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Current Differential and Overcurrent Relay

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.

Starting At

$5,250 USD

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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.

Two-, Three-, and Four-Winding Current Differential Protection
Sensitive current differential protection with programmable single- or dual-slope percentage restraint, supervised by a choice of second- and fourth-harmonic blocking or restraint elements, plus fifth-harmonic and dc blocking elements for secure protection of up to four windings. Phase current harmonic blocking is set for either common or independent winding basis. Unrestrained high-set differential elements provide fast operation for high-magnitude internal faults. "Around the clock" phase angle compensation settings and automatic tap calculations simplify settings.

Individual Winding Overcurrent Protection
Torque-controllable overcurrent elements, including one instantaneous, one definite-time, and one inverse-time element each for phase, negative-sequence, and residual ground currents, provide comprehensive overcurrent protection on each winding input. Combined current feature sums current from two CTs for ring-bus and breaker-and-a-half overcurrent applications.

Through-Fault Recording and Monitoring
Through-fault duty is recorded and accumulated for use in SELogic control equations or manual monitoring.

Protection and Control Logic
Restricted Earth Fault (REF) logic for sensitive grounded-wye winding ground fault protection. SELogic Control Equations with SELogic variables, timers, latch bits, and remote control elements for customizing advanced protection and control schemes. Local programmable control elements and programmable text display points for advanced local operator interface.

Metering and Reporting
Oscillographic event reports (up to seven 60-cycle reports), Sequential Events Recorder (SER) reporting, and accurate metering eliminate or reduce external recorder and metering requirements. Station battery voltage monitor and circuit breaker contact wear monitor provide important data for Reliability Centered Maintenance (RCM) programs.

acSELerator QuickSet SEL-5030 Software
Develop relay settings off-line, program SELogic control equations, and analyze post-fault event reports.

  • Thermal modeling element for key information about transformer overload capability.
  • Panel-mount or rack-mount hardware package.
  • Chassis available for one additional I/O board.
  • I/O board with contact sensing inputs and standard outputs, or high-current interrupting outputs.
  • Connectorized packaging (includes additional I/O inputs and output contacts).
  • Additional local and remote control switches and binary SER messaging.
  • Distributed Network Protocol 3 (DNP3) Level 2 slave communications protocol available in SEL-387-5, -6 models.
  • Conformal coating (available in SEL-387-0, -5, -6 models) protects equipment from harsh environments and airborne contaminants such as hydrogen sulfide, chlorine, salt, and moisture.


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Minimum QuickSet Version

Minimum QuickSet Version

Product Certifications