Investigation on protective relays testing methods

This article describes some methods used in protective relay testing. Protective relays are a very important part of energy systems. Their purpose is to detect faults and switch circuit breakers in order to prevent the fault spreading to the nonaffected part of the power network. Modeling the energy system is necessary not only to test and evaluate the action of protective relays but also for personnel training in conditions similar to those in real networks. The model must therefore be realistic and must produce faults in real time. A variety of signal parameters must be simulated to mimic situations which occur in real networks. The paper gives methods for static and dynamic testing of protective relays. These methods require generation of signals with variable parameters for each different application. The paper describes signals used in research and manufacturing of relay equipment and for field tests of protective relays. To satisfy these requirements, there is a need for a simulator which is able to generate waveforms not only with the main frequency but also higher harmonics. The paper describes the block diagram and characteristics of a portable protective relay test set, designed in Bulgaria, and its possibilities for protective relay static and dynamic testing in comparison to the simulators, designed by ABB Relay Division in Sweden and Texas A&M Universities in USA.