SEL-787-3E/-3S/-4X 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.


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.