A Measurement Set-Up Method to Evaluate Motor Winding Quality and Winding Insulation by Exploring Discharge Characteristics

Paper i proceeding, 2018

The development of new semiconductor materials such as SiC and GaN based designs introduces shorter rise times as well as increased carrier frequencies in power electronic applications. One very common reason for motor winding failures is due to the presence of partial discharges (PDs). This paper presents a test method to detect and evaluate the presence of PDs employing wave shapes similar or close to what is used in applications. The waveform is generated by applying a novel three-level inverter circuit. The set-up and detection method can for example be used to evaluate the influence of rise times, reflections and insulation conductivity on simple twisted pair test samples or complete windings. Initial measurement results from tests on twisted pair aimed to resemble a random wound motor are presented. In particular, the influence of conductivity, permittivity and rise time is explored by applying square shaped waveforms. The PDs appearing after the unipolar flanks are compared with full size bipolar voltage steps. When the zero voltage was reached the remining charges within and surrounding the defect produced a PD pattern (PD echo) resembling the charge amount within the winding. Tests showed a significant difference due to the choice of material. The introduced measurement approach maintains the advantages of using impulses to evaluate windings but complemented with charge decay measurement.