INTER TURN FAULT ANALYSIS OF CAGE INDUCTION MOTOR

Abstract

Increasing interest: has been seen in condition monitoring techniques for rotating electrical machines in powea plants, because condition monitoring has the potential to reduce operating costs, enhance tlhhe reliability of operation, and improve power supply and service to customers. For fault identiifiecation in induction motors, apart from locating specific harmonic components in the line cu ent (popularly known as motor current signature analysis), other signals, such as speed, to-Irq uie,, noise, vibration etc., are also explored for their frequency contents. Sometimes, altothir different techniques, such as thermal measurements, chemical analysis, etc., are also emplco}7ed to find out the nature and the degree of fault. In addition, human involvement in the actual F*milt 'detection decision making is being replaced now by automated tools, such as expert systennts., neural networks, fuzzy-logic-based systems; to name a few. It is indeed evident that this area is potentially important. Computer sinmllattiron of motor operation can be particularly useful in gaining an insight into its dynamic b-elnaiviior and electro-mechanical interaction. With a suitable model, motor faults may be simullated and the change in corresponding parameters can be estimated. This can significantly reduicce tihe computer simulation time and make model-based condition monitoring more reliable am4ea;sily achievable. In the present wio c, two models with orthogonal axis are developed for simulation of three-phase induction motors having asymmetrical windings and inter-turn short circuits on the stator. The first model assnumi,es; that each stator phase winding has a different number of turns. To model shorted stator turns, the second model assumes phase as has two windings in series, representing the unaffected paorttion and the shorted portion. It uses the results of the first model to transfer phase as to rid nhat shorted portion is transferred to the q axis. Simulations results from the models are in good agreement with other studies and are validated with the experimental results obtaime•.dl..A third model has been developed with the same considerations which can incorporate the fa ulit in an induction motor under operation. The models have been successfully used to'studyi tihie transient and steady state behaviour of the induction motor with short-circuited turns. The study has been further extended to analyze the effect of voltage unbalance on the charactesis;tiies of an induction motor with inter turn fault.