US3842293A

US3842293A - Electrostatic generator

Info

Publication number: US3842293A
Application number: US00446955A
Authority: US
Inventors: W Allen; M Morris
Original assignee: Science Research Council
Current assignee: Science Research Council
Priority date: 1971-10-28
Filing date: 1974-02-28
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15

Abstract

An electrostatic generator comprises a series of electrically conductive members in the form of plates which are hingedly interconnected by electrically insulating mechanical hinge means so as to form the plates into an endless chain similar to a caterpillar track. The plates present front and rear faces of substantial dimensions so as to provide a large amount of chargeable surface area. For charging the plates, and likewise for transferring the conveyed charge to a high voltage terminal, both faces are exposed to induction electrodes. Such electrodes are arranged so that as little as 25 percent, or even less, of the total surface area of each plate remains unexposed.

Description

United States Patent 1191 1111 3,842,293

Allen et al. Oct. 15, 1974 [541 ELECTROSTATIC GENERATOR 3,056,052 9/1962 Hand 310 6 3,469,118 9 1969 Herbetal....

[75] Inventors: William Douglas Allen, Quirang 3 473 064 10/1969 Herb Burcot, near Abingdon; Michael 35,29,185 97 lsoyu 61 Morris, Frodsham, both of England 3.6l2,9l8 10/1971 Willotzki 310 6 Assigneez Science Research Council, London, 3,612,919 lO/l97l Herb et al 310/6 England [22] Filed: Feb. 28, 1974 21 Appl. No; 446,955

Primary Examiner-D. F. Duggan Attorney, Agent, or Firm-Larson, Taylor & Hinds Related US. Application Data [57] ABSTRACT [63] Continuatiommpan of Sen No. 297,838, Oct 16, An electrostatic generator comprises a series of elec- 1972, abandoned. trieally conductive members in the form of plates which are hmgedly interconnected by electrically msu- 391 Foreign Application p i i Data lating mechanical hinge means so as to form the plates Oct. 28, l97l Great Britain 50287/71 Into an endless Chain Similar to a caterpillar h plates present front and rear faces of substantlal d1- 52 mansions so as to Provide a large amount of i E 8 H02 310/6 able surface area. For charging the plates, and liken n l/00 [58] Field of Search 1 310/5 6 322/2 wise for transferring the conveyed charge to a hlgh voltage terminal, both faces are exposed to induction r59 a'szzzeefra1122:1 12?09112121532223;

UNITED STATES PATENTS of each plate remains unexposed. 2,578,908 l2/l95l Turner 310/6 X 3,048,720 8/1962 Cloud 310/5 7 Clams, 6 Drawing Flgures I: l 57-! I! PATENTEDBET I 51874 SHEET 10F 3 PATENIEUUET 1 5mm SHEET 2 OF 3 F/GL.

1 ELECTROSTATIC GENERATOR This invention relates to electrostatic generators and this application is a continuation-in-part of parent application Ser. No. 297,838 filed Oct. 16, 1972, now abandoned.

In the Van de Graff type of electrostatic generator electrical charges are conveyed to a high voltage terminal by way of a rapidly moving endless belt of insulating material. The charges are sprayed at earth potential from sharp corona points and collected at high potential from other corona points.

This arrangement has several disadvantages however. For example, the arrangement results in the formation of belt dust and the formation of corrosive products from the corona discharges.

A known improvement of the belt method of conveying electrical charges to a high voltage terminal is to add to the belt or an equivalent continuous insulator a series of electrically conductive elements which are charged by electric induction thereby dispensing with corona charging and the undesirable gaseous breakdown products to which this may lead. Various configurations for the electrically conductive elements have been postulated: for example wires embedded in belt material orconductive zones otherwise incorporated in a belt are to be found in US. Pat. Nos. 3,048,720 and 3,056,052, both issued in I962, and more recently in US. Pat. No. 3,469,1 18 there is disclosed the concept of electrically conductive elements in the form of metal pellets being strung on an endless insulating cord, a concept which may be practised by making the pellets into chain links and interposing stiff insulator between the links. However, a significant limitation of this kind of improvement is that the current carrying capacity tends to be low and in the case of the pellet concept there is a tendency to develop kinematic problems in use.

One object of the invention is to provide a new and I improved electrostatic generator in which the current carrying capacity is increased by forming an endless chain with greatly augmented conductive surface area and by utilising for the drive and tracking of this chain between charging and discharging stations a kind of pulley assembly which allows induction electrodes at these two stations to be presented towards the rear face of this surface area as well as towards the front face. The electric induction method of charging, with all the attendant advantages compared with corona charging, can therefore be applied in a way which gives enhancement in two respects, firstly by the augmentation of conductive surface and secondly by the use of both front and rear faces.

Another object of the invention is to give the endless chain a greater stability against undesirable movements during travel over the pulley assemblies by arranging that each such assembly makes tracking engagement with the chain along spaced apart track lines. This object, together with that previously stated, are conveniently achieved with a kind of pulley assembly which has two pulley means on a common axis with an induction electrode interposed between these means so as to present itself towards the rear face of the conductive surface.

A further object is to exploit to the utmost, consistent with the restraints of the environment in which the electrostatic generator is situated, the increased cutrent carrying capacity which the invention affords. To this end electrically conductive members for use in making the chain have a dimension measured across the faces in the lateral direction, that is to say, transverse of the chain travel, which is greater than the dimension measured across the faces in the other direction. Furthermore, it may be arranged that at the charging and discharging stations at least percent of the conductive surface area is exposed to the induction electrodes.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is a diagramatic side view of an electrostatic generator,

FIG. 2 is a section, to an enlarged scale and also diagrammatic, taken on the lines II II of FIG. 1,

FIG. 3 is an elevation, partly sectioned, of a short length of a charge carrying structure which in its full length forms an endless chain,

FIG. 4 is a section taken on the lines IV IV of FIG. 3,

FIG. 5 is a diagrammatic front elevation of a charging system for the charge carrying structure of FIG. 3, and

FIG. 6 is a diagrammatic side elevation of the charging system of FIG. 5.

In connection with FIGS. 1 & 2 and the descriptions appertaining thereto in the ensuing specification, it is to be noted that although the subject matter constitutes part of our generic invention no claims are directed solely thereto in the instant application, the subject matter thereof being covered in our copending application filed concurrently herewith as a continuation of parent application Ser. No. 297,838.

Referring now to the drawings, and especially to FIGS. 1 & 2, a high voltage electrostatic generator I forming part of a particle accelerator comprises a high voltage terminal 2, and a pair of side by side disposed endless chain/link means 3 with their bights rotatable about common axes provided by shafts 4, 5. Each chain/link means 3 is formed by a plurality of electrically conductive pellets 6 insulated from each other by nylon links 7. LateraIly-disposed electrically conductive members 8 interconnect the pellets 6 of one means 3 with the pellets of the other means 3 by interconnecting oppositely-facing pellets 6. The means 3 are rotated by an electrical drive unit 9. Charging means is indicated at 10 and discharging means at 11, the latter being for transfer of charge to the high voltage terminal 2.

In further detail, the generator 1 is housed in a pressure vessel I2 filled with a high density insulating gas. The pellets 6 are of stainless steel and the lateral members 8 are of aluminium. The means 3 are each supported by and run between grooved electroconductive pulleys l3, 14. The electrical drive unit 9 rotates both of the pulleys 13, the other pulleys 14 being idle and pulled around by the means 3. In plan view the means 3 and the lateral members 8 therebetween have a ladder-like form.

The means 3 and lateral members 8 run through apertures formed in a horizontally disposed insulator stack 15 comprising glass insulator plates 16 sandwiched between metal shielding plates 17. The insulator stack" 15 is used to support the high voltage terminal 2 within and to insulate it from the pressure vessel 12.

The charging means 10 comprise upper and lower induction electrodes 20, 21, disposed above and below the lateral members 8 and in close proximity to the pulleys 13. A power supply 22 is used to apply a negative voltage between the cooperating pairs of induction electrodes 20, 21 and the pulleys 13, which pulleys are earthed through their common shaft 4.

The discharging means 11 comprises a pair of cooperating induction electrodes identical in form to the electrodes 20, 21 andthese electrodes are also disposed in close-proximity to the pulleys 5. The common shaft of the pulleys 5 is electrically connected to the high voltage terminal 2 by a conductor 23 and the discharging means 11 is negatively charged, relative to the terminal 2.

The charging and discharging means 10, 11 are disposed so that the upper runs of the means 3 pass between theircooperating electrodes. Similar cooperating'pairs of electrodes, shown at 24 and 25, are disposed sothat the lower runs of the means 3 pass between them. The electrodes 24 are disposed in close proximity to the pulleys l3 and the electrodes 25 are disposed in close proximity to the pulleys 14. A power supply 26 is used to apply a positive voltage between the electrodes 24 and the pulleys 13. The electrodes 25 are positively charged, relative to thehigh voltage terminal 2.

In operation, the drive unit 9 is used to rotate the assembly of lateral members 8 and pellets around the

pulleys

13, 14 and in the direction shown by the arrow adjacent pulley l3.

The charging means serve to draw positive charges in a smooth manner onto the pellets 6 and the lateral members 8 before they break contact with the pulleys 13. These charges are bound on the pellets 6 and members 8 before they break contact with the pulleys 13 so that there is no substantial sparking on termination of contact.

As the positively charged pellets 6 and members 8 enter the negatively-charged discharging means 11 they give up their charges which pass to the high voltage terminal 2, by way of the pulleys 14, where the charges accumulate on the surface of the terminal 2. Again, the arrangement is such that the charges flow smoothly from the pellets 6 and members 8, with no negative charges are bound on them by means of the electrodes 25. They then move along to pass between the electrodes 24 where a positive voltage binds the negative charges on the pellets 6 and members 8 until after they contact the pulleys 13. The pellets 6 and members 8 then pass around the peripheries of the pulleys 13 to be recharged and the above-described cycle is repeated.

Referring now to FlGS. 3 & 4, it will be seen that the component shown therein corresponding to the previously described pellets 6 with interconnecting members is changed in form so as to assume basically the character of a plate 30 of generally rectangular outline with a dimension in one direction about four or five times greater than in the other direction. Althoughfor the most part of solid construction, each plate is developed adjacent opposite lateral edges into regions of

greater thickness

31, 32 in which are formed respective cylindrical bores 33, 34 each with an inserted

liner sleeve

35, 36 respectively. The plates are typically made of aluminium, or an aluminium base alloy, for lightness and in this case the liner sleeves will be of a material which is more resistant to spark erosion, a good example being stainless steel.

Links of insulating material, such as those indicated 37a, b & 0 adjacent one of the lateral edges of the plate assembly and 38a, b & 0 adjacent the other edge, are all of similar dumb-bell shape and are bored to rock on hollow link pins, such as those indicated 39a & b, which are fixed by socket head cap screws, such as 40 a & b, to pass diametrically across the cylindrical bores of the

greater thickness regions

31, 32 such that the links are for the most part shrouded within these bores. The arrangement of the links and link pins constitutes a mechanical hinge connection of each pair of consecutive plates so that the plates are joined together in an endless chain, are maintained in an edge to edge spaced relationship, and have a freedom for rocking articulation normal to the plate faces. Such an endless chain is therefore analagous to a caterpillar track.

In addition to being largely shrouded, which in itself is a protection against spark damage, the electrically insulating links 37 are each surrounded where they protrude from the

bores

33, 34 by a projecting annular boss, such as indicated at 41 a & b, which is formed integrally with the

greater thickness regions

31, 32. Opposing bosses on consecutive plates therefore define a narrower gap between the plates than pertains elsewhere and this has the effect of shielding the insulating links against spark impringement. For protection of the bosses themselves, the

liner sleeves

35, 36 have their end margins turned-over the crowns of the bosses in order to form a toroidal profile. As regards materials for the link and link pin arrangement, suitable choices are stainless steel for the pins and retaining screws and reinforced plastics, such as glass reinforced nylon, for the links.

Referring now to FIGS. 5 & 6, it will be seen that the induction charging system is in contrast to that appearing at 10 in FIGS. 1 & 2 in having inner and outer electrodes 42 & 43 respectively which have a three dimensionally flaring shape. Such flaring is developed in opposite directions from a central section extending between the lines marked A-A & 8-H and within this section the respective cross sectional shapes of the electrodes are uniform. The shape in each case is such that electrode surface is presented with constant narrow clearance over both the front and rear faces of the plates 30. This implies a shape in the central section which is similar but complementary to the exterior contours of the plates and hence an arrangement which approximates in cross section to the showing in FIG. 2, the main differences being, apart from the changed construction and shape of plate, the termination of the outer electrode edges at the median plane of the plates and the smoothly radiussed transitions of the outer electrode surface from the flat region 44 to the

curved regions

45, 46 in order to conform with the plate protile as seen in FIG. 4. The drive and tracking engagement of the spaced apart electroductive pulleys 13 with the increased

thickness regions

31, 32 of the plates precludes the provision of curved regions on the inner electrode 42 corresponding to the

curved regions

45, 46 on the outer electrode but otherwise the plates passing between the electrodes are exposed to electrode surface over almost the total surface area. Consequently no more than 25 percent of the total plate surface is left unexposed and preferably the unexposed portion is as little as percent.

The flaring in both directions from the central section is developed by an exponential increase in the clearance between the electrode surfaces and the plates. More specifically, at any transverse line, such as the marked X-X, the clearance is as near as possible uniform at all points of the plate, although of course larger than the central section clearance by virtue of the exponential increase, and this will explain why the width of the flat region 44 diminishes towards the ends of the outer electrode as indicated at 47 & 48. These diminishing width flat regions will also curve gently away from the plates in order to give the requisite clearance increase.

The object of this complex shaping of the electrodes, apart from providing extensive surface coverage, is to obtain a gradual transition of the moving plates from maximum metal proximity to virtually zero metal proximity. Two stages may be distinguished in this process: on the one hand the approach to and movement through the zone in the central section A-B where charging is most intense and on the other hand the departure from this zone. The progressive convergence of the plates and electrode surfaces in approach to the maximum intensity charging zone makes for a gradual build up of charge and'therefore avoids abrupt entry into this zone. Departure from this zone occurs at the point of break of the tracking engagement with the pulleys l3 and the centralsections A-B of the electrodes extend beyond this point in order to preserve a consis tent field strength and hence an unaltered charge distribution until the plates are well separated from the pulleys. Thereafter the progressive divergence of the plates and electrode surfaces gradually diminishes the field strength and a gradual adjustment of charge distribution can 'occur to achieve the condition ultimately prevailing on the plates on completion of their passage between the electrodes. There is a natural tendency for such redistribution to concentrate the charge to higher density at the curved surfaces of the plates and in the run of the endless chain between the charging and discharging means the capacitance coupling characteristics may be arranged in predetermined fashion to suppress such redistribution and hence reduce localised charge peaks.

It follows from the foregoing description that the extensiveness of surface area afforded by the plates, together with inductive charging applied to both faces, allows a massive generation of electrostatic charge to be transferred to the high voltage terminal. The electrode arrangement of FIGS. 5 & 6 may of course be installed at each of the stations indicated at 10, ll, 24 & of FIG. 1. At the discharging stations 11 & 24 the electrodes act as a suppressor to bring the potential on the plates gradually to a level which corresponds to the potential of the pulleys receiving the charge. Such correspondence of potential is aimed to eliminate sparklarious modifications, alterations and equivalents are within the scope and spirit of the invention as defined in the following claims.

We claim:

1. For electrostatically charging a high voltage terminal, the combination comprising a series of electrically conductive members each presenting front and rear faces extending between lateral edges and each having a dimension measured across the faces in the lateral direction which is greater than that measured across the faces in the other direction, hinge means situated symmetrically relative to the lateral edges to form electrically insulating mechanical interconnections between each pair of consecutive members in the series thereby to link the members in an endless chain, said hinge means allowing rocking articulation normal to the faces of the members and maintaining them in an edge to edge spaced relationship in a manner similar to a caterpillar track, a first induction electrode means for charging the members, a second induction electrode means for the transfer of charge from the members to the high voltage terminal, at least two pulley assemblies defining a path of travel of the endless chain from the first electrode means to the second electrode means, each pulley assembly being adapted to make tracking engagement with the endless chain along spaced apart track lines, and the first and second induction electrode means comprising electrodes presented towards the rear faces of the members, as well as electrodes presented towards the front faces, the former being situated between the pulley means of the pulley assemblies.

2. The combination according to claim 1 wherein the electrodes presented towards the front faces of the members extend over the whole of the dimension between the lateral edges and additionally extend at least in part around these edges whereby these electrodes in conjunction with the electrodes presented towards the rear faces of the members are directly effective on the whole of the surfacearea of the members except for portions which are not substantially greater than the surfaces making tracking engagement with the pulley means.

3. The combination according to claim 2 wherein the portions of surface area not exposed to the electrodes together constitute no more than 25 percent of the total surface area of each member.

4. The combination according to claim 1 wherein the hinge means is constituted by a link adjacent each of the lateral edges of the members and projections provided on these members are directed towards the neighbouring members in the chain to introduce a narrowing at locations close to the links of the spacing between the members.

5. The combination according to claim 4 wherein at least one of the front and rear faces of each member in non-planar.

6. The combination according to claim 5 wherein at least one of the front and rear faces is at least in part concave between the lateral edges thereby to form regions of greater thickness adjacent these edges than elsewhere in the plate, there being cavities in these greater thickness regions in which the links are mounted.

7. The combination according to claim 6 wherein the greater thickness regions of the members make tracking engagement with the pulley means and are complementary in exterior shape to peripheral grooves in said means.

Claims

2. The combination according to claim 1 wherein the electrodes presented towards the front faces of the members extend over the whole of the dimension between the lateral edges and additionally extend at least in part around these edges whereby these electrodes in conjunction wiTh the electrodes presented towards the rear faces of the members are directly effective on the whole of the surface area of the members except for portions which are not substantially greater than the surfaces making tracking engagement with the pulley means.