The SEL-387 Current Differential and Overcurrent Relay provides protection, control, and metering for transformers, buses, breakers, and feeders. Features include four three-phase current inputs with independent restrained and unrestrained differential protection, programmable single- or dual-slope differential characteristic, circuit breaker monitor, battery voltage monitor, and enhanced SELogic control equations.

Applications

Multiwinding Current Differential Protection—Protect power transformers with as many as four windings by using a combination of single- or dual-slope percentage differential characteristics, overcurrent protection, and restricted earth fault (REF) protection. The SEL-387A Current Differential and Overcurrent Relay is a low-cost solution for two-winding transformer protection.

Beyond Typical Transformer Protection—Protect reactors, generators, large motors, and other multiterminal power apparatus. Provide backup distribution bus or feeder protection with low-side overcurrent elements.

Individual Winding Overcurrent Protection—Provide comprehensive overcurrent protection for each winding input with the torque-controllable overcurrent elements. In the SEL-387, the combined current feature sums current from two CTs for ring-bus and breaker-and-a-half overcurrent applications.

Condition-Based Maintenance—Specify optional thermal monitoring to activate a control action or to issue an alarm when the transformer is in danger of excessive insulation aging or loss-of-life. Use through-fault monitoring to gather cumulative through-fault data and to schedule proactive maintenance.