Examination of the Sheath Surge Protection Methods for High Voltage Cable Line

In extra-high-voltage cable lines, a sheath surge voltage arises between insulation sleeves of GIS-CH and cross-bonded insulation joints (IJs) due to the high frequency and high voltage surge that arises from the operation of GIS-CB. To protect the cable sheath from the sheath surge voltage, surge by-pass capacitor and ZnO arresters are used with GIS-CH, and ZnO arresters are used with IJs. The slight impedance of the lead wires on these protection devices are also a problem with respect to high-voltage surge. Through experiments on extra-high-voltage cable lines we compared the effectiveness of these various protection methods. We found that all the protection methods for GIS-CH are effective, and that for IJs care must be taken to minimize the lead wire impedance of the protection devices, bacause a high-frequency surge might arise extending as far as the second crossbonded section. In simulating the sheath surge voltage by EMTP, we studied methods for conviniently attenuating the high frequency component of the surge voltage in the cable and obtained results that agree closely with the actually measured sheath surge voltage.