Voltage protection relay / digital / programmable / configurable
SEL-421 Schweitzer Engineering Laboratories


  • Measured/monitored value:


  • Other characteristics:

    digital, programmable, configurable, for recloser control


Protection, Automation, and Control System
Apply the SEL-421 Protection, Automation, and Control System for high-speed distance and directional protection and complete control of a two-breaker bay.

Protect any transmission line using a combination of five zones of phase- and ground-distance and directional overcurrent elements. A graphical user interface system provides logic and application templates for typical line protection schemes. Patented Coupling Capacitance Voltage Transformer (CVT) transient overreach logic enhances the security of Zone 1 distance elements. Best Choice Ground Directional Element logic optimizes directional element performance and eliminates many directional settings. Optional additional logic prevents Zone 1 overreach on series-compensated lines. Optional incremental components provide subcycle operation for application on critical lines requiring high-speed fault clearing.


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