油浸式电力变压器动态热路改进模型

油浸式电力变压器绕组的热点温度是指导变压器负载运行方式和影响变压器绝缘寿命的重要参数,准确计算绕组热点温度具有重要意义。在分析运行变压器散热过程的基础上,考虑油箱外壁与周围环境的热量传递,利用传热学原理和热电类比方法,定义非线性热阻和集总热容,并考虑油粘度随温度的变化,建立电力变压器动态等效热路的改进计算模型。将模型的计算结果与实验室自然油循环自然空气(oilnatural-air natural,ONAN)冷却方式下100 kVA/5 kV油浸式温升试验变压器实测数据和IEEE Std C57.91推荐方法计算值进行对比,比较结果表明:通过改进模型计算的变压器顶层油温和绕组热点温度具有较高的精度。

An Improved Dynamic Thermal Circuit Model of Oil-Immersed Power Transformer

The hottest spot temperature(HST) of windings of oil-immersed transformer is an important parameter that determines operation modes of power transformer and influences on insulation life of power transformer,therefore it is significant to calculate HST of winding accurately.On the basis of analyzing heat dissipation of transformer being operated and considering the heat transfer from outer wall of transformer oil tank to ambient environment,using the principle of heat transfer and thermal-electrical analogy the nonlinear thermal resistance and lumped thermal capacity are difined,and taking the variation of oil viscosity with temperature an improved calculation model of dynamic equivalent thermal circuit for power transformer is built.Comparing calculation results of a 100 kVA/5 kV oil immersed transformer for temperature rising test in laboratory under oil natural-air natural(ONAN) cooling mode by the proposed model with its measured data as well as comparing the calculated results by the proposed model with the results calculated by the recommended method in IEEE Std C57.91,both comparison results show that the temperature of transformer oil at the top layer in the oil tank and the HST of the windings calculated by the proposed improved model are more accurate.