SEL-421

Protection, Automation, and Control System

The SEL-421 is a high-speed line protection, automation, and control system that integrates high-speed distance and directional protection for critical transmission lines with complete control for a two-breaker bay. It is optimized to minimize transmission line damage and reduce repair costs through subcycle distance protection. Additionally, it supports modern digital secondary system technologies such as TiDL and SV, enabling substation modernization.

Key Features

Complete Distance Protection

Provides up to five zones of phase and ground mho and quadrilateral distance protection elements simultaneously.
High-Speed Subcycle Tripping

Uses optional high-speed distance elements to achieve half-cycle processing and subcycle operating speeds, enhancing system stability.
Bay Control and Reclosing

Includes control for up to two breakers and status indication for three breakers, supporting integrated single-pole and three-pole reclosing logic.
High-Accuracy Fault Locator

Accurately pinpoints fault locations, helping line crews quickly isolate problems and restore service faster.
Digital Process Bus Support

Implements SEL TiDL and SV technologies to replace copper wiring with fiber-optic cables, improving safety and reducing construction costs.
Real-Time Synchrophasors

Provides high-precision real-time system state measurement data according to the IEEE C37.118 standard for wide-area monitoring and control.
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Power Swing Blocking and Out-of-Step Tripping

Features blocking logic to prevent unnecessary trips during stable power swings and out-of-step tripping for unstable conditions.
Dual CT Inputs and Flexibility

Allows currents from two sets of CTs to be combined mathematically within the relay or monitored separately, maximizing protection design flexibility.

Front-Panel Display and HMI

Features an LCD that intuitively displays metering values, settings, and system status, supporting mimic displays in a one-line diagram format.
Customizable Interface

Provides programmable target LEDs and pushbuttons, with slide-in labels to easily change functional identification for specific field requirements.
Built-in Web Server

Allows read-only monitoring of relay status, Sequential Events Recorder (SER) data, and metering information via a standard web browser over an Ethernet network.
Powerful Configuration and Analysis Software

Enables offline settings development via ACSELERATOR QuickSet and Grid Configurator, with a Graphical Logic Editor (GLE) for visual editing of complex logic.
Multiple Standard Protocol Support

Supports a wide range of protocols, including IEC 61850 Edition 2.1, DNP3 LAN/WAN, PRP, and PTPv2, for easy integration with existing and new automation systems.
Advanced Equipment Monitoring

Provides real-time monitoring of breaker contact wear and station battery voltage to support proactive maintenance.
Flexible Hardware Options

Offers chassis sizes of 3U, 4U, and 5U with vertical or horizontal mounting options and various I/O board expansion capabilities.