Preventing Partial Discharge in Motor Winding Under Steep Voltage Pulses Using Functional Capacitive Field-Grading Composites

Power electronic converter (PEC)-fed transformers and motor insulation face a considerable challenge from the nonsinusoidal repetitive steep high-voltage pulses leading to premature breakdown. The increased local electric stresses in the winding insulation cause partial discharge (PD), leading to the degradation and aging of the windings. This study investigates functional capacitive field-grading composites (FCFGCs) to prevent the incidence of PD. PD tests are conducted on simplified test objects of motor windings, such as twisted pair samples, subjected to steeply rising square voltage waves. The FCFGC materials are fabricated by dispersing ferroelectric barium titanate (BTO) powder into polydimethylsiloxane (PDMS) matrix. The FCFGC demonstrates higher relative permittivity compared with pure PDMS, and this characteristic also shows dependence on the electric field. The current-voltage (I–V) characterization reveals that the electric field dependence of the FCFGC increases as the BTO filler contents are raised. PD experiments are carried out using unipolar square waveforms with slew rate as high as 0.22 kV/ns on enameled twisted pair wires. This involves applying a coating of pure PDMS and five distinct FCFGC samples with BTO loadings of 10%, 20%, 30%, 40%, and 50%. Experimental findings indicate that FCFGCs can reduce PD magnitudes and enhance PD inception voltage (PDIV) compared with neat PDMS insulation. Increasing the BTO filler loading reduces PD magnitudes and increases the PDIV by 2.68 times (i.e., 168%). In addition, numerical models are used to conduct electric field analyses of the twisted pair experiments. These models incorporate the field-dependent permittivity (FDP) of the FCFGC characterized experimentally, providing a more comprehensive understanding of the experimental outcomes.