Analysis of 330 kV Cable Sheath Transient Characteristics of Line Energization

The transient overvoltage generated by the line energization occasionally cause the breakdown accidents of power cable and accessories, and some of accidents occurred close to the energization side. Therefore, it is necessary to investigate the metal sheath overvoltage characteristics during no-load energization. This paper focuses on the sheath energization overvoltage of 330kV cable in both pure cable lines and overhead-cable hybrid lines. Influencing factors are taken as variables to investigate the distribution characteristics, including line configuration, sheath bonding methods, energization side, and the existence of sheath voltage limiters (SVL). Moreover, frequency characteristics of sheath energization overvoltage with 400Ω closing resistors are analyzed. Simulation results indicated that the maximum sheath overvoltage locates at the cable part near the sending side, which is opposite to that of core overvoltage. Higher sheath overvoltage will be obtained when energized from the single-point bonded section side for pure cable lines, and the cable side for overhead-cable hybrid lines. The single-point bonded section causes relatively severe sheath overvoltage at its ungrounded point compared with cross-bonding points. And the first surge caused by the input of the closing resistor has more high-frequency components than the second surge brought by the exit of the closing resistor, with the maximum spectrum peak at 20kHz and 4kHz respectively. It indicates more obvious high-frequency oscillation characteristics which may promote the development of defects in the insulation on both sides of the metal sheath in the repeated switching operations.