The SEL-321 Relay delivers outstanding extra-high-voltage (EHV) protection, performance, and features-at a price practical for all voltage levels and with the features you need for system integration.
Apply the SEL-321 Relay for primary and/or backup single-or three-pole trip transmission line protection, including series-compensated lines.
Use the advanced single-pole tripping logic with phase selection, open-pole interval protection, and phase discordance logic with three-pole trip to protect against excessive single-pole-open events.
Choose from among the many communications-assisted tripping schemes available (POTT, DCUB, DCB, PUTT, DUTT, and DTT), including unique Mirrored Bits communications.
Select the load-encroachment feature to prevent operation of three-phase elements under high load conditions.
Use the time-overcurrent elements to provide current-dependent, time-delayed fault detection along the protected line and backup protection for remote terminals.
Use weak-infeed logic to rapidly clear both line terminals for internal faults near the weak terminal.
Select the SEL-321-5 Relay for enhanced performance on 50 Hz systems, including single-pole tripping.
Comprehensive and Secure Distance Protection
Four zones of phase and ground mho elements plus four zones ground distance quadrilateral elements, each reversible, with independent phase and ground timers for complete distance protection. Positive-sequence memory voltage polarization with long memory time constant for three-phase fault directional security. Negative-sequence impedance directional element polarization for sensitive and secure operation during unbalanced faults.
Extensive Supplemental Protection Elements and Logic
Four residual and negative-sequence overcurrent elements with negative-sequence directional control. Phase, sequence, and ground time-overcurrent elements for backup protection. Out-of-step elements for power swing blocking and tripping. Phase and sequence under-and over-voltage elements. Load encroachment logic to protect against false operations during heavy load conditions. Single-pole tripping logic. Built-in communications-assisted tripping scheme logic. SELogic control equations for custom scheme logic.
Multiple Settings Groups
Six settings groups, for maximum protection scheme flexibility, allow application with bus-tie breakers or for remote system reconfiguration.
Use the built-in fault locator to efficiently dispatch line inspection and repair personnel.
Patented Mirrored Bits communications and communications-assisted tripping schemes.