How to determine the effectiveness of generator differential protection

Abstract

Differential protection is often touted as being The protection for generator stator windings. In this paper, we examine the degree of protection afforded by the various types of differential elements (phase, negative, and zero sequence) for stator winding faults. To understand why and how windings fail, we need to know how a stator is constructed, how the winding coils are made, and how they are mounted into the stator core. This paper examines various types of winding configurations and the makeup of the winding insulation. We analyze how different winding failures can be detected using the various differential elements mentioned. Because protection elements are not only required to be sensitive but also secure, we contrast the dependability and security of each element. Security of any differential element must include the performance of the primary current transformers (CTs); therefore, we extend the discussion to setting recommendations and CT selection rules. Finally, the paper answers the question, How much protection does each type of differential element provide? Knowing the limits to performance will allow protection engineers to set the elements for realistic sensitivity without unnecessarily risking any security.