Research On Hot Spot Temperature Detection Technology Of Oil Immersed Power Transformer Winding

The health status of power transformer is related to the safe and stable operation of power grid.Oil immersed power transformer with large capacity,good heat dissipation performance,low energy consumption advantages,is widely used in the construction of power grid.The end of the life of most transformers is due to the destruction of their insulation capacity,and the most important factor affecting the insulation capacity is the temperature in the hottest region of the winding,that is,the winding hot spot temperature.At the same time,too high hot spot temperature will cause additional power loss,which will affect the business efficiency of enterprises.Therefore,it is of great significance to accurately detect the winding hot spot temperature of the transformer in operation for prolonging the service life of the transformer and optimizing the utilization of the maximum load capacity of the transformer.This paper analyzes the structure and heat dissipation mechanism of oil immersed power transformer,deeply studies the detection method of winding hot spot temperature,and designs and develops a set of temperature detection system.The main research contents and achievements include:（1）The analysis of winding hot spot temperature characteristics of oil immersed power transformer is the basis of studying winding hot spot temperature detection technology.Therefore,the structure characteristics of oil immersed power transformer are compared and analyzed,and the internal heating principle and heat dissipation mechanism of the equipment are expounded.At the same time,the necessity of winding hot spot temperature detection of oil immersed power transformer is explained,and the advantages and disadvantages of different detection methods of winding hot spot temperature are compared.It is considered that the pre embedded temperature sensor is usually not the accurate location of the hot spot for the operating transformer,and the measured data can not fully reflect the real situation.On the basis of making full use of the existing conditions,the hot spot temperature of the winding can be obtained by the calculation method,which can more accurately reflect the actual situation of the internal temperature distribution of the transformer.（2）In order to solve the shortcomings of existing calculation methods and improve the calculation accuracy of winding hot spot temperature,an improved dynamic equivalent heat circuit calculation model with physical significance is proposed by referring to the internal heat flow process of transformer and combining with the basic knowledge of heat transfer.The equivalent thermal resistance R_m’of the radiator and the equivalent heat source power q_cu’of the hot spot based on the thermal distribution characteristics of the winding of the oil immersed self cooling transformer are defined;At the same time,the influence of temperature rise on oil density and viscosity is considered;L-M algorithm is used to optimize the time constant of transformer winding;Finally,the model is built by MATLAB for simulation verification.After verification,under the condition of constant load,the error of hot spot temperature simulation results and field measurement results is within 3℃;Under dynamic load,the maximum error is 2.1℃.The simulation results are compared with the simulation results of the guide model and the model without considering the heat sink,which proves the feasibility and high accuracy of the proposed method.（3）In order to meet the needs of engineering practice,according to the proposed improved thermal circuit model calculation method,the hot spot temperature detection system of oil immersed power transformer winding is developed,and the main control flow of the temperature detection system is designed,which realizes the self calibration of top oil temperature of oil immersed power transformer and the real-time detection of hot spot temperature.The device is applied to the operation site,and the error between the measured hot spot temperature and the measured value is within 2.3℃,which verifies the effectiveness of the hot spot temperature detection method proposed in this paper.