7SG12 DAD N Numerical High Impedance Siemens

The 7SG12 DAD-N overall differential protection uses the high impedance circulating current principle; a single line diagram of such a scheme is shown in fig. 1. The 7SG12 is a three phase relay providing high-speed, high impedance phase segregated current differential protection and phase segregated open circuit monitoring of the current transformer secondary circuits ( CT supervision) . Outputs from the differential and CT supervision elements operate when their input current exceeds their individual current settings. The programmed time delays, LEDs and output contacts are initiated. Relays can be supplied with binary input/ output and LED combinations as follows: 3BI + 5BO + 16 LEDs, E8 case 11BI + 13BO + 16 LEDs, E8 case 19BI + 21BO + 32LEDs, E12 case 27BI + 29BO + 32LEDs, E12 case. All output contacts are fully programmable to any relay function listed in the output relay menu. Output relays can be configured as self reset or hand reset. It is recommended that class ‘ PX’ current transformers to IEC 60044-1 are used with high impedance protection.