Exploitation of induction machine´s high-frequency behavior for online insulation monitoring

The trend to increased energy efficiency and profitable capital expenditure leads to the operation of drive systems at or near their rated values and to increased running time. Thus, down time due to machine breakdown (e.g. in a traction drive) leads to high economic losses for the operator. Furthermore, the breakdown of safety-critical devices may lead to dangerous situations. Due to the above stated reasons the demand for operation reliability is constantly increasing. The fast switching of the voltage source inverter (VSI) in adjustable speed drives (ASD) leads to increased stress for the winding insulation. Thus, it gets even more important to monitor the condition of the insulation in inverter-fed drives. Degradation of the insulation results in an alteration of the machine´s high-frequency behavior. The proposed method is capable of detecting such changes by evaluation of the transient current reaction on inverter switching.