Three-phase current sensor for motor protection against turn-to-turn and phase-to-phase short circuits

Abstract

The main causes of electric motor failures are transients at power supply interruption and short circuit in stator windings. Most of the failures are due to short circuits. Phase-to-phase short circuits refer to the most severe damage of electrical installations, which are also dangerous for other intact electric consumers. Therefore, electrical plants require a high-speed protection against phase-to-phase short circuits in the stator windings and connections with the commutator. The most difficult to detect are turn-to-turn (or inter-turn) faults in stator windings, especially when a small number of winding turns is shorted. Currently, there is no standard way to detect turn-to-turn short circuits in stator windings. It is difficult to detect turn-to-turn fault in magnitude of phase currents, so it is complicated to provide sufficient protection sensitivity. Thus, the development of new protection devices for detect turn-to-turn short circuit is considered relevant. The article presents a three-phase current sensor based on measuring the magnetic field from the three phases simultaneously. This method will identify turn-to-turn and phase-to-phase short circuits by magnetic-field pattern. The presented method increases the protection sensitivity and speed of protection response. The effectiveness of the proposed method is demonstrated by mathematical modeling.