Study of Generator Source Short-Circuit Currents with Respect to Interrupting the Duty of Generator Circuit Breakers, EMTP Simulation, ANSI/IEEE and IEC Methods

Abstract

Large generators have high effective X/R ratios and combined with other generator time constants and parameters, a current zero may not be obtained at the time of contact parting, i.e., the dc component of the short-circuit current at the contact parting time is higher than the peak ac component. This is well documented in the current literature. The paper presents calculations of the generator source short-circuit currents of a 234 MVA generator using ANSI/IEEE and IEC standards and EMTP simulation. The results are compared and the application of a generator breaker to meet the requirements of calculated duties are discussed. It shows considerable differences in the results, depending upon the method of calculation.