Discrimination of power transformer Inrush and internal fault currents Using signal processing and soft Computing techniques

Abstract

Power transformers are important equipment in power systems and their protection schemes are of vital significance to provide continuous power supply. The protection scheme depends on the size of the transformer. For large transformers, differential protections are popular. The protective system should be discriminative; that is, in the non-faulted condition, such as inrush current and external fault current it should not operate, and in the faulted condition, it should operate as fast as possible. One of the major concerns in protecting transformers lies in the accurate and rapid discrimination between the magnetizing inrush current and different internal fault currents. The magnetizing inrush current, which occurs during energizing of transformer, may have a magnitude several times that of full a load current, and therefore, may mal-operate a differential relay. Such mal-operation of the differential relay will adversely affect the reliability of the whole power system. This thesis presents several signal processing and soft computing methods for the discrimination of the inrush current from internal fault currents. The proposed protection scheme has been analyzed for varying switching angles, saturation points, different winding configurations, and faults between the winding terminals and the energization of the transformer. These sampled differential currents collected at the relaying point are used for the discrimination of the inrush and internal fault currents.iv Unlike the conventional schemes, using the second harmonic restrain, newline