A New Method in Power System Simulation to Approximate Transients of the Synchronous Machines Stator

Abstract

This paper presents a new method to approximate the effects of synchronous machines stator transients in power system transient stability simulations. The method can approximate the DC offset currents which arise from the stator and network transients during three phase short circuit faults. However, the method is based on the traditional model with stator and network transients neglected. INTRODUCTION.In this paper. a new method to evaluate the DC offset currents for stator circuits of synchronous generators during three phase short circuit faults is presented. In traditional simulations of the short circuit faults it is common to neglect the transients of the transmission networks and stator circuits of synchronous machines[1,2J. The simulation is carried out by solving simultaneous equations composed of steady state AC circuit equations for the transmission networks and the stator circuits, and the differential equations for rotor circuits. motion systems and control systems of synchronous machines. This is because it is difficult to express the transmission system by differential equations. Therefore. by standard method it is not possible to obtain instantaneous responses of state variables of generators. In addition, it has been reported that the traditional method can not evaluate the backswing phenomenon caused by stator transients during short circuit faults. In some cases the resulting error may be large [3.4J. Some reports have analyzed the physical aspects of the backswing phenomena [5-7J. However, there are few that present a general method to evaluate the effects of stator transients using the model with network and stator transients neglected. Report [8J presents an interesting method to consider the stator and network transients in power system simulation. However, its target is only a stiffly connected system. The new method proposed in this paper can approximate the DC offset currents, and thus the effects of backswing and the stator transients. However, it is also based on the traditional model with stator and network transients neglected. The basic concept of the new method has been presented in [9J. This paper presents more practical aspects of the method.