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Transformer Protection Relay

SEL recommends selecting the SEL-787-2/-3/-4 Transformer Protection Relay in place of the SEL-787. The SEL-787-2/-3/-4 offers additional protection and communications options, such as protection for two-, three-, and four-winding transformers and EtherNet/IP. It is also available with a color touchscreen display.

SEL will continue to support and warranty the SEL-787.

SEL-787/SEL-787-2 Comparison Chart

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Two-Winding Complete Protection—Apply two-winding, dual-slope differential protection with phase, negative-sequence, residual, and neutral-overcurrent elements for backup protection. Use breaker failure protection for two 3-pole breakers. Also, protect three-phase autotransformers with the SEL-787.

Cost-Saving Transformer Monitoring—Extend the life of your transformer by monitoring the ambient, load tap changer (LTC) tank, and transformer oil temperatures with optional 4–20 mA analog inputs or resistance temperature detector (RTD) thermal inputs. Monitor the number of through faults, accumulated I2t, and fault duration times to determine the frequency and impact of external faults on the transformer to prevent catastrophic failures.

Fan Bank Control—Provide fan bank control and protection with the optional single-phase CT channel in addition to the RTD thermal elements.

Beyond Basic Transformer Protection—Achieve comprehensive transformer protection with the optional single-phase sensitive REF input and the three-phase voltage inputs. Eliminate separately mounted metering devices with built-in metering functions, including harmonics, power, phase voltages and currents, neutral currents, and sequence voltages and currents.

Reliable Protection in Harsh Environments—The SEL-787 operates in extreme conditions, with an operating temperature of –40° to +85°C (–40° to +185°F), and it is designed and tested to exceed applicable standards, including vibration, electromagnetic compatibility, and adverse environmental conditions. In addition, the SEL-787 is ATEX- and Underwriters Laboratories (UL) Class I, Division 2-certified for use in hazardous and potentially explosive environments.


    1. 1

      Large 2 × 16 character LCD 

    2. 2

      Default messages or up to 32 customizable display labels notify personnel of power system events or the relay status 

    3. 3

      Programmable front-panel LEDs

    4. 4

      Customizable push-buttons and labels

    5. 5

      User-configurable label kit 

    6. 6

      Two programmable tricolor LEDs per pushbutton

    1. 1

      Power supply options include 24–48 Vdc or 110–250 Vdc/110–230 Vac

    2. 2

      Modbus TCP, Telnet, FTP, IEC 61850, and DNP3 LAN/WAN. Single or dual copper or fiber Ethernet port.

    3. 3

      Fiber-optic serial port

    4. 4

      IRIG-B input

    5. 5

      Mirrored Bits® communications

    6. 6

      Positions for optional expansion cards

    7. 7

      Shown with optional RTD inputs

    8. 8

      Optional voltage input

    9. 9

      Optional neutral CT input (REF)

    10. 10

      Two-winding CT inputs



Two-Winding Current Differential, Overcurrent, and Breaker Failure Protection
Apply two-winding dual-slope differential protection with phase, negative-sequence, residual, and neutral overcurrent elements for backup protection. Use breaker failure protection for two 3-pole breakers.

Secure and Dependable
Provide maximum security during external faults and transformer magnetizing inrush conditions. Detect internal faults quickly, during energization or normal operating conditions, using combined harmonic-blocking and -restraint differential elements.

Transformer Monitoring
Record and accumulate through-fault duty for use in SELogic control equations or manual monitoring. Monitor ambient, load tap-changer (LTC) tank and transformer oil temperature with optional 4–20 mA analog inputs or RTD thermal inputs to extend the life of your transformers.

Operator Control
Use four programmable front-panel pushbuttons, each with two programmable LEDs, for a wide variety of applications, including easy trip-and-close control and status indications for a breaker. Implement local and remote operator control schemes with 32 local and 32 remote control bits.

Metering and Reporting
Eliminate separately mounted metering devices with built-in metering functions. Analyze Sequential Events Recorder (SER) reports and oscillographic event reports for rapid commissioning, testing, and post-fault diagnostics. The unsolicited SER protocol allows station-wide collection of binary SER messages. SEL-787 metered quantities include harmonics, power, frequency, and energy; phase voltages and currents; neutral currents; sequence voltages and currents; and maximum/minimum logging of selected quantities.

Rugged Design
Trust the industry’s widest ambient operating temperature range, –40° to +85°C (–40° to +185°F). The SEL-787 withstands vibration, electrical surges, fast transients, and extreme temperatures, meeting stringent industry standards. A conformal-coating option for the printed circuit boards provides an additional barrier to airborne contaminants, such as hydrogen sulfide, chlorine, salt, and moisture. In addition, the SEL-787 is ATEX- and Underwriters Laboratories (UL) Class I, Division 2-certified for use in hazardous and potentially explosive environments.

  • Advanced Protection
    Protect grounded-wye transformers with sensitive REF elements. Provide volts/hertz protection with frequency tracking from 20 to 70 Hz for generator step-up and other variable frequency applications. Implement load shedding and other control schemes with over- and underfrequency and over- and undervoltage elements.
  • Flexible and Easy Communications
    Apply copper or fiber, single or dual fiber Ethernet (DNP3, IEC 61850, Modbus), and up to 4 serial ports.
  • Flexible I/O for Local Control and System Applications
    The base unit includes three digital outputs and two digital inputs. There are three card slots for optional SELect I/O cards including the following:
    • 3 digital inputs (DI)/4 digital outputs(DO)/1 analog input (AI)
      4 DO/4 DI
      4 AI/ 4 analog outputs (AO)
      8 DI
      Serial communication (EIA-232/EIA-485)
      10 internal RTD inputs (or add 12 external RTD inputs with an SEL-2600 RTD Module)
      Neutral ac current input with three-phase ac voltage inputs (1 ACI/3 AVI)
      Neutral ac current input (1 ACI)
  • Conformal Coating
    Protect equipment from harsh environments and airborne contaminants, such as hydrogen sulfide, chlorine, salt, and moisture. Learn more about conformal coating.
  • Projection Mounting
    Projection, flush, and easily extractable mounting solutions are available.

Minimum Software Version

Latest Firmware Versions

There are no firmware versions available for this product.

Product Revision Firmware ID Date Available Serial Number
SEL-787 R210-V3 SEL-787-R210-V3-Z004001-D20230601 6/29/23 ~3231800001
SEL-787 R209-V3 SEL-787-R209-V3-Z003001-D20230601 6/29/23 ~3231800001

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

Minimum Software Version

787 - Software Tab


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.

acSELerator Architect SEL-5032 Software

Architect allows users to configure and document IEC 61850 systems that include GOOSE, Sampled Values (SV), or Manufacturing Message Specification (MMS) communications. Architect automatically compares SCL files with IEC 61850 requirements to ensure standard compliance.

Learn more and download on the Architect 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