US3497739A - Homopolar electrical machines - Google Patents

Description

Feb. 24, 1970 l A. D. APPLETON n 3,497,739

HOMOPOLAR ELECTRICAL MACHINES Filed Dec. 26, 196'?` y 3 Sheets-Sheefl 1 Figi L A i V' a 2b 2c 2d 2e 2f 2g 2h 2L Z] 2.a 5a:I b/ 5c/ 5al 5/ 56./

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' HoMoPoLAR ELECTRICAL MACHINES Filed Dec. 26, 1967 3 Sheets-Sheet 2 Feb. 24, A1970 A. D. APPLETON HOMOPOLAR ELECTRI GAL MACHINES Filed Deo. 26, 19e? 5 Sheets-Sheet 3 v, n@ Mm ,4J Z d. a EP-l.. ...Mln-...Ilm w 2 !I. |l. in l. Il i i ...n In i iinlh E iin United States Patent HOMOPOLAR ELECTRICAL MACHINES Anthony D. Appleton, Newcastle-upon-Tyne, England, as-

signor to The International Research & Development Company Limited, Newcastle-upon-Tyne, England Filed Dec. 26, 1967, Ser. No. 693,548 Claims priority, application Great Britain, Jan. 3, 1967, 371/67; Jan. 26, 1967, 3,981/67, 3,982/67 Int. Cl. H02k 31/02 U.S. Cl. 310-178 7 Claims ABSTRACT OF THE DISCLOSURE A homopolar electrical machine in which the rotor has a plurality of mutually-insulated conducting paths and sets of stationary brushes engaging contact segments at the ends of the paths have a spacing which is a multiple of the contact segment spacing and are interconnected to provide a series connection between a number of the con ducting paths. The rotor is of disc form and is provided with a set of auxiliary conducting paths arranged in a. plane parallel to the main conducting paths and each main path has a separate auxiliary path connected in series with it.

This invention relates to homopolar electrical machines.

Such machines usually comprise a rotating disc or drum having electrically conducting paths thereon and operate at low voltage and high current. A machine having a disc or drum construction is described in our co-pending British patent application No. 1-0,062/65.

The voltage and power output of such machines is a direct function of the number of discs or drums used and the operating voltage can be increased by connecting a number of discs or drums electrically in series.

The need to use a number of discs or drums connected lin series for such purposes adds to the cost and comconducting path being associated with a first and second segment, first and second sets of brushes are mounted to co-operate with the first and second contact segmentsrespectively, the centre to centre spacing of the brushesin 'the two sets is the same and is two or more times the spacing of the segments of the associated set, the brushes are dimensioned to bridge adjacent contact segments in passing from one to thernext, and brushes of the first set are electrically connected to brushes of the second set to effect a series connection between terminals for connection to an external circuit of those conducting paths whose associated contact segments are both in contact with the brushes, the arrangement being such that at certain positions of the rotor some conducting paths are connected in series while between each pair of series-connected paths there is at least one path which is not seriesconnected.

The brushes may be solid brushes, for example, con- .Ventional graphite brushes, or formed of metal wire or strip, or may be constructed to make a liquid contact with the segments.

The brushes of the two sets may be electrically connected by leads which pass radially from a brush co-operating with the outer set of contact segments to a position adjacent the inner set of segments and then pass in a cir- ICC cumferential direction to a brush co-operating with the inner set of segments.

In a preferred construction a disc-type rotor comprises a support on one side of which the conducting paths and the sets of first and second contact segments are mounted and on the other side of which for each of the main conducting paths there is an auxiliary conducting path with associated third and fourth contact segments for co-operation `with brushes of third and fourth sets which correspond in number to those of the first and second sets, each of the main conducting paths being electrically connected between a first segment and a third segment and each of the auxiliary conducting paths being electrically connected between a fourth segment and a second segment, and each of the brushes of the third set being electrically connected to a corresponding brush of the fourth set to connect the third and fourth segments, associated with an auxiliary conducting path when the first and second segments associated with the corresponding main conducting path are in engagement with brushes of the rst and second sets, whereby the auxiliary path is placed in series with the main path between the brushes of the rst and second sets.

The invention will now be described in more detail with the aid of examples illustrated in the accompanying drawings, in which:

FIGURES l and 2 are schematic diagrams of the electrical arrangement of a rotor of a machine in accordance with the invention for two positions of the rotor,

FIGURE 3 is a perspective view of part of a disc-type rotor with its brushes, some elements being omitted for clarity,

FIGURE 4 is a diagram of an alternative form of disctype rotor,

FIGURE 5 is a view similar to that of FIG. 3 of a further form of disc-type rotor in accordance with the invention,

FIGURE 6 shows the electrical connections of the rotor of FIG. 5 in diagrammatic form similar to the diagrams of In FIGS. 1 and 2 individual conducting paths of a disctype rotor are shown as strips 1a to 1j running between a first set of contact segments 2a to 2 j and a second set of contact segments 3a to 3j. In the disc-type rotor the conducting paths extend radially and the dimension A represents the outer circumference of the disc and the dimension B represents the inner circumference. For convenience of explanation the strips 1a and 1i, which in a practical construction would be adjacent, have been shown again at each end of the series. f

A set of brushes 5a to Se are arranged to co-operate with the contact segments 2a to 2j and a second set of brushes 6a to 6e are arranged to co-operate with the contact segments 3a to 3]'. The brushes of the `two sets are interconnected by leads 7. The pitch PB of the brushes is twice the pitch Ps of the contact segments. Thus with the fixed brush sets and the rotating contact segments in the relative positions shown in FIG. l alternate conducting strips 1a, 1c, 1e, 1g and 1i have their contact segments in engagement with brushes 5a and 6a, 5b and 6b, 5c and 6c, 5d and 6d, 5e and 6e respectively and by virtue of the leads 7 connecting brushes 5a and 6b, 5b and 6c, and so on, are connected in series between terminals T1 and T2 which are connected to the external circuit. At this time the intervening conducting strips 1b, 1d, andso on are not in contact with any brush and are thus not part of the operating circuit.

When the rotor moves on to the position shown in FIG. 2 each brush bridges two contact segments and, for example, conducting strips 1a and 1b are connected in parallel between brushes 5a and 6a by way of the respective contact segments 2a, 3a and 2b, 3b. The voltage is unaltered but the current is shared between the two strips which are connected in series with other pairs of strips 1c and 1d, 1e and 1f, etc. It will be apparent that upon further rotation of the rotor a position similar to that of FIG. l is reached in which strips 1b, 1d, 1f, 1h and 1]' are connected in series and strips 1a, 1c, 1e, 1g and 1i are disconnected.

The connections T1 and T2 to the rotor supply power if the rotor forms part of a homopolar motor, or remove power if the rotor forms part of a homopolar generator.

If for the purpose of explanation it is assumed that an EMF` is generated in the conducting paths in a radially inward direction and that the EMF generated in each conductor is E volts, then for the rotor position shown sharting at T1 we have zero voltage on brush 5d, E volts on brushes 6d and 5c 2E volts on brushes 6c and 5b, 3E volts on brushes 6b and 5a, 4E volts on brushes 6a and 5e and 5E volts on brush 6e which is connected to output terminal T2. The output voltage for the example shown is thus ve times the voltage generated in each conducting path. the EMFs generated in the conducting paths 1b, 1d, 1f, and 1h do not contribute to the output. V The EMF generated is a direct function of the number of conducting paths connected in series and as a consequence of connecting the conducting paths in the manner shown the voltage at which the machine operates can be varied in a relatively simple and cheaper manner compared with the previous arrangements in which such voltage increases have been obtained by increasing the number of discs or drums. The arrangement in accordance with the invention does not preclude the use of a number of discs but for a given voltage output the duplication of discs is reduced compared with previous arrangements. The number of conducting paths which can be connected in series is limited only by practical constructural considerations.

FIG. 3 shows a double disc-type rotor having the conducting paths of the two discs connected in series. A pair of disc-shaped assemblies and 11 of conducting paths are mounted back to back on a common insulating support disc 12 to form a rotor which in conventional manner is disposed in a magnetic lield lwhose lines of force are generally parallel to the axis of rotation of the rotor and are thus cut by the radially extending conducting paths of the rotor as the rotor rotates. The assemblies 10 and 11 each have an inner set of mutually insulated contact segments 10a and 11a, respectively, and an outer set of mutually insulated contact segments 10b and 11b, respectively, and between each pair of opposite contact seg.- ments 10a and 10b is a radially-extending conducting path 10c while between each pair of opposite contact segments 11a and 11b is a radially-extending conducting path 11C. The insulation between adjacent contact segments is shown at 13. The conducting paths may be of copper or an alloy thereof. 'Ihe conducting paths 10c and 11C are sector-shaped but they could have other shapes. They could for example be in the form of rods or bars or parallel-sided strips. It will be seen that each contact segment extends transversely to the plane of the disc and the segments of each set form a cylindrical surface for engagement by the brushes. Solid burshes of electrical-conducting material such as carbon or graphite are arranged in sliding contact with the contact segments of each set, brushes 14 contacting the contact segments 10a, brushes 15 the segments 10b, brushes 16 the segments 11a and brushes 17 the segments 11b.

In the Iform illustrated the brush pitch or spacing `between the brushes is twice the pitch or spacing of the contact segments, but it could be a greater multiple so that in a position of the rotor corresponding to that shown there would be more than one intervening segment between a pair of adjacent brushes.

The brushes 14 and 15 are interconnected by leads 7 (only one of which is shown) in the manner described with reference to FIGS. 1 and 2. The leads 7 pass radially inwards from the brushes 15 for a large proportion of their length and close to the brushes 14 they are carried round circumferentially to the appropriate brush, as at 7a. Such an arrangement reduces the effect of armature reaction due to current flowing in a circumferential direction. i

The connections between the brushes 16 and 17 are similarly arranged so that a number of the conducting paths 11c are connected in series. The terminal lead 18 connected to one of the brushes 14 is connected to the terminal lead 19 connected to one of the brushes 16 and this places the conducting paths on the two sides of the rotor in series between a terminal lead 20 connected to one of the brushes 15 and a terminal lead 21 connected to one of the brushes 17.

FIG. 4 shows schematically an alternative form of disc type rotor in which the conducting paths between outer contact segments 22 and inner contact segments 23 are -formed by rods or spokes 24.

The inner segments 23 are made longer in the axial direction than the outer segments 22 in order to provide the necessary contact area for current collection. The rods 24 may be carried on a support. If desired several rods, bars or strips can be associated with a pair of contact segments to constitute a single conducting path.

Whilst in the embodiment of FIG. 3 the contact segments are formed by bending the strips which form the conducting paths, they could be separate members bonded to the conducting strips.

The brushes used to transfer current may be conventional graphite 'brushes or take the form of an electrically conducting metal strip or wire.

The conducting paths may themselves constitute the rotor or they may be mountedon a supporting member.

FIGS. 5 and 6 illustrate an alternative form of disc-type rotor in which instead of having a series-connected set of conducting paths on one side connected in series with a series-connected set of paths on the other side of the rotor, each conducting path on one side is connected in series with an auxiliary conducting path on the other side. This is achieved by the use of interconnected sets of stationary brushes and connections through the supporting disc ofthe rotor.

The rotor shown in FIG. 5 has a supporting disc 25 on one side of which are mounted a set of sector-shaped main conducting paths 26 and on the other side of which are mounted a set of sector-shaped auxiliary conducting paths 27. The conducting paths 26 are each individually connected to one of a first set of contact'segments 28 arranged at the inner periphery of the conducting paths 26. A second set of contact segments 29 are arranged around the outer periphery of the conducting paths 26 but are insulated therefrom by an insulating ring 30. Brushes 31 and 32 co-operate with the contact segments 28 and 29, respectively, and are interconnected by leads 33 in the manner previously described with reference to FIGS. 1 to 3.

On the other side of the disc 25 a third set of contact segments 34 are arranged around the other periphery and insulated from the conducting paths 27 by an insulating ring 35. Each of the conducting paths 26 on one side of the disc is connected to an individual one of the contact segments 34 on the other side of the disc by a pin 36 which passes through an insulating bush 37 in the contact segment 29, through a clearance hole in the disc 25 and into an insulating bush (not shown) in the correponding conducting path 27. The pin 36, which is in threaded and electrically conducting engagement 'with the conducting path 26 and the contact segment 34 and is in threaded engagement in the insulating bushes in the conducting path 27 and contact segment 29, serves for the mechanical assembly of the rotor as well as the required electrical connection. In a similar manner each of the conducting paths 27 is connected to an individual one of the contact segments 29 by a pin 38 which serves for mechanical assembly and electrical connection, passes through the disc 2S and engages an insulating bush 39 in the conducting path ,26.

Each of the conducting paths 27 is directly electrically connected to an individual segment of a fourth set of contact segments 40 at the inner periphery of the rotor. Sets of brushes 41 and 42 are arranged to co-operate with the contact segments 34 and 40, respectively, and each brush of one set is connected to the corresponding brush of the other set by a radially-extending lead 43.

The electrical layout of the rotor of FIG. 5 is shown schematically in FIG. -6. It will be seen that the upper half of FIG. 6 resembles FIG. l in the arrangement of the brushes 31 and 32 and contact segments 28 and 29v with the connecting leads 33 between the brushes to produce a series connection of conducting paths between terminals T1 and T2. However between each of the conducting paths 26 and the associated contact segment 29 an auxiliary conducting path 27 is connected by way of a pin 36, a contact segment 34, brushes 41 and 42 interconnected by a lead 43, and a contact segment 40, and by way of a pin 38 connecting the auxiliary path 27 to the contact segment 29.

To ensure continuity of current flow the brushes must be wide enough or the number of brushes on a given segment must be sufficient to ensure that a portion of a brush is always in contact with a slip-ring segment.

Whilst carbon brushes have been described the brushes could be in the form of metal strips or have other suitable forms.

The contact segments are individually insulated from one another.

The magnetic eld may be generated by electromagnets and a magnetic core or by means of a superconducting coil.

I claim:

1. A homopolar electrical machine having a disc-type rotor carrying a plurality of radially extending conducting paths disposed around the rotor and a stator comprising means for generating a magnetic field which is cut by the conducting paths as the rotor rotates wherein the rotor has a set of rst contact segments at the outer periphery of the disc and a second set of contact segments at the inner periphery of the disc, each set forming a cylindrical surface for contact by brushes, each conducting path being associated with a rst and second segment, rst and second sets of brushes are mounted to cooperate with the cylindrical surfaces formed by the rst and second sets of contact segments respectively, the center to center spacing of the brushes in the two sets is the same and is two or more times the spacing of the segments of the associated set, the brushes are dimensioned to bridge adjacent contact segments in passing from one to the next, and brushes of the rst set are electrically connected to brushes of the second set to effect a series connection between terminals for connection to an external circuit of those conducting paths whose associated contact segments are both in contact with the brushes, the arrangement being such that at certain positions of the rotor some conducting paths are connected in series while between each pair of series-connected paths there is at least one path which is not series-connected.

2. A homopolar machine as claimed in claim 1 wherein said first set of brushes is in engagement with the radial inner face of said irst contact segments.

3. A homopolar machine as claimed in claim 1 in which the brushes of the two sets are electrically connected by leads which pass radially from a brush co-operating with the radially outer set of contact segments to a position adjacent the radially inner set of segments and then pass in a circumferential direction to a brush co-operating with the radially inner set of segments.

4. A homopolar machine as claimed in claim 1 in which the rotor has two sets of conducting paths disposed on opposite sides of a suport disc and the arrangement 6 is such that for a given position of the rotor each of the series-connected paths of one set is connected in series with a corresponding conducting path of the other set and the series-connected pairs of conductors thus formed are themselves connected in series.

5. A homopolar machine as claimed in claim 1 in which the rotor comprises a support disc on one side of which the conducting pat-hs and the first and second sets of contact segments are mounted and on the other side of which for each of the main conducting paths there is an auxiliary conducting path with associated third and fourth contact segments for co-operation with brushes of third and fourth sets which correspond in number to those of the rst and second sets, each of the main conducting pat-hs being electrically connected between a first segment and a third segment and each of the auxiliary conducting paths being electrically connected between a fourth segment and a second segment, and each of the brushes of the third set being electrically connected to a corresponding brush of the fourth set to connect the third and fourth segments associated with an auxiliary conducting path when the first and second segments associated with the corresponding main conducting path are in engagement with brushes of the rst and second sets, whereby the auxiliary path is placed in series with the main path between the brushes of the first and second sets.

6. A homopolar machine as claimed in claim 1 in which the rotor comprises a support disc on each side of which are mounted a group of conducting paths and associated contact segments, separate sets of brushes being provided for connecting in series the conducting paths of the two groups and the two sets of brushes being connected in series.

7. A homopolar electrical machine having a disc-type rotor comprising a support carrying on one side a plurality of conducting paths disposed around the rotor and a stator comprising means for generating a magnetic field Which is cut by the conducting paths as the rotor rotates wherein the rotor has a set of rst contact segments and a set 0f second contact segments, each conducting path being associated with a rst and second segment, rst and second sets of brushes are mounted to cooperate with the rst and second contact segments respectively, the center to center spacing of the brushes in the two sets is the same and is two or more times the spacing of the segments Of the associated set, the brushes are dimensioned to bridge adjacent contact segments in passing from one to the next, and brushes of the first set are electrically connected to brushes of the second set to effect a series connection between terminals for connection to an external circuit of those conducting paths whose associated contact segments are both in contact with the brushes, the arrangement being such that at certain positions of the rotor some conducting paths are connected in series while between each pair of series-connected paths there is at least one path which is not series-connected, the support carrying on the other side, for each of the main conducting paths, and auxiliary conducting path with associated third and fourth contact segments for cooperation with brushes of third and fourth sets which correspond in number to those of the iirst and second sets, each of the main conducting paths being electrically connected between a rst segment and a third segment and each of the auxiliary conducting paths being electrically connected between a fourth segment and a second segment, and each of the brushes of the third set being electrically connected to a corresponding brush of the fourth set to connect the third and fourth segments associated with an auxiliary conducting path when the first and second segments associated with the corresponding main conducting path are in engagement with brushes of the first and second sets, whereby the auxiliary path is placed in series with the main path between the brushes of the first and second sets.

(References on following page) References Cited OTHER REFERENCES UNITED STATES PATENTS Steinmetz lublication, TK2181.57, Theory & Calcula- 1223094 4/1917 Neuland Hu 310 178` tlon of Electrlcal Apparatus; pp. 450-458. 1,255,838 2/1918 Knoll 310-178 Sykes 5 Pnmary Examlner 2,261,684 11/ 1941 Jones 31o-178 R. SKUDY, Asslstant Examiner 3,187,212 6/1965 Sears 310--178 Y U S C1 .X R FOREIGN PATENTS 310 268 290,592 1/1944 Germany. 10

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