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 R2 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.