Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-06-07
2001-12-04
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S114000, C310S180000, C336S131000, C336S118000
Reexamination Certificate
active
06326713
ABSTRACT:
This invention relates to new structures for alternating current electrical machines, and methods of transducing power.
Conventional, direct current rotating electrical machines are well known devices, each typically comprising a magnetic yoke providing a stationary magnetic field, within which an armature rotates. The armature typically comprises a laminated steel rotor carrying a set of electrically conductive coils, each of which is connected at the appropriate times to a direct current supply, via a commutator and associated brushes, so as to produce electric current in conductors surrounded by the main, stationary field, thus summating a stream of torque impulses over a wide range of rotational speeds. The essence of the action is that the stationary magnetic field, the current carried by the rotor conductors, and the direction of their permitted motion are all mutually at right angles, producing a torque reaction upon the rotor and that the stationary magnetic field flux is locally distorted, but largely unaltered by the armature current. This form of electric machine has advantages of speed and torque control and in small ratings can function even when supplied from alternating current supplies, but in common use, the need to convert the public A.C. supply to a D.C. supply at variable voltage introduces disadvantages of harmonic currents and reduced power factor. Moreover, the brushes gradually wear away and require periodic replacement, neglect of which can engender serious damage.
Conventional alternating current rotating machines are well known devices, typically comprising a magnetic yoke, carrying a set of coils connected to a multiphase mains supply and physically arranged to produce a rotating magnetic field within which is a rotor. The rotor is usually of laminated steel and may have one of several typical forms, as follows:
It may have magnetic saliency by virtue of shape, or by virtue of the injection of A.C. or D.C. electrical power via slip-rings and brush gear. It then rotates in magnetic synchronism with the stator field.
It may have a set of peripheral conductors, which are short-circuited, typified as the squirrel cage. It then rotates in equilibrium, asynchronously with the stator field. Sometimes the conductors are connected to slip-rings, so that external electrical resistance can be introduced for starting purposes.
The essence of the action is that the magnetic field rotates and the rotor is constrained to follow. Low-power, A.C. machines are usually connected to a single-phase, stator supply and equipped with additional devices to ensure that they rotate only in the desired direction. These forms of the electrical rotating machine have advantages of simple and robust construction, but have disadvantages for speed adjustment and torque control in that the source of the main power generally must be a variable frequency supply, which typically is generated by elaborate electronic control equipment switching the stator currents at relatively high frequencies.
It is an aim of the present invention to ameliorate at least some of the problems of the prior art.
According to a first aspect of the invention there is provided an a.c. electrical machine comprising at least two transformers balanced in magnetic fields being, inductively coupled and having interconnected secondaries adapted to permit balance of opposed induced voltages and further comprising an unbalancing means, the transformers being such that their primary coils are not rigidly attached to their secondary coils, the arrangement being such that the unbalancing means can be used to introduce an electrical or magnetic imbalance between the transformers, resulting in force between the primary and secondary coils, the magnetic fields being generated solely or substantially solely by current flowing through the transformer coils.
The skilled person will appreciate that when the two transformers are in balance no currents will flow in the secondary coils and only a magnetising current will flow in the primary coils.
According to another aspect of the invention there is provided an a.c electrical machine comprising at least two transformers and an unbalancing means for introducing an imbalance between the two transformers, the transformers being such that their primary coils are interleaved with each other and their secondary coils are interleaved with each other, the arrangement being such that the unbalancing means can be used to introduce an electrical imbalance between the transformers.
Such an arrangement may be used in a number of ways. For instance the secondary coils may arranged so that they are free to rotate with respect to the primary windings in which case the machine may be used as a motor or generator.
Alternatively, the secondary coils may be arranged so that they are fixed or can only be moved through a relatively small range of movement, for example there may be phase adjustment means provided to move the primary and secondary coils relative to each other angularly, between first and second operative positions. The relative movement may be through a number of degrees with respect to primary coils in which case the machine may be used as an electrical transformer.
The skilled person will appreciate that a transformer comprises a primary coil winding and a secondary coil winding which are linked by an electric/magnetic flux so that electrical power is transferred between the coils.
Flux linkage from the primary coils of the transformers to the secondary coils of the transformers may be across an air gap. Such an arrangement has the advantage that the primary and secondary coils are not physically attached to each other.
The secondary coils may be allowed to rotate with respect to the primary coils. Such a device may function as an alternating current rotary induction machine.
The alternating current induction machine may be adapted, in use, to be operated at variable speeds from a fixed frequency supply. Such a machine provides a simple structure such as that of an ac induction motor but which has the advantageous action of a dc machine.
The a.c. electrical machine may have a rotor and may have a stator.
Preferably the machine has at least two sets of main stator coils and preferably the stator coils form the primary coils of the transformers. This arrangement provides a convenient way of arranging the stator windings.
The rotor may have at least two three phase circuits. Such an arrangement is beneficial to co-operate with the three phase circuits arranged in the stator should three phase currents be flowing there. Preferably the three phase circuits comprise the secondary coils of the transformers.
The three phase circuits arranged on the rotor may comprise at least two distinct coils or they may comprise a single coil which acts as at least two three phase circuits, or there may be more than two coils.
In use, once the initial balance condition of the transformers is disturbed, current may be caused to flow in some or all of the three phase circuits of the rotor and a torque acting on the rotor may be caused. Such currents maintain equilibrium of the physical/electrical properties of the a.c. machine and the arrangement provides a way of producing rotation of the rotor.
Preferably, there are provided in addition to the main stator windings control stator windings. Such windings allow the main stator windings to be influenced.
There may be a control stator winding for each main stator windings. Such an arrangement allows each of the main stator windings to be unbalanced individually.
In use, the imbalance between the two transformers may be caused by inducing currents in the control windings which modify the currents flowing in the main stator windings. This provides a simple and controllable way of introducing the imbalance.
Alternatively, or additionally, in use, the imbalance between the transformers may be caused by adjusting the voltages across the main stator coils.
Yet another alternative or additional technique for, in use, imposing the imbalance between the transformers ma
Gridley Doreen J.
Miller Ice
Mullins Burton S.
Ster Brian T.
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