The main part of oil-immersed power equipment is oil-paper insulation. At lower ambient temperatures, transformer oil will become viscous. As a result, compared to those at room temperature or operating temperature, the frequency domain dielectric properties of oil-paper insulation at low temperatures are drastically different. For evaluating the insulation condition of electrical equipment, it is essential to accurately determine their dielectric properties. This paper described the FDS test, the DC conductivity test, and the transformer oil viscosity test, which was carried out in a laboratory environment for different ageing of oil-immersed pressboard and transformer oil at 233–373 K. The effects of temperature on the dielectric properties at the competing mechanisms of polarisation and conductivity loss were clarified based on variations of the FDS curves. Considering the viscosity change of ageing transformer oil at low temperatures, the Arrhenius and VFT viscosity equations were used to achieve a fitting calculation in the different temperature zones. Based on the molecular/ion transition model in the force field and electric field, the characterisation relationships between the dynamic viscosity, DC conductivity, and test temperature of transformer oil were established. The limitations of conventional transformer oil equivalent dielectric relaxation models over a wide temperature range were finally clarified by combining the test findings of the DC conductivity over a wide temperature range with observed and simulated calculations. This paper provides an essential theoretical reference when using the FDS test to diagnose the insulation performance of oil-immersed power equipment in extremely cold regions.

中文翻译：

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电力设备油纸绝缘宽温度范围介电性能变化研究

油浸式电力设备的主要部分是油纸绝缘。在较低的环境温度下，变压器油会变得粘稠。因此，与室温或工作温度下相比，低温下油纸绝缘的频域介电性能有很大不同。为了评估电气设备的绝缘状况，准确测定其介电性能至关重要。本文介绍了在实验室环境下对233~373 K的油浸纸板和变压器油进行不同老化的FDS测试、直流电导率测试和变压器油粘度测试。根据 FDS 曲线的变化，阐明了极化和电导率损耗竞争机制下的介电特性。考虑到老化变压器油在低温下的粘度变化，采用Arrhenius和VFT粘度方程实现了不同温区的拟合计算。基于力场和电场中的分子/离子转变模型，建立了变压器油的动力粘度、直流电导率和试验温度之间的表征关系。通过将宽温度范围内直流电导率的测试结果与观测和模拟计算相结合，最终阐明了传统变压器油等效介电弛豫模型在宽温度范围内的局限性。本文为极寒地区利用FDS试验诊断油浸式电力设备绝缘性能提供了重要的理论参考。