GB2170355A - Electromagnetic element - Google Patents

Abstract

A capacitative electromagnetic winding comprises elongate conducting films 12, 13 arranged on opposite faces of an insulating film 11, the electrical connections 16, 17 at opposite ends of the winding being connected respectively to films 12, 13. The winding may form a coil having a plurality of turns, in which case a further insulating film covers one of the conducting films. The winding may be used in transformers, solenoids or electric motors. <IMAGE>

Description

SPECIFICATION Electromagnetic element The present invention relates to an electromagnetic element such as a winding suitable for use in transformers, solenoids and electric motors etc.

Existing copper electromagnetic windings have the disadvantage of being expensive. The voltage supply maybe too high for an economic copper coil. Also the required inductance may necesitate fine enamelled copperwires, ofwhich the cost may be up to ten times that of the copper material alone.

The present invention seeks to provide an improved electromagnetic element.

According to a first aspect ofthe present invention there is provided an electromagnetic winding comprising conductive members extending along opposite surfaces of an insulating member arranged therebetween.

The term "insulating" as used herein is intended to cover materials of high dielectric strength, high dielectric constant and low powerfactor.

The insulating and conductive members are preferably in flat e.g. in the form of films. The insulating film is preferably of a plastics material, e.g. polypropylene, and the conducting films are preferably of aluminium which may be sprayed on to the insulating film as used now for capacitors.

In use a currrent supply has one connection attached to one of the conductive members at one end ofthe winding and the other connection attached to the other conductive member at the other end ofthe winding.

The invention also provides an alternating current device comprising an electromagnetic winding as set out above.

According to a second aspect ofthe present invention, there is provided an electromagnetic ele mentcomprising conductive members arranged at opposite sides of an insulating member, thereby forming a capacitor, wherein respective electrical connection meansforthe capacitor are connected to the conductive members at or adjacent opposite ends ofthe element.

Preferred embodiments ofthe present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figs. 1 a and 1 bare diagrams illustrating the theory behind the present invention; and Fig. 2 shows an electromagneticwinding according to the present invention.

Referring to Fig. 1, bars 50, 51 represent elongate plates of a capacitor 52 separated by a layer 54 of insulating material. When connections are made conventionally to a source 53 of alternating current, as shown in diagram (a),thecurrents flow in opposite directions in the plates and produce mutually-cancelling magnetic effects so thatthere is no net magnetic field.

When connections are made to the opposite ends of the plates, however, as shown in diagram (b), charging ordischargingcurrents flow in the plates in the same direction and there is a net magnetic field aroundthe conductors as indicated by loop 55.

Referring now to the embodiment of Fig. 2, a single turn electromagnetic winding 10 comprises a dielectric film 11, e.g. of polypropylene material, sandwiched between two conducting films 12, 13, e.g. of aluminium sprayed on to the film 11. The thickness of the dielectric film may be, for example, 4 pm, while the metal layers may be e.g. 4 pm to 40 pm. However, the thicknesses must be chosen according to the application. The winding serves as a capacitor winding with film 11 as the capacitor dielectric and films 12, 13 as the capacitor plates.

The drawing shows a substantially oneturn winding under direct current conditions showing how the currentwould be distributed asthe capacitor became charged and hence for 1 amp passing there would be only 1/2 amp turn magnetising effect.

Under alternating current conditions the diagram illustrates what would happen each half cycle. If n is the number ofturns and I the current the capacitor takes, the ampere turns will be only 1/2 nl.

It should be noted that the current supply leads 16, 17 are connected to opposite ends ofthe winding, with lead 16 being connected to film 12 and lead 17 being connectedtofilm 13.

The above-described arrangement has thefollow- ing advantages: (1) The capacitor winding can often be much cheaperthan the present equivalent copperwinding.

(2) This capacitor winding takes currentfrom the supply at a leading powerfactor and will be welcomed by supply authorities.

(3) The demand from the supply can be very low e.g.

filamentsupplyfrom 230 volt mains via a transformer; i.e. the-possibility of a low power consumption to achieve a desired effect.

(4) Thewinding savestime and labour during manufacture compared to existing copper windings, since for most applications approximately only one tenth ofthe number ofturns are required. For example a winding of less than 1,000 turns would be necessary to produce 40 ampere turns in a synchronous motor.

Althoughthe current might befive times itsvaluewith a conventional copper component, the other advantages (especially 2 above) are believed to offset th is.

(5) In connection with advantage (4) above, conse quentialsavings in size are also possible. The windingsmay be used in electric motors as disclosed in our British Patent 1600380. Such a motor can be produced which is only 2 cms diameter and 1/2 cm long (as opposed to an existing length of 1.2cms), andwhich can deliver7 kg cm atthe 1 rev/day shaft of a timeswitch.Thiswill be adequatefor most requirements.

Windings in accordance with the present invention may also be used in modifications ofthe above electric motors in accordance with British Patent 2093277B and PatentApplication 2164209A.

Windings in accordance with the present invention may be used in e.g. transformers, electric bells, hooters, motors, no volt releases, etc. etc. In a transformer both primary and secondary windings or only one of them may be as described above. The transformer may be connected as an auto transformer or as an isolated transformer.

Thecapacitorwindinmaybe usedfortheshunt coil of a watt hour meter, with a rotor reacting with the leakage flux from this winding with some flux diverted through a lag loop. If used to directly replace a conventional meter shunt coil it will cause the rotorto rotate the wrong way, since the leakage flux will lead the voltage. However, it is only necessary to reverse the connections to the series coil orto alterthe gearing to the meter dial.

The invention is of particular advantage at voltages over 10 volts with a power consumption of below5 watts.

Although the winding shown in Fig. 2 has only one turn, coils having any desired numberofturns may be provided. Thus hollow cylindrical coils may be provided producing an alternating magneticflux in the hollow. The axial hollow has a cross-section which maybe circular, generally square or rectangular, or any other desired shape. Furthermore the axial hollow may be arranged to receive a magnetic core.

The flat materials ofthe conductive and insulating members may be in theform of sheets, orstrips.

For multiturn windings it is convenientto use a laminate comprising, in order, a conductive layer, an insulating layer, a second conductive layer, and a second insulating layer. The firstthree layers correspond to the winding 10 shown in Fig. 2, with thefourth layer covering either conductive film 12 or 13 so as to preventthese conductive films coming into contact as the laminate is wound into a coil. Care muststill be taken to ensurethatthe end connections are made to different conductivefllms.

In one example, a motor has thefollowing parameters: motor diameter: 2 cms a.c. voltage: 240 volts a.c. frequency: 50 Hz dielectricthickness: 4x 1Q < cm conductorthickness: 4x 10cm dielectric constant: 2.2 (polypropylene) numberofturns: 256 Capacitance: 0.424,ends Current: 0.3196 amps Ampturns: 8.182 This magnetomotiveforce is sufficientto drive motors of the type disclosed in the above-mentioned patent documents.

Claims (11)

1. An electromagneticwinding comprising conductive members extending along opposite surfaces of an insulating member arranged therebetween.

2. An electromagnetiowinding according to claim 1 wherein first electrical connection means are connected to one ofthe conductive members at or adjacent one end ofthewinding and second electrical connections means are connected to the other conductive member at or adjacentthe other end ofthe winding

3. An electromagnetic winding according to claim 1 or 2, wherein a second insulating member of sheet material is provided at the side of one ofthe conductive members remote from the first-mentioned insulating member.

4. An electromagnetic winding according to any preceding claim defining a coil which is hollow.

5. Anelectromagneticwinding according to any of claims 1 to 4 defining a coil which has a magnetic core.

6. An electromagnetic winding according to any preceding claim, wherein the conductive members each comprise a film applied to an insulating film the insulating film constituting the insulating member, or one ofthe insulating members.

7. An electromagneticwinding substantially as herein describedwith reference to Fig. 2 ofthe accompanying drawings.

8. Atransformerhavinga primaryanda secon darywinding,atleastoneofwhich isawindingin accordance with any preceding claim.

9. An alternating current device comprising an electromagnetic winding according to any of claims 1 to7.

10. An electromagnetic element comprising conductive members arranged at opposite sides of an insulating member,therebyforming a capacitor, wherein respective electrical connection means for the capacitor are connected to the conductive members at or adjacent opposite ends ofthe element.

11. An electromagnetic elementsubstantially as herein described with reference to Fig. 1 or Fig. 2 ofthe accompanying drawings.