极寒条件下纳米SiO_(2)改性变压器油的导热和绝缘特性

Thermal Conductivity and Insulation of Nano-SiO_(2) Modified Transformer Oil Under Extremely Low Temperatures

提高极寒条件下变压器油的导热和绝缘特性,对保障变压器的冷启动和安全运行至关重要。为此系统研究了极寒条件下纳米SiO_(2)改性变压器油(45号)的导热和绝缘特性,对不同SiO_(2)体积分数(0.5%、1%和1.5%)和不同含水率(质量分数5.6×10^(-6)、15.4×10^(-6)、23.0×10^(-6)和33.4×10^(-6))的纳米SiO_(2)改性变压器油(改性油)的导热系数、介电性能和击穿场强进行测量,并分析其对改性油绝缘特性的影响。试验结果表明:随着温度从30℃降低到–45℃,改性油的导热系数不断减小,相对介电常数呈线性增加,介质损耗因数先增大到峰值后减小。改性油的击穿场强受到水分和纳米SiO_(2)的综合影响:不同SiO_(2)体积分数改性油的击穿场强均随温度的降低先减小后增大,在–10~0℃取得极小值。当含水率均为15.4×10^(-6)时,SiO_(2)体积分数为0.5%的改性油绝缘性能较纯净油(未掺入SiO_(2))得到明显提升,击穿场强极小值提升14.7%;当改性油的含水率较低(质量分数≤5.6×10^(-6))时,纳米SiO_(2)的加入并不能提升变压器油绝缘性能;当改性油的含水率较高(质量分数>15.4×10^(-6))时,纳米SiO_(2)的加入可以大幅提高改性油的绝缘性能,含水率为33.4×10^(-6)时改性油击穿场强极小值较纯净油提升71.6%。

Improving the thermal conductivity and insulation of transformer oil under extremely low temperatures is very important to ensure the cold start and safe operation of transformer. In this paper, the thermal conductivity and insulation of nano-SiO_(2)modified transformer oil(no.45) under extremely low temperatures were systematically studied. The thermal conductivity, dielectric properties and breakdown field strength of transformer oil with different SiO_(2)concentrations(0.5%, 1% and 1.5%) and different moisture contents(5.6×10^(-6), 15.4×10^(-6), 23.0×10^(-6)and 33.4×10^(-6)) were measured.And their effects on the insulation properties of modified oil were analyzed. The test results show that, with the temperature decreasing from 30 ℃ to –45 ℃, the thermal conductivity of nano-SiO_(2)modified transformer oil decreases, the relative dielectric constant increases linearly, and the dielectric loss factor first increases to the peak and then decreases.The breakdown field strength of nano-SiO_(2)modified transformer oil is comprehensively affected by water and nano-SiO_(2):the breakdown field strength of modified oil with different SiO_(2)concentration first decreases and then increases with the decrease of temperature, and the minimum value is obtained near –10~0 ℃. When the moisture content is 15.4×10^(-6), the insulation performance of modified oil with SiO_(2)concentration of 0.5% is significantly improved compared with pure oil(without SiO_(2)), and the minimum breakdown field strength is increased by 14.7%;When the moisture content of the modified oil is low(5.6×10^(-6)), the addition of nano-SiO_(2)can not improve the insulation performance of transformer oil;When the moisture content of the modified oil is high(more than 15.4×10^(-6)), the addition of nano-SiO_(2)can greatly improve the insulation performance of the modified oil. When the moisture content is 33.4×10^(-6), the minimum breakdown field strength of the modified oil is 71.6% higher than that of the pure oil.