Schweitzer Engineering Laboratories SEL-251 User manual

SEL-251
SEL-251-2
SEL-251-3
DISTRIBUTION RELAY
PHASE OVERCURRENT RELAY
WITH VOLTAGE CONTROL
NEGATIVE-SEQUENCE OVERCURRENT RELAY
GROUND OVERCURRENT RELAY
MULTIPLE SHOT RECLOSING RELAY
SELECTABLE SETTING GROUPS
CIRCUIT BREAKER MONITOR
FAULT LOCATOR
SELOGIC™ CONTROL EQUATIONS
INSTRUCTION MANUAL
SCHWEITZER ENGINEERING LABORATORIES, INC.
2350 NE HOPKINS COURT
PULLMAN, WA USA 99163-5603
TEL: [phone] FAX: [phone]

The software (firmware), schematic drawings, relay commands, and relay messages are copyright protected by the United States Copyright
Law and International Treaty provisions. All rights are reserved.
You may not copy, alter, disassemble, or reverse-engineer the software. You may not provide the software to any third party.
All brand or product names appearing in this document are the trademark or registered trademark of their respective holders.
Schweitzer Engineering Laboratories, Inc., SELOGIC, and are registered trademarks of Schweitzer Engineering Laboratories, Inc.
This product is covered by U.S. Patent Nos: 5,041,737; 5,477,408; 5,479,315; and 5,602,707.
Copyright SEL 1992, 1993, 1994, 1995, 1996, 1997, 2000
(All rights reserved)
Printed in USA

Date Code 20000421 Manual Change Information i
SEL-251, -2, -3 Instruction Manual
MANUAL CHANGE INFORMATION
The date code at the bottom of each page of this manual reflects the creation or revision date.
Date codes are changed only on pages that have been revised and any following pages affected
by the revisions (i.e., pagination). If significant revisions are made to a section, the date code on
all pages of the section will be changed to reflect the revision date.
Each time revisions are made, both the main table of contents and the affected individual section
table of contents are regenerated and the date code is changed to reflect the revision date.
Changes in this manual to date are summarized below (most recent revisions listed at top).
Revision
Date Summary of Revisions
The Manual Change Information section has been created to begin a record of revisions to
this manual. All changes will be recorded in this Summary of Revisions table.
20000421 Section 2: Specifications:
− Updated to include details for 1-amp nominal current input model.
− Added frequency and rotation information
− Incorporated "New SEL-200 Series Optical Isolator Logic Input Rating"
addendum.
− Combined specifications for Conventional Terminal Block models and Plug-
In Connector models.
− Incorporated "SEL-151/151C/251/251C Instruction Manual Addendum
for 1 Amp Version Relays"
Section 5: Applications
− Added note to Settings Sheets to indicate different setting ranges for 1-amp
nominal current input relays.
Section 6: Installation
− Incorporated "Jumper Installation Instructions" addendum.
− Incorporated "SEL-200 Series (Shallow) Relay Hardware" addendum.
− Added Figure 6.5: LP Relay Dimensions and Drill Plan (for relays with
1-amp nominal current inputs).
Section 7: Maintenance and Testing
− Added note to indicate that the Low-Level Test Interface is not available on
LP chassis relays.
Appendix B
− Added note below Figure B.1 that describes the difference in test point
locations for LP chassis relays.
− Reissued all Appendices.

ii Manual Change Information Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Revision
Date Summary of Revisions
971121 Added Settings Sheets to end of Section 5.
971107 Section 2 - Corrected logic in Figure 2.22.
971028 Section 2 - Corrected Drawings in Figures 2.1 and 2.2.
970418 Appendix A - Added New Firmware Versions.

Date Code 20000421 Table of Contents i
SEL-251, -2, -3 Instruction Manual
SEL-251, -2, -3 INSTRUCTION MANUAL
TABLE OF CONTENTS
SECTION 1: INTRODUCTION
SECTION 2: SPECIFICATIONS
SECTION 3: COMMUNICATIONS
SECTION 4: EVENT REPORTING
SECTION 5: APPLICATIONS
SECTION 6: INSTALLATION
SECTION 7: MAINTENANCE AND TESTING
SECTION 8: APPENDICES
Appendix A: Firmware Versions in this Manual
Appendix B: Main Board Jumper Connector and Socket Locations
Appendix C: Onebus: Program to Compute Test Set Settings for
Testing Distance Relays

Date Code 970103 Table of Contents i
SEL-251, -2, -3 Instruction Manual
TABLE OF CONTENTS
SECTION 1: INTRODUCTION 1-1
Getting Started.............................................................................................................................. 1-1
Overview...................................................................................................................................... 1-1
Conventional Terminal Block Model................................................................................... 1-1
Plug-In Connector Model..................................................................................................... 1-2
General Description: Conventional Terminal Block Model....................................................... 1-2
SELOGIC Control Equations: The Next Step in Programmable Relay Logic ..................... 1-2
Phase, Ground, and Negative-Sequence Overcurrent Protection......................................... 1-2
Sophisticated Multiple-Shot Reclosing Relay Includes Reset Inhibit and Sequence
Coordination................................................................................................................. 1-3
Six Selectable Groups of Settings and Logic....................................................................... 1-3
Circuit Breaker Monitor Tracks Breaker Performance and Helps Maintenance
Planning........................................................................................................................ 1-3
Fault Locator Reduces Line Patrol and Outage Time.......................................................... 1-3
Analyze Operations Using Event Reports............................................................................ 1-3
Comprehensive Metering Supports Protection, Operation, and Demand Analysis ............. 1-3
Access SEL-251 Relay Information via the SEL-RD Relay Display................................... 1-4
General Description: Plug-In Connector Model ......................................................................... 1-4
Wiring Harnesses ................................................................................................................. 1-4
High Current Interrupting Output Contacts.......................................................................... 1-4

Date Code 970103 Introduction 1-1
SEL-251, -2, -3 Instruction Manual
SECTION 1: INTRODUCTION
GETTING STARTED
If you are not familiar with this relay, we suggest that you read this introduction, then perform
the Initial Checkout Procedure in Section 7: Maintenance & Testing.
OVERVIEW
Conventional Terminal Block Model
The SEL-251 Relay is designed to protect distribution lines for all fault types. The following list
outlines protective features, performance, and versatility gained when applying the SEL-251
Relay to your installations.
• Develop traditional and advanced schemes using flexible SELOGICTM Control Equations
• Phase-overcurrent elements have voltage control for load security
• Negative-sequence elements reject load for more sensitive phase fault protection
• Ground and residual overcurrent elements cover ground faults
• Choose fast or electromechanical reset characteristic for time-overcurrent elements
• Overcurrent elements inhibit recloser reset to prevent nuisance "trip-reclose" cycling
• Sequence coordination avoids unnecessary tripping for faults beyond line reclosers
• Undervoltage logic detects high-side transformer fuse operations
• Six selectable setting groups cover all feeder protection contingencies
• Circuit breaker monitor sums interrupted current in each pole to aid maintenance
• Fault locator reduces line patrol and outage time for increased service reliability
• Eleven-cycle event report simplifies fault and system analysis
• Comprehensive voltage, current, power, unbalance, and demand metering
• Connects to SEL-RD Relay Display for easy information access
• Improved Fast Meter
• Improved Fast Operate
The SEL-251 Relay improves every aspect of feeder protection.
• Security: Undervoltage supervision and negative-sequence avoid load encroachment
• Reliability: Field-proven hardware; new backup concepts
• Sensitivity: Negative-sequence overcurrent elements for better phase fault coverage
• Flexibility: SELOGIC Control Equations handle virtually every conceivable scheme

1-2 Introduction Date Code 970103
SEL-251, -2, -3 Instruction Manual
• Capability: Brings transmission relay features to distribution applications
• Economy: Low price and unique features make the relay an exceptional value
Plug-In Connector Model
• All features included in the standard terminal block model
• High current interrupting output contacts
• Quick connect/release hardware for rear-panel terminals
• Time code input access on all rear communications ports
GENERAL DESCRIPTION: CONVENTIONAL TERMINAL BLOCK MODEL
The SEL-251 Relay protects, controls, and monitors distribution feeders. It offers important new
and unique features, like user-programmable SELOGIC Control Equations, negative-sequence
overcurrent elements, and selectable setting groups. The advanced relay design enhances
security, reliability, sensitivity, and operation.
SELOGIC Control Equations: The Next Step in Programmable Relay Logic
In 1987, SEL invented Programmable Mask Logic. The SEL-251 Relay offers SELOGIC Control
Equations, the next step in user-programmability. SELOGIC Control Equations include ANDing,
ORing, and inverting functions, timing, and programmable inputs and outputs. SELOGIC Control
Equations add power and flexibility while simplifying programming.
Phase, Ground, and Negative-Sequence Overcurrent Protection
Phase and negative-sequence overcurrent elements detect phase faults. Negative-sequence
overcurrent elements reject three-phase load to provide more sensitive coverage of
phase-to-phase faults. Phase overcurrent elements are needed only for three-phase faults where
negative-sequence quantities are not produced.
On heavily-loaded feeders, undervoltage torque control of phase overcurrent elements adds
security. Choose between three-phase and single-phase-pair undervoltage torque control. When
phase overcurrent elements are used only for three-phase faults, the three-phase undervoltage
option enhances security.
Ground/Residual overcurrent elements detect ground faults, and external inputs can torque
control selected overcurrent elements.
There are two reset characteristic choices for the time-overcurrent elements. One choice resets
the elements if current drops below pickup for at least one cycle. The other choice emulates
electromechanical induction disc elements where the reset time depends on the time dial setting,
the percentage of disc travel, and the amount of current between zero and pickup.

Date Code 970103 Introduction 1-3
SEL-251, -2, -3 Instruction Manual
Sophisticated Multiple-Shot Reclosing Relay Includes Reset Inhibit and Sequence
Coordination
The reclosing relay allows up to four reclosing shots with separate, settable open interval timers
and reset interval timer. Overcurrent conditions during the reclosing relay reset interval inhibit
the reset interval timer. This prevents the reclosing relay from resetting when a trip condition is
imminent. A close failure timer can limit CLOSE output contact assertion. Reclose cancel
conditions are programmable. A programmable input can be used as a reclose enable input to
disable/enable the reclosing relay.
The SEL-251 Relay includes easily programmable sequence coordination to keep the relay in
step with line reclosers, preventing undesired tripping for faults beyond line reclosers.
Six Selectable Groups of Settings and Logic
The relay stores six setting groups. Select the active setting group by contact input or command.
Use these setting groups to cover a wide range of distribution feeder protection contingencies.
Selectable setting groups make the SEL-251 Relay ideal for bus-tie and substitute breaker
applications and other applications requiring frequent setting changes.
Circuit Breaker Monitor Tracks Breaker Performance and Helps Maintenance Planning
Separate circuit breaker trip counters differentiate and tally relay-initiated trips and external trips.
Running sums of interrupted current for relay and external trips indicate breaker wear and tear on
a pole-by-pole basis. Use these data to schedule breaker maintenance.
Trip failure logic provides alarm and breaker failure functions. A close failure alarm indicates
circuit breaker closing circuit or mechanism problems. The trip circuit monitor detects abnormal
open or short circuits in the circuit breaker tripping circuit or status input.
Fault Locator Reduces Line Patrol and Outage Time
The SEL-251 Relay includes a fault locator which uses fault type, prefault, and fault conditions
to provide an accurate estimate of fault location without communications channels or special
instrument transformers, or source impedance information, even during conditions of substantial
load flow and fault resistance. Fault locating reduces line patrol and outage time.
Analyze Operations Using Event Reports
Eleven-cycle event reports triggered by user selected conditions provide the current, voltage, and
sequence-of-events information you need to understand relay and circuit breaker performance, as
well as stress on the feeder for every fault.
Comprehensive Metering Supports Protection, Operation, and Demand Analysis
The relay measures phase, negative sequence, and zero-sequence voltage and current, as well as
MW and MVAR. Demand and peak demand values for current, MW, and MVAR are also
available. Metering also supports protection, because you can inspect the quantities monitored

1-4 Introduction Date Code 970103
SEL-251, -2, -3 Instruction Manual
by relay elements. Check for load encroachment and unbalance through instantaneous, demand,
and peak-demand measurements.
Access SEL-251 Relay Information via the SEL-RD Relay Display
You can connect up to four SEL-251 Relays to one SEL-RD Relay Display. Access relay target,
meter, status, fault history, and circuit breaker information via the relay display. You can even
change the active setting group via the display.
GENERAL DESCRIPTION: PLUG-IN CONNECTOR MODEL
The General Description presented for the Conventional Terminal Block model relay fully
applies to the Plug-in Connector model. In addition, the following information applies strictly to
the Plug-in Connector model.
Wiring Harnesses
Custom wiring harnesses can be pre-wired, which enables quick and easy relay installation. The
plug-in connectors attach to dc power, ct and pt inputs, and contact inputs and outputs. Ct
secondaries are automatically shorted inside the plug-in connector when removed from the relay.
During in-service testing, spare connectors can be wired to auxiliary test equipment and plugged
directly into the relay. The actual source and I/O connectors may simply be unplugged before
each test and reconnected afterwards. If there is a need to replace a relay, the connectors can be
unplugged and reconnected to the new relay in a matter of minutes. There is no need for a wiring
check because the connections were verified at installation and no wiring was disturbed during
the replacement process.
High-Current Interrupting Output Contacts
High-current interrupting contacts are standard on the SEL-251 plug-in connector model. These
contacts use an electromechanical relay with solid state circuitry to interrupt dc current far in
excess of a typical contact output. No SCRs are employed in this circuitry. The circuit is
designed to make 30 Adc, carry 6 Adc, and interrupt 10 Adc. The circuit can interrupt 10 A four
times in one second, and then must be allowed to cool for two minutes to prevent thermal
damage.

Date Code 20000421 Specifications i
SEL-251, -2, -3 Instruction Manual
TABLE OF CONTENTS
SECTION 2: SPECIFICATIONS 2-1
General Specifications ................................................................................................................. 2-1
Functional Specifications............................................................................................................. 2-7
Phase Overcurrent Elements for Phase and Three-Phase Faults - See Figure 2.18 and
Figure 2.21.................................................................................................................... 2-7
Negative-Sequence Overcurrent Elements for Phase-to-Phase Faults - See
Figure 2.19.................................................................................................................... 2-7
Ground/Residual Overcurrent Elements for Ground Faults - See Figure 2.20 .................... 2-8
Voltage Element for Healthy/Low Voltage Indication or Internal Control (27) - See
Figure 2.21.................................................................................................................... 2-8
Time Delayed 52A or 52B Functions Handle Fuse-Saving and Inrush ............................... 2-8
Trip Failure Timer Detects Breaker Failure or Slow Trip - See Figure 2.24....................... 2-9
Close Failure Timer Detects Failure to Close or Slow Close - See Figure 2.25................. 2-9
Trip Circuit Monitor Alarm Checks Trip Circuit and Verifies Circuit Breaker Status
Input.............................................................................................................................. 2-9
SEL-251 Relay SELOGIC®Control Equations........................................................................... 2-10
Assign Inputs to the Functions You Need.......................................................................... 2-11
Select Combinations of Relay Elements for Tripping and Other Purposes....................... 2-13
Time Delayed Variables ST, KT, and ZT.......................................................................... 2-15
Use !L for Inversion ........................................................................................................... 2-16
Programming Output Contacts........................................................................................... 2-16
Viewing Logic Equations................................................................................................... 2-16
SELOGIC Control Equations Settings in Each Setting Group............................................ 2-17
Targets........................................................................................................................................ 2-17
Multiple Shot Reclosing Relay .................................................................................................. 2-17
Reclose Cancel Conditions................................................................................................. 2-18
Sequence Coordination....................................................................................................... 2-19
Selectable Setting Groups .......................................................................................................... 2-20
Circuit Breaker Monitor............................................................................................................. 2-22
Metering..................................................................................................................................... 2-22
Serial Interfaces.......................................................................................................................... 2-22
Self-Tests.................................................................................................................................... 2-23
Offset.................................................................................................................................. 2-23
Power Supply...................................................................................................................... 2-23
Random-Access Memory ................................................................................................... 2-23
Read-Only Memory............................................................................................................ 2-24
Analog-to-Digital Converter............................................................................................... 2-24
Master Offset...................................................................................................................... 2-24
Settings............................................................................................................................... 2-24
IRIG-B Input Description........................................................................................................... 2-25
Signal Processing ....................................................................................................................... 2-25
Torque Control........................................................................................................................... 2-26
External Torque Control..................................................................................................... 2-26
Internal Torque Control...................................................................................................... 2-27

ii Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Transformer Blown-Fuse Detection........................................................................................... 2-27
What Happens When a High-Side Fuse Blows?................................................................ 2-28
How Does the SEL-251 Relay Detect Transformer Fuse Operations?.............................. 2-28
Use the Detection Logic to Trip or Indicate....................................................................... 2-29
Demand Ammeters..................................................................................................................... 2-29
Fault Locator.............................................................................................................................. 2-30
Nomographs........................................................................................................................ 2-31
Event Report............................................................................................................................... 2-32
Event Report Triggering..................................................................................................... 2-32
Time-Overcurrent Element Curve-Timing and Time Delay Reset Equations........................... 2-33
TABLES
Table 2.1: Trip Circuit Monitor Alarm (TCMA) Truth Table............................................................... 2-10
Table 2.2: SEL-251 Relay Word............................................................................................................ 2-14
Table 2.3: Setting Group Selection Input Truth Table........................................................................... 2-21
Table 2.4: Power Supply Self-Test Limits............................................................................................. 2-23
Table 2.5: Self-Test Summary................................................................................................................ 2-25
FIGURES
Figure 2.1: SEL-251 Relay Conventional Terminal Block Model Inputs, Outputs, and Targets
Diagram ......................................................................................................................... 2-5
Figure 2.2: SEL-251 Relay Plug-In Connector Model Inputs, Outputs, and Targets Diagram ................ 2-6
Figure 2.3: Time Delayed 52A and 52B Functions................................................................................... 2-9
Figure 2.4: Trip Circuit Monitor (TCM) DC Voltage Connections ......................................................... 2-9
Figure 2.5: Trip Circuit Monitor Alarm (TCMA) Logic ........................................................................ 2-10
Figure 2.6: SEL-251 Relay SELOGIC Control Equations Block Diagram.............................................. 2-13
Figure 2.7: Relay Word Bit Realizations................................................................................................ 2-15
Figure 2.8: Relay Word Bit Realization.................................................................................................. 2-16
Figure 2.9: SEL-251 Relay Front Panel Target LEDs ............................................................................ 2-17
Figure 2.10: Sequence Coordination, Ground/Residual Overcurrent Elements ..................................... 2-19
Figure 2.11: Distribution Transformer Bank Protected by High-Side Fuses.......................................... 2-28
Figure 2.12: Current-Limiting Reactor and Line Impedances ................................................................ 2-30
Figure 2.13: Nomograph for Fault Locating........................................................................................... 2-32
Figure 2.14: Moderately Inverse Curves................................................................................................. 2-34
Figure 2.15: Inverse Curves .................................................................................................................... 2-34
Figure 2.16: Very Inverse Curves ........................................................................................................... 2-34
Figure 2.17: Extremely Inverse Curves................................................................................................... 2-34
Figure 2.18: SEL-251 Phase Overcurrent Logic Diagrams..................................................................... 2-35
Figure 2.19: SEL-251 Negative-Sequence Overcurrent Logic Diagrams............................................... 2-36
Figure 2.20: SEL-251 Ground/Residual Overcurrent Logic Diagrams................................................... 2-37
Figure 2.21: SEL-251 Overcurrent and Undervoltage Elements ............................................................ 2-38
Figure 2.22: SEL-251 Transformer Blown-Fuse Detection Logic.......................................................... 2-39
Figure 2.23: SEL-251 Demand Ammeters.............................................................................................. 2-40
Figure 2.24: SEL-251 Programmable Trip Logic Diagram .................................................................... 2-41
Figure 2.25: SEL-251 Close Logic Diagram........................................................................................... 2-41

Date Code 20000421 Specifications 2-1
SEL-251, -2, -3 Instruction Manual
SECTION 2: SPECIFICATIONS
GENERAL SPECIFICATIONS
Voltage Inputs 120-volt nominal phase-to-phase, three-phase, four-wire connection
150-volt phase-to-neutral saturation limit
Current Inputs 5 A nominal 1 A nominal
(some LP chassis models only)
15 A continuous 3 A continuous
110 A saturation limit 20 A saturation limit
500 A one-second thermal rating 100 A one second thermal rating
Frequency and
Rotation 60 Hz, ABC (50 Hz is an ordering option on some models, ACB rotation is an ordering option on some models)
Output Contacts Conventional Terminal Blocks
Per IEC 255-0-20 : 1974, using the simplified method of assessment
6 A continuous carry
30 A make per IEEE C37.90 : 1989
100 A for one second
270 Vac/360 Vdc MOV for differential surge protection.
Pickup/dropout time: < 5 ms
Breaking Capacity (L/R = 40 ms):
48 V 0.5 A 10,000 operations
125 V 0.3 A 10,000 operations
250 V 0.2 A 10,000 operations
Cyclic Capacity (L/R = 40 ms):
48 V 0.5 A 2.5 cycles per second
125 V 0.3 A 2.5 cycles per second
250 V 0.2 A 2.5 cycles per second
Plug-In Connectors (High-Current Interrupting)
6 A continuous carry
30 A make per IEEE C37.90 : 1989
330 Vdc MOV for differential surge protection
Pickup time: < 5 ms
Dropout time: < 8 ms (typical)
Breaking Capacity: 10 A 10,000 operations
48 and 125 V (L/R = 40 ms)
250 V (L/R = 20 ms)
Cyclic Capacity: 10 A 4 cycles in 1 second, followed
by 2 minutes idle for thermal dissipation
48 and 125 V (L/R = 40 ms)
250 V (L/R = 20 ms)
Note: Do not use high-current interrupting output contacts to switch ac control
signals. These outputs are polarity dependent.

2-2 Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Optoisolated Inputs The SEL-251 available input ratings are different for the three chassis types.
The nominal input rating is not field adjustable - it is determined at the time of
order, and is identical for all six inputs. The inputs are not polarity dependent.
Conventional Terminal Blocks – SLP chassis (5 A nominal current inputs)
Nominal
Input Rating Operating Range Burden at Rated Voltage Level Sensitive?
24 Vdc 15 – 30 Vdc 4 mA No
48 Vdc 30 – 60 Vdc 4 mA No
125 Vdc 100 – 150 Vdc 6 mA Yes, off below 75 Vdc
250 Vdc 150 – 300 Vdc 4 mA No
Conventional Terminal Blocks – LP chassis (1 A nominal current inputs)
Nominal
Input Rating Operating Range Burden at Rated Voltage Level Sensitive?
24 Vdc 15 – 30 Vdc 4 mA No
48 Vdc 30 – 60 Vdc 4 mA No
125 Vdc 80 – 150 Vdc 4 mA No
250 Vdc 150 – 300 Vdc 4 mA No
Plug-In Connectors
Nominal
Input Rating Operating Range Burden at Rated Voltage Level Sensitive?
24 Vdc 15 – 30 Vdc 4 mA No
48 Vdc 38 – 60 Vdc 5 mA Yes, off below 29 Vdc
125 Vdc 100 – 150 Vdc 6 mA Yes, off below 75 Vdc
250 Vdc 150 – 300 Vdc 4 mA No
Power Supply 24/48 Volt: 20 - 60 Vdc; 125/250 Volt: 85 - 350 Vdc or 85 - 264 Vac
10 watts nominal, 14 watts max. (all output relays energized)
Communications Two EIA-232 serial communications ports, Port 2 of the SEL-251 Relay has
front- and rear-panel connectors.
Dimensions See Figure 6.3 for SLP chassis models (5-amp nominal current inputs)
See Figure 6.5 for LP chassis models (1-amp nominal current inputs)
Time Code Input Relay accepts demodulated IRIG-B time code input
Mounting Available in horizontal and vertical mounting configurations
Dielectric Strength V, I inputs: 2500 Vac for 10 seconds
Other: 3000 Vdc for 10 seconds (excludes EIA-232)
Routine Tested.
Operating
Temperature -40°F to 158°F (-40°C to 70°C)

Date Code 20000421 Specifications 2-3
SEL-251, -2, -3 Instruction Manual
Environmental
Type Tests IEEE C37.90-1989 IEEE Standards for Relays and Relay Systems Associated with Electrical Power
Apparatus, Section 8: Dielectric Tests
Severity Level: 2500 Vac on analog inputs; 3000 Vdc on power supply, contact
inputs and contact outputs
IEEE C37.90.1-1989
IEEE Standard Surge Withstand Capability (SWC) Tests for Protective Relays
and Relay Systems
Severity Level: 3.0 kV oscillatory, 5.0 kV fast transient
IEEE C37.90.2 (Issued for trial use December 1987)
IEEE Trial-Use Standard, Withstand Capability of Relay Systems to Radiated
Electromagnetic Interference from Transceivers
Severity Level: 10 V/m
Exceptions:
5.5.2 (2) Performed with 200 frequency steps per octave
5.5.3 Digital Equipment Modulation Test not performed
5.5.4 Test signal turned off between frequency steps to simulate
keying
IEC 68-2-1 Fifth Edition - 1990
Environmental testing, Part 2: Tests - Test Ad: Cold
Severity Level: 16 hours at -40°C
IEC 68-2-2 Fourth Edition - 1974
Environmental testing, Part 2: Tests - Test Bd: Dry heat
Severity Level: 16 hours at +85°C
IEC 68-2-30 Second Edition - 1980
Basic environmental testing procedures, Part 2: Tests - Test Db and guidance:
Damp heat, cyclic (12 + 12-hour cycle)
Severity Level: 55°C, 6 cycles
IEC 255-5 First Edition - 1977
Electrical relays, Part 5: Insulation tests for electrical relays,
Section 6: Dielectric Tests
Severity Level: Series C (2500 Vac on analog inputs; 3000 Vdc on power
supply, contact inputs and contact outputs)
Section 8: Impulse Voltage Tests
Severity Level: 0.5 Joule, 5000 volt
IEC 255-21-1 First Edition - 1988
Electrical relays, Part 21: Vibration, shock, bump, and seismic tests on
measuring relays and protection equipment, Section One - Vibration tests
(sinusoidal)
Severity Level: Class 1
IEC 255-21-2 First Edition - 1988
Electrical relays, Part 21: Vibration, shock, bump, and seismic tests on
measuring relays and protection equipment, Section Two - Shock and bump tests
Severity Level: Class 1

2-4 Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
IEC 255-22-1 First Edition - 1988
Electrical disturbance tests for measuring relays and protection equipment,
Part 1: 1 MHz burst disturbance tests
Severity Level: 2.5 kV peak common mode, 1.0 kV peak differential mode
IEC 255-22-3 - 1989
Electrical relays, Part 22: Electrical disturbance tests for measuring relays and
protection equipment, Section Three - Radiated electromagnetic field
disturbance tests
Exceptions:
4.3.2.2 Frequency sweep approximated with 200 frequency steps per
octave
IEC 801-2 Second Edition - 1991-04
Electromagnetic compatibility for industrial-process measurement and control
equipment, Part 2: Electrostatic discharge requirements
Severity Level: 3
IEC 801-3
Electromagnetic compatibility for industrial process measurement and control
equipment, Part 3: Radiated electromagnetic field requirements
Severity Level: 10 V/m
Exceptions:
9.1 Frequency sweep approximated with 200 frequency steps per
octave.
IEC 801-4 First Edition - 1988
Electromagnetic compatibility for industrial process measurements and control
equipment, Part 4: Electrical fast transient/burst requirements
Severity Level: 4 (4 kV on power supply, 2 kV on inputs and outputs)
Unit Weight SLP Chassis: 12 pounds (5.5 kg) - 5 amp nominal current inputs
LP Chassis: 16 pounds (7.3 kg) - 1 amp nominal current inputs

Date Code 20000421 Specifications 2-5
SEL-251, -2, -3 Instruction Manual
Figure 2.1:SEL-251 Relay Conventional Terminal Block Model Inputs, Outputs, and
Targets Diagram

2-6 Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Figure 2.2:SEL-251 Relay Plug-In Connector Model Inputs, Outputs, and Targets
Diagram