The Electrical-Thermal Coupling Simulation of Grafted Polypropylene Used in High-Voltage Direct Current Cables

Under direct current (DC) operation conditions, local electric field in insulation layer will be distorted, leading to insulation failure. Since the conductivity of insulating materials generally corresponds positively with temperature, a temperature gradient will form inside the insulating material during cable operation, making the conductivity distribution uneven and causing the “electric field reversal” phenomenon in the cable insulation layer. The distribution of the electric field and temperature field of the polypropylene grafted as the cable insulation under the electric heating-coupling field is yet to be studied. Studies have proved that by grafting modification the insulating properties of materials can be improved. This paper studied the and conductivity characteristics of grafted polypropylene materials, and selected one type for more experiments to obtain the material's conductivity-temperature-electric field strength characteristic equation through data fitting. A model of a 100 kV DC cable was established in COMSOL, and simulation of the cable section’s electric heating-coupling field was performed, revealing the temperature and electric field distribution inside the insulation layer when the cable is rated, overloaded, or short-circuited. This paper can provide some reference for operational analysis of polypropylene-insulated HVDC cables.