500kV GIL Magneto-Thermal-Fluid Multi-physics Coupling Simulation and Characteristic Analysis

The temperature rise characteristics of Gas-Insulated Metal-enclosed Transmission Lines (GIL) are critical to their reliability design and safe operation. This study analyzed the coupling relationships between magnetic, thermal, and fluid fields during normal GIL operation. The temperature distribution within a 500 kV GIL system was accurately simulated using the finite element method. The model innovatively incorporated the enclosed tunnel air domain, while accounting for the temperature-dependent nonlinearity of material electrical conductivity, gas physical properties, and the bidirectional magneto-fluidic coupling mechanism. Variations in temperature, fluid dynamics, and magnetic fields were systematically investigated. Simulation results demonstrated a radial temperature gradient distribution within the GIL, characterized by elevated temperatures in upper regions and lower temperatures in bottom regions. At an ambient temperature of 25 °C, the maximum temperature rises of the conductor and enclosure reached 59.3 °C and 31.6 °C, respectively. A dual convective circulation pattern of SF6 gas was observed between the conductor and enclosure, featuring ascending gas near the walls and descending flow in the central region. This flow drives a high-velocity circulation zone at the top and a thermal stagnation zone at the bottom. The external magnetic field was attenuated to the order of 10−5 T due to the shielding effect of the GIL enclosure.