A Setting-Free Approach to Detecting Loss of Excitation in Synchronous Generators

Synchronous generators of any size require protection against loss of excitation because it can cause harmful effects to the generator and power grid. This paper proposes a new setting-free approach to detect loss of excitation in synchronous generators. Unlike the conventional method, which requires demanding work to set the relays, the proposed method does not require any threshold to act. It will be shown that after loss of excitation, the rate of change of resistance measured by relay 40 (ANSI Code for protection against loss of excitation) will become negative and remain negative for a while. On the other hand, it will be shown that during the slowest power swings, the rate of change of resistance cannot remain negative for more than 1.7 s. This, therefore, can be used as a criterion for detecting the loss of excitation of a synchronous generator. The main advantages of the proposed method are that it is setting-free and meanwhile acts faster than the most famous method introduced in 1949.