Temperature normalisation and moisture assessment of oil‐paper insulation based on dielectric response in extremely cold conditions

Frequency domain spectroscopy (FDS) is widely used for assessing the condition of oil‐paper insulated electrical equipment. However, in low temperatures, measurement results often deviate from expected values. This study investigates the low‐temperature dielectric response characteristics of oil‐paper insulation under large temperature differences (−60°C to 30°C), wide frequency ranges (1 mHz–5 kHz) and varying moisture contents (0.41%–3.91%). The mechanisms of low‐temperature effects on oil‐paper insulation relaxation polarisation are revealed. Further, a novel low‐temperature normalisation method and a moisture evaluation method are proposed based on the improved Havriliak–Negami model. Compared to traditional methods, the new approach significantly enhances the accuracy. The goodness of fit R 2 for temperature normalisation improves from 0.9526 to 0.9757, and the error in moisture content evaluation has reached 0.498%. Finally, the novel approach is applied to diagnose the condition of a damped bushing model, demonstrating high potential for practical applications. This study enables condition diagnosis of oil‐impregnated electrical equipment in extremely cold environments, filling a critical gap in the field.