The function of protective relaying is to promptly remove from service any element of the power system that starts to operate in an abnormal manner due to a fault. Therefore, protection systems are critical power system components. The comprehensive testing of a protection system is needed before the relay is put into service.; Combined computer simulation of power systems and protective relays can be used as a valuable preliminary step for relay performance testing. In this dissertation a novel relay simulation scheme, an automatic pseudo closed loop simulation method, is proposed to allow for closed loop simulation of the interaction between power systems and protective relays.; The protection algorithm plays a very important role in a protection scheme. Computer simulation can provide a tool to evaluate different algorithms for a specified application. A new algorithm to eliminate the exponentially decaying component from the Fourier algorithm is proposed and evaluated using the new simulation approach. Three simplified methods are proposed to alleviate the computation burden. The performance of these algorithms is evaluated both in the ideal and real power system conditions.; A commercial digital power transformer relay (WBX-500) is selected as the object of this study. This relay is described by Matlab, a high level language. The power system in the Electrical Power Dynamic Laboratory (EPDL), Huazhong University of Science and Technology, China, is modeled by the Electromagnetic Transients Program (EMTP). A new method to estimate the RL parameters which can be used to describe the transient behavior of the transformer internal winding fault is proposed in this dissertation. The interaction between the EMTP and relay modeling program illustrates that this novel simulation method allows for implementation of the closed loop simulation, and there is no need to modify the transient signal generation program itself.; The test result in EPDL is used as the reference to verify if the computer simulation result presented in this dissertation is consistent with the laboratory test result. The comparison result is encouraging. It demonstrates that the computer simulation is a very good tool for protection system evaluation.
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