Analysis of Current and Potential Characteristics of UHVAC GIL Tunnel Project

Abstract

In order to master the safety of the GIL shell grounding system of the 1000kV AC UHV GIL tunnel project and support the design and construction of the project, a shell grounding system model consisting of the main grounding grid of connection stations on both sides, the tower grounding grid of overhead ground wires on both sides and the tunnel grounding grid is established. The GIL current and potential distribution under normal operation and short-circuit fault are calculated, and the influence and setting of grounding poles and three-phase connection poles are analyzed. The results show that: under normal operation, the current of connection poles and grounding poles along the GIL presents a U-shaped distribution. In case of short-circuit fault, besides the two ends, the current of the connection poles and grounding poles near the fault point also presents a peak, which can reach hundreds of amperes; and the distribution of potential and potential difference along the GIL also presents a similar U-shaped feature. The spacing of grounding poles can be set within 300m, which can ensure that the potential difference is within the safety limit. The copper bar of 50mm×5mm can be selected for both the grounding pole and the intermediate connecting pole, and the conductor with larger cross section is needed for the connection pole at both ends due to the long-term passing current close to the rated value.