Short-circuiting switch and electromagnetic projectile launcher

Details Short-circuiting switch and electromagnetic projectile launcher Short-circuiting switch and electromagnetic projectile launcher

1990-12-13

1992-02-25

Bentley, Stephen C.

Ordnance

Accelerating

124 3, 200144R, F41B 600, H01H 3314

Patent

active

050902920

DESCRIPTION:

BRIEF SUMMARY
This invention relates to an electrical switch and an electromagnetic projectile launcher incorporating the switch.
Electromagnetic projectile launchers (usually referred to as "railguns") utilise high direct currents (DC) to launch projectiles. The basic construction of a railgun (see FIG. 1) comprises a power supply circuit having two generally parallel rails bridged by a projectile armature. In operation the rails are short-circuited until the current level required for launch is achieved whereupon the current is allowed to flow through the projectile armature. The projectile armature is accelerated to launch speed owing to the interaction of the current in the projectile armature with the magnetic field induced between the rails.
The typical requirements for the switch short-circuiting the rails during the current build up are: very low resistance (usually less than 10 micro-ohms); high-current bearing capability (usually of the order of 1 MA for periods of 200 ms); rapid commutation of the current (typically in 0.5 ms or less); capacity for repeated operation; and capacity for current transfer without damage to itself. Damage during current transfer in this type of switch is most frequently caused by arcing.
It is an object of the present invention to provide an electrical switch which is arc-resistant during switching, and to provide an electromagnetic projectile launcher incorporating the switch.
According to one aspect of the present invention, an electrical switch comprises a pair of terminals, each terminal having first and second conducting arms, a first conductive contact member demountably connected across the respective first conducting arms of the two terminals, a second conductive contact member demountably connected in parallel relationship to the first member across the respective second conducting arms of the two terminals, the two conductive contact members being liftable in different outward directions to sever contact with the terminals, lifting means for lifting at least one of the contact members off the terminals, and connecting means for electrically connecting a direct current power supply across the terminals to provide conductive paths for current flow which diverge outwards along the first and second conducting arms of one terminal, pass across the first and second contact members, and converge inwards along the first and second conducting arms of said other terminal, whereby lifting of one contact member to sever the conductive path during current flow therethrough nullifies the electromagnetic forces of attraction between the contact members and provides an electromagnetic lifting force on said other contact member generated by the combined outward flow of current thereto and inward flow of current therefrom.
The provision of a switch which has two conductive pathways according to the invention has the advantage when the switch is closed that the build-up of current through the closed switch produces increasing electromagnetic forces of attraction between the contact members and so urges them into ever closer and better electrical contact with the terminals. Since the pathways diverge then coverage, a symmetrical shape of current pathways can be provided to ensure matched, equalised current flow through each opposing pair of arms, which balances out any undesirable laterally asymmetric electromagnetic forces which might otherwise act upon the switch if large asymmetrical currents were present. When the switch is opened, simultaneity and rapidity of current severance is assisted by the residual electromagnetic forces of repulsion which act upon whichever of the two contact members is the later of the two to break contact with the terminals. These fast and virtually simultaneous switching characteristics suppress both asymmetrical forces and arcing which might otherwise occur at the moment the switch is opened.
The lifting means, which may comprise a fluid (gas or liquid) pressure generating means, or an electromagnetic or a mechanical lifting means, preferably acts on both co

REFERENCES:
patent: 2480553 (1949-08-01), Cooper et al.

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