DISTRIBUTION BUS RELAY

SEL

-

251

C, -

2

, -

3

DISTRIBUTION BUS

RELAY

PHASE OVERCURRENT RELAY

WITH

VOLTAGE AND DISTANCE CONTROL

NEGATIVE

-

SEQUENCE OVERCURRENT

RELAY

GROUND

OVERCURRENT RELAY

SELECTABLE SETTING GROUPS

CIRCUIT BREAKER MONITOR

SELOGIC

®

CONTROL EQUATIONS

INSTRUCTION MANUAL

SCHWEITZER ENGINEERING LABORATORIES

,

INC

.

2350 NE HOPKINSCOURT

PULLMAN,WA USA 99163

-5603

Thesoftware(firmware), schematicdrawings,relaycommands,and relay messages arecopyrightprotected by theUnitedStatesCopyright Lawand InternationalTreatyprovisions.All rights are reserved.

You maynotcopy,alter, disassemble,orreverse-engineerthesoftware.You maynotprovidethe software to any third party. All brand or productnamesappearingin thisdocumentarethetrademark or registeredtrademarkoftheir respective holders.

Schweitzer EngineeringLaboratories,SELOGIC, Connectorized,JobDone,SEL-PROFILE,SEL-5030ACSELERATOR,and|SEL|are registeredtrademarksof Schweitzer EngineeringLaboratories,Inc.

The Englishlanguagemanualis the only approved SELmanual.

Copyright© SEL 1992, 1993,1994,1995,1996,1997,2000, 2002(Allrightsreserved)PrintedinUSA. This product iscoveredbyU.S.Patent Numbers: 5,041,737;5,477,408;5,479,315;and 5,602,707.

This product iscoveredbythe standard SEL 10-yearwarranty.For warranty details,visitwww.selinc.comorcontactyourcustomerservice

This device is

shipped with default passwords

.

Default passwords

should be

changed

to

private

passwords

at

installation

.

Failure to change each

default password

to

a private password

may

allow

unauthorized

access

.

SEL

shall

not be

responsible for any damage resulting from

unauthorized

access

.

Warning

Cet

equipement

est

expedie

avec

des

mots

de

passe

par

defaut

.

A Installation

,

les

mots de

passe par defaut

devront

etre changes

pour

des

mots de passe confidentiels

.

Dans

le

cas

contraire

,

un acces non

-

_autorise

_a

_I

_'

_equipement

pourrait

etre

possible

.

SEL

decline

toute

responsabilite pour

tout

dommage

resultant de

cet acces non

-

_autorise

_.

ATTENTION!

MANUAL CHANGE INFORMATION

Thedate code at the bottomof eachpageof this manual reflects the creation orrevisiondate.

Date codes arechanged onlyon pagesthat have been revised andany following pagesaffectedby

therevisions(i.e., pagination). Ifsignificantrevisionsare madetoasection,the date codeon all

pagesof the section will be changedtoreflect the revision date.

Each time revisions are made, both the main table of contents and the affectedindividual section

table ofcontentsareregenerated and the date code is changed to reflect the revision date.

Changesinthis manual to datearesummarized below (mostrecentrevisions listed at top).

ivision .. . " Summaryof Revisioi .. . . ' V.: '

TheManual Change Informationsection has been created to begin a record of revisions to

this manual. Allchanges will be recordedinthis Summary of Revisions table

.

20020212 This revision includes thefollowingchanges:

- Replaced Standard Product Warrantypagewith warranty_statementoncover

page.

AppendixA:

- Updated Firmware Version information.

20000421 This revisionincludesthe followingchanges:

- Reissued entire manual.

Section2:

- Updatedtoincludedetailsfor1

-

ampnominalcurrent inputmodel.

- AddedFrequencyand Rotation information

- Incorporated "NewSEL-200 Series Optical Isolator LogicInputRating"

- Incorporated "SEL-151/151C/251/251C Instruction Manual_Addendumfor

1AmpVersion Relays"

Section 5:

- _{Added note to Settings Sheets to indicate different setting ranges for 1}

-

_amp

nominal currentinputrelays.

Section6:

- Incorporated"JumperInstallation Instructions" addendum.

- Incorporated"SEL

-

200 Series (Shallow)Relay Hardware"addendum.

-

AddedFigure6.4:LP RelayDimensions andDrillPlan (forrelays with1

-

amp

nominalcurrent inputs)

- Added Figure 6.5:Panel CutoutDiagramsforPanel

-

Mount Relays

Section7:

- Addednotetoindicate that theLow

-

LevelTestInterface isnotavailableon

LP chassis relays

.

Date Code20020212 Manual Change Information SEL

-

251C,

-

2,

-

3 Instruction Manual

Revision

Date Summaryof Revisions '

Appendix B:

- Added note below FigureB. l that describes the difference in test point

locationsforLP chassis relays.

970421 This revision includes the followingchanges:

Appendix A:

- AddedNewFirmware Version.

Manual Change Information SEL

-

251C,

-

2,

-

3 Instruction Manual

Date Code 20020212

SEL

-

251

C

,

-

2,

-

3

INSTRUCTION

MANUAL

TABLE OF CONTENTS

INTRODUCTION

SECTION

1

SECTION

2: SPECIFICATIONS

SECTION

3 COMMUNICATIONS

SECTION

4 EVENT REPORTING

SECTION

5: APPLICATIONS INSTALLATION

SECTION

6

SECTION

7 MAINTENANCE AND TESTING

SECTION

8 APPENDICES

Appendix A: Firmware Versions in this Manual

AppendixB: Main Board Jumper Connector and Socket Locations Appendix C: Onebus: Program to Compute Test Set Settings for

TestingDistance Relays

TableofContents

SEL

-

251C,

-

2,

-

3Instruction Manual Date Code20020212

INTRODUCTION

TABLE OF CONTENTS

Getting Started . . . Overview General Description 1-1 1-₁ 1-2

DateCode20000421 Introduction

SEL

-

251C,-2,-3 Instruction Manual

SECTION 1

:

INTRODUCTION

GETTING STARTED

Ifyou arenotfamiliar with this relay, wesuggestthatyou readthis introduction,then

perform the Initial Checkout Procedure in Section 7: MAINTENANCE &TESTING.

OVERVIEW

TheSEL

-

251C Relay is designed to protectdistribution buses and backup distribution feeders for all fault types

.

The following listoutlinesprotectivefeatures, performance,andversatility gained when applying the SEL

-

251C Relay toyour installations

.

Developtraditional and advanced schemes using flexibleSELOGIC ControlEquations

Phase overcurrent elements have voltage and distance controlfor load security Negative

-

sequence elements reject load for moresensitive phase fault protection Ground/Residual overcurrent elementscover groundfaults

Choosefast orelectromechanical reset characteristicfor time

-

overcurrentelements Undervoltage logic detects high

-

sidetransformer fuse operations

Six selectable setting groupscoverall bus protection contingencies

Circuit breakermonitor sumsinterrupted current in each pole toaid maintenance Selectively backup distribution feeder relays

Eleven

-

cycle event reportsimplifies fault and system analysis

Comprehensive voltage, current, power,unbalance, and demand metering

Connects to SEL

-

RD Relay Display for easy informationaccess

TheSEL

-

251C Relay improveseveryaspectof bus protection

.

Security: Phase distance supervision avoids load encroachment Reliability: Field

-

proven hardware; new backupconcepts

Sensitivity: Negative

-

sequence overcurrent elements for better phase faultcoverage Flexibility: SELOGIC Control Equationshandlevirtuallyeveryconceivable scheme Capability: Brings transmission relay featuresto distribution applications

Economy: Low price and unique features make the relayanexceptional value

Date Code 20000421 Introduction

SEL-251C,-2, -3 InstructionManual

GENERAL

DESCRIPTION

TheSEL

-

251C Relay protectsand monitors distributionbussesand backs up distribution feeder relays. It offers importantnew and unique features, likeuser

-

programmable SELOGIC Control Equations, negative

-

sequence overcurrentelements,and selectablesettinggroups. Theadvanced relay designenhancessecurity, reliability, sensitivity,and operation

.

SF

_-

T

_-

orar Control Equations: The Next Step inProgrammable Relay _Logic

In1987, SEL inventedProgrammableMask Logic

.

TheSEL

-

251C Relay offers SELOGIC Control Equations, the nextstep inuser

-

programmability

.

SELOGIC Control Equations

include ANDing,ORing, and inverting functions, timing, and programmable inputs and outputs

.

SELOGICControlEquations add power and flexibility while simplifying programming.

Phase.Ground, and Negative

-

Sequence Overcurrent Protection

Phaseand negative-sequence overcurrentelements detectphase faults

.

Negative

-

sequence

overcurrent elementsrejectthree

-

phaseload toprovidemoresensitive coverage of

phase

-

to

-

phase faults

.

Phase overcurrentelements areneeded onlyfor three

-

phase faults

wherenegative

-

sequence quantitiesarenot produced

.

On heavily

-

loaded feeders, phasedistanceor undervoltagetorquecontrol of phaseovercurrent

elements adds security

.

Choosebetweenthree

-

phase and single

-

phase

-

pair phasedistance or

undervoltagetorquecontrol

.

When phase overcurrentelementsareused only for three

-

phase

faults, three

-

phase, phase distanceorundervoltagetorquecontrol enhances security

.

Ground/Residualovercurrentelements detectgroundfaults, andexternal inputscantorque

control selected overcurrent elements

.

Therearetworesetcharacteristic choices forthetime

-

overcurrentelements

.

Onechoice

resets the elements if current drops below pickup for at least one cycle

.

Theotherchoice emulates electromechanical induction disc elements wheretheresettime dependsonthe time

dialsetting,the percentageofdisc travel, and the amountof current betweenzeroand pickup

.

Six SelectableGroups of Settingsand Logic

The relaystoressix setting groups

.

Selecttheactive setting group by contact inputor command. Usethesesettinggroups tocover a wide rangeof distribution bus protection contingencies

.

Selectablesettinggroups make the SEL

-

251C Relay ideal for applications requiring frequentsetting changes.

Introduction

SEL-251C,-2y -3InstructionManual

Date Code 20000421 1-2

Circuit Breaker Monitor Tracks Breaker Performance and Helps MaintenancePlanning

Separate circuit breaker trip counters differentiate and tally relay

-

initiated trips and external trips

.

Runningsumsof interrupted current for relay and external trips indicate breaker wear on apole

-

by

-

pole basis

.

Use these data to schedule breaker maintenance

.

Trip failurelogicprovides alarm andbreaker failure functions

.

A close failure alarmindi

-catescircuit breaker closing circuitormechanism problems

.

The tripcircuit monitor detects abnormal openorshortcircuits in the circuitbreaker trippingcircuitorstatus input

.

Analyze_{Operations Using Event Reports}

Eleven

-

cycle event reportstriggered by userselected conditions provide the current,voltage, andsequence

-

of

-

events informationyou needto understandrelay and circuitbreaker perfor

-mance, aswell asstressonthe protected system foreveryfault

.

Comprehensive Metering Supports Protection

.

Operation, and DemandAnalysis

Therelay measures phase, negative

-

sequence, andzero

-

sequencevoltageand current,aswell asMW and MVAR

.

Demand and peak demandvalues for current, MW, and MVARare also available

.

Metering also supportsprotection,becauseyoucaninspectthequantities monitored by relayelements. Checkfor load encroachment and unbalancethrough instantaneous,

demand, and peak

-

demand measurements.

AccessSEL

-

251CRelay _{Information Via the SEL}

_-

_RDRelay Display

Youcanconnect up to four SEL

-

251C RelaystooneSEL

-

RD Relay Display

.

Access relay

target, meter,status

,

fault history, andcircuit breaker information via the relaydisplay. You

can evenchange theactive setting group via the display

.

Introduction

SEL-251C,-2,-3InstructionManual

SPECIFICATIONS

TABLE

OF CONTENTS

GeneralSpecifications

FunctionalSpecifications

SEL

-

251C Relay SELOGIC® ControlEquations Targets

Selectable Setting Groups Circuit Breaker Monitor Metering

SerialInterfaces Self

-

Tests

IRIG

-

B Input Description SignalProcessing

Torque Control Demand Ammeters Event Report

Time

-

Overcurrent Element Curve

-

Timing and Time Delay ResetEquations

2

-

1 2-5 2

-

9 2

-

15 2

-

16 2

-

17 2

-

17 2

-

18 2

-

18 2

-

21 2-22 2-22 2

-

26 2

-

27 2

-

28

TABLES

2-8

Trip Circuit Monitor Alarm (TCMA)Truth Table SEL

-

251C Relay Word

SettingGroup Selection Input TruthTable

Power Supply Self

-

TestLimits

Self

-

TestSummary TCI Settings Table2.1 Table2.2 Table 2.3 Table 2.4 Table2.5 Table2.6 2-₁₂ 2

-

16 2

-

19 2

-

21 2

-

24 Specifications

SEL-251C,-2, -3InstructionManual

FIGURES

SEL

-

251C Relay Inputs, Outputs, and Targets Diagram

. . .

Time Delayed 52A and 52B Functions

Trip Circuit Monitor(TCM) DCVoltageConnections

. . . .

Trip Circuit Monitor Alarm(TCMA)Logic

SEL

-

251C Relay SELOGIC Control Equations Block Diagram Relay Word BitRealizations

2

-

4 Figure2.1: Figure2.2: Figure2.3: Figure2.4: Figure2.5: Figure2.6:

Figure2.7: Relay Word BitRealization

Figure2.8: SEL

-

251C Relay Front Panel Target LEDs

Figure2.9: Distribution Transformer Bank Protected by High

-

SideFuses Figure2.10: Moderately Inverse Curves

Figure2.11: Inverse Curves Figure2.12: Very Inverse Curves Figure2.13: Extremely Inverse Curves

Figure2.14: SEL-251C Phase Overcurrent Logic Diagrams

Figure2.15: SEL

-

251C Negative-_{SequenceOvercurrent Logic Diagrams}

Figure2.16: SEL

-

251C Ground/Residual Overcurrent Logic Diagrams

.

Figure 2.17: SEL

-

251C Overcurrent and Undervoltage Elements

Figure2.18: SEL

-

251C Transformer Blown

-

Fuse Detection Logic

Figure2.19: SEL

-

251C OvercurrentandDistanceElements

Figure2.20: SEL

-

251C Demand Ammeters

Figure2.21: SEL

-

251C Programmable Trip Logic Diagram

Figure2.22: SEL

-

251CCloseLogic Diagram

2

-

7 2-8 2

-

9 2

-

11 2

-

13 2-14 2

-

15 2-₂₅ 2

-

29 2

-

29 2

-

29 2

-

29 2

-

30 2

-

31 2

-

32 2

-

33 2

-

34 2

-

35 2

-

36 2

-

37 2

-

38 Specifications

SEL-251C,-2, -3InstructionManual

Date Code20000421

SECTION 2

:

SPECIFICATIONS

GENERAL

SPECIFICATIONS

Voltage Inputs

120

-

volt nominal phase

-

to

-

neutral,three

-

phase, four

-

wireconnection

(Connect anyvoltage up to 150Vac

.

)

Current 5

-

amp nominal

15

-

ampcontinuous 110-ampsaturationlimit

500

-

amp 1

-

secondthermalrating

1

-

amp nominal

(somemodels, only in LP chassis)

3

-

amp continuous 20

-

amp saturation limit

100

-

amp 1

-

secondthermal rating

Inputs

60Hz, ABC(50Hz is

an

ordering optionon somemodels,ACBrotation is

anorderingoptionon somemodels)

Frequency

and Rotation

Output Contacts PerIEC

-

255

-

0

-

20 :1974

,

usingthesimplified method ofassessment 6 A continuouscarry

30A make per IEEEC37.90:1989

100 A for one second

270 Vac/360 Vdc MOV for differentialsurgeprotection.

Pickup/dropouttime:

_<

5ms Breaking Capacity (L/R

=

40 ms): 0.5 A 0.3 A 0.2 A CyclicCapacity (L/R

₌

40ms): 0.5 A 0.3 A 0.2 A 10,000operations 10,000operations 10,000operations 48 V 125 V 250 V

2.5 cycles per second 2.5 cycles per second

2.5cyclesper second

48 V 125V 250 V

OptoisolatedInputs _{Thefollowingoptoisolatedinputs draw 4 mA when nominal controlvoltage is}

applied (relays equipped withconventionalterminal blocks):

24Vdc: 15- ₃₀Vdc 48Vdc: 30

-

60Vdc

125 Vdc: 80

-

150Vdc (LP chassis only)

250 Vdc:150

-

300Vdc

Fixed "Level

-

Sensitive" inputsare provided on SLP chassis relays with 125

Vdc optoisolated inputs

.

The125 Vdcoptoisolated inputseach draw 6 mA

when nominal voltageisapplied

.

Theinputs operateasshown below: 125 Vdc: onfor 100

-

150Vdc; off below 75 Vdc

Power Supply 24/48 Volt:20

-

60Vdc; 125/250Volt: 85

-

350Vdcor 85

-

264Vac 10 wattsnominal, 14wattsmax

.

(all outputrelaysenergized)

DateCode 20000421 Specifications

SEL-251C,-2,-3 InstructionManual

Two EIARS

-

232

-

C serial communications ports; Port 2 of the SEL

-

251C Relay

hasfront

-

and rear

-

panel connectors

.

Communications

SeeFigure6.3 for SLP chassis models (5

-

amp nominal current inputs)

See Figure 6.4 for LP chassis models (1

-

amp nominal current inputs)

Dimensions

Relay accepts demodulated IRIG

-

B timecodeinput

Time CodeInput

Available in horizontalandvertical mounting configurations

Mounting

V, I inputs: 2500 Vacfor10 seconds Other:

RoutineTested

.

Dielectric

3000Vdcfor 10 seconds(excludes EIA

-

232)

Strength

-

40°to 158°F(

-

40° to70°C)

Operating Temperature

IEEE C37.90: 1989

IEEE Standards for Relays and Relay SystemsAssociatedwith Electrical Power

Apparatus

,

Section 8: Dielectric Tests

SeverityLevel: 2500 Vaconanalog inputs;3000Vdconpower supply,

contact inputs,and contactoutputs

Environmental Type Tests

IEEEC37.90.1: 1989

IEEE Standard SurgeWithstand Capability (SWC)TestsforProtectiveRelays

and Relay Systems

SeverityLevel: 3.0kVoscillatory, 5.0 kV fast transient IEEEC37.90.2(issued for trialuseDecember 1987)

IEEE Trial

-

Use Standard

,

Withstand CapabilityofRelay Systems to Radiated ElectromagneticInterference fromTransceivers

Severity Level: 10 V/m

Exceptions:

5.5.2 (2) Performed with200 frequencystepsper octave

5.5.3 5.5.4

Digital Equipment Modulation Test not performed

Test signal turned off between frequency steps to simulate keying IEC68

-

2

-

1 Fifth Edition : 1990

Environmental testing

,

Part 2: Tests

-

Test Ad: Cold

Severity Level: 16 hours at

-

40°C

IEC68

-

2

-

2FourthEdition: 1974

Environmentaltesting,Part2: Tests

-

TestBd: Dry heat SeverityLevel: 16 hours at

+

85°C

Specifications

SEL-251C,-2, -3InstructionManual

IEC 68-2-30 SecondEdition : 1980

Basicenvironmental testing procedures, Part2: Tests-Test Dbandguidance: Damp heat, cyclic (12 + 12-hourcycle)

Severity Level: 55°_C,6 cycles IEC255-5FirstEdition: 1977

Electricalrelays, Part5: Insulation testsforelectrical relays, Section6: DielelectricTests

Severity Level: Series C(2500 Vac on analog inputs; 3000Vdconpower supply,contactinputs,andcontactoutputs)

Section8: Impulse Voltage Tests

Severity Level: 0.5 Joule, 5000volt IEC255-21-_{1 First Edition}: 1988

Electrical relays, Part 21:Vibration,shock,bump,and seismic testson

measur

-ing relaysand protectionequipment, SectionOne -Vibrationtests (sinusoidal)

Severity Level: Class 1

IEC255-21-2 First Edition : 1988

Electrical relays, Part 21: Vibration,shock,bump,and seismictestson

measuring relaysand protectionequipment, Section Two - Shockand bump tests Severity Level: Class1

IEC255-22-1 First Edition : 1988

Electrical disturbancetests for measuring relaysand protectionequipment,

Part 1: 1 MHzburstdisturbance tests

Severity Level: 2.5 kVpeak commonmode, 1.0 kV peakdifferentialmode IEC255-₂₂-3: 1989

Electricalrelays, Part22: Electricaldisturbancetests for measuring relays and

protectionequipment,Sectionthree- Radiatedelectromagnetic fielddisturbance

tests

Exceptions:

4.3.2.2 Frequency sweep approximated with 200 frequency stepsper

octave

IEC801-2Second Edition: 1991-04

Electromagnetic compatibility forindustrial-processmeasurementand control

equipmentm, Part2: Electrostatic dischargerequirements Severity Level: 3

IEC801-3

Electromagnetic compatibility forindustrialprocess measurement andcontrol

equipment, Part3: Radiated Electromagneticfieldrequirements

Severity Level: 10V/m

Date Code 20000421 Specifications

SEL-251C,-2, -3 InstructionManual

Exceptions:

Frequencysweep approximatedwith 200 frequencystepsper

octave

9.1

IEC801

-

4First Edition: 1988

ElectromagneticCompatibility for industrialprocess measurementsand control

equipment

,

Part 4:Electrical fasttransient/burst requirements

SeverityLevel:4 (4kV onpower supply, 2kV oninputsand outputs)

SLP chassis: 12 pounds (5.5kg)

-

5

-

amp nominalcurrentinputs LP chassis: 16 pounds(7.3kg)

-

l

-

amp nominal currentinputs

UnitWeight 1 17 2 18 19 IN2 3 TRIP 20 ₄ 21 IN3 _{APPLY 5} CONTROL VOLTAGE TO OPTO-ISOLATOR INPUTS TOASSERT CLOSE 2 2 ₆ 23 IN4 7 24 A1 8

25 IN5 _{CANBECONFIGURED}

AS EITHER FORM"_A" OR"_B"_OUTPUT CONTACTS 9 26 _{A 2} 10 27 IN6 28 11 A3 12 29 13 IA A4 30 14 31 IB 15 32 _ALARM 16 33 IC 34 DEMODULATEDIRIG-_B AUX INPUT _ _

rrrn

-JTnoru, VB

vc

37 _VA 38 PORT1 39 EiA RS-232-C 300- 9600BAUD 40 _N PORT2R _> PORTS IN PARALLEL (PORT2F HAS PRIORITY) + 44 _POWER SUPPLY < PORT2F (FRONT PANEL) 45 CHASSIS GROUND 46 TARGETLEDs INST A B C Q N EN ALRM

O O O O O O O O C E T

FAULTTYPE STATUS _RESET

Figure 2.1: SEL

-

251C Relay Inputs, Outputs, and Targets Diagram

Specifications

SEL-251C,-2,-3InstructionManual

DateCode 20000421

FUNCTIONAL SPECIFICATIONS

Overcurrent Elements

Values shownarefor5

-

amp nominal current input models

.

(Divide current values byfive for 1-amp nominal current input models

.

)

PhaseOvercurrent Elementsfor Phase and Three

-

Phase Faults

-

SeeFigures2.14

,

2.17

,

and2.19

51T Phase Time

-

Overcurrent Element

•

Curve families: moderatelyinverse, inverse, veryinverse, extremely inverse

•

Timedial: 0.5 to 15.00in0.01steps

.

•

Pickup (51P): 1 to 12 A

+

2% ofsetting

_±

0.1Asecondary

•

Timedelayor

one

cycleresettime

•

Timing:

+

5% and

_±

1 cycle for currents between 2and20 multiplesofpickup

•

Internally and externallytorquecontrollable Phase Definite

-

TimeOvercurrentElement

•

Pickup (50L): 0.5to 100 A

_±

2 % of setting

_±

0.1A secondary

•

Time delay: 0 to 16,000 cycles in 1 cyclesteps

•

Internally and externally torquecontrollable 50LT

50MT Phase Definite

-

Time Overcurrent Element

•

Pickup (50M): 0.5to100 A

_±

2% of setting

_±

0.1A secondary

•

Time delay: 0 to 16,000 cycles in 1 cyclesteps

•

Internally and externallytorquecontrollable PhaseInstantaneous Overcurrent Element

•

Pickup: 0.5 to100 A

_±

2 % of setting

_±

0.1 A secondary

50H

50C PhaseInstantaneousOvercurrent Element

•

Pickup: 0.5 to 100A

_±

2% ofsetting

_±

0.1 A secondary

•

Can be usedto overridevoltagecontrol throughTCIsettingchoice

Negative

-

SequenceOvercurrent ElementsforPhase

-

to

-

Phase Faults

-

SeeFigure2.15

51QT Negative

-

Sequence Time

-

Overcurrent Element

•

Element

measures

3 I2negative

-

sequence current

•

Curve families: moderately inverse, inverse,

very

inverse, extremelyinverse

•

Timedial: 0.5 to 15.00 in 0.01steps

.

•

Pickup (51QP): 1to12 A

_±

3 % ofsetting

_±

0.18Asecondary

•

Time delay or

one

cycleresettime

•

Timing:

_±

5% and

_±

1 cycle forcurrentsbetween 2 and 20 multiplesof pickup

•

Externallytorquecontrollable

Specifications

SEL-251C, -2, -3 InstructionManual

50QT Negative

-

Sequence Definite

-

TimeOvercurrentElement

•

Element measures3 I2negative

-

sequence current

•

Pickup (50Q): 0.5to 100 A

_±

3% of setting

+

0.18 A secondary

•

Time delay: 0 to 16,000 cycles in 1 cyclesteps

•

Externallytorquecontrollable

Ground/Residual Overcurrent Elements for Ground Faults

-

See Figure2.16

Ground/Residual Time

-

Overcurrent Element

•

Curvefamilies: moderatelyinverse, inverse, very inverse, extremely inverse

•

Time dial: 0.5to 15.00in0.01steps

•

Pickup (51NP): 0.25 to 12 A secondary

•

Time delayor onecycle reset time

•

Timing:

_±

5% and

_±

1 cycle forcurrentsbetween 2 and20 multiplesof pickup

•

Externallytorquecontrollable

51NT

50NLT Ground/Residual Definite

-

TimeOvercurrentElement

•

Pickup (50NL): 0.5 to 100 A secondary(for 1 < 51NP < 12 A secondary)

0.25 to 50 A secondary(for0.5 < 51NP

_<

1 A secondary)

0.125 to 25 A secondary(for 0.25 < 51NP

_<

0.5 A secondary)

•

Time delay: 0 to 16,000 cycles in 1 cyclesteps

•

Externallytorquecontrollable

50NH Ground/Residual Instantaneous OvercurrentElement

•

Pickup: same range as 50NLT

•

Externallytorquecontrollable

Accuracy

•

Residual element pickupaccuracy is dependent uponthe51NPsetting

.

Pickup

accuracy of the 51NP,50NL, and50NHelements is shown below inthegiven 51NP setting range

.

1.0 < 51NP < 12.0 A sec 0.5 < 51NP

_<

1.0 A sec 0.25 < 51NP

_<

0.5 Asec Pickup

_±

2%

+

0.100 A sec Pickup

_±

2%

+

0.050Asec Pickup

_±

2%

+

0.025 Asec

Phase Distance Torque Control Elements for Load Security (_21P1

_-

_{See Figure 2.19}

•

21AB, 21BC, 21CA Phase

-

to

-

Phase Distance Elements

•

SettingRange: 1 to64 ohms,secondary;0° to90° maximumtorque angle

•

User selects either three

-

phaseorphase

-

to

-

phase distanceelement

•

Singlezone, self

-

polarized mho

•

Controlcanbe overridden by50C element through TCI setting choice

Specifications

SEL-251C,-2,-3InstructionManual

DateCode 20000421 2-6

Voltage_{Element for Healthv/Low} Voltage_{Indicationor Internal Control} (₂₇)

-

_SeeFigure_2.17

•

27AB, 27BC, 27CA Phase

-

to

-

PhaseUndervoltage Elements

•

SettingRange: 0to 250 Vline

-

to

-

line secondary

_±

5%,

+

1V

•

Two setting limits: 27H and 27L (highandlow,respectively)

•

27element asserts only if voltageisbetween 27Hand 27L

•

Userselects either three

-

phaseorphase

-

to

-

phase voltagecondition

•

Implement undervoltage loadshedding scheme

•

Internallytorquecontrol selected phase overcurrent elements

•

Detect high

-

sidetransformer fuse operations

Time Delayed_{52Aor52B Functions HandleInrush}

The time delay pickup and timedelay dropout settings (52APU and 52ADO, respectively)are provided to generatethe 52AT and 52BT functions

.

The52AT and 52BT bitscanbe used to supervise overcurrent elements for inrush conditions.

52APU

52A 52AT (RELAY WORD BIT]

52ADO

52BT (RELAY WORD BIT] Figure2.2: TimeDelayed52Aand 52B Functions

TripFailure Timer Detects Breaker Failure or Slow Trip

-

See Figure2.21

A relay tripstartsa trip failure timer

.

If the trip condition lasts longer than the TFTsetting,

theTF bit in the Relay Word asserts

.

The TF bit deasserts 60 cycles after the trip condition drops out. TheTF bit can be assignedto anoutputcontact toalarmfor slow tripsorto provide breaker failure tripping

.

Itcanalso be used to triggeranevent report

.

Close Failure Timer DetectsFailure to Closeor Slow Close

-

See Figure2.22

A closefailure timer monitors the lengthof timetheCLOSEoutputcontact remains asserted

.

If CLOSEoutputcontact assertionexceeds theCFTtime setting, the close attemptis

unsuc-cessful

.

Therelayopens the CLOSEoutput contact and theCFbitin theRelay Word

asserts

.

TheCF bit asserts for60 cycles

.

UsetheCFbitto alarmforclosefailures or slow

-close conditions and totriggerevent reports

.

Specifications

SEL-251C,-2,-3InstructionManual

TripCircuitMonitor Alarm Checks Trip Circuit and Verifies Circuit BreakerStatusInput

You

can

assignoneof the six programmable inputs to the trip circuit monitor (TCM) logic

.

+ 52A 52A TCM SEL-251C RELAYPARTIAL TRIP 52A TC TC

Figure 2.3: Trip Circuit Monitor(TCM)DC Voltage Connections

When the circuit breaker is closed (consequently 52

AXC

is closed)and the TRIP output contact is notasserted, the TCM input allows

a

few milliamperes of current through the trip coil

.

The voltagedrop isacross theTCM input because the input hasa much higher impedance

thanthe trip coil

.

Tripcircuitmonitor logicensuresthat the52A and TCM inputs agree

.

Whenthecircuit breaker is closed, inputs 52A and TCMare energized; 52A and 52

_ATC

contactsareclosed

.

When the circuitbreaker isopen, inputs52AandTCMaredeenergized; 52Aand52

_ATC

contacts areopen

.

If the two inputs disagree for 60 cycles, the trip circuit monitoralarm

(TCMA) bit asserts in the Relay Word

.

TheTCMA bit deasserts60 cycles after the TCMA condition ends

.

Table 2.1: Trip Circuit Monitor Alarm (TCMA)Truth Table

TCM input

TCMA Relay_{Word bit}

52A Notes 0 0 0 0 1 1 (a) 1 0 1 (b) 1 1 0 Specifications

SEL-251C,-2, -3Instruction Manual

DateCode20000421 2-8

(a) _{Abnormal open circuit in TCM}input/lower trip circuitpath

orashort circuit exists acrossthe TCMinput (e

.

g

.

, TRIPoutputisasserted)

or52A contact short circuitedor "stuck closed"

.

(b) 52

_ATC

short circuitedor "stuckclosed"

orthere isanabnormalopencircuit in the 52Ainput circuit path

.

60CYCLES

52A

TCMA (RELAYWORDBIT) TCMINPUT

60CYCLES

Figure2.4: Trip Circuit Monitor Alarm(TCMA)Logic

Besides alarmingfor anabnormal open circuit in the trip circuit, the TCMA bitprovides52A

inputverification. It effectively comparesthe circuitbreakerstatusinputto 52

_AXC

.

The TCMA bitcanbe used to alarm, cancel reclosing,ortrigger event reports

.

In Figure2.3,a52Acontact isconnected to relay input 52A

.

You can connect a 52B contact

instead

.

Wirea52B contact to arelay input!52A toperform the52A function(see SEL

-

251C Relay SELOGIC® ControlEquations)

.

SEL

-

251C

RELAY

SELOGIC

CONTROL

EQUATIONS

SELOGICControlEquations putrelaylogicinthehandsof the relayapplicationsengineer

.

Assign theinputs to suityourapplication, logicallycombineselected relay elements for

variouscontrol functions,usenon

-

dedicated timers for special applications, andassign output

relays to

your

logicfunctions

.

Programming SELOGIC Control Equations consist of assigning functions to theprogrammable

inputs, designing the internal logicyou need, expressing that logic in termsofthe relay

elements and internal logicvariables, and defining the output functions

.

The SET command controls all SELOGICControlEquations programming (See Section3: COMMUNICA

-TIONS)

.

Section5: APPLICATIONS givesseveralexamples of implementing protection

schemes withSELOGICControl Equations

.

SampleSELOGIC Control Equations aregiven in

ExampleEvent Report 2 in Section 4: EVENT REPORTING

.

Figure2.5showshow Relay Word rowsR5and R6 in Table 2.2 and the outputfunctions are

derived

.

Date Code20000421 Specifications

SEL-251C,-2,-3 InstructionManual

Assign_InputstotheFunctions You Need

Program thesix isolated inputs (INI throughIN6) to thefunctionsyourapplication requires.

Choose from thefollowingfunctions:

Default

Logic_States

SettingGroup Selection Input 1 (assign toINI only)

SettingGroupSelection Input 2 (assign toIN2 only)

SettingGroup SelectionInput3 (assignto IN3 only)

0 SSI 0 SS2 0 SS3

External Torque Control (Phase and Negative

-

Sequence Elements) 1

(invertedsenseofTCP)

TCP

0

!TCP

External Torque Control(Residual Overcurrent Elements)

(inverted senseofTCG)

TCG 1

!TCG 0

CircuitBreaker Status (inverted senseof52A)

N/A

52A

N/A !52A

(requirescircuit breakerstatus) (requires circuit breaker status)

Direct Close

Trip Circuit Monitor

0

DC

N/A TCM

ET ExternalTriggerofEvent Report

DT Direct Trip

(blank) Unassignedinput

0 0

InputsIN5andIN6also appear directly intheRelay Word for usein theprogrammablelogic

.

InputsINI,IN2,andIN3canbe assigned to functions other than just SSI, SS2, and SS3,

respectively

.

Assert

an

input by applyingcontrol voltage to thecorrespondingrear panelinput terminals

.

Control voltage polarity is not important

.

Whenafunction is not assignedto aninput, the relayusesthe respective default logic state shown above

.

Specifications

SEL-251C, -2,-3InstructionManual

DateCode20000421

RELAY WORD

ROWS RELAYWORDELEMENTS(BITS)

51P 50L 50M 51QP 5DQ 51NP 50NL 50NH 51T 50LT 50MT 51QT 50QT 51NT 50NLT 50H 21P 50C 27 52AT 52BT IN6 IN5 PDEM QDEM NDEM TF CF TCMA(ST) TRIP R1 R 2 R3 R4 TS ANY BITS IN R1, R2 AND R3 — ST ANY BITSIN

R1ANDR 2 ANY BITSR 3ANDR4IN R5

B, C AND DSIMILAR F, G ANDHSIMILAR TIC ANYBITS IN R1;R 2 R 3AND R4 ANY BITS IN R1,R 2 R3AND R4 — KT R6

<

(FIRST PART) ANYBITS INR1,R2 R 3 AND R4 TZ Z ANY BITS

A THROUGH !L ANYA THROUGH !LBITS

R6 _{AND V AND — ZT} (LAST PART) W,X AND YSIMILAR ANYBITS INR1,R2 R4 AND R6 ANY BITS INR1,R 2 R3AND R4 ER SIMILAR A2 SIMILAR ANYBITS INR1,R3 R4 AND R6 ANYBITS IN R 2,R3 R4A N D R6

I

closeTRIPoutputcontacts = TR+... closeA1output contact= A1 trigger event report =ER+... closeA 4output contact =A4

Figure 2.5: SEL

-

251C Relay SELOGIC Control Equations Block Diagram

Select Combinations of Relay_{Elements You Need forTripping} andOther Purposes

The48

-

bit RelayWordcontains relay elements, intermediatelogicresults, and programmable logicvariables

.

Specifications

SEL-251C,-2, -3InstructionManual

Table 2.2: SEL

-

251C Relay Word

R1 51P 50L 50M 51QP 50Q

51T 50LT 50MT 51QT 50QT

21P 50C 27

PDEM QDEM NDEM TF

51NP 50NL 50NH 51NT 50NLT 50H 52AT 52BT IN6 IN5 CF TCMA ST TRIP R2 R3 R4 R5 A B C D E F G H R6

J

KT !L V W X Y ZT ! indicates NOT

Phase time

-

overcurrent element pickup

Phasedefinite

-

timeovercurrent element pickup Phase definite

-

time overcurrent element pickup Negative

-

sequencetime

-

overcurrent element pickup

Negative

-

sequence definite

-

timeovercurrent elementpickup Ground/Residual time

-

overcurrent elementpickup

Ground/Residual definite

-

time overcurrent element pickup Ground/Residual instantaneousovercurrent element

51P 50L 50M 51QP 50Q 51NP 50NL 50NH

Phase time

-

overcurrent element Phase definite

-

timeovercurrentelement Phase definite

-

time overcurrent element Negative-sequencetime-overcurrent element

Negative

-

sequencedefinite

-

timeovercurrent element Ground/Residual time

-

overcurrent element

Ground/Residual definite

_-

timeovercurrent element Phase instantaneous overcurrent element

51T 50LT 50.MT 51QT 50QT 5INI 50NLT 50H

Single zone, self

-

polarized mho phase distance element for internal torquecontrol Phase instantaneousovercurrent element (can override control by 21Por27) Phaseundervoltage elementfor internaltorque controland blown

-

fuse detection

21P 50C

27

Time delayed 52A Inverse of52AT

InputIN6 bit;assertsfor control voltage applied to inputIN6 InputIN5bit;assertsfor control voltage applied to inputIN5

52AT 52BT

IN6 INS

Phasedemand current threshold exceeded

Negative

-

sequencedemandcurrent threshold exceeded Ground/Residual demandcurrentthreshold exceeded Trip failure condition

Closefailure condition

Trip circuit monitor alarm: assertsfor abnormal open or short circuit in the circuit breaker tripping circuit or circuit breaker status input(52A)

Outputfrom timer TS, drivenbyanyOR

-

combinationofelementsinR1throughR3 assignedtosettingS

Followsstate of theTRIP output contacts

PDEM QDEM NDEM TF CF TCMA ST TRIP Specifications

SEL-251C, -2,-3Instruction Manual

Date Code 20000421 2-12

A B C D

E F G H

Select any OR-combinationofelementsin R1andR2 Select any OR-combinationofelements in R3andR4

Select any OR-combinationof elements in R1throughR4

Output fromtimer TK, drivenby anyselectedOR-combinationofelementsinR1through

R4 assignedtosetting K

Output from an inverter, drivenbyanyselectedOR-combinationof elements in R1

throughR4 assignedtosetting L

Select any AND-combinationofelementsA through !L

Output from timerTZ, drivenbyanyselected AND-combination of elementsAthrough

!Lassignedtosetting Z J K T !L V W X Y Z T

TimeDelayed _VariablesST

.

_KT

.

_andZT

Relay Word variablesST, KT, and ZT areoutputs from time delay pickup/dropout timers TS, TK and TZ, respectively

.

TS and TKaredriven by anyOR

-

combination of Relay Word elements in R1

...

R3 and R1

...

R4, respectively

.

Any AND

-

combination of Relay Word elements A through !Lmay drive timerTZ

.

TS TSPU

ST(RELAY WORD BIT)

S

TSDO TK TKPU

KT(RELAY WORD BIT)

K

TKDO TZ TZPU

ZT (RELAYWORDBIT)

Z

TZDO

Figure2.6: Relay WordBit Realizations

Use !L for Inversion

VariableLisanyOR

-

combinationof elements in R1 through R4

.

The inverseofL(!L) is in the Relay Word

.

Also, output contactsA1throughA4and theALARMcanbefactory

-configured aseither "a" or "b" contactsfor anadditional inversion

.

Specifications

SEL-251C,-2,-3InstructionManual

IL (RELAYWORDBIT)

L

Figure2.7: Relay Word Bit Realization

Programming OutputContacts

Writeoutputequations to define trippingand other control functions

.

Select anyOR

-

combinationof elements in Rl, R2, R4, andR6via theTR(1246)

variable

.

Direct Trip input andOPEN command also assert TRIP

.

See Figure2.21 for information about TRIP outputcontact operation

.

Select anyOR

-

combinationof elements in Rl, R2, R3, and R4.

SelectanyOR

-

combinationof elements in Rl, R3

,

R4, and R6

.

SelectanyOR

-

combinationof elements inR2,R3, R4, and R6

.

Optionally, A4

canoperateas anALARM by placement of jumper JMP3 (the jumperhas

positionsA4 and ALARM)

.

TRIP:

Al, A2 A3 A4

TheCLOSEandALARM functions have dedicated outputs:

Asserts by DC input,orCLOSE command (seeFigure2.22 for an illustrationof CLOSEoutputcontact operations)

.

The ALARM outputclosesforthefollowing conditions:

-

Three unsuccessfulLevel 1access attempts: 1 second pulse

-

Any Level 2attempt: 1secondpulse

-

Self-testfailures: permanentcontactclosureor 1second pulse dependingon

whichtestfails (seeTable2.5)

-

TheALARMoutputcloses momentarilywhen relaysettings,settinggroups, or

passwordsare changed

.

It also closes whenadate is entered, if theyear

stored inEEPROM differs fromtheyear entered (seeDATEcommand)

.

CLOSE:

ALARM:

All output relay contactsmay be configuredas "a" or "b" contactswith soldered wire jumpers JMP4 through JMP11(each jumper has positions Aand B)

.

All relay contacts areratedfor circuit breaker tripping duty

.

Viewing LogicEquations

UsetheSHOWSET command to print all relay settingsincludingtheSELOGIC Control

Equations configuration

.

Youcaninspect settings inthesample eventreport in Section 4: EVENT REPORTING

.

Specifications

SEL-251C, -2, -3Instruction Manual

DateCode 20000421

SELOGICControl Equations Settings_{in Each}Setting _Group

When you switch groups, youswitchlogic settings aswell as relayelement settings. You can program groupsfor different operating conditions, suchasfeeder paralleling, station main

-tenance, seasonal operations, andcogenerationon/off

.

TARGETS

Read targeting information locally by inspecting the LEDsorremotely with theTARGET command and event reports

.

TheTARGETcommandcan accessother informationaswell

(seeSection 3: COMMUNICATIONS)

.

TheINSTtargetindicates thatnoovercurrentcondition in RelayWord row R1 has been

asserted longer than the ITT (instantaneous targettime)timer settingbefore TRIP asserts

.

Thisgivesyou controlover what qualifiesasa close-in fault.

The phasecurrent indicators (A, B

,

C) show whichphases exceed the 5IP pickup settingat

the time of trip

.

The negative

-

sequence and residualcurrent indicators(Q, N)similarly show if these currents exceed the respective 51QPand51NP pickup settings at the time of trip

.

Thelasttwoindicators (EN, ALRM)show the state of the relay (enabled/normaloperation or

system alarm)

.

EN ALRM

INST A B C Q N

FAULTTYPE STATUS

Figure 2.8: SEL

-

251C Relay Front Panel Target LEDs

The FAULT TYPE LEDslatch and remainlit until the TRIPoutputdeasserts andoneof the followingoccurs:

•

Nexttripoccurs

•

Operator presses front panel TARGET RESETbutton

•

Operator executesTARGET R command

Whena new TRIP occurs, the FAULT TYPE LEDs clear,then display and latchthe FAULT

TYPEtargetsfor thenew TRIP condition

.

When anoperator presses the TARGET RESET button, all eight LEDs illuminate fora one

-secondlamp testand toindicate that the relay is operational

.

Specifications

SEL-251C,-2,-3InstructionManual

SELECTABLE SETTING GROUPS

The relay acceptssixgroupsof relay and logic settings

.

Program relay elements and logicwith theSET command

.

To programGroup 1 settings and logic,useSET 1andprovidetherequested information

.

TheCOPYcommandmakes iteasy to copy settings and logicfromonegroup to another (e

.

g

.

, COPY 1 4 copies Group 1to

Group4)

.

Afterward, youcan edit Group 4settingsandlogicwith theSETcommand.

Therelay determines which group of settings and logictouse by monitoringthe setting group selection inputs (SSI, SS2, andSS3)

.

Touseinputs, programoneor more of the setting selection inputs SSI, SS2, and SS3 to the respective inputsINI, IN2,and IN3. Youcan also use the GROUPcommand tospecify asettinggroup

.

Table2.3: Setting Group Selection Input Truth Table

SS3 SS2 SSI

0 0 GROUPCommand Selection

Group1 Group2 Group3 Group 4 Group 5 Group6

GROUPCommand Selection

0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

If SSI, SS2,orSS3 is not assignedto aninput, itdefaultsto 0

.

If noinputs areassignedas

settinggroupselection inputs theGROUP command entrycontrols group selection

.

With

only SSI assigned, GROUP command selection determines settings touseif theinput assigned to SSI is not asserted

.

If the input is asserted, setting Group 1 is used

.

Forexample, to switch betweenGroup 1and Group 5, program input INI toSSI andusethe

GROUP command toselectGroup 5. WithINI asserted, the relay usesGroup 1. WithINI deasserted, ituses Group 5

.

When thestatusof any assignedsettinggroup selection input changes, the relay waitsa settabletime period(TGR)for inputs to stabilize before changing the active setting group

.

Thus, ifa settinggroup selection input status changes and revertsto its previous state before TGR expires, the relay does not change the active setting group. The TGR setting isoneof several global settings and is enteredwiththeSET Gcommand

.

Active setting groupchanges (via settinggroup selection inputsorGROUP command)disable the relayfor less than0.5 seconds to allow loading ofnew active settings. TheALARM

outputcontactsclose duringthis time and all timers and relay elementsreset.

Specifications

SEL-251C, -2, -3InstructionManual

DateCode20000421 2-16

The DEMRsetting allowsyou tospecify whether or notdemand valuesfor current, MW, and

MVARare resetwhentheactive setting group changes. Therelay resetsdemand values

as

it

wouldfor METER RD execution

.

The followingexample illustratesa situationwhenyou

should resetdemand values

.

You might want to change the active setting group for distribution feeder switchingwhere significant load is removed from the feeder

.

Ifthenew activesettinggroup has lower demand current thresholds (PDEM, QDEM, and NDEMsettings) than the previous active setting group, the corresponding PDEM, QDEM, and NDEMdemandammeter thresholdbits

couldassert

.

This is because the respective demand ammeters have not yet adjusted to the

lower loading level, asdictated by the relatively long demand ammeter time constant(setting

DATC

₌

5

-

60 minutes)

.

IfPDEM, QDEM, and NDEM areassigned to programmable

outputcontacts(A1

-

A4), afalse alarm would result. Toovercomethis problem, setDEMR

=

Y

.

With this setting, the relay resets demand values tozero when theactive settinggroup changes

.

TheDEMR setting is entered with the SET G command

.

See Section3: COMMUNICA

-TIONS formoredetailsontheSET, COPY, GROUP, and METER RDcommands.

CIRCUIT BREAKER MONITOR

The SEL

-

251C Relaydetectsevery circuit breaker trip operation

.

It designateseachtrip as onecaused by the relayor

an

external device and maintains arunning count of each

.

The relay also maintains arunningsumof theinterrupted current in each circuit breaker pole for relay and external trips

.

Runningsumsfor relay tripsusethe current presentonecycle

after the tripoutput contacts assert

.

Runningsumsfor external tripsusethe currentspresent

when the circuit breaker status input (52A or!52A)indicates that the circuit breaker has

opened

.

You can accessthe circuit breaker operation data using the BREAKERcommands

.

See Section3: COMMUNICATIONS for moredetailsonthese commands.

METERING

TheSEL

-

251C Relay provides complete voltage and current metering

.

It alsodetermines real

and reactivepower values,demand values, peak demand values, and negative

-

andzero

-sequencecomponentsof the voltages and currents

.

You can access and reset metering data using different METER commands

.

See Section3: COMMUNICATIONSfor moreinformation

.

DateCode20000421 Specifications

SEL-251C,-2,-3InstructionManual

SERIAL

INTERFACES

Port 1 and Port 2 are EIA RS

-

232

-

Cserial data interfaces.

Port 1islocatedontherear panel and is generally used for remote communications viaa modem ortheSEL

-

PRTU

.

Port 2hasconnectors onboth thefront and rearpanels, designated Port 2F and Port 2R, respectively. Port 2F has priorityover Port2R

.

These portsaregenerally used for local communications. Port 2R is typically connected toaprinter, SEL

-

RD,orSEL

-

DTA

.

Port 2F is typically used for temporary communications via aportable terminal.

Whena device is plugged intoPort 2F, the relay automaticallybegins addressingPort 2F and discontinues communication with Port 2R

.

Whena deviceunplugged fromPort 2F, the relay automaticallyresumescommunication with the device connected to Port 2R

.

Thebaud rateof eachportis setby jumpersnear thefront of the main board

.

Youcan access these jumpers byremovingeither the topcoverorfront panel

.

Available baudrates

are300, 600, 1200, 2400, 4800,or 9600.

Theserialdataformat is: Eight data bits

Twostopbits(

-

E2model)or onestopbit(

-

E1 model)

No parity

Thisformatmay notbe changed. The serial communications protocol andportpindefinitions

appear in Section 3: COMMUNICATIONS

.

SELF

-

TESTS

The relay runsa varietyofself

-

tests

.

Some tests have warningandfailure states, others only

havefailurestates

.

Therelaygenerates a statusreport after any change in self

-

teststatus

.

The relay closes the ALARM contactsafteranyself

-

testfails

.

Whenit detectscertain

failures, the relay disables the breaker control functions and places itsoutputdriverportinan input mode

.

Nooutputsmay be asserted whentheinstrument is in this configuration. The

relay

runs

all self

-

testson power up and before enablingnew settings

.

During normal operation, it performs self

-

testsat leastevery few minutes.

Specifications

SEL-251C, -2, -3 InstructionManual

Date Code 20000421

Offset

Therelay

measures

the offsetvoltage ofeach analog inputchannel andcompares thevalue

againstfixed limits

.

It issuesa warningwhen offset isgreater than50 millivolts inany

channel and declares a failurewhenoffset exceeds 75 millivolts

.

Theoffset levels ofall

channels appear in the STATUS command format

.

Power Supply

Power supplyvoltagesarelimit

-

checked

.

The table below summarizesvoltagelimits

.

Table 2.4: Power Supply Self

-

Test Limits

Supply Warning_{Thresholds FailureThresholds}

+

5.4 V

+

4.6 V +5V +5.3 Y

+

4.7V

+

15.8 Y

+

14.2 V +16.2 V +13.8 V +15 V

-

15.8 V

-

14.2 V

-

16.2 V

-

13.8 V

-

15 V

Therelay transmits aSTATUSmessage forany self

-

test failureorwarning

.

A

+

5volt

supply failure deenergizes alloutputrelays and blocks theiroperation

.

A

₊

15 volt supply failure disables protective relay functions whilecontrol functionsremainintact

.

TheALARM relay remainsclosed after a powersupplyfailure

.

Random

-

Access Memory

The relay checks random

-

access memory (RAM) toensurethat each bytecanbe written to and read from

.

Thereisno warningstateforthistest

.

If the relay detects a problem, it transmits a STATUSmessage with the socketdesignationof theaffected RAM IC

.

A RAM failure disables protective andcontrolfunctionsand closes theALARM outputrelay contacts

.

Read

-

Only Memory

The relay checks read

-

onlymemory (ROM) bycomputinga checksum

.

If thecomputed value

does not agreewiththe stored value, the relay declaresa ROM failure

.

It transmitsa STATUSmessage with the socket designation of the affected ROM IC

.

A ROM failure disables protective and control functions andclosesthe ALARM outputrelay contacts

.

DateCode20000421 Specifications

SEL-251C,-2,-3InstructionManual

Analog

-

fo

-

Digital Converter

Theanalog

-

to

-

digital converter (ADC)changes voltage signals derived from power system

voltages and currents into numbersfor processing by the microcomputer

.

TheADC test

verifies converter function by checking conversion time

.

The test fails if conversiontimeis excessiveora conversion starts andneverfinishes. There isnowarning statefor this test

.

While anADC failure disables protective functions, control functions remain intact. The relay transmitsa STATUS message and closes theALARMrelay contacts

.

Master Offset

The master offset(MOF) test checksoffset inthemultiplexer/analog todigital converter

circuit

.

Agroundedinputis selected and sampledfor dc offset

.

The warning threshold is

50mV;failure threshold is75 mV. Afailure pulsesthe ALARM contact closedfor one

second. TherelaytransmitsaSTATUSmessagefor both warning and failure conditions.

Settings

The relay storestwoimagesof the system settings in nonvolatilememory. Thetestcompares them when the relay is initially set and periodically thereafter

.

If theimagesdisagree, the

settingtestfails and the relaydisables allprotective and control functions

.

It transmits the

STATUSmessage to indicateafailed test

.

The ALARM relay remains closed after asetting

failure.

Specifications

SEL-251C,-2,-3InstructionManual

Date Code20000421

Table2.5 shows relay actions for any self

-

test condition: warning(W)or failure(F)

.

Table2.5: Self

-

Test Summary

Self

-

Status Message Protection Disabled Control Disabled Alarm Output Limits Test

RAM F YES YES permanent contact assertion

ROM F YES YES permanentcontactassertion

SETTINGS F YES YES permanent contact assertion

A/D F YES NO permanent contact assertion

+5 V _±0.3 Y +0.4 V

W NO NO noALARM contact assertion permanent contact assertion

F YES YES

+15V _±0.8V

+1.2 V

W NO NO noALARM contact assertion permanent contact assertion

F YES NO

50mV 75mV CHANNEL

OFFSETS

W NO NO noALARM contact assertion onesecond contact pulse

F NO NO

50mV 75 mV MASTER

OFFSET

W NO NO noALARM contact assertion onesecond contact pulse

F NO NO

IRIG

-

B INPUT DESCRIPTION

The portlabeledJ201/AUX INPUT receives demodulated IRIG

-

B time code input. The

IRIG

-

B input circuit isa56 ohm resistor in series withanoptocoupler input diode

.

The input diode hasaforward dropof about1.5 volts. Drivercircuits shouldputapproximately 10 mA

through thediodewhen "on."

TheIRIG

-

B serial data format consists of a one second frame containing100pulses and divided into fields

.

The relay decodes second, minute, hour, month, and day fields and sets the relay clock accordingly

.

WhenIRIG

-

B data acquisition is activated either manually (with the IRIG command)or automatically, the relay reads two consecutive frames

.

Itupdates the older frame byone second and compares the frames. If they do not agree, the relay considers the dataerroneous

anddiscards it.

The relay reads the time code automatically aboutonce everyfive minutes

.

It stopsIRIG

-

B

dataacquisition ten minutes before midnighton New Year’s Evesotherelay clockcan implement theyearchangewithout interference from theIRIG-Bclock

.

Date Code 20000421 Specifications

SEL

-

251C,

-

2,

-

3 Instruction Manual

SIGNAL

PROCESSING

The relay low

-

pass filters all analog input channels toremovehighfrequency components.

Next it samples each channel four times per power system cycle

.

After low

-

pass filtering, the relay digitally filters each sample with the CAL digital filter method

.

TheCAL filter

eliminates dc offset and reduces the decaying exponential offset thatmay bepresentonthe

inputsignal following a fault

.

The digitalfilterhasthepropertiesofa double differentiatorsmoother and requires only addition and subtraction of data samples

.

Let the latest four samples of onechannel beXI, X2, X3, andX4

.

Then thedigital filter is defined:

P

₌

XI

-

X2

-

X3

+

X4

.

This filter eliminates dc offsets

.

When all samplesaresetto thesamevalue, thefilter output

iszero. Italsoeliminatesramps, whichyou may verify by setting the samples equal to 1, 2, 3, and 4

.

Again, theoutput iszero.

Every quarter

-

cycle, the relay computesa new valueof P for each input

.

The current value of Pcombineswith theprevious value (renamed Q) toformaCartesian coordinate pair

.

This pair represents theinput signalasa phasor (P, Q)

.

Therelay processes these phasor

representations of the input signals

.

TORQUE

CONTROL

Elementsin Relay Wordrow R1maybetorque controlled

.

Elements derived fromrow R1

elements aretorquecontrolled if the row R1element is torque controlled. For example, if

row R1elements51Pand50NL aretorquecontrolled, rowR2elements51T and 50NLT are

alsotorquecontrolled

.

51P and 50NLarethe pickups for 51T and 50NLT, respectively

.

SeeFigures2.14, 2.15, and 2.16formore information.

Phase overcurrent elementscanbeexternally andinternallytorquecontrolled

.

Negative

-sequenceand ground/residual overcurrent elements can only be externallytorquecontrolled

.

External Torque _Control

TheETC(l) setting selects overcurrentelements tobe externallytorquecontrolled

.

Only overcurrentelements in Relay Wordrow R1canbe selected

.

Asanexample:

51P, 50Q, 50NL, and consequently 51T, 50QT, and

50NLTareselectedfor external torque control

ETC

₌

51P, 50Q, 50NL

ExternalTorque Control (Phase and Negative

-

SequenceOvercurrentElements)

TCP

Specifications

SEL-251C,-2,-3InstructionManual

DateCode20000421 2-22

TCG External Torque Control (Ground/Residual OvercurrentElements)

TCPand TCGare assignedto programmableinputs

.

The inverted senseof TCP or TCGisavailable,too(!TCP

or

!TCG, respectively)

.

If input IN3

₌

TCP, the phase and negative

-

sequence overcurrent elementsselectedin the

ETC(l) setting (51P and 50Qand consequently51T and 50QT in this example) areenabled for operationwhen input IN3 is energized

.

If input IN3

₌

!TCP, the phaseand negative

-sequence overcurrent elements selected in the ETC(l)settingare enabled for operation when

inputIN3is de

-

energized

.

If neither TCPor !TCP is assigned toaninput, the phase and negative-sequenceovercurrent

elementsselected intheETC(l)setting arenot externallytorquecontrolled

.

The selected

phase and negative

-

sequence overcurrent elements are always enabled withrespect to external

torquecontrol

.

If input IN4

₌

TCG, the ground/residual overcurrent elements selected in the ETC(l)setting

(50NL and consequently 50NLT in this example)areenabled for operationwheninputIN4 is energized

.

If input IN4

₌

!TCG, the ground/residual overcurrentelements selected in the

ETC(l) settingare enabled for operation when input IN4 is de

-

energized

.

If neither TCGnor!TCG is assigned to aninput, the ground/residual overcurrent elements selected in the ETC(l) settingarenotexternallytorquecontrolled

.

The selected ground/ residual overcurrent elements arealways enabled withrespect to externaltorque control

.

InternalTorque _Control

TheITC(l)setting selects phaseovercurrentelements to be internallytorquecontrolled

.

Only phase overcurrent elements in Relay Word row R1canbe selected

.

As anexample:

51P, 50M, and consequently 51T and 50MTare selectedfor internaltorquecontrol

ITC

₌

51P, 50M

Specifications

SEL-251C,-2, -3InstructionManual

2-23 Date Code 20000421

TheTCI setting selects the elements which perform internaltorquecontrol:

Table2.6: TCI Settings

setting TCI ₌ Element choices for TCI 50C 27 21P 0 0 0 0 0 0 1 V 1 0 0 I 3 0 1 1 0 0

z

1 5 1 0 1 6 1 1 0 7 1 1 1

TCI setting examples:

Ifyou setTCIequal to V,the 27 elementtorquecontrols phaseovercurrent elements

selected in theITC(l) setting (51P and 50M and consequently 51T and 50MT inthis

example). If 27 asserts,the selected phaseovercurrentelements areenabled withrespect

to internaltorquecontrol.

If youset TCI equalto 3, thephase overcurrent elements selected in the ITC(l)setting

(51P and 50M and consequently 51T and50MT in this example) aretorquecontrolled

by "27 + 50C". If either 27or50C assert, the selected phaseovercurrentelements are enabled withrespectto internaltorquecontrol

.

IfyousetTCI equal to0,thephase overcurrent elements selected in the ITC(l)setting

(51P and 50M and consequently 51T and 50MT in this example)arenotinternally

torquecontrolled

.

Thephaseovercurrentelementsarealways enabled withrespect to

internal torquecontrol

.

Transformer Blown

-

FuseDetection

Delta

-

wyeconnected distributiontransformer banks arefrequentlyprotected by fuses connected in the bank high side,asshown in Figure 2.9

.

Whenonehigh

-

sidefuse blows, unbalanced voltagesareapplied to thetransformer bank and its connectedload

.

TheSEL

-

251C Relay includes logic that detectshigh

-

fuseoperationsby measuring thelow

-side voltages

.

The logic also rejects operationsoflow

-

side VoltageTransformer (VT) fuses.

DateCode20000421

Specifications

SEL-251C,-2,-3InstructionManual