用于变压器负载能力评估的改进热电类比模型

Improved Thermal-Electrical Analogy Model for Evaluating Loading Capability of Transformer

油浸式电力变压器的负载能力与油温、热点温度密切相关.为了更加准确地计算顶层油温和热点温度,以助于变压器的负载能力评估,文中基于传热学理论和电路定律,对一种变压器热电类比模型作了改进.首先引入油黏度重新定义了变压器相关部件的非线性热导,并考虑变压器与其环境温度之间热传递的影响;然后在模型中引入热点温度节点,使模型能够真实反映变压器内部热传导的基本过程,并采用遗传算法来对模型中的热参数进行全局优化.以某180000 k VA变压器为例,将改进前后的热电类比模型分别计算得到的热点温度、顶层油温、底层油温与导则推荐的经验公式的计算值以及在线监测值进行比较,结果表明改进后模型有较好的计算准确性.之后使用改进热电类比模型计算该变压器在给定运行工况下的日相对寿命损失、最大顶层油温、最大热点温度,并用以评估该变压器的负载能力,为变压器增容提供参考.

The loading capability of an oil-immersed power transformer is closely related to oil temperatures and hot-spot temperatures( HST). In order to accurately calculate top-oil temperatures( TOT) and HSTs and thus help evaluate the loading capability of the oil-immersed transformer,a thermal-electrical analogy model for the transformer is improved based on the principle of heat transfer and the circuit laws. In the improved model,first,the oil viscosity is introduced to redefine the nonlinear thermal conductance of the relative parts of the transformer,and the heat transfer between the transformer and the ambient environment is taken into account. Then,a hot-spot temperature node is introduced into the improved model,so that this model can really reflect the general process of the heat transfer in the transformer. Finally,a genetic algorithm( GA) is employed to globally optimize thermal parameters. By taking a 180 000 k VA oil-immersed power transformer as an example,the calculated results of the HSTs,TOTs and bottom-oil temperatures of the original and improved models are compared with the on-line data and the results calculated by the recommended empirical formulas in the transformer loading guide. It is found that the improved model is more accurate. Then,the improved model is used to calculate the relative daily loss of life,the maximum TOT and the maximum HST of a large oil-immersed power transformer in given working conditions,so as to evaluate the loading capability of the tested transformer and thus provide a reference for the load rating increase of the tested transformer.