Detecting high-resistance connection asymmetries in inverter fed AC drive systems

The wiring system between inverter and the machine consists of different parts connected by metal-to-metal joints. High load currents lead to an increase temperature of the connections and higher material degradation. Basically, these effects result in an increased resistance in one phase. If such faults are not identified timely an unexpected outage of the whole system can be a consequence. However, the degree of reliability of the wiring system should not be less than that of the machine or inverter. Detecting such small resistance incensement provide the possibility to react timely on the occurred fault. In this paper a method is presented to detect open-circuit faults in the stator windings of an inverter fed drive. The method gets along with the hardware already present and doesn't need additional sensors etc. By applying voltage phasor steps to the machine terminals and measuring the resulting current the phase resistance can be estimated. By combination of the current direction with the phase resistance value resistance phasors can introduced. With these phasors a high sensitive fault indicator is generated able to detect connection fault severity and position. Measurements on a laboratory test stand for different fault configurations prove the applicability and accuracy of the proposed method.