Trigger Properties of an Ejected-Plasma-Triggered SF Gas Gap for 10-kV Smart Distribution Network

Aimed at developing a rapid control and protection switch for a 10-kV smart distribution network, a gas switch triggered by ejected plasma was designed and tested. The switch met the requirements of fast and reliable triggering at an extremely low operating coefficient. The gas switch employed sulfur hexafluoride (SF6) as its insulating medium for miniaturization requirements and was triggered by capillary discharge excited by a pulse transformer for high potential isolation considerations. The influence of a capillary cavity structure and pulse transformer parameters on the switch trigger characteristics was investigated. The results showed that the plasma ejection was enhanced by increasing trigger energy, but was also saturated with a limited cross section of the magnetic core of the pulse transformer, which determined the maximum transferred trigger energy. Employing a long capillary, shrinking nozzle, and small transformer ratio promoted plasma ejection, resulting in an increase in the triggering reliability and lowering the trigger threshold voltage. A 4-mm capillary cavity with a shrinking nozzle driven by a 37/2 pulse transformer was used to trigger an 80-kV SF6 gas switch at a 4.7% operating coefficient, and 1200 times successive and successful triggering was performed, with the trigger delay ranging from 62.5 to
$73~\mu \text{s}$
, which met the technical requirements of rapid control and protection for a 10-kV smart distribution network.