3.12 guidelines for monitoring control and protection of shp stations

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Draft

July 10, 2008

STANDARDS / MANUALS / GUIDELINES FOR

SMALL HYDRO DEVELOPMENT

SPONSOR:

MINISTRY OF NEW AND RENEWABLE ENERGY

GOVERNMENT OF INDIA

Electro Mechanical Works

SPECIFICATION FOR

MONITORING, CONTROL AND PROTECTION OF

SMALL HYDROPOWER STATION

LEAD ORGANIZATION:

ALTERNATE HYDRO ENERGY CENTRE

INDIAN INSTITUTE OF TECHNOLOGY, ROORKEE



CONTENTS

ITEMS PAGE NO

1.0 Objective 1

2.0 General 1

3.0 References and Codes 14.0 Monitoring of SHP 2

4.1 Systems for Monitoring 2

4.2 Requirements of Monitoring System 4

5.0 Levels of Monitoring 5

6.0 Control Of Units Of Small Hydropower Plant 5

6.1 General 5

6.2 Generator Connection to Systems 5

6.3 Unit Control 6

6.4 Control Functions 10

6.5 Control of Hydroelectric Power Plants 12

6.6 Modern practice Regarding governor and Plant

Control

15

7.0 Protection of SHP Generating Units 16

7.1 General 16

7.2 Equipment Trouble 17

7.3 Devices used in a Typical Protection System 18

8.0 Generator Connected in Parallel to Grid 30

9.0 Generators Connected in Parallel on a Common Bus 30

10.0 Protection Groups 31

10.1 Controlled Action Shut Down 31

10.2 Emergency Shut Down 31

10.3 Immediate Action Shut Down 31

10.4 Electrical Shut Down 32

11.0 Protection of Power Transformers 32

12.0 Fire Protection Shut Down 32

Annexure-I List of Generator Panel Indication and Relays 33

Annexure-II List of Protection Elements in Micro Processor Based Relays 34



AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations 1

SPECIFICATIONS FOR MONITORING CONTROL AND

PROTECTION OF SHP STATIONS

1.0 OBJECTIVES

This guide is intended to assist in preparation of specification for monitoring of various parameters of various operations, control and protection of main generating

equipment viz turbine, generator, transformer and other associated auxiliaries.

2.0 GENERAL

The generating units of a small hydropower plant may have its shaft vertical,

horizontal or inclined with the type of turbine selected to suit the site’s physical conditions.

Small hydro turbines may be selected as per site conditions, head and discharge available.

Small hydro-generator are of the alternating current type and may be either synchronous or

induction type. Usually small hydro units upto 5 MW are expected to require minimum

amount of field assembly and installation work. While machine having capacity from 5 MW

to 25 MW may have slow speed, large diameter and with split generator stator that require

final winding assembly in the field.

Mini & micro power stations are generally provided system suiting to these being run

unattended or with few attendants while bigger machines upto 5 MW capacity have more

elaborate arrangement of control monitoring and protection. Machine having capacity upto 25

MW and provision of parallel operation with other systems will have more comprehensive

control, monitoring & protection system.

This guide, therefore, describes control, monitoring and protection requirement of

SHP having capacity upto 5 MW and also 5 to 25 MW.

This guide will serve as a reference document alongwith available national &

international codes standards, guide & books. For the purpose of convenience this guide has

been subdivided as follows

• Monitoring

• Control

• Protection

3.0 REFERENCES AND CODES

IEEE Std 1020 - IEEE guide for control of small hydro electric power

plantsIEEE Std 1010 - IEEE guide for control of hydro electric power plants

IEEE Std 60545:1976 - Guide for commissioning operation and maintenance of

Hydraulic Turbines

IEC 61116:1992 - Electro mechanical guide for small hydroelectric

installations

IEEE std 1046 - IEEE application guide for distributed digital control

and monitoring for power plants

IEEE std. 1249 - IEEE guide for computer–based control for power




plant automation

IEEE std. C 37101 - IEEE guide for generator ground protection

IEEE std. C 5012 - IEEE standard for salient pole 50 Hz and 60 Hz

synchronous generator and generator / motors for

hydraulic turbine application rated 5 MVA and above

IEEE std 4214 - IEEE guide for preparation of excitation system

specificationANSI/ IEEE std 242:1996 - IEEE recommended practice for protection and

coordination of industrial and commercial power

systems

ANSI/ IEEE std C 372-1987 - IEEE standard electrical power systems device function

numbers

ANSI/ IEEE std C 37.95 : 1974 - (R1980) IEEE guide for protective relaying of utility

ANSI/ IEEE std C 37.102:1987 - IEEE guide for generator protection

MASON, CR - Art & science of protective relaying 1956

AHEC/PFC/FINAL REPORT 2002 -

4.0 MONITORING OF SHP

Monitoring of operating parameters of the generating unit and their auxiliaries is very

important for the life and optimum utilization of available discharge for generation. The

efficient running of unit require regular monitoring. The primary input data and generation

output data are monitored periodically. The details of data required for monitoring

performance of a generating station is as following.

4.1 SYSTEMS FOR MONITORING

4.1.1 Water Conductor System

• Storage level at dam / barrage / weir

•

River discharge• Headrace channel discharge

• Discharge at outlet of disilting basin

• Forebay level

• Discharge of spillway

• Penstock pressure

• Tail water level

4.1.2 Hydro-mechanical Parameters

• Turbine and accessories

o Pressure and levels in oil pressure system

o Bearing temperatures (oil & pads)o Oil level in bearing sumps (if provided)

o Cooling water pressure and temperatures

o Clean water pressure for shaft gland

o Vibration in shaft for large machines

o Status of inlet and other valves.

• Generator and accessories

o Stator winding temperature




o Rotor winding temperature

o DE/NDE end bearing temperatures

o Cooling water and air temperatures

o Air gap monitoring

• Transformers

o Winding temperature

o Oil temperatureo Oil level

o Cooling water temperature and pressures

4.1.3 Electro-mechanical Operating Parameters

• Turbine & accessories

o Speed

o Guide vane opening & limits (precent)

o Runner blade opening in Kaplan Turbine (percent)

o Nozzle opening in impulse turbine (percent)

• Generator & auxiliaries

o Governor actuator balance current (Amp)

o Generated power (kW or MW)

o Generated hour (kWh)

o Kilovolt ampere (kVA)

o Kilovolt ampere reactive (kVAR)

o Power factor (PF)

o Frequency (Hz)

o Excitation voltage (Volts)

o Excitation current (Amp)

o Recorder for kW, Hz, kWh etc

• Transformers

o

Tap positiono HV/LV current

o Primary/ secondary voltage

• Grid system & transmission line

o Grid voltage

o Grid frequency

o Power export / import (kW)

o Current (Amp)

o Kilowatt hour (kWh) export / import

• Station auxiliaries

o Voltage and current on LT AC system

o Kilowatt hour (kWh)

o Diesel generator running hour, kWh & other parameterso Drainage & dewatering system

Running hours of pumps

Water level in sump

o Fire extinguisher – periodical testing

o Battery set- Regular monitoring as per manufacturers recommendations

o Battery chargers & distribution boards – voltage current etc.

o Air compressors – HP /LP pressures and running hours

o OPU system




Running hours of pumps

Level in pressure accumulators

Pressure of oil

4.2 REQUIREMENTS OF MONITORING SYSTEM

4.2.1 Instrument Transformers & Sensors

CTs & VTs

Current and voltage transformers of rated voltage and appropriate ratio, class of

accuracy is selected as per the requirement of the system.

Sensors

The sensors for temperatures, pressures, levels speed are installed at the proper

location.

4.2.2 Indicating Meters

Analogue type of meters, separate for each parameter with selector switches etc were

being used earlier installed on control panels. Now a days digital meters are being used for

such parameters. Digital multifunction meters are now in use, only one meter provides

several parameters an selection, as well as provides routine display. Few analogue meters like

power meters (kW), voltmeters, ameters with selector switches are provided for operational

facilities.

4.2.3 Temperature Scanners

Digital temperature scanners indicating the temperatures of stator winding, bearing

pads, oil coolers etc. are provided and installed on the generator control panels. These

scanners get the signals from the sensor installed at specific location preferably through

screened cables.

4.2.4 Indicating Lamps

Indicating lamps of suitable colours as per code and practices should be provided on

control panels for indication status of machine and various auxiliaries, pumps, electrical

equipment like breaker, isolator, AC/DC supply system etc. Lists of such indication and

relays are enclosed as Annexure-I&II.

4.2.5 Alarm & Annunciations

The protection system relays and auxiliary relays also provided signals to alarm and

annunciation system. A set of annunciation windows are provided on control panels for each

fault clearing relay with accept test and reset facility through push buttons. Alarm and trip

annunciation indicate the fault and advise operating personnel of the changed operating

conditions.




4.2.6 PLC Based System

Recently control of machine and auxiliaries is done through PLC based control

system automatically in addition to manual systems with local and remote facilities. The data

are acquired through sensors and operation of machine is achieved on present values through

PC Monitors etc.

The PLC will acquire data from generating units, transformers, switchgears auxiliaries

through transducers / sensors/ CTs/ VTs wherever signals are week, noise level is high

shielded cables should be used for carrying data / signals. For sending output signal PLC will

use relays for operating breakers etc and comparators for giving ON/OFF signal.

5.0 LEVELS OF MONITORING

Normally two levels of monitoring is provided in SHP as per recommendation of IEC

1116. The levels are:

• Alarm

• Tripping

In case of manned power plant ‘alarm’ comes first so as to make the operator alert if

no corrective action is possible then tripping command with indication / hooter and

annunciation will be there.

But in case of unattended power plant direct tripping command will be initiated and

shut off the facility to avert possibility of any damage to the plant.

6.0 CONTROL OF UNIS OF SMALL HYDROPOWER PLANT

6.1 GENERAL

For small hydro installation simplicity of control system is advised, however, the

sophistication of control should be based on the complexity and size of the installation,

without compromising unit dependability and personal safety. Simplicity of control is

desirable to keep total cost of installed equipment as well as cost of maintenance, repair and

tests at economical level. Moreover a simpler system is more reliable as compared to

complex one.

6.2 GENERATOR CONNECTION TO SYSTEMS

6.2.1 Synchronous Generator

For conventional method of synchronizing the generator is started, accelerated to near

synchronous speed and excitation is applied. The voltage and the frequency are matched andunit is synchronized to the system, by closing generator circuit breaker or contactor, when

done perfectly no current surge will occur. Normally both manual and automatic

synchronizing of generator are provided. In addition the speed of some types of turbines

under no load conditions is so sensitive to small adjustments in runner blade angle or inflow

as to make only automatic synchronizing practical.




Small hydropower plants will certainly require unattended automatic synchronizing.

Manual synchronizing necessitates availability of continuous display of voltage, frequency,

phase angle and devices to control voltage and speed on the control panel.

Transducers or signal transmitters are provided either at the control panel or at the

equipment.

6.2.2 Induction Generator

For conventional method of connecting induction generator to the grid, the generator

is started and accelerated to synchronous speed. In fact, the rotor speed of generator shall be

(1% slip) more than grid frequency. This is done to avoid monitoring action of generator.

Once the generator frequency matches with grid frequency the generator breaker is closed.

Now the generator is connected with the grid and running at no load.

At this stage grid power factor is to be checked and capacitor banks are switched on

as per requirement to provide necessary reactive power and further loading of unit is done

upto full load.

All these functions can be performed manually as well as automatically through PLC,

computer, microprocessor based control system.

For smaller machines which are unattended provision of integrated digital control &

SCADA system is preferred.

6.2.3 Status and Alarm Requirements

• Unit ready to start

• Breaker position (no alarm if manual operation only)

•

Intrusion alarm• Fire alarm

• Emergency status alarm (requires immediate attention0

• General status alarm (response can be differed)

• Trash rack differential alarm

• Unit stopped (when not required)

• Unit turning (when not required)

• High bearing temperatures

• Loss of lubrication or cooling or both

• Low hydraulic system pressure

• Incomplete start or stop sequence

• Loss of power

6.3 UNIT CONTROL

The control logic system for small hydro start stop sequencing can be provided by

hardwired relay logic, programmable controllers microprocessor based systems or a

combination of these.

The unit control system should be designed to perform following functions:




• Data gathering and monitoring

• Start stop control sequence

• Annunciation & alarm conditions

• Temperature monitoring

• Metering & instrumentation

• Event recording

• Synchronizing and connecting the unit to grid

• Control of real & reactive power

The unit control system must be able to provide startup and shutdown sequencing

under both normal and abnormal conditions. Under normal conditions, the unit is started and

stopped in manner that produces minimal disturbance to the system. For instance of normal

stop sequence entails a controlled unloading of machine and when completely unloaded, the

generator breakers or contactor is tripped. On the other hand protective relay operation will

initiate immediate tripping of the unit and complete shutdown as quickly as possible.

For certain mechanical troubles the unit is unloaded as quickly as possible beforetripping, in order that the potential damage from over speed is avoided.

The unit control system, in order to control and monitor various control sequences,

must interface with number of plant systems, including the following:

• Auxiliary system – pumps & valves

• Governor load control rollers – setters, solenoids & brake control

• Excitation – setters, contactors and circuit breakers

Typical startup and shutdown sequence are shown in fig. 1-3 for a Francis turbine

unit, which, for the sake of illustration, are shown as including synchronous generator and

governing system.




Fig. 1: Typical Start Sequence of Synchronous Generator




Fig. 2: Typical Normal Shut Down and Mechanical Trouble Stop Sequence of

Synchronous Generator




Fig. 3: Typical Electrical Trouble Stop Sequence for Synchronous Generator

6.4 CONTROL FUNCTIONS

There are many functions to be controlled in a small hydropower system. For example

turbine governor controls the speed of turbine, plant automation covers operations as auto

start, auto synchronization, remote control startup or water level control and data acquisition

and retrieval covers such operation as relaying plant operating status, instantaneous system

efficiency or monthly plant factor.

6.4.1 Turbine Control

This is the speed / load control of turbine in which governor adjusts the flow of water

through turbine to balance the input power with load.




In case small plants in the category of micro hydel (100 kW unit size), load

controllers are used, where excess load is diverted to dummy load to maintain constant speed.

With an isolated system, the governor controls the frequency of the system.

In interconnected system, the governor may be used to regulate unit load and may

contribute to the system frequency control. Figure 4 shows the different types of controlapplicable to turbines.

Fig. 4: Turbine Control

6.4.2 Generator Control

This is the excitation control of synchronous generator. The excitation is an integral

part of synchronous generator which is used to regulate operation of generator. The main

functions of excitation system of a synchronous generator are:

• Voltage control in case of isolated operation and synchronizing

• Reactive power or power factor control in case of inter connected operation.

The different generator controls are shown in fig. 5.

Fig. 5: Generator Controls

6.4.3 Plant Control

Plant control deals with the operation of plant. It includes sequential operation like

startup, excitation control, synchronization, loading unit under specified conditions, normal

shutdown, emergency shutdown etc. The mode of control may be manual or automatic and




may be controlled locally or from remote location. Plant control usually include monitoring

and display of plant conditions. Different plant controls are given in fig 6.

Fig. 6: Overview of Plant Automatic Control

6.5 CONTROL OF HYDROELECTRIC POWER PLANTS

6.5.1 Vertical Array of Control System

For hydroelectric power plants the components of the control system can be shown in

vertical array as shown in fig 7.

Fig. 7: Hierarchy of Controls of Hydropower Plants




• At lowest level (process level) process which includes, generator exciter, turbines,

switchgears, motors, pumps, valve etc is being controlled.

• At middle level there is control interface equipment which sends signals to the

apparatus from controlling equipment and for apparatus to transmit data back to

controlling equipment. Auxiliary contacts of motor starter, relays instrument

transformer signal conditioner, transducers or other interface devices.

• At top level there is controlling system which initiate control signals and receives thedata transmitted from apparatus control interface equipment. At this level itself

human-machine interface is included.

6.5.2 Categorization of Control System

The control system can further be defined by identifying following three categories of

control:

• Location:

a. Local - control is local at the controlled equipment with in the sight of

the equipment

b. Centralised - control is at other place, but with in the plant

c. Off site - control is at remote place which may be quite far from the

plant (Remote)

• Control mode:

a. Manual - Each operation requires a separate and distinct initiation.

However it may be applicable for any of the three locations

b. Automatic - With single initiation several operations in appropriate

(PLC/ computer/ sequence are done. This system can also be applicable to any

Microprocessor of the above three locations

Controlled)

• Operation (supervision)

a. Attended - Operators are all the time available at the plant to performcontrol action either locally or centralized control

b. Unattended - Operating staff is not available at the plant. There may be

occasional visits by operation & maintenance people to ensure

security of plant.

6.5.3 Information and Control Signals

Following four types of signals are provided between control board and particular

equipment

• Analog inputs for variable signals from CTs, VTs, RTDs, pressure, flow, level,

vibration etc.• Digital inputs provides digitalized values of variable quantities from the equipment

• Digital outputs – command signals from control boards to equipment

• Analog outputs – transmit variable signals from control to equipment e.g. governor,

voltage regulator etc.




6.5.4 Communication Links

a. Communication links with remote control

Following methods are available for implementing control from a remote location:

• Hardwired communication circuits (telephone type line, optical cables etc.)

• Leased telephone lines• Power line carries communication system

• Point to point radio

• Microwave radio

• Satellite

Metallic circuit in hardwire communication circuits and leased telephone lines,

requires special protection for equipments and personnels against ground potential rise (GPR)

due to electric system fault, since the hydro-generator is source of fault current. GPR is also

caused by lightening transmitted through power lines entering the power plant. As such

suitable mitigation has to be provided.

Power line carrier including insulated ground wire system can be used for

communications purposes. This method couples a high frequency signal on the power line or

insulated ground wire and is decoupled at an off site point.

Space radio can be used, utilizing power frequencies and micro wave radio can be

practical if hydro plant owner has an existing microwave system.

b. Communication with control boards

Data and control signals of following equipments will be required to be transmitted

between control board & equipments.

• Generator neutral and terminal equipment

• Head water and tail water level equipment

• Water passage shut off or bye pass valves gates etc.

• Turbine

• Unit transformer

• Circuits breaker and switches

• Generator

• Intake gates or main inlet valve and draft tube gates

• Turbine governing system

• Generator excitation system

The communication link between control board and equipment should be reliable.

c. Communications with Auxiliaries

Data and control signals of following auxiliaries equipments will be required to be

transmitted between control board and equipments.




• Fire protection

• AC Power supply

• DC Power supply

• Service water

• Service air

• Water level monitoring

• Turbine flow monitoring

6.6 MODERN PRACTICE REGARDING GOVERNOR AND PLANT CONTROL

6.6.1 Previous Practice

Control of a hydro plant generating unit was typically performed from central control

board located in centralize control room. The control board contained.

• Iron vane meters

• Hardwired control switches

• A large number of auxiliary relays to perform unit start / stop operations

• All the sensors and controls required to operate unit or units were hardwired to controlpanels allowing control of power station from cotnralised control room

6.6.2 Modern Practice

Modern digital integrated control and protection system including programmable

logistic controller (PLCs), distributed computer control system or personal computer control

system not only provide supervisory control and data acquisition (SCADA) but also

flexibility in control, alarm, sequencing, remote communication in a cost effective manner

and has been specifically recommended for SHPs in India, under UNDP – GEF projects.

Control functions of small hydro plants are standardized in following US standards

a. IEEE guide for control of small hydro electric plants, “ANSI/IEEE standard 1011,

1990’.

b. IEEE guide for control of hydroelectric power plants “ANSI/IEEE standard 1010,

1991.

Specific hardware or software to be utilized for implementation is not however

addressed in these standards.

Architecture and communication are two potential problem area for computerized

control system.

In 1990, the International Organisation for standardistion developed a model for open

architecture and protocol, know as SI (open system interconnection) – ISO mode.

Programmable Logic Controllers (PLC) type plant controllers combine with PC based

SCADA system are used as Governors and for plant control & data acquisition. This makes

the system less costly and reliable and therefore, can be used for small hydropower

generation control.




Personal computer based dedicated digial control system can perform all functions of

governing, unit control, protection and also data acquisition & storage and are more

economical and reliable. These dedicated systems with back up manual control facility of

turbine control in emergency by dedicated semic automatic digital controllers can be a low

cost option for small hydropower station.

7.0 PROTECTION OF SHP GENERATING LIMITS7.1 GENERAL

Small hydro turbine-generators should be protected against mechanical, electrical,

hydraulic and thermal damage that may occur as a result of abnormal conditions in the plant

or in the utility system to which the plant is electrically connected.

The abnormal operating conditions that may arise should be detected automatically

and corrective action taken in a timely fashion to minimize the impact. Relays (utilizing

electrical quantities), temperature sensors, pressure or liquid level sensors, and mechanical

contacts operated by centrifugal force, etc., may be utilized in the detection of abnormal

conditions. These devices in turn operate other electrical and mechanical devices to isolate

the equipment from the system.

Where programmable controllers are provided for unit control, they can also perform

some of the desired protective functions.

Operating problems with the turbine, generator, or associated auxiliary equipment

require an orderly shutdown of the affected unit while the remaining generating units (if more

than one is in the plant) continue to operate. Alarm indicators could be used to advise

operating personnel of the changed operating conditions.

Loss of individual items of auxiliary equipment may or may not be critical to the

overall operation of the small plant, depending upon the extent of redundancy provided in the

auxiliary systems. Many auxiliary equipment problems may necessitate loss of generation

until the abnormal conditions has been determined and corrected by operating or maintenance

staff.

The type and extent of the protection provided will depend upon many considerations,

some of which are: (1) the capacity, number, and type of units in the plant; (2) the type of

power system; (3) interconnecting utility requirements; (4) the owner’s dependence on the

plant for power; (5) manufacturer’s recommendations; (6) equipment capabilities; and (7)

control location and extent of monitoring. Overall, though, the design of the protective

systems and equipment is intended to detect abnormal conditions quickly and isolate the

affected equipment as rapidly as possible, so as to minimize the extent of damage and yet

retain the maximum amount of equipment in service.

Small hydroelectric power plants generally contain less complex systems than large

stations, and therefore tend to require less protective equipment. On the other hand, the very

small stations should be typically unattended and under automatic control, and frequently

have little control and data monitoring at an off-site location. This greater isolation tends to

increase the protection demands of the smaller plants.




An inherent part of the power plant protection is the design of the automatic controls

to recognize and act on abnormal conditions or control failures during startup. Close

coordination of the unit controls and other protection is essential.

7.2 EQUIPMENT TROUBLE

7.2.1 Plant Mechanical Equipment Troubles

7.2.1.1 Turbines

(a) Excessive vibration

(b) Bearing problems

(c) Over speed

(d) Insufficient water flow

(e) Shear pin failure

(f) Grease system failure

7.2.1.2 Hydraulic Control System

(a) Low accumulator oil level

(b) Low accumulator pressure(c) Electrical, electronic or hydraulic malfunctions within the governing or gate

positioning system

7.2.1.3 Water Passage Equipment

(a) Failure of head gate or inlet valve

(b) Head gate inoperative

(c) Trash rack blockage

(d) Water level control malfunction

7.2.2 Plant Electrical Equipment Troubles

7.2.2.1 Generator

(a) Abnormal electrical conditions

(b) Stator winding high temperature

(c) Low frequency

(d) Bearing problems

(e) Motoring

(f) Fire

(g) Excessive vibration

(h) Cooling failure

(i) Over speed

7.2.2.2 Main Transformer

(a) Insulation failure

(b) High temperature

(c) Abnormal oil level

(d) Fire




7.2.2.3 Generator Switchgear and Bus

(a) Electrical fault

(b) Mechanical failure

(c) Loss of control power

7.2.3 General Plant Troubles7.2.3.1 Station Service

(a) Transformer failure

(b) Unbalanced current

(c) DC System Trouble

(d) Station Air System Trouble

(e) Service Water System Trouble

(f) Flooding

(g) Fire

(h) Unauthorized Entry

(i) Protection or Control Logic System Malfunction

(j) Water level Monitoring System Malfunction

7.2.4 Utility System Troubles

Utility line faults and other abnormal utility system conditions should be detected and

the plant be disconnected from the utility system. Abnormal utility system conditions include

the following situations:

a. Ground or phase faults

b. Single phasing

c. Abnormal voltage

d. System separation (islanding)

Coordination with the utility is needed in selecting specific protective equipment,

particularly for line fault detection.

7.3 DEVICES USED IN A TYPICAL PROTECTION SYSTEM

There are numerous ways of providing the functional protective requirements of the

plant. While standard devices are generally available that can provide the protective functions

required, however each station should have specific design suitable for protection

requirements of the power plant equipment as well as the interconnection.

The following section describes components of a typical protection system that mightbe applied to a small hydro plant. Discussions and diagrams are included to illustrate location

and arrangement of relays.

7.3.1 Protective Devices

7.3.1.1 Temperature

A temperature device, possibly incorporating display and contacts for alarm

annunciation and tripping to monitor bearing stator and transformer winding temperatures.




Resistance temperature devices operating relays can also be used to detect generator stator

overheating.

7.3.1.2 Pressure and Level

Pressure and level switches installed in the turbine air and oil systems, to alarm, block

startup, or trip, as necessary.

7.3.1.3 Over and underspeed

Direct-connected or electrically driven speed switches for alarm, control, and tripping.

7.3.1.4 Vibration

Vibration detectors monitoring turbine or generator shaft sections, with alarm and trip

contacts.

7.3.1.5 Water level

A measuring system incorporating level sensors and monitoring equipment, to alarm,

trip, or control turbine output on limiting values of headwater or tail water level, or head.

7.3.1.6 Fire

Sensors located in areas where fire can occur and connected to a central fire monitor

for alarm. Small generators usually do not have fire sensors or suppression equipment, since

they are not usually enclosed.

7.3.1.7 Miscellaneous mechanical

Sensing devices are integral to the protected systems, such as automatic greasing

system, wicket gate shear pins, transformer, cooling and station sump drainage system.

7.3.2 Protective Relay and Protection System

7.3.2.1 Features of relays

The protective relays stand watch and in the event of failures short circuits or

abnormal operating conditions help de-energize the unhealthy section of power system and

restrain interference with rest of it and limit damage to equipment and ensure safety of

personals. The protective relays should possess following features:

• Reliability – To ensure correct action even after long period of inactivity and also to

offer repeated operation under sever condition.

• Selectivity – To ensure that only the unhealthy part of system is disconnected

• Sensitivity – Detection of short circuit or abnormal operating condition.

• Speed – To prevent and minimize damage and risk to instability of rotating plant.




• Stability – The ability to operate only under those conditions that calls for its

operation and to remain either passive or biased against operation under all other

conditions.

7.3.2.2 Type of relays

There are several types of relays being used for protection systems

- Electromagnetic relays

- Static relays

- Numerical relays

The old conventional electromagnetic relays are now being replaced with static relays

with are much faster and maintenance free. These relays are more reliable and sensitive.

These microprocessor based relays have different protections elements and therefore separate

relays for each protection is not required. A list of protections generally available in these

microprocessor based relays is enclosed as Annexure-II. The numerical relays are having

LED indications for power ON, trip status for different protection elements, time / current

characteristics selected and contacts for trip signals. However, some individualelectromagnetic conventional / static relays for few important protections are recommended

to be provided as standby relays.

• Advantages of numerical relays

It has been a practice to use electro-mechanical / solid state relays for all above

protections. The present trend is to use numerical relays which offer many advantages as

follows, over the earlier technology.

PARAMETER NUMERIC CONVENTIONAL

Accuracy 1% 5%/7.5%Burden <0.5 VA >5 VA

Setting Ranges Wide Limited

Multi Functionality Yes No

Size Small Large

Field Programmability Yes No

Parameter Display Yes No

System Flexibility Yes No

Co-ordination Tools Many Two

Communication Yes No

Remote Control Yes No

Special Algorithms Many Limited

Special Protections Yes No

Self Diagnostics Yes No

The user’s worry that numerical relays are very expensive is now removed due to

continuous production, improvement in techniques which have made numerical relays above

all, with features listed as above. Numerical relays are more user friendly and are gaining

popularity every where.




Following annexures are enclosed for ready reference

• Annexure-I - List of SHP Generator panel indications & relays

• Annexure-II - List of protection elements in Microprocessor based relays

7.3.2.3 Criteria of selection of protection system

The designer must balance the expense of applying a particular relay against the

consequences of losing a generator. The total loss of generator may not be catastrophic if it

represents a small percentage of the investment in an installation. However, the impact on

service reliability and upset to loads supplied must be considered. Damage to equipment and

loss of product in continuous processes can be dominating concern rather than generating

unit. Accordingly there is no standard solution based on MW-rating. However, it is rather

expected that a 500 kW, 415 V hydro machine will have less protection as compared to 25

MW base load hydro electric machine.

With increasing complications in power system, utility regulation, stress on cost

reduction and trends towards automation, generating unit protection has become a high focus

area. State of the art, micro controller based protection schemes offer a range of economical,

efficient and reliable solution to address the basic protection and control requirements

depending upon the size and specific requirement of the plant.

7.3.3 Requirements of Protection of Turbine

Two level protection is recommended as per IEC 1116. Elements to be considered

are:

(a) Speed rotation

(b) Oil levels in bearing

(c) Circulation of lubricants(d) Oil level of the governing system

(e) Oil level of speed increaser (if provided)

(f) Bearing temperatures

(g) Oil temperature of governing system

(h) Oil temperatures of speed increasers

(i) Oil pressure of governing system

(j) Pressure of cooling water

Immediate tripping is required for a, c, i, and j. While for item b, d, e, f, g and h only

alarm and annunciation is required to alert the operate and take corrective action, but in case

corrective action is not taken, tripping will eventually follow. Applying brakes at a particular

speed (30% of full speed) is done to reduce time to achieve stand still position of machine.

It is recommended two independent devices must be provided for over speed shut

down on larger machines. One for alarm mostly at 110% and other for tripping at 140%,

specially for machines which are not designed for continuous run away speed.

7.3.4 Requirements of Protection of Generator

Elements to be considered normally are




a. Stator temperature

b. Over current (stator and rotor)

c. Earth fault with current limits (stators & rotor)

d. Maximum and minimum voltage

e. Power reversal

f. Over/ under frequencyg. Oil level in bearing sumps

h. Pad & oil temperature of bearings

i. Cooling air temperature

Immediate tripping is required for items b, c, d, e & f while for items a, g, h and i first

alarm and annunciation is required for taking correcting measure and then tripping if

correcting measure is not taken within permissible time.

It is advisable to provide heating arrangement to prevent condensation in generator.

7.3.5 Generator Protection System and Relay Selection

7.3.5.1 Categorisation

In view of the economy and plant requirements generator protection for small

hydropower stations is categorized a follows:

• Generator size less than 300 kVA

• Generator size 300 to 1000 kVA

• Generator size 1 MVA to 10 MVA

• Generator size above 10 MVA

7.3.5.2 Transient overvoltage and surge protection

Transient over-voltages and lightning surges are controlled by lightning arrestors.

Surge capacitors are provided to restrict rate of rise of surge voltages and their magnitudes.

Every generator is provided with a set of lightening arrestors / surge diverter of appropriate

rating and generated voltage.

7.3.5.3 Minimum protection for a small machine with low resistance grounding are proposed

as follows:

Device No. Description

Basic Package

51V Voltage-restrained time over current relay

51GN Neutral ground over current relay

Options

27 Under voltage relay

32 Reverse power relay

40 Loss of excitation relay

46 Negative phase sequence relay

49R Stator over temperature relay

50GS Ground sensor over current relay




51VC Voltage controlled over current relay

64B Generator ground over voltage relay (in place of 51GN

where generator is ungrounded)

81 L/H Under / over frequency relay

86G Lockout auxiliary relay

87G Self-balancing current differential relay

12 Over speed relay

7.3.5.4 Minimum protection for a large machine with high resistance grounding

Basic Package

21 Distance

24 Over excitation

27 Under voltage

27TN Third harmonic under voltage

32 Reverse power

40 Loss-of-excitation

46 Current unbalance (negative sequence)

51GN Ground over current (backup to 64G)

51V Voltage-restrained over current

59 Over voltage

60V VT fuse failure detection

64G Stator ground

64F Ground (field)-I




81L/H Under/ Over frequency

87G Percentage differential

50/27 Accidental energization protection

95 Trip circuit monitoring

86G Lockout auxiliary relay

12 Over speed relay

Options

21G System backup distance relay (in place of 51V)

49R Stator over temperature relay (RTD)

60V2 Voltage ground relay-II

78 Out-off step relay

7.3.5.5 Typical schemes

With increasing complications in the power system, utility regulations, stress on cost

reduction and trend towards automation, generator protection has become a high focus area.State of the art, microcontroller based protection schemes from various manufactures offer a

range of solutions to customers to address the basic protection and control requirements

depending upon the size and plant requirements.




7.3.5.6 Generators-size less than 300 kVA

Normally these generators are controlled by MCCBs, which offer O/C and short

circuit protections. It is advisable to have following protections in addition to MCCB.

E/F protection (51 N): This will protect the generator from hazardous leakages and

ensure operator safety. Many organizations have already made E/F protection as mandatory.

Since these units are very remotely located and less manpower is available for operation and

maintenance, the system need more automization and fool proof protections. Therefore,

recently several optional protections are also being used for micro/mini units including over

speed (12) protections.

7.3.5.7 Generators – size 300 to 1000 kVA

There are two major differences when compared with the small machines considered

above.

• IDMT over current + E/F relay will be required in addition to normal MCCB or ACB

releases – since the generator may need shorter trip time for faults in the range 100%

to 400% level.




• By virtue or larger power level, any faults inside the stator or fault between the neutral

of the machine and the breaker terminals can reach very high intensity.

Such internal faults must be cleared instantaneously. Normal IDMT over current E/F

relays are not adequate to monitor this internal fault status-otherwise the machine can

circulate very high fault currents resulting in severe damage.

A high impedance differential relay scheme, is the best suited for this purpose. If the

neutral is formed inside the machine, the differential relay scheme will not bepossible. In this case a restricted E/F scheme is the solution. Care should be taken to

provide adequate number of CTs.

• Machine of this size are likely to have external controls for frequency and excitation –

so that they can be run in parallel with other power sources (other generators on the

same bus or the local grid). This necessitates voltage and frequency related

protections as well.

7.3.5.8 Generators – size 1 MVA to 10 MVA

• Stator side protections

o Voltage restrained over current protection (50V/51V)

Normal IDMT O/C will not work here-when an over current fault occurs, due

to higher current levels, there would be a drop in terminal voltage. For the

same fault impedance, the fault current will reduce (with respect to terminal

voltage) to a level below the pick up setting. Consequently normal IDMT may

not pick up. It is necessary to have a relay whose pick up setting will

automatically reduce in proportion to terminal voltage. Hence the over current

protection must be voltage restrained. Two levels of over current protection

are required – low set and high set (for short circuit protection).

o Thermal overload (49)

This protection is a must – it monitors the thermal status of machine for

currents between 105% to the low set O/C level (Normally 150%)

o Current unbalance (46)

Generators are expected to feed unbalanced loads-whose level has to be

monitored. If the unbalance exceeds 20%, it may cause over heating of the

windings. This heating will not be detected by the thermal overload relay-

since the phase currents will be well within limits. A two level monitoring for

unbalance is preferred-first level for alarm and the second level for trip.

o Loss of excitation (40)

When excitation is lost in a running generator, it will draw reactive power

from the bus and get over heated. This condition is detected from the stator

side CT inputs – by monitoring the internal impedance level & position of thegenerator.

o Reverse Power (32)

Generators for this size may operate in parallel with other sources, which may

cause reverse power flow at certain times.

- During synchronization

- PF change due to load/ grid fluctuations

- Prime mover failure




When reverse power happens, the generator along with prime mover will

undergo violent mechanical shock – hence reverse power protection is

necessary.

o Under Power (37)

It may not be economical to run generators below a certain load level. This

protection will monitor the forward power delivered by the machine and givealarm when the level goes below a set point. This may however be optional.

o Under/ over voltage (27/59)

This will protect the machine from abnormal voltage levels, particularly

during synchronization and load throw off conditions.

o Under/ over frequency (81)

This will protect the machine from abnormal frequency levels, particularly

during synchronization and load throw off conditions. This will also help in

load shedding schemes for the generator.

o Breaker failure protectionThis protection detects the failure of breaker to open after receipt of trip

signal. Another trip contact is generated under breaker fail conditions, with

which more drastic measures can be taken, like opening of bus coupler or

feeder breaker etc.

o Stator earth fault (64F)

This element tuned to the fundamental frequency can be used for the

protection of stator winding from earth fault.

o PT Fuse failure protection

This relay will detect any blowing of PT secondary fuse and give a contact

which can be used to lock the under voltage trip.

This protection is very impartment since the machines of this size have to be

protected for severe damages that may occur due to internal faults.

Considering the large power levels, it is necessary to have a percentage biased,

low impedance differential relay. These relays generally have following

advantages.

- Percentage biased differential protection with dual slope characteristics

- REF protection element (87 N), which will monitor the generator for

internal earth faults

- Over current protection, as a back up




• Rotor side protections

Generators of this size will need rotor side protections listed below:

o Diode failure relay

Brushless excitation systems will have rotor mounted diodes, which can

become short or open during operation. Diode failure relay will monitor the

condition of these diodes, for both open circuit and short, and give alarm

o Rotor excitation current

This is a DC current relay which will monitor the excitation current.

o Rotor excitation voltageThis is a DC voltage relay which will monitor rotor voltage

The above three protections are normally part of the excitation system of the

generator.

o Rotor earth fault

Relay for this protection will monitor the rotor winding status for the earth

fault, it will detect the first earth fault occurred in the winding and provide an

alarm. The relay employs proven DC rejection method for the detection of

E/F. there are other two methods as shown in the diagram for field ground

detection.




EXCITER

FIELDBREAKER

AC

RR

64F

BRUSH

FIELD

C1 C2

Fig. 13 Field ground detection using pilot brushes

7.3.5.9 Generator above 10 MVA

For large generators above 10 MVA size, the philosophy of main protection and back

up protection has to be followed. In addition to the protections listed above following extra

protections are to be considered.




o 100% earth fault protection

This will help in sensing earth faults close to neutral. Third harmonic content

in the zero sequence voltage will be detected by the replay for the above

protection.

o Inadvertent breaker closure

This will avoid closing of generator to bus during process to stop, or whenstand still or before synchronism.

o Under impedance

This will be required as a back up protection for the whole system including

the generator transformer and the associated transmission line. If the distance

relay fails to pick for some reason, this under impedance function will pick up

and save the generator.

o Over excitation

This will protection the generator from over fluxing conditions

8.0 GENERATOR CONNECTED IN PARALLEL TO GRID

Whenever generators are running parallel to grid, a comprehensive auto

synchronizing & Grid islanding scheme will be required. This scheme will help in

synchronizing the generator to the bus and opening the incomer breaker of the plant

whenever there is a severe grid disturbance, thus protecting the generator from ill effects of

disturbed grid.

• Grid disturbances

Under-voltage / Over-voltages

Under-frequency/Over-frequency

Rapid fall/ rise of frequency (df / dt),

Grid failure or other faults

Generator may not be able to operate below a certain power-factor. At low power-

factor, reverse reactive power flow may damage the generator.

• Grid fault detection

Over current and directional earth fault,

Rapid fall/ rise of frequency (df/dt),

Vector surge relay,

9.0 GENERATORS CONNECTED IN PARALLEL ON A COMMON BUS

Whenever more than one generator is operating in parallel, it is necessary to see that

the plant load is equally shared by the generators in parallel. If there is unequal sharing, there

would be sever hunting amongst the generators and eventually this will lead to cascaded

tripping of all generators, causing a total black out. Specific load sharing relays are available

in the market which provide the most effective, online load sharing system for generators in

parallel.




10.0 PROTECTION GROUPS

The protective relays and devices of generator and turbine are proposed to be grouped

into following four categories for an orderly shutdown of the affected unit with the remaining

generating units and auxiliaries continue to operate.

10.1 CONTROLLED ACTION SHUT DOWN

Controlled action shutdown will be initiated by any of the following conditions

• Generator thrust bearing pads temperature very high

• Generator guide bearing pads temperature very high

• Turbine guide bearing pads temperature very high

• Governor OPU oil level low stage-II

• Governor OPU oil pressure low stage-II

10.2 EMERGENCY SHUT DOWN

Emergency shutdown will be initiated by any of the following conditions.

• Sped 115% and deflector/ guide vanes/ runner blades apparatus not moved to closing

• Deflector etc. fails to close in preset time

• Unit over speed (electrical) > 140%

• Unit over speed (mechanical)>150%

• Stop push button on control panel in control room is pressed

Emergency shut down system will perform following functions:

• Trip generator breaker

• Stop turbine by governor action

• Trip generator field circuit breaker• Operate trip alarm in control room

• Energizes emergency solenoid valve in governor cubicle to stop the turbine by

bypassing governor

• Close main inlet valve

10.3 IMMEDIATE ACTION SHUT DOWN

Immediate action shut down will be initiated by any of the following conditions

• Generator differential protection operates

•

Generator stator earth fault protection operates• Generator field failure protection operates

• Generator transformer stand by earth fault protection operates

• Over current in stator

• Over current instantaneous protection in the excitation circuit

The immediate action shut down perform following function




Trip generator breaker

Trip field breaker

Initiates controlled action shut down stop turbine by governor action

Trip annunciation in control room

10.4 ELECTRICAL SHUT DOWN

Electrical shutdown system will be initiated by any of the following conditions

• Over current in the excitation circuit

• Generator back up protection operates

• Generator over voltage protection operates

• Excitation failure protection operates

• Reverse power protection operates

• Generator T/F IDMT over current, over current instantaneous & earth fault protection

operates

Electrical shut down system will perform following functions

• Trip generator breaker

• Trip field breaker

• Governor brings the unit to spin at no load

11.0 PROTECTION OF POWER TRANSFORMERS

Following protections are generally provided on transformers

I. Fuses

II. Sudden pressure protection (Buchholtz Relay)

III. Oil temperature highIV. Winding temperature high

V. Over current/ earth fault

VI. Over frequency

VII. Differential protection

VIII. Restricted earth fault protection

IX. Over flux protection (in large grid)

X. Over all differential protection (Gen. Trans. Both in large machines)

XI. Fire protection system

Fire extinguishers

Mulsyfire protection

Fire buckets-sand filled

12.0 FIRE PROTECTION SYSTEM

For large generators, fire protections system will use CO2 as the quenching medium

which will operate automatically. Hot spot/ smoke detectors are provided all around the

periphery of generator winding. Bank of CO2 cylinders with control panel etc. are provided

common for all the generators. The individual pipes let the CO2 enter in the faulty generator

and quench the fire. Generator is isolator from the bus bar and machine stopped. The system

is more effective in closed cycle cooling systems of generators.




ANNEXURE-I

LIST OF GENERATOR PANEL INDICATION AND RELAYS

Sl.

No.

Designation Inscription Colours

1 L1 DC Supply on Yellow

2 L2 AC Supply on Red

3 L3 Generator Circuit Breaker Close Red

4 L4 Generator Circuit Breaker Open Green

5 L5 Generator Circuit Breaker Trip Amber

6 L6 Generator Circuit Spring Charge Blue

7 L7 Trip Coil Healthy Yellow

8 L8 DC Supply Failed Red

9 L9 Spare Red

10 R R Phase Bus Healthy Red

11 Y Y Phase Bus Healthy Yellow12 B B Phase Bus Healthy Blue

13 IPB Immediate Action Trip Push Button Red

14 PB1 Controlled Action Shut Down Push Button Green

15 PB2 Spare Push Button Red

16 TS Temperature Scanner

17 DMF Digital Multi Function Meter

18 H Hooter Black

19 ANN Annunciator Black

20 T Test Push Button Black

21 A Accept Push Button Yellow

22 R Reset Push Button

23 BAPB Bell Accepted Push Button

24 27 Under Voltage Relay

25 32P Reverse Power Relay

26 51V Voltage Controlled Over Current Relay

27 59 Over Voltage Relay

28 60 PT Fuse Failure Relay

29 64S Stator Earth Fault Relay

30 46 Negative Phase Sequence Relay

31 40 Loss of Field Relay

32 95 Trip coil Supervision relay

33 87G Generator Differential Relay

34 52G Generator Circuit Breaker35 KWTR Kilowatt Transducer

36 BL Electrical Bell

37 86G1 Master Trip Relay




41 Aux Relays As Required



ANNEXURE-II

LIST OF PROTECTION ELEMENTS IN MICRO PROCESSOR BASED RELAYS

Symbol Description

21 Under Impedance

24 Over Fluxing26 Field Winding Temp

27 Under Voltage

27NT 100% Stator E/F

32 Reverse Power

38 Bearing Temp

40 Loss of Field

46 Negative Phase Sequence

49 Stator Winding Temp

50BF Breaker Failure

50P Instantaneous Phase Over Current

50N Instantaneous Neutral Over Current50/27 Unintentional Energisation at Stand Still

51P Time Delayed Phase Over Current

51N Time Delayed Neutral Over Current

51N Voltage Controlled Over Current

59 Over Voltage

59N Residual Over Voltage

64R Restricted E/F

78 Pole Slipping Protection

81 Over/ Under Frequency

87G Generator Differential

CTS Current Transformer Supervision

VTS Voltage Transformer Supervision

3.12 guidelines for monitoring control and protection of shp stations

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