Distribution Transformer Winding Material Identification Method Based On Thermoelectric Effect

"Replacing copper with aluminum " means replacing copper with aluminum as the material of transformer winding which is a hidden rule of distribution transformer in China. It’s a shoddy product if there is no special mark on the aluminum transformer. This phenomenon not only bring economic losses, but also buried a security risk. China State Grid Corp has found such cases, but the traditional method is opening the transformer which is complicated and high cost. So researching a convenient and effective nondestructive testing method is valuable.This paper provides a convenient and effective nondestructive testing method to identify winding material based on thermoelectric effect. The inverse application of thermocouple temperature measurement is the starting point of the method. The thermocouple measures temperature by measuring the thermal potential of known material, and the method of this paper is to determine the material by measuring the thermal potential and temperature. Transformer temperature rise will produce thermoelectric effect, the nondestructive testing can be realized by the difference of the thermal potential.The seebeck coefficient difference of copper and aluminum is about 4μV/K through theoretical calculation and experimental measurement, and it’s less than 1μV/K between different copper. Based on the analysis of the process of the thermoelectric effect of the transformer, the relationship between the total thermal potential and the winding material is derived. The threshold value Um is determined to be 80μV combined with the actual situation and considered a certain margin. The establishment of transformer winding temperature difference is the key of the method, so the temperature field of transformer winding is analyzed. The temperature field is mainly established by contact heat conduction and heat convection with transformer oil, because the transformer is not running.The finite element method software ANSYS is used to simulate the temperature field. The temperature of the key point is above 30 degrees C, which can meet the requirements of the detection method. Based on the research on temperature field, this paper continues to analyze the electric field distribution of transformer winding circuit using the thermoelectric coupling of ANSYS software. The simulation results accord with the theoretical expectation, and can meet the requirements of the experiment. Finally, this paper makes experiments study on single windings and real power distribution transformers. The experimental results can effectively distinguish that the material of distribution transformer winding is copper or not.