Abstract: The structure of high-voltage power cables is complex, and the insulation failure time is different from that of low-voltage cables under fire condition. Firstly, the fire test platform is built in this paper. The insulation withstand voltage breakdown test of 110 kV and 10 kV flame-retardant power cables under fire conditions is carried out. The insulation failure time is recorded, and the internal condition of the cable is dissected and analyzed. Then a 3D simulation model is established to analyze the temperature change of the insulation layer inside the cable under fire. Referring to the breakdown field strength of insulating layer material at high temperature, the insulation failure mechanism of high-voltage cable under fire is analyzed in combination with simulation and test. The results show the insulation layer of high-voltage cable softens and melts before breakdown under fire condition. The metal sheath breaks and the melt drops. The insulation failure time of 110 kV and 10 kV power cables under 200 kW fire source power is about 130 min and 60 min, respectively. The simulation results show that the melting time of insulation layer of 110 kV power cable is about 25 min, and the average temperature of breakdown time is about 378 ℃. The discharge develops gradually in the molten insulation layer and finally forms breakdown. The insulation failure time can not be determined by a single insulation material failure temperature, which is related to the insulation structure and temperature rise change.

Key words: high-voltage power cable, breakdown test, simulated fire, temperature distribution, insulation failure