Fast Multichannel Field Distortion Foil Switch for 500 kV

A field distortion solid dielectric switch has been developed for starting water immersed capacitor banks with operating voltages up to 450 kV. It consists of two flat main electrodes insulated by two plastic foils with a thin aluminum trigger strip embedded between them. A simple and cheap method is used for triggering by applying an ordinary 60 kV gas trigatron, i.e. no additional high voltage pulse generator is needed. Depending upon the main voltage and upon the thicknesses of the insulating foils 8 to 50 parallel breakdown channels have been observed on a switch with a width of 20 cm. The time interval between the begin of the trigger pulse and the closure of the switch (switching time) is typically 20 ns with a jitter of less than 3 ns; the resistive phase of the switch can be kept shorter than 3 ns. Due to multichannel breakdown and to the small electrode spacing resulting from solid dielectric insulation, the switch inductance, including the connection line, is only 9 nH, the major part being due to the connection. A 15 kJoule bank with 300 kA maximum current was discharged by a single switch.