On-line detection of high-resistance connections in the incoming electrical circuit for induction motors

High-resistance(R) connections in the induction motor electrical circuit result in localized overheating and supply voltage unbalance, which leads to decreased efficiency, reliability, and increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for reliable, efficient, and safe operation of the industrial facility. This paper focuses on the development of a sensorless on-line technique for detecting poor connections based on monitoring the asymmetry in the electrical circuit. The development of the technique begins with the derivation of the dynamic model of an induction motor with high-R connections. Based on the analysis of the model, two approaches for detecting poor contacts using the negative sequence current and zero sequence voltage are proposed. In addition to detecting the existence of faults, the location and severity of the fault can also be determined using the proposed method. An experimental study on a 10 hp induction machine under simulated and realistic high-R conditions shows that the proposed techniques provide a simple low cost solution for reliably detecting poor contact problems at an early stage. It is also shown that the severity and location of the high-R contact fault can be assessed with high accuracy.