A Surge Analysis of a Cable System Composed of Submarine and Underground-Overhead cables

This paper presents experimental observations of surge propagation characteristics on various cables, i.e. overhead, on a building floor, on the earth surface, underground and in water. Fig. 1 illustrates the experimental circuits, and Fig. 2 shows measured results. From the measured results, it becomes clear that a coaxial mode of surge propagation does not depend on the cable outer medium, either overhead or underground, as is well-known. However, an earth return mode is heavily dependent on the outer medium. EMTP simulations of the experiments are carried out, and the simulation results show a satisfactory accuracy in comparison with the experimental results. Surge characteristics of a cable system composed of submarine and underground / overhead cables are investigated based on EMTP simulation results considering cable cross-bonding and the length of a minor section. Table 1 summarizes the maximum overvoltage on phase of a 3-phase cable. It is clear from the table that the core overvoltage is not influenced by the outer medium of the cable. The cross-bonding reduces the core voltage by about 20%. Therefore it is better to adopt the crossbonding for the insulation of the cable core. On the contrary, the sheath overvoltage becomes much higher in a cross-bonded cable, especially if there is a submarine cable in the system. Thus the cross-bonding should not be used in a submarine part which costs a lot for re-installation.