One example of a type of high voltage switch which is effective in situations which require fast-closing, high voltage, one-shot switching, is know in the art as a"stab switch". A"stab switch"utilises a piston means (usually in form of a pointed rod i. e. a nail) capable of penetrating two conductive elements. The conductive elements are held in open circuit, usually by an insulating material, and the action of the piston or rod penetrating both conductive surfaces and insulating material rapidly completes the circuit. Such"stab switches"are by their very nature not suitable for general commercial applications and are usually confined to laboratory applications.

With a view to overcoming the problems associated with the prior art, our invention provides a fast-closing, one-shot, high voltage switch, suitable for commercial application, which can be re-armed to provide repeatability of the switching action.

Accordingly there is provided a fast-closing electrical switch, said switch means having at least one conductive pin means, said pin means being electrically insulated from, and so disposed in relation to at least one conductive piston means, such that on activation of said piston means, said piston means is rapidly urged into contact with said pin means, thereby completing an electrical circuit which is connected to ground via a ground.

A description of the invention will now be given by way of example only, with reference to the following drawings in which; Figure 1 shows a side view schematic diagram of a switch in accordance with the invention with the piston retracted, and Figure 2 shows a plan view of the switch shown in Figure 1, and Figure 3 shows a side view of the switch with the piston extended.

Figure 1 shows a preferred embodiment of the invention. The switch 2 comprises an insulated high voltage pin 4 that is partially surrounded by a U-section ground conductor means 6. (Equally, the pin 4 could be held at ground and the U-section conductor 6 held at high voltage.) The ground conductor means is preferably made of aluminium, but the invention is not limited to this material which can provide a suitable conductive path could readily be utilised.

The pin 4 is preferably made of copper, but the invention is not limited to this material, and any other material which can provide a suitable electrical conductive path could readily be utilised. Switch operation is achieved by triggering a fast acting conductive pin or piston 8, which is located within, and electrically connected to the ground conductor 6. On activation of the switch 2, the pin or piston 8 extends towards, and contacts with, the central high voltage pin 4 (as shown in Figure 3). The electrical connection occurs initially by electrical breakdown between the pin 4 and the ground conductor 6, and ultimately by the pin or piston 8 and high voltage pin being held in contact.

The embodiment described herein utilises a single pin means 4 and a single pin or piston means 8, but the invention is not limited to the switching of only one electrical circuit, and either single or multiple pin means 4 could be so arranged with single or multiple pin or piston means 8 such that multiple switching Experiments have shown that a switch in accordance with the invention has significantly lower losses than a comparable voltage air spark-gap.

The pyromechanism 10, comprises a tube 12 containing a pin or piston 8 and a small amount of electrically-initiated propellant 14. When a voltage is applied to the firing terminals 20 via the wires 18, the propellant ejects the metal pin or piston 8, the pin or piston 8 making electrical contact with the pin 4 by penetrating the solid insulating block 16. The switch is expected to have very low losses and can be triggered with a delay of a few milliseconds. The protractor used in the prototype of the invention required an electric current of 0.9 A for initiation.

The high voltage design utilises a combination of solid 16 and liquid 18 dielectrics to obtain both the electrical and mechanical requirements for the switch. The use of dielectrics with similar permittivities can lead to optimised electrical characteristics, although such equivalence is not essential to the operation of the switch. Equally, the switch can be designed to utilise only a solid, or indeed only a liquid dielectric material to provide the required insulating characteristics Electrical breakdown tests on the prototype have demonstrated that the switch can currently hoid-off up to 70 kV for at least 5 minutes with no degradation in the insulating properties of the dielectric.

In the preferred embodiment of the invention the pyromechanical protractor 10 as described is a commercially available product. The protractor 10 is itself highly reliable in operation and is driven by expanding gas generated from rapidly burnt explosive 14. Equally, any mechanism which could provide sufficient propulsive force to drive a conductive pin or piston 8 into contact with a pin 4 could be utilised, and accordingly the invention is not limited to use of a pyromechanical protractor.

The prototype compact triggerable single shot switch was developed to operate at hold-off voltages in the order of 50 kV, but by increasing the scale of the components, the design is equally applicable for use where the hold-off voltages are in the order of 1 MV.

The switch is so designed that subject to some instances where replacement of some dielectric components may be required, the switch can be re-used by replacing the spent pyromechanism.