油浸式电力变压器匝间故障早期的电热特性研究

Study on Electrothermal Characteristics of Oil-immersed Power Transformers in Early Stage of Interturn Faults

油浸式电力变压器匝间绝缘的老化和劣化会造成匝间绝缘电阻减小,从而引起故障线圈上电流和产生热量增加。因此,研究变压器匝间故障早期的电热特性具有重要意义。该文分析匝间故障电阻对变压器等效电路和绕组损耗的影响,提出基于电磁、热–流体场耦合的变压器匝间故障模型。基于数字孪生(digital twin,DT)的理念,建立变压器的高保真仿真模型,通过传递变压器实体的结构、尺寸、材料参数等,实现对绕组电流和不同部件温度的准确模拟。采用此高保真仿真模型,研究高压绕组发生1%匝间故障的电热特性,结果表明低压绕组电流幅值仅增加2%,而顶层油温升高了9.4℃(25.7%),油箱外壳整体温度升高了10℃。在匝间故障早期阶段,顶层油温和油箱外壳温度的变化较绕组电流更为显著,因此,顶层油温、油箱外壳温度和绕组电流等电热特性参量可用于辨识早期故障。

The aging and deterioration of interturn insulation in oil-immersed power transformers cause interturn insulation resistance to decrease,which results in an increase in current and heat generation on the faulty coils.Therefore,it is important to study the electrothermal characteristics of the transformer in the early stage of interturn faults.By analyzing the effect of interturn fault resistance on the transformer equivalent circuit and winding losses,a transformer interturn fault model based on coupling the electromagnetic and thermal-fluid fields is proposed in this paper.Based on the idea of digital twin(DT),a high-fidelity simulation model of the transformer is established to achieve the accurate simulation of winding currents and temperatures of different components by transferring the transformer entity’s structure,size,and material parameters.The high-fidelity simulation model is used to study the electrothermal characteristics of the transformer with a 1%interturn fault in the high-voltage winding.The results show that the current amplitude of the low-voltage winding only increases by 2%,while the top oil temperature rises by 9.4℃(25.7%),and the overall temperatures of the tank wall rise by 10℃.In the early stage of interturn fault,the changes in top oil and tank wall temperatures are more significant than the winding currents,so the electrothermal characteristic parameters such as top oil temperature,tank wall temperature and winding currents can be adopted to identify the early fault.