GB2175147A

GB2175147A - Homopolar rotary electric machine

Info

Publication number: GB2175147A
Application number: GB08607127A
Authority: GB
Inventors: Carl Erik Stille
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-03-28
Filing date: 1986-03-21
Publication date: 1986-11-19
Also published as: GB8607127D0; GB8508040D0

Abstract

A rotary electrical machine using a homopolar magnetic field has a rotor 3 comprising soft magnetic material arranged to produce a rotating non-uniform field pattern which is coupled to windings 18 mounted on the stator 16. The homopolar field may be generated by excitation windings (4, Fig. 1) within the rotor connected to slip-rings (7, Fig.1), or the excitation windings 4 may be mounted on fixed end pieces 2A. Various forms of rotor winding arrangement are described including run magnetic covers 12 to support winding against centrifugal forces. Cooling passages (14, 13) (Fig. 1) are disclosed. <IMAGE>

Description

SPECIFICATION Rotary electrical machine The invention relatesto a rotary electrical machine capable of operation as a generator or a motor While the invention is applicable in principle to both DC and AC machines, it is primarily useful for AC generators and motors, as will be described herein.

AC and DC motors and generators are normally of heteropolar design, that is to say the magnetic field reverses in polarity as one passes round the gap between rotor and stator Homopolar machines, that is to say in which the field is everywhere radially outward or everywhere radially inward, have been proposed for DC generation, but have not come into widespread use, mainly because,forthegeneration of morethan a quite small voltage, large numbers of slip-ring connections are required with attendant slip-ring losses.

In this connection, reference may be madetothe book "The performance and Design of direct current machines" by Clayton (Second Edition 1938).

The present invention proposes a novel design of homopolarmachine particularlysuitablefor alternat- ing current use.

According to the invention a rotary electrical machine incudes means for generating a homopolar field between rotor and stator, a rotor comprising soft magnetic material so arranged as in rotation to produce a rotating non-uniform field pattern, and windings mounted on the stator coupled to the field.

The homopolarfield may be produced buy a permanent magnet system, or by excitation windings within the rotor energised through slip-rings, and the rotor may comprise a cylinder of soft magnetic material such as soft iron, parts of which have been machined away to leave lobes through which the radial field is concentrated, or the rotor may be cup-shaped with lobes. Alternatively the excitation windings may be mounted on the stator, thus avoiding the need for slip-rings, in which case the central part of the rotor must be of soft iron to complete the magnetic circuit.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is an axial section through the shaft of a machine according to the invention: Figure 2 is a transverse section through the machine of Figure 1 at the middle of one ofthe rotor excitation windings; Figure 3 is a simplified axial section of the rotor; Figure 4 is a very much simplified transverse section of the rotor of Figure 3, and illustrating the connection of the statorwindings for a star-connected generator motor; Figures 5 and 6 are embodiments of the invention showing different shapes for the rotor and stator; and Figure 7 is an axial secflon of a modification in which the excitation windings are mounted on the stator.

Referringfirstto Figures 1 and 2, the rotor is mounted on a central shaft 1 and comprises a pair of end discs 2 and a core 3. The shape ofthe rotor provides spaces to accommodate windings 4 to maintain the homopolarfield required for operation.

The central shaft is mounted in journal bearings 5 and 6, the bearing being ofthethrust and locating type, and carries slip-rings7 for the supply of current to the windings 4. Aflange 8 on the shaft 1 provides means for coupling the machine to a power source if it is to function as a generator, ortothe equipment to be driven if it is to function as a motor. The construction oftherotorwill be more clearlyseen inthe simplified sections of Figures 3 and 4.

The windings 4 generate a field in a magnetic circuit which is completed through the stator 16. The stator is separated from the end discs ofthe rotor byan axial air gap 9, and from the rotor core 3 by a radial air gap 10.

The bobbins 11 which carrythewindings4are surrounded by a non-magnetic cover 12 to support the windings againstthecentrifugal forces which arise during rotation. Air passages 13, 14 allow cooling air toflowthrough the windings 4 in operation.

The stator 16 is constructed in two halves and is provided with slots 23 forthe windings 18. A cylinder 17, which may be of magnetic or non-magnetic material, supports the external coils ofthe windings 18 and is supported by supports (not shown in the drawing) of non-magnetic material, leaving a gap through which cooling air mayflow. Slots 15 in the stator 16 facilitate thewinding of the coils 18 with many turns formed from a continuous strand of insulated wire. In Figure 2 for clarity, some only ofthe slots 15 and windings 18 are shown.

The two rotorwindings 4 are arranged in magnetic opposition so thatthey energise two magneticcir- cuits, each flowing through an end disc 2, across the axial air gap 9, along the stator 16, across the radial air gap 10, through the rotor core, and then backto the shaft 1 and the winding 4. This results in the formation of a homopolar magnetic field which rotates with the rotor.

The rotor 3 may be constructed from an iron cylinderfrom which two opposite quadrants have been machined away along its full length. The magneticfield produced by the windings 4 is concentrated into the material of the remaining two quadrants and as this revolves the field strength at the windings 18 rises and falls, and an alternating voltage is induced in them. Rings 21 non-magnetic material supportthe ends of the rotorfrom the end discs 2, as shown in Figure3, againstcentrifugal force.

Figure 4 shows schematically the interconnections ofthe windings in a star-connected three-phase machine.

Figures 5 shows, in axial section, a modification of the machine as so far described in which the rotor 3 is cup-shaped, only a single end disc2 is required, and only a single set of windings 4.

Figure 6 is an alternative modification in which the end discs 2 have been modified into a cup shape. The air gap 9 in this embodiment is therefore no longer axial, butformsa continuationofthe radial gap 10.

Figure 7 is a further modification in which the The drawing(s) originaily filed were informal and the print here reproduced is taken from a later filed formal copy.

excitation windings4are mounted on the stator. The rotor3 is solid, as shown in the right-hand sketch, and soft iron end-pieces 2A with capping pieces as shown, complete the magnetic circuit This construction has the advantage of requiring noslip-ringsforsupplying currentto the excitation windings.

In these last two embodiments, corresponding components have been similarly numbered to those in the embodiments of Figures 1 and 2, and the details of construction will be clearfrom the foregoing description.

Claims

1. A rotary electrical machine including meansfor generating a homopolar radial field between a rotor (3) and a stator (16), the rotor (3) comprising soft magneticmaterial so arranged astoproducea rotating non-uniform field, the machine having windings (18) mounted on the stator and coupled to the field.

2. A rotary electrical machine according to Claim 1 in which the homopolar radial field is generated by windi ngs (4) withinthe rotor coupled to slip-rings (7).

3. A rotary electrical machine according to Claim 1 in which the homopolar radial field is generated by windings (4) mounted on the stator.

4. A rotary electrical machine according to Claim 1 or Claim 2to which the rotor comprises portions of a cylinder of soft magnetic material (3) and end plates (2).

5. A rotary electrical machine according to Claim 1 or Claim 2 in which the rotor (3) is of cusp shape and includes a single energising winding (4), and the magneticcircuit is completed by a single end disc (2).

6. A rotary electrical machine according to any preceding claim in which the statorwindings are star connected so asto form a three phase AC motor or generator.

7. A rotary electrical machine substantially as shown in and as herein described with reference to Figures 1,2 and 3 ofthe drawings or with the modification shown in any of Figures 5,6 or7 ofthe drawings.