Temperature Rise Calculation Model And Load Capacity Evaluation Of Buried Transformer

With the proceeding of urbanization,the above-ground substations have gradually revealed drawbacks in the problems of urban beautification and land resource utilization.The emergence of buried substations has brought about many new problems while effectively solving the above problems.Because of the closed buried space,the temperature rise problem of the buried transformer is more prominent than that of the above-ground transformer.However,the research on the temperature rise problem and the design of the heat dissipation scheme are mostly based on the design criteria of the general box-type substation,with a smaller power supply load for design standard.Under the background of the continuous increase of total electricity consumption in society,studying the temperature rise process of buried transformers is of great significance for the safe and efficient operation of power systems.In this regard,this paper studies the temperature rise and heat dissipation of buried transformers.The main research of the thesis is as follows:(1)A calculation method for temperature rise model of buried transformer considering the environment inside buried substation and the thermal properties of soil outside the station is proposed.Combined with the heat dissipation process of the buried transformer,the parameters and mathematical modeling of the heat transfer links such as the internal environment of the station and the soil outside the station in the thermal circuit model are carried out to obtain the differential equation of the thermal circuit model.The temperature rise calculation of the buried transformer is carried out by this method.This method is used to calculate the temperature rise of buried transformers,and the results show that the calculation accuracy of the steady-state hot-spot temperature-rise is 1.73%,1.05%,and 1.94% higher than the calculation method provided by the load guide for transformers when the load rate is 0.8,1 and 1.05,respectively.The obtained temperature rise curve is also closer to the actual process.(2)The numerical simulation method is used to simulate and optimize the temperature distribution under different ventilation and heat dissipation schemes of a buried substation.Modeling and simulation calculation of a brand of buried substation under the ANSYS Icepak simulation platform,and proposing different ventilation and heat dissipation measures for optimization simulation.Modeling and simulation calculation of a brand of buried substation under the ANSYS Icepak simulation platform,and proposing different ventilation and heat dissipation measures for optimization simulation.The actual temperature rise test data is used to verify the validity of the numerical simulation method.The simulation results show that the proposed scheme can reduce the average temperature in the buried substation to a certain extent.The heat dissipation effect is optimal when the fan is turned on,and the average temperature of the pit is reduced by about 43.5%.Changing the vent position is optimal when the ventilator is not turned on.The simulation method also provides the foundation for the following research.(3)A dynamic temperature rise calculation method considering heat accumulation in the pit is proposed to evaluate the dynamic load capacity of the buried transformer.By means of numerical simulation method,the dynamic process of pit heat accumulation is simulated and analyzed,and the dynamic temperature rise calculation and load capacity evaluation are carried out by combining the thermal path model in chapter 2.In case one,the allowable load table under short-term emergency load is established.Case two,three analysis shows that the heat accumulation process of the pit will slow down the temperature rise and thus reduce the hot-spot temperature-rise.In the calculation of buried transformers operating under equivalent multistage matrix load and dynamic load,the expected value of load capacity increased by 4.4% and 1.3%,the expected value of life loss decreased by 23.5% and 10.45%,respectively,after considering the heat accumulation of pit.The accuracy of the load capacity assessment is improved.In conclusion,this paper proposes a thermal circuit model for temperature rise calculation taking into account pit heat accumulation,which improves the calculation accuracy of hot-spot temperature-rise and the accuracy of load capacity evaluation,provides a new idea for fully exploring the load capacity of buried transformer,and also provides a reference for the heat dissipation design of buried substation.