Modeling Air Pressure Impact on PDIV for Rectangular Wire Turn-to-Turn Insulation of Inverter-Fed Motors Under Different Voltage Waveform Excitations

This study investigates the partial discharge inception voltage (PDIV) in turn-to-turn insulation of form-wound windings in inverter-fed motors under nine different air pressures, ranging from 1013 mbar to 10 mbar. The research evaluates three voltage waveform excitations: 50 Hz AC, unipolar positive (UP), and bipolar (BP) steep-fronted square waves. The pulse width modulation (PWM) excitations are characterized by a switching frequency of 2.5 kHz, a rise time of 80 ns, and a pulse width of $100~\mu $ s. The experimental analysis focuses on peak and peak-to-peak PDIV values, comparing the variations between 50 Hz AC and PWM excitations across different air pressures. In addition, a novel predictive PDIV model is developed using Schumann’s streamer inception criterion (SCSIC) to account for air pressure variations across the three waveform excitations. As another innovation, the model examines streamer inception parameters (SIPs) in rectangular turn-to-turn insulation, incorporating factors such as critical field line length (CFLL), effective ionization coefficient ( $\alpha _{\mathrm {eff}}$ ), partial discharge inception field ( $E_{\mathrm {inc}}$ ), and firing voltage ( $V_{\mathrm {firing}}$ ) under varying air pressures and voltage waveforms. This study provides critical insights into partial discharge phenomena and their potentially destructive effects on rectangular insulated wires. These findings are vital for insulation designers seeking to develop PD-free designs by considering the impact of air pressure, voltage waveform, and variations in SIPs.