Coordination between loss of excitation protection and minimum excitation limit function of voltage regulation system

Established practice is such that the relay protection system and excitation system are adjusted independently of each other, which very often leads to non-coordinated action. When network disturbance occur, it is necessary to provide that basic protection functions eliminate the fault if it is necessary, and that all generators respond so as to preserve system stability and use the most of their capabilities. The basic task of under excitation protection is to prevent damage to the generator in a not allowed mode of operation. Also it is important to prevent the absorption of large amounts of reactive power from system that can lead to voltage collapse or line failure in the transmission system. This paper deals with under excitation protection and minimal excitation limiter, which is a part of excitation system, as well as with coordination between them. In the paper the current and the proposed settings are presented regarding case studies of generators in power plants in "EPS".