The Effect of Dynamic Out-of-Phase Operation of Synchronous Generators on the Short-Circuit Currents in Electric Power Systems

Abstract

The growing levels of short-circuit currents (SCC) in electric power systems (EPS) generate the need of improving the SCC calculation methods. Factors causing the occurrence of dynamic out-of-phase operation of synchronous generators (SGs) and its effect on the SCC are studied. To analyze the effect the out-of-phase operation of SGs has on the SCC, an analysis model was developed in the EMTP-RV software package (Powersys, France), and variant calculations were carried out. The study was carried out for an SG operating in parallel with the EPS. The parameters of electrical equipment installed in the EPS of Russia and CIS countries were used as initial data. The effects the mechanical inertia and electromagnetic parameters of the rotor and stator windings have on the occurrence of out-of-phase operation of generators was considered. It is shown that the analysis of SCC carried out without taking into account the dynamic out-of-phase operation of SGs yields SCC values significantly overestimated in comparison with those calculated according to the standards that are currently in force. By the short-circuit clearing time, the initial phase of the SCC component from the SG may differ from the initial phase of the SCC component from the network source by 90 degrees or more; i.e., the total SCC obtained taking into account the SG current phase becomes less than the current from the network source. It is recommended to take into account the dynamic out-of-phase operation of SGs in solving matters concerned with coordinating the SCC levels and to improve methods for calculating SCC in the EPS.