SEL-787-2/-3/-4

Transformer Protection Relay

The SEL-787 series integrates powerful protection features into a compact form factor designed specifically for transformers. Depending on the model, it supports differential protection for two to four terminals (windings) and is optimized for the protection of power transformers, autotransformers, and reactors. Despite its slim design, which can replace larger traditional relays, it is a versatile solution that accommodates the latest sensor technologies and communication protocols.

Key Features

Multi-Terminal Differential Protection (87)

Supports up to four terminals with dual-slope percentage-restrained differential protection to quickly detect internal faults and prevent unnecessary operations during through-faults.
Negative-Sequence Current Differential (87Q)

Provides a negative-sequence percentage-restrained differential element to precisely detect low-magnitude faults, enhancing protection sensitivity.
Restricted Earth Fault (REF)

Includes user-configurable REF elements to sensitively detect internal ground faults in solidly or resistance-grounded wye-connected transformers.
Harmonic Control

Maintains stability during transformer energization or overexcitation through 2nd, 4th, and 5th harmonic blocking and restraint features.
Advanced Sensor Interface Support

Compatible with modern digital equipment, supporting Low-Energy Analog (LEA) voltage sensors, Rogowski coils, and Low-Power Current Transformer (LPCT) inputs.
Enhanced Overcurrent Protection

Includes phase, neutral, residual, and negative-sequence overcurrent elements, supporting settings as low as 5% of nominal current to detect minor abnormal currents.
Improved Breaker Failure Logic

Increases the integrity of system protection with retrip logic, independent breaker failure trip logic, and settable breaker failure seal-in delay.

5-inch Color Touchscreen Display

Features a large 800x480 resolution screen for direct on-site monitoring of mimic diagrams, real-time metering data, and control.
Embedded Web Server

Allows for convenient remote status checks, event record viewing, and setting interrogation via a standard web browser.
High-Reliability Communication Redundancy

Ensures uninterrupted communication even during network path failures by supporting Parallel Redundancy Protocol (PRP) and Rapid Spanning Tree Protocol (RSTP).
Broad Standard Protocol Support

Easily integrates into automated systems with support for IEC 61850 Edition 2, DNP3, Modbus TCP/RTU, EtherNet/IP, and IEEE C37.118-2005 (synchrophasors).
Precision Event Analysis

Enables clear analysis of root causes with high-resolution event reports (32 samples/cycle) and Sequential Events Recorder (SER) functions.
Asset Management and Monitoring

Assists in preventative maintenance with features like transformer thermal modeling, breaker contact wear monitoring, and station battery voltage monitoring.
Flexible Installation Options

Saves panel space with its compact size and offers various I/O slot configurations to meet specific field requirements.