Experimental Investigation of the Influence of Branch Busbar Length on VFTO Amplitude in Gas-Insulated Equipment

In recent years, with the rapid development of new power grid structures such as pumped storage power stations and high-voltage direct current transmission, ultra-high voltage (UHV) and extra-high voltage (EHV) equipment have experienced multiple insulation failures. The unclear failure mechanisms, prolonged repair durations, and significant economic losses pose a serious threat to the safe operation of the power grid. Very fast transient overvoltage (VFTO) caused by disconnector switching operations is often suspected to be a contributing factor to defect formation due to its high amplitude (up to 3 p.u.) and high frequency (up to 100 MHz). This paper presents an experimental study on VFTO measurements conducted at the Wuhan UHV AC test base. The maximum VFTO amplitude is significantly influenced by the length of the branch busbar. Specifically, the maximum VFTO values measured at Point 4 were 1.75 p.u., 1.88 p.u., and 2.23 p.u. for branch busbar lengths of 0 m, 3 m, and 9 m, respectively.