Improving the performance of the stator current limiter of excitation control systems

This paper is concerned with the operation of the stator current limiter and its influence on the performance of the generator. The basic functional properties of the stator current limiter are reviewed and operational scenarios where the inductive stator current limiter can potentially have adverse impact on the generator´s stability are outlined. The main problem of the inductive stator current limiter is the dependence of the associated control loop on the terminal voltage of the generator. Under certain circumstances this control loop can become unstable and cause generator tripping. Two new methods for alleviating the potential problem caused by the inductive stator current limiter are proposed. The features of the proposed methods are studied and demonstrated by means of nonlinear computer-aided simulations involving detailed models of the of the synchronous generator and a modern excitation system equipped with a stator current limiter. The simulations indicate that the proposed methods are capable of substantial reducing the risk of encountering the generator instability due to the action of the inductive stator current limiter.