564 / 2017-05-14 18:13:13

Numerical Analysis of Transient Overvoltages from Sequential Switching of 220 kV Tunnel Cables

880,14177,14176,4392,14175

The 220 kV XLPE cables laid in tunnel had a wide utilization urbanely. 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 the transient overvoltages especially the ones caused by a sequence of switching on and off un-loaded lines with the re-strikes of circuit breaker. In order to clarify the cause of the damages and characteristics of switching overvoltages on the 220 kV tunnel cables, the models of simulating calculations were established based on a typical cable transmission line in Zhuhai of China and with the PSCAD/ EMTDC software in this paper. The modeling processes for the cables with cross-bonding connection and re-strikes of circuit breaker were also presented. The switching transient overvoltages caused by the various line faults were calculated as well as the operation states on the transmission system before a short-circuit fault in practice were simulated. And the characteristics and distributions of switching transient voltages along the cables were obtained. In addition, the influences to these switching overvoltages were also discussed. The calculation results indicated that the operation of switching off un-loaded lines with the sequential re-striking of circuit breaker would lead to serious overvoltages on the cables, and the phases and phase position that the re-striking happened on would have an effect on the maximum peak value of overvoltages. Besides the overvoltages caused by switching on un-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 overvoltages caused by switching off un-loaded lines which were more serious and could do the substantial damage to the cables and their joints. The study could provide some advices for the insulation coordination of 220 kV XLPE cables laid in tunnel.