GB1599909A

GB1599909A - Electrical machines

Info

Publication number: GB1599909A
Application number: GB2268177A
Authority: GB
Original assignee: WINTERBOTHAM H
Current assignee: WINTERBOTHAM H
Priority date: 1978-04-19
Filing date: 1978-04-19
Publication date: 1981-10-07

Description

(54) IMPROVEMENTS IN ELECTRICAL MACHINES (71) I, HAROLD WINTERBOTHAM, of Fern Howe, Braithwaite, Keswick, Cumbria, CA12 5SZ, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to electrical machines, and in particular to a novel arrangement of windings and permanent or electro-magnets within the machine.

More particularly, although not exclusively, the invention relates to an electrical rotating machine designed for use as a generator from wind or water power.

Energy by wind power is frequently converted at the site into electricity, so that the wind tower can be built in the windiest available position and the power then transmitted to the house or the consumer.

An ideal type of wind driven generator would desirably need to have some or all of the following features:- (a) rotating magnets in order to eliminate the use of brushes; (b) a vertical axis drive at speeds of about 300 R.P.M. at full load; (c) a high efficiency and good power output over the whole range of speeds and particularly at low speeds; (d) ease of rotation at low torque; (e) reasonably low manufacturing costs; (f) easy adaption to a simple form of automatic load control; and (g) minimum maintenance and accessibility for servicing.

All forms of mechanical electrical generators currently in use operate by using energy to move conductors across magnetic lines of force or vice-versa. The flux is concentrated at the junction between moving and stationary parts of the machine by high permeability material such as iron.

The conventional method of construction is to wind the conductors around an iron core.

The flux alternates in the iron, thus cutting the conductors to generate an E.M.F.

therein. This method shortens the winding but introduces losses, both from eddy currents and hysteresis. Eddy currents can be reduced in conventional manner by laminating the core, but hysteresis losses are inescapable. In addition, there are other disadvantages in conventional electrical generators. These are as follows:- (a) efficiency is only high for a narrow range of speeds; (b) operation is non-linear because the flux is not a linear function of the M.M.F.; (c) a considerable torque is required to pull the poles out of a minimum energy position when starting.

It will be seen from the above facts taken in conjunction with the desired features for the generation of electricity by wind power listed earlier, that conventional types of electrical machines are unsuitable for use as wind driven generators particularly at low wind speeds.

A particular type of electro-dynamic machine known in the art comprises: a first part carrying a plurality of permanent or electro-magnets arranged to form an airgap; a second part carrying a plurality of conductors formed into electrical windings and arranged within the air-gap; at least one of said machine parts being movable with respect to the other part.

All machines having this disposition of parts have in common the characteristic that the conductors are not wound round an iron core and therefore the flux in the iron remains constant at all times, thus eliminating iron losses.

According to the present invention there is provided an electrical rotating machine including: a first part carrying a plurality of magnets arranged in equi-spaced relation around a circumferential zone of a circle, the poles of said magnets lying in two rings separated axially to form an air-gap and being formed so that their air-gap faces are elongated in the radial direction, the polarity of said magnetic surfaces alternating both across the air-gap and arround the circumferential zone, the magnetic circuit being completed in the radial direction within said circumferential zone; a second part carrying a plurality of conductors located within the air-gap, said electrical conductors being formed into a plurality of separate coil units which are equi-spaced and supported by a structure outside the air-gap, the coil units being electrically connected in accordance with the sequence of alternating polarity of the pairs of poles around the circle so that the induced E.M.Fs of the coil units are in phase; at least one of said machine parts being rotatable with respect to the other part.

In one preferred form, the second machine part with the windings is fixed, and the first machine part which carries two rings of permanent magnets rotates above and below the windings.

In the same preferred form the permanent magnets are carried around the periphery of a box girder rotor, each pair of magnets being carried by a pair of carrier members clamped together at one end and being spaced apart at their free ends to carry the permanent magnets which define the annular air-gap around the machine therebetween.

In the same preferred form a plurality of electrical conductors of the stator are formed into a coil unit, the coil units being arranged in two separate interleaved groups around the machine, so that they lie selfsupported in the annular air-gap.

The present invention will now be described in greater detail be way of example with reference to the accompanying drawings, wherein: Fig. 1 is an elevation view of one preferred form of electrical generator designed to be driven by wind power; Fig. 2 is a part cross sectional elevation of the machine shown in Fig. 1; Fig. 3 is a plan view of the rotor construction; Figs. 4A and 4B are respectively a cross sectional elevation and a plan of one of the permanent magnet pole-pieces in the rotor; Fig. 5 shows a stator coil assembly and the arrangement of two independent winding circuits each formed from a plurality of interleaved coil units; and Figs. 6A and 6B are respectively a plan and an elevation view of a coil unit; Referring first to Figs. 1 and 2, it will be seen that the electrical machine is shaped like a disc. The machine is supported on a base 10 which may be secured to the ground or other base member by bolts passing through bolt holes 12. The base 10 is provided with an upwardly extending support shaft 14 which is hollow at its lower end 14a. The upper solid end 14b of the shaft 14 carries bearings 16 and 18 which are interconnected by a hollow shaft 20 coaxial with the upper end 14b of the shaft 14.

A box girder rotor 22 comprises radial sections 24, upper and lower annular sections 25 and 26 and a circumferential section 28, all these sections being welded, bolted or riveted together to form an annular shaped box which tapers in the radial outward direction. Apertures 30 are provided in the sections 24, 25 and 26 being mainly for the purpose of lightening its construction, without reducing its rigidity.

The box girder rotor 22 is secured to the hollow shaft 20, the whole rotor structure thus being capable of rotation about the shaft 14. A flange 21 is welded to annular member 23 which in turn is welded to the cover 42, 43 and this in turn is bolted to upper member 25 as the last assembly operation. Bolt holes 27 enable a corresponding flange on the end of the windmill drive shaft to be secured thereto by means of a flexible coupling.

As will be seen from Fig. 3, the box girder rotor carries 48 pairs of permanent poles 32 which are equi-spaced around its circumference. Referring also to Figs. 4A and 4B, each pair of poles is formed from rectangular blocks 34 of permanent magnetic material, preferably a magnetic material embedded in a plastics material, the blocks providing a uniform magnetic field. The upper and lower permanent magnet blocks 34 are secured to respective pole carriers 36 each of which comprise a flat piece of high permeability soft iron.

Each carrier 36 is provided with an elongated 'S' shaped portion 38 whereby the ends 39 of a pair of carriers remote from the permanent magnets 34 are in contact with one another whilst the ends which carry the permanent magnets 34 are held in a fixed spaced relation so that the permanent magnets define an air-gap between opposing faces. The two pieces 36 when attached together form a path for the magnetic flux which is closed except for the air-gap. The polarity of the permanent magnets alternates around the rotor viz: a first pair have north poles on their upper faces whilst adjacent pairs have south poles on their upper faces. The ends 39 of a pair of carriers 36 are provided with three holes 40, which enable the permanent magnet pole pieces 32 to be clamped between a pair of flanges 29 by bolts 41, the flanges 29 being themselves secured to the inside of the circumferential section 28 of the box girder rotor 22 through apertures therein.

A cover 42 is secured to the top of upper section 25 of the box girder rotor 22 by bolts 45 and is extended over the pole pieces 32 to terminate in a downwardly projecting circumferential portion 43. This cover carries the drive flange 21. The bolts 45 engage in threaded holes provided in tag members 31 welded to the upper annular section 25.

The coil assemblies which comprise the stator are supported on a circumferential ring member 44 which is supported by a dish-shaped member 47 strengthened by a plurality of external equi-spaced radially extending fins 46. The dish-shaped member 47 is secured to the hollow portion 14a of the shaft 14 by means of bolts 48.

The stator coil units are shown in greater detail in Figs. 5, 6A and 6B. Each coil unit 50 has the shape shown in Fig. 6A, with straight "active" portions 52 and inner and outer curved "headspool" portions 54. The parts of the "headspool" portions at the points where they merge into the straight "active" portions are slightly bent to form an elongated S as indicated at 56 in Fig. 6B.

Each coil unit 50 comprises a plurality of turns, 16 in the machine here described, in the inner end of the coil being led out to form a conductor 57 and the outer end to form a conductor 58, these ends protruding through an outer ring of epoxy for the purpose of interconnection. These ends come from the part of the coil which is outermost from the centre of the machine.

All coil units are identical.

Referring specifically to Fig. 5, the stator contains two independently connected sets of coil units, the object of this arrangement being to make full use of the available space. The coil units 50 of one set are arranged side by side in one plane and the coil units 50' of the second set are arranged in the same plane but positioned the other way up so that the "active" portions 52 of both sets lie in the same plane whereas the headspool portions lie in adjacent planes on either side thereof, such positioning being permitted due to the elongated S portions 56 of the two sets of coil units. The coil units of the respective sets are connected as shown so that the current flow in the adjacent sides of two coil units in the same set is in the same direction. Inner conductors 57 and outer conductors 58 are interconnected as shown by conductors 62 and 64 respectively. The two sets are not connected, but provide two independent outputs. The "headspool" portions are held at their inner and outer ends by being encased in an epoxy resin, the outer headspool portions being clamped to the stator ring 44 by bolts 60.

Terminals 49 are located on the ring member 44 to enable the two sets of stator coils to be connected to external circuits.

Each set of coil units contains 48 such units arranged arround the machine, each coil unit 50 subtending an angle of 7.5 .

Four coils from each set (8 in all) are preformed into a sub-assembly as shown in Fig.

5 for ease of assembly.

The particular electrical machine described above is of medium capacity, having 48 poles and a maximum output of 6 KW. By way of explanation it has been previously shown that each of the two sections comprising the machine can be represented as a source of E.M.F. of peak value 65.7 volts per R.P.S. The R.M.S.

value is found to be 1/47.3 of the peak (compare l/T2 for a sinusoidal waveform), and is therefore 43.34 volts per R.P.S. The internal resistance of each section is 1.92 ohms as previously stated.

Output power is only limited by two factors: maximum allowable speed and maximum allowable internal heat dissipation. Taking conservative limits of 5 R.P.S. 1 KW heat dissipation (500 watts per section), the output power at these limits is, by Ohms Law, 3 KW per section, which means that the total R.M.S power output available is 6 KW. Similarly, a smaller size of machine having 36 poles would have maximum output of 2.53 KW, whilst a larger size of machine having 60 poles would have a maximum output of 11.7 KW. Whilst these three types of machine are suitable for domestic use for heating purposes, the same basic principle can be applied to larger machines suitable for industrial use or for feeding power into the grid with the aid of appropriate synchronizing equipment.

Whilst in the above described generator the windings are fixed and the permanent magnets rotate above and below the windings, it would be possible to construct the machine such that the permanent magnets were fixed and the coil units constituting the windings rotated within the annular gap defined by the permanent magnets. This alternative construction has the advantage that electro-magnets could be used, but the disadvantage that slip rings would have to be used to obtain the outputs from the two sets of windings.

A further possibility is to mount both the permanent magnets and the coil units for rotation in opposite directions. Such a construction would of course mean having separate drives either from separate windmills or from the same windmill using a set of gears to obtain rotation in the other direction. Whilst such a construction is obviously more complicated from the mechanical point of view, it does have the advantage that the overall efficiency of the generator would be increased.

Whilst the above described machine has two independent windings and gives two outputs which are identical but at a phase difference of 90 , a further possibility is to utilize three separate windings of very similar arrangement. If then the magnet width circumferentially is increased from one quarter of a pole pitch (the angular spacing allotted to a pair of poles and a pair of spaces between poles) to one third, the spaces being correspondingly reduced from one quarter to one sixth, then three outputs are produced, identical but 1200 apart in phase. The machine then becomes a true three-phase generator. The total output from the machine is increased because of the increased proportion of the circumference occupied by magnets, and the higher RMS value of the waveform, but is decreased by the greater length of inactive conductors, which leads to greater winding resistance; there is also added complexity of coil overlaps. A three-phase machine would find better application as a motor, as now to be mentioned.

Whilst the above described machine is used as an alternator, the same principle can be applied with equal advantages to motors, and in fact the machine described above will operate with the same efficiency as a motor, either in the synchronous mode if fed by single phase AC, or, with a commutator, as a DC motor. Similarly the three-phase alternator will become a true rotating field machine if fed with 3-phase AC and operate as a permanent magnet induction motor; the two phase machine described will also function in this way if the two windings are fed with two phase AC at 90" phase difference, but not so efficiently.

As these machines have two or perhaps three windings it is practical to drive the magnet rotor using one winding and take an output from the other or others, thus making a rotary converter. A variety of combinations is possible. The drive shaft may also be used to put power in or to extract it and this, together with the two or three electrical outputs, provides a three or four terminal power transfer device in which the common factor is the frequency (rate of rotation in the case of the drive shaft).

WHAT I CLAIM IS: 1. An electrical rotating machine: including a first part carrying a plurality of magnets arranged in equispaced relation around a circumferential zone of a circle, the poles of said magnets lying in two rings separated axially to form an air-gap and being formed so that their air-gap faces are elongated in the radial direction, the polarity of said magnetic surfaces alternating both across the air-gap and around the circumferential zone, the magnetic circuit being completed in the radial direction within said circumferential zone; a second part carrying a plurality of conductors located within the air-gap, said electrical conductors being formed into a plurality of separate coil units which are equi-spaced and supported by a structure ouside the air-gap, the coil units being electrically connected in accordance with the sequence of alternating polarity of the pairs of poles around the circle so that the induced E.M.Fs of the coil units are in phase; at least one of said machine parts being rotatable with respect to the other part.

2. An electrical machine according to claim 1, wherein the second machine part with the windings is fixed, and the first machine part carries two rings of permanent magnets which are arranged to rotate above and below the windings.

3. An electrical machine according to claim 2, wherein the permanent magnets are carried around the periphery of a box girder rotor, each pair of magnets being carried by a pair of carrier members clamped together at one end where they are secured to the rotor and being spaced apart in parallel relation at their free ends to carry the permanent magnets which define the annular air-gap around the machine therebetween.

4. An electrical machine according to claim 3, wherein said carrier members each consist of a pair of flat pieces of high permeability soft iron provided with an elongated 'S' shaped portion near the ends where they are clamped to the box girder rotor.

5. An electrical machine according to any one of the preceding claims 2 to 4, wherein each permanent magnet comprises a rectangular block of magnetic material, the blocks providing a uniform magnetic field within the annular air-gap between two adjacent blocks constituting a pair of magnets.

6. An electrical machine according to claim 5, wherein each permanent magnet block comprises a magnetic material embedded in a plastics material.

7. An electrical machine according to any one of the preceding claims wherein two separate sets of coil units are provided, the two sets of coil units being interleaved around the machine to provide two separate equal electrical outputs from the machine.

8. An electrical machine according to claim 7, wherein each coil unit comprises substantially straight radially oriented active portions within the air-gap and substantially arcuate headspool portions outside the annular air-gap.

9. -An electrical machine according to claim 8, wherein the junctions between the active and headspool portions of the windings are bent to form an elongated S

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. utilize three separate windings of very similar arrangement. If then the magnet width circumferentially is increased from one quarter of a pole pitch (the angular spacing allotted to a pair of poles and a pair of spaces between poles) to one third, the spaces being correspondingly reduced from one quarter to one sixth, then three outputs are produced, identical but 1200 apart in phase. The machine then becomes a true three-phase generator. The total output from the machine is increased because of the increased proportion of the circumference occupied by magnets, and the higher RMS value of the waveform, but is decreased by the greater length of inactive conductors, which leads to greater winding resistance; there is also added complexity of coil overlaps. A three-phase machine would find better application as a motor, as now to be mentioned. Whilst the above described machine is used as an alternator, the same principle can be applied with equal advantages to motors, and in fact the machine described above will operate with the same efficiency as a motor, either in the synchronous mode if fed by single phase AC, or, with a commutator, as a DC motor. Similarly the three-phase alternator will become a true rotating field machine if fed with 3-phase AC and operate as a permanent magnet induction motor; the two phase machine described will also function in this way if the two windings are fed with two phase AC at 90" phase difference, but not so efficiently. As these machines have two or perhaps three windings it is practical to drive the magnet rotor using one winding and take an output from the other or others, thus making a rotary converter. A variety of combinations is possible. The drive shaft may also be used to put power in or to extract it and this, together with the two or three electrical outputs, provides a three or four terminal power transfer device in which the common factor is the frequency (rate of rotation in the case of the drive shaft). WHAT I CLAIM IS:

1. An electrical rotating machine: including a first part carrying a plurality of magnets arranged in equispaced relation around a circumferential zone of a circle, the poles of said magnets lying in two rings separated axially to form an air-gap and being formed so that their air-gap faces are elongated in the radial direction, the polarity of said magnetic surfaces alternating both across the air-gap and around the circumferential zone, the magnetic circuit being completed in the radial direction within said circumferential zone; a second part carrying a plurality of conductors located within the air-gap, said electrical conductors being formed into a plurality of separate coil units which are equi-spaced and supported by a structure ouside the air-gap, the coil units being electrically connected in accordance with the sequence of alternating polarity of the pairs of poles around the circle so that the induced E.M.Fs of the coil units are in phase; at least one of said machine parts being rotatable with respect to the other part.

shaped portion, whereby the coil units of the second set may be interleaved within the coil units of the first set by placing them the other way up so that the active portions of both sets of coil units all lie in the same plane.

10. An electrical machine according to claim 8 or 9, wherein the headspool portions are held in fixed relation by being encased in an epoxy resin, the outer headspool portions being clamped to the supporting structure.

11. An electrical machine according to any one of the preceding claims 2 to 10, wherein an annular cover is secured to the top of the box girder rotor and extends over the permanent magnets and coil units and terminates in a downwardly projecting circumferential portion.

12. An electrical machine according to claim 1, wherein the second machine part with the windings is arranged to rotate, and the first machine part carries two rings of permanent magnets which are fixed, the windings rotating in the annular air-gap defined by the electro-magnets.

13. An electrical machine according to claim 1, wherein the second machine part with the windings is arranged to rotate, and the first machine part carried two rings of permanent magnets which are arranged to rotate above and below the windings, the windings and the permanent magnets rotating in opposite directions.

14. An electrical machine according to any one of the preceding claims, wherein said machine is an alternator and is driven by a windmill.

15. An electrical machine according to any one of the preceding claims 1 to 13, wherein said machine is a motor.

16. An electrical machine constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.