SEL-787-3/-4 Transformer Protection Relay
Protect and monitor most three- and four-terminal transformers 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.
Front- and Rear-Panel Diagrams
The SEL-787-3/-4 provides dual-slope differential protection with harmonic blocking and restraint for as many as four terminals, and as many as three independent REF elements for sensitive ground-fault detection in grounded-wye transformers. Standard overcurrent elements provide backup protection, including phase, negative-sequence, residual-ground, and neutral-ground elements. Breaker failure protection for as many as four three-pole breakers is available.
Measure and track accumulated through-fault current levels, and use optional 4 to 20 mA or resistance temperature detector (RTD) thermal inputs to monitor ambient, load tap changer (LTC) tank, or transformer oil temperatures.
Advanced protocols, such as IEC 61850, IEC 60870-5-103, Modbus® (RTU and TCP/IP), Simple Network Time Protocol (SNTP), DNP3 (serial and LAN/WAN), ASCII, Telnet, FTP, and DeviceNet™, support communications using legacy and modern supervisory and control systems.
The SEL-787-3/-4 Relays operate in extreme conditions, with an operating temperature range of –40° to +85°C (–40° to +185°F). They are designed to work in harsh substation environments and tested to verify that they exceed requirements for reliable operation in the presence of vibration, electromagnetic interference, and other adverse environmental conditions. Optional conformal coating provides extra protection in caustic environments.