Adaptive Differential Protection of Large-Scale Generator Considering CT Saturation Phenomenon

Synchronous generators are the most complex machines in the power plant requiring protection against constant and transient stresses for reliable operation of the power system. A differential protection scheme and a current transformer (CT) are provided to protect the stator from internal faults. CT saturation in the event of external disturbances may influence relay operation which is not intended. The standard differential protection of synchronous generator lags to distinguish between faults internal and external to the stator which may lead to false tripping of the relay causing disturbances in the power system. This requires modification in relay characteristics to provide adaptive operation. This paper proposes an adaptive differential protection technique with increased sensitivity using DFT for stator protection of a large-scale 3-phase synchronous generator from internal faults considering various levels of CT saturation. The simulation of synchronous generator is done using PSCAD software. To study the impact of CT saturation under conditions of internal fault and external fault various situations were intentionally developed. The basis of discrimination is the slope of flux density with respect to time in the core of CT. System outcomes of simulations for such situations were obtained. The results demonstrate the potency of the suggested relaying technique in discriminating between faults internal and external to the stator of the synchronous generator.