US3700965A

US3700965A - Transformer shorting device

Info

Publication number: US3700965A
Application number: US112356A
Authority: US
Inventors: Kunio Tone
Original assignee: Tokyo Keiki Inc
Current assignee: Tokyo Keiki Inc
Priority date: 1970-02-04
Filing date: 1971-02-03
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24

Abstract

A small size transformer comprises a short-circuit inducing device placed within a coil of coils of the transformer and electrically connected between a primary coil and a power supply. The device comprises a spacer of an electrically insulative material capable of melting at a given temperature, and a pair of conductors electrically insulated from each other by the spacer, but closely spaced enough to contact each other upon melting of the spacer. This arrangement prevents the burning of the transformer upon occurrence of an overcurrent flow through or short-circuit condition across the transformer coils by disconnecting the primary coil from the power supply.

Description

United States Patent Tone [4 1 Oct. 24, 1972 [73] Assignee: Tokyo Keldenlkl Kabushikl Keisha,

Ota-ku, Tokyo, Japan 221 Filed: Feb. 3, 1971 [211 Appl.No.:1l2,356

[30] Foreign Application Priority Data Feb. 4, 1970 Japan ..45/11614 May 11, 1970 Japan ..45/45823 [52] US. Cl ..3l7/15 [51] Int. Cl. ..H02h 7/04 [58] field otSearch ..317/l5 [56] References Cited UNITED STATES PATENTS 2,956,210 10/1960 Yatsushiro...................317/15 Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney-Ernest A. Greenside ABSTRACT A small size transformer comprises a short-circuit inducing device placed within a coil of coils of the transformer and electrically connected between a primary coil and a power supply. The device comprises a spacer of an electrically insulative material capable of melting at a given temperature, and a pair of conductors electrically insulated from each other by the spacer, but closely spaced enough to contact each other upon melting of the spacer. This arrangement prevents the burning of the transformer upon occurrence of an overcurrent flow through or short-circuit condition across the transformer coils by disconnecting the primary coil from the power supply.

12 Claims, BDraWingFigures PATENTEDncr 24 m2 SHEEI 2 0F 2 FIG. 8

TRANSFORMER SHORTING DEVICE The invention relates to a small size transformer for use primarily in electrical communication system or other similar applications, and more particularly, to such a transformer which is provided with a device which prevents the occurrence of burning with an abnormal temperature rise in the coils.

Abnormal temperature rise within a transformer as caused by overload or short-circuiting conditions may not only result in the burning of the associated coils, but also generally involves the possibility to induce fire and electric shocks. Where such transformer is built in a larger apparatus, adjacently located components and interconnection wires therein may be subject to the adverse influence of the high temperatures within the transformer. As a result, various characteristic demands are imposed on the transformer to provide sufficient security against such danger, and the Underwriter's standards in the US. require that there occurs no danger of fire or electric shock upon short-circuiting the secondary side of a transformer with 120V, 60I-IZ applied to the primary side thereof.

It is known to connect a temperature sensitive fuse comprising a low melting metal in the service lines to a transformer and locate it in contact with the outer surface of the transformer, thereby serving the prevention of burning. Thus upon occurrence of an overcurrent to cause an abnormal temperature rise, the thermal energy conducted from the interior of the coils to the outer surface causes the fuse to be melted for disconnection of the transformer from the power supply. While this represents a simple procedure, it is known to have certain drawbacks. Thus, the temperature fuse is inactive to a local overheating of the transformer coils, in par ticular when such abnormal temperature rise occurred at a position within the coils remote from the location of the fuse, or if it could respond to such occurrence, the response involves a large time delay. This is undesirable in view of the difiiculty inherent to such sort of fuse to ensure a correct timing of action. Consequently there remains the danger for the transformer coils to burn before the temperature fuse can be fused. Placing the temperature fuse within the transformer would overcome such disadvantage, but is impracticable in view of the necessity to house the temperature fuse in a separate casing to secure a sufficient space to allow fusing of the low melting metal, which space cannot be obtained with usual transformer construction. In addition, the temperature fuse must be mounted in a restricted position or attitude, and this necessitates its mounting on the exterior of the transformer.

Accordingly, it is an object of the invention to provide a transformer which completely eliminates the above mentioned disadvantages of the prior art.

It is another object of the invention to provide a transformer provided with a short-circuit inducing device arranged to produce a short-circuit condition across the primary coil automatically when the temperature within the coils exceeds a predetermined level, thereby disconnecting the primary coil from a power supply by the operation of the device to cause a breakage therein.

It is a further object of the invention to provide a transformer provided with the short-circuit inducing device which is simple in construction and is flat or linear in shape together with sufficient flexibility to permit it to be inserted into either coil together with its lead wires.

In accordance with the invention, the opposite ends of a primary coil of a transformer are connected with the respective service lines through a short-circuit inducing device that is placed in said coil or the other coil or between the both coils, with the short-circuit inducing device being operable in response to the temperature of the location in which it is mounted to disconnect the primary coil from its associated service lines. The short-circuit inducing device comprises a spacer of an electrically insulative material capable of melting at a given temperature, and a pair of conductors insulated from each other by the spacer, but closely spaced enough to contact each other upon melting of the spacer, the conductors forming at least one cross-over point.

It is desirable that with a temperature range experienced during the normal use of the transformer, the spacer undergoes no or little change in its nature, but rapidly melts at a given temperature higher than the temperature range mentioned above. Suitable material for such a spacer can be selected from a group of thermoplastic resins such as polyester, polypropylene, nylon or the like. It will be understood by those skilled in the art that the term a given temperature depends upon the specification of a transformer such as power and voltage ratings and coil insulation ratings. Since the spacer should electrically insulate the pair of conductors from each other during normal operation of the transformer, it may comprise a film interposed between the conductors or comprise a coating on the conductors. Each of the conductors in the short-circuit inducing device may comprise the end portions of or lead wires to the primary coil with their customary insulation removed. Alternatively, the short-circuit inducing device may be separate from the primary coil and connected to the opposite ends thereof by its conductors.

While it is not intended to disclose herein all of such possible modifications and variations, the features and advantages of the invention will be best understood from the following detailed description of specific embodiments thereof with reference to the drawings, wherein:

FIG. 1 is a schematic circuit diagram of a transformer incorporating the short-circuit inducing device according to the invention;

FIG. 2 is a section of a transformer embodying the principle of the invention;

FIG. 3 is a perspective view of the short-circuit inducing device shown in FIG. 2;

FIG. 4 is a perspective view illustrating a modification of the device shown in FIG. 3;

FIG. 5 is a perspective view of a short-circuit inducing device which includes conductors comprising bundies of fine wires;

FIG. 6 is a perspective view of a device similar to that shown in FIG. 3 except that conductors are pinned to the spacer;

FIG. 7 is a perspective view of a device similar to that shown in FIG. 6 except that pins are replaced by adhesive tapes; and

FIG. 8 is a perspective view of a slotted spacer.

Referring to the drawings, the transformer circuit embodying the principle of the invention is shown in FIG. 1 wherein it will be noted that the circuit is conventional except that at least one short-circuit inducing device generally shown at 3 is connected between a power supply 1 and a primary coil 2. A load 5 is shown connected across a secondary winding 4. The short-circuit inducing device 3 is specifically shown in various forms in FIGS. 3 to 8 inclusively, and comprises a spacer 6 of an electrically insulative material capable of melting at a given temperature, and a pair of

conductors

7, 7 electrically insulated from each other, but closely spaced enough to contact each other upon melting of the spacer and forming at least one crossover point. The pair of

conductors

7, 7 are connected so as to constitute the lines between the power supply 1 and the primary coil 2.

In FIG. 2, the short-circuit inducing device 3:5 shown as mounted within a transformer coil. In the example shown, the transformer is of concentric type, comprising a center core 8 around which is arranged a spool 9 receiving the primary coil 2 and the secondary coil 4. The short-circuit inducing device 3 is placed intermediate the primary and

secondary coils

2 and 4, as surrounded by insulations l and 11. While the shortcircuit inducing device 3 is exaggerated in the drawing to occupy a substantial space, it should be understood that this showing is for the purpose of clarity, but that in practice, it is rolled between the insulations l0 and II without the need for a special space therefor. It will be also noted that the device 3 may be placed within either coil instead of being interposed between the coils, and hence the particular position it is located is a matter of choice. It will also readily occur to these skilled in the art that a plurality of short-circuit inducing devices distributed throughout the coils may be connected in series. It should be emphasized that the form or type of the transformer does not form any part of the invention. The short-circuit inducing device 3 of the invention need only and can be located anywhere within the coils where it is most convenient to sense the temperature therein.

Specific embodiments of the short-circuit inducing device are shown in FIGS. 3 to 8 wherein same reference characters are used throughout these Figures to denote like parts. In the arrangement of FIG. 3, the spacer 6 is in the form of a film and the pair of

conductors

7, 7 are solid wires. Parts of the conductors smeared out in black represents insulative coatings on the enamelled solid wires. The pair of

conductors

7, 7 have oppositely oriented bends l2, 12 on the opposite surfaces of the spacer 6, thereby forming a pair of

cross-overs

13, 13 in plan projection. These

conductors

7, 7 are partially or entirely bonded to the spacer 6 along their length on the spacer. In FIG. 4, the arrangement is similar to FIG. 3, but is advantageous in that it has four cross-overs 13 any of which can be effective to provide short-circuit across the both conductors. FIG. shows the use of bundles of fine wires for the

conductors

7, 7. in this instance, the need for forming the cross-over as is produced with solid wires is in effect eliminated by spreading these fine wires.

In the operation of the devices illustrated in FIGS. 3 to 5, it is found that one or both of the conductors become interrupted upon melting of the film spacer. While this phenomenon is not completely understood, it is believed that upon melting of the spacer, there occurs a spark discharge across the pair of conductors at the cross-over to cause the breakage or interruption in the conductors.

FIGS. 6 to 8 show the alternative methods of securing the pair of

conductors

7, 7 to the spacer 6. While in the preceding embodiments, the

conductors

7, 7 have been bonded to the spacer 6 by means of an adhesive, several small pins 14 in FIG. 6 or adhesive tape segments in FIG. 7 may be used. FIG. 8 shows a slotted spacer 6, that is, the spacer is formed with

grooves

16, 16 in its opposite surfaces which receive and define the location of the

conductors

7, 7. Adhesive may be additionally applied to assure firm attachment.

In the transformer according to the invention, upon occurrence of an overcurrent flow through the transformer to cause abnormal temperature rise within its coils which is sufficient to raise the temperature to the melting temperature of the material from which the spacer is made, the spacer melts to cause contact between the pair of conductors located on opposite sides of the spacer, yielding a short-circuit at that position of contact. As a result, the primary coil is disconnected from the power supply to prevent the burning of the transformer.

Specific examples are given below in order to illustrate the invention.

EXAMPLE 1 transformer output: 10 watts The short-circuit condition across the conductors occured at l C.

EXAMPLE 2 10 watts I00 turns of 0.23 mm at wire 200 turns of 0.5 mm 45 wire polypropylen film, 0.05 mm thick transformer output: primary coil: secondary coil: spacer:

The short-circuit condition occured at C.

As will be appreciated from the foregoing, the invention is practicable in a number of manners and the embodiments shown herein are merely illustractive of the invention. Therefore, it should be understood that further modifications and variations are possible without departing from the spirit of the invention as defined by the appended claims,

Having described the invention, what is claimed is:

1. A transformer comprising at least a primary and a secondary coil winding respectively adapted for connection to a source of current and a load, and a shortcircuit inducing device within said windings and provided with at least two independent conductors for connecting at opposed ends to said source of current and to said primary winding, said device being constituted of an elongated planar spacer of an electrically insulative material capable of melting at a predetermined temperature and carrying said independent conductors in spaced apart relation on opposite sides of said spacer and coextensive therewith along the longitudinal extent thereof, said conductors defining along the longitudinal length of the spacer multiple crossover points at which electrical contact between said conductors may be made upon melting of said planar spacer.

2. A transformer comprising at least a primary and a secondary coil winding respectively adapted for connection to a source of current and a load, and a shortcircuit inducing device within said windings and provided with at least two independent conductors for connecting at opposed ends to said source of current and to said primary winding, said device being constituted of an elongated planar spacer of an electrically insulative material capable of melting at a predetermined temperature and carrying said two independent conductors in spaced apart relation on opposite sides of said spacer and coextensive therewith along the longitudinal extent thereof, one of the independent conductors on one side of the spacer having a series of undulations along the longitudinal extent of the spacer defining peaks and troughs, the other of the independent conductors on the other side of said spacer having a series of undulations along the longitudinal extent of the spacer also defining peaks and troughs, with the peaks and troughs of the undulations of the other independent conductor occurring at the troughs and peaks respectively of said one conductor providing thereby, between the peaks and troughs of the respective undulations of said conductors, a plurality of cross-over points at which electrical contact between said conductors may be made upon melting of said planar spacer.

3. A transformer according to claim 2, in which the spacer is in the form of a film.

4. A transformer according to claim 3. in which the pair of conductors comprise bundles of fine wires.

5. A transformer according to claim 3, in which the pair of conductors are secured to the spacer by adhe- 81011.

6. A transformer according to claim 3, in which the pair of conductors are secured to the spacer by pins struck into the spacer.

7. A transformer according to claim 3, in which the pair of conductors are secured to the spacer by adhesive tapes.

8. A transformer according to claim 3, in which the spacer is formed with grooves in its opposite surfaces for receiving the pair of conductors therein.

9. A transformer according to claim 2, in which the spacer comprises a thermoplastic resin.

10. A transformer according to claim 9, in which the thermoplastic resin is polyester.

11. A transformer according to claim 9, in which the thermoplastic resin is polypropylene.

12. A transformer according to claim 9, in which the thermoplastic resin is nylon.

Claims

1. A transformer comprising at least a primary and a secondary coil winding respectively adapted for connection to a source of current and a load, and a short-circuit inducing device within said windings and provided with at least two independent conductors for connecting at opposed ends to said source of current and to said primary winding, said device being constituted of an elongated planar spacer of an electrically insulative material capable of melting at a predetermined temperature and carrying said independent conductors in spaced apart relation on opposite sides of said spacer and coextensive therewith along the longitudinal extent thereof, said conductors defining along the longitudinal length of the spacer multiple cross-over points at which electrical contact between said conductors may be made upon melting of said planar spacer.

2. A transformer comprising at least a primary and a secondary coil winding respectively adapted for connection to a source of current and a load, and a short-circuit inducing device within said windings and provided with at least two independent conductors for connecting at opposed ends to said source of current and to said primary winding, said device being constituted of an elongated planar spacer of an electrically insulative material capable of melting at a predetermined temperature and carrying said two independent conductors in spaced apart relation on opposite sides of said spacer and coextensive therewith along the longitudinal extent thereof, one of the independent conductors on one side of the spacer having a series of undulations along the longitudinal extent of the spacer defining peaks and troughs, the other of the independent conductors on the other side of said spacer having a series of undulations along the longitudinal extent of the spacer also defining peaks and troughs, with the peaks and troughs of the undulations of the other independent conductor occurring at the troughs and peaks respectively of said one conductor providing thereby, between the peaks and troughs of the respective undulations of said conductors, a plurality of cross-over points at which electrical contact between said conductors may be made upon melting of said planar spacer.

4. A transformer according to claim 3, in which the pair of conductors comprise bundles of fine wirEs.

5. A transformer according to claim 3, in which the pair of conductors are secured to the spacer by adhesion.