Transient analysis of a crossbonded cable system underneath a bridge

Transients on a crossbonded cable installed underneath a bridge and connected with overhead lines are analyzed using the EMTP (ElectroMagnetic Transients Program). Calculated results of the sheath voltages on a system composed of only a cable show that the maximum overvoltages on the cable installed underneath the bridge, which is a kind of overhead cable, are higher by about 2.5 times than those on an ordinary underground cable. The iron framework of the bridge, which is simulated as parallel overhead conductors to the cable, reduces the overvoltages by about 20% to 50% due to mutual coupling. When overhead lines are connected to the cable system at both terminals, the sheath overvoltages are reduced to about 20% of those in the case of the cable system alone, but the reduction by the iron frameworks of the overvoltages becomes less pronounced. It is emphasized that special attention should be paid to the insulation coordination of a crossbonded cable installed to a bridge