Distance Protection Relay

Simscape Electrical Specialized Power Systems model of a Distance Protection Relay

The distance protection method is widely used for power system transmission line protection. Distance relays are one of the main protection devices in a transmission line. Distance protection relay approximates the impedance down the line to a fault using currents and voltage measurement units.

The test system consists of two fully symmetrical sources (735 kV) linked together by two 230-kV lines of 200 km length. The internal angles of the two sources have been adjusted to obtain a power transport of 1660 MW on each of these lines (Transit going from the bar B1 to B2) [24]. Line 1 is protected by two MHO digital distance relays. The disturbance event is a severe phase A to ground fault applied at t=0.1 s at the center point of the line and cleared at t=0.25 s.

The model calculates the six impedances Za , Zb , Zc , Zab , Zbc , and Zac from the three-phase phasor voltages and currents measured by the measurement unit at the breaker substation. Then, using a fault detection subsystem, the relay triggers when one of the six measured impedances falls within the protection zone. Finally, the Trip signal is transmitted to the line circuit breaker, and the SPT signal is transmitted to the relay located at the other end of the line.

For more information see this publication:

A. Delavari, P. Brunelle and C. F. Mugombozi, "Real-Time Modeling and Testing of Distance Protection Relay Based on IEC 61850 Protocol," in Canadian Journal of Electrical and Computer Engineering, vol. 43, no. 3, pp. 157-162, Summer 2020, doi: 10.1109/CJECE.2020.2968404.