Numerical analysis of transient overvoltages from sequential switching of 220 kV tunnel cables

220 kV cross linked polyethylene (XLPE) cables laid in tunnel had a wide utilization urbanely, and the cables, linked by cable joints with cross-bonding connection, are also convenient for maintenance and installation. However, there were a few short-circuit faults happening in recent years due to the damages on the 220 kV cables or their joints which were probably caused by switching the no-loaded cable lines. In order to clarify the cause of the damages and characteristics of switching overvoltage on the 220 kV tunnel cables, the models of simulating calculations were established with PSCAD/ EMTDC software based on a typical transmission system, and the modelling processes for the cables with cross-bonding connection and re-strikes of circuit breaker were presented. The switching overvoltages caused by the typical line faults were calculated. And the characteristics and distributions of overvoltages along the cables were obtained. The calculation results indicated that the operation of switching off no-loaded lines with the concomitant re-striking of circuit breaker would lead to most serious overvoltage on the cables. Besides the overvoltage caused by switching on no-loaded lines could be effectively limited by the installation of the closing resistor of circuit breaker. Furthermore, the short-circuit faults in practice might be the consequence of the overvoltage caused by switching off no-loaded lines which were more serious and could produce the substantial damage to the cable and its joints. The study could provide some advice for the insulation coordination of 220 kV XLPE cables laid in tunnel.