GB1574326A

GB1574326A - Dynamo-electric machines

Info

Publication number: GB1574326A
Application number: GB1572177A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-01-17
Filing date: 1978-01-17
Publication date: 1980-09-03

Description

(54) DYNAMO-ELECTRIC MACHINES (71) I, HAROLD HOSGOOD JONES, a Britlsh Subject of West Lodge, High Street, Chipstead, Kent, TN13 2RR, 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: This invention is concerned with dynamo-electric machines and particularly with synchronous motors and motor alternators.

The invention provides a synchronous motor comprising an inner wound stator, a rotor mounted for rotation about the stator, and high coercivity permanent magnets equal in number to the number of poles of the stator embedded in the rotor between the outer circumference thereof and conductors of the rotor at the inner surface of the rotor, these magnets extending circumferentially over 90 electrical degrees and being spaced 180 electrical degrees apart. According to a further feature of the invention, a plurality of permanently magnetised axial strips are spaced around the outer circumference of the rotor and an outer stator wound with at least one winding surrounds the rotor and the machine runs as a synchronous motor alternator.

Among the advantages of a machine constructed according to the invention as compared with existing designs are: firstly, it is economical of space occupied; secondly, by the use of high coercivity permanent magnets. no power is lost in providing excitation of the several magnetic flux paths; thirdly, the rotating member is of relatively high moment of inertia so that speed oscillation or 'swinging' about the synchronous speed and hence frequency and voltage modulation of the output is minimized; fourthly short coil lengths of the primary winding produce a machine with reduced primary resistance, therefore reduced resistive loss.

Other parts of the invention will now be described in some detail with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-section; and Figure 2 is a transverse cross-section of one form of machine according to the invention.

The machine shown in the drawing is a combination of a two pole single phase synchronous motor and a sixteen pole three phase alternator intended to produce 400 Hz. from a 50 Hz. supply. The invention is not however restricted to these combinations and includes other combinations of poles and windings incorporating the same features.

The machine comprises an inner stationary core 26 comprising a stack of insulated, slotted laminations of electrical grade steel pressed on to a centre shaft 24. The slots round the outer periphery of this core are insulated and wound in the same way as are the stators of induction motors except that in this case the core is wound in slots around the outside whereas the normal induction motor is wound in slots in the bore. A 50 Hz. single phase input is fed to this winding by flexible insulated conductors 25 entering the machine through the centre shaft 24.

End bells 17 mounted on the outer races of ball bearings 20 on the ends of the shaft 24 support a ring shaped rotor core 27 surrounding the inner core 26 and separated therefrom by a small air gap. This ring shaped rotor core 27 is constructed from the same insulated electrical grade steel laminations as the stator 26 and is slotted around its internal surface. Cage bars 8 fill these slots.

End rings 14 of the same conducting material of the bars oin all the cage bars 8 together at each end of the rotor. The exterior of the rotor core 27 is pressed into a soft steel tubular member 5 which retains the shape of the laminated rotor stack and which also provides a magnetic flux path between the mag nets of the alternator as described below.

Within the rotor core 27 and at a radius intermediate between the cage bars 8 and the outer steel tubular member 5 a layer 6 of high coercivity permanent magnet material is embedded for each pole of the motor. The permanent magnet layers 6 extend the full length of the core 27 from one end ring to the other. As seen in Figure 2 each arcuate magnet 6 spans approximately 4 radians and is spaced 7r radians from the next magnet.

These magnets in strip form of length equal to the core length are inserted into slots cut in the laminations. From each of the four extremities of these arcuate magnet slots, narrow approximately radial inward slot extensions 7 are cut, having a width approximately twice the air gap between the stator 26 and rotor 27. These slot extensions 7 span the distance from the magnet slot ends radially inwards to as near the cage bar slots as can conveniently be manufactured.

Strengthening narrow bridges may also be left across the magnet slots to aid manufacture. The magnets 6 are magnetized so as to produce alternate north and south magnetic poles around the inner bore of the rotor one motor pole pitch apart.

The permanent magnets are preferably proportioned so as to apply a greater magneto-motive force across the air gap between the inner stator and the rotor than the inner stator winding magnetizing current applies across the same gap for example about 1 times as great.

The stator 26 and rotor 27 as so far described comprises a synchronous motor which starts and runs up to near synchronous speed by the torque produced by the product of the stator magnetizing flux and the currents induced in the cage bars and finally locks into synchronism when the synchronizing torque exceeds the induction motor torque.

On the outside of the soft steel tubular member 5 enclosing the laminated rotor 27 are attached a number of high coercivity magnets 4 equal in number to the number of alternator poles and spaced one alternator pole pitch apart. They are magnetised alter natelv with north and south poles. These magnets are parallelogram shaped of curved section. Their outer surfaces. which are eon- centre and true with the axis of rotation.

form one surface of an air gap between the rotor and stator of the alternator. The other surface of the air gap is formed by an outer stationary laminated ring core 1 which is slotted. insulated and wound on its internal surfacc. This alternator core 1 is supported by end covers 11 supported on outer ball bearing 19 mounted on the bearing receptacles 18 enclosing the inner ball bearings 20. The bearing receptacles 18 are secured to the end bells 17 and one of them is extended beyond the bearings to provide an output shaft. Currents induced in the conductors of the alternator winding by the passing of the magnets 4 at the synchronous speed produce alternating current outputs at the exact multiple frequency of the poles of the alternator divided by the poles of the motor times the input frequency. In the form shown there are 16 poles on the alternator so that the output frequency is 400 Hz. The stator 1 may be wound to provide a number of outputs of different voltages, the ends of the relevant windings being brought to terminals 21.

Blades 15 are mounted on the end bells 17 to draw air through aligned kidney shaped holes 16 in the end covers 11 to pass over the alternator zone and out through holes 22.

It will be understood that the invention is not restricted to the details of the preferred forms which have been described by way of example and which may be modified without departure from the scope of the accompany

Claims

ing claims. WHAT I CLAIM IS:

1. A synchronous motor comprising an inner wound stator, a rotor mounted for rotation about the stator and high coercivity permanent magnets equal in number to the number of poles of the stator embedded in the rotor between the outer circumference thereof and conductors of the rotor at the inner surface of the rotor, these magnets extending circumferentially over 90 electrical degrees and being spaced 180 electrical degrees apart.

2. A synchronous motor alternator comprising a synchronous motor as claimed in Claim 1, having a plurality of permanently magnetized axial strips spaced around the outer circumference of the rotor and an outer stator surrounding the rotor and wound with at least one winding.

3. A synchronous motor alternator as claimed in Claim 2 in which the permanently magnetized strips on the circumference of the rotor are of curved parallelogram shape in cross-section with their outer surfaces forming one surface of the air gap between the rotor and the outer stator.

A. A dynamo-electric machine as claimed in any of the preceding claims, in which the magnets embedded in the rotor are in strip form inserted into slots cut in the rotor laminations and narrow approximately radially inward extensions of these slots span the distance from the magnet slot ends close to slots containing a cage bar winding of the rotor.

5. A dynamo-electric machine as claimed in Claim 4. in which narrow strengthening bridges extend across the magnet slots in the laminations.

6. A dvnamo-electric machine as claimed in any of the preceding claims, in which the embedded permanent magnets apply a greater magneto-motive force across the air gap between the inner stator and the rotor than the inner stator winding magnetizing current applies across the same gap.

7. A dynamo-electric machine as claimed in any of the preceding claims, in which the rotor core is enclosed in a soft steel tubular member.

8. A dynamo-electric machine substantially as described with reference to the accompanying drawings.