SEL-787Z

High-Impedance Differential Relay and SEL-HZM High-Impedance Module

The SEL-787Z is a flexible protection relay designed primarily for high-impedance bus protection. It provides a high-speed, cost-effective solution for busbars and is also suitable for motor protection or sensitive Restricted Earth Fault (REF) protection on grounded, wye-connected power transformer windings. When combined with the dedicated SEL-HZM High-Impedance Module, it creates a stable and robust differential protection system.

Key Features

High-Impedance Differential Protection (87V)

Designed to provide ultra-fast tripping for in-zone faults while maintaining high security during heavy through-faults and CT saturation.
SEL-HZM Module Integration

Uses a dedicated module with built-in stabilizing resistors and Metal-Oxide Varistors (MOVs) to protect CT wiring and the relay against high-voltage surges during in-zone faults.
Comprehensive Overcurrent Protection

Independent overcurrent elements can be used to complement high-impedance differential elements, providing multiple layers of protection.
Voltage Protection Elements

Includes undervoltage (27) and overvoltage (59) elements to detect abnormal voltage-based conditions.
Arc-Flash Protection

Supports arc-flash detection elements (TOL1–TOL8) with a very fast pickup time of 2–5 ms, minimizing equipment damage and risk to personnel.
Precise Sampling

Processes data with high precision at a rate of 40 samples per cycle for 60 Hz systems and 48 samples per cycle for 50 Hz systems.

5-inch Color Touchscreen Display

An optional large color screen allows for direct on-site system monitoring and setting configuration, supporting multiple languages including English and Spanish.
Broad Protocol Support

Easily integrates into existing automation systems with support for IEC 61850 Edition 2, DNP3, EtherNet/IP, Modbus TCP/RTU, FTP, and Telnet.
Network Reliability

Supports Parallel Redundancy Protocol (PRP) and Rapid Spanning Tree Protocol (RSTP) to ensure continuous data transmission even during communication path failures.
Precision Event Analysis

Features Sequential Events Recorder (SER) and high-resolution event reporting to help clearly analyze the root cause of disturbances.
Precise Time Synchronization

Provides microsecond-level timing accuracy through IEEE 1588 PTP and IRIG-B inputs.