The differential method of detecting coil circuitsfaults in three-phase transformer

Abstract

Idle voltages proportional to corresponding magnetic flows of three-phase transformer of general purpose are measured using differential methods aimed at detection of inter turn faultin windings of three-leg transformers.The standard method of determining the inter turn fault in the transformer windings is based on measuring idling current and measuring loss power. In addition, differential methods well known in relay protection are proposed to determine the presence of inter turn faultin three-phase linear transformers. The methods are based on the fact that the inter turn fault increases the magnetic resistance of the phase rod of the transformer core, in the phase winding of which there is a inter turn fault. When one-phase voltage is applied to the winding of phase B in the windings of side phases A and C of the linear three-phase transformer, the same voltage phase and amplitude shall be induced. When phase A and C windings are connected in opposition and differential signal is measured, voltage difference of phases A and C is as follows. If, in the original, intact state, the differential signal was close to zero, the inter turn faultin one of the side phases A or C introduces an imbalance and the differential signal increases. The differential signal is easily measured against the background of the near zero differential signal in the intact state of the transformer, which causes a high sensitivity of the differential method to the presence of inter turn fault. In case of a inter turn faulton the winding of the central phase B, it is necessary to take into account the differential signal in the intact state of the transformer.

Keywords

• magnetic system
• differential method
• magnetic flux