Commissioning Motor Variable Speed Drives (VSDs)

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 Aramco’s 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: EEX30206 W.A. Roussel on 874-6160

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Commissioning Motor

Variable Speed Drives (VSDs)

Engineering Encyclopedia Electrical

Commissioning MotorVariable Speed Drives (VSDs)

Saudi Aramco DeskTop Standards

Content Page

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

SAUDI ARAMCO REQUIREMENTS................................................................................. 2

EVALUATING MOTOR VARIABLE SPEED DRIVES UPON RECEIPT ......................... 6

Visual Inspection....................................................................................................... 6

Verification Against Specifications ............................................................................ 6

Nameplate Requirements ............................................................................... 7

Design Requirements ..................................................................................... 7

Instrumentation and Control Requirements .................................................... 8

EVALUATING MOTOR VARIABLE SPEED DRIVE INSTALLATION ANDTESTING............................................................................................................................. 9

Visual Inspection....................................................................................................... 9

Suitability .....................................................................................................10

Physical Damage...........................................................................................10

Solid State Devices .......................................................................................10

Cleanliness....................................................................................................11

Mechanical Inspection ..............................................................................................11

Operating Mechanism ...................................................................................11

Mounting Bolts.............................................................................................12

Lubrication ...................................................................................................12

Electrical Inspection and Test ...................................................................................12

Point-to-Point Wiring and Continuity............................................................13

Contact Resistance........................................................................................13

Insulation Resistance.....................................................................................14

Phase Sequence and Rotation........................................................................15

High-Pot Testing ..........................................................................................15




SYSTEM PRE-OPERATIONAL CHECK-OUT PHASE ....................................................18

SYSTEM OPERATIONAL OBSERVANCE PHASE .........................................................20

WORK AID 1: REFERENCES FOR EVALUATING MOTORVARIABLE SPEED DRIVES UPON RECEIPT.......................................21

Work Aid 1A: Motor Variable Speed Drive Technical and ConstructionRequirements ....................................................................................21

Work Aid 1B: Instrumentation and Controls.............................................................31

Work Aid 1C: Alarm and Indicating .........................................................................32

Work Aid 1D: Input and Output Interfaces...............................................................33

Work Aid 1E: VSD Microprocessor.........................................................................34

Work Aid 1F: Data Schedule....................................................................................34

WORK AID 2: REFERENCES FOR EVALUATING MOTORVARIABLE SPEED DRIVE INSTALLATION AND TESTING..............36

Work Aid 2A: Testing Requirements ........................................................................36

Work Aid 2B: Visual Inspection ...............................................................................37

Suitability .....................................................................................................37

Physical Damage...........................................................................................37

Solid State Devices .......................................................................................37

Cleanliness....................................................................................................37

Work Aid 2C: Mechanical Inspections, Tests, and Checks ........................................38

Operating Mechanism ...................................................................................38

Mounting Bolts.............................................................................................38

Lubrication ...................................................................................................38

Work Aid 2D: Electrical Tests and Checks ...............................................................38

Manufacturing Facility Checks and Tests ......................................................38

Point-to-Point Wiring and Continuity............................................................39

Contact Resistance........................................................................................40

Insulation Resistance.....................................................................................40

Phase Sequence and Rotation........................................................................41

High-Pot Testing ..........................................................................................41

Work Aid 2E: Operational Checkouts and Tests .......................................................42




Power and Terminal Verification...................................................................43

Drive Operation Testing with the Motor Disconnected..................................43

Motor Rotation Check ..................................................................................44

Work Aid 2F: Excerpts from GI 2.710 .....................................................................45

GLOSSARY........................................................................................................................49

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Table of Figures Page

Figure 1: VSD With Self-Commutating Inverter and Constant Current Control ........ 4

Figure 2: Typical Results of High-Pot Tests.............................................................17

Figure 5: VSD Vendor Requirements and Equipment Site Conditions(from 17-SAMSS-517) ...........................................................................21

Figure 6: General VSD Design Requirements (from 17-SAMSS-517)......................22

Figure 7: VSD Construction Requirements (from 17-SAMSS-517) .........................23

Figure 7: VSD Construction Requirements (from 17-SAMSS-517) (Cont'd)............24

Figure 7: VSD Construction Requirements (from 17-SAMSS-517) (Cont'd)............25

Figure 8: VSD Component Design Requirements (from 17-SAMSS-517)................26

Figure 8: VSD Component Design Requirements (from 17-SAMSS-517) (Cont'd) ..27




Figure 9: VSD Microprocessor Diagnostic and Event Recording System(from 17-SAMSS-517) ...........................................................................34

Figure 10: Medium Voltage Induction Motor Variable Speed Drives DataSchedule (from 17-SAMSS-517).............................................................35

Figure 11: Manufacturing Facility Checks and Tests (from 17-SAMSS-517)............39

Figure 12: Dielectric Absorption Ratio Chart...........................................................40

Figure 13: Example of DC Hi-Pot Test (Good and Bad Cable Insulation) ................42

Figure 14: GI 2.710 Excerpt....................................................................................46

Figure 14: GI 2.710 Excerpt (Cont'd) ......................................................................47

Figure 14: GI 2.710 Excerpt (Cont'd) ......................................................................48



Saudi Aramco DeskTop Standards 1

INTRODUCTION

When speed control of industrial motors is required for an installation, motor variable speeddrives (VSDs) are used. Applications for motor VSDs include pumps, blowers, fans, cranes, andcompressors. Once a motor VSD for a given installation is chosen, the drive is ordered, shipped,and received. Once received, the VSD is receipt inspected and tested as part of thecommissioning process. The commissioning process for motor VSDs that are installed in SaudiAramco facilities ensures that a safe and cost-effective system is installed that performs to thespecifications of the facility for the projected operating lifetime of the facility. Experience hasshown that the time and effort that are expended up front to ensure safety, quality control, andadherence to Saudi Aramco and industry standards minimizes subsequent equipment failure.

The motor VSD commissioning process involves evaluations, verifications, and checks thatdetermine whether the proper equipment specifications and installation requirements are met.Tests are performed and the test results are evaluated to determine whether the motor VSD willoperate properly and safely after it is placed in service. When a motor VSD is inspected andtested satisfactorily during the commissioning process, it should operate in accordance withmanufacturer's specifications for its maximum useful life.

Electrical Engineers must be able to direct the commissioning of new motor VSDs. This Moduleprovides information on the following topics that are pertinent to the commissioning of motorVSDs for Saudi Aramco installations:

• Saudi Aramco Requirements

• Evaluating Motor Variable Speed Drives Upon Receipt

• Evaluating Motor Variable Speed Drive Installation and Testing

• System Pre-Operational Check-Out Phase

• System Operational Observance Phase




SAUDI ARAMCO REQUIREMENTS

Large process equipment and large process support equipment rely on motors for primary andancillary functions throughout the manufacturing process (e.g., fans, circulation pumps, blowers).During the commissioning process, the Electrical Engineer will be required to be familiar with thedesign and construction requirements of motor VSDs. This section of the module will describethe Saudi Aramco requirements for motor VSDs.

There are many different kinds of electronic ac drives that vary the speed of a motor. Electronicvariable speed drives can be divided into the following three general categories:

• Static frequency changers

• Variable voltage controllers

• Rectifier/inverter systems

Static frequency converters convert the incoming line frequency directly into the desired loadfrequency. A typical example of a static frequency converter is the cycloconverter, which is usedto drive both synchronous and squirrel-cage motors. Variable voltage controllers vary theincoming ac voltage, and they are commonly used in squirrel-cage and wound rotor inductionmotors. Variable voltage speed control is the least expensive, and it provides satisfactory speedcontrol for small and medium voltage fans, centrifugal pumps, and hoists. Rectifier/invertersystems rectify the incoming ac and convert the resulting dc back to ac at the desired frequency.

For Saudi Aramco squirrel-cage induction motor VSD installations, self-commutating invertersare used. Power thyristors are used to rectify the ac, and they are arranged in a conventionalthree-phase bridge circuit. Self-commutating inverters convert dc power to ac power. In additionto power thyristors, auxiliary components (e.g., capacitors, diodes, coils, and other thyristors) areused to vary the commutation of the power thyristors to provide reactive power generation in thesystem.

Figure 1 shows a simplified one-line diagram of a VSD that uses a self-commutating inverter withconstant current control. The VSD consists of a thyristor-based rectifier bridge that converts acpower to dc power, dc link smoothing reactors on the positive and negative legs, and a thyristor-based current source inverter bridge that converts the dc power into variable voltage, variablefrequency, current regulated ac waveforms.




In Figure 1, the three-phase line is applied to the thyristors in the power converter. High powersurge arrestors are used in the three-phase line to protect against voltage surges. The thyristorsare mounted in modular groups that contain all of the associated surge suppression and gateisolation components. The thyristor gate control signals are transmitted from the gate triggeringprocessor through fiber optic cables. The gate triggering processor regulator monitors voltages(e.g., E1 and E2) and individual thyristors to ensure that the gate signal is provided at the propertime. The gate signal causes each thyristor to conduct (or block) in response to control settings,limit settings, and external inputs, such as motor speed or dc current.

Because large power thyristors generate heat, a power converter cooling system is used on VSDsystems for motors that are rated more than 746 kW (1,000 hp). The power converter coolingsystem provides optimum efficiency and increased reliability, and it minimizes the size of anddependence on air conditioning units.

Dc link reactors (DCLRs) are used on the dc side of the power converters to control the currentduring normal operation and fault conditions. Two DCLRs are provided: one for the positive dcside and one for the negative dc side of the power converter. During normal and fault conditions,the DCLRs provide a constant current to the inverter and limit any dc ripple to a maximum of 10percent. Figure 1 shows the direction of dc current (Idc) through the DCLRs (L1 and L2).

From the DCLRs, the constant dc current is sent to the self-commutated inverter. At the inverter,the constant dc current is gated through a thyristor assembly that creates rectangular currentpulses (Iac) that are 120 electrical degrees apart. The inverter creates the rectangular currentpulses at a frequency and magnitude in response to thyristor gate control signals from the gatetriggering processor. The frequency and magnitude of the rectangular current pulses will result involtage drops (E) across each motor stator winding phase (A, B, and C) for proper squirrel-cageinduction motor operation.




Figure 1: VSD With Self-Commutating Inverter and Constant Current Control

To allow the retrofit of an existing motor without derating the system, the VSD output is filtered.The output filter provides a sinusoidal waveform that contains a maximum of five percent totalharmonics to minimize motor heating. When required, a withdrawable output contactor is alsoprovided to disconnect and isolate the drive and filter from the motor.

When required for the installation, a bypass is incorporated into the VSD design and construction.A bypass is used to bypass the VSD in case of a VSD failure or to operate the motor at full speed.A VSD bypass is accomplished through use of a withdrawable contactor or breaker (as shown onthe engineering drawings). Bypass protection must be in accordance with 16-SAMSS-506 (forcontactors) or 16-SAMSS-501 (for breakers). The bypass system must provide a smooth, closed-transition synchronous transfer of the induction motor from the drive to the main ac line and fromthe main ac line back to the drive.




Transition is accomplished without stopping or slowing the motor and without significanttransients on the line. When an isolation transformer is installed in the VSD system, the isolationtransformer must allow full voltage starting when a VSD bypass is specified in the Data Schedule.

The minimum mandatory technical requirements for the procurement and installation of VSDs tocontrol the speed of three-phase, 4 kV and 6.6 kV, squirrel-cage induction motors that areinstalled in Saudi Aramco industrial facilities are defined in 17-SAMSS-517. 17-SAMSS-517covers specific references, design requirements, construction requirements, testing, andengineering studies that must be used in conjunction with the procurement and installation ofVSDs. Excerpts from 17-SAMSS-517 are provided in Work Aid 1.




EVALUATING MOTOR VARIABLE SPEED DRIVES UPON RECEIPT

The installation of motors in Saudi Aramco facilities is a process that occurs over a period oftime. Variable speed motors drive specialized equipment that is critical to the manufacturing orrefining process. Variable speed motor installations begin with an identified need for speedcontrol of motors in a new facility. After the facility design is approved, variable speed motorsand their associated VSDs are ordered from the manufacturer. When the VSDs are received fromthe manufacturer, they must be evaluated to ensure that they are proper for the installation. Thepurpose of the evaluation is to verify that the correct VSDs were received from the manufacturerand that the proper installation specifications and parameters were met. This section will describehow VSDs are evaluated upon receipt during the commissioning process.

Visual Inspection

When VSDs are received from the manufacturer, a visual inspection should be performed. Thepurpose of the visual inspection is to verify that the VSD that was received from the manufactureris in good physical condition and that the enclosures and cooling equipment (if present) have notbeen damaged during shipment. During the initial visual inspection, the inspection personnel lookfor obvious equipment damage and determine whether all necessary equipment (e.g., contactors,alarm panels, and instrumentation) are present. A detailed inspection of the VSD equipment isalso performed when it is completely installed at the site or facility.

Verification Against Specifications

When a new facility or facility modification is at the equipment installation stage, the design of theinstallation has already been completed. The design and ratings of a motor VSD that is selectedfor a specific installation should be shown in the drawings, prints, or specifications for theinstallation. The purpose of verifying VSDs against the specifications is to ensure that the VSDthat is being installed meets Saudi Aramco and industry standards.

Generally, the verification against specifications consists of a determination of whether the VSDthat is to be installed matches the VSD that is specified for the installation. In most cases, thisdetermination is accomplished by reading an electrical plan that identifies the motor size, thespeed control parameters, and additional or optional items (e.g., bypass, isolation transformer, orcooling system). The Electrical Engineer inspects the manufacturer's nameplate data on the VSD,and he compares them to the requirements on the electrical plan to determine whether the VSD iscorrect for the installation. In other situations, the Electrical Engineer must rely on his knowledgeof the correct application of motors and motor VSDs to determine whether the correct VSD isbeing used. The data schedule that was used to order the VSD from the manufacturer should alsobe consulted. The data schedule for medium voltage induction motor variable speed drives isprovided in Work Aid 1. Any quality control, quality assurance, and test data that are providedwith the motor VSD by the manufacturer should also be reviewed.




Nameplate Requirements

Nameplates are required for all variable speed induction motor VSDs that are used in SaudiAramco facilities. All devices that are located within a panel must be provided with suitablenameplates to identify item and their function. The nameplate should contain manufacturer-typeinformation. The information that describes the machine manufacturer's information shouldconsist of the manufacturer's name, the serial or model number, and system parameters (e.g.,voltage output and speed range). The system parameters on the nameplate should be inaccordance with system prints or electrical one-line diagrams. Nameplate physical constructionrequirements are provided in Work Aid 1.

Design Requirements

Design requirements for variable speed motor VSDs should be in accordance with system printsor electrical one-line diagrams that are attached to the data schedule. Design requirements mustinclude the following information:

• Input ac isolation transformer (when required)

• Thyristor bridge cubicle

• Control cubicle

• Liquid cooling cubicle (when required)

• DC link reactor cubicle

• Contactor/switchgear cubicle

• Output filter cubicle

• Heat exchanger cubicle (for outdoor-liquid cooled systems only)

• VSD bypass (when specified)

The cubicles are bolted together to form a continuous switchgear assembly, and the entire VSDsystem should be constructed for ease of maintenance in order to minimize downtime. SpecificSaudi Aramco design requirements for VSD installations are provided in Work Aid 1. VSDindoor enclosure, wiring, and external connection requirements are also provided in Work Aid 1.




Instrumentation and Control Requirements

The instrumentation and controls for VSDs must be designed for ease of operation andmaintenance of the equipment. The minimum instrumentation and controls equipment that isrequired on VSDs for Saudi Aramco installations is provided in Work Aid 1. Indications must beprovided (both local and remote) for VSD abnormal and alarm conditions. The minimumrequirements for alarm and trip annunciators are provided in Work Aid 1.

For overall control and indication, it is necessary for the VSD to interface with remote controland indicating equipment. For Saudi Aramco VSD installations, input and output interfaces arerequired. Minimum VSD input and output signal and contact requirements are provided in WorkAid 1.

Because of the rapid speed of the converter/inverter process and because of the tight controls andtolerances that are required, VSDs use a microprocessor to control the process. VSDmicroprocessor diagnostic and event recording system requirements are provided in Work Aid 1.




EVALUATING MOTOR VARIABLE SPEED DRIVE INSTALLATION AND TESTING

The process of determining whether motor VSDs should be commissioned is to verify that all ofthe electrical inspections and tests have been properly performed and to verify that the test resultsmeet the specifications that are designated by the applicable Saudi Aramco and industry standards.

Installation inspections are performed to verify that proper VSD installation materials are used,that installation specifications and parameters are met, and that proper installation procedures arefollowed. The installation inspection is conducted to ensure that VSDs will function properlyonce they are installed. Electrical tests are performed to check the ability of VSDs to functionunder all operating conditions and loads. Installation tests should detect shipping or installationdamage, gross manufacturing defects, or errors in workmanship or installation. Although there isno Saudi Aramco Pre-Commissioning Form for induction motor VSD installations, acceptedengineering practices should be used during the installation and testing phase of VSDcommissioning.

The proper evaluation of inspection and testing data during the commissioning process canmaximize the operating time of VSD installations through a determination of trends towardsfailure. Failure prediction can drastically reduce equipment downtime. 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 it can avoid a malfunction that can cause associated (or nearby)equipment damage and disruption of service that can make the activation of emergency repaircrews necessary. A failure in any one of the many inspections, checks, or tests that are performedon VSDs during the installation and testing evaluation is sufficient to prevent the VSD from beingcommissioned.

Visual Inspection

Visual inspections are used to assess the physical condition of VSDs during the commissioningprocess. A visual inspection is a pass/fail verification about a particular aspect of the physicalcondition or the operation of the VSD. Because the criteria that are established to determine theacceptability of the visual inspections can be subjective, the visual inspections should beperformed by an experienced Electrical Engineer. This section will describe visual inspectionitems for induction motor VSDs.

Because of the different manufacturers, models, and configurations of VSDs, there may be severaldifferent courses of action for a visual inspection failure. The course of action depends on thepart of the machine that failed the visual inspection. For example, a failure of cleanliness visualinspection can generally be corrected through cleaning. A physical damage or suitabilityinspection failure will probably require the replacement of the damaged component. Thefollowing visual inspections are used to assess the condition of VSDs in Saudi Aramco systems:




• Suitability

• Physical Damage

• Solid State Devices

• Cleanliness

Suitability

The purpose of the suitability visual inspection is to determine whether the motor VSD isappropriate for the application. Under normal circumstances, the suitability of the VSD should bedetermined before it is placed in the system; however, a visual inspection should be performed toensure that the motor VSD is correct for the installation. To determine the suitability of a motorVSD, a visual inspection of the nameplate data should be performed, and the motor VSD shouldbe compared to what is specified in the electrical system single-line diagram.

Physical Damage

Physical damage to a motor VSD can lead to motor failure or improper operation. Becausemotors support fluid flow (e.g., lubricating or cooling oil), a motor VSD failure can lead tocatastrophic equipment failure, fire, personal injury, or death. Any physical damage to a motorVSD or any missing parts that are noted during the physical damage visual inspection requires theimmediate replacement of the damaged component. The most obvious and common forms ofphysical damage are cracks, dents, missing or broken pieces, and bent ventilation openings. Thepurpose of the physical damage inspection is to identify whether corrective maintenance orcomponent replacement is necessary. Motor VSDs that show any form of physical damage, nomatter how small, should be determined to have failed the physical damage inspection.

Solid State Devices

Solid state devices require a visual inspection prior to the VSD commissioning. Power thyristorsgenerate a great deal of heat, and visual indications of overheating indicate damaged thyristors,improper cooling, or wiring problems. Printed circuit boards (PCBs) should be inspected todetermine whether they are properly seated at the board edge connectors. Board locking tabsshould also be in place. When PCBs require cleaning, only manufacturer-approved cleaningsolutions may be used. Solvents must not be used on PCBs.




Cleanliness

The purpose of the cleanliness visual inspection is to ensure the proper operation of the VSD overits maximum operating life. Although a VSD is static (i.e., there are no rotating parts), theaccumulation of dirt over a period of time can still impede the proper operation of the VSD bylowering the efficiency of the cooling system and by reducing the dielectric strength of theinsulation. The accumulation of heavy amounts of dust and dirt should be cleaned away from theVSD during maintenance cycles.

Contacts that are used in isolation, supply, or bypass components, such as contactors or circuitbreakers, should be checked for excessive wear and the accumulation of dirt. A slightdiscoloration or pitting at the contact's surface is normal and will not affect the proper operationof the contact.

Mechanical Inspection

A mechanical inspection is used to assess the ability of the machine to physically perform what isnecessary for proper operation. Because there are several mechanical inspection items that areassociated with motor VSDs, there are a number of corrective actions for a mechanical inspectionfailure. The corrective action depends on the part of the VSD that failed the inspection. Forexample, a mounting bolt inspection failure can usually be corrected through adjustment of thebolts with a torque wrench.

The general mechanical inspections and tests that are performed on motor VSDs that are installedin Saudi Aramco systems are as follows:

• Operating Mechanism

• Mounting Bolts

• Lubrication

Operating Mechanism

The operating mechanism for isolation, supply, or bypass components must be inspected duringthe commissioning process. During the mechanical inspection of the operating mechanism ofVSDs, the Electrical Engineer should check for the proper operation of all moving parts. Theoperating mechanism's moving parts should exhibit freedom of movement with no evidence ofsticking or binding. All operating mechanism fasteners and linkages should be checked for loose,broken, or badly deformed parts. Improperly operating or damaged components must be replacedprior to commissioning.




Mounting Bolts

The purpose of a mounting bolt inspection is to verify that the motor's mounting bolts are securelyfastened. The bolts and frame mounts must be capable of preventing the VSD cabinets andinternal equipment from coming loose during mechanical failure or electrical fault conditions. Toperform the mounting bolt check, the manufacturer's technical manual is consulted for the properbolt torque value. A torque wrench is then used to determine the amount of torque at the bolt.Improper torque values are immediately corrected.

Lubrication

The lubrication system visual inspection should be performed in conjunction with the cleanlinessvisual inspection. The purpose of the lubrication visual inspection is to ensure that the movingparts of the VSD are provided with the proper lubrication. The items that are inspected in theperformance of the lubrication system visual inspection are dependent on the type of lubricationsystem with which the VSD is equipped. Some magnetic starters and contactors are designed tooperate without lubrication. Lubrication of components that do not require lubrication can causeimproper operation. The manufacturer's technical manual should be consulted for lubricationrequirements.

Electrical Inspection and Test

During the commissioning process, electrical inspections and tests are performed to check theability of induction motor VSDs 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. Oncethe installation and inspection data have been recorded and assembled, a methodical andconsistent program of periodic data collection and evaluation should be established. As each newmaintenance item, test, system addition, or system reconfiguration occurs, new inspections anddata 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 type of troubleshooting or maintenance activityshould be performed on the faulty equipment. For example, an insulation resistance (megger) testfailure can usually be rectified by cleaning the interior of the VSD to remove dirt or moisture.Some electrical inspection or test failures are not repairable, and they will require the replacementof the equipment before the VSD can be commissioned.




The following electrical inspections, checks, and tests are performed on induction motor VSDs:

• Point-to-Point Wiring and Continuity

• Contact Resistance

• Insulation Resistance

• Phase Sequence and Rotation

• High-Pot Testing

Point-to-Point Wiring and Continuity

Point-to-point wiring checks are performed to verify that VSDs comply with Saudi Aramcowiring diagrams and manufacturer's specifications. Terminations and terminal blocks within theVSD operations and controls cabinets are also checked for routing and labeling. During thepoint-to-point wiring checks, control and metering equipment (e.g., transformers and fuses) ischecked for proper application and type. All VSD wiring is also checked for continuity andcompared against the wiring diagrams that are provided. The VSD wiring continuity test isperformed with a buzzer or bell-type continuity tester. Written checklists or drawings are used asreference material during the continuity tests.

Contact Resistance

The purpose of the VSD contact resistance test is to identify contacts that are defective ordetrimental to the operation of the contactor or the starter that is contained in the VSD. Thecontact resistance test may also identify loose connections in the contactor or starter. To conductthe contact resistance test, the equipment that is to be tested must be disconnected from thesystem, if possible. Generally, contactors or starters have removable cubicles or drawers tofacilitate temporary removal for maintenance or testing. Once the equipment is removed, andwith the contacts in the closed position, the leads of a digital, low-resistance ohmmeter are placedacross the line and load sides of the contacts, and measurements are taken. A digital low-resistance ohmmeter can deliver enough power to the contacts to make accurate readings thathave more validity than do those readings that can be obtained through the use of an ordinarymultimeter. The contact resistance is recorded on a test data sheet and retained in Saudi Aramcomaterial history records.

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 microohms 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 equipmentmanufacturer's technical manual or in the Saudi Aramco Pre-Commissioning form, P-000, TestingGuide Lines.




Insulation Resistance

The purpose of the insulation resistance (megger) test is to directly measure the insulationresistance of the induction motor VSD components. An induction motor VSD takes ac powerfrom the electrical distribution system, rectifies it, and then converts it to ac power at specifiedfrequencies. The inverter/converter section of VSDs consists of static semiconductor devices.Because the voltage potentials that are generated during the megger test can damage anyconnected semiconductor equipment, megger tests must not be performed on semiconductorequipment. Insulation resistance tests on induction motor VSDs are usually conducted on the acinput and the ac output sections of the VSD. Example VSD components that are megger testedare the input breaker or the contactor, the bypass (if used), and the ac output connections to theinduction motor.

In the insulation resistance test, the megger produces a voltage that causes leakage currents toflow in the insulation between conductors. The amount of leakage current flow that is detectedthrough use of the megger results in a megger meter readout of insulation resistance in megohms.

To conduct the insulation resistance megger test, each component that is to be meggered iselectrically disconnected from the system. The megger is connected between each phase and fromeach phase and ground, and the megger is operated. Insulation resistance megger tests are beconducted for each phase combination. The insulation resistance values are recorded on acommissioning test data sheet.

During the commissioning process, the Electrical Engineer should evaluate the insulationresistance (megger) test values to ensure that the megger values that were recorded are greaterthan the manufacturer's minimum values. Information that is used to evaluate megger readingsare provided in Work Aid 2. Any value of insulation resistance that is less than the minimumspecifications should be investigated by the Electrical Engineer who performs the test dataevaluation.

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 dielectric absorption ratio is useful inrecording information about the insulation. If the ratio is a ten-minute reading that is divided by aone-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 oneminute and at ten minutes will give the polarization index. An explanation of the evaluation of thedielectric absorption ratio is provided in Work Aid 2.




Phase Sequence and Rotation

In addition to the more familiar electrical tests, such as insulation resistance, Electrical Engineerswho are commissioning VSDs should be familiar with the phase sequence and rotation tests thatare performed.

Phase sequence and rotation tests are performed to ensure that the power supply inputs to theVSD are at the proper voltage and in the proper phase sequence. Sequence and rotation testingare performed to ensure that the motor (when connected) will rotate in the correct direction. Ifthe motor that is being supplied by the VSD rotates in the wrong direction, damage can occur tothe motor bearings and to the connected motor load. Phase rotation and phase sequence testingare usually final pre-energization requirements because they are performed through energizationof a portion of the VSD.

During the phase sequence and rotation tests, the ac power input leads are checked for propermarkings to ensure that the sequence coincides with the incoming power system. A visualverification of the motor leads is also conducted to ensure that the motor leads are properlymarked to coincide with the VSD output leads. The motor lead markings and the VSD outputlead markings must match so that the motor shaft will rotate in the correct direction.

High-Pot Testing

When VSDs are installed for motors that are greater than 746 kW (1,000 HP), the powerconverters in the VSD must use a closed-loop liquid cooling system for optimum efficiency andincreased reliability and to minimize the size of and dependence on air conditioning units. Theclosed-loop cooling systems have additional construction and testing requirements that aredescribed in 17-SAMSS-517.

The closed-loop cooling system must be designed with a separate low voltage cubicle to allowcoolant replacement or pump servicing with the drive completely operational. All coolingmedium hoses must consist of flexible, high-dielectric material, and they must be high-pot testedto 50 kV.

The dc high potential (high-pot) test is performed to provide positive proof that insulation hassufficient voltage strength to ride out overvoltage surges. The dc high-pot test should be doneprior to the initial energization of the motor VSD and after satisfactory megohmmeter testing.The dc high-pot testing technique involves the measurement of increased dc voltage that isapplied to the equipment under test. The value of the leakage current is tracked as the testvoltage is increased through several steps, and this value becomes a criterion of the condition ofthe equipment insulation.




The Electrical Engineer should evaluate the dc high-pot test leakage current test data to ensurethat the high-pot test data meets the minimum requirements of a successful test. To conduct thedc high-pot test on cooling medium hoses, a test set is connected between the hose and ground.After the test set is connected, the initial test voltage of approximately 16.5 kV (33% of themaximum test voltage of 50 kV) is applied to the hose. The initial test voltage is held for tenminutes, and the leakage current, as read on the test set, is monitored. The value of leakagecurrent is recorded at the end of each one-minute interval. The polarization index is calculatedfrom this test data through division of the leakage current after one minute by the leakage currentthat is obtained after ten minutes.

When the first ten minutes of the test are complete, the test voltage should be raised from theinitial value to the maximum value in ten equal steps. After each step increase in voltage, thevoltage should be held at the new level for a period of one minute, and the leakage current shouldbe recorded at the end of each minute.

The results of a high-pot test are not compared to a specific value to determine whether theresults are acceptable. Instead, the results of a high-pot test are analyzed for trends that indicatewhether the insulation has sufficient strength to ride out overvoltage surges. A polarization indexvalue of less than two, or dc high-pot test data curves that indicate a steady increase in leakagecurrent over the duration of the test, should be investigated by the Electrical Engineer whoperforms the test data evaluation.

Figure 2 shows a graphic display of the typical results of high-pot tests for both good and badinsulation. The graph that is shown in Figure 2A is for the first ten minutes of a high-pot test.The curve that represents good insulation shows a steep rise in leakage current over the first one-minute interval that is followed by a steady decrease in the value of leakage current over theremainder of the ten-minute interval. The curve that represents bad insulation shows a steadyincrease in the value of leakage current throughout the ten-minute interval. Such a curveindicates unsatisfactory insulation, and the high-pot test should be stopped.

The graph that is shown in Figure 2B is for the last ten minutes of the high-pot test. The curvethat represents good insulation shows a slow, steady increase in the value of leakage current asthe test voltage is raised from the initial value to the maximum value. The curve that representsbad insulation shows a sharp upturn or knee when the test voltage is increased to the point atwhich the insulation starts to break down. A knee in the leakage current curve indicatesunsatisfactory insulation, and the high-pot test should be stopped.




Figure 2: Typical Results of High-Pot Tests




SYSTEM PRE-OPERATIONAL CHECK-OUT PHASE

Although thorough checks and tests are performed at the manufacturing facility prior to shipmentto identify any components that may be subject to premature failures, a pre-operational check-outphase of the commissioning process is conducted at the VSD installation site. Checks and teststhat are performed at the manufacturing facility include thyristor testing, PCB burn-in (at 65oC),phase cell balance testing, and a complete VSD burn-in at full load amps for 24 hours.Microprocessors, printed circuit boards, diagnostic boards, and similar devices (includingsoftware) are also tested at the manufacturing facility for proper operation, sequencing, logic, anddiagnostics. When load testing is specified in the data schedule, load testing at the manufacturingfacility is performed and the manufacturer must determine the VSD efficiency. Data from allmanufacturing facility checks and tests should be reviewed during the commissioning process.

Once a VSD is installed, the system pre-operational check-out phase of the commissioning cyclefor induction motor VSDs provides an opportunity for Saudi Aramco personnel to perform onsitewiring checks, subsystem component checkouts, and VSD component interlock tests. Before anytesting that requires energization is conducted, however, all of the discrepancies that wereidentified during the prior portion of the commissioning process that could result in equipmentdamage or personnel injury must be corrected.

During the pre-operational checkout phase, the VSD is still isolated and independent from theconnected motor load. Subsystem testing before the VSD is connected to the motor load iscritical to ensure the proper and safe operation of the VSD protection and control subsystems.Each VSD component is checked to ensure that it works individually and as a complete system.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 andcheckout of the controls and protective devices.

Although there are many different manufacturer's configurations of VSDs, most VSDs havesimilar subsystem and component operation and checkout test procedures. For a specific VSD'ssubsystem and component operation and checkout tests, the manufacturer's technical manualsshould be consulted; however, a brief overview of testing is provided in the following paragraphs.

VSD speed control operation and checkout testing is performed at both the local and remotecontrol panels. Speed control operation and checkout testing consists of start, stop, ramp,reversing, jog, and frequency skip operations. The start, stop, and ramp operations are performedby starting and stopping the VSD and by observing different frequency outputs. VSDs can havecoast, brake, and ramp stop features. The ramp and brake operations must be tested for properoperation. The time that it takes for the VSD to accelerate to the required speed and the time thatit takes for the VSD to stop (for all stopping modes) must be within the manufacturer's specifiedtime period. The controlled change of speed at a fixed ramp rate for start, stop, and frequencychange operations is tested, as well as the VSD minimum and maximum speeds.




The controlled operation and checkout of the VSD protective devices is performed to ensure thatthe various VSD protective devices' operational interlocks function properly. Various VSDalarms, indications, trips, and interlocks that are provided with a VSD can vary with the size, thetype, and the manufacturer of the VSD. Generally, VSDs are provided with overvoltage,undervoltage, overspeed, and overcurrent trips. If a VSD is equipped with a bypass, a bypassinterlock is provided. Each control alarm, indication, trip, and interlock is tested during thecontrolled operation and checkout phase of the commissioning process.




SYSTEM OPERATIONAL OBSERVANCE PHASE

The system operational observance phase allows Saudi Aramco personnel an extended operationalobservance period to determine whether any abnormal conditions exist that were not uncoveredduring any previous tests or checks. Although an extended system operational observance phasewould be an ideal way to determine the long-term operational capabilities of a newly installedsystem, it is not always practical. The added expense of conducting an extended operationalobservance of a newly installed system can sometimes outweigh the expense of simple systemisolation and repairs in the event of a component or system failure. A careful study in each caseshould be conducted to determine whether a system operational observance phase is cost-effectivefor the given installation.

The induction motor VSD operational observance phase of the commissioning cycle provides anopportunity for Saudi Aramco personnel to perform the following:

• VSD system and component temperature checks.

• VSD operational inspections.

VSD system and component temperature checks are performed through the use of temperaturemonitoring equipment. During the VSD operational observance phase of the commissioningcycle, temperatures are monitored hourly on all operating VSD equipment. Any abnormalreadings or conditions are investigated immediately before damage can occur. Noticeableabnormal conditions include any vibrations, noises, smells, or sounds that indicate damage or thepotential for damage to the operating equipment. The system and component electricalparameters (e.g., voltage and current) are also monitored and recorded.

The operational observance phase of the system and component operating conditions is completeafter the operating conditions are normal and when no problem conditions exist.




WORK AID 1: REFERENCES FOR EVALUATING MOTOR VARIABLE SPEEDDRIVES UPON RECEIPT

The minimum mandatory technical requirements for a VSD to control the speed of three-phase, 4kV and 6.6 kV, squirrel-cage induction motors that are installed in Saudi Aramco industrialfacilities are defined in 17-SAMSS-517, Medium Voltage Induction Motor Variable SpeedDrives. 17-SAMSS-517 covers specific references, design requirements, constructionrequirements, testing, and engineering studies that must be used in conjunction with theprocurement and installation of VSDs.

The information in this Work Aid contains combined excerpts from the following resources:

• 17-SAMSS-517, Medium Voltage Induction Motor Variable Speed Drives

• GI-2.710

• Related Industry Standards

Work Aid 1A: Motor Variable Speed Drive Technical and Construction Requirements

Figure 5 contains information regarding VSD Vendor requirements and installation siteconditions.

VendorRequirements

The Vendor must supply a User's List that indicates the User companyname, installation site, date of installation, and equipment characteristicsthat are similar to the equipment that is proposed.Vendor has total responsibility for design, procurement, production, qualitycontrol, testing, and documentation, as necessary to furnish a completedsystem conforming to the requirements of 17-SAMSS-517.The Vendor's system must be compatible with the main AC power system,with the electric motor, and with the driven equipment.The Vendor must be capable of providing any technical assistance that isnecessary during the installation and start-up of the system.

SiteConditions

Equipment that is located indoors must be able to withstand temperaturesthat are below 35 deg C and a 50 percent relative humidity.Equipment that is located outdoors must be able to withstand exposure to:

• A desert area with high concentrations of windborne dust and sand.• Major pollutants present such as H(2)S and hydrocarbons.• A maximum ambient temperature of 50 deg C.• Metallic surface temperatures as high as 75 deg C.• A maximum relative humidity of 100 percent.

Figure 5: VSD Vendor Requirements andEquipment Site Conditions (from 17-SAMSS-517)




Figure 6 contains general VSD design requirements.

GeneralDesignRequirements

The VSD must consist of the following:• A thyristor-based rectifier bridge to convert ac power to dc power.• DC link-smoothing reactors on the positive and negative legs.• A thyristor-based current source inverter bridge to convert dc

power to a variable voltage, variable frequency, current-regulatedwaveform.

The VSD must soft start the motor, limiting current so that no more thanmotor full load current is required to start and accelerate the load.The system must be in accordance with the attached electrical one-linediagram that is attached to the Data Schedule and must include thefollowing:

• Input AC isolation transformer (when required)• Thyristor bridge cubicle• Control cubicle• Liquid cooling cubicle (when required)• DC link reactor cubicle• Contactor/switchgear cubicle• Output filter cubicle• Heat exchanger cubicle (outdoor-liquid cooled systems only)• VSD by-pass (when specified)

The VSD system voltage must be either 4,160 V or 6,900 V as specified inthe Data Schedule.The VSD must be electrically protected from damaging incoming lineconditions of overvoltage, undervoltage, overcurrent, or phase failure.The motor that is being controlled must be protected from damaging VSDoutput conditions of overvoltage and overfrequency.The VSD must control the motor's speed proportional to a 4-20 mAautomatic process signal.The VSD must be able to continuously operate the driven load over thespeed range specified in the Data Schedule.

Figure 6: General VSD Design Requirements (from 17-SAMSS-517)




Figure 7 shows VSD construction requirements.

GeneralConstructionRequirements

The drive must be constructed for ease of maintenance to minimizedowntime.

The components must be grouped by function and provide inter-changeability between any assemblies that have the same function.The unit must be designed to permit ready access to thyristor modules,control modules and printed circuit boards.The placement of components, test points, and terminals must be such thatthey are accessible for circuit checking, adjustment, troubleshooting, andmaintenance from the front of enclosure without removal of any adjacentmodule or assembly.The weight must be kept to a minimum to allow removal of assemblies byone person without the aid of lifting devices.The power bus must be tin-plated copper and conservatively rated formaximum current rating per NEMA standards.Short circuit bracing must be designed for available symmetrical faultcurrent.A ground bus must be provided in the cabinets of the VSD and contactors,running the full length of all of the cabinets.The minimum size must be 6.4 mm by 50.8 mm (0.25 in by 2.0 in) and berated for available short circuit current.The cubicles must be bolted together to form a continuous switchgearassembly.Power and control terminals must be easily accessible for cable entry in thecubicle top or bottom.Power terminations must be suitable for bolt-on lugs.Audible noise that is generated by the controller must not exceed a soundpressure level of 75 dBA measured 1.5 M (5 ft) from any surface of theenclosure.

Figure 7: VSD Construction Requirements (from 17-SAMSS-517)




IndoorEnclosures

Enclosures must be either carbon steel or aluminum, designed in accordancewith NEMA ICS-6.Power conversion equipment enclosures must be free-standing, dead-front,ventilated NEMA ICS-6 Type 1A and designed for front access only.Access panels (doors) must be double or full-length hinged. Doors must belockable with identical lock and key combinations for each lineup.Handles, screws and hinges must be corrosion resistant as defined in NEMAICS-6.A warning sign, written in both Arabic and English, must be installed on thefront of each cabinet warning of interference that may be caused by portablecommunications transmitters.The enclosures must be cleaned, primed and painted with the Vendor'sstandard finish in accordance with standard practice for indoor enclosures.The color must be ANSI 61 light gray.

Nameplates All devices located within a panel must be provided with suitablenameplates to identify item and function.Device nameplates must be engraved laminated plastic with black 6.4 mm(0.25 in) characters on a white 64 mm by 25 mm (2.5 inch by 1 in)background as a minimum and must be in the English language.Warning nameplates must be engraved laminated plastic with whitecharacters on a red background and must be written in both Arabic (Naskhscript) and English.Exterior-mounted nameplates must be attached with stainless steel or brassscrews.Nameplates within the compartments may be attached with permanentadhesives.Warning plates must be provided on each compartment door in which anexternal voltage source is terminated, reading: "CAUTION - THIS UNITCONTAINS AN EXTERNAL VOLTAGE SOURCE."

Figure 7: VSD Construction Requirements (from 17-SAMSS-517) (Cont'd)




Wiring The controller internal wiring practices, materials, and coding must be inaccordance with the latest edition of the National Electric Code (NFPA 70)and other applicable standards.All internal wiring must be identified at each termination, junction box, anddevice.Identification must be made with permanently embossed wire markers of theheat-shrinkable, slip-on type. Adhesive type markers are prohibited.Wire markers must directly correspond to the schematic and wiringdiagrams furnished with the unit.All control wiring must be stranded copper conductors, rated 90 deg C,abrasion resistant type.Insulated compression (crimped) ring tongue type terminals must beprovided for all wiring terminating of terminal blocks. Soldered terminalsare not acceptable for connection to terminal blocks.Terminal blocks must be provided for all externally-connected wiring.Terminal blocks must be one piece, phenolic, barrier type with pan headscrews.A maximum of two wires per terminal point is permitted.All control wiring must be isolated from power wiring and all AC voltagesmust be isolated from all DC voltages.

ExternalConnections

All line and load power connections must be compression bolted type lugsfor reliability.The connections must include lock washers and anti-galvanic corrosionprotection joint compound to assure long-term integrity.

Figure 7: VSD Construction Requirements (from 17-SAMSS-517) (Cont'd)




Figure 8 shows VSD component design requirements.

IsolationTransformerDesignRequirements

Isolation transformer, when required, must be in accordance with Buyer'Specification 14-SAMSS-531, "Power Transformers" or 14-SAMSS-533,"Three-Phase Dry-Type Power Transformers". (Specifications may beamended to ensure suitability of the transformer for supplying the staticpower converter.)The transformer must limit the available fault current to a value which issafe for the converter thyristors.The transformer must allow full voltage starting when a VSD bypass isspecified in the Data Schedule.

PowerConverterGeneralRequirements

The input to the power converters must be protected against voltage surgeson the incoming line by the utilization of high power surge arrestors.

The thyristors must be mounted in modular groups. Each thyristor modulemust contain all associated suppression and gate isolation components andmust be front accessible and front removable.Each module must contain a positive and negative leg of series connectedthyristors. The thyristors must be standard, proven, readily available,converter grade.The system must be designed to continuously provide rated power in a 50deg C ambient with a maximum thyristor junction temperature of 95 deg Cwithout derating the system.All high voltage must be isolated at the module for operator safety in theregulator compartment.Gate pulses must be transmitted using fiber optic techniques.The regulator must monitor individual thyristors to ensure they receive theirgate signal at the proper time and that each thyristor conducts and blocks atthe proper times.

Figure 8: VSD Component Design Requirements (from 17-SAMSS-517)




PowerConverter

Should either the gate firing or thyristor conduction be improper, an alarmindication of the individual failed device must be provided.

GeneralRequirements(Cont'd)

Each leg of the power bridge must contain series thyristors which have aminimum Peak Inverse Voltage (PIV) rating of 250 percent with all devicesoperating.The failure of one device, in any or all legs, must not cause a shutdown.With one device shorted, the PIV rating of the thyristors must be aminimum of 200 percent.All thyristors in the VSD must be tested to ensure they have similarcharacteristics so they will share the power reliably during turn-on,operation, and turn-off.

PowerConvertersfor Motors746 kW

Power converters must be air cooled.

(1,000 HP) orLess

The cooling system must have redundant air ventilating fans so that one fanprovides 100 percent converter enclosure cooling capacity at 100 percent ofthe motor nameplate load.Monitoring and alarm systems for cooling system failure must be provided.

PowerConvertersfor Motors

Power converters must use a closed loop liquid cooling system for optimumefficiency, increased reliability, and to minimize the size of and dependenceon air conditioning units.

Greater than746 kW

Converter cooling must be accomplished using a chemical mixture that hasan operating range from 0 deg C to 50 deg C.

(1,000 HP) The cooling system must have the following major components:• Redundant 100 percent close coupled, centrifugal pumps with

mechanical seals.• A remote liquid to air heat exchanger• A high temperature mixed bed resin filter.

Figure 8: VSD Component Design Requirements (from 17-SAMSS-517) (Cont'd)




PowerConvertersfor MotorsGreater than746 kW(1,000 HP)(Cont'd)

The cooling system must use NEMA frame motors in accordance withSaudi Aramco's Specification 17-SAMSS-503.

The cooling system must be designed with a separate low voltage cubicle toallow coolant replacement or pump servicing with the drive completelyoperational.All hoses must be comprised of flexible, high-dielectric material, rated to aminimum of 1724 kPa (250 psig) with an operating temperature range of-40 deg C to 121 deg C.All hoses must be Hi Pot tested to 50 kV.

DC LinkReactors(DCLRs)

Two DCLRs must be provided. One for the positive and one for thenegative DC side of the power bridges to properly control current flowduring normal operation and any fault condition. Each link reactor mustlimit the DC ripple to 10 percent.The reactor must be dry-type, air-core, convection-cooled, with Class Finsulation not to exceed Class B temperature rise suitable for outdoorapplication in a maximum ambient temperature of 50 deg C.The reactor enclosure must be NEMA 1 indoor or NEMA 3R outdoor withscreened or louvered openings. The enclosure must be provided withground bus.

PrintedCircuitBoards

All printed circuit board (PCB) components must be high quality, industrialgrade type, designed to operate within modules using only internalnatural-draft air circulation, (no external fans), up to 50 degrees C., with arelative humidity of 95 percent.PCB components must be wave soldered to PCBs.





PrintedCircuitBoards(Cont'd)

Component leads must not act as thru-board connection pins or be solderedon the component side of the board.

Each component on the board must be clearly identified by means of etchingor high-temperature curing ink in accordance with Vendor's circuitschematics.Each PCB module must also be identified by type/revision number.All PCBs incorporating or supporting edge connectors must be providedwith gold plated contacts. All edge connectors must incorporate a keyingsystem to prevent improper board or module placement or orientation.LEDs which are installed on PCBs within modules must be mechanicallyprotected by a transparent cover, and be identified externally.

Output Filter The VSD output must be filtered to allow retro-fitting an existing motorwithout derating the system.The output filter must provide a sinusoidal waveform containing amaximum of 5 percent total harmonics to minimize motor heating.Filter capacitors must include resistors which will discharge the capacitorsto a safe voltage within approximately one minute after removal of externalpower.Voltage rise in the converter filter must not exceed 5 percent of nominal busvoltage.The manufacturer must supply a withdrawable output contactor which willdisconnect and isolate the drive and filter from the motor.

HarmonicFilter

When specified on the Data Schedule, the filter must also maintain a unitypower factor under all normal operating conditions.The power factor must be automatically maintained with stepless control.





HarmonicFilter (Cont'd)

When specified on the Data Schedule, the filter must also maintain a unitypower factor under all normal operating conditions.The power factor must be automatically maintained with stepless control.

Bypass When specified in the Data Schedule, the system must include awithdrawable contactor or breaker (as shown on the engineering drawings)to bypass the drive in case of a VSD failure or to operate the motor at fullspeed.When specified in the Data Schedule, the bypass protection and controlmust be as shown on the engineering drawings.Bypass protection and control must be in accordance with 16-SAMSS-506for contactors or 16-SAMSS-501 for breakers.The bypass system must be incorporated to provide a smooth, closedtransition synchronous transfer of the induction motor from the drive to themain AC line and from the main AC line back to the drive.Transition must be accomplished without stopping or slowing the motorand without significant transients on the line.





Work Aid 1B: Instrumentation and Controls

The instrumentation and controls for VSDs must include the following:

• Input ammeter with phase selector switch

• Input voltmeter with phase selector switch

• Output kW meter

• Motor speed meter power factor meter

• Output frequency meter

• Output voltmeter with phase selector switch

• Output ammeter with phase selector switch

• Local speed potentiometer

• Motor "start-stop" control

• "Local"-"Off"-"Remote" switch for motor "start-stop" control

• Emergency shutdown push button

• Cooling pump and blower control switch

• Alarm status lamps

• Logic power lamp

• Red motor output contactor "closed" lamp (when required)

• Green motor output contactor "open" lamp (when required)

• Bypass contactor control (when required)

• Red input contactor "closed" lamp (when required)

• Green input contactor "open" lamp (when required)

Ammeters that are used must have scales that range from 0 to 150 percent of the maximum ratedcurrent. Voltmeters that are used must have scales that range from 0 to 120 percent of ratedvoltage. All meters must have +/- 2 percent full-scale accuracy and must be designed inaccordance with ANSI C39.1. Meter scales must be 90 mm (3.5 in) or larger.




Work Aid 1C: Alarm and Indicating

An alarm annunciator must be provided and must include, at a minimum, the followingindications:

• Motor stalled

• Loss of speed command

• Heat exchanger blower shutdown

• Low cooling fluid level (liquid-cooled system)

• Coolant purifier failure (liquid-cooled system)

• High cooling fluid temperature (liquid-cooled system)

• Output ground fault

• One series thyristor failure (with indication of the actual device)

• High ambient air temperature

• Loss of any cooling water pump (liquid-cooled system)

• Loss of any cooling fan (air-cooled system)

A trip annunciator must be provided and must include, at a minimum, the following indications:

• Incoming phase loss

• Gate drive circuit failure

• Inverter overvoltage

• Inverter undervoltage

• Output overfrequency

• Output overcurrent

• Output overvoltage

• Input overcurrent

• Input overvoltage

• Capacitor filter failure

• Converter over temperature (air-cooled system)

• Cooling fan failure (air-cooled system)




• Cooling fluid over temperature (liquid-cooled system)

• Cooling fluid low level (liquid-cooled system)

• DC link reactor over temperature

• Two series thyristor failures (with indication of the actual devices)

• Manual emergency shutdown

• Ground fault

• Total cooling water pump failure (liquid-cooled system)

• Loss of speed command

Work Aid 1D: Input and Output Interfaces

Each output must be an isolated form "C" contact that is rated 10 A at 600 Vac. The followingminimum outputs from the VSD must be provided:

• Alarm annunciator-summary

• Trip annunciator-summary

• Local control

• Remote control

• Output contactor open

• Output contactor closed

• Bypass contactor closed

• Spare

The following 4-20 mA dc output signals must be provided:

• Output voltage

• Output current

• Output frequency




Input contacts must be rated 10 A at 600 Vac. The following minimum inputs to the VSD mustbe provided:

• Input signal (4-20 mA-frequency command)

• Motor start

• Motor stop

• Input breaker open

• User alarm

• User trip

Work Aid 1E: VSD Microprocessor

Figure 9 shows the requirements for the VSD microprocessor diagnostic and event recordingsystem.

Micro-ProcessorDiagnosticSystem

The VSD must be provided with a diagnostic system with an event recorderand printer providing first out fault detection.

The control and regulation functions must be separate from the protectionand annunciation functions to ensure that the integrity of one function ismaintained in the event of a failure of the other.The microprocessor based diagnostic system must monitor all trip and alarmfunctions and display them on a front panel for analysis.The system must be capable of remotely transmitting alarm conditions, tripconditions, digital signals and analog signals.Conditions and signals must include the voltage and current waveforms ofthe induction motor, the input voltage and current to the drive, and regulatoranalog functions.Information must be able to be sent via a two wire RS232 port.The Vendor must provide normally open and normally closed fault contacts,pre-wired to terminal blocks for Buyer's use, for all alarm and shutdownconditions.

Figure 9: VSD Microprocessor Diagnostic andEvent Recording System (from 17-SAMSS-517)




Work Aid 1F: Data Schedule

Figure 10 shows the data schedule from 17-SAMSS-517 that is used to order medium voltageinduction motor variable speed drives.

DATA SCHEDULEFOR 17-SAMSS-517

MEDIUM VOLTAGE INDUCTION MOTORVARIABLE SPEED DRIVES

_______________________________________________________________________

INFORMATION SUPPLIED BY BUYER

1. Buyer's Quotation Request/Purchase Order No.: _____________________ 2. Buyer's B.I./J.O. No.: ____________________________________________ 3. Buyer's Line Item No.: ____________________________________________ 4. Motor Rating: ______________________________ kW; ( ___________ HP) 5. Motor Voltage: ( ) 4,000 V; ( ) 6,600 V 6. Motor Full Load Amps: ____________ amps 7. Synchronous Speed: _______________ rpm 8. Driven Equipment wk (sq): _____________ Kg- m2 (________lb - ft2) 9. Supply bus voltage: ___________________ volts 10. Available Short Circuit Current: ______ rms symmetrical amps 11. Power factor correction required: ( ) yes ( ) no 12. The driven load will have a

( ) variable ( ) constant torque vs. speed profile over a speed rangefrom _________ percent to ___________ percent speed.

13. Bypass Contactor/breaker required: ( ) yes ( ) no 14. Bypass synchronous transfer required: ( ) yes ( ) no 15. VSD Efficiency test at 1/2 load, 3/4 load, and full load required:

( ) yes ( ) no 16. One-Line Diagram Attached: ( ) yes ( ) no

________________________________________________________________________

Approved: ______________ Dwg. No. NT- ___________ Date : ______________ Revision No. ___________ Sheet 1 of 1

Figure 10: Medium Voltage Induction MotorVariable Speed Drives Data Schedule (from 17-SAMSS-517)




WORK AID 2: REFERENCES FOR EVALUATING MOTOR VARIABLE SPEEDDRIVE INSTALLATION AND TESTING

The information in this Work Aid contains combined excerpts from the following resources:

• 17-SAMSS-517, Medium Voltage Induction Motor Variable Speed Drives

• GI-2.710

• Related Industry Standards

Work Aid 2A: Testing Requirements

In addition to the manufacturing facility tests and checks, the following inspections, checks, andtests are performed on induction motor VSDs:

Visual Inspection

• Suitability

• Physical damage

• Solid state devices

• Cleanliness

Mechanical Inspections, Tests, and Checks

• Operating mechanism

• Mounting bolts

• Lubrication

Electrical Tests and Checks

• Manufacturing facility checks and tests

• Point-to-point wiring and continuity

• Contact resistance

• Insulation resistance

• Phase sequence and rotation

• High-pot testing




Operational Checkouts and Tests

• Power and terminal verification

• Drive operation testing with the motor disconnected

• Motor rotation check

Work Aid 2B: Visual Inspection

Visual inspections are used to assess the physical condition of VSDs during the commissioningprocess. A visual inspection is a pass/fail verification about a particular aspect of the physicalcondition or the operation of the VSD. Because the criteria that are established to determine theacceptability of the visual inspections can be subjective, the visual inspections should beperformed by an experienced Electrical Engineer.

Suitability

A visual inspection of the VSD to determine the suitability is performed prior to the VSDcommissioning. To determine the suitability of a motor VSD, a visual inspection of the nameplatedata is performed and compared to the electrical system single-line diagram.

Physical Damage

A visual inspection of the VSD for physical damage is performed prior to the VSDcommissioning. To determine whether there is any physical damage to the VSD, a visualinspection for cracks, dents, missing or broken pieces, and bent ventilation openings is performed.

Solid State Devices

A visual inspection of the solid state devices is performed prior to the VSD commissioning.During the inspection of the solid state devices, the Electrical Engineer inspects the solid statedevices for indication of overheating. Printed circuit boards (PCBs) are inspected to determinewhether they are properly seated at the board edge connectors. PCBs are also inspected todetermine whether board locking tabs are in place.

Cleanliness

A visual inspection of the cleanliness of the VSD is performed prior to the VSD commissioning.The purpose of the cleanliness visual inspection is to ensure the proper operation of the VSD overits maximum operating life. During the VSD cleanliness inspection, the Electrical Engineer looksfor the accumulation of dust and dirt, and he checks the contacts of circuit breakers or contactorsfor excessive wear and the accumulation of dirt.




Work Aid 2C: Mechanical Inspections, Tests, and Checks

A mechanical inspection is used to assess the ability of the VSD to physically perform what isnecessary for proper operation.

Operating Mechanism

The operating mechanism for VSD isolation, supply, or bypass components must be inspectedprior to the VSD commissioning. During the mechanical inspection of the operating mechanismof VSDs, the Electrical Engineer checks the operation of all moving parts for freedom ofmovement with no evidence of sticking or binding. All operating mechanism fasteners andlinkages are checked for loose, broken, or badly deformed parts.

Mounting Bolts

The VSD mounting bolts are inspected prior to the VSD commissioning. The mounting bolts areinspected to ensure that they are securely fastened and that the bolts and frame mounts arecapable of preventing the VSD cabinets and internal equipment from coming loose duringmechanical failure or electrical fault conditions. To perform the mounting bolt check, themanufacturer's technical manual is consulted for the proper bolt torque value. A torque wrench isthen used to determine the amount of torque at each mounting bolt. Improper torque values areimmediately corrected.

Lubrication

The VSD lubrication system is inspected prior to the VSD commissioning. The lubrication visualinspection is performed in accordance with the VSD manufacturer's instructions.

Work Aid 2D: Electrical Tests and Checks

Electrical inspections and tests are performed to check the ability of induction motor VSDs tooperate 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 grossdefects or errors in workmanship in equipment construction.

Manufacturing Facility Checks and Tests

Figure 11 shows the major checks and tests that are performed on induction motor VSDs at themanufacturing facility prior to shipment. Checks and tests are performed to identify anycomponents that may be subject to premature failures.




PCB Testing All PCB's must be burned-in continuously for 168 hours at 65 deg C.The PCB's must be tested after burn-in to insure they are functioning withinspecification.

ComponentTesting

Thyristors must have the following critical parameters tested at ratedcurrent:

• gate pulse level• turn-on• turn-off• high temperature• forward blocking• reverse blocking• waveform characteristics

All assembled phase cells must be tested for cell balance at rated voltage,maximum current, maximum dV/dT and maximum dI/dT.

Operationaland ControlTesting

The complete drive must be burned-in at full load amps for continuous 24hours.

Control power must be applied to microprocessors, printed circuit boards,diagnostic boards and similar devices, (including software) to test for properoperation, sequencing, logic and diagnostics.When load testing is specified in the data schedule, the vendor mustdetermine the VSD efficiency through use of the summation of segregatedloss method at 1/2 load, 3/4 load, and full load.

Figure 11: Manufacturing Facility Checks and Tests (from 17-SAMSS-517)

Point-to-Point Wiring and Continuity

Point-to-point wiring checks are performed to verify that a VSD complies with Saudi Aramcowiring diagrams and manufacturer's specifications prior to the VSD commissioning. During thepoint-to-point wiring checks, terminations and terminal blocks are checked for routing andlabeling, and control and metering equipment (e.g., transformers and fuses) is checked for properapplication and type. All VSD wiring is also checked for continuity, and it is checked against thewiring diagrams that are provided. The VSD wiring continuity test is performed with a buzzer orbell-type continuity tester. Written checklists or drawings are used as reference material duringthe continuity tests.




Contact Resistance

Prior to the VSD commissioning, contact resistance checks are performed to identify contacts thatare defective or detrimental to the operation of the contactor or starter that is contained in theVSD prior to the VSD commissioning. To conduct the contact resistance test, the equipment thatis to be tested is disconnected from the system. Once the equipment is removed and the contactsare in the closed position, the leads of a digital, low-resistance ohmmeter are placed across theline and load sides of the contacts, and measurements are taken. The contact resistance isrecorded on a test data sheet and retained in Saudi Aramco material history records.

Values of contact resistance in excess of 200 microohms and deviations of more than +/-20%should be investigated. Technical data to evaluate the results of the contact resistance test can befound in the equipment manufacturer's technical manual or in the Saudi Aramco Pre-Commissioning form, P-000, Testing Guide Lines.

Insulation Resistance

The results of all commissioning insulation resistance (megger) tests that are performed must bedocumented on the appropriate manufacturer or Saudi Aramco commissioning form.

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

PI10

1

minute

minute

reading

reading=

Figure 12 provides insulation conditions for 60/30 second ratio results and for 10/1 minute ratioresults.

Insulation Condition 60/30 - Second Ratio 10/1 - Minute Ratio(Polarization Index)

Dangerous ---- Less than 1

Questionable 1.0 to 1..25 1.0 to 2

Good 1.4 to1.6 2 to 4

Excellent Above 1.6 Above 4

Figure 12: Dielectric Absorption Ratio Chart




Phase Sequence and Rotation

Phase sequence and rotation tests are performed to ensure that the power supply inputs to theVSD are at the proper voltage and in the proper phase sequence. Sequence testing and rotationtesting are performed to ensure that the motor (when connected) will rotate in the correctdirection. During the phase sequence and rotation tests, the ac power input leads are checked forproper markings to ensure that the sequence coincides with the incoming power system. A visualverification of the motor leads is also conducted to ensure that the motor leads are properlymarked to coincide with the VSD output leads. The motor lead markings and the VSD outputlead markings must match so that the motor shaft will rotate in the correct direction.

High-Pot Testing

For the commissioning of VSDs for motors that are 746 kW (1,000 HP) or larger, a high-pot testmust be conducted on the cooling medium hoses. The maximum test voltage for the high-pot testis 50 kV.

A polarization index (PI) test is performed by applying an initial voltage step of 16.5 kV(approximately one-third of the maximum voltage of 50 kV). The initial voltage step must bemaintained at a constant level for ten minutes. The PI is calculated by dividing the one-minuteleakage current by the ten-minute leakage current. A PI value of 2.0 or less must be investigated.

After the initial ten-minute test, the dc test voltage is increased in approximately ten uniformsteps. Each step should have a one-minute duration. The voltage is increased until the maximumrecommended dc value is reached.

The following are the acceptable results of a high potential test:

• The microamperes leakage current should decrease in value during the initial tenminutes of the test at the initial voltage step. The microamperes leakage current shouldshow a steady rise for the remainder of the test until the maximum test voltage isreached.

• A steady-state or rising value during the initial ten minutes of the test indicates poorinsulation and, as a result, the insulation should be rejected. A sharp or an exponentialrise in leakage current that occurs during the step voltage changes or prior to theapplication of the maximum test voltage also indicates poor insulation.




The dc high-pot test should be secured if one of the following situation occurs:

• The duration of the test has expired.

• A rapid rise in leakage current occurs.

• The polarization index < 1.

The following are the characteristics of a satisfactory dc high-pot test:

• The leakage current gets smaller over time.

• The polarization index > 1.

• The leakage current increases on a straight line as voltage is increased. No "knee"is noticeable in the leakage current curve.

An example of dc high-pot test data is shown in Figure 13. Figure 13 shows both good and badinsulation test data.

Motor InsulationClass

Maximum AllowableInsulation Temperature

in °CB 130F 155H 180

Figure 13: Example of DC Hi-Pot Test (Good and Bad Cable Insulation)

Work Aid 2E: Operational Checkouts and Tests

The proper operation of all VSD subsystems is tested through use of controlled operation andcheckout of the controls and protective devices. Although there are many different manufacturer'sconfigurations of VSDs, most VSDs have similar subsystem and component operation andcheckout test procedures. For a specific VSD's subsystem component operation and checkoutstests, the manufacturer's technical manuals should be consulted. For any testing, extreme careshould be taken due of the presence of electric power and rotating equipment. Failure to exerciseextreme caution when conducting operation and checkout testing can result in personnel injury orequipment damage. This section of the Work Aid contains a brief overview of generic VSDtesting.




Power and Terminal Verification

Prior to a test of the VSD with the motor disconnected, a power and terminal verification isperformed as follows:

1. Remove power to the VSD through use of a disconnect device.

2. With all power to the VSD removed, remove the drive cover and verify that theincoming ac power and motor connections are in accordance with manufacturer'sspecifications. The individual phase voltages (A-B, B-C, and A-C) should be equalto the nameplate voltage rating ±10%.

3. Verify that all control and logic interconnections are made in accordance withmanufacturer's specifications.

4. Verify that the ac line power at the disconnect device is within the rated value ofthe drive.

5. Disconnect the motor leads from the terminals at the drive.

Drive Operation Testing with the Motor Disconnected

1. Replace the cover of the VSD and assume local control of the VSD. Set theSTART/STOP switch to the STOP position and the speed setting to the fullyCCW (stopped) position.

2. Apply input power to the VSD and verify that no abnormal conditions or faults aredisplayed on the control panel.

3. Start the VSD. Verify that the desired minimum and maximum frequencies areobtained.

4. Stop the VSD. Verify that the drive immediately stops. If the VSD has a rampstop mode, verify that the drive ramps to a stop within the predetermined ramptime.

5. Start the VSD and set to the maximum frequency. Observe and record theacceleration time.

6. Stop the VSD and observe and record the deceleration time for each stop modethat is present (e.g., coast, brake, and ramp).




7. If skip frequencies have been programmed, start the VSD and slowly increase thefrequency. Verify that the VSD skips over the selected frequencies.

8. If the VSD has a reverse feature, test the reverse operations of the VSD.

9. If the VSD has a jog feature, test the jog operations of the VSD.

10. Remove power to the VSD through use of the disconnect device.

11. Remove the VSD cover and reconnect the motor leads from the terminals at thedrive. Replace the VSD cover.

Motor Rotation Check

1. Verify that the VSD is in the local control mode and that the local controls havethe VSD stopped. If the VSD is equipped with forward and reverse modes, theVSD must be in the forward direction.

2. Apply power to the VSD through use of the disconnect device.

3. Set the frequency to the minimum, and start the VSD. Slowly increase thefrequency until the motor rotates. Observe that the motor rotates in the correctdirection.

4. If the motor does not rotate in the correct direction, stop the motor, remove thepower to the VSD, and consult the VSD technical manual.




Work Aid 2F: Excerpts from GI 2.710

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 14 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 14: GI 2.710 Excerpt




Figure 14: GI 2.710 Excerpt (Cont'd)




GLOSSARY

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

insulation resistance The amount of opposition to the flow of electric current that isoffered by an insulation.

polarization index The ratio of a ten-minute insulation resistance reading divided by aone-minute insulation resistance reading.

squirrel-cage A motor in which the secondary circuit consists of a scroll-cagewinding.

Commissioning Motor Variable Speed Drives (VSDs)

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Transcript of Commissioning Motor Variable Speed Drives (VSDs)