The Ohio State University Partial Discharge Detection Platform for Electric Machine Windings Driven by PWM Voltage Excitation

Unexpected premature insulation breakdown has been reported for many electric machines driven by variable speed drives (VSDs). A major cause is the reflected voltage overshoots at the machine winding caused by the pulse voltage excitation, leading to severe stress on the insulation system. At The Ohio State University (OSU), we have started a series of efforts to understand the degradation and breakdown of the insulation systems in electric machines driven by VSDs. This paper reports our activities on partial discharge (PD) detection and characterization for random-wound low voltage and form-wound medium voltage coils excited by PWM voltages. A PD detection platform has been established consisting of three main systems: the testing samples and setups, the pulsed voltage generation system, and the PD detection system. One silicon (Si) based and two silicon-carbide (SiC) based pulsed voltage generators were employed to produce voltage excitations with a magnitude up to 10 kV and a $dV/dt$ up to $\mathbf{70\ kV}/\mu\mathbf{s}$. The PD detection system, moreover, installed nine sensors catering to five different physical manifestations during PD: electrical current, electromagnetic wave, optical light emission, acoustic ultrasound emission and chemical ozone emission. The detection effectiveness of each type of sensor is presented and compared using twisted pairs of magnet wire samples. The demonstrated results hope to provide a better understanding of the effect of VSDs on the behaviors of PDs in electric machine winding insulation systems, and also some insight for the selection and evaluation of PD detectors for various VSD applications.