Project Description

SEL551/SEL-551C Overcurrent/Reclosing Relay

SEL-551C Overcurrent/Reclosing Relay

The SEL-551C Relay provides overcurrent relay users with new flexibility in distribution system protection. The SEL-551C provides six inputs and three outputs, with up to two communications ports, for more control options. The SELOGIC®control equations have added rising and falling edge triggers and latches for custom logic applications.

Functional Overview

 SEL-551C Functional Overview
50 (P, G, Q) Overcurrent (Phase, Ground, Neg. Seq.)
50N Neutral Overcurrent
51 (P, G, Q) Time-Overcurrent (Phase, Ground, Neg. Seq.)
51N Neutral Time-Overcurrent
79 Auto-Reclosing
DFR Event Reports
LGC SELOGIC Control Equations


Front- and Rear-Panel Diagrams

SEL-551C Front Panel SEL-551C Rear Panel
Front Rear


Complete Overcurrent Protection

Protect lines and equipment using a sensitive and secure mix of phase, negative-sequence, and ground overcurrent elements. Have complete ground fault protection with residual ground and neutral ground overcurrent elements. Provide high-speed operation, even with severe CT saturation, using the SEL Adaptive Overcurrent Element.

Multishot Reclosing With Sequence Coordination

Program up to a four-shot reclose sequence with reclose initiate supervision, skip-shot sequencing, and stall-open interval timing.


Integrate into industrial protection and control schemes with Modbus® RTU protocol. Order the serial communications port as either EIA-232 or EIA-485.

Field-Proven With Robust I/O

Program the two inputs and five outputs to meet your application needs using SELogic® control equations. A wide operating temperature range (—40° to +85°C) allows for installation in a control building or outdoor enclosure. Hardware options of high-current interrupting output contacts and plug-in connectors provide high reliability and

ease of installation/removal.

Programmable Logic and Local/Remote Controls

Use acSELErator® QuickSet™ SEL-5030 Software to configure traditional or advanced protection and control schemes. Quickly make logic changes or improvements without rewiring. Use the front panel or serial port to actuate separate control switches.



451 351 351A 751 751A 551/
Distribution Feeder Protection
Breaker Failure Protection f f
Generator Intertie Protection + +
Synchronism Check + +
Underfrequency Load Shedding f
Undervoltage Load Shedding f +
27/59 Under-/Overvoltage +
32 Directional Power Elements f + +
49 Thermal Overload f
50 (P,N,G,Q) Overcurrent Element (Phase, Neutral, Ground, Neg. Seq.)
51 (P,N,G,Q) Time-Overcurrent Element (Phase, Neutral, Ground, Neg. Seq.)
67 (P,N,Q) Directional Overcurrent (Phase, Neutral, Neg. Seq.) +
81 Over-/Underfrequency
Separate Neutral Overcurrent
Load-Encroachment Supervision +
Mirrored Bits Communications +
Sensitive Earth Fault Protection + + +
Directional Sensitive Earth Fault Protection + +
Pilot Protection Logic
Rate-of-Change-of-Frequency (df/dt) f +
Harmonic Blocking +
Arc Sense Technology (AST) High-Impedance Fault Detection + +
Arc-Flash Detection + +
Phantom Phase Voltage
Current/Voltage Channels 6/6 4/4 4/4 4/4 4/4 4/0
Complete Two-Breaker Control
79 Automatic Reclosing + +
Fault Locating
SELogic Control Equations With Remote Control Switches
SELogic Counters
Voltage Check on Closing + +
Operator Control Pushbuttons
SELogic Nonvolatile Latch +
Nonvolatile Local Control Switches +
Display Points +
Multiple Settings Groups
Substation Battery Monitor + +
Breaker/Recloser Wear Monitor
Trip Coil Monitor f f f f f f
Voltage Sag, Swell, and Interruption (VSSI) +
Load/Signal Profile Recorder +
Sequential Events Recorder
Demand Meter +
DNP3 Level 2 Outstation + + +
Modbus Outstation +
IEEE C37.118 Synchrophasors
Bay Control
Ethernet + + +
IEC 61850 + + + + +
Simple Time Network Protocol (SNTP)
Independent Trip/Close Pushbuttons + + +
Harmonic Metering
RMS Metering
Standard Feature
+ Model Option
f This function may be created using settings

Product Literature