Abstract
The aim of this paper is to analyze the performance of a three-phase wound-rotor induction motor (WRIM) under rotor windings asymmetry. The dynamic performance of the WRIM under healthy and rotor windings asymmetry with one-open-phase fault conditions is analyzed using a dynamic model in the ABC frame. Under opening one phase of the rotor windings, the WRIM suffers from operation at a speed near to the half of its synchronous speed, which is known as the Georges phenomenon. The behavior of the WRIM is simulated and investigated experimentally under faulty conditions for four different possible connections of rotor windings. The stator and rotor currents are analyzed using fast Fourier transformation technique to identify the fault signatures. The results prove that under opening one phase of the rotor windings the WRIM suffers from pulsating electromagnetic torque, high oscillatory stator currents and high unbalanced rotor currents. Also the results prove that the performance of the motor under rotor windings asymmetry conditions and the occurrence of Georges phenomenon depend on the type of connection of the rotor windings and fault location. Therefore, the authors suggest a special delta connection for the rotor winding to reduce the effects of this phenomenon. The simulation and experimental results show good agreement and prove the validity of the suggested delta connection.
Highlights
The squirrel cage induction motors have dominated the industry due to their wellknown advantages, but in some application wound-rotor induction motor (WRIM) is still more used
The rotor asymmetry results in unbalanced rotor currents combined with high values for all connections especially for star connection and normal delta connection
It operates at a speed slightly less than its full load speed in case of opening one phase of rotor circuit during normal running if the load torque < 67% of its full load torque, and at speed near to half of its synchronous speed if the load torque is > 67% of its full load
Summary
The squirrel cage induction motors have dominated the industry due to their wellknown advantages, but in some application wound-rotor induction motor (WRIM) is still more used. The capability of the large WRIMs in developing a high starting torque at low starting currents by the means of adding external resistances in series with the rotor windings makes them ideal for some applications. Besides limiting the starting current, this resistance can be used in controlling the motor speed. These advantages make the WRIMs suitable for large power industrial application such as cranes, pumps, conveyors and hoists [1]. Magnetic circuit and motor mechanical system (mainly bearing failures) faults are the three main categories of faults of induction motors [7]. In [13], a method to discriminate between different faults in the stator and rotor windings of wound-rotor induction machines was presented. The magnetic equivalent circuit (MEC) model has been used to simulate machine performances under different winding fault conditions with Matlab/Simulink software
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