Sel 551 User manual

20110408
SEL-551 Relay
Overcurrent Relay
Reclosing Relay
Instruction Manual
*PM551-01-NB*

SEL-551 Relay Instruction Manual Date Code 20110408
The relay contains devices sensitive to Electrostatic Discharge
(ESD). When working on the relay with the front panel removed,
work surfaces and personnel must be properly grounded or
equipment damage may result.
!
CAUTION
This procedure requires that you handle components sensitive
to Electrostatic Discharge (ESD). If your facility is not equipped
to work with these components, we recommend that you
return the relay to SEL for firmware installation.
!
CAUTION
There is danger of explosion if the battery is incorrectly
replaced. Replace only with Ray-O-Vac®no. BR2335 or
equivalent recommended by manufacturer. Dispose of used
batteries according to the manufacturer’s instructions.
!
CAUTION
Verify proper orientation of the new EPROM in the socket
before applying pressure to engage it. Note the orientation
indication provided by the notched inside socket corner and
the notched corner.
!
CAUTION
Do not connect external voltages to the relay contact inputs.
Because the contact inputs are internally wetted, permanent
damage to the relay or external equipment may result from
connecting external voltage to a relay contact input.
!
CAUTION
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
Operator safety may be impaired if the device is used in a
manner not specified by SEL.
!
WARNING
Contact with instrument terminals can cause electrical shock
that can result in injury or death.
!
DANGER
Contact with this circuitry may cause electrical shock that can
result in injury or death. Removal of enclosure panels exposes
circuitry which may cause electrical shock which can result in
injury or death.
!
DANGER
Le relais contient des pièces sensibles aux décharges
électrostatiques. Quand on travaille sur le relais avec les
panneaux avant ou du dessus enlevés, toutes les surfaces et le
personnel doivent être mis à la terre convenablement pour
éviter les dommages à l’équipement.
!
ATTENTION
Cette procédure requiert que vous manipuliez des composants
sensibles aux décharges électrostatiques (DES). Si vous n'êtes
pas équipés pour travailler avec ce type de composants, nous
vous recommandons de les retourner à SEL pour leur
installation.
!
ATTENTION
Il y a un danger d’explosion si la pile électrique n’est pas
correctement remplacée. Utiliser exclusivement Ray-O-Vac®
No. BR2335 ou un équivalent recommandé par le fabricant. Se
débarrasser des piles usagées suivant les instructions du
fabricant.
!
ATTENTION
Vérifier l’orientation du nouvel EPROM avant d’appliquer la
pression pour l’insérer dans sa base. Noter l’orientation
indiquée par le coin marqué à l’intérieur de la base et le coin
marqué du composant.
!
ATTENTION
Ne pas raccorder de tensions externes sur les bornes des
entrées de contact. Parce que les contacts sont trempés au
mercure, des dommages permanents peuvent résulter pour le
relais ou l’équipement externe à la suite du raccordement
d’une tension externe à une entrée de contact du relais.
!
ATTENTION
Cet appareil est expédié avec des mots de passe par défaut. A
l’installation, les mots de passe par défaut devront être
changés pour des mots de passe confidentiels. Dans le cas
contraire, un accés non-autorisé á l’équipement peut être
possible. SEL décline toute responsabilité pour tout dommage
résultant de cet accés non-autorisé.
!
AVERTISSEMENT
La sécurité de l’opérateur peut être compromise si l’appareil
est utilisé d’une façon non indiquée par SEL.
!
AVERTISSEMENT
Tout contact avec les bornes de l’appareil peut causer un choc
électrique pouvant entraîner des blessures ou la mort.
!
DANGER
Tout contact avec ce circuit peut être la cause d’un choc
électrique pouvant entraîner des blessures ou la mort. Le
retrait des panneaux du boîtier expose le circuit qui peut
causer des chocos électriques pouvant entraîner des blessures
ou la mort.
!
DANGER
© 1998–2011 by Schweitzer Engineering Laboratories, Inc. All rights reserved.
All brand or product names appearing in this document are the trademark or registered trademark of their respective holders. No SEL
trademarks may be used without written permission. SEL products appearing in this document may be covered by US and Foreign patents.
Schweitzer Engineering Laboratories, Inc. reserves all rights and benefits afforded under federal and international copyright and patent laws in
its products, including without limitation software, firmware, and documentation.
The information in this manual is provided for informational use only and is subject to change without notice. Schweitzer Engineering
Laboratories, Inc. has approved only the English language manual.
This product is covered by the standard SEL 10-year warranty. For warranty details, visit www.selinc.com or contact your customer service
representative. PM551-01

Date Code 20110408 Instruction Manual SEL-551 Relay
Table of Contents
List of Tables.......................................................................................................................................................................... v
List of Figures.....................................................................................................................................................................vii
Preface..................................................................................................................................................................................... ix
Manual Overview .............................................................................................................................................. ix
Conventions ........................................................................................................................................................ x
Section 1: Introduction and Specifications
Overview ......................................................................................................................................................... 1.1
SEL-551 Model Changes ................................................................................................................................ 1.2
SEL-551 Applications ..................................................................................................................................... 1.2
Hardware Overview......................................................................................................................................... 1.3
Specifications .................................................................................................................................................. 1.4
Overcurrent Elements...................................................................................................................................... 1.6
CT Saturation Protection ................................................................................................................................. 1.7
Timer Specifications........................................................................................................................................ 1.8
Section 2: Installation
Overview ......................................................................................................................................................... 2.1
Relay Mounting............................................................................................................................................... 2.1
Rear-Panel Connections .................................................................................................................................. 2.5
SEL-551 AC/DC Connection Diagrams for Example Applications ............................................................... 2.9
EIA-485 Rear-Panel Adapter......................................................................................................................... 2.14
Circuit Board Jumpers and Battery ............................................................................................................... 2.15
Section 3: Relay Elements and Logic
Relay Word Bits and SELOGIC Control Equations.......................................................................................... 3.1
Optoisolated Inputs.......................................................................................................................................... 3.3
Local Control Switches ................................................................................................................................... 3.5
Remote Control Switches ................................................................................................................................ 3.7
Instantaneous Overcurrent Elements............................................................................................................... 3.8
Time-Overcurrent Elements .......................................................................................................................... 3.12
Trip Logic ...................................................................................................................................................... 3.17
Close Logic.................................................................................................................................................... 3.20
Reclosing Relay............................................................................................................................................. 3.22
SELOGIC Control Equation Variables/Timers ............................................................................................... 3.38
Output Contacts............................................................................................................................................. 3.39
Demand Ammetering .................................................................................................................................... 3.41
Front-Panel Target LEDs............................................................................................................................... 3.47
Section 4: Setting the Relay
Overview ......................................................................................................................................................... 4.1
Settings Changes Via the Front Panel ............................................................................................................. 4.1
Settings Changes Via the Serial Port ............................................................................................................... 4.1
Time-Overcurrent Element Setting Reference Information ............................................................................ 4.2
Relay Word Bit Setting Reference Information ............................................................................................ 4.14
Settings Explanations .................................................................................................................................... 4.18
Settings Sheets............................................................................................................................................... 4.20
Settings Sheets for the SEL-551 Relay

ii
SEL-551 Relay Instruction Manual Date Code 20110408
Table of Contents
Section 5: Serial Port Communications and Commands
Overview..........................................................................................................................................................5.1
Port Connector and Communications Cables ..................................................................................................5.1
Communications Protocol................................................................................................................................5.4
Serial Port Automatic Messages......................................................................................................................5.7
Serial Port Access Levels.................................................................................................................................5.8
Command Summary ........................................................................................................................................5.9
Command Explanations.................................................................................................................................5.11
SEL-551 Command Summary
Section 6: Front-Panel Interface
Overview..........................................................................................................................................................6.1
Front-Panel Pushbutton Operation...................................................................................................................6.1
Functions Unique to the Front-Panel Interface ................................................................................................6.4
Rotating Default Display ...............................................................................................................................6.11
Section 7: Standard Event Reports and SER
Overview..........................................................................................................................................................7.1
Standard 15-Cycle Event Reports....................................................................................................................7.1
Sequential Events Recorder (SER) Event Report ............................................................................................7.8
Example Standard 15-Cycle Event Report ....................................................................................................7.11
Example Sequential Events Recorder (SER) Event Report...........................................................................7.17
Section 8: Testing and Troubleshooting
Overview..........................................................................................................................................................8.1
Testing Methods and Tools ..............................................................................................................................8.1
Acceptance Testing ..........................................................................................................................................8.4
Commissioning Testing .................................................................................................................................8.14
Maintenance Testing ......................................................................................................................................8.15
Relay Self-Tests .............................................................................................................................................8.16
Relay Troubleshooting...................................................................................................................................8.17
Relay Calibration ...........................................................................................................................................8.18
Factory Assistance .........................................................................................................................................8.18
Appendix A: Firmware and Manual Versions
Firmware .........................................................................................................................................................A.1
Instruction Manual..........................................................................................................................................A.3
Appendix B: Firmware Upgrade Instructions
EPROM Firmware Upgrades.......................................................................................................................... B.1
Flash Firmware Upgrades............................................................................................................................... B.5
Appendix C: SEL Distributed Port Switch Protocol
Overview......................................................................................................................................................... C.1
Settings............................................................................................................................................................ C.1
Operation ........................................................................................................................................................ C.1
Appendix D: Configuration, Fast Meter, and Fast Operate Commands
Overview.........................................................................................................................................................D.1
Message Lists..................................................................................................................................................D.1
Message Definitions........................................................................................................................................D.2

iii
Date Code 20110408 Instruction Manual SEL-551 Relay
Table of Contents
Appendix E: Compressed ASCII Commands
Overview .........................................................................................................................................................E.1
CASCII Command—General Format .............................................................................................................E.1
CASCII Command—SEL-551........................................................................................................................E.3
CSTATUS Command—SEL-551 ....................................................................................................................E.3
CHISTORY Command—SEL-551 .................................................................................................................E.4
CEVENT Command—SEL-551 .....................................................................................................................E.4
Appendix F: Setting Negative-Sequence Overcurrent Elements
Setting Negative-Sequence Definite-Time Overcurrent Elements .................................................................. F.1
Setting Negative-Sequence Time-Overcurrent Elements ................................................................................ F.1
Coordinating Negative-Sequence Overcurrent Elements................................................................................ F.2
Other Negative-Sequence Overcurrent Element References........................................................................... F.7
Appendix G: Modbus RTU Communications Protocol
Overview ........................................................................................................................................................ G.1
Modbus RTU Communications Protocol ....................................................................................................... G.1

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Date Code 20110408 Instruction Manual SEL-551 Relay
List of Tables
Table 1.1 Overcurrent Elements............................................................................................................. 1.6
Table 2.1 Required Control Voltage Jumper Positions for Applied Nominal Control Voltage
(SEL-551 With the Conventional Terminal Blocks Option) ............................................ 2.15
Table 2.2 Required Position of Jumper JMP13 for Desired Output Contact OUT4 Operation........... 2.17
Table 3.1 Processing Order of SELOGIC Control Equation Operators................................................... 3.1
Table 3.2 Processing Order of Relay Elements and Logic (Top to Bottom).......................................... 3.3
Table 3.3 Correspondence Between Local Control Switch Positions and Label Settings..................... 3.5
Table 3.4 Correspondence Between Local Control Switch Types and Required Label Settings........... 3.6
Table 3.5 Relay Word Bit and Front-Panel Correspondence to Reclosing Relay States ..................... 3.23
Table 3.6 Shot Counter Correspondence to Relay Word Bits and Open Interval Times ..................... 3.27
Table 3.7 Demand Ammeter Settings and Settings Range .................................................................. 3.43
Table 3.8 SEL-551 Front-Panel Target LED Definitions..................................................................... 3.47
Table 4.1 Serial Port SET Commands.................................................................................................... 4.1
Table 4.2 SET Command Editing Keystrokes........................................................................................ 4.2
Table 4.3 Equations Associated With U.S. Curves ................................................................................ 4.3
Table 4.4 Equations Associated With IEC Curves................................................................................. 4.3
Table 4.5 SEL-551 Relay Word Bits.................................................................................................... 4.14
Table 4.6 Relay Word Bit Definitions.................................................................................................. 4.14
Table 5.1 Serial Communications Port Pin Function Definitions .......................................................... 5.4
Table 5.2 Communications Settings....................................................................................................... 5.6
Table 5.3 Serial Port Automatic Messages ............................................................................................ 5.7
Table 5.4 Serial Port Command Summary........................................................................................... 5.10
Table 5.5 ACC and 2AC Commands ................................................................................................... 5.11
Table 5.6 SEL-551 Relay Word and Its Correspondence to TAR Command
and Front-Panel LEDs ...................................................................................................... 5.21
Table 5.7 SEL-551 Control Subcommands.......................................................................................... 5.23
Table 5.8 Valid Password Characters ................................................................................................... 5.24
Table 7.1 Event Types ............................................................................................................................ 7.4
Table 7.2 Standard Event Report Current Columns............................................................................... 7.5
Table 7.3 Other Standard Event Report Columns.................................................................................. 7.6
Table 7.4 SEL-551 Input/Output Event Report Columns ...................................................................... 7.8
Table 7.5 SER Report Row Commands and Format.............................................................................. 7.9
Table 8.1 Instantaneous Overcurrent Elements and Corresponding Settings/Relay
Word Bits/TAR Commands .............................................................................................. 8.10
Table 8.2 Inverse-Time Overcurrent Elements and Corresponding Settings/Relay
Word Bits/TAR Commands .............................................................................................. 8.12
Table 8.3 Relay Self Tests.................................................................................................................... 8.16
Table 8.4 Troubleshooting Procedures................................................................................................. 8.17
Table A.1 Firmware Revision History ................................................................................................... A.1
Table A.2 Instruction Manual Revision History .................................................................................... A.3
Table D.1 Binary Message List.............................................................................................................. D.1
Table D.2 ASCII Configuration Message List....................................................................................... D.2
Table D.3 A5C0 Relay Definition Block ............................................................................................... D.2
Table D.4 A5C1 Fast Meter Configuration Block ................................................................................. D.2
Table D.5 A5D1 Fast Meter Data Block................................................................................................ D.4
Table D.6 A5C2/A5C3 Demand/Peak Demand Fast Meter Configuration Messages........................... D.4
Table D.7 A5D2/A5D3 Demand/Peak Demand Fast Meter Message ................................................... D.5
Table D.8 A5CE Fast Operate Configuration Block.............................................................................. D.6
Table D.9 A5E0 Fast Operate Remote Bit Control................................................................................ D.7
Table D.10 A5E3 Fast Operate Breaker Control ..................................................................................... D.7
Table G.1 Modbus Query Fields ............................................................................................................ G.1
Table G.2 SEL-551 Modbus Function Codes ........................................................................................ G.2
Table G.3 SEL-551 Modbus Exception Codes ...................................................................................... G.2
Table G.4 01h Read Coil Status Commands.......................................................................................... G.3

vi List of Tables
SEL-551 Relay Instruction Manual Date Code 20110408
Table G.5 02h Read Input Status Command ..........................................................................................G.4
Table G.6 03h Read Holding Register Command..................................................................................G.5
Table G.7 04h Read Holding Register Command..................................................................................G.5
Table G.8 05h Force Single Coil Command ..........................................................................................G.6
Table G.9 SEL-551 Command Coils......................................................................................................G.6
Table G.10 06h Preset Single Register Command ...................................................................................G.7
Table G.11 07h Read Exception Status Command ..................................................................................G.7
Table G.12 08h Loopback Diagnostic Command ....................................................................................G.8
Table G.13 10h Preset Multiple Registers Command ..............................................................................G.9
Table G.14 64h Scattered Register Read Command ..............................................................................G.10
Table G.15 SEL-551 Modbus Command Region...................................................................................G.11
Table G.16 Modbus Command Codes....................................................................................................G.11
Table G.17 Assign Event Report Channel Using Address 00B2 ........................................................... G.13
Table G.18 Modbus Map........................................................................................................................G.13

Date Code 20110408 Instruction Manual SEL-551 Relay
List of Figures
Figure 1.1 SEL-551 Relays Applied Throughout the Power System...................................................... 1.2
Figure 1.2 SEL-551 Inputs, Outputs, and Communications Port............................................................ 1.3
Figure 1.4 SEL-551 Instantaneous Overcurrent Element Pickup Time Curve........................................ 1.7
Figure 1.5 SEL-551 Relay Instantaneous Overcurrent Element Reset Time Curve................................ 1.7
Figure 2.1 SEL-551 Dimensions, Panel Cutout, and Drill Plan .............................................................. 2.2
Figure 2.2 Relay Dimensions and Drill Plan for Mounting Two SEL-500 Series Relays Together
Using Mounting Block (SEL P/N 9101) ............................................................................ 2.3
Figure 2.3 Relay Dimensions and Drill Plan for Mounting an SEL-551 With Rack Mount Bracket
9100 (Bracket on Right Side in Front View)...................................................................... 2.4
Figure 2.4 SEL-551 Fitted with Mounting Bracket (SEL P/N 9100) for Mounting
in 19-Inch Rack .................................................................................................................. 2.4
Figure 2.5 SEL-551 Front Panel, Rack-Mount Version (Half-Rack Width)........................................... 2.5
Figure 2.6 SEL-551 Front Panel, Panel-Mount Version ......................................................................... 2.5
Figure 2.7 SEL-551 Rear Panel (Conventional Terminal Blocks Option) .............................................. 2.6
Figure 2.8 SEL-551 Rear Panel (Plug-In Connectors Option) ................................................................ 2.7
Figure 2.9 SEL-551 Provides Overcurrent Protection and Reclosing for a Utility Distribution
Feeder (Includes Fast Bus Trip Scheme)............................................................................ 2.9
Figure 2.10 SEL-551 Provides Overcurrent Protection for an Industrial Distribution Feeder
(Core-Balance Current Transformer Connected to Current Input Channel IN)............... 2.10
Figure 2.11 SEL-551 Provides Overcurrent Protection for a Delta-Wye Transformer Bank ................. 2.11
Figure 2.12 SEL-551 Provides Overcurrent Protection for a Transformer Bank with a Tertiary
Winding ............................................................................................................................ 2.12
Figure 2.13 SEL-551 Provides Overcurrent Protection for a Distribution Bus (Includes Fast Bus
Trip Scheme) ....................................................................................................................2.13
Figure 2.14 SEL-551 Provides Dedicated Breaker Failure Protection.................................................... 2.14
Figure 2.15 Input and Output Jumper Locations (SEL-551 Relay With the Conventional Terminal
Blocks With Jumper-Selectable Control Input Voltage Option)...................................... 2.16
Figure 2.16 Output Contact OUT4 Control Jumper Location................................................................. 2.17
Figure 3.1 Example Operation of SEL-551 Optoisolated Inputs ............................................................ 3.3
Figure 3.2 Local Control Switches Drive Local Bits LB1–LB8 ............................................................. 3.5
Figure 3.3 Remote Control Switches Drive Remote Bits RB1–RB8 ...................................................... 3.8
Figure 3.4 Phase Instantaneous Overcurrent Elements 50P1–50P6........................................................ 3.9
Figure 3.5 Single-Phase Instantaneous Overcurrent Elements 50A, 50B, and 50C.............................. 3.10
Figure 3.6 Neutral Ground Instantaneous Overcurrent Elements 50N1 and 50N2............................... 3.10
Figure 3.7 Residual Ground Instantaneous Overcurrent Elements 50G1 and 50G2............................. 3.11
Figure 3.8 Negative-Sequence Instantaneous Overcurrent Elements 50Q1 and 50Q2 ......................... 3.11
Figure 3.9 Phase Time-Overcurrent Elements 51P1T and 51P2T......................................................... 3.12
Figure 3.10 Neutral Ground Time-Overcurrent Element 51N1T ............................................................ 3.15
Figure 3.11 Residual Ground Time-Overcurrent Element 51G1T .......................................................... 3.15
Figure 3.12 Negative-Sequence Time-Overcurrent Elements 51Q1T and 51Q2T.................................. 3.16
Figure 3.13 Trip Logic............................................................................................................................. 3.17
Figure 3.14 Close Logic .......................................................................................................................... 3.20
Figure 3.15 Reclosing Relay States and General Operation.................................................................... 3.22
Figure 3.16 Reclosing Sequence From Reset to Lockout With Factory Settings ................................... 3.25
Figure 3.17 Voltage Relay (27/59) Provides Reclose Block Signal to SEL-551 .................................... 3.32
Figure 3.18 Sequence Coordination Between the SEL-551 and a Line Recloser ................................... 3.35
Figure 3.19 Operation of SEL-551 Shot Counter for Sequence Coordination With Line Recloser
(Additional Settings Example 1) ...................................................................................... 3.35
Figure 3.20 Operation of SEL-351 Relay Shot Counter for Sequence Coordination With Line
Recloser (Additional Setting Example 2)......................................................................... 3.37
Figure 3.21 SELOGIC Control Equation Variables/Timers ...................................................................... 3.38
Figure 3.22 Dedicated Breaker Failure Scheme Created With SELOGIC Variables/Timers.................... 3.39
Figure 3.23 Logic Flow for Example SEL-551 Output Contact Operation............................................. 3.40
Figure 3.24 Response of Thermal Demand Ammeter to a Step Input
(Setting DMTC = 15 minutes).......................................................................................... 3.42
Figure 3.25 Voltage VSApplied to Series RC Circuit............................................................................. 3.43
Figure 3.26 Demand Current Logic Outputs ........................................................................................... 3.44
Figure 3.27 Raise Pickup of Residual Ground Time-Overcurrent Element for Unbalance Current ....... 3.45

viii List of Figures
SEL-551 Relay Instruction Manual Date Code 20110408
Figure 4.1 U.S. Moderately Inverse Curve: U1 .......................................................................................4.4
Figure 4.2 U.S. Inverse Curve: U2...........................................................................................................4.5
Figure 4.3 U.S. Very Inverse Curve: U3..................................................................................................4.6
Figure 4.4 U.S. Extremely Inverse Curve: U4.........................................................................................4.7
Figure 4.5 U.S. Short-Time Inverse Curve: U5 .......................................................................................4.8
Figure 4.6 IEC Class A Curve (Standard Inverse): C1............................................................................4.9
Figure 4.7 IEC Class B Curve (Very Inverse): C2 ................................................................................4.10
Figure 4.8 IEC Class C Curve (Extremely Inverse): C3........................................................................4.11
Figure 4.9 IEC Long-Time Inverse Curve: C4 ......................................................................................4.12
Figure 4.10 IEC Short-Time Inverse Curve: C5 ......................................................................................4.13
Figure 5.1 Nine-Pin Serial Communications Port Connector..................................................................5.1
Figure 6.1 SEL-551 Front-Panel Pushbuttons—Overview ......................................................................6.1
Figure 6.2 SEL-551 Front-Panel Pushbuttons—Primary Functions........................................................6.2
Figure 6.3 SEL-551 Front-Panel Pushbuttons-Primary Functions (continued) .......................................6.3
Figure 6.4 SEL-551 Front-Panel Pushbuttons-Secondary Functions.......................................................6.4
Figure 6.5 Local Control Switch Configured as an ON/OFF Switch ......................................................6.7
Figure 6.6 Local Control Switch Configured as an OFF/MOMENTARY Switch ..................................6.7
Figure 6.7 Local Control Switch Configured as an ON/OFF/MOMENTARY Switch............................6.7
Figure 7.1 Example Event Summary .......................................................................................................7.3
Figure 7.2 Example SEL-551 Standard 15-Cycle Event Report (1/8-Cycle Resolution)......................7.14
Figure 7.3 Derivation of Event Report Current Values and RMS Current Values From Sampled
Current Waveform ............................................................................................................7.15
Figure 7.4 Derivation of Phasor RMS Current Values From Event Report Current Values ..................7.16
Figure 7.5 Example Sequential Events Recorder (SER) Event Report .................................................7.17
Figure 8.1 Low-Level Test Interface ........................................................................................................8.2
Figure 8.2 Relay Part Number and Hardware Identification Sticker .......................................................8.5
Figure 8.3 Test Connections for Balanced Load With Three-Phase Current Sources .............................8.9
Figure 8.4 Test Connections for Balanced Load With Two-Phase Current Sources................................8.9
Figure B.1 EPROM Socket...................................................................................................................... B.2
Figure B.2 Insertion of the Extraction Tool in the EPROM Socket ........................................................ B.3
Figure B.3 Proper Orientation of the EPROM and EPROM Socket ....................................................... B.3
Figure F.1 Minimum Response Time Added to a Negative-Sequence Time-Overcurrent Element ........F.2
Figure F.2 Distribution Feeder Protective Devices .................................................................................. F.3
Figure F.3 Traditional Phase Coordination ..............................................................................................F.4
Figure F.4 Phase-to-Phase Fault Coordination.........................................................................................F.5
Figure F.5 Negative-Sequence Overcurrent Element Derived From “Equivalent” Phase
Overcurrent Element, 51EP ................................................................................................F.6

Date Code 20110408 Instruction Manual SEL-551 Relay
Preface
Manual Overview
The SEL-551 Relay Instruction Manual describes common aspects of relay
application and use. It includes the necessary information to install, set, test,
and operate the relay and more detailed information about settings and
commands.
An overview of each manual section and topics follows:
Preface. Describes the manual organization and conventions used to
present information.
Section 1: Introduction and Specifications. Describes the basic features
and functions of the SEL-551; lists the relay specifications.
Section 2: Installation. Describes how to mount and wire the SEL-551;
illustrates wiring connections for various applications.
Section 3: Relay Elements and Logic.Describes operating characteristics
of elements through the use of logic diagrams and text and explains
how to calculate their settings; describes contact output logic.
Section 4: Setting the Relay.Describes how to enter and record settings.
Section 5: Serial Port Communications and Commands. Describes how to
connect the SEL-551 to a PC for communication; shows serial port
pinouts; lists and defines serial port commands.
Section 6: Front-Panel Interface.Explains the features and use of the front
panel, including front-panel command menu, default displays, and
automatic messages.
Section 7: Standard Event Reports and SER.Describes event summary
data, standard event reports, and Sequential Events Recorder (SER)
report.
Section 8: Testing and Troubleshooting.Describes protection element test
procedures, relay self-test, and relay troubleshooting.
Section 9: Appendices. Contains the following appendices:
Appendix A: Firmware and Manual Versions
Appendix B: Firmware Upgrade Instructions
Appendix C: SEL Distributed Port Switch Protocol
Appendix D: Configuration, Fast Meter, and Fast Operate Commands
Appendix E: Compressed ASCII Commands
Appendix F: Setting Negative-Sequence Overcurrent Elements
Appendix G: Modbus RTU Communications Protocol
SEL-551 Command Summary. Briefly describes the serial port commands
that are fully described in Section 5: Serial Port Communications
and Commands.

x
SEL-551 Relay Instruction Manual Date Code 20110408
Preface
Conventions
Typographic
Conventions
There are three ways to communicate with the SEL-551:
➤Using a command line interface on a PC terminal emulation
window.
➤Using the front-panel menus and pushbuttons.
➤Using ACSELERATOR QuickSet®SEL-5030 Software
The instructions in this manual indicate these options with specific font and
formatting attributes. The following table lists these conventions:
Typographic Conventions
Examples This instruction manual uses several example illustrations and instructions to
explain how to effectively operate the SEL-551. These examples are for
demonstration purposes only; the firmware identification information or
settings values included in these examples may not necessarily match those in
the current version of your SEL-551.
Safety Information This manual uses three kinds of hazard statements, formatted as follows:
Indicates a potentially hazardous
situation that, if not avoided, may
result in minor or moderate injury or
equipment damage.
!
CAUTION
Indicates a potentially hazardous
situation that, if not avoided, could
result in death or serious injury.
!
WARNING
Indicates an imminently hazardous
situation that, if not avoided, will
result in death or serious injury.
!
DANGER
Example Description
STATUS Commands typed at a command line interface on a PC.
<Enter> Single keystroke on a PC keyboard.
<Ctrl+D> Multiple/combination keystroke on a PC keyboard.
Start > Settings PC software dialog boxes and menu selections.
The > character indicates submenus.
{CLOSE} Relay front-panel pushbuttons.
ENABLE Relay front- or rear-panel labels.
MAIN > METER Relay front-panel LCD menus and relay responses visible on
the PC screen.
The > character indicates submenus.

Date Code 20110408 Instruction Manual SEL-551 Relay
Section 1
Introduction and Specifications
Overview
The SEL-551 Overcurrent Relay and Reclosing Relay provides overcurrent
protection and up to four shots of reclosing in one compact package. The relay
measures phase and neutral currents—no voltages.
SEL-551 Feature
Highlights
➤Numerous Phase, Ground, and Negative-Sequence Overcurrent
Elements
➤Multiple-Shot Reclosing Relay with Sequence Coordination
➤Enhanced SELOGIC®Control Equations to Create Traditional
or Advanced Schemes
➤Local/Remote Control Logic to Enable/Disable Schemes,
Operate Circuit Breakers, etc.
➤Sequential Events Recorder (SER) Report and Event Reports
Stored in Nonvolatile Memory
➤Hardware Options for Rear-Panel Terminals, Output Contacts,
and Serial Communications Port
➤Demand Ammetering
Use the SEL-551 for
Overcurrent
Protection in New
Installations and
Retrofits
➤Utility Distribution Feeders—includes reclosing
➤Industrial Distribution Feeders—includes connections for a
core-balance current transformer
➤Distribution Buses—includes fast bus trip scheme
➤Transformer Banks—includes connections for a separate
neutral current transformer
➤Other Power System Apparatus—capacitors, reactors, circuit
breakers, etc.
Differences Between
the SEL-551/SEL-551C
Relays
The SEL-551C Relay differs from the SEL-551 Relay in the following major
areas:
➤Different I/O mix.
SEL-551 SEL-551C
5 output contacts
(OUT1–OUT4, ALARM)
3 output contacts
(OUT1–OUT3)
2 input contacts
(IN1, IN2)
6 input contacts
(IN1–IN6)

1.2
SEL-551 Relay Instruction Manual Date Code 20110408
Introduction and Specifications
SEL-551 Model Changes
➤Relay Word bit differences because of I/O mix and addition of
programmable alarm conditions SALARM and HALARM.
➤Latch Control Switches to Replace Traditional Latching
Relays.
➤Optional front-panel EIA-232 serial communications port.
➤Available with conventional terminal blocks and level-sensitive
optoisolated inputs (see Specifications, General on page 1.4 for
optoisolated inputs ratings).
SEL-551 Model Changes
Old model 05510J has been superseded by model 05510W. This is because of
improvements in the Connectorized®SEL-551 Relay (plug-in connectors)—
see Section 2: Installation for more details (following Figure 2.8). Unless
otherwise noted, references to model 05510W also apply to old model 05510J.
SEL-551 Applications
qSee Figure 2.14; wsee Figure 2.11; esee Figure 2.13; rsee Figure 2.9; tsee Figure 2.10.
Figure 1.1 SEL-551 Relays Applied Throughout the Power System
52
SEL-551
BF
Initiate
BF
Trip
Transmission Bus
ABC
Retrip
52
SEL-551
ABC
Trip
BF
Trip
N
Trip
ABC
SEL-551
52
BF
Trip
Breaker
Failure
Protection q
Distribution
Bus
Protection e
Transformer
Bank
Protection w
Fast Bus Trip Scheme
Distribution Bus
Trip
BF SEL-551 ABC
52
Utility Distribution
Feeder Protection
and Reclosing r
52a
or
52b
Trip and
Close
ABC
Trip
BF SEL-551 Trip
52
N
Core-Balance
Current Transformer
Industrial Distribution
Feeder Protection t

1.3
Date Code 20110408 Instruction Manual SEL-551 Relay
Introduction and Specifications
Hardware Overview
Hardware Overview
➤Rear-panel: conventional terminal blocks or plug-in connectors
(see Figure 2.7 and Figure 2.8)
➤High-current interrupting output contacts: 10 A for L/R =
40 ms at 125 Vdc (included in the rear-panel plug-in
connectors option only—see Figure 2.8)
➤Rear-panel serial communications port: EIA-232 or EIA-485
(4-wire)-either option includes a demodulated IRIG-B time-
code input (see Figure 2.7 and Figure 2.8)
qSee Figure 2.8; wsee Figure 2.10; esee Figure 2.11; rsee Figure 2.12; tsee Figure 2.9, Figure 2.13, and Figure 2.14.
Figure 1.2 SEL-551 Inputs, Outputs, and Communications Port
time-code input)
(includes
demodulated
IRIG-B
–
+
Supply
Power
– Ground residual circuit
current transformer
– Tertiary winding
current transformer
– Separate neutral
current transformer
– Core-balance
channel IN to:
neutral current input
Connect the separate
connectors option only)
in the rear-panel plug-in
connector available (included
Unique current input channel
Serial Port
EIA-485
or
EIA-232
GND
– Breaker status
– Overcurrent element
torque-control
to assert optoisolated inputs.
Apply nominal dc control voltage
Example Functions:
Optoisolated Inputs
Programmable
plug-in connectors option.
output contacts in the rear-panel
with the high-current interrupting
There is a polarity dependence
– Breaker failure
– Close
– Trip
Example Functions:
Output Contacts
Programmable
IN2
IN1
ALARM
OUT4
IN
OUT3
OUT2
OUT1
IC
IB
IA
SEL-551 RELAY
q
w
e
r
t
q

1.4
SEL-551 Relay Instruction Manual Date Code 20110408
Introduction and Specifications
Specifications
Specifications
Section 1 Introduct ion and Specifica tions
General
AC Input Currents
5 A nominal: 15 A continuous, 500 A for 1 s,
linear to 100 A symmetrical.
Limiting Dynamic
Valu e:
1250 A for 1 cycle (sinusoidal
waveform)
Burden: 0.16 VA at 5 A
1.15 VA at 15 A
1 A nominal: 3 A continuous, 100 A for 1 s,
linear to 20 A symmetrical.
Limiting Dynamic
Valu e:
250 A for 1 cycle (sinusoidal
waveform)
Burden: 0.06 VA at 1 A
0.18 VA at 3 A
Power Supply
125/250 Vdc or Vac
Range: 85–350 Vdc or 85–264 Vac
Burden: <6.2 W
Interruption: 100 ms at 250 Vdc
Ripple: 100%
48/125 Vdc or 125 Vac
Range: 36–200 Vdc or 85–140 Vac
Burden: <5.5 W
Interruption: 100 ms at 125 Vdc
Ripple: 5%
24 Vdc
Range: 16–36 Vdc polarity dependent
Burden: <6.2 W
Interruption: 25 ms at 36 Vdc
Ripple: 5%
Note: Interruption and Ripple per IEC 60255-11:1979.
Output Contacts
Conventional Terminal Blocks Option:
Per IEC 255-0-20:1974, using the simplified method of assessment
Make: 30 A
Carry: 6 A continuous carry
1 s Rating: 100 A
MOV Protection: 270 Vac/360 Vdc
Pickup Time: <5 ms
Dropout Time: <5 ms
Breaking Capacity (10000 operations):
24 V 0.75 A L/R = 40 ms
48 V 0.50 A L/R = 40 ms
125 V 0.30 A L/R = 40 ms
250 V 0.20 A L/R = 40 ms
Cyclic Capacity (2.5 cycle/second):
24 V 0.75 A L/R = 40 ms
48 V 0.50 A L/R = 40 ms
125 V 0.30 A L/R = 40 ms
250 V 0.20 A L/R = 40 ms
Plug-In Connectors Option on SEL-551
(High Current Interrupting):
Make: 30 A
Carry: 6 A continuous carry
MOV Protection: 330 Vdc
Pickup Time: <5 ms
Dropout Time: < 8 ms, typical
Breaking Capacity (10000 operations):
24 V 10.0 A L/R = 40 ms
48 V 10.0 A L/R = 40 ms
125 V 10.0 A L/R = 40 ms
250 V 10.0 A L/R = 20 ms
Cyclic Capacity (4 cycles in 1 second followed by 2 minutes idle
for thermal dissipation):
24 V 10.0 A L/R = 40 ms
48 V 10.0 A L/R = 40 ms
125 V 10.0 A L/R = 40 ms
250 V 10.0 A L/R = 20 ms
Note: Do not use high current interrupting output contacts to
switch ac control signals. These outputs are polarity dependent.
Note: Make per IEEE C37.90:1989; Breaking and Cyclic Capacity
per IEC 60255-23 [IEC 255-23]:1994.
Optoisolated Inputs
Note: The input type is dependent on the relay ordering options.
Level-sensitive inputs differ from jumper-selectable inputs in that
they are guaranteed to deassert below a certain voltage level and
they are not user-settable. The inputs are not polarity dependent.
With nominal control voltage applied, each input draws
approximately 4 mA of current.
Conventional Terminal Blocks Option
Note: The conventional terminal blocks model of the SEL-551 can
be ordered with either jumper-selectable voltage optoisolated
inputs or level-sensitive optoisolated inputs.
Jumper Selectable Control Voltage:
Both inputs may be individually user-configured to operate on
any of the following nominal voltages:
24 Vdc: on for 15–30 Vdc (also available on
the SEL-551C, but not jumper
selectable)
48 Vdc: on for 30–60 Vdc
125 Vdc: on for 80–150 Vdc
250 Vdc: on for 150–300 Vdc
Level-Sensitive:
Both inputs are factory configured for a fixed voltage level that
cannot be changed:
48 Vdc: on for 38.4–60 Vdc;
off below 28.8 Vdc
110 Vdc: on for 88–132 Vdc;
off below 66 Vdc
125 Vdc: on for 105–150 Vdc;
off below 75 Vdc
220 Vdc on for 176–264 Vdc;
off below 132 Vdc
250 Vdc: on for 200–300 Vdc;
off below 150 Vdc
Plug-In Connectors Option
Standard (Non-Level Sensitive):
24 Vdc: on for 15–30 Vdc
Level-Sensitive:
The plug-in connectors model is equipped with fixed “level-
sensitive” inputs. Both inputs are factory-configured to the
control voltage specified at the time of ordering:
48 Vdc: on for 38.4–60 Vdc;
off below 28.8 Vdc
110 Vdc: on for 88–132 Vdc;
off below 66 Vdc
125 Vdc: on for 105–150 Vdc;
off below 75 Vdc

1.5
Date Code 20110408 Instruction Manual SEL-551 Relay
Introduction and Specifications
Specifications
250 Vdc: on for 200–300 Vdc;
off below 150 Vdc
Frequency and Rotation
System Frequency: 50 or 60 Hz
Phase Rotation: ABC or ACB
Serial Communications
9-pin sub-D connector
Baud Rate: 300, 1200, 2400, 4800, 9600, 19200,
38400; settable baud rate and
protocol
Protocols
ASCII
Distributed Port Switch Protocol (LMD)
Modbus® RTU (rear port only; baud rate limited to 19200)
Operating Temperature
IEC Performance Rating: –40°to +85°C (–40°to +185°F)
Humidity
0% to 95% without condensation
Altitude
2000 m maximum
Operating Environment
Pollution Degree: 2
Overvoltage Category: II
Indoor Use
Tightening Torque
Terminal Block:
Minimum: 0.9 N-m (8-inch-pounds)
Maximum: 1.4 N-m (12-inch-pounds)
Connectorized®
Minimum: 0.5 N-m (4.4-inch-pounds)
Maximum: 1.0 N-m (8.8-inch-pounds)
Terminal Connections
Terminals or stranded copper wire. Ring terminals are
recommended. Minimum temperature rating of 105°C.
Routine Dielectric Strength
AC current inputs: 2500 Vac for 10 s
Power supply,
optoisolated inputs,
and output contacts: 3000 Vdc for 10 s
The following IEC 60255-5 Dielectric Tests:1977 are performed on all
units with the CE mark:
2500 VAC for 10 s on analog inputs.
3100 Vdc for 10 s on power supply, optoisolated inputs, and output
contacts.
Weight
2.5 kg (5 lbs, 8 oz.)
Type Tests
Environmental Tests
Cold: IEC 60068-2-1:1990 +A1:1993
+A2:1994 [BS EN 60068-2-1:1993
+REAF:2005]
Test Ad; 16 hr at –40°C
Damp Heat Cyclic: IEC 60068-2-30:1980
Test Db; 25° to 55°C,
6 cycles, 95% humidity
Damp Heat Steady State IEC 60068-2-3:1969
Test Ca; 40°C ±2°C,
93% humidity +2%, –3%
4 days, Energized > 1 day
Dry Heat: IEC 60068-2-2:1974 +A1:1993
+A2:1994 [BS EN 60068-2-2:1993
+REAF:2005]
Test Bd: 16 hr at +85°C
Dielectric Strength and Impulse Tests
Dielectric: IEC 60255-5:1977
IEEE C37.90-1989
2500 Vac on analog inputs;
3100 Vdc (3000 Vdc for
Plug-in Connectors option)
on power supply, contact inputs,
and contact outputs
Impulse: IEC 60255-5:1977 0.5 J, 5000 V
Electrostatic Discharge Test
ESD: IEC 60255-22-2:1996
[BS EN 60255-22-2:1997]
IEC 801-2:1991 Level 4
RFI and Interference Tests
Fast Transient
Disturbance:
IEC 60255-22-4:1992
IEC 801-4:1988 Level 4
Radiated EMI: IEC 60255-22-3:1989
IEC 801-3:1984
IEEE C37.90.2-1987
Surge Withstand: IEC 60255-22-1:1988
2.5 kV peak common mode,
1.0 kV peak differential mode
IEEE C37.90.1-1989
3.0 kV oscillatory; 5.0 kV fast
transient
Vibration and Shock Tests
Shock and Bump: IEC 60255-21-2:1988
[BS EN 60255-21-2:1996
+A1:1996] Class 2
IEC 60255-21-3:1993
[BS EN 60255-21-3:1995
+A1:1996] Class 2
Sinusoidal Vibration: IEC 60255-21-1:1988
[BS EN 60255-21-1:1996
+A1:1996]
Class 1 Endurance,
Class 2 Response
Object Penetration
Object Penetration: IEC 60529:1989 IP 30, IP 54 from the
front panel using the SEL-9103
front- cover dust and splash
protection
Product Safety
C22.2 No. 14-95
UL 508
Certifications
ISO: Relay designed and manufactured using ISO 9001 certified
quality program.
Processing Specifications
8 times per power system cycle
Metering Accuracy
Instantaneous and Demand Ammetering Functions.
Currents IA, IB, IC
5 A Nominal: ±2% (0.5–80.0 A)
1 A Nominal: ±2% (0.1–16.0 A)
Currents IN
5 A Nominal: ±5% (0.5–80.0 A)
1 A Nominal: ±5% (0.1–16.0 A)

1.6
SEL-551 Relay Instruction Manual Date Code 20110408
Introduction and Specifications
Overcurrent Elements
Section 1
Introduction and Specifications
Overcurrent Elements
The OFF setting disables the overcurrent element.
Time-Overcurrent
Element
Specifications
See Section 4: Setting the Relay for complete setting range information.
Instantaneous
Overcurrent Element
Specifications
See Section 4: Setting the Relay for complete setting range information.
Instantaneous
Overcurrent Element
Pickup and Reset
Time Curves
Figure 1.4 and Figure 1.5 show pickup and reset time curves applicable to all
the instantaneous overcurrent elements in the SEL-551 (60 Hz or 50 Hz
relays). These times do not include output contact operating time and, thus,
are accurate for determining element operating time for use in internal
SELOGIC control equations. See Output Contacts on page 1.4 for information
on output contact operating times (pickup/dropout time). Output contact
operating time has to be added to the pickup time given in Figure 1.4 to
calculate the overall instantaneous overcurrent element tripping time.
Table 1.1 Overcurrent Elements
Instantaneous Time-Overcurrent
Phase 50P1–50P6 51P1T, 51P2T
Single-Phase 50A, 50B, 50C
Neutral Grounda
aThe neutral ground overcurrent elements (50N1, 50N2, and 51N1T) operate from the separate
neutral current input channel IN. All other overcurrent elements (including the residual ground
overcurrent elements) operate from the phase current input channels IA, IB, and IC.
50N1, 50N2 51N1T
Residual Ground 50G1, 50G2 51G1T
Negative-Sequence (3I2)b
bIMPORTANT: See Appendix F: Setting Negative-Sequence Overcurrent Elements for information
on setting negative-sequence overcurrent elements
50Q1, 50Q2 51Q1T, 51Q2T
Setting Range,
5 A nominalc
cThe available current channel ratings (5 A or 1 A) for phase (IA, IB, and IC) and neutral (IN) are
specified separately-refer to the ordering information sheets for the SEL-551.
OFF, 0.5–80.0A OFF, 0.5–16.0A
Setting Range,
1 A nominalc
OFF, 0.1–16.0A OFF, 0.1–3.2A
Pickup Accuracy: ±0.10 A secondary and ±5% of setting
(5 A nominal channel)
±0.02 A secondary and ± 5% of setting
(1 A nominal channel)
Curve Timing Accuracy: ±1.5 cycles, and ±2% (Inom/Isec), and ±4% of curve time for
currents between (and including) 2 and 30 multiples of
pickup
Curves operate on definite-time for currents above 30 multi-
ples of pickup or 16 times nominal current.
Transient overreach: <5% of pickup
Pickup Accuracy: ±0.10 A secondary and ±5% of setting
(5 A nominal channel)
±0.02 A secondary and ±5% of setting
(1 A nominal channel)
Transient overreach: <5% of pickup

1.7
Date Code 20110408 Instruction Manual SEL-551 Relay
Introduction and Specifications
CT Saturation Protection
Figure 1.4 SEL-551 Instantaneous Overcurrent Element Pickup Time Curve
Figure 1.5 SEL-551 Relay Instantaneous Overcurrent Element Reset Time
Curve
CT Saturation Protection
The SEL-551 phase instantaneous overcurrent elements normally operate
using the output of a cosine filter algorithm. During heavy fault currents when
the relay detects severe CT saturation, the overcurrent elements can operate on
the adaptive current algorithm.
The adaptive current algorithm is only used for phase instantaneous
overcurrent elements if and only if the corresponding pickup setting is greater
than eight times the nominal phase current. For example, if 50P1P = 45 A (in a
5 Amp nominal phase current relay), then the 50P1 element operates on the
adaptive current algorithm. However, if 50P1P = 35 A, then the 50P1 element
operates on the output of a cosine filter algorithm. No other overcurrent
elements use the adaptive current algorithm.
Based on the level of a “harmonic distortion index,” the adaptive current is
either the output of the cosine filter or the output of the bipolar peak detector.
When the harmonic distortion index exceeds the fixed threshold that indicates
severe CT saturation, the adaptive current is the output of the bipolar peak
detector. When the harmonic distortion index is below the fixed threshold, the
adaptive current is the output of the cosine filter.
The cosine filter provides excellent performance in removing dc offset and
harmonics. However, the bipolar peak detector has the best performance in
situations of severe CT saturation when the cosine filter magnitude estimation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.2 2 3 4 5 6 7 8 9 10
Minimum
Maximum
Applied Current (Multiples of Pickup Setting)
Pickup Time (Cycles)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.2 2 3 4 5 6 7 8 9 10
Applied Current (Multiples of Pickup Setting)
Reset Time (Cycles)
Minimum
Maximum

1.8
SEL-551 Relay Instruction Manual Date Code 20110408
Introduction and Specifications
Timer Specifications
is significantly degraded. Combining the two filters provides an elegant
solution for ensuring dependable phase instantaneous overcurrent element
operation.
Timer Specifications
The SEL-551 has reclosing relay timers, programmable timers, and other
timers (see Section 4: Setting the Relay). All timers are set in cycles, in 1/8
cycle (0.125 cycle) increments. The relay rounds the entered time setting up or
down to the nearest 1/8 cycle. For example:
Enter setting
79OI1 = 264.685
and the relay rounds it down to
79OI1 = 264.625
Enter setting
SV10PU = 1567.318
and the relay rounds it up to
SV10PU = 1567.375
The timing accuracy for these timers is: ±0.25 cycles and ±0.1 percent of
setting.