Using Clarke Vector Approach for Stator Current and Voltage Analysis on Induction Motors with Broken Rotor Bars

摘要

Condition monitoring and diagnostic of induction motors has become an important issue for companies and industries whose production depends on the reliability of electrical drives. As the number of induction motors is growing in time, so is the importance of their diagnostics. The majority of all stator and rotor faults are caused by a combination of various stresses, which can be thermal, electromagnetic, residual, dynamic, mechanical or environmental [1]. Broken rotor bars of squirrel-cage induction motors can be classified as one of the most common faults along with bearing faults and gearbox failures. Broken rotors bars can lead to vibration problems, but more likely, in severe cases, the bar pounds out of the slot and makes contact with the stator core or winding [1]. If not detected and treated in time, fault such as cracking or broken rotor bars will propagate until the whole rotor cage is destroyed. During the last years many papers have been written about condition monitoring of induction machines. However, even though thermal and vibration monitoring have been utilized for decades, most of the recent research has been directed toward electrical monitoring of the motor with the emphasis on inspecting the stator current [2]. It has been suggested that stator current monitoring can provide the same indications as vibration based monitoring, but it can be done without requiring access to the motor. This is a very important benefit of such diagnostic approach, as the motors that are diagnosed will not suffer any changes in their working cycle and all the processes can be continued completely undisturbed. As stator current pattern is highly dependent from the supply quality and load conditions of the motor, authors of this paper have tried to find solutions for improving the diagnostic possibilities of induction motors using simple mathematic methods such as Clarke vector approach. To lessen the impact of the factors mentioned before, implication of Clarke vector approach on stator voltage is proposed. Using voltage as an indicator for detection of broken rotor bars can have its own advantages which are described latter in this paper.