An enhanced plasma injection method for triggering a 10 cm-magnitude high-pressure SF6 gas gap for a megavolt ultrafast bypass switch

Aiming at developing a megavolt ultrafast bypass switch (UFBPS) that operates at a very low working coefficient, an enhanced plasma injection (EPI) method was proposed, which ejected high-density plasmas up to several centimeters in height in a high-pressure SF6 and thus has an extremely strong triggering ability. The EPI method employed a thin polytetrafluoroethylene microcavity embedded inside the ground electrode and a metal wire electrically exploded inside the microcavity, generating a high-density metal vapor plasma that was rapidly ejected outward from the nozzle and inducing a breakdown of the residual gas gap. In this study, the ejected plasma properties by EPI and main influencing factors were examined and the EPI triggering ability was experimentally verified. The results showed that EPI evolution presented three stages: ellipsoid-shaped, mushroom-shaped, and dissipation stages. In 0.5-MPa SF6, when the trigger energy was 960 J and the exploded aluminum wire was 300 µm in radius, the EPI maximum height reached over 9 cm within 0.7 ms, with an initial evolution velocity >800 m/s. Then, an EPI cavity array was set to repetitively trigger a 10 cm-magnitude SF6 gas gap at 0.5 MPa, with a theoretical breakdown voltage >2 MV. The gas gap was successfully triggered with an average trigger delay of 538 µs when a DC 100 kV voltage (undervoltage ratio <5%) was applied. These results indicated that EPI was an effective method for triggering megavolt-magnitude high-pressure SF6 gas gaps at a low undervoltage ratio and meeting the submillisecond trigger requirement of the UFBPS.