Determination of Hotspot Temperature Margin for Rectangular Wire Windings Considering Insulation Thermal Degradation and Partial Discharge

Increasing current density is a common way to improve the power density of electrical machines (EMs) which also boosts the winding temperature. Higher winding temperature accelerates the thermal degradation of insulation and also increases the risk of partial discharge (PD). Commonly, the winding hotspot temperature constraint is decided based on an over-engineering approach (i.e., the winding hotspot temperature is 30°C below the wire thermal class) constraining the EM's performance. In this paper, the margin of winding hotspot temperature is precisely determined focusing mainly on the insulation degradation issues through experimental investigation. The partial discharge inception voltage and partial discharge extinction voltage have been measured under different temperature conditions for samples with different thermal aging statuses. Rectangular wires which find application in automotive motors are selected as test samples. The results link the temperature with the PD risk and the thermal lifetime of the insulation, and the winding hotspot temperature margin is accordingly determined. An automotive case study is presented to prove the applicability of the investigation outcomes.