Optimization of Sensor Setup and Filter Frequency for End-of-Line Partial Discharge Testing of Electrical Machines

Repetitive partial discharges (PDs) occurring within minor faults in the insulation system of an electrical machine accelerate insulation degeneration and cause premature failure. Therefore, reliable PD testing is crucial at the end of the production line for automotive traction machines to ensure the required service life. However, the PD detection capability and the test results depend on the sensitivity of the utilized sensors. This paper thoroughly assesses various sensor setups, including ultrahigh frequency (UHF) antennas and a high-frequency current transformer (HFCT), to identify the optimal test configuration for automotive hairpin stators. First, an optimization procedure is introduced to determine the most appropriate frequency range for each sensor to detect PD. In addition, an analysis of noise interference is conducted. Secondly, the signal-to-noise ratio (SNR) and the repetitive partial discharge inception voltage (RPDIV), as defined in IEC/TS 61934, are compared for the HFCT and different antennas at varying positions and distances. The HFCT has been found to have the highest sensitivity, resulting in lower RPDIV values in most test runs. Broadband UHF antennas provide a higher SNR than the antenna of the commercial PD tester, which only utilizes a narrow frequency band for PD detection. The sensitivity of all antennas under consideration increases when the distance to the test object is reduced. Synchronous acquisition with two identical antennas at different positions or a combined evaluation of the HFCT and an antenna promises a more reliable PD detection for a few test objects. Further, the choice of the sensor cannot systematically influence the RPDIV variation of several consecutive test runs, as the stochastic nature of PD occurrence causes this variation.