Commissioning Protective Relay Systems

8 EVALUATING PROTECTIVE RELAY SYSTEMS UPON RECEIPT ...11 Visual Inspection...11 Verification Against Specifications ...12 EVALUATING PROTECTIVE RELAY SYSTEM INSTALLATION AND TESTING ...1

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

Commissioning Protective Relay Systems

Content Page

INTRODUCTION 1

SAUDI ARAMCO REQUIREMENTS 2

Types 2

Electro-Mechanical 3

Solid State 6

Characteristics 8

EVALUATING PROTECTIVE RELAY SYSTEMS UPON RECEIPT 11

Visual Inspection 11

Verification Against Specifications 12

EVALUATING PROTECTIVE RELAY SYSTEM INSTALLATION AND TESTING 16

Mechanical Checks 16

Electrical Tests 18

Insulation Test 18

Pickup Test 19

Timing Test 20

Miscellaneous Electrical Tests 20

SYSTEM PRE-OPERATIONAL CHECK-OUT 21

PDD Point-to-Point Wiring Check 21

Subsystem Checks 21

WORK AID 1: REFERENCES FOR EVALUATING PROTECTIVE RELAY SYSTEMS UPON RECEIPT 22

Work Aid 1A: Protective Relay System Ratings and Requirements 22

Work Aid 1B: Standard Electrical Symbols and Device Numbers 26

Work Aid 1C: Device Suffix Letters 32

Work Aid 1D: Saudi Aramco Pre-Commissioning Form P-021 Excerpts 35

Work Aid 2A: Procedures and Methods for Evaluating Instrument Transformer

and Meter Installation and Testing 38

Mechanical Checks 38

Electrical Tests 39

Work Aid 2B: Saudi Aramco Pre-Commissioning Form P-021 Excerpts 39

GLOSSARY 44

Table of Figures Page

Figure 1: Example Induction-Type Relay 4

Figure 2: Basic Electro-Mechanical Relay Circuit 5

Figure 3: Block Diagram of a Solid State Current Relay 7

Figure 4: Protective Relay Time-Current Characteristics 9

Figure 5: Overcurrent Device Coordination 10

Figure 6: Typical Electro-Mechanical Overcurrent Relay 12

Figure 7: Typical Saudi Aramco Bus Overcurrent Protection Scheme 15

Figure 8: Electro-Mechanical Overcurrent Relay That Has Been Removed From Its Case 17

Figure 12: Standard Current and Voltage Ratings for Relays (From ANSI/IEEE C37.90) 22

Figure 13: Saudi Aramco Protective Relay System General Requirements (From SAES-P-114) 23

Figure 13: Saudi Aramco Protective Relay System General Requirements (From SAES-P-114)(Cont'd) 24

Figure 14: Relaying Electrical Symbols 26

Figure 15: NEMA Device Function Numbers 27

Figure 15: NEMA Device Function Numbers (Cont'd) 28

Figure 15: NEMA Device Function Numbers (Cont'd) 29

Figure 15: NEMA Device Function Numbers (Cont'd) 30

Figure 15: NEMA Device Function Numbers (Cont'd) 31

Figure 16: Sheet 1 (of 12) of the Saudi Aramco Pre-Commissioning Form, P-021, Protective Relays 36

Figure 17: Sheet 3 (of 12) of the Saudi Aramco Pre-Commissioning Form, P-021, Protective Relays 37

Figure 18: Sheet 1 (of 12) of the Saudi Aramco Pre-Commissioning Form, P-021, Protective Relays 40

Figure 19: Sheet 2 (of 12) of the Saudi Aramco Pre-Commissioning Form, P-021, Protective Relays 41

Figure 20: Sheet 3 (of 12) of the Saudi Aramco Pre-Commissioning Form, P-021, Protective Relays 42

Protective relay systems are installed to cause the prompt removal from service of any element of

a power system when it suffers a short circuit or when it starts to operate in any abnormal mannerthat might cause damage or otherwise interfere with the effective operation of the rest of thesystem Protective relay systems consist of three types of elements that work together to performthe desired protective function: the sensing devices, the protective relays, and the controlling (orisolating) devices

The sensing devices (e.g., CT or VT) continuously monitor power systems from generation,through transmission and distribution, to utilization Faults or abnormal conditions are detectedthrough use of the sensing devices The protective relays receive signals from the sensing devicesand provide outputs to the controlling devices (e.g., circuit breakers) When faults or abnormalconditions are detected by the sensing devices, rapid corrective action is initiated to isolate thefaulted portion of the system Rapid fault isolation provides a high degree of power continuity,reduces potential personnel hazards, and limits equipment damage

The correct selection, installation, and inspection of protective relay systems will directly affectthe overall safety, accuracy, and performance of electric power generation, transmission, anddistribution systems This Module provides information on the following topics that are pertinent

to commissioning protective relay systems:

• Saudi Aramco Requirements

• Evaluating Protective Relay Systems Upon Receipt

• Evaluating Protective Relay Systems Installation and Testing

• System Pre-Operational Check-Out

SAUDI ARAMCO REQUIREMENTS

Relaying provides a critical function in electric power system protection Relays are versatile andreliable, and they can perform a wide variety of functions Relays of various kinds can be set todetect abnormal conditions, such as faults, overloads, power swings, frequency changes, andover/undervoltages Through initiation of a trip of the appropriate circuit breakers, relays canisolate and deenergize a zone of protection to minimize the effect of the disturbance or fault onthe remainder of the electric power system A zone of protection is an area in a power systemthat a protection relay is configured to protect

The safe and proper operation of Saudi Aramco electrical generation, transmission, anddistribution system installation depends on the proper selection and installation of protective relaysystems Because the protective relay system functions to isolate faulted portions of the electricalsystems to prevent hazards to personnel and damage to equipment, the improper selection orinstallation of a protective relay system can lead to disastrous or catastrophic results The typesand characteristics of protective relay systems are described in Saudi Aramco standards and in thefollowing text A detailed description of protective relay systems is provided in EEX 106.SAES-P-114, 16-SAMSS-513, and ANSI C37 provide specific guidance that pertains to thematerial requirements for protective relay systems These requirements must be followed whenthe equipment is specified in initial project design and also when the commissioning processoccurs

A protective relay gets voltage and/or current information from an external sensing element in theform of current flow This current flow is some small percentage of the parameter that is beingsensed The small representative current flow causes the relay operating element (usually a coil)

to open or close The relay operating element opens or closes contacts, which actuate a warningsignal or which complete the trip circuit of a circuit breaker The relay usually includes someform of visual indicator, which is known as a target, to show that the relay has operated SpecificSaudi Aramco protective relay design requirements are provided in Work Aid 1

Types

The components that are used to construct the various types of relays are often similar in natureacross a wide spectrum of relays; such components can generally be grouped into the electro-mechanical type and the solid state type

Electro-mechanical relays use a combination of electrical fields and mechanical motion Anelectrical field that is proportional to the measured quantity (e.g., system voltage or current)causes mechanical motion within the electro-mechanical relay Electro-mechanical units can befurther subdivided into magnetic attraction units and magnetic induction units

A magnetic attraction unit uses instrument transformer secondary outputs (either voltage orcurrent) to create magnetic fields within the relay unit An example of a magnetic attraction unit

is a simple plunger relay When the current or voltage magnitude that is applied to the coilexceeds a predetermined value, the magnetic field that is formed will cause a plunger to moveupward The action of the moving plunger closes or opens a set of contacts Plunger relays areoften used as components in overcurrent relays

A magnetic induction unit uses the principle of an induction motor in which torque is developedthrough use of induction onto a rotor Induction-type relays are only used in ac applications Therotating element of an induction-type relay is usually a disk or a cylinder The two basic designs of

a magnetic induction relay are the induction disk and the induction cup A typical induction-diskrelay is shown in Figure 1

In Figure 1, the operating torque on the disk is produced through use of an electromagnet that has

a main coil and a lag coil The coil terminals receive current from the external sensing element.The current from the external sensing element becomes the main coil operating current The lagcoil produces a magnetic flux that is out of phase with the main coil The electromagnetic fieldflows in the laminated core of the relay, across the disk air gap, and through the keeper Thecombination of the in-phase and out-of-phase magnetic flux across the disk air gap causes torque

to be produced on the rotating disk The magnitude and direction of the input quantitiesdetermine the speed and direction of the rotating disk, which can be adjusted for a specific time-delay As the disk rotates, trip contacts are opened or closed The three-dimensional view of thedisk and the contacts, which is also shown in Figure 1, shows a simplified example of thestationary and movable trip contact operation

Figure 1: Example Induction-Type Relay

The operational objective of an electro-mechanical relay is to actuate an alarm or to initiate acircuit breaker trip when a power system parameter exceeds a preset value Each relay designachieves its operational objective through a variation of the basic electro-mechanical relay circuitthat is shown in Figure 2

The basic electro-mechanical relay circuit receives an input signal from the secondary winding of

an instrument transformer The instrument transformer primary winding receives an input signalfrom the power system The electro-mechanical relay operating element uses the input signalfrom the secondary winding to produce a magnetic field The electro-mechanical relay operatingelement compares the force of the produced magnetic field to a known value (e.g., gravity orspring) When the force of the produced magnetic field exceeds the force that is exerted bygravity or by a spring, the relay contacts close and complete the circuit for the output signal Theoutput signal then flows from the power supply for circuit breaker tripping through the circuit

Figure 2: Basic Electro-Mechanical Relay Circuit

Electro-mechanical relays can be used as follows:

• Overcurrent Relays

• Overvoltage Relays

• Undervoltage Relays

• Undervoltage Frequency

• Directional Overcurrent Relays

• Directional Power Relays

• Differential Relays

• Distance Relays

• Phase Balance Current Relay

• Loss of Excitation Relays

• Lockout Relays

Solid State

Solid state relays are electronics-based units that perform the same function as the mechanical units; however, solid state circuits replace the moveable elements of a relay In solidstate relays, electronic logic circuits are used to determine whether the direction and magnitude ofthe input values are sufficient to require protective action Although solid state and electro-mechanical relays use different methods to initiate protective action at pre-determined levels, theyaccomplish the same results

electro-Solid state devices are available for use as individual protective relays or as a protection package

A protection package is a group of individual protective relays that have been combined into asingle unit All electro-mechanical devices are available in solid state versions Although the solidstate devices are different in construction and operation, the solid state devices can perform thesame functions and can be applied in the same manner as the electro-mechanical devices

Figure 3 shows a block diagram of a typical solid state current relay The function of this relay is

to provide instantaneous and time overcurrent protection for a load The current flow to the load

is sensed through use of the main current transformer The main current transformer transmitsthis current signal to the auxiliary transformer The current flow through the auxiliary currenttransformer develops a voltage signal across the secondary resistor The voltage across thesecondary resistor will be proportional to the original current flow through the main currenttransformer The voltage signal provides the input signal to the inverse time circuit and theinstantaneous circuit of the solid state relay

The inverse time circuit consists of a rectifier, a solid state switch, a solid state timer, a trigger,and a memory coil The ac input voltage that is proportional to the line current is converted to dcthrough use of diodes in the rectifier of the inverse time circuit The dc output from the rectifierprovides an input signal to the solid state switch When the input signal exceeds a preset value,the solid state switch starts to conduct and provides an output signal to the solid state timer Theinput signal to the solid state timer starts to charge a capacitor in the solid state timer Thecapacitor charging time varies with the magnitude of the original input signal When the capacitor

is fully charged, the trigger circuit emits a pulse through the memory coil, which actuates the tripunit The trip unit trips the circuit breaker to isolate power to the load

The instantaneous circuit consists of a breakdown diode, a solid state switch, and a memory coil.The breakdown diode starts to conduct when the input voltage exceeds a preset value The presetvalue is determined through the construction of the diode When the diode conducts, thebreakdown diode converts the input ac voltage to a dc output voltage The dc output voltageprovides an input to the solid state switch When the breakdown diode conducts, the solid stateswitch emits a pulse through the memory coil, which actuates the trip unit The trip unit trips the

Figure 3: Block Diagram of a Solid State Current Relay

Solid state relays can be used as follows:

• Overcurrent Relays • Differential Relays

• Undervoltage Relays • Phase Balance, Voltage, and Current Relays

• Underfrequency Relays • Loss of Excitation Relays

• Directional Overcurrent Relays • Lockout Relays

• Directional Power Relays • Synchronism Relays

Some solid state relays contain microprocessors that enhance the versatility, the performance, andthe reliability of the solid state relay Microprocessor relays have coded chips that have addedlogic capabilities The addition of a microprocessor creates a solid state circuit that can makedecisions about output signals based on input signals Microprocessors also provide the ability tocontinuously perform operational self-checks that ensure proper operation If an electro-mechanical or simple solid state relay were to be faulty, the most likely time that this malfunctionwould be discovered is when the relay fails to operate properly when an actual system faultoccurs Continuous self-checking uncovers relay malfunctions as they occur so that corrective

Protective relay systems are designed to trip the circuit breaker when a protective device senses

an overload or fault condition Through variation of design and sensitivity, the protective devicecan be used to control the operation of a circuit breaker during overload or fault conditions.Because overloads or faults result in overcurrent conditions, overcurrent relays are the mostcommon electrical protective devices for use in electrical distribution systems Overcurrent relaysare used as both primary and backup protective devices The two main types of overcurrent relayprotection are the time-delay overcurrent and the instantaneous overcurrent In general, overloadprotection is provided through use of time-delay overcurrent relays, and fault protection isprovided through use of magnetic instantaneous overcurrent relays

Time-delay overcurrent devices have an inverse-time characteristic An inverse-timecharacteristic means that as the fault current gets larger, the time it takes for the device to operategets smaller The time delay device can be designed so that the length of this time delay can bevaried Generally, time-delay overcurrent devices are selected and set to provide short timedelays or long time delays Short time delays are used to provide selective tripping when a circuitbreaker is used in series with other circuit breakers, and long time delays are used for overloadprotection The following are the three different classes of time-delay overcurrent devices:

The inverse and very inverse time characteristics are usually applied to feeder circuits in whichproblems with coordination of in-line devices are not present Feeder circuits can readily handlewide variations in levels of fault current The extremely inverse characteristic is used when there

is a small variation in fault current from minimum to maximum because the extremely inversecharacteristic can provide faster clearing times for faults

Figure 4: Protective Relay Time-Current Characteristics

The time-delay overcurrent device is used to coordinate with other protective devices or relays.The time before the trip signal is sent from the protective relay to the breaker varies inversely tothe magnitude of the fault current Figure 5 shows the various time-delay coordinationcharacteristics for various multiples of the pickup current and for various time-delay responsetime settings

In Figure 5, the fault is located downstream of power circuit breaker #1 If the fault were fartherdownstream of breaker #1, it would take longer for the breaker to trip because the impedance ofthe distribution lines would result in less current being sensed at the protective relay A smalleramount of current that is sensed (with the inverse-time characteristic of the relay) means a longertime for the breaker to trip

The time it takes for breaker #1 to trip is finite (for a finite fault current) If breaker #1 failed totrip, the backup protection is breaker #2, which would trip "S" time units after breaker #1 shouldhave tripped To provide protection for the generator, each of these time delays creates acoordinated backup sequence of trips that would occur when any breaker fails to trip In theexample, each breaker backs up the one directly to its right, and the "S" time units between tripsensures a definite breaker backup sequence.

Figure 5: Overcurrent Device Coordination

Instantaneous protection is provided through the use of an element that exhibits a very small timelag between the sensed overcurrent condition and the circuit breaker trip signal For operationalcases, the time lag is so small that it is virtually instantaneous

EVALUATING PROTECTIVE RELAY SYSTEMS UPON RECEIPT

When protective relays are received as a part of the total inventory of equipment for a protectiverelay system installation, a receipt inspection must be performed to ensure that the protectiverelays are of the proper type as specified in the installation drawings and that no damage hasresulted during the shipping process The inspection process involves a physical inspection of theprotective relays and a verification of nameplate data against the installation specifications Anydeviation from specifications and any observed damage to these items must be evaluated andaction must be taken to obtain the correct equipment or to replace any damaged equipment Thereceipt inspection should be performed as soon as the equipment is received on the job site Ifdiscrepancies are noted, immediate corrective action can be taken, which will prevent excessiveinstallation delays This section provides information on the following topics that are pertinent toevaluating protective relay systems:

Figure 6 shows a typical electro-mechanical time overcurrent relay During the visual inspectionportion of protective relay system commissioning, each protective relay should be checked forphysical damage that could have occurred during manufacturing or shipping The relay housingcover, the glass, and the gasket should be removed and inspected for damage The relay housingitself should be inspected for the presence of cracks, foreign material, and moisture The relayshould be inspected for tarnished contacts, loose screws, or other imperfections that could affectthe freedom of mechanism movement or proper mechanism alignment In addition, all appropriatevendor operating and maintenance instruction manuals should also be verified to be present Ifthe relay is installed in the switchgear or in the control panel, the connected wiring should bechecked for the proper creepage, clearance, bend radius, insulation, and tightness during thevisual inspection

Figure 6: Typical Electro-Mechanical Overcurrent Relay 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 type of protective relays that are selected for aspecific protective relay system should be shown in the design package drawings, prints, or

specifications for the installation The purpose of verifying protective relay systems against the

Generally, the verification against specifications consists of a determination of whether the typeand rating of the equipment that is to be installed matches the size and type of the equipment that

is required for the installation This determination is accomplished by reading up-to-date meteringand relaying one-line diagrams and relay and control ac and dc schematics The Engineer inspectsthe manufacturer's nameplate data on each protective relay and compares them to the

requirements on the electrical prints and schematics to determine whether the correct relay isbeing used Saudi Aramco Pre-Commissioning Form P-021, Protective Relays, contains a checklist that itemizes what should be included in the verification of protective relays against SaudiAramco and industry specifications

During the verification against specification, the Engineer should ensure that the protective relays

in the protective relay system meet the minimum requirements for Saudi Aramco installations inaccordance with SAES-P-114, 16-SAMSS-513, and industry standards Saudi Aramco

Engineering Standard SAES-P-114 provides drawings that show the specific applications forprotective relays in Saudi Aramco electrical systems Each drawing shows the minimum

mandatory protection that must be provided for a particular portion of the power system or for aparticular piece of electrical equipment The relays that are shown in these drawings are identifiedthrough use of standard device function designations These device function designations havebeen developed over years of usage as an abbreviated method of designating the function of arelay This abbreviated method allows the use of a few numbers to completely describe the

function of a relay rather than writing a note to describe the function of each device on a drawing

The device function numbers are used on drawings and elementary and connection diagrams, inrelay instruction books, in publications, in standards, and in specifications In addition, thesenumbers are usually placed on nameplates that are adjacent to the device on switchgear or

relaying panels for identification of the designated function of that relay in the system Thesedesignated functions may refer to the actual function the device performs when it is installed, orthey may refer to the electrical or other quantity to which the device is responsive Because achoice of function numbers for a given device is sometimes available, the preferable choice is thefunction number that is recognized to have the narrowest interpretation

When alternate names and descriptions are included under the function, only the name and

description that applies to each specific case should be used In general, only one name for eachdevice, such as relay, contactor, circuit breaker, switch monitor, or other device, is included ineach function designation If the function of the relay is not inherently restricted to any specifictype of device, and if the type of device itself is incidental, any one of the alternative names may

be substituted as applicable

Device function numbers and suffixes are found in the most recent revision of ANSI StandardC37.2, "IEEE Standard Electrical Power System Device Function Numbers." A portion of thestandard electrical device function designations is provided in Work Aid 1 to assist in the

verification against specification during the commissioning process

A detailed discussion of each system and equipment protection scheme is beyond the scope of thismodule; however, a typical Saudi Aramco bus overcurrent protection scheme is shown in Figure

7 The protection devices that are shown in Figure 7 are identified through use of the followingstandard device function numbers:

• 51 is a time-delay overcurrent relay

• 52 is a circuit breaker

• 50/51 is an overcurrent relay with an instantaneous and a time-delay element

• 50/51G is a residually connected ground-fault overcurrent relay with an

instantaneous and a time-delay element

• 86B is a bus lockout relay

The 51 device (time-delay overcurrent relay) provides overcurrent protection for bus 1 as

measured at CT-1 When an overcurrent condition exists at CT-1 for a sufficient length of time,time-delay relay 51 operates and sends a signal to the bus lockout relay (device 86B) Device 86Bcauses the source breaker, 52-1, to trip (open)

The 50/51 device (instantaneous and time-delay overcurrent relay) provides overcurrent

protection against faults that occur downstream of load breaker 52-2 as measured at CT-2 When

an overcurrent condition exists at CT-2 (either large enough to activate the instantaneous element

or of a sufficient length of time to activate the time-delay element) the 50/51 device will trip(open) load breaker 52-2

The 50/51G device (instantaneous and time-delay ground-fault overcurrent relay) provides

overcurrent protection against ground faults as measured at the wye of the three-phase, connected current transformer (CT-2) Under ground fault conditions, unbalanced residual

wye-current conditions cause either the instantaneous element or the time-delay element of the 50/51Gdevice to trip (open) load breaker 52-2

Figure 7: Typical Saudi Aramco Bus Overcurrent Protection Scheme

EVALUATING PROTECTIVE RELAY SYSTEM INSTALLATION AND TESTING

After protective relay systems have been installed and prior to the equipment being placed intoservice, specific tests are required by Saudi Aramco The tests that are performed are designed toprove that the protective relay system will perform its job under the conditions of use and withinthe accuracy that is required by Saudi Aramco and industry standards Additionally, the

installation of protective relays must be inspected to determine whether the wiring and associatedcomponents are correctly installed or assembled If the results of testing during the

commissioning process indicate that the protective relay system does not meet Saudi Aramcorequirements, steps must be taken to rectify any deficiency

This section provides information on the following topics that are pertinent to evaluating

protective relay system installation and testing:

overcurrent unit The combination of tap block and adjustable pole piece settings will determinethe operation of the instantaneous unit The calibration plate is used to set the adjustable polepiece The main stationary brush and contact assembly will make contact if the system currentexceeds preset current levels, and the seal-in stationary contact assembly will operate the targetand seal-in unit

Figure 8: Electro-Mechanical Overcurrent Relay That Has Been Removed From Its Case

As shown in Figure 8, electro-mechanical protective relays have moving parts (e.g., disks,

contacts, etc.) that are critically aligned and must be checked for proper mechanism operationduring the commissioning process Proper mechanism operation includes freedom of movement,alignment, contact travel, contact wipe, and spring tension During the mechanical check, therelay should be inspected for friction Friction can be caused by a warped or bent disk, or byimproper clearance between the disk and the magnet poles The disk rotation should be checked

by hand The disk should move freely and should reset smoothly If auxiliary target devices,plunger relays, or annunciator coils are present, they should also be checked for friction and

A detailed mechanical inspection procedure is provided in Work Aid 2 Mechanical inspectionchecks are provided on sheets 1 and 3 of the Saudi Aramco Pre-Commissioning Form P-021,Protective Relays A representative portion of Saudi Aramco Pre-Commissioning Form P-021,Protective Relays, is provided in Work Aid 2 Solid state protective relays have no moving parts,

so the commissioning process mechanical checks for solid state relays are limited to the properinstallation of the protective relay unit and the proper connection of the power supply and inputand output wiring

Electrical Tests

After the protective relay system has been installed and inspected, it must be tested prior to beingcommissioned During the electrical tests of protective relay systems, all electrical safety

precautions must be taken to prevent personnel injury or equipment damage Because the settings

of protective relays must be coordinated with other relays in the electric power system, the relaysmust be set by Saudi Aramco It is assumed that all protective relay settings have been madeprior to the commencement of the commissioning process

Directions for testing electro-mechanical and solid state relays are given in manufacturer's

manuals or instruction books for each device In general, there are three specific types of

electrical tests and some miscellaneous electrical tests that are performed on protective relays.The electrical tests that are performed on protective relays are as follows:

commissioning is a megohmmeter test, which consists of application of a megohmmeter from eachprotective relay circuit branch to ground The resistance value is measured in megohms

Pickup Test

For both electro-mechanical and solid state protective relays, a pickup test should be performed

on each operating element During the pickup test, specific test equipment is used to determinethe pickup current that will cause the relay to operate The manufacturer's instruction literatureshould be consulted for the test equipment that must be used, as well as time/current curves andtolerances for the specific protective relay that is being tested In older electro-mechanical

systems, test plugs are available to assist in protective relay system testing Test plugs are

provided by the switchgear or protective equipment manufacturer, and they install directly into theswitchgear or panelboards

When the pickup value of current on electro-mechanical (e.g., plunger and solenoid type) relays isreached, the ammeter reading at the instant the relay operates should be noted Solid state relays(and solid state test equipment) generally contain electronic circuitry that will retain the systemparameters in chip memory at the time the relay operates The system parameters can then berecalled by the operator for entry on the proper data forms The pickup current value should bewithin 5% of the calibrated or tap setting value An example would be an electro-mechanicaltime-overcurrent induction relay with an instantaneous unit The induction unit of the exampleprotective relay has an operating coil with 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 ampere taps Withthe operating coil set at the minimum tap, the coil should pick up at a test current that is between1.425 and 1.575 amperes The manufacturer's technical manuals should be consulted for the exactvalue of the pickup current because deviations to the 5% tolerance do exist

The pickup test should be conducted with the relay in its normal operating position For mechanical relays, once the relay has picked up, the relay should be checked for quiet operation.After the pickup current value is established, the current that is applied to the relay should beslowly reduced until the relay drops out (or resets) The current value at the point that the relaydrops out should be between 90% and 95% of the pickup current value Pickup tests should also

electro-be performed on any target or seal-in units that are present in the protective relay When thepickup tests are performed, a check should also be made to ensure that the proper relay positionindicators function

Timing Test

With protective relays, not only must the relay pick up at a predetermined value of sensed current,but the relay operation must be coordinated with other relays or devices in the protection system.The coordination of a relay is accomplished by setting the pickup value at a specific point If atime delay is incorporated into the operation of the relay, the coordination of the relay is

accomplished through a combination of the pickup value and the time delay of the relay Inelectro-mechanical relays, the time dial determines the length of time that the unit requires toclose its contacts when the unit reaches a predetermined value Most electro-mechanical relaytime dials have settings from zero (no time delay) to ten (the maximum time delay) The timedelay of a protective relay on some electro-mechanical relays can also be set by moving the

position of the drag (or permanent) magnet

The timing test is conducted to determine whether the time delay of the relay is correct for theinstallation During the pickup test of a protective relay, the relay operating coil is set to theminimum tap, and the induction unit time dial is set at some mid-point value Because the

induction unit time dial generally has ten settings, a mid-point value of five is generally selected.Three different multiples of the tap pickup current are applied, and the relay operation time ismeasured The relay operation time for various multiples of pickup current is provided in graphform in the manufacturer's technical manual There is also a tolerance for pickup times (usually5%), but the manufacturer's technical manuals should be consulted for the exact value of thepickup time because deviations to the 5% tolerance do exist

Miscellaneous Electrical Tests

Several other miscellaneous electrical tests are performed on protective relays, and such testsdepend upon the type relay that is installed in the system A directional protective relay is

designed to operate in only one direction of current (or power flow) In addition to the pickupand timing tests, a directional relay should be tested in the reverse direction to ensure that it doesnot operate A differential relay is designed to operate with current (or power flow) in bothdirections In addition to the pickup and timing tests, a differential relay should be tested in thereverse direction to ensure that it operates correctly Voltage relays (e.g., undervoltage or

overvoltage) should be tested at the dropout and pickup voltage levels in a manner that is similar

to the pickup and timing tests that have been previously described