GB2267785A - Transfer of electric current by electric arcing in Electromagnetic Rail Launchers. - Google Patents

Abstract

The armature comprises electrically conducting regions 10 and 12 with members 17 and 19 of insulating or high resistivity materials positioned immediately behind and in front of the armature conducting regions and in close contact with or in close proximity to the current contact surfaces 16 of the rails. Electric current is constrained to flow from the rails to and from the armature by electric arcing directly across the arcing regions 10 at the rail/armature conducting region interfaces. The resulting electromagnetic forces on the armature accelerate it and any attached projectile along the rails in the forward direction 27. Arcing erosion products are exhausted to chambers 23 and 25 as indicated by arrows 21 and 22. <IMAGE>

Description

ARMATURE ARCING CURRENT TRANSFER This invention relates to improvements in the transfer of electric current by electric arcing to the armatures of Electromagnetic Rail Launchers thereby to increase their electrical efficiency.

Rail Launchers consist of stationary parallel rails, rail insulators and a moving armature positioned between them such that electric current flows from the end of one rail through the armature between opposed rail contact surfaces and back to the same end of the opposite rail. The resultant electromagnetic forces produced in the armature accelerate the armature and if present a projectile associated with it in the direction away from the ends of the rails supplied with current. To achieve a high conversion efficiency from power supply electrical energy to projectile kinetic energy requires the efficient transfer of current from the rails to and through the armature with minimum armature resistance and mass and without significant damage due to electric arcing and erosion at the rail and rail insulator surfaces.

Rail Launchers in present use have solid, plasma or hybrid armatures. Solid armatures are usually of solid metal and therefore have a relatively high mass and also have difficulty in maintaining a low resistivity metal-to-metal contact with the rail at high velocities when transition to arcing occurs.

Current conduction through a plasma armature is obtained by establishing electric arcs between the rails which result in a high armature resistance and significant rail insulator damage. The latter can also result in electrical breakdown between the rails behind the armature due to contamination by arcing erosion products. The hybrid armature is in principle a solid armature with small gaps between the rails and armature contact surfaces across which current flows by electric arcing.

However, experiments shew that the hybrid armature resistance is almost as high as that of plasma armatures. It is considered that this is because arcing mainly occurs between the rails behind the solid hybrid armature resulting in a long arc path and high arc voltage. Thus the efficiency of present Rail Launchers is significantly reduced by the use of armatures having a high electrical resistance and/or relatively high mass.

According to the present invention there is provided an armature intended to be accelerated between the stationary parallel rails of an Electromagnetic Rail Launcher wherein the armature comprises one or more electrically conducting regions and one or more members of insulating or high resistivity materials positioned rearwardly (relative to the intended direction of armature movement) of said region or regions and in contact with or sufficiently in close proximity to opposed contact surfaces of the rails such that, in use, electric current flowing from and to adjacent ends of the rails via the armature is constrained to substantially pass, by electric arcing, forwardly of said member or members and directly across the interfaces between said rail surfaces and one or more of the armature conducting regions.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a representation of the present invention shewing in longitudinal-section the rail/armature contact region of a Rail Launcher.

Figure 2 shews in cross-section a Rail Launcher similar to that shewn in Figure 1 viewed along the armature axis Figure 3 shews in longitudinal-section the rail/armature contact region of a Rail Launcher similar to that shewn in Figure 1 with exhaust of arcing erosion products through the armature conductors and having an initial metal-to-metal contact.

Figure 4 shews in longitudinal-section the rail/armature contact region of a Rail Launcher with current flow by electric arcing directly between the rails and to structural members.

Figure 5 shews in cross-section a Rail Launcher similar to that shewn in Figure 4.

Figure 6 shews in longitudinal-section the rail/armature contact region of a Rail Launcher with the solid conductors separated by a central arcing gap.

Figure 7 shews in cross-section a Rail Launcher similar to that shewn in Figures 1 and 2 with solid conductors occupying only the outer regions of the armature.

Figure 8 shews in cross-section a Rail Launcher similar to that shewn in Figure 4 with the central arcing region bounded by solid conductors.

Figure 9 shews in cross-section a Rail Launcher similar to that shewn in Figure 2 with a projectile.

Figure 10 shews in cross-section a Rail Launcher similar to that shewn in Figure 8 with a projectile.

Figure 11 shews in longitudinal-section the rail/armature contact region of a Rail Launcher with current flow by electric arcing directly between the rails and to the front structural member.

Figure 12 shews in longitudinal section the rail/armature contact region of a Rail Launcher with arcing and exhaust chambers formed by insulating members.

Referring to the drawings, Figure 1 shews in longitudinal-section the rail/armature contact region of a Rail Launcher having an armature with electrically conducting regions comprising solid conductors 12 and an arcing region 10 between the rail surface 16 and the solid conductors' surfaces 13.

Electric current flows from and to the ends of the rails 11 as indicated by arrows 14, across the arcing regions 10 as indicated by arrows 15 and through the solid conductors 12 and structural member 28 as indicated by arrows 29. The resulting electromagnetic forces on the armature accelerate it and any attached projectile (not shewn) in the direction of arrow 27, referred to as the forward direction. The rear member 17 and forward member 19 of insulating or high resistivity materials are attached to and accelerated with the armature and are located immediately behind and in front of the arcing region 10 respectively. Members 17 and 19 are in contact with or sufficiently in close proximity to rail surface 16 such that electric current 15 flows across the arcing regions 10 mainly by electric arcing substantially forward of the leading edge 1 8 of member 17 and behind the trailing edge 20 of member 19. Arcing erosion products and explosive pressures are released away from the arcing region 10 into one or both exhaust chambers 23 and 25 directly as indicated by arrows 22 and/or between the solid conductors 12 as indicated by arrows 21. The exhaust chambers can be enclosed or open to release the erosion products forward and/or to the rear of the armature as indicated by arrows 24.

Figure 2 shews in cross-section viewed along the armature axis a Rail Launcher having an armature similar to that shewn in Figure 1. The rails 11 and the rail insulators 33 provide a circular internal bore through which the armature is accelerated. The arcing erosion products are exhausted from the arcing region 10 through the ducts 31 between the solid conductors 12 and thence axially to the forward and/or rear exhaust chambers 23 and 25 as shewn in Figure 1. The solid conductors 12 are joined by structural members 26 which can be split along the armature mid-plane 32 to form a 2piece armature. Exhaust products from the space between the rail insulators 33 and outer solid conductors 12 are released through spaces 30 in the outer solid conductors 12 into the main ducts 31.

Figure 3 shews in longitudinal-section the rail/armature contact region of a Rail Launcher having an armature with forward and rear structural members 36 and 39 which maintain the insulating members 37 and 38 respectively in contact with or sufficiently in close proximity to the rail surface 16. The forward structural member 36 is extended to establish a metal-to-metal pressure contact 34 with rail surface 16. The solid conductors 12 are located immediately behind and insulated from the forward structural member 36 by insulation layer 42. Initially current flow occurs to the metal-tometal contact 34 as indicated by arrow 35 and through the forward structural member 36 as indicated by arrow 44 until this contact melts and vaporises Thereafter current flow occurs mainly across arcing regions 10 as indicated by arrow 15. The solid conductors 12 are joined to the rear structural member 39 and to the armature structure forwardly (not shewn) by central structural member 41. The regions of the solid conductors 12 adjacent to the arcing region 10 are separated by spaces 40 to improve the direct access for erosion products, as indicated by arrows 21, from the arcing region 10 to the rear exhaust chamber 25 which can be open or enclosed.

Figure 4 shews in longitudinal-section the rail/armature contact region of a Rail Launcher having an armature in which current flows by electric arcing directly between the rails 11 through outer arcing regions 10 and central arcing region 43, defined by solid conductors 49 and 50, as indicated by arrows 55. Current also flows by electric arcing through the outer arcing regions 10 to rear and front solid conductors 49 and 50, which are extensions to the rear and forward structural members comprising solid conductors 53 and 45, as indicated by arrows 51 and 46 respectively. The latter currents flow to and through the ends of the armature structure (not shewn) as indicated by arrows 47 and 52. The forward and rear structural members are joined by side solid conductors 56 to which current flows by electric arcing across the outer arcing region 10 as indicated by arrows 48 in Figure 5. The proportion of electric current flowing in each of the three parallel paths indicated by arrows 55, 47 and 52 depends on the distances between rail surfaces 16, solid conductors 49 and 50 and side conductors 56. The central arcing region 43 is closed forwardly by the central insulating member 54 so that arcing erosion products are released into or through the rear exhaust chamber 25.

Figure 5 shews in cross-section viewed along the armature axis in the forward direction a Rail Launcher having an armature similar to that shewn in Figure 4 and rail and rail/insulator bore geometry similar to that shewn in Figure 2. Solid conductors 56 define outer arcing regions 10 and a central arcing region 43 as described with reference to Figure 4. Current flows by electric arcing across outer regions 10 as indicated by arrows 48 and through the central arcing region 43 as indicated by arrows 55. Side members 58 of insulating or high resistivity materials are located between the solid conductors 56 and the rail insulators 33 and are in contact with or sufficiently in close proximity with the rail insulators 33. The armature can be split along either or both mid-planes 61 and 60 to make either a 2-piece or 4-piece armature respectively. Current flow between solid conductors 56 is by electric arcing as indicated by arrow 59 if the armature is split along mid-plane 60 or the armature structure is electrically non-canducting. If the armature structure is electrically conducting and not split along mid-plane 60 current flow between solid conductors 56 will be mainly through the armature structure as indicated by arrows 47 and 52 in Figure 4.

Figure 6 shews in longitudinal-section the rail/armature region of a Rail Launcher having an armature in which the solid conductors 12 are separated into two groups by a central arcing gap 64 defined by arcing electrodes 65 and closed forwardly by an insulating arcing plate 67. Current flows across the central gap 64 as indicated by arrow 66. The solid conductors 12 are extended and joined to forward and rear structural members 62 and 63 respectively to form an armature structure which maintains the rear insulator 38 in contact with or sufficiently in close proximity with the rail surfaces and an initial pressure contact at the metal-to-metal contact surface 34. Arcing erosion products are released from the central arcing gap 64 into the rear exhaust chambers 25 as indicated by arrow 69 and form arcing regions 10 as indicated by arrows 21 and described with reference to Figures 1 and 2. The armature is divided along its mid-plane 68 to form a 2-piece armature and can also be divided as shewn along mid-plane 32 in Figure 2 to form a 4-piece armature. An armature with a central arcing gap 64 is also applicable to the armatures described with reference to Figures 1,2,3 and 9.

Figure 7 shews in cross-section, viewed along the armature axis in the forward direction, a Rail Launcher having an armature similar to that shewn in Figure 3 with solid conductors 72 occupying only the armature outer regions and current flow as indicated by arrow 73. Arcing erosion products pass from the arcing region 10 through spaces 75 in the solid conductors 72 into a central exhaust chamber 74. Side members of insulating or high resistivity materials (not shewn) can be located between the solid conductors 72 and the rail insulators 33.

Figure 8 shews in cross-section, viewed along the armature axis in the forward direction, a Rail Launcher having an armature similar to those shewn in Figure 4 with the central region 43 bounded laterally by side conductors 80. The latter are separated from the rail insulators 33 by insulating members 81. Current flow across the outer arcing regions 10 and the central arcing region 43 is as described with reference to Figures 4 and 5. Current flow through the side conductors 80 is as indicated by arrow 82. The proportion of current flowing in the parallel paths indicated by arrows 55 and 82 is controlled by the distance between side conductors 80 and their height relative to the size of the central arcing region 43.

Figure 9 shews in cross-section, viewed along the armature axis, a Rail Launcher having an armature similar to those shewn in Figure 7 in which a projectile 90 is positioned along the armature axis and attached to the armature structure 91 such that it is accelerated by armature electromagnetic forces. Central structural member 91 ensures adequate contact with the projectile 90 with insulating layer 92 ensuring that current flow is through solid conductor 72 as indicated by arrow 73.

Figure 10 shews in cross-section, viewed along the armature axis in the forward direction, a Rail Launcher having an armature similar to that shewn in Figure 8 in which a projectile 90 is positioned along the armature axis and attached to the armature structure (not shewn) such that it is accelerated by armature electromagnetic forces. Current flow across the outer arcing region is as described with reference to Figure 8. Current flow in the central arcing region 100 is influenced by the presence of the projectile 90. If the latter is electrically conducting with an insulating layer 102 or is substantially of an insulating material current flow in the central arcing region 100 will be substantially as shewn by arrows 103. If the projectile 90 is electrically conducting and not insulated significant current will flow through the projectile as indicated by arrow 101.

Figure 11 shews in longitudinal cross-section the rail/armature contact region of a Rail Launcher having an armature in which current flows directly between the rails through the central region 112 as indicated by arrow 111 and to the extension 50 of the forward structural member 45 as described with reference to Figure 4. The central arcing region 112 is bounded on its sides by side member 114 of insulating or high resistivity material and forwardly by central insulating member 113. The rear exhaust chamber 25 is formed by the rear insulating member 110 and the side insulating member 114. Insulating members 110, 113 and 114 and structural members 45 are combined to meet structural requirements and to form the central armature assembly. The rear exhaust chamber 25 can have partitions 115 (indicated by dotted lines) to provide additional surfaces to cool erosion products.

Figure 12 shews in longitudinal cross-section the rail/armature contact region of a Rail Launcher having an armature in which current flows by electric arcing directly between the rails through the central region 123 as indicated by arrows 120. The central arcing region 123 is closed forwardly by the front insulating member 122 and on its sides by side insulating members 114. Insulating members 110, 114 and 122 are combined to meet structural requirements and form the central armature assembly. The rear exhaust chamber 25 can have partitions 11 5 (indicated by dotted lines) to provide additional surfaces to cool erosion products.

The initial metal-to-metal contacts 34 shewn in Figures 3, 4, 6 and 11 supported from the forward structural member 36 are also applicable to the armatures described with reference to Figures 7, 8, 9 and 10. Thus these armatures can operate as a 2-stage armature, the first stage being by means of metal-to-metal rail/armature contact and the second stage being by means of electric arcing contact between rail surfaces and solid conductors. In addition initial acceleration of all armatures from rest can be achieved by non-electromagnetic means if required.

The armatures described with reference to Figures 7, 8, 9 and 10 can be operated as a 3-stage armature, the first two stages being metal-to-metal and electric arcing rail/armature contacts respectively as described with reference to Figure 3. The third stage follows the melting and vaporisation of the solid conductors 72 in Figure 7 resulting in a change in the solid conductor shape similar to that of the side conductors 80 in Figures 8 and 9. In the third stage significant current flow occurs by electric arcing directly between the rails as indicated by arrows 55 in Figure 8.

In the armature described above large forward magnetic pressure is exerted on the arc plasma carrying current flow by electric arcing. It is desirable to contain the arc plasma against this pressure by ensuring an adequate seal (not shewn) between the armature and rail/insulator bore surfaces forward of the armature conducting regions.

Claims (13)

1. An armature intended to be accelerated between the stationary parallel rails of an electromagnetic rail launcher wherein the armature comprises one or more electrically conducting regions and one or more members of insulating or high resistivity materials positioned rearwardly (relative to the intended direction of armature movement) of said region or regions and in contact with or sufficiently in close proximity to opposed contact surfaces of the rails such that, in use, electric current flowing from and to adjacent ends of the rails via the armature is constrained to substantially pass, by electric arcing, forwardly of said member or members and directly across the interfaces between said rail surfaces and one or more of the armature conducting regions.

2. An armature as claimed in claim 1 wherein the electrically conducting regions comprise a single solid conductor.

3. An armature as claimed in claim 1 wherein the electrically conducting regions comprise two or more solid conductors.

4. An armature as claimed in claims 1, 2 or 3 wherein one or more members of insulating or high resistivity materials are positioned forwardly of said region or regions.

5. An armature as claimed in claim 1 wherein arc erosion products can exhaust forwardly and/or rearwardly of said conducting regions.

6. An armature as claimed in claim 5 wherein an open-ended passageway extends along the length of the armature.

7. An armature as claimed in claim 1 wherein the or one of the electrically conducting regions is such that, in use, current flows by direct electric arcing between said opposed rail surfaces.

8. An armature as claimed in claim 7 wherein the direct electric arcing region is associated with one or more electrically conducting regions comprising solid conductors.

9. An armature as claimed in claim 8 wherein the direct electric arcing region is positioned centrally relative to two or more opposed electrically conducting regions comprising solid conductors.

10. An armature as claimed in any of claims 2, 3, 4, 8 or 9 wherein the or one of the solid conductors makes direct contact with an adjacent rail surface such that, in use, electric current initially passes preferentially across the interface defined by said direct contact.

11. An armature as claimed in claim 3 wherein said conductors define an axial arcing gap.

12. An armature as claimed in any preceding claim split such that it divides into discrete parts on discharge from an electromagnetic rail launcher.

13. An armature substantially as described herein and as shewn in the accompanying drawings.