Experimental Study on Grounding Mode of Secondary Cable Shielding Layer of UHV Converter Station

Because of a lightning strike, short circuit fault, and switch operation, grounding grid will be impacted by high-frequency current, which makes the grounding grid appear uneven distribution of transient grounding potential, this kind of transient grounding potential rise will be coupled to the core wire through the outer surface of the cable and will invade the secondary system, which may have an impact on the normal operation of the secondary equipment and Endanger the safe and stable operation of substation or converter station. In addition, with the digitalization, electronization, and localization of the secondary equipment in the UHV converter station, a large number of precision secondary equipment used for protection, control and communication is placed in the high-voltage switching field of the converter station, which greatly increases the probability of interference with the secondary system of the UHV converter station. It is well known that using shielded cables and choosing correct grounding mode of the shielding layer is an important measure to improve the electromagnetic compatibility of converter stations. In this paper, based on a test method to research transient grounding potential rise in converter station, the transient overvoltage of multi-segment secondary cables and their shielding layer with different grounding modes are measured in the field of an AC filter in a UHV converter station. The test results show that the grounding of the shielding layer between the first and the last sections is the key to suppress transient overvoltage for the multi-segment control cable. The best grounding method is to increase the shielding layer and armor layer of the control cable between the on-site control cabinet to be grounded at the single end of the B-phase on-site control cabinet based on the cable grounding mode. That is to say, the cable of the shielding layer and the armor layer between the on-site control cabinet should consider the grounding at the signal gathering point.