15 Years of Exerience with 100% Generator

This paper discusses the application of three different 100% stator ground fault protection schemes. Two third-harmonic methods and a low frequency-injection method are discussed. Third-harmonic schemes have been widely applied on generators within the U.S. to provide stator ground fault protection over the entire stator winding. In many cases, however, these schemes have been found not to be applicable. In many cases, these shortcomings were discovered during commissioning or when they operated improperly resulting in a false tripping of the generator. This paper discusses situations in which third-harmonic schemes will work and outlines the limitations of such schemes. It also discusses the use of low frequency-injection schemes which are gaining acceptance in the U.S.