Thermal Analysis Of 12kV Cubicle Gas Insulated Switchgear

Medium voltage switchgear is an important part of power distribution system.The overheating of the switchgear is easy to cause aging material,dropping the strength of mechanical and insulation and reducing the working life span.This will badly affect electrical equipment and even causes power grid accidents.In this paper,under stable condition and short time overload condition,the three-dimensional temperature field and fluid field of 12kV C-GIS are calculated and analyzed with math model and finite element analysis software.The effect of temperature rise on internal current-carrying is calculated for the high thermal conductive material and different size of switchgear structure,which provides the theoretical analysis on heat radiation of the current-carrying loop in enclosure space.The optimization of design on the switchgear radiation is presented,which is great significance to ensure the safe and reliable operation of GIS.The main research work includes the following aspects:1.Temperature rise test is carried out,according to the national temperature rise test standard of the medium voltage switchgear.The main loop resistance is measured,for each key point,the temperature rise with steady state is obtained by thermocouple measurement with the reasonable experiment layout of a certain type of switchgear.2.The heating problem of the switchgear are related to heat source and heat transferring,so it needs combined solution of the temperature field and fluid field.The GIS switchgear coupling heat transferring mathematical model is established based on the differential equation of heat conduction and fluid motion control equation and the radiation heat transferring equation.And the zero equation turbulence model and wall function are used for treatment on the surface of the solid and fluid coupling convective thermal dissipation.The calculation time is saved and the calculation procedure is simplified with the precision of numerical calculation.The influence on temperature rise from all factors is included as follows:the effects of SF₆ gas physical parameters on temperature rise,current skin effect and proximity effect,conductor contact resistance and so on.3.The convection and radiation heat transferring effect of the switchgear and the characteristics of the fluid physical property change with temperature are taken into account for the temperature field calculation,which reduces the error caused by applying fixed coefficient and constant parameters.The numerical calculation results of steady state condition matches with the temperature rise test values and the error is within 3K.The phase B has the worst heat dissipation condition in the current-carrying loop cooling.The Contact of three position switch and vacuum circuit breaker has the highest temperature,and the heat dissipation effect is enhanced by internal gas circulating near the current-carrying loop.Three-dimensional temperature field and fluid field distribution of the switchgear are analyzed;from the aspect of system,the proportion of the total heat transfer are respectively calculated for circuit breaker room,the shell convective heat transfer and thermal radiation,which providing theoretical basis for C-GIS’s cooling optimization.4.The three-dimensional temperature field and fluid field distribution of C-GIS under the short-time overload situation is calculated with the initial condition of the steady state condition numerical results,which verifies the switchgear load ability.The temperature rise time curve is obtained for the temperature rise point of the switchgear,and temperature rise has no changes with current because of the thermal lag.Finally,the influence of the temperature rise of current-carrying loop with thermal conductive polymer materials and the structure size of switchgear are numerically calculated and analyzed.The results provide the reference for the optimization and thermal design of the switchgear.