Simulation of Thermal and Electrical Transient Field Distribution of a HVDC Cable Laid in a Tunnel

The rapid development of high voltage direct current (HVDC) transmission technology has put forward increasingly higher requirements for the key technologies of HVDC cables. Compared to the steady-state operation characteristics, the performance of DC cables under transient working conditions is more worthy of attention. In this paper, the electrical and thermal transient field distribution of a 320 kV DC XLPE cable laid in a tunnel is simulated by finite element analysis (FEA) method under two typical conditions, load current fluctuation and surrounding temperature variation. The results show that the thermal and electrical field of the cable will be affected by the amplitude and duration of the transient load current, and the large thermal time constant enables the cable to transmit a certain short-term overload without being overheated. Besides, a short-time variation of the atmospheric temperature at the soil surface will not cause a noticeable change of the thermal and electrical field in the cable, but the change of the air temperature in the tunnel will affect the cable both thermally and electrically. Under transient conditions, attention should not only be paid to the temperature rise of the cable conductor, but also to the temperature gradient across the insulation.