html{display:none} SEL-387A Current Differential and Overcurrent Relay | Schweitzer Engineering Laboratories


Current Differential and Overcurrent Relay

The SEL-387A Current Differential and Overcurrent Relay offers restrained and unrestrained differential protection for two terminals. Second-, fourth-, and fifth-harmonic elements, augmented by the dc element, provide security during transformer energization and overexcitation conditions in a user-defined choice of either harmonic restraint or harmonic blocking. Overcurrent elements provide backup protection that contributes to the versatility of the SEL-387A.

Starting At


Request a Follow-Up



Request a Follow-Up

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 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.

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-Winding Current Differential Protection
The SEL-387A offers 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 two 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.

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 provides sensitive grounded-wye winding ground fault protection. SELogic control equations with SELogic variables, timers, latch bits, and remote control elements are used for customizing advanced protection and control schemes. Local programmable control elements and programmable text display points provide an 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. Use with the SEL-2600A RTD Module to meter temperatures from as many as 24 RTDs.

acSELerator QuickSet Software
Develop relay settings offline, program SELogic control equations, and analyze post-fault event reports.

  • Two Restricted Earth Fault (REF) elements for sensitive protection of wye-connected windings.
  • 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.
  • DNP3 Level 2 Slave communications protocol.
  • Conformal Coating: Protect equipment from harsh environments and airborne contaminants, such as hydrogen sulfide, chlorine, salt, and moisture.

Minimum Software Version

Latest Firmware Versions

There are no firmware versions available for this product.

Product Revision Firmware ID Date Available Serial Number
SEL-387A R611 SEL-387A-R611-V0-Z004004-D20140124 3/14/14 ~1140730001

The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.

Minimum Software Version

3xx software tab - no acSELerator Architect

Configuration Software

acSELerator QuickSet SEL-5030 Software

QuickSet is a tool for engineers and technicians to quickly and easily configure, commission, and manage power system devices. QuickSet includes a Graphical Logic Editor and a device template tool to reduce configuration time and streamline deployment.

Learn more and download on the QuickSet software page.

Automated Data Collection

SEL Data Management and Automation (DMA) Application Suite

Available on the Blueframe platform, DMA applications automatically collect, store, and manage device-specific information like oscillography, Sequence of Events (SOE) data, device settings, and property information. They also provide automated password rotation and streamlined device audits.

Learn more on the DMA software page.

Visualization and Analysis

SEL-5601-2 synchroWAVe Event Software

synchroWAVe Event helps engineers diagnose a protective relay’s behavior during a power system fault. It is a powerful and easy-to-use solution for displaying and analyzing SEL relay event reports and COMTRADE files.

Learn more and download on the synchroWAVe Event software page.

Product Certifications