Refurbishment of an 800 kV impulse generator

This paper describes work done on refurbishing a Ferranti 800 kV impulse generator. The multi-gap firing system which was originally designed by Ferranti Ltd. to avoid using the traditional variable spark gaps, gradually failed. This has been replaced by an alternative design based on a conventional system (single sphere gap per stage). The first stage has two spark gaps, the main electrodes gap and the pilot gap between the earth electrode and the trigger electrode. The latter provides a spark that initiates the breakdown of the main gap. The design of the trigger electrode and trigger pulse is described. The eight sphere gaps are simultaneously adjusted by a remotely controlled motorised and monitored system.