A comprehensive protection scheme for generator loss of excitation

Power system is constantly evolving with application of new technology to improve the reliability and security of the system. At the same time technology up-gradation is being undertaken to reduce the cost of various power system components, which can have an impact on protection techniques. The paper evaluates the performance of loss of excitation protection scheme for increase in generator direct axis synchronous reactance. It is shown that for higher values of direct axis synchronous reactance, the coordination between loss of excitation protection, excitation control and capability limit is not adequate. This may restrict the generator reactive power absorption capability. The paper also reviews the conventional philosophy for setting the excitation limiters and discusses its impact on loss of excitation protection and system behavior. A conventional protection scheme is modified to allow for full utilization of machine capability and new power swing blocking criteria is developed to improve the reliability during stable power swings.