Study On Temperature Rise And Insulation Performance Of 12kV Switchgear Under Forced Air Cooling Conditions Based On Multi-physical Simulation

With the development of the global energy network,the capacity of electrical equipment is increasing,and the air-insulated alternating current metal-enclosed switchgear is widely used in electric power system.12 kV switchgear plays an important role in opening and closing,control and protection in the power system transmission,distribution and energy conversion process,it is the core equipment of the distribution system.In order to meet the requirements of large capacity,high reliability and intelligent for 12 kV switchgear,this also put forward with higher requirements of temperature rise and insulation performance on the high current switchgear.Thus,this paper studies the temperature rise and insulation performance of the switchgear under forced air cooling.The main work is as follows:Firstly,the solid model of 12kV/3150 A switchgear was modeled by three-dimension modeling software,and then simplified according to the requirements of the finite element simulation software.Taking consideration on the effect of skin effect,proximity effect,temperature on resistance and electrical contact on the heat volume of current carrying circuit parts,calculate the volume heat of each current-carrying circuit part in order to add the boundary condition when finite element simulation calculates.Secondly,the distribution of the temperature rise,the distribution of the airflow field and the insulation performance of the switchgear under forced air cooling were analyzed by the finite element analysis method.Firstly,the temperature rise and the distribution of the airflow field were analyzed under the condition of forced exhaust.Under the condition of forced exhaust,two cases were analyzed including the two axial fans of each compartment and the three axial fans of each compartment.The results show that the cooling effect of switchgear is better under the condition of forced exhaust,and with the increase in air volume,cooling effect is getting better and better.When there are threeaxial fans in each compartment,the temperature rise of switchgear is in line with the national standard temperature limit requirements with the use of temperature test to verify.The insulation performance of the switchgear was studied based on Bashen's Law by analyzing the distribution of the airflow field under the condition of forced exhaust,it was concluded that the switchgear had low insulation performance under forced exhaust.Then,the temperature distribution and airflow field distribution of the switchgear were analyzed by simulation with the circuit breaker room and the cable room installing cross flow fan respectively,the results were compared to the temperature rise test.Research indicates that the heat dissipation of switchgear is better under blast conditions,the temperature rise is in line with national standard temperature limit requirements,and the insulation performance of the switchgear is enhanced under forced blast conditions by analysis on airflow field distribution based on Bashen's Law.Then,the distribution of the pure gas flow field under the forced ventilation and blast conditions is analyzed respectively,and compared with the distribution of the airflow field under the current carrying conditions.The results show that the distribution of the airflow field caused by the current-carrying circuit itself has little effect on the total airflow field distribution of the switchgear under forced air-cooling conditions.It provides a theoretical basis that when carrying out insulation test of switchgear with forced air-cooled conditions,the switchgear does not need to provide current.At last,the forced blast is used as the way of forced air cooling in this subject by comparing the distribution of the thermal field and the insulation performance under forced and ventilated conditions.The maximum field strength is 27.296 kV / cm by the electric field simulation of the switchgear bus room,concluded that forced air cooling does not lead to insulation failure because there is a certain margin of insulation.According to the negative analysis of the insulation performance of the switchgear under forced air cooling,it is found that the insulation performance in the case of blast is higher than that of the ventilation,and corresponds to the above conclusions.Finally,under the forced blast condition,the switchgear was designed to optimize the heat flow field and verified by the temperature rise test.First of all,in order to reduce the cost of switchgear,the performance of insulation and temperature rise with thecondition of the switchgear circuit breaker room using cross-flow fan blast and cable room using axial fan blast are simulated and studied,verifying the test of temperature rise,at the same time comparing to the situation with the circuit breaker room and cable room are used cross-flow fan blowing.The research shows that temperature rise of the Phase A and Phase B bus-bar joints in the bus-bar room exceed the national standard temperature limit requirements when the cable chamber cross flow fan is replaced by the axial fan blower.And then simulate the situation of the cable chamber adds a baffle in order to change the air flow field distribution,which is not effectively.Secondly,the area of the through hole of the lower part of the bus-bar room is optimized,and the analysis shows that the temperature rise of the bus-bar room decline about 10 K and the heat dissipation capacity is improved with verifying by the temperature rise test.Finally,the structure of the bus-bar room front partition is optimized and verified by temperature rise test.The research shows that temperature rise of the phase of A and B bus lap in the bus-bar room decline about 6K,and the temperature rise of switchgear is in line with the national standard temperature limit requirements,achieve the purpose of reducing costs.