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Transmission Protection

SEL revolutionized the protection industry by building the first microprocessor-based protective relays. These relays integrated, economized, and simplified the art of transmission line protection while introducing two powerful tools: fault locating and event reporting.

SEL-411L Advanced Line Differential Protection

Apply the SEL-411L Relay for complete protection and control of any transmission line. The SEL-411L provides differential protection with both phase- and sequence-based operating elements for sensitivity and high-speed operation.

SEL-421 Distance Relay

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.

SEL-311L Line Current Differential Protection

Use the SEL-311L Line Current Differential Relay with integral four zone distance backup for easy-to-apply, high-speed line protection. Apply subcycle current differential protection with included four zone distance and directional overcurrent backup. Use single or dual differential channels for reliability.

SEL-387L Line Current Differential Relay

Use SEL-387L Line Current Differential Relays for economical, easy-to-apply line protection.

SEL-311C Transmission Protection System

Apply the SEL-311C Relay for protection, reclosing, monitoring, and control of transmission lines. Features include a four-shot recloser, patented capacitance voltage transformer (CVT) transient overreach logic to enhance security of Zone 1 distance elements, and overcurrent elements.