Electro-Thermal Simulation on Gas Insulated Switchgear: Influence of High Altitude on Thermal Ampacity

In high altitude area, the gas insulated switchgear (GIS) design is a challenge due to the decreased air density, especially for non-SF6 filled GIS. Thermal ampacity and gas filling pressure needs to be studied taking both thermal and structure aspects into consideration. An electrothermal simulation method is conducted to analyze both temperature distribution and pressure difference in temperature rise test at high altitude condition (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1000 \sim 5500 \mathrm{m}$</tex>). The model is firstly finetuned to meet test records at certain altitude to ensure the accuracy, and then expanded to more precise altitudes. Proper current alternating (AC) derating factors are studied to meet both thermal and structural requirements. Overall, this simulation method provides reasonable design guidance in thermal design of high-altitude GIS.