Engineering Encyclopedia: Commissioning Automatic Transfer Switches

Engineering Encyclopedia Saudi Aramco DeskTop Standards

Commissioning Automatic Transfer Switches

Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.

Chapter : Electrical File Reference: EEX30210

For additional information on this subject, contact W.A. Roussel on 874-6160

Engineering Encyclopedia

Electrical Commissioning Automatic Transfer Switches

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INTRODUCTION................................................................................................................ 1 SAUDI ARAMCO PRACTICES, APPLICATIONS, AND REQUIREMENTS FOR AUTOMATIC 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 AND TESTING............................................................................................................................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

Saudi Aramco DeskTop Standards



Operational Transfer .....................................................................................22 AUTOMATIC TRANSFER SWITCH PRE-OPERATIONAL CHECKOUT PHASE REQUIREMENTS ........................................................................................23 Point-to-Point Wiring Check ....................................................................................23 Subsystem Check-Out ..............................................................................................23 AUTOMATIC TRANSFER SWITCH OPERATIONAL TESTING PHASE REQUIREMENTS ..............................................................................................................24 Source Feed Compatibility........................................................................................24 Complete System Functional Test.............................................................................24 WORK AID 1: REFERENCES FOR EVALUATING AUTOMATIC TRANSFER SWITCHES UPON RECEIPT ..............................................25 Automatic Transfer Switch Applications Checklist....................................................29 NETA Checklists......................................................................................................31 Information, Formulas, and Tables for Use in Evaluating the Results of Insulation Resistance (Megger) Tests ................................33 Saudi Aramco Pre-Commissioning Forms.................................................................33 GLOSSARY........................................................................................................................40




Table of Figures

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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 Mediumand 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 Ranges for 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




INTRODUCTION An automatic transfer switch is a switch or a group of switches that automatically transfers a load to another source of power when the original source fails. Another name for an automatic transfer switch is a "throw-over" switch. Automatic transfer switches are used when the continuity of power to a load is critical to the safe and proper operation of process or support equipment. Because of the dangerous electrical energy potentials that are present at medium and high voltages, automatic transfer switches are not currently available at these voltage levels. To provide automatic transfer capabilities at the higher voltage levels, groups of coordinated loadbreak switches are used. A loadbreak switch is a disconnect switch that is capable of interrupting load current. Although loadbreak automatic transfer switch configurations will be discussed, 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 reference instructions (e.g., GI 2.710) use 480 volts as the "cut-off" voltage. In accordance with SADP-P116, the voltage values for medium voltage loadbreak and transfer switches are from 5 kV to 15 kV 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, the installation, and the economic requirements of a facility. The technical requirements of a facility for an automatic transfer switch include the system voltage level, fault current, and the number and 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 is ordered from the manufacturer and installed. The commissioning process for automatic transfer switches in Saudi Aramco facilities ensures that a safe and cost-effective system is installed that performs 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, quality control, and adherence to Saudi Aramco and industry standards and practices minimizes subsequent equipment failure. The commissioning process for automatic transfer switches involves inspections, verifications, and checks that determine whether the automatic transfer switch specifications and installation requirements are met. Tests are also performed that determine whether the electric power distribution system will operate properly and safely once the switch is installed. When an automatic transfer switch is inspected and tested satisfactorily during the commissioning process, the system should operate in accordance with manufacturer's specifications for its maximum useful life.


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This Module provides information on the following topics and subtasks that are pertinent to commissioning automatic transfer switches for Saudi Aramco installations: • Saudi Aramco Practices, Applications, and Requirements for Automatic Transfer Switches • 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


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SAUDI ARAMCO PRACTICES, APPLICATIONS, AND REQUIREMENTS FOR AUTOMATIC TRANSFER SWITCHES Large process and process support equipment in industrial facilities requires electric power to function. The operations, maintenance, and support personnel who work in an industrial facility require electric power for lights, fans, computers, and other support equipment. The electric power that is required to run the equipment is passed through a distribution system that routes the electric power to the correct equipment. The distribution system also provides electric power control capabilities, as well as rapid fault isolation and protection. In some instances, the safe and proper operation of the process and support equipment requires a constant and reliable source of power. Because power interruptions do occur, automatic transfer switches are used to provide continuity of power to important or critical loads. Automatic Transfer Switch Types Automatic transfer switches transfer loads to an alternate power source upon the failure or interruption of the original power source. Automatic transfer switches may also be configured to automatically transfer the load back to the original power source, under specific conditions, when the original power source is restored. The three types of automatic transfer switches that are available are nonpreferential, fixed-preferential, and selective-preferential. In all three types of automatic transfer switches, the loads are automatically transferred to an alternate power source upon loss or interruption of the original power source. In a nonpreferential automatic transfer switch, the loads are automatically transferred back to the original power source only when the alternate power source fails. In a fixed-preferential automatic 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-preferential automatic transfer switch will automatically transfer the loads to the preferred power source upon its reenergization. In a selective-preferential automatic transfer switch, either power source may serve as the preferred or the emergency power source. The selective-preferential automatic transfer switch will automatically transfer the loads to the preselected preferred power source upon its reenergization. Each type of automatic transfer switch can be designed to transfer the power supply in two different ways: either with no interruption of power to the loads, or with a momentary power interruption to the loads. Automatic transfer switches that operate with no power interruption to the loads are called continuous-circuit restoration automatic transfer switches, and automatic transfer switches that operate with a momentary power interruption to the loads are called interrupted-circuit restoration automatic transfer switches.


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Continuous-circuit restoration automatic transfer switches use contacts that overlap to permit the transfer of electrical loads from one power source to another without power interruption. When power is restored to the preferred source in both the fixed- and selective-preferential types of automatic transfer switches, the load is transferred from the emergency power source to the preferred power source with both power sources energized. If a phase or voltage mismatch is present when the load is transferred from the emergency power source to the preferred power source, dangerous system transients could result. To prevent dangerous system transients that result from inadvertently paralleling two sources out of phase, interrupted-circuit (e.g., internal contacts do not overlap) restoration automatic transfer switches can be used. Some automatic transfer switches have both continuous-circuit and interrupted-circuit restoration capabilities. Microprocessor controls are used in automatic transfer switches that have both continuous-circuit and 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 system automatic power supply transfer applications. When loadbreak switches are used, the applicable Saudi Aramco and industry switchgear requirements must be met. Loadbreak and switchgear recommended 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 two three-phase incoming power supply connections (preferred and emergency), a three-phase load connection, and control circuitry. The automatic transfer switches that are normally used in Saudi Aramco installations are manufactured by either Westinghouse or ASCO. Minimum mandatory Saudi Aramco requirements and industry references for the design and construction of automatic transfer switches are provided in Work Aid 1. Figure 1 shows a typical automatic transfer switch with the covers on and with the covers removed. In Figure 1A, the load terminals are shown at the top, and the normal (preferred) and emergency 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 power supply 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 transfer switch with the covers removed. With the covers removed, the normal (preferred) and emergency power supply contact arc chute assemblies are visible.


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Figure 1: Typical Automatic Transfer Switch


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Automatic transfer switches are required to transfer critical loads rapidly and safely upon loss of the preferred power. Figure 2 shows how one type of automatic transfer switch accomplishes this power supply transfer. In Figure 2A, power is provided from the normal (preferred) power source 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 the coil and the link moves the rotating weight. The motion of the rotating weight causes the pin to push the contact arm assembly yoke. As the contact arm assembly yoke moves, the contact arm assembly pivots at the contact arm assembly pivot point. Once the contact arm assembly completes its movement, the load is connected to the emergency power source, as shown in Figure 2B.

Figure 2: Typical Automatic Transfer Switch Contact Arm Assembly Saudi Aramco DeskTop Standards

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Some automatic transfer switches have a bypass isolation switch that is incorporated into the switch design. A bypass isolation switch can bypass either the normal (preferred) or the emergency power source. When the bypass isolation switch is used, the load is directly fed from one source, which allows for isolation of the transfer switch for inspection or maintenance. Some bypass switch designs allow the isolation of the transfer switch with no power interruption. The bypass switch can also function as a manual transfer switch, which allows the load to be transferred from one source to the other, if required, with the automatic transfer switch totally removed 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 Aramco requirements and industry references for the design and construction of loadbreak switches are provided in Work Aid 1. Figure 3 shows and example of loadbreak switches that are used as automatic transfer switches. In Figure 3, loadbreak switches "X" and "Y" enable the preferred or the emergency supply to be selected. A manual transfer method is required to be included in the design of the automatic transfer switch. The manual transfer method is necessary for system test and maintenance operations. Key interlocks (e.g., Kirk-Key) may also be used on loadbreak switches with manual operation capabilities that are used in automatic transfer schemes to prevent paralleling of the preferred and emergency supply. In Figure 3, loadbreak switches are used to provide transfer capabilities. 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 one time. During the normal operation of a loadbreak switch that is used for automatic transfer, the automatic 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 necessary to delay the transfer from normal to emergency for the following reasons: • To prevent "pumping" of the switches if the normal (preferred) power supply feeder trips on a transient fault and is then re-energized. • To allow the residual voltage of any motor loads to decay before re-energizing the loads.


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Figure 3: Loadbreak Switches Used as Automatic Transfer Switches

In some instances, delayed transfer schemes may not be suitable for switching critical loads. Some applications (such as loads that are served from local generators) may require a fast transfer. The delay 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-immersed loadbreak switch. Oil switches are being removed from service in Saudi Aramco installations and replaced with SF6 switches. In addition, devices are provided to monitor the voltage of the normal (preferred) supply to the switch and, on failure of this supply, to initiate transfer of the load to the emergency supply. The devices that are used to monitor the supply voltage are normally voltage relays that are set to operate at approximately 65% of the nominal operating voltage, depending on the type of load. If the normal supply falls below the preset limit, the transfer to the emergency supply must be initiated after a preset time delay to ensure that transient fluctuations of the normal supply voltage do not cause nuisance transfer and also to allow any residual voltage of motor loads (if any) to decay. Transfer may only take place if the emergency supply voltage is normal.


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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 transfer schemes. Although vacuum-interrupting switches that are used in automatic transfer schemes are expensive to manufacture, the high cost is outweighed by the improved operational characteristics. The improved characteristics of the vacuum switches are small size and weight, high speed interrupting time, long life, reduced maintenance, low operational energy requirements, and improved safety. Because the contacts are housed in a vacuum chamber, examination of the contacts for wear during pre-commissioning or maintenance periods without opening the vacuum housing is difficult. Vacuum switches must contain a contact wear indicator to enable maintenance and operation personnel to determine the conditions of the contacts.


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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., a new facility). Power is necessary for critical loads at the new facility, so an automatic transfer switch installation is designed. After the design is approved, the automatic transfer switch (or loadbreak switches and switchgear) are ordered from the manufacturer. Once the automatic transfer switch is received from the manufacturer, it must be evaluated to ensure that it is proper for the installation. The purpose of the evaluation is to verify that the correct automatic transfer switch (or loadbreak switch combination) was received from the manufacturer and that the proper installation specifications and parameters are met. This section will describe how automatic transfer switches are evaluated upon receipt. Visual Inspection When an automatic transfer switch is received from the manufacturer, a visual inspection must be performed. The purpose of the visual inspection is to verify that the automatic transfer switch that was received from the manufacturer is in good physical condition and that all of the requested parts and accessories are present. Because of the damage that can occur to the moving parts that are associated with automatic transfer switches during installation, a cursory inspection is performed at the receiving point. During the cursory inspection, the inspection personnel would look 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 transfer switch 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 the installation has already been completed. The type of automatic transfer switch that is selected for a specific power system should be shown in the drawings, prints, or specifications for the installation. The purpose of verifying the automatic transfer switch against the specifications is to ensure that the equipment that is being installed meets Saudi Aramco and industry standards.


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Generally, the verification against specifications consists of a determination of whether the type and rating of the equipment that is to be installed match the size and type of the equipment that is required for the installation. In some cases, this determination is accomplished by reading an electrical plan that identifies the automatic transfer switch size and type. The Electrical Engineer inspects the manufacturer's nameplate data on the automatic transfer switch compares it to the requirements on the electrical plan to determine whether the correct equipment is being used. In other situations, the Electrical Engineer must rely on his knowledge of the correct application of automatic transfer switch sizes and types to determine whether the correct equipment is being used. Any data sheets or manufacturer information that were used to order the switchgear from the manufacturer must also be consulted. Any quality control, quality assurance, and test data that are provided with the automatic transfer switch must also be reviewed. An automatic transfer switch applications check list is provided in Work Aid 1. The check list itemizes what should 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 a nameplate that is clearly visible on the front of the switch. If an automatic transfer switch consists of a combination of loadbreak switches, each loadbreak switch must have a nameplate, and the panelboard (or switchgear) that contains the loadbreak switches must also have an externallyattached nameplate. The nameplate must contain manufacturer-type information. The information that describes the type 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, the manufacturer and rating information that must appear on an automatic transfer switch nameplate is 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 that describes the type of automatic transfer switch includes the manufacturer name, the type designation, and the serial number.


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Voltage and Frequency Ratings - Automatic transfer switches are designed for and must be marked with the maximum voltage at which the automatic transfer switch can be applied. 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, the rated maximum voltage of the automatic transfer switch is the highest rms voltage for which the loadbreak switch is designed, and it is the upper limit for automatic transfer switch operation. Automatic transfer switches in electric power distribution systems are designed to operate at a specific frequency. Saudi Aramco electrical distribution systems are designed to operate at 60 Hz. Continuous Current Rating is the amount of current that can be continuously carried by the automatic transfer switch without exceeding the equipment allowable temperature rise. This rating applies for both automatic transfer switches and loadbreak switches that are combined for use as an automatic transfer switch. Suitability (As Applicable) - Additional markings must be included in the automatic transfer switch nameplate that lists the suitability of the automatic transfer switch for use with specific loads, use for emergency or standby service, and use as service equipment, as applicable. Interrupting or Short-Circuit Ratings (As Applicable) - The rated short circuit current is the maximum current that a switch will withstand at the maximum voltage. For automatic transfer switches that have short circuit ratings, the type and rating of the shortcircuit protective device must also be included. Cautions, Warnings, or Both - Electrical safety caution and warning labels are required for all electrical equipment. If a panelboard contains a switch that is marked "Suitable for Use as Service Equipment," a "Service Disconnect" marking must be provided. The marking must be provided in the form of a pressure-sensitive label in an envelope or on a card. If an insulated neutral that can be grounded is installed in the panelboard, the neutral assembly ampere rating, catalog number, or equivalent identification must be provided. Any additional shock hazard, burn, or rotating equipment warning information must be prominently displayed on the outside of the panelboard or on the inside door or cover.


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Bypass Isolation Switch Nameplate If an automatic transfer switch uses a bypass isolation switch, the bypass isolation switch must have a nameplate that is clearly visible on the front of the switch. The bypass isolation switch nameplate must contain the following information: • Name of Manufacturer and Catalog (or Serial) Number • Voltage and Frequency Ratings • Continuous Current Rating


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EVALUATING AUTOMATIC TRANSFER SWITCH INSTALLATION AND TESTING The process to determine whether automatic transfer switches should be commissioned is to verify that all the inspections and tests have been performed properly and to verify that the test results are within the specifications that are designated by the applicable Saudi Aramco and industry standards. Installation inspections are performed to verify that proper automatic transfer switch installation materials are used, that installation specifications and parameters are met, and that proper installation procedures are followed. The installation inspection is conducted to ensure that the automatic 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 the associated switchgear to function under all operating conditions and loads. Installation tests should detect shipping or installation damage, gross manufacturing defects, or errors in workmanship or installation. Saudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches, contains guidance on the items that should be inspected, checked, and tested during the commissioning of automatic transfer switches. Saudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches, is provided in Work Aid 2. For automatic transfer switches that consist of a combination of loadbreak switches, the Saudi Aramco Switchgear-General Pre-Commissioning Form, P-023, should be used in conjunction with Saudi Aramco Pre-Commissioning Form, P-002, Automatic Transfer Switches. P-023 was described in EEX 302.09. The proper evaluation of inspection and testing data during the commissioning process can maximize the operating time of equipment installations through a determination of trends towards failure. 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 can be replaced in a controlled manner. If a problem is corrected before it causes damage, operating costs 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 many inspections, checks, or tests that are performed on an automatic transfer switch during the evaluation of installation and testing is sufficient to prevent the equipment from being commissioned. Visual Inspection Visual inspections are used to assess the physical condition of automatic transfer switches. A visual inspection is a pass/fail verification about a particular aspect of the physical condition or the operation of equipment. Because the criteria that are established to determine the acceptability of the visual inspections can be subjective, the visual inspections should be performed by an experienced Electrical Engineer.


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There are several courses of action for visual inspection failure. The course of action depends on the part of the equipment that failed the visual inspection. A failure of alignment, mechanism/linkage, lubrication, or cleanliness inspection can usually be corrected through maintenance procedures. A physical damage or suitability inspection failure will probably require the replacement of the damaged component. The visual inspection of an automatic transfer switch should be performed during the initial installation and commissioning. Technical data to evaluate the results of the visual inspection can be found in the manufacturer's technical manual. For visual inspections of automatic transfer switches that consist of loadbreak switches, panelboard or switchgear technical manuals (as appropriate) should also be consulted. The following visual inspections are used to assess the condition 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 transfer switch is appropriate for the application in which it is placed. Under normal circumstances, the suitability of equipment is determined before it is placed into the system; however, a visual inspection must be performed to ensure that changes that may have been made to the system have not exceeded the ratings of the automatic transfer switch. To determine the suitability of an automatic transfer switch, a visual inspection of the nameplate data 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 the electrical 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 verified against the electrical system single line diagram.


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Physical Damage Physical damage to an automatic transfer switch can prevent the supply of electric power to critical loads, or it can lead to switchgear or load failure during critical system operations. The magnitude of the electric energy that passes through automatic transfer switches and the forces that are used to operate automatic transfer switches (or loadbreak switches) can propagate and amplify any minor installation damage. Damage to automatic transfer switches can lead to critical equipment failure, fire, personal injury, or death. Any physical damage to an automatic transfer switch that is noted during an inspection requires the immediate replacement of the damaged component. The most obvious and common forms of physical damage are cracks, dents, missing or broken pieces, bent doors, and burned out indicator lights. The purpose of the physical damage inspection is to identify whether corrective maintenance or component replacement is necessary. Automatic transfer switches that show any form of physical damage, no matter how small, 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 will properly pass current when it is connected to the rest of the electrical system. When an automatic transfer 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 connections are properly made to the automatic transfer switch when the automatic transfer switch is connected to the circuit. Improper alignment of the automatic transfer switch contacts can cause contact heating and wear. Cleanliness The purpose of the cleanliness visual inspection is to ensure the proper operation of the automatic transfer switch over its maximum operating life. The accumulation of dirt over a period of time will impede the proper operation of the automatic transfer switch and will reduce the dielectric strength of the automatic transfer switch insulation. Dust and dirt can also reduce the speed and sensitivity of automatic transfer switches under power supply transfer conditions. Accumulation of dust and dirt should be cleaned away from the automatic transfer switch during maintenance cycles. Automatic transfer switches that are installed in extremely dirty, dusty, or humid areas may have to be frequently maintained.


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Arc Chute Assembly The arc chute assemblies of an automatic transfer switch are responsible for the suppression of the arc that forms when the contacts open. The purpose of the visual inspection of the arc chute assemblies is to ensure that the arc chutes can safely suppress the arc that forms when the automatic transfer switch transfers power from an energized power source to another energized power source. When a visual inspection of the arc chute assembly is performed, three conditions exist that will cause the arc chute assembly to fail inspection: burn marks, scale, and cracks. Burn marks change the consistency of the surface of an arc chute. If burn marks are present on an arc chute, the arc chute should be replaced. Scale is the accumulation of foreign material in the arc chutes that can impede the ability of the arc chutes to extinguish an arc. Scale should not be removed from the surface of the arc chutes, so the inspector must determine whether the scale will impede the ability of the arc chute to extinguish an arc. If the inspector determines that the scale will impede the ability of the arc chute to extinguish an arc, the arc chute is replaced. Cracks form in the arc chutes during the normal operation of a switch. The inspector must determine whether the cracks will interfere with the ability of the arc chute to extinguish an arc, and he should replace the arc chute accordingly. Oil-immersed switches are also used for medium- and high-voltage loadbreak automatic transfer switch applications; however, they are being removed from service in Saudi Aramco, and they are being replaced with SF6. Oil-immersed medium- and high-voltage loadbreak automatic transfer switch schemes are commonly used by Saudi Aramco for industrial applications. Oil-immersed switches are only suitable for outdoor use. For high making and breaking capacity, the oilimmersed switch should incorporate either a spring toggle mechanism or some form of arc control. The preferred type of switch construction has spring toggle mechanisms enclosed inside the tank under oil. Regular inspection and maintenance of oil-immersed switches are necessary to remove accumulated sludge and to test the quality of the oil. Contacts The contacts provide a current path through the automatic transfer switch and interrupt the current when the load power is transferred from the emergency power source to the preferred power source upon restoration of the preferred power source. Damage can occur at the contacts as a result of the mechanical stress from closing operations and the electrical arc that forms during contact opening operations. The purpose of the contact visual inspection is to ensure that the contacts provide a low resistance current path and that the contacts can safely interrupt current during automatic transfer operating.


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Small burn and pock marks can develop on the surface of the contacts over the operating life of an automatic transfer switch. These small burn and pock marks will not interfere with the operation of the contacts, but the contacts will need to be replaced when they erode over time to some wear point that is defined by the manufacturer. For vacuum loadbreak automatic transfer switches, a contact wear indicator is checked. Operating Mechanism The operating mechanism assembly of an automatic transfer switch performs the actual movement of the contacts when the automatic transfer switch transfers the load from one power supply to the other. The purpose of the operating mechanism inspection is to ensure that the operating mechanism can move freely. Free movement of the operating mechanism will ensure that the automatic transfer switch can properly and rapidly operate the contacts. The inspector should visually determine that no obstructions exist that will impede the movement of the operating mechanism. This inspection will also ensure that, when the power supply transfer test is performed, no automatic transfer switch damage can occur. Mechanical Inspection A mechanical inspection is used to assess the ability of an automatic transfer switch to physically perform the mechanical movements that are necessary for proper operation. Tests are also performed during the mechanical inspection to assess automatic transfer switch safety functions. Quality control, quality assurance, and test data should also be provided with the automatic transfer switch by the manufacturer for use during the mechanical inspection. There are several courses of action for mechanical inspection failure; however, the course of action depends on the part of the equipment that failed the inspection. A failure of the mechanism operation can usually be corrected through maintenance procedures. The general mechanical inspections and tests that are performed on switchgear and circuit breakers 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 cable connections and joints in place during automatic transfer switch operations. To determine the amount 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 (or loadbreak) switch manufacturer's technical manuals. Saudi Aramco DeskTop Standards

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Interlocks Interlocks are provided in automatic transfer switches to prevent the inadvertent simultaneous connection of both the preferred and emergency power supplies. During the mechanical inspection, the automatic transfer switch is checked to ensure that a positive interlock is present between the preferred and emergency power sources. If a bypass isolation switch is provided in the 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 the mechanical inspection, a manual transfer operation must be performed to ensure that the manual power supply transfer during emergency and maintenance operations is possible. If a bypass isolation switch is provided in the automatic transfer switch, the bypass isolation switch manual transfer is checked for proper operation. Electrical Inspection and Tests During the commissioning process, electrical inspections and tests are performed to check the ability of the automatic transfer switch to operate for a reasonable future period of time under all operating conditions and loads. Acceptance or installation tests will usually detect shipping or installation damage and gross defects or errors in workmanship in equipment construction. Quality control, quality assurance, and test data should also be provided with the automatic transfer switch by the manufacturer for use during the electrical inspections and tests. Once the installation and inspection data have been recorded and assembled, a methodical and consistent program of periodic data collection and evaluation should be established. As each new maintenance item, test, splice, system addition, or system reconfiguration occurs, new inspections and 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 activity should be performed on the faulty equipment. For example, a contact resistance test failure can be 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 of the equipment before the automatic transfer switch can be commissioned. For example, an insulation resistance test failure usually indicates a gross imperfection in the automatic transfer switch insulation.


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The following electrical inspections, checks, and tests are performed on Saudi Aramco automatic transfer 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 switch insulation resistance through use of a megger. In the insulation resistance test, the megger is used to set up an electromagnetic field, and the field that is created is used to produce leakage currents that will flow between the automatic transfer switch contacts phase and ground, or from phase to phase, through the insulation. The amount of leakage current flow that is detected by the megger results 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 automatic transfer switch. Insulation resistance tests must be conducted phase-to-phase and phase-toground with the automatic transfer switch in both the preferred and emergency positions. The insulation resistance values are recorded on a test data sheet and should be attached to the appropriate Saudi Aramco pre-commissioning form. The Electrical Engineer should evaluate the insulation resistance (megger) test values to ensure that the insulation resistance values that were recorded are greater than the manufacturer's minimum value. The acceptable insulation resistance values should be determined through consultation with the appropriate automatic transfer switch manufacturer's technical manual. If the manufacturer's minimum value is not provided, the value of the insulation resistance must be greater than the rated voltage + 1 kV in megohms. For example, a 600 V rated system must have a measured insulation resistance that is greater than 1.6 megohms. Any value of insulation resistance that is less than the minimum specifications should be investigated by the Electrical Engineer who performs the test data evaluation. The ratio of two time-resistance readings (such as a 60-second reading that is divided by a 30second reading) is called a dielectric absorption ratio. The absorption ratio is useful in recording information about the insulation. If the ratio is a ten-minute reading that is divided by a oneminute reading, the value is called the polarization index.


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Because constant cranking is required for hand-cranked megger instruments, it is easier to run the test for only 60 seconds and take the first reading at 30 seconds. When a power-operated megger instrument is used, the results of running the test for a full ten minutes and taking readings at one and ten minutes will give the polarization index. An explanation of the evaluation of the dielectric absorption ratio is provided in Work Aid 2. Contact Resistance The purpose of the automatic transfer switch contact resistance test is to identify contacts that are defective or detrimental to the operation of the automatic transfer switch. The contact resistance test may also identify loose connections in an automatic transfer switch. With the automatic transfer switch in the preferred position, the leads of a digital, low-resistance ohmmeter should be placed across the line and load sides of the automatic transfer switch, and measurements should be taken across the contacts of each phase. The automatic transfer switch is then transferred to the emergency position and similar measurements are taken. A digital, low-resistance ohmmeter can deliver enough power to the circuit breaker to make accurate readings that have more validity than those readings that can be obtained through the use of an ordinary multimeter. The contact resistance is recorded on a test data sheet and attached to the Saudi Aramco pre-commissioning form. Increased contact resistance may be caused by contacts that do not make proper contact or by pitting on the surface of the contacts. The contact resistance values that are recorded should be consistent with the manufacturer's recommended values. Generally, values of contact resistance in 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 automatic transfer 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 the automatic transfer switch electrical contacts. The dielectric tests verify the integrity of the arcinterrupting vacuum chamber. To perform the dielectric test, an ac potential should be applied across the automatic transfer switch open contacts. The magnitude of the test potential should be in accordance with manufacturer's technical manuals. Once the test potential has been determined, it should be applied for a short amount of time, usually five seconds. If no breakdown occurs across the contacts, the vacuum integrity is acceptable.


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Operational Transfer The operational transfer test of the automatic transfer switch ensures that all of the switch parts are able to work in conjunction with each other so that the automatic transfer switch can perform its power supply transfer responsibilities. Most of the tests that have been performed so far have been tests that ensure the proper performance of the individual parts of the automatic transfer switch. The operational transfer test will ensure that the parts will work together so that the automatic 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 of a loss of the preferred power source. Once the automatic transfer switch is selected to the emergency power supply, the preferred power is restored and the automatic transfer switch is restored to the preferred power source. During the transfer operations, the correct operation and timing of the automatic transfer switch is monitored. Electrical interlocks and limit switches (if present) are also monitored during the functional operation test. The operational transfer test information (e.g., proper operation and time delay) is recorded on a test data sheet or in the Saudi Aramco correct pre-commissioning form.


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AUTOMATIC TRANSFER SWITCH PRE-OPERATIONAL CHECK-OUT PHASE REQUIREMENTS The system pre-operational check-out phase of the commissioning cycle for automatic transfer switches provides an opportunity for Saudi Aramco personnel to perform wiring checks, subsystem component check-outs, and circuit breaker interlock performance tests. Each automatic transfer switch component is checked to ensure that it works individually and as a complete system. Point-to-Point Wiring Check Point-to-point wiring checks are performed to verify automatic transfer switch compliance with wiring diagrams and manufacturer specifications. Terminations and terminal blocks are also checked for routing and labeling. During the point-to-point wiring checks, control and metering transformers and fuses are checked for proper application and type. If necessary, adjustments are made to components such as relays, annunciators, alarms, and targets. Subsystem Check-Out Subsystems are checked to ensure that electrical continuity exists for control and protective devices. The proper operation of all subsystems is tested through use of controlled operation and check-out of the controls and protective devices. Each subsystem is performance tested through the application of full operational voltage to each subsystem through the proper protective devices. A complete operational test is performed on equipment controls, interlocks, protective devices, and components with each subcircuit connected to its main system. During the performance test, the main systems are still isolated and independent from plant systems. Before the equipment is connected to the plant system, subsystem performance testing is critical to ensure the 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 must be checked and verified against the phase sequence of the connected loads.


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AUTOMATIC TRANSFER SWITCH OPERATIONAL TESTING PHASE REQUIREMENTS The operational testing phase of the commissioning cycle for automatic transfer switches provides an 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 through application of the full system voltage onto the panelboard or switchgear with the automatic transfer switch installed. With the voltage applied, voltage phasing, synchronizing, device rotation, 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 total operation 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 the entire electric power distribution system functions in accordance with the system design. During the complete system functional test of the automatic transfer switch, the automatic transfer switch is allowed to assume a fully-loaded condition with power supplied from the preferred power source. The power from the preferred source is maintained for a period of time that is adequate to obtain the maximum system temperature, and the panelboard (or switchgear) temperatures are monitored. The automatic transfer switch is then transferred to the emergency source and maintained for a similar period of time, and the temperatures are again monitored. Cable and termination temperatures can be monitored locally through use of temperature monitoring equipment or through use of thermographic surveys. Temperature monitoring equipment can be temporarily installed at the panelboard (or switchgear) vents. Particular attention should be paid to wiring and terminal connections during the complete system functional test.


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WORK AID 1:

REFERENCES FOR EVALUATING AUTOMATIC TRANSFER SWITCHES UPON RECEIPT

The information that is presented in the checklists and information tables has been assembled from 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 table of Saudi Aramco loadbreak switch general requirements.

General Automatic transfer switches must be designed, rated, manufactured, and Loadbreak tested in accordance with the latest issue or revision of the following: Switch Requirements • 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 of switchgear and control equipment are found in SAES-P-116. Deviation from the requirements specified in SAES-P-116 must not be made without the written approval of the Manager, Consulting Services Department. Although loadbreak switches are not normally required to interrupt fault current, they must be capable of: • Breaking currents equal to their continuous current rating at load power factor and system voltage. • Interrupting small inductive or capacitive currents for applications where they are used for disconnecting unloaded transformers, cables, or overhead lines. • Closing onto a terminal short circuit. Loadbreak switches must have independent operators. Switches with dependent manual operators must not be used because they do not have a fault making capacity. Figure 7: Saudi Aramco General Loadbreak Switch Requirements


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

General Switches, circuit breakers, motor controllers, and fuses must not be located Requirements in Division I classified areas. Refer to SAES-B-068 for electrical area classification requirements. Switches that are used for automatic transfer in Saudi Aramco installations are required to be equipped with electrical operators. Control power transformers are required on the preferred source and on the emergency source. Automatic transfer switches may be used to automatically sense voltage loss and switch alternate supplies to critical loads. Vacuum A vacuum automatic transfer switch is an acceptable alternative to an oil Automatic break automatic transfer switch. Transfer Vacuum switches must contain the same facilities as other types of switches. Switches Vacuum is preferred for dead front, pad mount types. Vacuum switches must be equipped with a contact wear indicator. Low-Voltage Transfer switches must: Automatic • Be capable of switching continuous load current. Transfer • Have a withstand and fault close rating of at least 105 of the Switches 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 NEMA ICS-10 for further information on automatic transfer switches. Figure 8: Saudi Aramco Automatic Transfer Switch Requirements


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Medium-and High-Voltage Loadbreak Switches

Frame-mounted, oil-immersed, transfer switches are the most prevalent type that is used by Saudi Aramco for industrial applications. Frame-mounted, oil-immersed, transfer switches are only suitable for outdoor use. Refer to 16-SAMSS-510 for specification requirements. Oil-immersed switches are available with electrical operators and associated control power transformers. Transfer switch cable terminations must be of dry-type dead-front construction. Potheads must not be used. Switches are available with terminations for either solid dielectric or other types of power cables. Current-limiting and conventional power fuses are available for use in oil-immersed loadbreak switches. For high making and breaking capacity, the switch must incorporate either a spring toggle mechanism or some form of arc control. The preferred type of switch construction has spring toggle mechanisms enclosed inside the tank under oil. Regular maintenance of this type of switch is necessary to 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 of medium- and high-voltage loadbreak switches.

All switches must be group-operated. Switch operating mechanisms must be protected from damage due to weather, dust, and corrosion. Mechanisms, linkages, and springs must be located inside tanks on outdoor units. Synchronism check devices must be provided in situations where it is possible to interconnect 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 they provide protection equal to metal enclosures. Figure 9: Requirements for the Application and Selection of Medium- and High-Voltage Loadbreak Switches Saudi Aramco DeskTop Standards

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

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


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

Figure 11: Control Power Rated Voltages and Operating Ranges for Automatic Switchgear Devices (From ANSI C37.33) When the requirements of an automatic transfer switch are evaluated, specific characteristics of the normal (preferred) and alternate power supplies must be specified. Upon initial receipt of an automatic transfer switch, the following items must be checked, inspected, and verified to ensure that 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 sources simultaneously • 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


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Automatic Transfer Switch Applications Checklist Automatic transfer switch rating information can be found on the equipment nameplate or in the manufacturer'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 the application based on Saudi Aramco and industry standards: • Verify that the automatic transfer switch meets the Saudi Aramco requirements that are shown in Figures 7 through 9. • Verify that the automatic transfer switch matches the information that is provided in the latest single line diagram (e.g., name of manufacturer, catalog or serial number). • Verify that the automatic transfer switch frequency rating is correct for the application. • Verify that the automatic transfer switch voltage ratings are correct for the application. • Verify that the automatic transfer switch current ratings are correct for the application. • Verify that the automatic transfer switch operational characteristics are suitable for the electrical loads that are supplied by the automatic transfer switch and that any cautions or warnings are listed on the nameplate.


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WORK AID 2:

REFERENCES FOR EVALUATING AUTOMATIC TRANSFER SWITCH INSTALLATION AND TESTING

The information that is presented in the checklists and information tables has been assembled from 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 diagram and report any discrepancies. • Inspect for proper alignment, anchorage, and grounding. • Inspect all bus connections for high resistance with a resistance ohmmeter. Check the 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 operate properly 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 operating positions.

• 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.


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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 (both mechanical 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-toground with the automatic transfer switch in both positions. Values of insulation resistance that are less than the manufacturer's minimum (or kV + 1 in megohms) must be investigated.

-

Perform contact resistance tests for all sets of contacts. The manufacturer's technical manual should be consulted to determine a range of acceptable contact 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, of the preferred power source.

-

Monitor and verify the correct operation and timing of the automatic transfer switch sensing, timing, and operation equipment.

Figure 12 shows insulation resistance test voltages for automatic transfer switches. Voltage Rating 150 - 600 V 601 - 5000 V 5001 -

Test Voltage 1000 Vdc 2500 Vdc 5000 Vdc

Figure 12: Insulation Resistance Test Voltages


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Information, Formulas, and Tables for Use in Evaluating the Results of Insulation Resistance (Megger) Tests The results of all commissioning megger tests that are performed must be documented on the appropriate 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 be determined through use of the following equation: Figure 13 provides insulation conditions for 60/30 second ratio results and for 10/1 minute ratio results.

Insulation Condition Dangerous

60/30 - Second Ratio ---

10/1 - Minute Ratio (Polarization Index) 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, P002. This form provides a field installation checklist for automatic transfer switch installations and contains a broad checklist of visual and mechanical inspections, as well as the listed electrical and tests that are required for automatic transfer switch installations. Pre-commissioning forms are subject to periodic revision.


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

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

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The following is an excerpt from GI 2.710, New Construction Check List Example, that illustrates the overall checklist and sign-off for major pieces of electrical equipment. 3.

Electrical Equipment All substations, power cable, electrical equipment, including lighting and wiring, to be checked for proper application, operation, and grounds. Distribution panels, switches properly identified, and all energization certificate requests signed.

Construction Agency

Power Distribution Dept.

Project Inspection

Commissioning (Note 1)


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

Figure 15: Electrical Inspection Excerpt from GI 2.710


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


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


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


A ratio that consists of a ten-minute insulation resistance reading divided by a one-minute insulation resistance reading.

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Engineering Encyclopedia: Commissioning Automatic Transfer Switches

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