Coordination between relay protection functions and excitation system with generator capability curve

It is common practice for relay protection and excitation systems to be adjusted independently. That practice leads to the uncoordinated operation of some protective functions. This article presents the tuning of some important protection functions. The first step is loss of excitation protection adjusting and its coordination with the minimum excitation limiting function. Analyzing the coordination settings of this protection with the minimum excitation limiter in practice, it is often noticed that these functions are inadequately adjusted, so the capacitive part of the generator capability curve is not optimally used. That is in contradiction with the high need for capacitive reactive power in the transmission system. The second step refers to the coordination of the maximum stator current limiter in the excitation system with stator overload protection, overcurrent protection, and permitted generator stator overload. It is noted here that this coordination is often not adequately adjusted, leading to the following irregularities: -malfunction of the automatic voltage regulator in certain operating situations, which can lead to voltage collapse in the transmission system; -in some operating situations, there is no forcing of excitation current when it is most needed to preserve system stability.