commissioning switches, automatic transfer

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramcos employees.Any material contained in this document which is not already in the publicdomain may not be copied, reproduced, sold, given, or disclosed to thirdparties, or otherwise used in whole, or in part, without the written permissionof the Vice President, Engineering Services, Saudi Aramco.

Chapter : Electrical For additional information on this subject, contactFile Reference: EEX30210 W.A. Roussel on 874-6160

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Commissioning Automatic Transfer Switches

Engineering Encyclopedia Electrical


Saudi Aramco DeskTop Standards

Content Page

INTRODUCTION................................................................................................................1

SAUDI ARAMCO PRACTICES, APPLICATIONS, AND REQUIREMENTS FORAUTOMATIC TRANSFER SWITCHES.............................................................................3

Automatic Transfer Switch Types..............................................................................3

Automatic Transfer Switch Construction and Operation............................................4

Loadbreak Switches for Automatic Transfer Capabilities...........................................7

EVALUATING AUTOMATIC TRANSFER SWITCHES UPON RECEIPT......................10

Visual Inspection......................................................................................................10

Verification Against Specification.............................................................................10

Automatic Transfer Switch Nameplate..........................................................11

Bypass Isolation Switch Nameplate...............................................................13

EVALUATING AUTOMATIC TRANSFER SWITCH INSTALLATION ANDTESTING............................................................................................................................14

Visual Inspection......................................................................................................14

Suitability.....................................................................................................15

Physical Damage...........................................................................................16

Alignment.....................................................................................................16

Cleanliness....................................................................................................16

Arc Chute Assembly.....................................................................................17

Contacts.......................................................................................................17

Operating Mechanism...................................................................................18

Mechanical Inspection..............................................................................................18

Tightness......................................................................................................18

Interlocks......................................................................................................19

Manual Transfer............................................................................................19

Electrical Inspection and Tests..................................................................................19

Insulation Resistance.....................................................................................20

Contact Resistance........................................................................................21

Vacuum Bottle..............................................................................................21




Operational Transfer.....................................................................................22

AUTOMATIC TRANSFER SWITCH PRE-OPERATIONAL CHECK-OUT PHASE REQUIREMENTS........................................................................................23

Point-to-Point Wiring Check....................................................................................23

Subsystem Check-Out..............................................................................................23

AUTOMATIC TRANSFER SWITCH OPERATIONAL TESTING PHASEREQUIREMENTS..............................................................................................................24

Source Feed Compatibility........................................................................................24

Complete System Functional Test.............................................................................24

WORK AID 1: REFERENCES FOR EVALUATING AUTOMATICTRANSFER SWITCHES UPON RECEIPT..............................................25

Automatic Transfer Switch Applications Checklist....................................................29

NETA Checklists......................................................................................................31

Information, Formulas, and Tables for Use inEvaluating the Results of Insulation Resistance (Megger) Tests................................33

Saudi Aramco Pre-Commissioning Forms.................................................................33

GLOSSARY........................................................................................................................40




Table of Figures Page

Figure 1: Typical Automatic Transfer Switch............................................................5

Figure 2: Typical Automatic Transfer Switch Contact Arm Assembly.......................6

Figure 3: Loadbreak Switches Used as Automatic Transfer Switches........................8

Figure 7: Saudi Aramco General Loadbreak Switch Requirements...........................25

Figure 8: Saudi Aramco Automatic Transfer Switch Requirements..........................26

Figure 8: Saudi Aramco Automatic Transfer Switch Requirements (Cont'd).............27

Figure 9: Requirements for the Application and Selection of Medium-and High-Voltage Loadbreak Switches....................................................27

Figure 10: High- and Medium-Voltage Loadbreak Switch Preferred Ratings(From SADP-P-116)...............................................................................28

Figure 11: Control Power Rated Voltages and Operating Rangesfor Automatic Switchgear Devices (From ANSI C37.33)........................29

Figure 12: Insulation Resistance Test Voltages........................................................32

Figure 13: Dielectric Absorption Ratio Chart...........................................................33

Figure 14: Saudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches.................................................................34

Figure 14: Saudi Aramco Pre-Commissioning Form, P-002,Automatic Transfer Switches (Cont'd).....................................................35

Figure 15: Electrical Inspection Excerpt from GI 2.710...........................................37

Figure 15: Electrical Inspection Excerpt from GI 2.710 (Cont'd)..............................38

Figure 15: Electrical Inspection Excerpt from GI 2.710 (Cont'd)..............................39



Saudi Aramco DeskTop Standards 1

INTRODUCTION

An automatic transfer switch is a switch or a group of switches that automatically transfers a loadto another source of power when the original source fails. Another name for an automatictransfer switch is a "throw-over" switch. Automatic transfer switches are used when thecontinuity of power to a load is critical to the safe and proper operation of process or supportequipment. Because of the dangerous electrical energy potentials that are present at medium andhigh voltages, automatic transfer switches are not currently available at these voltage levels. Toprovide automatic transfer capabilities at the higher voltage levels, groups of coordinatedloadbreak switches are used. A loadbreak switch is a disconnect switch that is capable ofinterrupting load current. Although loadbreak automatic transfer switch configurations will bediscussed, the focus of this Module will be restricted to low voltage automatic transfer switches.Low voltages in industrial systems are generally 600 volts and below; however, some referenceinstructions (e.g., GI 2.710) use 480 volts as the "cut-off" voltage. In accordance with SADP-P-116, the voltage values for medium voltage loadbreak and transfer switches are from 5 kV to 15kV and the voltage value for high voltage loadbreak and transfer switches is 34.5 kV.

The selection of the type and size of an automatic transfer switch is based on the technical, theinstallation, and the economic requirements of a facility. The technical requirements of a facilityfor an automatic transfer switch include the system voltage level, fault current, and the numberand criticality of the electrical system loads that are supplied by the automatic transfer switch.Once the type of automatic transfer switch for a given installation is selected, the switch isordered from the manufacturer and installed. The commissioning process for automatic transferswitches in Saudi Aramco facilities ensures that a safe and cost-effective system is installed thatperforms to the specifications of the facility for the projected operating lifetime of the facility.Experience has shown that the time and effort that is expended upfront to ensure safety, qualitycontrol, and adherence to Saudi Aramco and industry standards and practices minimizessubsequent equipment failure.

The commissioning process for automatic transfer switches involves inspections, verifications, andchecks that determine whether the automatic transfer switch specifications and installationrequirements are met. Tests are also performed that determine whether the electric powerdistribution system will operate properly and safely once the switch is installed. When anautomatic transfer switch is inspected and tested satisfactorily during the commissioning process,the system should operate in accordance with manufacturer's specifications for its maximumuseful life.




This Module provides information on the following topics and subtasks that are pertinent tocommissioning automatic transfer switches for Saudi Aramco installations:

Saudi Aramco Practices, Applications, and Requirements for Automatic TransferSwitches

Evaluating Automatic Transfer Switches Upon Receipt

Evaluating Automatic Transfer Switch Installation and Testing

Automatic Transfer Switch Pre-Operational Check-Out Phase Requirements

Automatic Transfer Switch Operational Testing Phase Requirements




SAUDI ARAMCO PRACTICES, APPLICATIONS, AND REQUIREMENTS FORAUTOMATIC TRANSFER SWITCHES

Large process and process support equipment in industrial facilities requires electric power tofunction. The operations, maintenance, and support personnel who work in an industrial facilityrequire electric power for lights, fans, computers, and other support equipment. The electricpower that is required to run the equipment is passed through a distribution system that routes theelectric power to the correct equipment. The distribution system also provides electric powercontrol capabilities, as well as rapid fault isolation and protection. In some instances, the safe andproper operation of the process and support equipment requires a constant and reliable source ofpower. Because power interruptions do occur, automatic transfer switches are used to providecontinuity of power to important or critical loads.

Automatic Transfer Switch Types

Automatic transfer switches transfer loads to an alternate power source upon the failure orinterruption of the original power source. Automatic transfer switches may also be configured toautomatically transfer the load back to the original power source, under specific conditions, whenthe original power source is restored. The three types of automatic transfer switches that areavailable are nonpreferential, fixed-preferential, and selective-preferential.

In all three types of automatic transfer switches, the loads are automatically transferred to analternate power source upon loss or interruption of the original power source. In anonpreferential automatic transfer switch, the loads are automatically transferred back to theoriginal power source only when the alternate power source fails. In a fixed-preferentialautomatic transfer switch, the original power source always serves as the preferred power source,and the alternate power source serves as the emergency power source. The fixed-preferentialautomatic transfer switch will automatically transfer the loads to the preferred power source uponits reenergization. In a selective-preferential automatic transfer switch, either power source mayserve as the preferred or the emergency power source. The selective-preferential automatictransfer switch will automatically transfer the loads to the preselected preferred power sourceupon its reenergization.

Each type of automatic transfer switch can be designed to transfer the power supply in twodifferent ways: either with no interruption of power to the loads, or with a momentary powerinterruption to the loads. Automatic transfer switches that operate with no power interruption tothe loads are called continuous-circuit restoration automatic transfer switches, and automatictransfer switches that operate with a momentary power interruption to the loads are calledinterrupted-circuit restoration automatic transfer switches.




Continuous-circuit restoration automatic transfer switches use contacts that overlap to permit thetransfer of electrical loads from one power source to another without power interruption. Whenpower is restored to the preferred source in both the fixed- and selective-preferential types ofautomatic transfer switches, the load is transferred from the emergency power source to thepreferred power source with both power sources energized. If a phase or voltage mismatch ispresent when the load is transferred from the emergency power source to the preferred powersource, dangerous system transients could result. To prevent dangerous system transients thatresult from inadvertently paralleling two sources out of phase, interrupted-circuit (e.g., internalcontacts do not overlap) restoration automatic transfer switches can be used. Some automatictransfer switches have both continuous-circuit and interrupted-circuit restoration capabilities.Microprocessor controls are used in automatic transfer switches that have both continuous-circuitand interrupted-circuit restoration capabilities to determine which type of restoration is used.

A combination of loadbreak switches may also be used to construct an automatic transfer switch.Loadbreak switch combinations are generally used in medium- and high- voltage systemautomatic power supply transfer applications. When loadbreak switches are used, the applicableSaudi Aramco and industry switchgear requirements must be met. Loadbreak and switchgearrecommended practices, requirements, and references are provided in Work Aid 1.

Automatic Transfer Switch Construction and Operation

Automatic transfer switch assemblies must be furnished from the manufacturer complete with twothree-phase incoming power supply connections (preferred and emergency), a three-phase loadconnection, and control circuitry. The automatic transfer switches that are normally used in SaudiAramco installations are manufactured by either Westinghouse or ASCO. Minimum mandatorySaudi Aramco requirements and industry references for the design and construction of automatictransfer switches are provided in Work Aid 1.

Figure 1 shows a typical automatic transfer switch with the covers on and with the coversremoved. In Figure 1A, the load terminals are shown at the top, and the normal (preferred) andemergency power supply terminals are shown below and slightly in front of the load terminals.The automatic transfer switch nameplate data contain normal (preferred) and emergency powersupply voltage and current rating information and manufacturer model and serial numbers.Nameplate data will be covered later in this module. Figure 1B shows the automatic transferswitch with the covers removed. With the covers removed, the normal (preferred) and emergencypower supply contact arc chute assemblies are visible.




Figure 1: Typical Automatic Transfer Switch




Automatic transfer switches are required to transfer critical loads rapidly and safely upon loss ofthe preferred power. Figure 2 shows how one type of automatic transfer switch accomplishes thispower supply transfer. In Figure 2A, power is provided from the normal (preferred) powersource and passes through the main and arcing contacts to the load. When the normal (preferred)power supply is lost, the coil energizes. When the coil energizes, the core is pulled up into thecoil and the link moves the rotating weight. The motion of the rotating weight causes the pin topush the contact arm assembly yoke. As the contact arm assembly yoke moves, the contact armassembly pivots at the contact arm assembly pivot point. Once the contact arm assemblycompletes its movement, the load is connected to the emergency power source, as shown inFigure 2B.

Figure 2: Typical Automatic Transfer Switch Contact Arm Assembly




Some automatic transfer switches have a bypass isolation switch that is incorporated into theswitch design. A bypass isolation switch can bypass either the normal (preferred) or theemergency power source. When the bypass isolation switch is used, the load is directly fed fromone source, which allows for isolation of the transfer switch for inspection or maintenance. Somebypass switch designs allow the isolation of the transfer switch with no power interruption. Thebypass switch can also function as a manual transfer switch, which allows the load to betransferred from one source to the other, if required, with the automatic transfer switch totallyremoved from the system.

Loadbreak Switches for Automatic Transfer Capabilities

For Saudi Aramco medium voltage installations that require automatic transfer capabilities,loadbreak switches are used as automatic transfer switches. Minimum mandatory Saudi Aramcorequirements and industry references for the design and construction of loadbreak switches areprovided in Work Aid 1. Figure 3 shows and example of loadbreak switches that are used asautomatic transfer switches.

In Figure 3, loadbreak switches "X" and "Y" enable the preferred or the emergency supply to beselected. A manual transfer method is required to be included in the design of the automatictransfer switch. The manual transfer method is necessary for system test and maintenanceoperations. Key interlocks (e.g., Kirk-Key) may also be used on loadbreak switches with manualoperation capabilities that are used in automatic transfer schemes to prevent paralleling of thepreferred and emergency supply. In Figure 3, loadbreak switches are used to provide transfercapabilities. Figure 3 shows that switches "X" or "Y" can be closed only if key K1 is available.Because only one key is provided, only one of the two switches can be manually closed at any onetime.

During the normal operation of a loadbreak switch that is used for automatic transfer, theautomatic transfer sequence is initiated upon the failure or interruption of the normal (preferred)power supply. When loadbreak switches are used as an automatic transfer switch, it is necessaryto delay the transfer from normal to emergency for the following reasons:

To prevent "pumping" of the switches if the normal (preferred) power supplyfeeder trips on a transient fault and is then re-energized.

To allow the residual voltage of any motor loads to decay before re-energizing theloads.




Figure 3: Loadbreak Switches Used as Automatic Transfer Switches

In some instances, delayed transfer schemes may not be suitable for switching critical loads. Someapplications (such as loads that are served from local generators) may require a fast transfer. Thedelay could cause (or amplify) current transient problems during the transfer process.

In some loadbreak switch automatic transfer schemes, oil is used as the arc-interrupting medium.The construction of an oil-immersed auto-transfer switch is similar to that of an oil-immersedloadbreak switch. Oil switches are being removed from service in Saudi Aramco installations andreplaced with SF6 switches. In addition, devices are provided to monitor the voltage of thenormal (preferred) supply to the switch and, on failure of this supply, to initiate transfer of theload to the emergency supply. The devices that are used to monitor the supply voltage arenormally voltage relays that are set to operate at approximately 65% of the nominal operatingvoltage, depending on the type of load. If the normal supply falls below the preset limit, thetransfer to the emergency supply must be initiated after a preset time delay to ensure that transientfluctuations of the normal supply voltage do not cause nuisance transfer and also to allow anyresidual voltage of motor loads (if any) to decay. Transfer may only take place if the emergencysupply voltage is normal.




For high voltages, industry uses oil as the predominant arc-interrupting medium; however,vacuum switches are replacing air- and oil- interrupting switches in newer automatic transferschemes. Although vacuum-interrupting switches that are used in automatic transfer schemes areexpensive to manufacture, the high cost is outweighed by the improved operationalcharacteristics. The improved characteristics of the vacuum switches are small size and weight,high speed interrupting time, long life, reduced maintenance, low operational energyrequirements, and improved safety.

Because the contacts are housed in a vacuum chamber, examination of the contacts for wearduring pre-commissioning or maintenance periods without opening the vacuum housing isdifficult. Vacuum switches must contain a contact wear indicator to enable maintenance andoperation personnel to determine the conditions of the contacts.




EVALUATING AUTOMATIC TRANSFER SWITCHES UPON RECEIPT

The installation of an automatic transfer switch is a process that takes place over a period of time.The installation begins with an identified need for an automatic transfer switch installation (e.g., anew facility). Power is necessary for critical loads at the new facility, so an automatic transferswitch installation is designed. After the design is approved, the automatic transfer switch (orloadbreak switches and switchgear) are ordered from the manufacturer. Once the automatictransfer switch is received from the manufacturer, it must be evaluated to ensure that it is properfor the installation. The purpose of the evaluation is to verify that the correct automatic transferswitch (or loadbreak switch combination) was received from the manufacturer and that the properinstallation specifications and parameters are met. This section will describe how automatictransfer switches are evaluated upon receipt.

Visual Inspection

When an automatic transfer switch is received from the manufacturer, a visual inspection must beperformed. The purpose of the visual inspection is to verify that the automatic transfer switchthat was received from the manufacturer is in good physical condition and that all of the requestedparts and accessories are present. Because of the damage that can occur to the moving parts thatare associated with automatic transfer switches during installation, a cursory inspection isperformed at the receiving point. During the cursory inspection, the inspection personnel wouldlook for obvious equipment damage and determine whether the necessary support equipment(e.g., relays and technical manuals) are present. A detailed inspection of the automatic transferswitch is performed when it is completely installed at the site or facility.

Verification Against Specification

When a new facility or facility modification is at the equipment installation stage, the design of theinstallation has already been completed. The type of automatic transfer switch that is selected fora specific power system should be shown in the drawings, prints, or specifications for theinstallation. The purpose of verifying the automatic transfer switch against the specifications is toensure that the equipment that is being installed meets Saudi Aramco and industry standards.




Generally, the verification against specifications consists of a determination of whether the typeand rating of the equipment that is to be installed match the size and type of the equipment that isrequired for the installation. In some cases, this determination is accomplished by reading anelectrical plan that identifies the automatic transfer switch size and type. The Electrical Engineerinspects the manufacturer's nameplate data on the automatic transfer switch compares it to therequirements on the electrical plan to determine whether the correct equipment is being used. Inother situations, the Electrical Engineer must rely on his knowledge of the correct application ofautomatic transfer switch sizes and types to determine whether the correct equipment is beingused. Any data sheets or manufacturer information that were used to order the switchgear fromthe manufacturer must also be consulted. Any quality control, quality assurance, and test datathat are provided with the automatic transfer switch must also be reviewed. An automatictransfer switch applications check list is provided in Work Aid 1. The check list itemizes whatshould be included in the verification of the automatic transfer switch against specifications.

Automatic Transfer Switch Nameplate

All automatic transfer switches that are used in Saudi Aramco power systems must have anameplate that is clearly visible on the front of the switch. If an automatic transfer switch consistsof a combination of loadbreak switches, each loadbreak switch must have a nameplate, and thepanelboard (or switchgear) that contains the loadbreak switches must also have an externally-attached nameplate.

The nameplate must contain manufacturer-type information. The information that describes thetype of automatic transfer switch must be comprised of the manufacturer name, type designator,and catalog (or serial) number. In accordance with ANSI C37 and NEMA ICS 10-1993, themanufacturer and rating information that must appear on an automatic transfer switch nameplateis to include the following:

Name of Manufacturer and Catalog (or Serial) Number

Voltage and Frequency Ratings

Continuous Current Rating

Suitability (As Applicable)

Interrupting or Short-Circuit Ratings (As Applicable)

Cautions, Warnings, or Both

Name of Manufacturer and Catalog (or Serial) Number - The information thatdescribes the type of automatic transfer switch includes the manufacturer name, the typedesignation, and the serial number.




Voltage and Frequency Ratings - Automatic transfer switches are designed for and mustbe marked with the maximum voltage at which the automatic transfer switch can beapplied. The system voltage ratings for automatic transfer switches are 120, 208, 240,480, and 600 Vac. For automatic transfer switches that consist of loadbreak switches, therated maximum voltage of the automatic transfer switch is the highest rms voltage forwhich the loadbreak switch is designed, and it is the upper limit for automatic transferswitch operation.

Automatic transfer switches in electric power distribution systems are designed to operateat a specific frequency. Saudi Aramco electrical distribution systems are designed tooperate at 60 Hz.

Continuous Current Rating is the amount of current that can be continuously carried bythe automatic transfer switch without exceeding the equipment allowable temperature rise.This rating applies for both automatic transfer switches and loadbreak switches that arecombined for use as an automatic transfer switch.

Suitability (As Applicable) - Additional markings must be included in the automatictransfer switch nameplate that lists the suitability of the automatic transfer switch for usewith specific loads, use for emergency or standby service, and use as service equipment, asapplicable.

Interrupting or Short-Circuit Ratings (As Applicable) - The rated short circuit currentis the maximum current that a switch will withstand at the maximum voltage. Forautomatic transfer switches that have short circuit ratings, the type and rating of the short-circuit protective device must also be included.

Cautions, Warnings, or Both - Electrical safety caution and warning labels are requiredfor all electrical equipment. If a panelboard contains a switch that is marked "Suitable forUse as Service Equipment," a "Service Disconnect" marking must be provided. Themarking must be provided in the form of a pressure-sensitive label in an envelope or on acard. If an insulated neutral that can be grounded is installed in the panelboard, the neutralassembly ampere rating, catalog number, or equivalent identification must be provided.Any additional shock hazard, burn, or rotating equipment warning information must beprominently displayed on the outside of the panelboard or on the inside door or cover.




Bypass Isolation Switch Nameplate

If an automatic transfer switch uses a bypass isolation switch, the bypass isolation switch musthave a nameplate that is clearly visible on the front of the switch. The bypass isolation switchnameplate must contain the following information:

Name of Manufacturer and Catalog (or Serial) Number

Voltage and Frequency Ratings

Continuous Current Rating




EVALUATING AUTOMATIC TRANSFER SWITCH INSTALLATION AND TESTING

The process to determine whether automatic transfer switches should be commissioned is toverify that all the inspections and tests have been performed properly and to verify that the testresults are within the specifications that are designated by the applicable Saudi Aramco andindustry standards.

Installation inspections are performed to verify that proper automatic transfer switch installationmaterials are used, that installation specifications and parameters are met, and that properinstallation procedures are followed. The installation inspection is conducted to ensure that theautomatic transfer switch and associated switchgear will function properly once they are installed.Electrical tests are performed to check the ability of the automatic transfer switch and theassociated switchgear to function under all operating conditions and loads. Installation testsshould detect shipping or installation damage, gross manufacturing defects, or errors inworkmanship or installation. Saudi Aramco Pre-Commissioning Form, P-002, AutomaticTransfer Switches, contains guidance on the items that should be inspected, checked, and testedduring the commissioning of automatic transfer switches. Saudi Aramco Pre-CommissioningForm, P-002, Automatic Transfer Switches, is provided in Work Aid 2.

For automatic transfer switches that consist of a combination of loadbreak switches, the SaudiAramco Switchgear-General Pre-Commissioning Form, P-023, should be used in conjunction withSaudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches. P-023 wasdescribed in EEX 302.09.

The proper evaluation of inspection and testing data during the commissioning process canmaximize the operating time of equipment installations through a determination of trends towardsfailure. Failure prediction can drastically reduce equipment down-time; if a failure is predicted,operational changes can be made, maintenance can be performed, or equipment that is failing canbe replaced in a controlled manner. If a problem is corrected before it causes damage, operatingcosts will be lower because a malfunction can cause associated (or nearby) equipment damage,disruption of service, or can activate emergency repair crews. A failure in any one of the manyinspections, checks, or tests that are performed on an automatic transfer switch during theevaluation of installation and testing is sufficient to prevent the equipment from beingcommissioned.

Visual Inspection

Visual inspections are used to assess the physical condition of automatic transfer switches. Avisual inspection is a pass/fail verification about a particular aspect of the physical condition or theoperation of equipment. Because the criteria that are established to determine the acceptability ofthe visual inspections can be subjective, the visual inspections should be performed by anexperienced Electrical Engineer.




There are several courses of action for visual inspection failure. The course of action depends onthe part of the equipment that failed the visual inspection. A failure of alignment,mechanism/linkage, lubrication, or cleanliness inspection can usually be corrected throughmaintenance procedures. A physical damage or suitability inspection failure will probably requirethe replacement of the damaged component.

The visual inspection of an automatic transfer switch should be performed during the initialinstallation and commissioning. Technical data to evaluate the results of the visual inspection canbe found in the manufacturer's technical manual. For visual inspections of automatic transferswitches that consist of loadbreak switches, panelboard or switchgear technical manuals (asappropriate) should also be consulted. The following visual inspections are used to assess thecondition of automatic transfer switches in Saudi Aramco systems:

Suitability

Physical Damage

Alignment

Cleanliness

Arc Chute Assembly

Contacts

Operating Mechanism

Suitability

The purpose of the suitability visual inspection is to determine whether the automatic transferswitch is appropriate for the application in which it is placed. Under normal circumstances, thesuitability of equipment is determined before it is placed into the system; however, a visualinspection must be performed to ensure that changes that may have been made to the system havenot exceeded the ratings of the automatic transfer switch.

To determine the suitability of an automatic transfer switch, a visual inspection of the nameplatedata must be performed and compared to the electrical system single line diagram. For example,if the nameplate information on an automatic transfer switch does not match the ratings of theelectrical system, the automatic transfer switches must be replaced with one that is correctly rated.The automatic transfer switch terminations and termination labels (tags) must also be verifiedagainst the electrical system single line diagram.




Physical Damage

Physical damage to an automatic transfer switch can prevent the supply of electric power tocritical loads, or it can lead to switchgear or load failure during critical system operations. Themagnitude of the electric energy that passes through automatic transfer switches and the forcesthat are used to operate automatic transfer switches (or loadbreak switches) can propagate andamplify any minor installation damage. Damage to automatic transfer switches can lead to criticalequipment failure, fire, personal injury, or death. Any physical damage to an automatic transferswitch that is noted during an inspection requires the immediate replacement of the damagedcomponent. The most obvious and common forms of physical damage are cracks, dents, missingor broken pieces, bent doors, and burned out indicator lights. The purpose of the physicaldamage inspection is to identify whether corrective maintenance or component replacement isnecessary. Automatic transfer switches that show any form of physical damage, no matter howsmall, should be determined to have failed the physical damage inspection.

Alignment

The purpose of the alignment inspection is to ensure that the automatic transfer switch willproperly pass current when it is connected to the rest of the electrical system. When an automatictransfer switch (e.g., frame or moving contacts) is installed in the panelboard or switchgear,proper alignment of the automatic transfer switch will ensure that the supply and load connectionsare properly made to the automatic transfer switch when the automatic transfer switch isconnected to the circuit. Improper alignment of the automatic transfer switch contacts can causecontact heating and wear.

Cleanliness

The purpose of the cleanliness visual inspection is to ensure the proper operation of the automatictransfer switch over its maximum operating life. The accumulation of dirt over a period of timewill impede the proper operation of the automatic transfer switch and will reduce the dielectricstrength of the automatic transfer switch insulation. Dust and dirt can also reduce the speed andsensitivity of automatic transfer switches under power supply transfer conditions.

Accumulation of dust and dirt should be cleaned away from the automatic transfer switch duringmaintenance cycles. Automatic transfer switches that are installed in extremely dirty, dusty, orhumid areas may have to be frequently maintained.




Arc Chute Assembly

The arc chute assemblies of an automatic transfer switch are responsible for the suppression of thearc that forms when the contacts open. The purpose of the visual inspection of the arc chuteassemblies is to ensure that the arc chutes can safely suppress the arc that forms when theautomatic transfer switch transfers power from an energized power source to another energizedpower source.

When a visual inspection of the arc chute assembly is performed, three conditions exist that willcause the arc chute assembly to fail inspection: burn marks, scale, and cracks. Burn marks changethe consistency of the surface of an arc chute. If burn marks are present on an arc chute, the arcchute should be replaced. Scale is the accumulation of foreign material in the arc chutes that canimpede the ability of the arc chutes to extinguish an arc. Scale should not be removed from thesurface of the arc chutes, so the inspector must determine whether the scale will impede the abilityof the arc chute to extinguish an arc. If the inspector determines that the scale will impede theability of the arc chute to extinguish an arc, the arc chute is replaced. Cracks form in the arcchutes during the normal operation of a switch. The inspector must determine whether the crackswill interfere with the ability of the arc chute to extinguish an arc, and he should replace the arcchute accordingly.

Oil-immersed switches are also used for medium- and high-voltage loadbreak automatic transferswitch applications; however, they are being removed from service in Saudi Aramco, and they arebeing replaced with SF6. Oil-immersed medium- and high-voltage loadbreak automatic transferswitch schemes are commonly used by Saudi Aramco for industrial applications. Oil-immersedswitches are only suitable for outdoor use. For high making and breaking capacity, the oil-immersed switch should incorporate either a spring toggle mechanism or some form of arccontrol. The preferred type of switch construction has spring toggle mechanisms enclosed insidethe tank under oil. Regular inspection and maintenance of oil-immersed switches are necessary toremove accumulated sludge and to test the quality of the oil.

Contacts

The contacts provide a current path through the automatic transfer switch and interrupt thecurrent when the load power is transferred from the emergency power source to the preferredpower source upon restoration of the preferred power source. Damage can occur at the contactsas a result of the mechanical stress from closing operations and the electrical arc that forms duringcontact opening operations. The purpose of the contact visual inspection is to ensure that thecontacts provide a low resistance current path and that the contacts can safely interrupt currentduring automatic transfer operating.




Small burn and pock marks can develop on the surface of the contacts over the operating life ofan automatic transfer switch. These small burn and pock marks will not interfere with theoperation of the contacts, but the contacts will need to be replaced when they erode over time tosome wear point that is defined by the manufacturer. For vacuum loadbreak automatic transferswitches, a contact wear indicator is checked.

Operating Mechanism

The operating mechanism assembly of an automatic transfer switch performs the actual movementof the contacts when the automatic transfer switch transfers the load from one power supply tothe other. The purpose of the operating mechanism inspection is to ensure that the operatingmechanism can move freely. Free movement of the operating mechanism will ensure that theautomatic transfer switch can properly and rapidly operate the contacts. The inspector shouldvisually determine that no obstructions exist that will impede the movement of the operatingmechanism. This inspection will also ensure that, when the power supply transfer test isperformed, no automatic transfer switch damage can occur.

Mechanical Inspection

A mechanical inspection is used to assess the ability of an automatic transfer switch to physicallyperform the mechanical movements that are necessary for proper operation. Tests are alsoperformed during the mechanical inspection to assess automatic transfer switch safety functions.Quality control, quality assurance, and test data should also be provided with the automatictransfer switch by the manufacturer for use during the mechanical inspection. There are severalcourses of action for mechanical inspection failure; however, the course of action depends on thepart of the equipment that failed the inspection. A failure of the mechanism operation can usuallybe corrected through maintenance procedures.

The general mechanical inspections and tests that are performed on switchgear and circuitbreakers that are installed in Saudi Aramco systems are as follows:

Tightness

Interlocks

Manual Transfer

Tightness

The purpose of a tightness inspection is to ensure that enough force is present to hold the cableconnections and joints in place during automatic transfer switch operations. To determine theamount of force that exists at cable connections or bus joints, a torque wrench may be required.Torque values for switchgear and buswork are listed in the associated automatic transfer (orloadbreak) switch manufacturer's technical manuals.




Interlocks

Interlocks are provided in automatic transfer switches to prevent the inadvertent simultaneousconnection of both the preferred and emergency power supplies. During the mechanicalinspection, the automatic transfer switch is checked to ensure that a positive interlock is presentbetween the preferred and emergency power sources. If a bypass isolation switch is provided inthe automatic transfer switch, the bypass isolation switch interlock is also checked.

Manual Transfer

An automatic transfer switch must be provided with manual transfer capabilities. During themechanical inspection, a manual transfer operation must be performed to ensure that the manualpower supply transfer during emergency and maintenance operations is possible. If a bypassisolation switch is provided in the automatic transfer switch, the bypass isolation switch manualtransfer is checked for proper operation.

Electrical Inspection and Tests

During the commissioning process, electrical inspections and tests are performed to check theability of the automatic transfer switch to operate for a reasonable future period of time under alloperating conditions and loads. Acceptance or installation tests will usually detect shipping orinstallation damage and gross defects or errors in workmanship in equipment construction.Quality control, quality assurance, and test data should also be provided with the automatictransfer switch by the manufacturer for use during the electrical inspections and tests. Once theinstallation and inspection data have been recorded and assembled, a methodical and consistentprogram of periodic data collection and evaluation should be established. As each newmaintenance item, test, splice, system addition, or system reconfiguration occurs, new inspectionsand data records will be required and should be added to the existing data on file.

Because an electrical inspection or test failure can be caused by a design flaw, construction error,equipment age, or operational misuse, some kind of troubleshooting or maintenance activityshould be performed on the faulty equipment. For example, a contact resistance test failure canbe rectified by cleaning the contacts to remove carbon build-up or by replacing the contacts.Some electrical inspection or test failures are not repairable and will require the replacement ofthe equipment before the automatic transfer switch can be commissioned. For example, aninsulation resistance test failure usually indicates a gross imperfection in the automatic transferswitch insulation.




The following electrical inspections, checks, and tests are performed on Saudi Aramco automatictransfer switches:

Insulation Resistance

Contact Resistance

Vacuum Bottle

Operational Transfer

Insulation Resistance

The purpose of the insulation resistance test is to directly measure the automatic transfer switchinsulation resistance through use of a megger. In the insulation resistance test, the megger is usedto set up an electromagnetic field, and the field that is created is used to produce leakage currentsthat will flow between the automatic transfer switch contacts phase and ground, or from phase tophase, through the insulation. The amount of leakage current flow that is detected by the meggerresults in a megger meter readout of insulation resistance (in megohms).

To conduct the insulation resistance test, the megger is connected between two conductors(phases) and the megger is operated. Megohmmeter test voltages are provided in Work Aid 2.Similar megger readings are taken across each remaining phase contact pair in the automatictransfer switch. Insulation resistance tests must be conducted phase-to-phase and phase-to-ground with the automatic transfer switch in both the preferred and emergency positions. Theinsulation resistance values are recorded on a test data sheet and should be attached to theappropriate Saudi Aramco pre-commissioning form.

The Electrical Engineer should evaluate the insulation resistance (megger) test values to ensurethat the insulation resistance values that were recorded are greater than the manufacturer'sminimum value. The acceptable insulation resistance values should be determined throughconsultation with the appropriate automatic transfer switch manufacturer's technical manual. Ifthe manufacturer's minimum value is not provided, the value of the insulation resistance must begreater than the rated voltage + 1 kV in megohms. For example, a 600 V rated system must havea measured insulation resistance that is greater than 1.6 megohms. Any value of insulationresistance that is less than the minimum specifications should be investigated by the ElectricalEngineer who performs the test data evaluation.

The ratio of two time-resistance readings (such as a 60-second reading that is divided by a 30-second reading) is called a dielectric absorption ratio. The absorption ratio is useful in recordinginformation about the insulation. If the ratio is a ten-minute reading that is divided by a one-minute reading, the value is called the polarization index.




Because constant cranking is required for hand-cranked megger instruments, it is easier to run thetest for only 60 seconds and take the first reading at 30 seconds. When a power-operated meggerinstrument is used, the results of running the test for a full ten minutes and taking readings at oneand ten minutes will give the polarization index. An explanation of the evaluation of the dielectricabsorption ratio is provided in Work Aid 2.

Contact Resistance

The purpose of the automatic transfer switch contact resistance test is to identify contacts that aredefective or detrimental to the operation of the automatic transfer switch. The contact resistancetest may also identify loose connections in an automatic transfer switch. With the automatictransfer switch in the preferred position, the leads of a digital, low-resistance ohmmeter should beplaced across the line and load sides of the automatic transfer switch, and measurements shouldbe taken across the contacts of each phase. The automatic transfer switch is then transferred tothe emergency position and similar measurements are taken. A digital, low-resistance ohmmetercan deliver enough power to the circuit breaker to make accurate readings that have more validitythan those readings that can be obtained through the use of an ordinary multimeter. The contactresistance is recorded on a test data sheet and attached to the Saudi Aramco pre-commissioningform.

Increased contact resistance may be caused by contacts that do not make proper contact or bypitting on the surface of the contacts. The contact resistance values that are recorded should beconsistent with the manufacturer's recommended values. Generally, values of contact resistancein excess of 200 micro-ohms and deviations of more than +/- 20% should be investigated.Technical data to evaluate the results of the contact resistance test can be found in the automatictransfer switch (or loadbreak switch) manufacturer's technical manual.

Vacuum Bottle

The vacuum bottle test is a dielectric test that is conducted across the open contacts of theautomatic transfer switch electrical contacts. The dielectric tests verify the integrity of the arc-interrupting vacuum chamber.

To perform the dielectric test, an ac potential should be applied across the automatic transferswitch open contacts. The magnitude of the test potential should be in accordance withmanufacturer's technical manuals. Once the test potential has been determined, it should beapplied for a short amount of time, usually five seconds. If no breakdown occurs across thecontacts, the vacuum integrity is acceptable.




Operational Transfer

The operational transfer test of the automatic transfer switch ensures that all of the switch partsare able to work in conjunction with each other so that the automatic transfer switch can performits power supply transfer responsibilities. Most of the tests that have been performed so far havebeen tests that ensure the proper performance of the individual parts of the automatic transferswitch. The operational transfer test will ensure that the parts will work together so that theautomatic transfer switch operates correctly when it is installed in an electrical system.

To perform the operational transfer test, an automatic transfer is performed through simulation ofa loss of the preferred power source. Once the automatic transfer switch is selected to theemergency power supply, the preferred power is restored and the automatic transfer switch isrestored to the preferred power source. During the transfer operations, the correct operation andtiming of the automatic transfer switch is monitored. Electrical interlocks and limit switches (ifpresent) are also monitored during the functional operation test. The operational transfer testinformation (e.g., proper operation and time delay) is recorded on a test data sheet or in the SaudiAramco correct pre-commissioning form.




AUTOMATIC TRANSFER SWITCH PRE-OPERATIONAL CHECK-OUT PHASEREQUIREMENTS

The system pre-operational check-out phase of the commissioning cycle for automatic transferswitches provides an opportunity for Saudi Aramco personnel to perform wiring checks,subsystem component check-outs, and circuit breaker interlock performance tests. Eachautomatic transfer switch component is checked to ensure that it works individually and as acomplete system.

Point-to-Point Wiring Check

Point-to-point wiring checks are performed to verify automatic transfer switch compliance withwiring diagrams and manufacturer specifications. Terminations and terminal blocks are alsochecked for routing and labeling. During the point-to-point wiring checks, control and meteringtransformers and fuses are checked for proper application and type. If necessary, adjustments aremade to components such as relays, annunciators, alarms, and targets.

Subsystem Check-Out

Subsystems are checked to ensure that electrical continuity exists for control and protectivedevices. The proper operation of all subsystems is tested through use of controlled operation andcheck-out of the controls and protective devices. Each subsystem is performance tested throughthe application of full operational voltage to each subsystem through the proper protectivedevices. A complete operational test is performed on equipment controls, interlocks, protectivedevices, and components with each subcircuit connected to its main system. During theperformance test, the main systems are still isolated and independent from plant systems. Beforethe equipment is connected to the plant system, subsystem performance testing is critical to ensurethe proper and safe operation of the equipment protection and control subsystems.

Because phasing of power supplies is critical to the proper operation of rotating equipment loads(e.g., pumps and motors), the proper phase sequence at each of the power supply terminals mustbe checked and verified against the phase sequence of the connected loads.




AUTOMATIC TRANSFER SWITCH OPERATIONAL TESTING PHASEREQUIREMENTS

The operational testing phase of the commissioning cycle for automatic transfer switches providesan opportunity for Saudi Aramco personnel to perform the following:

Source Feed Compatibility Checks

Complete System Functional Test

Source Feed Compatibility

Source feed compatibility checks are performed on automatic transfer switches throughapplication of the full system voltage onto the panelboard or switchgear with the automatictransfer switch installed. With the voltage applied, voltage phasing, synchronizing, devicerotation, protective relay calibration, and other source feed compatibility checks are performed.Both the preferred and emergency power sources are connected to the loads to ensure the totaloperation of the major component loads of the system.

Complete System Functional Test

A complete system functional test is performed on the automatic transfer switch to ensure that theentire electric power distribution system functions in accordance with the system design. Duringthe complete system functional test of the automatic transfer switch, the automatic transfer switchis allowed to assume a fully-loaded condition with power supplied from the preferred powersource. The power from the preferred source is maintained for a period of time that is adequateto obtain the maximum system temperature, and the panelboard (or switchgear) temperatures aremonitored. The automatic transfer switch is then transferred to the emergency source andmaintained for a similar period of time, and the temperatures are again monitored. Cable andtermination temperatures can be monitored locally through use of temperature monitoringequipment or through use of thermographic surveys. Temperature monitoring equipment can betemporarily installed at the panelboard (or switchgear) vents. Particular attention should be paidto wiring and terminal connections during the complete system functional test.




WORK AID 1: REFERENCES FOR EVALUATING AUTOMATIC TRANSFERSWITCHES UPON RECEIPT

The information that is presented in the checklists and information tables has been assembledfrom SADP-P-116, SAES-P-116, ANSI C37, and associated industry standards.

Saudi Aramco uses loadbreak switches for automatic transfer switching. Figure 7 shows a tableof Saudi Aramco loadbreak switch general requirements.

GeneralLoadbreakSwitchRequirements

Automatic transfer switches must be designed, rated, manufactured, andtested in accordance with the latest issue or revision of the following:

ANSI/IEEE Standard C37.20.1 ANSI/IEEE Standard C37.30 ANSI/IEEE Standard C37.32 ANSI/IEEE Standard C37.72

The minimum mandatory requirements for the design and installation ofswitchgear and control equipment are found in SAES-P-116.Deviation from the requirements specified in SAES-P-116 must not bemade without the written approval of the Manager, Consulting ServicesDepartment.Although loadbreak switches are not normally required to interrupt faultcurrent, they must be capable of:

Breaking currents equal to their continuous current rating at loadpower factor and system voltage.

Interrupting small inductive or capacitive currents for applicationswhere they are used for disconnecting unloaded transformers,cables, or overhead lines.

Closing onto a terminal short circuit.Loadbreak switches must have independent operators. Switches withdependent manual operators must not be used because they do not have afault making capacity.

Figure 7: Saudi Aramco General Loadbreak Switch Requirements




Figure 8 shows a table of Saudi Aramco automatic transfer switch general requirements.

GeneralRequirements

Switches, circuit breakers, motor controllers, and fuses must not be locatedin Division I classified areas. Refer to SAES-B-068 for electrical areaclassification requirements.Switches that are used for automatic transfer in Saudi Aramco installationsare required to be equipped with electrical operators.Control power transformers are required on the preferred source and on theemergency source.Automatic transfer switches may be used to automatically sense voltageloss and switch alternate supplies to critical loads.

VacuumAutomatic

A vacuum automatic transfer switch is an acceptable alternative to an oilbreak automatic transfer switch.

Transfer Vacuum switches must contain the same facilities as other types ofswitches.

Switches Vacuum is preferred for dead front, pad mount types.Vacuum switches must be equipped with a contact wear indicator.

Low-VoltageAutomaticTransferSwitches

Transfer switches must: Be capable of switching continuous load current. Have a withstand and fault close rating of at least 105 of the

available three-phase RMS symmetrical fault current. Transfer switches using circuit breakers equipped with overcurrent

protection must have a current interrupting rating of at least 105%of the available three-phase RMS fault current. Refer to NEMAICS-10 for further information on automatic transfer switches.

Figure 8: Saudi Aramco Automatic Transfer Switch Requirements




Medium-andHigh-VoltageLoadbreakSwitches

Frame-mounted, oil-immersed, transfer switches are the most prevalenttype that is used by Saudi Aramco for industrial applications.Frame-mounted, oil-immersed, transfer switches are only suitable foroutdoor use. Refer to 16-SAMSS-510 for specification requirements.Oil-immersed switches are available with electrical operators and associatedcontrol power transformers.Transfer switch cable terminations must be of dry-type dead-frontconstruction. Potheads must not be used. Switches are available withterminations for either solid dielectric or other types of power cables.Current-limiting and conventional power fuses are available for use inoil-immersed loadbreak switches.For high making and breaking capacity, the switch must incorporate eithera spring toggle mechanism or some form of arc control. The preferredtype of switch construction has spring toggle mechanisms enclosed insidethe tank under oil. Regular maintenance of this type of switch is necessaryto remove accumulated sludge and to test the quality of the oil.Askarel or any polychlorinated bi-phenyl (PCB) dielectric (insulating fluid)must not be used.

Figure 8: Saudi Aramco Automatic Transfer Switch Requirements (Cont'd)

Figure 9 shows a table of Saudi Aramco requirements for the application and selection ofmedium- and high-voltage loadbreak switches.

All switches must be group-operated.Switch operating mechanisms must be protected from damage due to weather, dust, andcorrosion. Mechanisms, linkages, and springs must be located inside tanks on outdoorunits.Synchronism check devices must be provided in situations where it is possible tointerconnect two systems out of synchronism.Fuses must be readily accessible without draining oil in oil-filled switches.For industrial applications, a blown fuse must initiate the opening of an associated switch.Switches must be of deadfront construction.Enclosures will generally be of metal, although fiberglass enclosures are acceptable if theyprovide protection equal to metal enclosures.

Figure 9: Requirements for the Application and Selectionof Medium- and High-Voltage Loadbreak Switches




For consistency, rated insulation levels and fault-make ratings applicable to air switches (asdefined in ANSI C37.32) must be used for automatic transfer loadbreak switches. Figure 10shows the preferred ratings for high- and medium-voltage loadbreak switches that are used bySaudi Aramco.

Figure 10: High- and Medium-Voltage Loadbreak SwitchPreferred Ratings (From SADP-P-116)




Figure 11 shows the control power rated voltages and operating ranges for automatic switchgeardevices (e.g., automatic transfer switches) that are used by Saudi Aramco.

Figure 11: Control Power Rated Voltages and Operating Rangesfor Automatic Switchgear Devices (From ANSI C37.33)

When the requirements of an automatic transfer switch are evaluated, specific characteristics ofthe normal (preferred) and alternate power supplies must be specified. Upon initial receipt of anautomatic transfer switch, the following items must be checked, inspected, and verified to ensurethat the automatic transfer switch equipment is properly matched to the power system:

Voltage

Number of phases

Number of wires

Frequency

Number of switched poles

Type of load

Requirements of the load (continuous current, horsepower, or both)

Whether it is necessary to disconnect the load from both power sourcessimultaneously

Whether the switch is intended for emergency or standby service

Whether the switch is to be suitable for use as service equipment

Whether the switch is to include integral overcurrent protection

Whether it is necessary to provide a bypass isolation switch




Automatic Transfer Switch Applications Checklist

Automatic transfer switch rating information can be found on the equipment nameplate or in themanufacturer's technical manual. The following is a checklist that is used to verify that the type,the rating, and the operational characteristics of automatic transfer switches are correct for theapplication based on Saudi Aramco and industry standards:

Verify that the automatic transfer switch meets the Saudi Aramco requirements thatare shown in Figures 7 through 9.

Verify that the automatic transfer switch matches the information that is provided inthe latest single line diagram (e.g., name of manufacturer, catalog or serial number).

Verify that the automatic transfer switch frequency rating is correct for theapplication.

Verify that the automatic transfer switch voltage ratings are correct for theapplication.

Verify that the automatic transfer switch current ratings are correct for theapplication.

Verify that the automatic transfer switch operational characteristics are suitable forthe electrical loads that are supplied by the automatic transfer switch and that anycautions or warnings are listed on the nameplate.




WORK AID 2: REFERENCES FOR EVALUATING AUTOMATIC TRANSFERSWITCH INSTALLATION AND TESTING

The information that is presented in the checklists and information tables has been assembledfrom NETA specifications, SAES-P-116, ANSI C37, and associated industry standards.

NETA Checklists

The following checklist is excerpted from the International Electrical Testing Association (NETA)checklist for the inspection of switchgear - general:

Inspect the physical, electrical, and mechanical condition.

Compare the equipment nameplate information with the latest single-line diagramand report any discrepancies.

Inspect for proper alignment, anchorage, and grounding.

Inspect all bus connections for high resistance with a resistance ohmmeter. Checkthe tightness of the bolted bus joints through use of a calibrated torque wrench.Refer to the manufacturer's instructions for the proper foot-pound levels.

Key interlock systems (if used) must be physically tested to ensure that they operateproperly as follows:

- Attempt to close a locked open device.

- Attempt to open a locked closed device.

- Attempt to exchange keys with devices that are not in their normal operatingpositions.

All switchgear doors, panels, and sections must be inspected for paint, dents,scratches, and proper fit.

Inspect the switchgear for cleanliness and proper lubrication.

Exercise all active components.

Inspect all indicating devices for proper operation.




The following checklist is excerpted from the International Electrical Testing Association (NETA)checklist for the inspection of automatic transfer switches:

Visual and Mechanical Inspection

- Inspect the automatic transfer switch for physical damage.

- Check the automatic transfer switch to ensure a positive interlock (bothmechanical and electrical) between the normal and alternate power sources.

- Check the tightness of all control and power connections.

- Perform a successful manual transfer operation.

- Check the proper operation of the mechanical breaker reset function.

Electrical Tests

- Perform insulation resistance tests from phase-to-phase and from phase-to-ground with the automatic transfer switch in both positions. Values ofinsulation resistance that are less than the manufacturer's minimum (or kV + 1in megohms) must be investigated.

- Perform contact resistance tests for all sets of contacts. The manufacturer'stechnical manual should be consulted to determine a range of acceptablecontact resistances. The contact resistance must not exceed 500 micro-ohms.

- Check the calibration of sensing and control relays.

- Perform an automatic transfer by simulating a loss, and subsequent return, ofthe preferred power source.

- Monitor and verify the correct operation and timing of the automatic transferswitch sensing, timing, and operation equipment.

Figure 12 shows insulation resistance test voltages for automatic transfer switches.

Voltage Rating Test Voltage

150 - 600 V 1000 Vdc601 - 5000 V 2500 Vdc5001 - 5000 Vdc

Figure 12: Insulation Resistance Test Voltages




Information, Formulas, and Tables for Use in Evaluating the Results of InsulationResistance (Megger) Tests

The results of all commissioning megger tests that are performed must be documented on theappropriate Saudi Aramco pre-commissioning form.

The following are the types of megger tests that can be conducted:

Short time or spot reading

Time resistance

Dielectric absorption ratio

When the dielectric absorption ratio megger test is performed, the polarization index can bedetermined through use of the following equation:

Figure 13 provides insulation conditions for 60/30 second ratio results and for 10/1 minute ratioresults.

InsulationCondition

60/30 - SecondRatio

10/1 - Minute Ratio(Polarization Index)

Dangerous --- Less than 1

Questionable 1.0 to 1.25 1.0 to 2

Good 1.4 to 1.6 2 to 4

Excellent Above 1.6 Above 4

Figure 13: Dielectric Absorption Ratio Chart

Saudi Aramco Pre-Commissioning Forms

Figure 14 shows the Saudi Aramco Automatic Transfer Switches Pre-Commissioning Form, P-002. This form provides a field installation checklist for automatic transfer switch installationsand contains a broad checklist of visual and mechanical inspections, as well as the listed electricaland tests that are required for automatic transfer switch installations. Pre-commissioning formsare subject to periodic revision.




Figure 14: Saudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches




Figure 14: Saudi Aramco Pre-Commissioning Form,P-002, Automatic Transfer Switches (Cont'd)




The following is an excerpt from GI 2.710, New Construction Check List Example, thatillustrates the overall checklist and sign-off for major pieces of electrical equipment.

3. Electrical Equipment

All substations, powercable, electrical equipment,including lighting andwiring, to be checked forproper application,operation, and grounds.Distribution panels,switches properly identified,and all energizationcertificate requests signed.

Construction Agency

Power Distribution Dept.

Project Inspection

Commissioning (Note 1)




Figure 15 shows an excerpt from GI 2.710, General Instruction Manual, that illustrates theinspections and tests that should be performed on major pieces of electrical equipment prior to theturnover of a facility.

Figure 15: Electrical Inspection Excerpt from GI 2.710




Figure 15: Electrical Inspection Excerpt from GI 2.710 (Cont'd)




GLOSSARY

dielectric absorption ratio The ratio of two timed insulation resistance readings (such as a 60-second reading that is divided by a 30-second reading).

polarization index A ratio that consists of a ten-minute insulation resistance readingdivided by a one-minute insulation resistance reading.

commissioning switches, automatic transfer

Documents

transfer switch nameplate

transfer switch construction

transfer switch types

isolation switch nameplate

aramco practices

loadbreak switches

technical material

visual inspection