Detection of defects in stator winding of inverter fed induction machines

Inverter fed drive has become to one of the most important components of modern industrial facilities and propulsion systems. Growing demands on efficiency lead to higher wear of the drive systems and the risk of breakdowns. Unexpected outages of the drive system lead to high economic and/or safety losses. Detecting faults in an early stage helps increase the reliability and reduce the risk of breakdown. Beside short-circuit faults, open-circuit faults count to the most frequent reasons for the breakdown of the winding system. Starting with a crack or cross section deformation of the stator winding conductors the open-circuit fault induces an increased resistance in the corresponding phase. Detecting such small resistance changes provides the possibility to react timely on the developing fault. In this paper a method is presented to detect incipient open-circuit faults in the stator windings of an inverter fed drive. The method gets along with the hardware already present in modern drives, no additional sensors are required. By Applying voltage steps to the machine terminals and measuring the resulting current the phasor resistance can be estimated. By spatially combining the phase measurements of the resistance a phasor of the resistance symmetry can be introduced. With this phasor a high sensitive fault indicator is generated able to detect fault severity and position. Measurements on a laboratory test stand for different fault configurations prove the applicability and accuracy of the proposed method.