html{display:none} SEL-787-3E/-3S/-4X Transformer Protection Relay | Schweitzer Engineering Laboratories


Transformer Protection Relay

Protect and monitor most three- and four-winding transformers and terminals with the versatile SEL-787 Transformer Protection Relay platform. Select SEL-787-3E/-3S models, and apply three-phase current and voltage inputs with options for either a single-phase restricted earth fault (REF) input or a single-phase voltage input for comprehensive transformer protection. Select the SEL-787-4X for current-based, four-winding differential protection. Benefits include advanced automation and flexibility; single or dual copper or fiber Ethernet communications ports; asset management data; and easy retrofit of most electromechanical relays.

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Multiwinding Protection—Select the SEL-787 for standard dual-slope differential protection with harmonic blocking and restraint for as many as four windings. The SEL-787 offers as many as three independent REF elements for sensitive ground-fault detection in grounded-wye transformers. The relay also comes with a variety of overcurrent elements for backup protection, including phase, negative-sequence, residual-ground, and neutral-ground elements. Breaker failure protection for as many as four 3-pole breakers is also standard.

Frequency Tracking—Choose the SEL-787-3E and SEL-787-3S for generator step-up and variable-frequency applications. These relays have voltage inputs to provide volts/hertz protection with frequency tracking from 20 to 70 Hz. Use over-/underfrequency and over-/undervoltage elements to implement load shedding and other control schemes with the relay.

Synchronism Check/Station DC Battery Monitor—Program the VS/VBAT voltage channel in the SEL-787-3S to perform a synchronism check across a circuit breaker or to monitor dc voltage levels of the substation battery.

Through-Fault Monitoring and Protection—Measure accumulated through-fault levels with the transformer through-fault monitor. Additionally, use the optional 4–20 mA or RTD thermal inputs to monitor ambient, load tap-changer (LTC) tank, and transformer oil temperatures.

Metering and Reporting—Eliminate separately mounted metering devices with the 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.

Local/Remote Operator Controls—Employ eight programmable front-panel pushbuttons, each with two programmable tricolor LEDs, for a wide variety of uses, including easy trip/close control and status indication for all the breakers. With the operator control interface pushbuttons, easily implement local and remote operator control schemes using 32 local and 32 remote control bits. Use SELogic control equations and slide-in, configurable front-panel labels to change the function and identification of target LEDs and operator control pushbuttons and LEDs.

Integration and Automation—Select from an array of communications features and protocols to support all of your integration and automation solutions. Standard features include Mirrored Bits communications, advanced SELogic control equations, and IEEE C37.118 synchrophasors, while IEC 61850, Modbus TCP/IP, Simple Network Time Protocol (SNTP), DNP3 LAN/WAN, DNP3 Serial, and IEC 60870-103 are optional. Elective communications ports include EIA-232 or EIA-485 and single or dual, copper or fiber-optic Ethernet ports. Several digital/analog I/O options are also available for advanced integration. Spanish language support is optional in the PC software, ASCII ports, and HMI.



Three- and Four-Winding Current Differential, Overcurrent, Voltage, and Breaker Failure Protection
Apply three- or four-winding dual-slope differential protection with phase, negative sequence, residual, and neutral overcurrent elements for backup protection. Set elements in SEL-787-3E/-3S models for voltage- and frequency-based protection. Provide breaker failure protection for up to four three-pole breakers.

Security and Dependability
Provide maximum security during external faults and transformer magnetizing inrush conditions. Detect internal faults quickly during energization or normal operating conditions by 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, LTC tank, and transformer oil temperatures with optional 4–20 mA analog inputs or resistance temperature detection (RTD) thermal inputs to extend the life of your transformers.

Operator Control
Use eight programmable front-panel pushbuttons, each with two programmable, tricolored 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 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. The printed circuit boards are conformally coated to provide an additional barrier to airborne contaminants, such as hydrogen sulfide, chlorine, salt, and moisture.

  • SEL-787-3E
    • 9 differential current inputs
    • 3 phase voltage inputs
    • 1 neutral current input
  • SEL-787-3S
    • 9 differential current inputs
    • 3 phase voltage inputs
    • 1 voltage input (Vsynch or Vbattery)
  • SEL-787-4X
    • 12 differential current inputs
  • Communications/Protocols
    • IEC 60870-5-103
    • IEC 61850
    • DNP3-Serial and Ethernet
    • Modbus-Serial and Ethernet
    • Mirrored Bits
    • SNTP
    • Event Messenger
  • SELect I/O Options

Fiber-Optic Port Options:

SELect I/O Option CardDigital Inputs (DI)Digital Outputs (DO)Analog Inputs (AI)Analog Outputs (AO)RTD Inputs
4 DI/4 DO44  
4 AI/4 AO  44 
8 DI8   
8 DO 8  
3 DI/4 DO/1 AO34 1 
4 DI/3 DO43   
10 RTD    10
  • 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.


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