Project Description

SEL-787 Transformer Protection Relay

SEL-787 Transformer Protection Relay

Protect and monitor most industrial transformer applications with the versatile SEL-787 Transformer Protection Relay. Apply 2 three-phase winding inputs, and an optional single-phase restricted earth fault input and three-phase voltage inputs for comprehensive transformer protection. Benefits include advanced automation and flexibility, single or dual, copper or fiber Ethernet communications ports, asset management data, and easy retrofit of most electromechanical relays.

Functional Overview

24 Volts/Hertz
27P Phase Undervoltage
32 Power
49 Thermal
50BF Breaker Failure Overcurrent
50N Neutral Overcurrent
50 (P,G,Q) Overcurrent (Phase, Ground, Neg. Seq.)
51N Neutral Time-Overcurrent
51 (P,G,Q) Time-Overcurrent (Phase, Ground, Neg. Seq.)
59 (P,Q) Overvoltage (Phase, Neg. Seq.)
67G Restricted Earth Fault
81 (O,U) Over-/Underfrequency
87 Current Differential
DFR Event Reports
LGC SELogic Control Equations
PMU Synchrophasors
SER Sequential Events Recorder

* Optional


Front- and Rear-Panel Diagrams

SEL-787 Front Panel SEL-787 Rear Panel
Front Rear


Standard Protection Features

Two-winding dual-slope differential protection with harmonic blocking and restraint. Phase, negative-sequence, residual-ground, and neutral-ground overcurrent elements for backup protection. Breaker failure protection for two three-pole breakers.

Optional Protection Features

Use the SEL-787 with optional voltage inputs to provide volts/hertz protection with frequency tracking from 20 to 70 Hz for generator step-up and other variable frequency applications. Implement load shedding and other control schemes with over- and underfrequency and over- and undervoltage elements. In addition, use Sensitive Restricted Earth Fault (REF) protection for grounded-wye transformers.

Transformer Monitoring

Use transformer through-fault monitoring to measure accumulated through-fault levels of the transformer. Monitor ambient, load tap-changer (LTC) tank and transformer oil temperature using optional 4–20 mA or RTD thermal inputs.

Operator Controls

Four programmable front-panel pushbuttons each with two programmable LEDs allow for a wide variety of uses, including easy trip and close control and status indications for a breaker. Implement local and remote operator control schemes using 32 local and 32 remote control bits.

Relay and Logic Settings Software

ACSELERATOR QuickSet® SEL-5030 Software reduces engineering costs for relay settings and logic programming. Tools in ACSELERATOR QuickSet make it easy to develop SELOGIC® control equations. Use the built-in phasor display to verify proper CT polarity and phasing.

Metering and Reporting

Built-in metering functions eliminate separately mounted metering devices. Analyze Sequential Events Recorder (SER) reports and oscillographic event reports for rapid commissioning, testing, and post-fault diagnostics. Unsolicited SER protocol allows station-wide collection of binary SER messages.

Additional Standard Features

Includes Modbus® RTU, Event Messenger support, MIRRORED BITS® communications, load profile, support for 12 external RTDs (SEL-2600 series module), IRIG-B input, advanced SELOGIC, configurable labels, IEEE C37.118-compliant synchrophasor protocol, and SEL-2812 compatible ST® connectors fiber-optic serial port.

Optional Features

Select from a wide offering of optional features, including IEC 61850, Modbus TCP/IP, Simple Network Time Protocol (SNTP), DNP3 LAN/WAN, DNP3 Serial, 10 internal RTDs, expanded digital/analog I/O, voltage inputs, additional EIA-232 or EIA-485 communications ports, and single or dual, copper wire or fiber-optic Ethernet ports.


487E 387E 387 387A 787 787-3E 787-3S 787-4X 587
Breaker Failure Protection f f f f
Transformer and Machine Current Differential
Low-Impedance Bus Differential
Underfrequency Load Shedding f +
Undervoltage Load Shedding f +
Three-Phase Current Inputs 5 3 4 2 2 3 3 4 2
Three-Phase Voltage Inputs 2 1 1+ 1 1
24 Overexcitation (Volts/Hertz) +
25 Synchronism Check
27/59 Under-/Overvoltage +
32 Directional Power +
46 Current Unbalance
49 Equipment Thermal Monitoring +
50FO Flashover Protection f f f f f f
50 (N,G) Overcurrent (Neutral, Ground)
50P Phase Overcurrent
50Q Negative-Sequence Overcurrent
51 (N,G) Time-Overcurrent (Neutral, Ground)
51P Phase Time-Overcurrent
51Q Negative-Sequence Time-Overcurrent
67 (P,G,Q) Directional Overcurrent (Phase, Ground, Neg. Seq.)
81 Under-/Overfrequency +
81R Change-in-Rate-of-Frequency f
87 Current Differential
REF Restricted Earth Fault + +
SELogic Control Equations
Voltage Check on Closing f f f
Transformer Cooling Fan Control f f f f f
Nonvolatile Latch Control Switches
SELogic Remote Control Switches
SELogic Local Control Switches
Display Points
Multiple Settings Groups
Substation Battery Monitor
Breaker Wear Monitor
Event Report (Multicycle Data)
Sequential Events Recorder
Instantaneous Meter
Demand Meter
Load and Temperature Profile Report
RTD (Resistance Temperature Detector) Inputs + + + +
Built-In Web Server
IEEE C37.118 Synchrophasors
IEC 61850 + + + + + +
IEC 60870-5-103 + + +
Simple Network Time Protocol (SNTP)
Parallel Redundancy Protocol (PRP)
Through-Fault Monitor +
2600 RTD Module Communications
Thermal Model +
Connectorized (Quick Disconnect) Available + + + + + + +
Standard Feature
+ Model Option
f This function may be created using settings

Product Literature