of improved technical specifications that reduce wear and tear on the engines, the establishment of EDG reliability programs, and the development of performance-based maintenance programs that minimize intrusive EDG inspections.

Owing to performance trends of the equipment over the last 20 years, much of the industry’s attention was focused on mechanical aspects of system performance. Though overall performance has improved, recent aging and obsolescence issues have indicated that more attention to electrical and electronic control system performance is needed. One electronic component critical to successful EDG operation is the voltage regulator.

Voltage regulators maintain a constant generator terminal voltage for emergency operation and control the VAR output from the generator when it is in parallel with the grid for testing purposes. These voltage regulators, typically of 1950–60 vintage, have recently experienced aging and obsolescence problems that have heightened awareness among nuclear utilities because of the threat to overall EDG performance. Over 40% of domestic U.S. nuclear power plant EDG voltage regulators are obsolete. It is noted that all Basler Model voltage regulators are not completely obsolete (other than the systems provided by Basler to support the EMD Mag Amp design), and their line is currently supported by nuclear EDG manufacturers or distributors and a Basler teaming arrangement with a third-party company. The industry’s situation is complicated by parts shortages, limited or nonexistent manufacturer support, and limited station knowledge of EDG voltage regulator issues or operating principles—making troubleshooting difficult.

NMAC has developed a series of reports to address concerns about the maintenance of EDG voltage regulators and to assist utility personnel with maintenance, testing, and troubleshooting of this equipment. These reports provide thorough system descriptions of specific voltage regulators and includes provisions on tuning, bench testing, troubleshooting, obsolescence,

1-1

EPRI Licensed Material Introduction

failures and problems, preventive maintenance, EDG testing, post-maintenance testing, and good practices.

The reports also identify voltage regulator systems in service at domestic U.S. nuclear power plants. The first in the series provides generic information applicable to all nine models of voltage regulators in service at domestic U.S. nuclear plants, including a section on the status of obsolescence issues with each voltage regulator system. This report for Basler SR8A voltage regulators and subsequent reports for the Portec (NEI Peebles), Basler SBSR, the EMD Mag Amp, and the Basler SER voltage regulators provide component-specific information. The EPRI report numbers are as follows:

1011232 – Emergency Diesel Generator Voltage Regulator Maintenance Issues (generic document) 1011108 – Portec (NEI Peebles) Voltage Regulators 1011109 – Basler SR8A Voltage Regulators 1011110 – Basler SBSR Voltage Regulators 1011111 – EMD Mag Amp Voltage Regulators 1011218 – Basler SER Voltage Regulators

1.2 Contents

This report provides component-specific information for the Basler SR8A voltage regulator in nuclear EDG applications.

Section 2 provides an introductory overview of the Basler SR8A voltage regulator.

Detailed descriptions of the Basler SR8A’s functional circuits are provided in Section 3; support circuits are provided in Section 4; and connections are provided in Section 5.

Section 6 provides detailed information on tuning of the Basler SR8A voltage regulator, and Section 7 provides information on its bench test.

Section 8 provides a discussion on experienced and anticipated failures and problems with Basler SR8A voltage regulators, and Section 9 provides detailed troubleshooting information for these regulators.

Section 10 addresses obsolescence concerns with the Basler SR8A voltage regulator along with other parts issues.

Section 11 addresses preventive maintenance for this voltage regulator, including a section on thermography.

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Introduction

1.3 Highlighting of Key Points

Throughout this report, important information is summarized in “Key Points.” Key Points are bold-lettered boxes that succinctly restate information covered in detail in the surrounding text, making the key point easier to locate.

The primary intent of a Key Point is to emphasize information that will allow individuals to take action for the benefit of their plant. NMAC personnel and the utility personnel who prepared and reviewed this report selected the information included in these Key Points.

The Key Points in this report are technical with an identifying icon, as shown below, to draw attention to it when quickly reviewing the guide.

Key Technical Point Targets information that will lead to improved equipment reliability.

Appendix A contains a listing of all Key Points in each category. The listing restates each Key Point and provides a reference to its location in the body of the report. By reviewing this listing, users of this guide can determine if they have taken advantage of key information that the writers of the guide believe would benefit their plants.

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2 BASLER SR8A

2.1 Overview of the Basler SR8A Voltage Regulator

The Basler SR8A voltage regulator is from the family of SR-A static voltage regulators. The voltage regulator is a static type that has no electrolytic capacitors. Specifically, the SR8A is used in applications requiring a 125 VDC field and 7 amperes maximum field current. The SR8A can be used in all three types of excitation systems (brushless rotating exciter, brush-type rotating exciter, and static exciter). Of the three types, the SR8A is most commonly used as part of a brushless excitation system. For nuclear EDG applications, the SR8A is used only as part of a brushless excitation system. In the nuclear industry to date, SR8As have been provided with EMD and Cooper-Bessemer engines.

For this type of excitation system, the exciter is enclosed within the generator housing and is mounted on the same shaft with the generator field windings. A rotating rectifier (sometimes called a diode wheel) is also mounted on the generator shaft.

Exciter field current is controlled by the SR8A voltage regulator, which can be varied as necessary to maintain the required generator output voltage. The brushless excitation system utilizes an AC exciter whose armature windings are mounted on the generator shaft, and the exciter field windings are mounted on the stator. The regulator controls the amount of field flux (proportional to field current) associated with the field windings. The rotation of the prime mover creates relative motion between the field flux and the rotating exciter armature windings. The AC output from the exciter armature windings is rectified by a rotating rectifier bridge and supplied directly to the generator field windings (see Figure 2-1). This greatly simplifies and reduces generator maintenance because it eliminates collectors, brushes, and brush riggings.

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EPRI Licensed Material Basler SR8A

Figure 2-1 Brushless Exciter

2.1.1 Ratings and Features

The SR8A has seven optional features that enhance the performance of the regulator. These features also provide unique system adaptations. These options are visible in the model number of the regulator. These features include:

• Parallel compensation

• Single- or three-phase sensing

• Voltage buildup relay

• Sensing voltage

• Cover type

• Voltage adjust rheostat

• Type of stability circuit

See Figure 2-2 for a model number breakdown.

The ratings of the SR8A are as follows:

Input Voltage Range 190–277 VAC Frequency 50/60 Hz VA 1680 Max. Continuous Output 125 VDC 7 Amperes 1-Minute Forcing 180 VDC 10 Amperes Sensing Voltage 120-139/208/240/416/480/600VAC ±10%

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Basler SR8A

Parallel Compensation 5 Amperes 25 VA burden Field Resistance 18 ohms

Although referred to as the Basler SR8A voltage regulator, the full designation would actually be something like SR8A2B06B3A:

SR8A - Model 2 - Has parallel provisions with an adjustable slide wire resistor B - Has voltage buildup provisions using a standard relay 06 - Sensing voltage is three-phase, 120 VAC B - Has a solid cover with perforated ends 3 - Has an externally mounted volts adjust rheostat A - Designates the type of stability circuit

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EPRI Licensed Material Basler SR8A

Figure 2-2 Typical Model Number

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3 FUNCTIONAL CIRCUITS

The voltage regulator senses the generator output voltage, compares a rectified sample of that voltage with a reference voltage (zener diode), and supplies the exciter field current required to maintain the predetermined ratio between the generator output voltage and the reference voltage. This unit consists of five basic circuits: a sensing circuit, an error detector, an error amplifier, a power controller, and a stabilization network. The block diagram is shown in Figure 3-1.

Figure 3-1 Block Diagram

3-1

EPRI Licensed Material Functional Circuits

3.1 Sensing Circuit

This circuit consists of sensing transformers T1 and T2; diodes CR1, CR2, CR3, CR4, and CR6; capacitor C1; resistor R16; and filter choke L1. Generator output voltage is sensed from potential transformers (PTs) connected to the generator terminals. This sensed voltage is applied to the E1, E2, and E3 terminals where it is transformed down by the T1 and T2 transformers. The sensed voltage is then rectified and filtered. The resultant DC voltage, which is proportional to generator output voltage, is applied to the error detector and error amplifier (see Figure 3-2).

A poor connection at the PTs will result in generator terminal voltage swings because the sensed voltage will appear to be changing. The voltage regulator will respond by varying exciter field current, which will cause generator terminal voltage to actually change.

A loss of one phase of the sensed voltage from the PTs will result in the voltage regulator driving excitation high. This can be caused by a blown PT fuse or an open connection at the PT cubicle, which typically occurs when the PTs are racked in following maintenance, but one of the stabs does not make contact. The next time the EDG is started, voltage builds up to an excessively high value, possibly causing damage. PT issues and problems are discussed in more detail later in this section.

Figure 3-2 Sensing Circuit

3.2 Error Detector

The error detector consists of reference (zener) diode VR1 and a voltage divider network consisting of resistors R1, R2, R3, and R5. This network provides a DC signal that is proportional to generator output voltage. The voltage at the junction of R3 and R5 is compared to the voltage of VR1 to develop the error signal, which is applied to the error amplifier (see Figure 3-3).

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Functional Circuits

R1 is the set point potentiometer that is motor driven. The Basler designation for this motor-operated potentiometer is a motor-operated controller (MOP), although it is more commonly referred to as a motor-operated potentiometer (MOP). R1 is a 175-ohm, 25-watt potentiometer that has been problematic at a number of plants. This problem is generic in that motor-driven potentiometers are routinely the weakest link in any voltage regulating system. The problem is typically a case of having a “dirty potentiometer.” A dirty potentiometer can be due to oxidation of the resistive element or fouling with foreign material (dust or dirt, for example). Indications of a dirty potentiometer for R1 are voltage or VAR swings.

R3 is the range potentiometer, although it really adjusts level, and range is established based on the setting of the end-of-travel limit switch cams on the MOC. R3 is a 150-ohm, 5-watt, wire-wound potentiometer that has also been problematic at a number of plants. The problem is typically a case of having a dirty potentiometer. Indications of a dirty potentiometer for R3 are voltage or VAR swings. This potentiometer has a locknut to secure it once adjusted.

Figure 3-3 Error Detector

3.3 Error Amplifier

This amplifier consists of a two-stage transistor amplifier (Q1 and Q2), a unijunction transistor (Q3), emitter follower (Q4), and their associated components. The error signal drives Q1, which, in turn, controls Q2. Transistor Q2 controls the charging time of capacitor C4 in the emitter circuit of Q3, thus providing phase angle control of the firing signal applied to the SCRs in the

3-3


power controller. Transistor Q4 provides the correct voltage to Base 2 of Q3 to maintain uniform SCR firing (see Figure 3-4).

Figure 3-4 Error Amplifier

3.4 Power Controller

The controller consists of thyristors (SCRs) CR11 and CR12 and conventional diodes CR13 and CR14 in a bridge rectifier circuit. The amount of output current depends on the conduction time of the SCRs and the exciter field resistance. This circuit can be compared to a variable rectifier, placed between the power source (terminals 3 and 4) and the exciter field (terminals F+ and F-). See Figure 3-5.

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Functional Circuits

Figure 3-5 Power Controller

3.5 Stabilization Network

This circuit provides stable operation under all operating conditions. It consists of capacitors C6 and C7; resistors R27, R28, and R33; and variable resistor R4. This RC network injects a stabilizing signal from the power stage to the error amplifier to prevent hunting. R4 determines the amount of stability signal applied to the error amplifier (see Figure 3-6).

R4 is a 2500-ohm, 5-watt, wire-wound potentiometer that has been problematic at a number of plants. Like the R1 and R3 potentiometers, the problem is typically a case of having a dirty potentiometer. Indications of a dirty potentiometer for R4 are voltage or VAR swings. This potentiometer has a locknut to secure it once adjusted. The basis for the setting of this potentiometer is to achieve an acceptable transient response characteristic.

3-5


Figure 3-6 Stabilization Network

3.6 Automatic Voltage Buildup

The K1 relay provides for rapid voltage buildup on EDG start. Normally, closed contacts (relay de-energized) provide a current path around the SCRs to increase the rate of voltage buildup. When the generator voltage reaches approximately 75% of rated, the relay is energized, allowing the SCRs to take control (see Figure 3-7).

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Functional Circuits

Figure 3-7 Voltage Buildup Circuit

3.7 Operational Description

When generator output voltage increases with no adjustment, the voltage at the junction of R3, R4, and R5 becomes less positive with respect to the voltage on the emitter of Q1. Because Q1 is a PNP transistor, this causes the base-emitter junction of Q1 to become more forward biased. The emitter-collector junction of Q1 acts like a variable resistance in the voltage divider R11, Q1, and R6. The base of Q2 is tied to the junction of R11 and Q1 collector. When Q1 becomes more forward biased, the emitter-collector junction of Q1 passes more current. When this happens, the voltage at the junction of R11 and Q1 collector (Q2 base) becomes a greater positive. This causes transistor Q2 to conduct less. The effect of Q2 conducting less is seen at C4 as a greater resistance. The transistor Q2 emitter-collector junction controls the charge-discharge time of C4. When Q2 conducts less, it appears as a greater resistance in the series RC circuit of C4. This causes C4 charge-discharge time to increase. This, in turn, causes UJT Q3 emitter-to-B1 junction to take longer to forward bias. The gate pulse for the SCRs CR12 and CR11 is developed when capacitor C4 discharges through the emitter-B1 junction of Q3 through R27. When C4 takes longer to charge, it takes longer to forward bias the emitter of Q3. This causes the discharging of C4 to take longer, thus delaying the firing pulse to SCRs C11 and C12. Delaying the firing pulse causes less current to be delivered to the field, and generator voltage will decrease.

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Once generator output voltage starts to decrease, the stabilization circuit—C6, C7, R27, R28, and R29—injects a signal opposite of the voltage at the R4 and R5 junction to slow the response of the amplifier circuit. The resistance of R4 controls the amount of signal injected, thus changing the response time or stability of the regulator.

Change in the resistance of voltage-adjust potentiometer R1 will also change the current to the exciter field. If the resistance of R1 is increased, the junction of R3 and R5 will become less positive with respect to the emitter of Q1, and voltage will decrease as in the example above (see Figure 3-8).

Figure 3-8 Lower Signal

When the resistance of R1 is decreased, the voltage at the junction of R3 and R5 becomes more positive. This causes less forward bias to the base-emitter junction of Q1, which causes the voltage at the junction of R11 and Q1 collector to become less positive. Therefore, the base of Q2 is less positive, and Q2 is more forward biased. The resistance of the Q2 emitter-collector junction decreases, decreasing the RC time constant of C4.

This causes C4 to charge more quickly and forward bias the emitter-B1 junction of UJT Q3 more quickly. C4 will discharge through Q3 emitter-B1 earlier in the positive half-cycle, causing a gate pulse to be delivered earlier in the half-cycle. This causes more current to be delivered to the exciter field, raising generator output voltage (see Figure 3-9).

3-8


Functional Circuits

Figure 3-9 Raise Signal

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4 SUPPORT CIRCUITS

4.1 Droop

Operation of the SR8A automatic voltage regulator has been discussed thus far in terms of an isochronous mode (sometimes referred to as unit mode). Isochronous mode operation means that the automatic voltage regulator is performing only one function: maintaining generator terminal voltage at the set-point value established by the R1 motor-operated set-point potentiometer (MOP). Isochronous is the mode that the automatic voltage regulator is in when its associated EDG is called on to perform its design function of supplying emergency bus loads by itself.

Isochronous mode is satisfactory until the EDG is operated in parallel with the grid on the emergency bus, which is necessary to verify operability. In this condition, the grid—not the EDG—controls emergency bus voltage and, therefore, generator terminal voltage. This is a problem for the automatic voltage regulator because it is trying to regulate a voltage that is largely dictated by the grid.

Imagine that the set point, as established by the MOP, is 4160 V for the automatic voltage regulator. If the EDG is in parallel with the grid and the grid voltage changes, so will the terminal voltage of the EDG. Let us assume that grid voltage goes down, resulting in emergency bus and generator terminal voltage dropping to 4100 V. The automatic voltage regulator will then respond by causing an excitation increase to raise voltage back to 4160 V. The increase in excitation will result in an increased VAR output from the generator, but generator terminal voltage will not rise appreciably. The automatic voltage regulator will continue to increase excitation in the attempt to return voltage to 4160 V, which will continue to increase the VAR output. The end result is that the automatic voltage regulator will drive excitation and VAR output to the maximum in the attempt to control what it cannot. Had grid voltage increased instead of decreased, the automatic voltage regulator would have driven excitation low in response. Both of these scenarios result in tripping the EDG.

So although the isochronous mode of operation is desired when the EDG is supplying loads by itself (in emergency mode), it does not work when it is in parallel with the grid. Another mode is needed for parallel operation of the diesel generator; this is called droop mode (sometimes referred to as parallel mode). With the automatic voltage regulator in droop mode, the new role of the regulator is to maintain a constant VAR output for a given voltage. In other words, if grid voltage changes, the VAR output from the generator will change to a new steady-state value. With no operator action, the VAR output will be maintained at this new value by the automatic voltage regulator (as long as voltage stays the same). In order to modify a voltage regulator’s mode of operation, an actual droop circuit is needed.

4-1

EPRI Licensed Material Support Circuits

A droop circuit can best be viewed as a “liar” circuit. The droop circuit adds a small voltage, proportional to VAR load, to the sensing path. The automatic voltage regulator sees the sensed voltage after it has been modified by the droop circuit. Using the previous scenario again as an example, when grid voltage drops, causing generator terminal voltage to drop to 4100 V, the automatic voltage regulator responds by increasing excitation. This occurs because the sensing voltage from the PTs to the regulator dropped along with generator terminal voltage.

The excitation increase results in an increase in VAR output from the generator. This, in turn, causes the liar voltage, developed by the droop circuit, to increase. This voltage is summed with the sensing voltage from the PTs, causing the total voltage to be larger. When this voltage rises to its value prior to the voltage drop, the automatic voltage regulator is satisfied, and a new steady state is reached at a lower voltage and higher VAR output. In effect, the automatic voltage regulator was tricked into thinking that it successfully returned voltage to 4160 V.

Generator output current is measured by a current transformer (CT) (called the droop or parallel CT). This is a current transformer that measures current in a phase that is 90° displaced from the phase-to-phase sensed voltage that droop affects. The CT is generally placed in the B phase, and the affected sensed voltage is the A and C phase-to-phase combination. This type of connection is called a quadrature connection and results in out-of-phase current associated with VARs having an effect on voltage and in-phase current associated with watts having no effect. This current is converted to a voltage and added vectorially to two phases of voltage sensing (A and C). The effect is that the automatic voltage regulator senses that generator terminal voltage is higher than it actually is. Figure 4-1 shows the 90° relationship between B phase with respect to neutral and the A and C phase-to-phase combination. Because this naturally occurring 90° relationship is the way in which out-of-phase current associated with VARs has an effect on voltage and in-phase current associated with watts has no effect, care must be taken to ensure that no wiring errors occur that change the phase relationship between these electrical quantities.

Figure 4-1 Quadrature Connection

The droop circuit associated with the SR8A is composed primarily of resistor R25, transformer T3, and a CT.

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Support Circuits

The CT is installed in the B phase of the generator output. It develops a signal that is proportional in amplitude and phase to the line current. This current signal develops a voltage across resistor R25. A slide on R25 supplies part of this voltage to the primary of the transformer T3. The secondary windings of T3 are connected in series with the leads from the secondary of the sensing transformer T1 and the sensing rectifiers located on the printed circuit board. The AC voltage applied to the sensing rectifier bridge is the vector sum of the stepped-down sensing voltage (terminals E1 and E3) supplied through the T1 and T2 transformers and the droop CT signal supplied through the T3 transformer (terminals 1 and 2). The A phase is associated with terminal E1, and the C phase is associated with terminal E3. The voltage supplied from the droop circuit via T3 is very small in relation to the sensing voltage supplied via T1 and T2. As previously stated, care must be taken to ensure that the sensing voltage (terminals E1 and E3) and the droop signal (terminals 1 and 2) are connected to provide the correct phase and polarity relationship.

When the output from the EDG is strictly kW and no VARs, the voltage that appears across R25 (and T3 winding) leads the sensing voltage by 90° (because of the pre-established 90° offset from the quadrature connection). The vector sum of the two voltages is nearly the same as the original sensing voltage from the PTs; consequently, there is no effect on the automatic voltage regulator (see Figure 4-2).

Figure 4-2 Unity Power Factor

When there is a lagging VAR output from the EDG (VARs out), in addition to the kW output, the voltage across R25 becomes more in phase with the sensing voltage (because of the pre-established 90° offset from the quadrature connection). The combined vectors of the two voltages results in a larger voltage being applied to the sensing rectifier of the automatic voltage regulator. The result is that the out-of-phase current associated with VARs has an effect, yet the in-phase current associated with watts does not (see Figure 4-3).

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Figure 4-3 Lagging Power Factor

4.2 Excitation Support: Series Boost Option

The purpose of the series boost option (SBO) is to provide motor-starting or fault-clearing capability to generators with brushless exciters. The system allows the use of a brushless exciter in applications that would normally require the use of a brush-type exciter or series-boost exciter.

Many generators equipped with brushless exciters are required to sustain very substantial current overloads. These are normally associated with the starting of large motors. Typically, such overloads can be several times the normal running current. Some generators may also be required to maintain line current during brief short-circuit fault conditions. Generators equipped with brushless exciters are unable to meet these requirements due to the generator output providing the voltage regulator power. As the generator output decreases, the ability of the regulator to supply exciter field power also decreases. The SBO compensates for this limitation.

The SBO uses the principle of ferroresonant regulation to provide a stable, regulated voltage for the voltage regulator. Ferroresonance in this application is the property of the transformer design in which the transformer contains two separate magnetic paths with limited coupling between them. The output contains a parallel resonant tank circuit. This tank circuit draws power from the primary to deliver to the load. This resonance reduces changes in the supply voltage and provides a constant voltage to the load.

The SBO is supplied from two sources: a voltage source and a current source. The basic circuit is shown in Figure 4-4; an internal diagram of the SBO is shown in Figure 4-5. The voltage source is generator output voltage stepped down to 240 VAC. The current source is generator output current by use of two CTs. Components T1, L1, and C1 make up a reservoir assembly, which supplies the excitation power requirements when the generator is at no-load. During no-load conditions, the reservoir assembly should not be required to supply more than one-half of the total output capacity of the excitation system.

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Support Circuits

Figure 4-4 SBO Internal Diagram

Figure 4-5 SBO Internal Diagram

The current contribution is necessary to provide the additional excitation power for full-load requirements. Again, the current contribution is supplied by generator output current via two CTs. The current contribution is added vectorially to the current from the voltage source in the reservoir assembly.

During short-circuit or motor-starting conditions, the current contribution at the SBO must be correct for the amount of generator output current. The current transformer ratios are chosen based upon this. Correct phasing between the SBO input voltage and input current is vital: incorrect phasing will prevent the SBO from maintaining sufficient excitation current, and poor regulation will result.

The appropriate CT ratio is calculated in three steps, as described in the following paragraphs.

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First, the exciter field current supplied by the regulator during generator short circuit is calculated. This is a function of exciter field resistance and voltage regulator output at generator short circuit (180 VAC). During generator short-circuit conditions, the generator output is virtually zero. Because the regulator power stage is still receiving voltage from the excitation support system (SBO) and the regulator will be calling for full voltage, the voltage at the exciter field will be maximum, or 180 volts. The amount of exciter current developed will be a function of exciter field resistance.

Second, the amount of short-circuit generator line current that would result from the exciter field current above is determined. This is available from the generator manufacturer on a plot of exciter field current vs. generator line amps with the output of the generator shorted.

If generator line current is excessive (that is, >250–300% nominal) from the second step, resistance will need to be added in the exciter field circuit to limit generator line current to an acceptable value.

Third, the two values calculated above are crossed on a chart to find the appropriate CT ratio. Figure 4-6 shows the CT connections to the SBO.

Figure 4-6 SBO Connections to CTs

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Support Circuits

4.3 Motor-Operated Potentiometer

A motor-operated potentiometer is used to provide a remote means of adjusting the set point to the automatic voltage regulator. Basler’s name for this is a motor-operated controller (MOC). The potentiometer, which is designated R1 for the SR8A, is 175 ohms and rated for 25 watts. The MOP internals are shown in Figure 4-7. AC or DC input voltages of 24, 32, 48, or 120 volts can be used to drive the motor. For input voltages greater than 24 volts, series resistors are used to drop the additional voltage. The 24 VDC is applied to the motor through a network of external switches. These switches apply the 24 VDC to the motor in either polarity to operate the motor in the “raise” or “lower” direction. The raise and lower functions are generally controlled remotely by switches in the control room or locally by a panel.

Figure 4-7 Motor-Operated Potentiometer Internals

For EDG applications, 120 VDC is always used as the power source for MOP operation. Because of this, the internal rectifier allowing AC control power to be used provides no benefit. In fact, it is actually a liability in that if the internal rectifier fails, the MOP cannot be raised or lowered. A MOP is available from Basler that does not have the internal rectifier (part # 9 1481 00 106, MOC3502).

When “raise” is selected (positive applied to terminal 5, and negative applied to terminal 7), the potentiometer turns in the clockwise direction. This causes the wiper (terminal 15) to move toward terminal 14 of the MOP.

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When “lower” is selected, voltage is supplied to the motor (positive on terminal 7, and negative on terminal 5), causing it to turn in the counterclockwise direction. This causes the wiper to move toward terminal 16 of the MOP. Dynamic breaking is accomplished by shorting terminals 5 and 7, which will cause the shaft to stop within 10 milliseconds.

End-of-travel limit switches are used for both the raise and lower functions. These limit switches are cam operated. Two additional limit switches are provided to accomplish pre-positioning, and all limit switches are adjustable.

Pre-positioning allows the MOP to be positioned to a desired setting to ensure that the correct generator terminal voltage is achieved on EDG start. Pre-positioning is normally initiated on EDG shutdown.

4.4 Manual Voltage Control

Manual voltage control (MVC) is accomplished by use of a three-position switch, variable transformer, and rectifier assembly. The rectifier assembly consists of a single-phase full-wave diode bridge rectifier (see Figure 4-8).

Figure 4-8 Manual Voltage Control Connections

In manual mode, the auto-sensing portion of the SR8A voltage regulator is disconnected. The autotransformer and rectifier assembly provide the DC power to the exciter field. In manual mode, the MVC operates the SR8A voltage regulator as a field current regulator. The DC output from the variable supply at any one position depends on exciter and generator parameters and load conditions.

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Support Circuits

When in manual mode, generator output voltage must be controlled by the manual voltage adjust autotransformer. Complete system shutdown occurs when the switch is placed in the “Off” position. All terminals of the SR8A regulator are “maintenance safe” when the MVC is in the “Off” or “Manual” position.

4.5 Field-Conditioning Relay

The field-conditioning relay is used to minimize the transient upon the start of a large motor load. Upon a motor start, the field-conditioning relay inserts an additional resistance in the set-point path from the MOP to the automatic voltage regulator. This momentarily modifies the set-point input to the automatic voltage regulator. The additional resistance is in the form of a potentiometer, which is adjustable to determine the magnitude of the impact of the field-conditioning relay.

In addition to the field-conditioning relay, a synchronizer timer is often used. This timer is used to provide a short time delay prior to motor start. This allows sufficient time for raising generator terminal voltage in anticipation of a large motor start.

4.6 Under-Frequency/Overvoltage Module (UFOV)

The purpose of this unit is to reduce the generator terminal voltage in the event of a 4–7 Hz reduction in generator frequency. Additionally, this unit operates a shunt trip breaker that removes the input power to the automatic voltage regulator when the generator’s terminal voltage exceeds a preset level.

4.6.1 Under-Frequency Circuit

If the generator frequency decreases approximately 4–7 Hz below nominal frequency, the UFOV module assumes control of the regulator and reduces generator output voltage for any further decrease in frequency. This prevents the V/Hz ratio from becoming excessively high, which is damaging to downstream components that have windings. The curve and band are shown in Figure 4-9.

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Figure 4-9 Under-Frequency Characteristic

The graph indicates the percentage of generator output voltage obtained for a specific reduction in frequency. For example, if a 60-Hz generator is operating at 50 Hz, generator output voltage will be between 82% and 95% of nominal. The band in the envelope (that is, the shaded area in the figure) is a function of operational temperature and normal tolerance in components.

Once the speed of the generator is slow enough for the under-frequency circuit to function, a definite frequency-voltage relationship will be present. In general, the voltage will drop at a slightly faster rate than the speed. For example, at 50% of nominal frequency, generator output voltage will be less than 50% of nominal. The same relationship exists when generator frequency is increased. It should be noted that the field-flash relay overrides the function of the under-frequency circuit on initial start and voltage buildup.

4.6.2 Overvoltage Circuit

This circuit prevents a sustained overvoltage condition at the generator output. In the event of an overvoltage condition that exceeds the set point for this circuit, the automatic voltage regulator’s input power is interrupted by the circuit breaker. The circuit breaker is manually reset. If the overvoltage circuit breaker repeatedly trips on load rejection, the overvoltage trip is adjusted too low for the system requirements.

The tripping point for the breaker is factory preset at 130% of nominal generator output voltage. The adjustable range of the circuit breaker is 125–150% of nominal generator output voltage. If the circuit breaker trips at any time, the reason for the trip should be determined before the breaker is reset and voltage regulator operations are continued.

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Support Circuits

The UFOV module has an internal transformer with multiple taps to accommodate different input voltages. The module comes factory preset at 120 VAC. If the input to the power section of the regulator is other than 120 VAC, the tap can be adjusted to accommodate the input voltage.

If the UFOV is used with the SBO excitation support module, the UFOV sensing input should be installed on the SBO voltage input rather than the regulator input (see Figure 4-10).

Figure 4-10 UFOV Connection Diagram

4.7 Voltage Shutdown

For EDG applications, it is necessary to provide for the removal of excitation from the exciter field in an emergency or when the prime mover must be operated at reduced speed. The shutdown function is accomplished by removing the input power to terminals 3 and 4. When using the A- terminal for field flash, a double pole switch must be used.

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4.8 Field Flash

For EDG applications, automatic field flash is required to ensure a rapid buildup of generator terminal voltage and is typically initiated by speed switch. The DC field flash source is connected to the F+ and A- terminals. A station battery is used as the 125 VDC source in conjunction with a field flash resistor, which is necessary to drop voltage prior to application to the exciter field (because 125 VDC would be grossly excessive). Generally, the voltage applied to the field during field flash would be approximately 70% of no-load exciter field voltage (that is, the voltage required to yield nominal generator terminal voltage with the EDG output breaker open). Diode CR9 is provided to ensure that current is allowed to flow only from the station battery and not to the station battery.

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5 CONNECTIONS

Figure 5-1 illustrates brushless exciter connections in the SR8A voltage regulator.

Figure 5-1 Brushless Exciter Connections

5.1 Sensing Terminals

Terminals E1, E2, and E3 provide the sensing input connections to the SR8A for three-phase sensing. Internal sensing transformers (T1 and T2) are provided with taps for various sensing voltages, although 120 VAC is standard for EDG applications. As was discussed in Section 4.1, “Droop,” correct polarity to the sensing circuit must be maintained to ensure proper operation of the EDG in parallel with the grid on the emergency bus.

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EPRI Licensed Material Connections

There are some installations that use single-phase sensing. In those instances, the sensing input is on terminals E1 and E3. Voltage drop from the PTs to the sensing input terminals should be minimized for precise voltage regulation. In addition, a large voltage drop (from a bad connection or blown fuse, for example) will result in excessive generator terminal voltage.

5.2 Field Power Terminals F+ and F-

The exciter field is connected to terminals F+ and F-. The DC resistance of the field must be greater than 18 ohms for the SR8A in order to prevent exceeding the 7-amp rating of the SR8A at 125 VDC.

Good generator stability is obtained when the no-load output from the regulator at terminals F+ and F- is 10 VDC or greater. If the no-load voltage is less than 10 VDC, it may be necessary to add resistance to the exciter field if a stability problem exists.

5.3 Terminal A-

The SR8A regulator is equipped with an A- terminal for brushless exciters as a connection point for the field flash source (-) input.

5.4 Input Power (Terminals 3 and 4)

For EDG applications, the nominal power supplied to the SR8A input power stage is 240 VAC. These connections supply power to the full-wave bridge that directly supplies power to the exciter field through the SCRs, as previously discussed. The voltage source is the generator output after it is transformed down.

5.5 Droop Input Terminals 1 and 2

When a generator is required to be operated in parallel with the grid on the emergency bus (as all EDGs are), the SR8A must be equipped with the necessary droop circuitry. In addition to the internal circuitry, a CT connected to one phase of the generator output is required. This CT should deliver 3–5 amperes secondary current at full load and needs to be rated for at least 25 volt-amperes (VA). The phase relationship of this CT to the sensing input terminals must be correct for the EDG to share reactive load when it is in parallel with the grid on the emergency bus. For isochronous mode operation, the CT must be shorted to disable droop. Appropriate connections based on phase rotation are shown in Figure 5-2.

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Connections

Figure 5-2 CT Connections to the Droop Circuit

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6-1

6 TUNING

The SR8A has three adjustments associated with it: range, stability, and droop. These adjustments are normally performed following replacement of a failed SR8A. When a new SR8A is installed, R3, R4, and R25 should be set to the same resistance values as those in the SR8A that was removed. This provides only a starting point for the subsequent tuning to be performed; the tuning is described further in this section. Figures 6-1 and 6-2 show the wiring diagram and component locations, respectively. R1 is not provided as a part of the SR8A panel for EDG applications. As discussed previously, R1 is motor driven to allow for remote operation from the control room.


Tuning

6-2

Figure 6-1 Wiring Diagram


Tuning

Figure 6-2 Component Location

6.1 Range Adjustment (R3 Potentiometer)

As was stated previously, the R3 potentiometer actually adjusts level rather than range, even though it is called the range potentiometer. Range is adjusted by use of the end-of-travel limit switch cams.

The potentiometer used on the MOP (R1) has a total resistance value of 175 ohms. If the potentiometer were adjusted from end to end, therefore, a resistance change of 175 ohms would be expected. The effective resistance change is less, because the end-of-travel cams/limit switches prevent full travel of the potentiometer to ensure that it is not damaged as a result of being over-traveled. The effective resistance change value dictates the range. For example, assume that the end-of-travel cams are set such that the motor stops when the potentiometer is

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EPRI Licensed Material Tuning

15 ohms from each end. This would yield an effective resistance change value of 145 ohms. This would, in turn, result in some given range of generator terminal voltage based upon full travel of the potentiometer with the generator output breaker open. Assume that this generator terminal voltage change is 800 VAC for an R1 resistance change of 145 ohms end to end. The R3 potentiometer setting dictates whether this 800 VAC range is from 3500 to 4300 VAC or from 3700 to 4500 VAC but does not dictate that the range is 800 VAC. Again, this is dictated by the effective resistance change value of the R1 potentiometer (145 ohms). If the end-of-travel cams were adjusted such that the motor stops when the R1 potentiometer is 20 ohms from end to end, the resultant range would be less than 800 VAC. The R3 potentiometer setting would simply dictate the level of that range.

For EDG applications, the R3 potentiometer is adjusted based on the pre-positioning feature previously described. Pre-positioning is accomplished by the use of two additional MOP cams and limit switches. The intent is that the R1 potentiometer is placed in the appropriate position to achieve a generator terminal voltage of 4160 VAC on EDG start. The pre-positioning cams are adjusted to place the R1 potentiometer in a given position on EDG start (normally around the center of travel; however, there are exceptions to this). The R3 potentiometer would then be adjusted to achieve a generator terminal voltage of 4160 VAC with R1 in the pre-position.

This adjustment methodology results in a range that is more than adequate to operate the EDG from no load to full load. Basler states a range of ±10%, which is true only if the full 175 ohms of R1 are being used. Of course, the end-of-travel cams and limit switches prevent the full 175 ohms from being utilized. Because EDGs are not operated with a leading VAR output (VARs in), the necessary range would be about 7% total (+5% to achieve rated VAR output, -0% for leading VARs, and 1% on either side for margin). This assumes that droop is set within the industry standard band of 3–5%.

R3 is a 150-ohm, 5-watt, wire-wound potentiometer that is locked in place by use of a locknut. Because this potentiometer has been somewhat problematic, it is advisable to perform a “tap test” on this potentiometer once it is set and locked in place.

The intent of the tap test is to mechanically agitate the potentiometer to ensure that there is no resultant generator terminal voltage fluctuation (in effect, this is a way to simulate vibration at the potentiometer). This can also be performed on the bench with an ohmmeter connected to the potentiometer, although it is less effective because the potentiometer is at an arbitrary setting instead of its setting in the field.

In summary, if the SR8A has been replaced, set the R3 potentiometer to the same resistance value as the R3 potentiometer on the removed SR8A. Following EDG start, but prior to any manipulation of the MOP (ensuring that R1 is in the pre-position), adjust R3 to achieve the desired generator terminal voltage. Once R3 is set to the desired value, lock it in place and perform a tap test to ensure that the potentiometer is not erratic at this setting.

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Tuning

6.2 Stability Adjustment (R4 Potentiometer)

The terms feedback, dampening, and stability are all applicable to the R4 potentiometer, although it is most commonly referred to as the stability potentiometer. The R4 potentiometer controls the amount of feedback that is applied to the error amplifier stage. Normally, it is factory set between the 75% and 100% full clockwise (CW) position. This setting normally ensures good stability but tends to slow the response time of the automatic voltage regulator. For EDGs, this is an issue because aggressive automatic voltage regulator action is necessary for start time and load sequencing considerations.

If R4 is rotated counterclockwise (CCW), the automatic voltage regulator responds more aggressively to changes in generator terminal voltage; therefore, generator response time becomes faster. However, if rotated too far CCW, generator terminal voltage may oscillate (that is, hunt). It should then be rotated CW well above the point where oscillating occurs. The generator terminal voltage instability is likely to occur at no load.

The methodology for adjusting the R4 potentiometer is to introduce a step change in generator terminal voltage and observe the response of the automatic voltage regulator with a high-speed chart recorder monitoring generator terminal voltage (commonly referred to as a bump test). The acceptance criterion is that there is one overshoot and one undershoot prior to reaching steady-state set point (often referred to as quarter wave dampening). An industry standard is to cause a 5% step change or bump. A step change can be accomplished in several different ways, the most convenient of which is to transfer to the manual voltage regulator, create a 5% mismatch between the manual and automatic voltage regulators, and then transfer back to the automatic voltage regulator. It is advisable, for conservatism, to bump in the downward direction.

Other ways to cause a step change are to perform a full-load or partial-load reject. Keep in mind that this means rejecting VAR load, because kilowatt (kW) load has nothing to do with the automatic voltage regulator. This often proves to be more difficult logistically with EDGs in the nuclear industry.

Performing a bump test and capturing the applicable generator terminal voltage waveform data provide a way to adjust the R4 stability potentiometer to ensure optimal response of the automatic voltage regulator.

In summary, if the SR8A has been replaced, set the R4 potentiometer to the same resistance value as the R4 potentiometer on the removed SR8A. Use a recorder to capture the generator terminal voltage waveform on EDG start because this provides a first look at the response characteristic of the automatic voltage regulator. Introduce step voltage changes while capturing the generator terminal voltage waveform with a recorder, and adjust R4 as necessary to achieve the desired response characteristic (that is, one overshoot and one undershoot). Once R4 is set to the desired value, lock it in place and perform a tap test to ensure that the potentiometer is not erratic at this setting.

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Key Technical Point Adjusting the R4 potentiometer requires introducing a step change in generator terminal voltage and observing the voltage regulator response with a recorder; the step change is commonly referred to as a bump test. The bump needs to cause a 5% step change and one overshoot and one undershoot prior to reaching the steady-state set point. The bump can be accomplished in several different ways, the most convenient of which is to transfer to the manual voltage regulator, create a 5% mismatch between the manual and automatic voltage regulators, and then transfer back to the automatic voltage regulator. Other ways to cause a step change are to perform a full-load or partial-load reject. Keep in mind that this means rejecting VAR load because kW load has nothing to do with the automatic voltage regulator.

6.3 Droop Adjustment (R25 Slide Wire Resistor)

Unfortunately, the droop adjustment for the SR8A is made more difficult because the variable droop resistance is a slide wire resistor, not a potentiometer. A potentiometer would allow adjustment with the EDG in parallel with the grid on the emergency bus. This cannot be done when a slide wire resistor is used because of the risk of the slide losing contact during adjustment, which would result in a large VAR transient. As a result, the EDG has to be unloaded and the generator output breaker must be open prior to making an adjustment to R25. The EDG then must be paralleled and loaded again to check droop following the adjustment. An appropriate droop setting is 3–5%.

Note that if droop is set too low, small grid voltage changes will result in substantial VAR changes. If droop is set too high, generator terminal voltage may increase excessively on a load reject. For example, if a given EDG has 4% droop associated with its automatic voltage regulator and a load reject were performed by opening the EDG output breaker, generator terminal voltage would increase by 4% (4% of 4160 V ≈ 160 V). This assumes that the EDG was loaded to 100% of its kVAR rating. If the EDG were loaded to 50% of its kVAR rating, generator terminal voltage will increase by 80 V, and so on.

Performing load rejects is not the best means of checking droop as part of tuning a newly installed SR8A. However, when a scheduled load reject is performed, it is a convenient time to determine the percent droop of the SR8A to ensure that it is within the 3–5% band. The exception is that some plants perform their load reject test with a 0-kVAR output from the EDG—and droop cannot be determined in this case. The method by which percent droop is determined for load reject data is as follows:

1. Note the kVAR output from the EDG prior to opening the EDG output breaker.

2. Note the amount of generator terminal voltage increase when the EDG output breaker is opened.

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Tuning

3. Convert this voltage increase to what it would have been if 100% rated kVARs had been rejected.

4. Divide this voltage by the nominal generator terminal voltage to determine percent droop.

For example, assume that the 100% kVAR rating for a given EDG is 2000 kVARs, and the EDG was loaded to 1000 kVARs prior to rejecting load. Also assume that nominal generator terminal voltage is 4160 V for this EDG. Generator terminal voltage increases by 100 V upon opening the EDG output breaker. Because this is the 100% kVAR rating, if 2000 kVARs had been rejected, generator terminal voltage will have increased 200 V. Dividing 200 V by the nominal generator terminal voltage of 4160 V yields 4.8% droop.

The more accurately VARs and generator terminal voltage are measured, the more accurate the results.

Adjusting droop for a newly installed SR8A would start with setting the R25 slide wire resistor to the same resistance value as R25 on the removed SR8A. If droop was between 3% and 5% for the removed SR8A, it is likely to be between 3% and 5% for the newly installed SR8A; but, of course, this needs to be verified and adjusted if necessary. The process would be as follows for the same hypothetical EDG as described previously (2000 kVAR rating and nominal generator terminal voltage of 4160 V):

1. Start the EDG.

2. Raise generator terminal voltage 2% above the emergency bus voltage (approximately 80 V, in the example above).

3. Using a digital voltmeter (DVM), measure and record the voltage at the wiper of the R1 MOP (this provides a means of returning the MOP to the same position later).

4. Lower generator terminal voltage to what is appropriate for paralleling the EDG to the emergency bus.

5. Parallel the EDG to the emergency bus.

6. After establishing the desired kW output, raise the R1 MOP setting to achieve the same voltage at the wiper that was previously measured with a DVM and recorded.

7. If the kVAR output is 1000 kVARs (50% of rated), then droop is 4%. If the kVAR output is 1250 kVARs, then droop is 3%. If the kVAR output is 750 kVARs, then droop is 5%.

8. If droop is outside the 3–5% band, unload the EDG and open the output breaker.

9. Adjust the R25 slide wire resistor, parallel the EDG to the emergency bus, and check droop again.

6-7


Key Technical Point The SR8A has three adjustments associated with it: range (R3), stability (R4), and droop (R25). When a new SR8A is installed, set R3, R4, and R25 to the same resistance values as those in the SR8A that was removed. This provides only a starting point for the subsequent tuning to be performed. Following EDG start, but prior to any manipulation of the MOP (ensuring that R1 is in the pre-position), adjust R3 to achieve the desired generator terminal voltage. Next, while capturing the generator terminal voltage waveform with a recorder, introduce step changes and adjust R4 as necessary to achieve the desired response characteristic. Finally, set and check droop through adjustment of the R25 slide resistor, which is checked while the EDG is parallel with the grid.

6-8


7 BENCH TEST

An operational bench test may be performed on the SR8A before it is installed. The time is well spent to avoid installing a problematic voltage regulator, which, at a minimum, will delay restoring the EDG to operability. This test can be useful in troubleshooting as well as verifying that the regulator is functioning properly following repair.

1. Move SR8A T1 and T2 transformers to 240 VAC taps.

2. Adjust voltage stability potentiometer R4 completely CCW and R3 to mid-position.

3. Connect a dummy load, as shown in Figure 7-1. Light bulbs, if used, should be 120 volt, 100–200 watts (not more than 300 watts).

4. Connect a 175-ohm resistor as a substitute for R1, and adjust for maximum resistance.

5. Connect SR8A to a 240 VAC power source. (Light should flash momentarily.)

6. Slowly adjust the simulated R1 resistance toward minimum. The light should reach full brilliance before minimum resistance is attained. (If the light does not come on, adjust R3 until full brilliance is obtained.)

7. At the regulating point, a small change in voltage adjustment should turn the light bulb on or off.

Note: If the light stays on or off, the SR8A is defective.

8. This test may not reveal a stability problem; however, rotating the stability adjustment (R4) should affect the light’s turn-on and turn-off time.

9. Before reinstalling the SR8A into the system, change the T1 and T2 transformers back to the 120 VAC taps.

Note: An alternative method would be to use two power sources: one three-phase 120 VAC power source to provide the sensing input at terminals E1, E2, and E3 (Multi-Amp Pulsar or equivalent) and one single-phase 240 VAC power source to provide the power input to terminals 3 and 4 (variac).

7-1

EPRI Licensed Material Bench Test

Figure 7-1 Bench Test

In addition to performing the operational bench test, it is advisable to verify the condition of the R3 and R4 potentiometers because they are the most common source of problems with the SR8A. Connect an analog meter to each potentiometer and wipe it end to end. A smooth resistance change should be observed. If the resistance change is not smooth, wipe the potentiometer until it is. If wiping the potentiometer does not result in a smooth resistance change, do not install that SR8A. An additional test is to tap on each potentiometer with an analog meter connected and the locking nut tightened. If tapping on the potentiometer results in erratic meter movement, do not install that SR8A.

Key Technical Point An operational bench test can be performed to troubleshoot a problematic voltage regulator or to check a new voltage regulator prior to installation. The time is well spent to avoid installing a problematic voltage regulator, which, at a minimum, will delay restoring the EDG to operability. For the SR8A, this bench test should include verification of the condition of the R3 and R4 potentiometers, which have proven to be the most common source of problems with this voltage regulator.

7-2


8 FAILURES AND PROBLEMS

Table 8-1 lists problems, causes, and corrective actions for Basler SR8A voltage regulators identified from a search of voltage regulator problems taken from INPO databases over the past 16 years (1987 through 2004).

Table 8-1 Summary of Basler SR8A Voltage Regulator Experiences

Date Symptom Cause Corrective Action (Primary)

11/20/95 Large swings in VARs Failed potentiometer Replaced potentiometers on all EDGs

6/23/99 Voltage regulator selector switch to inoperable unit

No warning tag Revised procedure

11/14/01 Damaged voltage regulator

Faulty hookup of strip chart recorder

Training/communication on verification practices

5/30/02 VARs erratic R3 potentiometer failure Replaced potentiometer; investigating upgrade

10/16/02 Erratic generator reactive load

Inappropriate initial setting of R4: the value was set too low and the DG was overly sensitive to voltage/VAR transients from normal operation

Voltage regulator unit replaced and MOP cleaned

7/13/04 DG tripped on loss of excitation 3 hours into a 24-hour test run

Troubleshooting identified a failure of an oil-filled capacitor in the SBO portion of the voltage regulator

Replaced voltage regulator unit

The following list captures a vast majority of the failures/problems with the SR8A voltage regulator. Different from the information contained in Table 8-1, the following is based on direct industry voltage regulator failure analysis and troubleshooting experiences:

• Erratic R3 potentiometer

• Erratic R4 potentiometer

• Erratic R1 MOP

• Failure of SR8A electronics

• Failure of MOP diode bridge

8-1

EPRI Licensed Material Failures and Problems

• Voltage droop in isochronous mode

• Poor or open connection at the sensing PTs

8.1 Erratic R3 Potentiometer

As previously discussed, R3 is a 150-ohm, 5-watt, wire-wound potentiometer with a locknut to secure it in place. There have been a number of cases where a dirty R3 potentiometer has resulted in voltage/VAR swings. Wiping may “clean” the resistive element sufficiently to solve the problem; if not, the SR8A must be replaced.


R1 is a 175-ohm, 25-watt potentiometer. There have been a number of cases where a dirty R1 potentiometer has resulted in voltage/VAR swings. Wiping may clean the resistive element sufficiently to solve the problem; if not, the potentiometer needs to be replaced. It is typical to replace the whole MOP assembly rather than only the potentiometer.


R4 is a 2500-ohm, 5-watt, wire-wound potentiometer. There have been a number of cases where a dirty R4 potentiometer has resulted in voltage/VAR swings. Wiping may clean the resistive element sufficiently to solve the problem. If not, the SR8A must be replaced.

8.4 Failure of the SR8A Electronics

Failure of the SR8A electronics can be made evident by different symptoms, depending on the specific component that fails. Depending on the specific electronic component that fails, excitation can be driven low or high or can simply be erratic.

8.5 Failure of the MOP Diode Bridge

Failure of the bridge rectifier used by the MOP will result in the operator being unable to raise or lower excitation. This is an easy problem to identify: if there is no effect when the operator places the voltage control switch in the raise or lower positions, the first thing to check is whether the motor is turning the R1 potentiometer when the control switch is operated.

8.6 Voltage Droop in Isochronous Mode

Droop is disabled when the EDG is supplying loads on the emergency bus by itself (and not in parallel with the grid). This is accomplished by a contact (or contacts) being closed to short the secondary side of the droop CT. Because the R25 slide wire droop resistor is of a low ohmic value (typically <2 ohms), even an ohm or two of resistance in the shorting path will result in

8-2


Failures and Problems

some amount of droop. This would be noticeable during loss-of-coolant accident/loss of off-site power (LOCA/LOOP) testing because generator terminal voltage and, therefore, emergency bus voltage would be lower than they were originally after all loads had been sequenced on the bus.

Another scenario would be the lack of droop when the EDG is in parallel with the grid on the emergency bus. The result would be that EDG output VARs would be uncontrollable from the time that the EDG was paralleled to the emergency bus.

8.7 Poor or Open Connection at Sensing PTs

If a poor connection exists at the sensing PTs, voltage/VAR swings will result. A poor connection usually occurs at the stabs or a fuse/fuse holder. The sensing PTs are periodically racked out for EDG maintenance evolutions. The PT fuses are often pulled as well. Removing and installing these fuses repetitively over a period of years can cause a fuse to be loose in its holder, resulting in a poor connection. In addition, when the PTs are racked in, the contact stabs may not make good contact physically, or the surface could be oxidized or fouled.

If an open connection exists at the sensing PTs, the automatic voltage regulator will drive excitation high (this could be due to a blown PT fuse). This will result in generator terminal voltage being very high if not in parallel with the grid on the emergency bus. If the EDG is in parallel with the grid on the emergency bus, the lagging VAR output will be very high. For some installations, a voltage balance relay (60 device) is used to provide control room annunciation if there is an open connection from the sensing PTs.

Key Technical Point One of the most common problems with the SR8A voltage regulator is erratic performance of the R1, R3, or R4 potentiometers. The problem is typically a case of having a dirty potentiometer, which can be caused by oxidation of the resistive element or fouling with foreign material (dust or dirt, for example). Problems with these potentiometers are indicated by voltage or VAR swings.

8-3


9 TROUBLESHOOTING

Table 9-1 presents symptoms, possible causes, and possible solutions to problems with SR8A voltage regulators. Because voltage and/or VAR swings are the most common symptom, they are addressed in more detail following the table

Table 9-1 Symptoms, Possible Causes, and Solutions to Problems with SR8A Voltage Regulators

Symptom Possible Cause Solution (Primary) R1 voltage adjust potentiometer open

Replace R1 or entire MOP assembly

No firing pulses applied to SCRs Replace SR8A

Voltage builds up during field flash and then collapses

Blown power PT fuse Investigate cause and replace fuse No or low voltage from sensing PTs (terminals E1, E2, and E3)

Verify that there are no blown PT fuses and good connections at the PTs

R1 voltage adjust potentiometer shorted

Verify R1 condition with an ohmmeter

T1 and/or T2 transformer set to wrong tap (only possible if new SR8A was installed)

Verify tap setting of 120 VAC

Faulty K1 relay Replace relay

Faulty SR8A regulator Replace SR8A regulator

Voltage high and uncontrollable with R1 voltage adjust potentiometer

Shorted SCR or SCRs Replace SR8A regulator T1 and/or T2 transformer set to wrong tap (possible only if new SR8A was installed)


R3 range adjust potentiometer set too high (likely only if new SR8A was installed)

Perform R3 adjustment

Single-phase voltage applied to three-phase sensing regulator

Verify presence of three-phase voltage

Voltmeter inaccurate Verify operation and calibrate or replace voltmeter

Voltage high but controllable with R1 voltage adjust potentiometer

Faulty SR8A regulator Replace SR8A regulator

9-1

EPRI Licensed Material Troubleshooting

Table 9–1 (continued) Symptoms, Possible Causes, and Solutions to Problems with SR8A Voltage Regulators

Symptom Possible Cause Solution (Primary) R3 set too low (likely only if new SR8A was installed)

Perform R3 adjustment

Voltmeter inaccurate Verify operation and calibrate or replace meter

T1 and/or T2 transformer set to wrong tap (possible only if new SR8A was installed)


Voltage low but controllable with R1 voltage adjust potentiometer

Droop CT not shorted if in isochronous mode

Check resistance at terminals 1 and 2; terminals 1 and 2 should be shorted for isochronous mode operation

Voltage recovers slowly with load starts/stops

R4 adjusted incorrectly Perform R4 adjustment

UFOV module faulty Replace UFOV module Under-frequency circuit affects generator voltage output at normal speeds

Incorrect voltage applied to under-frequency circuit

Verify wiring and correct voltage applied to UFOV

Frequency not low enough UF threshold should be 4–7 Hz below nominal

Incorrect voltage applied to the UFOV module

Verify wiring and correct voltage applied to UFOV

Wrong model of UFOV module Check UFOV model number for correct application

Under-frequency circuit fails to reduce generator voltage as frequency is reduced

UFOV module faulty Replace UFOV module Faulty UFOV module Replace UFOV module UFOV fails to open circuit

breaker during overvoltage conditions

UFOV improperly adjusted Adjust the set point of the UFOV module

Voltage and/or VAR swings

Because this is the most common symptom, it warrants a more detailed discussion. The following are the most likely causes of voltage and/or VAR swings:

• Erratic R3 range adjust potentiometer

• Erratic R4 stability potentiometer

• Failed electronic component on SR8A PC board

• Erratic R1 voltage adjust potentiometer

• Poor connection at the sensing PTs

The first three require replacing the SR8A unless an erratic R3 or R4 potentiometer can be adequately cleaned by wiping. Many plants would choose to replace the SR8A simply to minimize the chance that the potentiometer could cause swings again. R3 and R4 can be checked once the EDG is shut down by measuring resistance with an analog meter while tapping on the potentiometers.

9-2


Troubleshooting

Because time is critical when an EDG is declared inoperable, there is merit to verifying that the problem is not the R1 voltage adjust potentiometer and not a poor connection at the sensing PTs and then replacing the SR8A. The specific faulty SR8A component can be determined in parallel with installing, tuning, and retesting the new SR8A. One method of identifying the faulty SR8A component is performing a bench test.

The method for finding a poor connection at the sensing PTs is to use an ohmmeter to measure resistance back through the PTs. If the leads are disconnected from the E1, E2, and E3 terminals, all three phase-to-phase combinations of resistance readings should be equal. Any additional parallel paths also need to be isolated to ensure that the measured resistance is associated with the PTs only.

The R1 voltage adjust potentiometer can be checked by measuring resistance with an analog meter and running the potentiometer end to end. If the voltage and/or VAR swings started when the operator made an adjustment to R1, that is the most likely faulty component. If the voltage and/or VAR swings started with no operator action, it is less likely, but still possible, that R1 is the faulty component. Also, if R1 is the cause because there is oxidation or foreign material on the resistive element, the symptoms may diminish as R1 is manipulated. For example, if there are VAR swings during an operability run, the operator is likely to unload and shut down the EDG. The process of unloading the EDG will necessitate the manipulation of R1 to bring the VAR output down to near zero. This manipulation may remove the fouling from the resistive element. Subsequent testing of R1 by use of an analog meter, as described above, may indicate that it is fine. This scenario results in not being able to find a “smoking gun.” It is important to be aware of this scenario, because it has occurred at many plants.

Key Technical Point The most common symptom of an SR8A voltage regulator problem is voltage and/or VAR swings, which, in many cases, can be caused by erratically performing potentiometers (R1, R3, or R4). In some cases, an erratic potentiometer can be adequately cleaned by wiping, though some plants choose to replace the SR8A simply to minimize the chance that the potentiometer could cause swings again. If the unit is replaced, a bench test can be used to help identify the faulty SR8A component.

9-3


10 OBSOLESCENCE

10.1 Obsolescence

As of the writing of this report, parts obsolescence is not a current or near-term concern for the Basler SR8A voltage regulator. The Basler SR series of voltage regulators has been supplied since the 1960s with a substantial number currently in service, particularly in non-nuclear, non-safety-related applications. Safety-related dedication is not performed by Basler but is performed by nuclear EDG suppliers and a third-party firm.

Lack of qualified service personnel is not currently a large issue in that Basler still has in-house personnel that are knowledgeable on the SR8A. In addition, there is at least one third-party company that has substantial SR8A expertise.

Based on the historical performance of the SR8A and the parts and service availability, there is no driving force to upgrade the system at this time.

Key Technical Point As of the writing of this report, parts obsolescence is not a current or near-term concern for the Basler SR8A voltage regulator. A substantial number of these units are currently in service, particularly in non-nuclear, non-safety-related applications. Safety-related dedication is not performed by Basler but is performed by nuclear EDG suppliers as well as a third-party firm. Based on the historical performance of the SR8A and the parts and service availability, there is currently no driving force to upgrade the system.

10.2 Other Parts Issues

As is the case with nearly all analog voltage regulating systems, the potentiometers are the weakest link. There have been discussions within utilities and with Basler to explore the possibility of using improved potentiometers in order to increase reliability. Specifically, there have been discussions with regard to using hermetically sealed potentiometers, especially as a replacement for R1. High-quality hermetically sealed potentiometers are available from companies such as Maurey Instruments. As long as the potentiometer has an appropriately sized shaft, it can be mounted to the motor drive as a replacement for R1. Qualifying a suitable replacement potentiometer would obviously need to be addressed.

Digital voltage regulators use electronic static voltage adjusters instead of a MOP to provide the set point. Woodward also makes a static adjuster that it refers to as a digital reference unit

10-1

EPRI Licensed Material Obsolescence

(DRU). Because these static adjusters are far more reliable than MOPs, there has been discussion within at least one owners group to replace the MOP with a DRU.

The SR8A utilizes no electrolytic capacitors.

Key Technical Point As noted previously, the potentiometers are the weakest link in the SR8A. Discussions are ongoing within utilities and with Basler to explore the possibility of using improved, more robust potentiometers in order to increase reliability. As such, improved potentiometers and other devices may become available in the near future to address this concern.

10-2


11 PREVENTIVE MAINTENANCE

The SR8A and its associated excitation system require very little maintenance compared to many of the other systems. The fact that this is a brushless excitation system eliminates maintenance associated with carbon brushes and collector rings that would otherwise have to be performed.

A thorough cleaning and visual inspection of the excitation system should be performed every two years. Most plants already have this as a maintenance task. Ensure that nonconductive hosing is used for dust removal and that the proper solvent is used—and in appropriate quantities. The sensing PTs need to be included in this cleaning and inspection to ensure that the contact points are clean and that the PT fuses are tight in their holders. In addition, it is beneficial to measure the resistance in the PTs once they are racked back in to ensure that there are good connections at the contact points.

It is also advisable to check the condition of the R1, R3, and R4 potentiometers every two years by measuring resistance with an analog meter. For the R1 voltage adjust potentiometer, resistance should be checked while it is run end to end, verifying a smooth resistance change. R3 and R4 should be checked once the EDG is shut down by measuring resistance with an analog meter while tapping on the potentiometers. Wiping the R3 and R4 potentiometers requires that they are adjusted afterward, as described in Section 6, “Tuning.” At least one owners group recommends periodic replacement of the R3 potentiometer.

Another item to note is that it is advantageous to capture the generator terminal voltage waveform on EDG start. This provides dynamic response trending data that can be valuable in detecting a degraded voltage regulator.

Key Technical Point The SR8A and its associated excitation system require very little maintenance compared to many other systems. The fact that this is a brushless excitation system eliminates maintenance associated with carbon brushes and collector rings. Because of the performance history of the potentiometers, they should be checked every two years. Some plants that have experienced poor performance of these potentiometers replace them periodically.

Currently, routine replacement intervals are not set for voltage regulators. If a station wants to set a replacement interval, it should consider all available station and industry experience in setting this interval for either the voltage regulator unit or subcomponents such as the potentiometers.

11-1

EPRI Licensed Material Preventive Maintenance

11.1 Thermography

As of the writing of this report, thermography is not commonly performed on the SR8A (or any other EDG excitation system). Thermography could be a very useful tool in identifying conditions that could affect reliability (due to the age of this system), but—with little data available—it would primarily be a trending tool.

Performing thermography on an operating EDG, just prior to a scheduled EDG outage, would be advantageous because it would allow any problems or suspected problems to be investigated and corrected during the outage.

When performing thermography, particular attention should be given to the power components such as the power current transformers, power potential transformer, and SBO.

Thermal compound used on power diodes and power SCRs can degrade over time, resulting in adverse thermal affects (for example, hot spots). In addition, the misapplication (usually over-application) of thermal compound can result in hot spots and premature failure of power diodes and power SCRs. Thermography would effectively detect these hot spots, and its results would be a useful data point in determining a replacement interval for aged components.

11-2


12 REFERENCES

Basler Publication Manual 9 0177 00 990, “Instruction Manual for Voltage Regulator Models SR4A & SR8A.”

Basler Publication Manual 90 37100 99X, “Excitation Support System.”

Basler Publication Number 9 0370 00 99X, “Instruction Manual for Manual Voltage Control Module Models MVC-104, MVC-108, MVC-232.”

Basler Publication Number 9 0723 00 99XX, “Instruction Manual for Motor-Operated Potentiometer Models MOC21XX–MOC24XX and MOC29XX.”

Basler Publication Number 9 1051 00 99X, “Instruction Manual for Under-frequency Overvoltage Module Models UFOV 250A, UFOV 260A.”

ProTec Basler SR8A Training Manual.

Emergency Diesel Generator Obsolescence Strategy, TXU/Comanche Peak, 8/7/91.

Search of INPO OEs on Voltage Regulators, March 30, 2003, and July 29, 2004.

INPO OE 7698, 11/20/95 INPO OE 10174, 6/23/99 INPO OE 13515, 11/14/01 INPO OE 14259, 5/30/02 INPO OE 18920, 7/13/04 INPO OE 15135, 12/04/02

12-1


A LISTING OF KEY INFORMATION

The following list provides the location of “Key Point” information in this report.

Key Technical Point Targets information that will lead to improved equipment reliability.

Section Page Key Point

6.2 6-6 Adjusting the R4 potentiometer requires introducing a step change in generator terminal voltage and observing the voltage regulator response with a recorder; the step change is commonly referred to as a bump test. The bump needs to cause a 5% step change and one overshoot and one undershoot prior to reaching the steady-state set point. The bump can be accomplished in several different ways, the most convenient of which is to transfer to the manual voltage regulator, create a 5% mismatch between the manual and automatic voltage regulators, and then transfer back to the automatic voltage regulator. Other ways to cause a step change are to perform a full-load or partial-load reject. Keep in mind that this means rejecting VAR load because kW load has nothing to do with the automatic voltage regulator.

6.3 6-8 The SR8A has three adjustments associated with it: range (R3), stability (R4), and droop (R25). When a new SR8A is installed, set R3, R4, and R25 to the same resistance values as those in the SR8A that was removed. This provides only a starting point for the subsequent tuning to be performed. Following EDG start, but prior to any manipulation of the MOP (ensuring the R1 is in the pre-position), adjust R3 to achieve the desired generator terminal voltage. Next, while capturing the generator terminal voltage waveform with a recorder, introduce step changes and adjust R4 as necessary to achieve the desired response characteristic. Finally, set and check droop through adjustment of the R25 slide resistor, which is checked while the EDG is parallel with the grid.

7 7-2 An operational bench test can be performed to troubleshoot a problematic voltage regulator or to check a new voltage regulator prior to installation. The time is well spent to avoid installing a problematic voltage regulator, which, at a minimum, will delay restoring the EDG to operability. For the SR8A, this bench test should include verification of the condition of the R3 and R4 potentiometers, which have proven to be the most common source of problems with this voltage regulator.

8.7 8-3 One of the most common problems with the SR8A voltage regulator is erratic performance of the R1, R3, or R4 potentiometers. The problem is typically a case of having a dirty potentiometer, which can be caused by oxidation of the resistive element or fouling with foreign material (dust or dirt, for example). Problems with these potentiometers are indicated by voltage or VAR swings.

A-1

EPRI Licensed Material Listing of Key Information

Section Page Key Point

9 9-3 The most common symptom of an SR8A voltage regulator problem is voltage and/or VAR swings, which, in many cases, can be caused by erratically performing potentiometers (R1, R3, or R4). In some cases, an erratic potentiometer can be adequately cleaned by wiping, though some plants choose to replace the SR8A simply to minimize the chance that the potentiometer could cause swings again. If the unit is replaced, a bench test can be used to help identify the faulty SR8A component.

10.1 10-1 As of the writing of this report, parts obsolescence is not a current or near-term concern for the Basler SR8A voltage regulator. A substantial number of these units are currently in service, particularly in non-nuclear, non-safety-related applications. Safety-related dedication is not performed by Basler but is performed by nuclear EDG suppliers as well as a third-party firm. Based on the historical performance of the SR8A and the parts and service availability, there is currently no driving force to upgrade the system.

10.2 10-2 As noted previously, the potentiometers are the weakest link in the SR8A. Discussions are ongoing within utilities and with Basler to explore the possibility of using improved, more robust potentiometers in order to increase reliability. As such, improved potentiometers and other devices may become available in the near future to address this concern.

11 11-1 The SR8A and its associated excitation system require very little maintenance compared to many other systems. The fact that this is a brushless excitation system eliminates maintenance associated with carbon brushes and collector rings. Because of the performance history of the potentiometers, they should be checked every two years. Some plants that have experienced poor performance of these potentiometers replace them periodically.

A-2


B U.S. PLANTS AND THEIR RESPECTIVE DIESEL MANUFACTURERS AND VOLTAGE REGULATOR MODELS

The following data represent the best information available to NMAC at the time of publication.

Table B-1 U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator Models

Plant EDG Quantity Voltage Regulator ANO 1 EMD 2 Basler SBSR ANO 2 FM-OP 2 Portec Beaver Valley 1 EMD 2 Basler SBSR Beaver Valley 2 FM-Pielstick 2 WPRX Braidwood 1 CB 2 Basler SR8A Braidwood 2 CB 2 Basler SR8A Browns Ferry 2 EMD 4 Basler Vickers Browns Ferry 3 EMD 4 Basler Vickers Brunswick 2 NORD 4 GE Static Byron 1 CB 2 Basler SR8A Byron 2 CB 2 Basler SR8A Callaway FM-Pielstick 2 WNR Calvert Cliffs 1 FM-OP 2 Basler SBSR Calvert Cliffs 2 SACM 1 Jeumont Snyder Calvert Cliffs 2 FM-OP 1 Basler SBSR Catawba 1 Enterprise 2 Portec Catawba 2 Enterprise 2 Portec Clinton EMD 4 Basler SR8A Columbia EMD 4 Portec Comanche Peak 1 Enterprise 2 Portec Comanche Peak 2 Enterprise 2 Portec Cook 1 WC 2 GE Static Cook 2 WC 2 GE Static Cooper 1 CB 2 Basler SBSR Crystal River 3 FM-OP 2 Basler SBSR

B-1

EPRI Licensed Material U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator Models

Table B-1 (continued) U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator Models

Plant EDG Quantity Voltage Regulator Davis Besse 1 EMD 2 EM Diablo Canyon 1 ALCO 3 Basler SBSR Diablo Canyon 2 ALCO 2 Basler SBSR Dresden 2 EMD 2 Basler Vickers Dresden 3 EMD 1 Basler Vickers Duane Arnold 1 FM-OP 2 Basler SBSR Farley 1 FM-OP 4 Basler SBSR Farley 2 FM-OP 1 Basler SBSR Fermi 2 FM-OP 4 Basler SBSR FitzPatrick 1 EMD 4 Basler SBSR Fort Calhoun 1 EMD 2 GE Static Ginna 1 ALCO 2 Basler SBSR Grand Gulf 1 Enterprise 2 Portec Grand Gulf 1 EMD 1 Portec Harris 1 Enterprise 2 Portec Hatch 1 FM-OP 3 Basler SBSR Hatch 2 FM-OP 2 Basler SBSR Hope Creek 1 FM-Pielstick 4 Basler SER Indian Point 2 ALCO 2 Basler SBSR Indian Point 2 ALCO 1 Basler SR8A Indian Point 3 ALCO 2 Basler SBSR Indian Point 3 ALCO 1 Basler SR8A Kewaunee 1 EMD 2 Basler SBSR LaSalle 1 EMD 2 Basler SR8A LaSalle 2 EMD 1 Basler SR8A Limerick 1 FM-OP 4 Basler SER Limerick 2 FM-OP 4 Basler SER McGuire 1 NORD 2 Basler SBSR McGuire 2 NORD 2 Basler SBSR Millstone 1 FM-OP 1 Basler SBSR Millstone 2 FM-OP 2 Basler SBSR Millstone 3 FM-Pielstick 2 WPRX Monticello 1 EMD 2 Basler Vickers Nine Mile Pt. 1 EMD 2 Basler Vickers Nine Mile Pt. 2 CB 2 Portec North Anna 1 FM-OP 2 Basler SBSR North Anna 2 FM-OP 2 Basler SBSR

B-2


U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator Models


Plant EDG Quantity Voltage Regulator Oconee EMD 1 Portec Oyster Creek 1 EMD 2 Basler Vickers Palisades 1 ALCO 2 Basler SBSR Palo Verde 1 CB 2 Portec Palo Verde 2 CB 2 Portec Palo Verde 3 CB 2 Portec Peach Bottom 2 FM-OP 4 Basler SBSR Perry 1 Enterprise 2 Basler SER Perry 1 EMD 2 Basler SR8A Pilgrim 1 ALCO 2 Basler SBSR Point Beach 1 EMD 2 Portec Point Beach 1 EMD 2 Basler Vickers Prairie Island 1 FM-OP 2 Basler SBSR Quad Cities 1 EMD 2 Basler Vickers Quad Cities 2 EMD 2 Basler Vickers River Bend 1 Enterprise 2 Portec River Bend 1 EMD 1 Basler SR8A Robinson 2 FM-OP 2 Basler SBSR Salem 1 ALCO 3 Basler SBSR Salem 2 ALCO 3 Basler SBSR San Onofre 2 EMD 4 Basler SR8A San Onofre 3 EMD 4 Basler SR8A Seabrook 1 FM-Pielstick 2 Basler SER Sequoyah 1 EMD 2 Basler SBSR South Texas 1 CB 3 Portec South Texas 2 CB 3 Portec St. Lucie 1 EMD 4 EM St. Lucie 2 EMD 4 Portec Summer 1 FM-Pielstick 2 Basler SER Surry 1 EMD 2 Basler Vickers Surry 2 EMD 1 Basler Vickers Susquehanna 1 CB 4 Portec Three Mile Island 1 FM-OP 2 Basler SBSR Turkey Pt. 3 EMD 2 Basler Vickers Turkey Pt. 4 EMD 2 Portec Vermont Yankee 1 FM-OP 2 Basler SBSR Vogtle 1 Enterprise 2 Portec

B-3

EPRI Licensed Material U.S. Plants and Their Respective Diesel Manufacturers and Voltage Regulator Models


Plant EDG Quantity Voltage Regulator Vogtle 2 Enterprise 2 Portec Waterford 3 CB 2 Portec Watts Bar EMD 4 Portec Wolf Creek 1 FM-Pielstick 2 WNR

B-4


C TRANSLATED TABLE OF CONTENTS

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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EPRI Licensed Material Translated Table of Contents

RESUME

Objectifs

• Fournir des conseils sur l'entretien (et les questions relatives) des régulateurs de tension de

type Basler SR8A des génératrice électriques diesel (EDG)

• Fournir des conseils d'entretien, ainsi qu’une description des systèmes particuliers des régulateurs de tension ; un examen de l'historique de défauts, les réglages, dépannages, tâches courantes d'entretien préventif ; et discussion des tâches spéciales d'entretien

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Translated Table of Contents

TABLE DES MATIERES

1 INTRODUCTION .................................................................................................................. 1-1 1.1 Contexte ........................................................................................................................ 1-1

1.2 Contenu ......................................................................................................................... 1-2

1.3 Mise en valeur des points clés ...................................................................................... 1-3

2 BASLER SR8A ..................................................................................................................... 2-1 2.1 Vue d’ensemble du régulateur de tension Basler SR8A ............................................... 2-1

2.1.1 Notations et caractéristiques ................................................................................. 2-2

3 CIRCUITS FONCTIONNELS ................................................................................................ 3-1 3.1 Circuit de détection......................................................................................................... 3-2

3.2 Détecteur d'erreur ......................................................................................................... 3-2

3.3 Amplificateur d'erreurs .................................................................................................. 3-3

3.4 Contrôleur de puissance ................................................................................................ 3-4

3.5 Réseau de stabilisation ................................................................................................. 3-5

3.6 Génération automatique de tension .............................................................................. 3-6

3.7 Description de fonctionnement ...................................................................................... 3-7

4 CIRCUITS SUPPORTS ........................................................................................................ 4-1 4.1 Abaissement .............................................................................................................. 4-1

4.2 Support d'excitation : Série d'option d’amplification ....................................................... 4-4

4.3 Potentiomètre moteur .................................................................................................... 4-7

4.4 Contrôle manuel de tension .......................................................................................... 4-8

4.5 Relais de Terrain de conditionnement ........................................................................... 4-9

4.6 Module de Sous-Fréquence/surtension (UFOV) ........................................................... 4-9

4.6.1 Circuit de Sous-Fréquence .................................................................................... 4-9

4.6.2 circuit de surtension ............................................................................................. 4-10

4.7 Arrêt de tension ........................................................................................................... 4-11

4.8 Flash de terrain ........................................................................................................... 4-12

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5 CONNEXIONS ...................................................................................................................... 5-1 5.1 Bornes de détection ...................................................................................................... 5-1

5.2 Bornes F+ et F- .............................................................................................................. 5-2

5.3 Borne A ......................................................................................................................... 5-2

5.4 Puissance d'entrée (bornes 3 et 4) ............................................................................... 5-2

5.5 Bornes 1 et 2 d’abaissement.......................................................................................... 5-2

6 REGLAGES .......................................................................................................................... 6-1 6.1 réglage de l’étendue (potentiomètre R3) ....................................................................... 6-3

6.2 Réglage de stabilité (potentiomètre R4) ........................................................................ 6-5

6.3 Réglage d'abaissement (résistance des fils guide R25) ............................................... 6-6

ESSAI AU BANC 7 .................................................................................................................. 7-1

8 AVARIES ET PROBLEMES ................................................................................................. 8-1 8.1 Potentiomètre R3 irrégulier ........................................................................................... 8-2

8.2 Potentiomètre R1 irrégulier ........................................................................................... 8-2

8.3 Potentiomètre R4 irrégulier ........................................................................................... 8-2

8.4 Défaut de l'électronique du SR8A ................................................................................. 8-2

8.5 Défaut du pont de diode MOP ....................................................................................... 8-2

8.6 Abaissement de tension en mode isochronique ............................................................ 8-2

8.7 Mauvaises connexions ou connexions ouvertes ........................................................... 8-3

9 DEPANNAGE ........................................................................................................................ 9-1

10 OBSOLESCENCE............................................................................................................. 10-1 10.1 Obsolescence ............................................................................................................ 10-1

10.2 Autres problèmes ....................................................................................................... 10-1

11 ENTRETIEN PREVENTIF ................................................................................................ 11-1 11.1 Thermographie .......................................................................................................... 11-2

12 REFERENCES ................................................................................................................. 12-1

A LISTE D'INFORMATIONS PRINCIPALES ......................................................................... A-1

B LISTE DES CENTRALES AMERICAINES ET DE LEUR FOURNISSEURS DE DIESEL RESPECTIFS FOURNISSEURS DE REGULATEURS DE TENSION...................... B-1

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LISTE DE FIGURES

Figure 2-1 excitatrice sans balais ............................................................................................. 2-2 Figure 2-1 modèle type ............................................................................................................. 2-4 Figure 3-1 schéma fonctionnel.................................................................................................. 3-1 Figure 3-2 circuit de détection................................................................................................... 3-2 Figure 3-3 détecteur d'erreur .................................................................................................... 3-3 Figure 3-4 amplificateur d'erreurs ............................................................................................. 3-4 Figure 3-5 contrôleur de puissance .......................................................................................... 3-5 Figure 3-6 réseau de stabilisation............................................................................................. 3-6 Figure 3-7 circuit de génération de tension .............................................................................. 3-7 Figure 3-8 de baisse de signal ................................................................................................. 3-8 Figure 3-9 d’augmentation de signal......................................................................................... 3-9 Figure 4-1 connexion de quadrature......................................................................................... 4-2 Figure 4-2 facteur de puissance ............................................................................................... 4-3 Figure 4-3 facteur de puissance de ralentissement .................................................................. 4-4 Figure 4-4 tableau interne SBO ............................................................................................... 4-5 Figure 4-5 tableau interne SBO ............................................................................................... 4-5 Figure 4-6 connexions SBO à CTs .......................................................................................... 4-6 Figure 4-7 potentiomètre moteur Internes ............................................................................... 4-7 Figure 4-8 connexions manuelles de contrôle de tension......................................................... 4-8 Figure 4-9 caractéristique de Sous-Fréquence....................................................................... 4-10 Figure 4-10 tableau de connexion UFOV .............................................................................. 4-11 Figure 5-1 connexions sans balais .......................................................................................... 5-1 Figure 5-2 connexions au circuit d'abaissement ....................................................................... 5-3 Figure 6-1 diagramme de câblage ............................................................................................ 6-2 Figure 6-2 localisation des éléments ........................................................................................ 6-3 Figure 7-1 essai au banc .......................................................................................................... 7-2

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LISTE DE TABLEAUX

Tableaux 8-1 Résumé des expériences de régulateur de tension de Basler SR8A .............. 8-1 Tableaux 9-1 Symptômes des causes possibles de défauts, et les solutions aux

problèmes avec des régulateurs de tension de SR8A ......................................................9-1 Tableaux 8-1 Constructeurs aux USA de régulateurs de tension........................................... B-1

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レポートの概要

目的

• 原子力発電所用EDG(非常用ディーゼル発電機)のBasler

SR8A電圧安定器保全及び保全に関連したガイドを提供すること。

• 特定電圧安定器システムに関する説明、不具合歴史に関するレビュー、調整、問題解決、通常予防保全タスク、特別な保全タスク議論を含む、メインテナンスガイドを提供すること

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目次

1つはじめに .............................................................................................................................. 1-1

1.1背景 ................................................................................................................................. 1-1

1.2内容 ................................................................................................................................. 1-2

1.3キーポイント................................................................................................................... 1-3

2 BASLER SR8A ..................................................................................................................... 2-1

2.1 Basler SR8A電圧安定器概要.......................................................................................... 2-1

2.1.1定格および機能 ....................................................................................................... 2-2

3機能回路.................................................................................................................................. 3-1

3.1検知回路 .......................................................................................................................... 3-2

3.2エラー検出器................................................................................................................... 3-2

3.3エラーアンプ................................................................................................................... 3-3

3.4パワーコントローラ ........................................................................................................ 3-4

3.5安定ネットワーク............................................................................................................ 3-5

3.6自動電圧上昇................................................................................................................... 3-6

3.7運転上の記述................................................................................................................... 3-7

4サポート回路 .......................................................................................................................... 4-1

4.1ドゥループ ...................................................................................................................... 4-1

4.2エキサイタサポート:シリーズブーストオプション ........................................................ 4-4

4.3 モータ駆動電位差計 ....................................................................................................... 4-7

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4.4手動電圧制御................................................................................................................... 4-8

4.5フィールド調節リレー ................................................................................................... 4-9

4.6低周波数/過電圧モジュール(UFOV) ............................................................................... 4-9

4.6.1低周波数回路 ........................................................................................................... 4-9

4.6.2過電圧回路............................................................................................................. 4-10

4.7電圧シャットダウン ...................................................................................................... 4-11

4.8フィールドフラッシュ .................................................................................................. 4-12

5接続......................................................................................................................................... 5-1

5.1センシングターミナル .................................................................................................... 5-1

5.2フィールドパワーターミナルF+およびF- ...................................................................... 5-2

5.3ターミナルA- .................................................................................................................. 5-2

5.4入力パワー (ターミナル3および4) ................................................................................. 5-2

5.5ドゥループインプットターミナル1および2.................................................................... 5-2

6調整......................................................................................................................................... 6-1

6.1レンジ調節(R3電位差計) ................................................................................................ 6-3

6.2安定性調節(R4電位差計) ................................................................................................ 6-5

6.3ドゥループ調節(R25スライドワイヤー抵抗器) .............................................................. 6-6

7ベンチテスト .......................................................................................................................... 7-1

8不良および問題....................................................................................................................... 8-1

8.1 R3電位差計不良 ............................................................................................................. 8-2

8.2 R1電位差計不良 ............................................................................................................. 8-2

8.3 R4電位差計不良 ............................................................................................................. 8-2

8.4 SR8A電子機器不良 ........................................................................................................ 8-2

8.5MOPダイオードブリッジ不良......................................................................................... 8-2

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8.6等間隔モード電圧ドゥループ.......................................................................................... 8-2

8.7 PTSにおける接続不良または開放.................................................................................. 8-3

9問題解決.................................................................................................................................. 9-1

10廃型..................................................................................................................................... 10-1

10.1廃型 ............................................................................................................................. 10-1

10.2他部品課題 .................................................................................................................. 10-1

11予防保全.............................................................................................................................. 11-1

11.1サーモグラフィー ....................................................................................................... 11-2

12参照..................................................................................................................................... 12-1

A. キー情報リスト ................................................................................................................... A-1

B. 米国プラントおよびそれぞれディーゼル製造業者および電圧安定器モデル..................を B-1

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図リスト

図2-1 ブラシレスエキサイタ .................................................................................................... 2-2

図2-2 典型的な型式番号 ........................................................................................................... 2-4

図3-1 ブロックダイヤグラム .................................................................................................... 3-1

図3-2 検知回線 .......................................................................................................................... 3-2

図3-3 誤り検出器 ...................................................................................................................... 3-3

図3-4 エラーアンプ................................................................................................................... 3-4

図3-5 出力コントローラ ........................................................................................................... 3-5

図3-6 安定ネットワーク ........................................................................................................... 3-6

図3-7 電圧集結回路................................................................................................................... 3-7

図3-8 シグナル低下................................................................................................................... 3-8

図3-9 シグナル上昇................................................................................................................... 3-9

図4-1直角位相接続.................................................................................................................... 4-2

図4-2ユニット力率.................................................................................................................... 4-3

図4-3ラギング力率.................................................................................................................... 4-4

図4-4 SBO内部図表 .................................................................................................................. 4-5

図4-5 SBO内部図表 .................................................................................................................. 4-5

図4-6SBOのCTsへの接続 ......................................................................................................... 4-6

図4-7モータ駆動電位差計内部 ................................................................................................. 4-7

図4-8手動電圧制御接続 ............................................................................................................ 4-8

図4-9低周波数特性.................................................................................................................. 4-10

図4-10 UFOV配線図 ............................................................................................................... 4-11

図5-1ブラシレスエキサイタ接続 .............................................................................................. 5-1

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図5-2ドゥループ回路へのCT接続 ............................................................................................. 5-3

図6-1配線図 .............................................................................................................................. 6-2

図6-2機器構成位置.................................................................................................................... 6-3

図7-1ベンチチェック ................................................................................................................ 7-2

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表リスト

表8-1 Basler SR8A電圧安定器運転経験の概要 ...................................................................... 8-1

表9-1 SR8A電圧安定器に関連した、徴候、考えられる原因および問題解決 ....................... 9-1

表B-1 米国プラントおよびそれぞれディーゼル製造業者および電圧安定器のモデル ...........B-1

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RESUMEN DEL REPORTE

Objetivos

• Para ofrecer guía en mantenimiento y aplicaciones relacionadas con mantenimientos los

reguladores de voltaje de Basler SR8A en servicio nuclear de EDG

• Para ofrecer guía en mantenimiento, incluyendo una descripción de los sistemas específicos del regulador de voltaje; una reseña a historias de la falla, sintonizando, localizando averías, tareas rutinarias del mantenimiento preventivo; y discusiones de las tareas especiales del mantenimiento

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CONTENIDO

1 INTRODUCCIÓN .................................................................................................................. 1-1 1.1 Antecedentes ................................................................................................................ 1-1

1.2 Contenido ...................................................................................................................... 1-2

1.3 Destacando los Puntos Dominantes ............................................................................. 1-3

2 BASLER SR8A ..................................................................................................................... 2-1 2.1 Resumen del Regulador de Voltaje de Basler SR8A .................................................... 2-1

2.1.1 Aforos y características ......................................................................................... 2-2

3 CIRCUITOS FUNCIONALES ............................................................................................... 3-1 3.1 Circuito Detector............................................................................................................. 3-2

3.2 Detector de Error............................................................................................................ 3-2

3.3 Amplificador de Error...................................................................................................... 3-3

3.4 Controlador de Potencia................................................................................................. 3-4

3.5 Red de Estabilización .................................................................................................... 3-5

3.6 Acumulación Automática del Voltaje ............................................................................. 3-6

3.7 Descripción Operacional ............................................................................................... 3-7

4 CIRCUITOS DE SOPORTE .................................................................................................. 4-1 4.1 Atenuación ..................................................................................................................... 4-1

4.2 Soporte de Excitación: Serie de Opción del Alza .......................................................... 4-4

4.3 Potenciómetro Operado a Motor ................................................................................... 4-7

4.4 Control de Voltaje Manual .............................................................................................. 4-8

4.5 Campo- Relé Condicionado .......................................................................................... 4-9

4.6 Módulo de la Bajo-Frecuencia/Sobretensión (UFOV) ................................................... 4-9

4.6.1 Circuito de Baja-Frecuencia .................................................................................. 4-9

4.6.2 Circuito de Sobretensión ..................................................................................... 4-10

4.7 Cierre del Voltaje ......................................................................................................... 4-11

4.8 Destello del Campo ..................................................................................................... 4-12

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5 CONEXIONES ...................................................................................................................... 5-1 5.1 Terminales Sensorias..................................................................................................... 5-1

5.2 Terminales de Potencia de Campo de F+ y F- .............................................................. 5-2

5.3 Terminal A- .................................................................................................................... 5-2

5.4 Entrada de Potencia (terminales 3 y 4) ......................................................................... 5-2

5.5 Terminales de Entrada de Atenuación 1 y 2 .................................................................. 5-2

6 SINTONIZACIÓN .................................................................................................................. 6-1 6.1 Ajuste de rango (Potenciómetro R3) ............................................................................. 6-3

6.2 Ajuste de Estabilidad (Potenciómetro R4) ..................................................................... 6-5

6.3 Ajuste de Atenuación (Resistor de Cable de Corredera R25) ....................................... 6-6

7 PRUEBA DE BANCO............................................................................................................ 7-1

8 FALLAS Y PROBLEMAS .................................................................................................... 8-1 8.1 Potenciómetro R3 Errático ............................................................................................. 8-2

8.2 Potenciómetro R1 Errático ............................................................................................ 8-2

8.3 Potenciómetro R4 Errático ............................................................................................ 8-2

8.4 Falla de Electrónica de SR8A ....................................................................................... 8-2

8.5 Falla del Puente Diodo MOP ......................................................................................... 8-2

8.6 Atenuación de Voltaje en Modo Isócrono ...................................................................... 8-2

8.7 Pobres o Conexiones Abiertas en Detectando PT......................................................... 8-3

9 LOCALIZANDO AVERÍAS ................................................................................................... 9-1

10 OBSOLESCENCIA............................................................................................................ 10-1 10.1 Obsolescencia ........................................................................................................... 10-1

10.2 Otros Problemas de Piezas........................................................................................ 10-1

11 MANTENIMIENTO PREVENTIVO ................................................................................... 11-1 11.1 Termografía................................................................................................................ 11-2

12 REFERENCIAS ................................................................................................................ 12-1

A LISTADO DE INFORMACIÓN DOMINANTE ..................................................................... A-1

B LISTADO DE PLANTAS DE LOS E.E.U.U. Y SUS RESPECTIVOS FABRICANTES DE DIESEL Y MODELOS DE REGULADOR DE VOLTAJE .................................................. B-1

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LISTA DE FIGURAS

Figura 2-1 Excitador Sin Cepillo ............................................................................................... 2-2 Figura 2-2 Numero del Modelo Típico ...................................................................................... 2-4 Figura 3-1 Diagrama de Bloque................................................................................................ 3-1 Figura 3-2 Circuito Sensor ........................................................................................................ 3-2 Figura 3-3 Detector de Error ..................................................................................................... 3-3 Figura 3-4 Amplificador de Error............................................................................................... 3-4 Figura 3-5 Controlador de Potencia.......................................................................................... 3-5 Figura 3-6 Red de Estabilización .............................................................................................. 3-6 Figura 3-7 Circuito de la Acumulación de Voltaje ..................................................................... 3-7 Figura 3-8 Señal Baja ............................................................................................................... 3-8 Figura 3-9 Señal Levantada...................................................................................................... 3-9 Figura 4-1 Conexión de Cuadratura ......................................................................................... 4-2 Figura 4-2 Factor de Potencia de Unidad ................................................................................. 4-3 Figura 4-3 Factor de Potencia de Laminación .......................................................................... 4-4 Figura 4-4 Diagrama Interno SBO .......................................................................................... 4-5 Figura 4-5 Diagrama Interno SBO ........................................................................................... 4-5 Figura 4-6 Conexiones para CT SBO ...................................................................................... 4-6 Figura 4-7 Intérnales de Potenciómetro Operado A Motor ...................................................... 4-7 Figura 4-8 Conexiones Manuales del Control de Voltaje.......................................................... 4-8 Figura 4-9 Característica de Baja-Frecuencia ....................................................................... 4-10 Figura 4-10 Diagrama de Conexión de UFOV ...................................................................... 4-11 Figura 5-1 Conexiones del Excitador Sin Cepillo..................................................................... 5-1 Figura 5-2 Conexiones CT al Circuito de Atenuación ............................................................. 5-3 Figura 6-1 Diagrama de Conexión............................................................................................ 6-2 Figura 6-2 Localización de Componentes ................................................................................ 6-3 Figura 7-1 Prueba de Banco..................................................................................................... 7-2

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LISTA DE TABLAS

Tabla 8-1 Resumen de Experiencias del Regulador de Voltaje de Basler SR8A .................... 8-1 Tabla 9-1 Síntomas, Causas Posibles, y Soluciones a los Problemas con los

Reguladores de Voltaje de SR8A .....................................................................................9-1 Tabla B-1 Listado de Plantas de los E.E.U.U. y sus Respectivos Fabricantes de Diesel y Modelos

de Regulador de Voltaje .....................................................................................................B1

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About EPRI

EPRI creates science and technology solutions forthe global energy and energy services industry.U.S. electric utilities established the Electric PowerResearch Institute in 1973 as a nonprofit researchconsortium for the benefit of utility members, theircustomers, and society. Now known simply as EPRI,the company provides a wide range of innovativeproducts and services to more than 1000 energy-related organizations in 40 countries. EPRI’smultidisciplinary team of scientists and engineersdraws on a worldwide network of technical andbusiness expertise to help solve today’s toughestenergy and environmental problems.

EPRI. Electrify the World

Export Control RestrictionsAccess to and use of EPRI Intellectual Property is grantedwith the specific understanding and requirement thatresponsibility for ensuring full compliance with all applicableU.S. and foreign export laws and regulations is being under-taken by you and your company.This includes an obligationto ensure that any individual receiving access hereunder whois not a U.S. citizen or permanent U.S. resident is permittedaccess under applicable U.S. and foreign export laws and regulations. In the event you are uncertain whether you oryour company may lawfully obtain access to this EPRIIntellectual Property, you acknowledge that it is your obligation to consult with your company’s legal counsel todetermine whether this access is lawful. Although EPRI maymake available on a case by case basis an informal assessmentof the applicable U.S. export classification for specific EPRIIntellectual Property, you and your company acknowledgethat this assessment is solely for informational purposes andnot for reliance purposes. You and your company acknowledge that it is still the obligation of you and yourcompany to make your own assessment of the applicableU.S. export classification and ensure compliance accordingly.You and your company understand and acknowledge yourobligations to make a prompt report to EPRI and the appropriate authorities regarding any access to or use ofEPRI Intellectual Property hereunder that may be in violationof applicable U.S. or foreign export laws or regulations.

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