A real time digital power system simulator for testing relays

The design and performance of a real time digital simulator (RTDS) for testing relays are described. The RTDS uses parallel processing architecture to run electromagnetic transient simulations in real time with a time step on the order of 100 μs. Relays can be tested in an interactive mode with the output from the relay trip circuit fed back into the simulation to control the appropriate breaker model. The solution runs on until stopped from the input keyboard and can be used to test primary protection, back-up protection and power swing blocking. Examples are given of tests on a commercial distance relay