Measurement of Multipath Transients in Secondary Cables Near a 500 kV Gas-Insulated Switchgear During Operations

Operation of SF
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gas-insulated switchgear (GIS) produces very fast transient overvoltage, which may interfere with the secondary system through many paths. As more and more smart devices are placed near GIS, their anti-EMI capability becomes more and more important. In response to the above problems, this paper carried out on-site measurement on the EMI in the secondary system during the operation of a 500 kV GIS. The EMI in the cable connecting the cabinet near the GIS and the control center 60 m away was paid attention to. By simultaneously measuring the electric field in space, the current through the grounding lead of the GIS, the EMI in the cables with different grounding methods, and the transient ground potential difference between the cabinet and the control center, the effects of different interference paths such as the spatial electromagnetic coupling and grounding system were analyzed. Results show that, the GIS operation will not only generate a spatial electric field, but also induce a circulating current on its grounding leads, resulting in an apparent ground potential difference on the grounding grid. When the shielding of the cable is grounded at both ends, the EMI is mainly determined by the spatial electric field and current in the shielding. As for the cable with single end grounded, the core-shielding voltage contains stronger high frequency components than that when the cable is grounded with both ends. The ground potential difference is the main source of core-ground voltage below 3 MHz when the cable is grounded at single end. Above 3 MHz the space electric field is the main source.