Protection of Asynchronous Motors From Internal Closes of Stator Winding

Abstract

A method for constructing a high-speed effective protection of large asynchronous motors from arc faults in the stator winding arising from weakening and electrical breakdown of insulation on the machine body and caused by the action of switching or impulse overvoltages has been developed and substantiated. The proposed scheme for detecting arc faults is based on monitoring the active and capacitive conductivity of the winding insulation relative to the machine body and violation of the conduction star in case of insulation damage. It is shown that the asynchronous motor protection according to the proposed method will effectively operate both in case of single-phase short-circuits to the case, and inter-turn and phase-to-phase closures, leading to significant damage to the insulation and winding conductors. The proposed protection has a speed that is inaccessible to modern means of relay protection of motors from such damages. It is proposed to build protection against internal faults on a two-level principle, due to an additional device for quickly extinguishing the residual EMF in the stator winding, induced in it after the motor is disconnected from the network.