Differential relay / three-phase / protection
SIEMENS Smart Grid
The 7PG21 is a three phase unit differential protection. It can detect in zone phases and earth faults. The relay is applied to underground cable circuits and overhead lines plus shorter connectors, including interconnectors. Dedicated metallic pilot wires are used to connect the relays which are installed at both ends of the protected circuit. Enabling straightforward installation, maintenance and commissioning, simple and robust protection is provided by the protection system.
The relays have 3 current inputs and they are housed in E6 cases. More components and relays can be added in order to increase the insulation level.
For Pilot Wire Supervision, send and receive end relays are used. The integrity of the pilot circuit is confirmed by injecting a small DC current onto the send end of the pilots and measuring the current at the receive end.