Humidity Impact on Streamer Inception Parameters for Turn-to-Turn Insulation of Inverter-Fed Motors

This study explores the impact of varying relative humidity (RH) levels (30%-90%) at 90°C on streamer inception parameters (SIPs) compared to those at 25°C. Schumann's streamer inception criterion (SCSIC) is used to assess the vulnerability of turn-to-turn insulation in inverter-fed motors with rising humidity at 90°C. The analysis includes SIPs such as effective ionization coefficient of air (α
eff
), partial discharge (PD) inception field (
$E$
inc
), critical field line length (CFLL), and firing voltage (
$V$
firing
). Furthermore, this study emphasizes the humidity-dependent shift in the Schumann constant (i.e., the natural logarithm of the critical electron number that determines the Townsend-to-streamer discharge transition,
$K$
) from 25°C to 90°C and advises caution when using the derived
$K$
at room temperature (e.g., 25°C) to predict PDIV at higher temperatures (e.g., 90°C), especially when RH≥50%.