US3668513A

US3668513A - Upright type bushing current transformer

Info

Publication number: US3668513A
Application number: US126121A
Authority: US
Inventors: Denji Tsubouchi; Susumu Ito; Eisuke Toyota; Kenji Wada
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1970-03-31
Filing date: 1971-03-19
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: DE2115663A1

Abstract

A bushing current transformer is provided and includes an auxiliary current transformer mounted on the top of a bushing. The primary and secondary coils of the auxiliary current transformer are connected parallel to each other and in series to an electrical power line having a high voltage and carrying a high current therethrough. A conductive lead is connected to the secondary coil of the auxiliary current transformer and is conducted to the bottom of the bushing to thereby form a primary coil of a main current transformer which is positioned on the bottom of the bushing and then conducted upwards again through the bushing. With such an arrangement the size of the line conductor being introduced into the bottom of the bushing can be made smaller, since the current transformation ratio between the primary and secondary coils of the auxiliary current transformer can be adjusted. Also, the current transformer can be standardized and thereby adapted for mass production due to the ability to fix the secondary current of the auxiliary current transformer at a constant amplitude.

Description

United States Patent [151 3,668,513 Tsubouchi et a1. June 6, 1972 54] UPRIGHT TYPE BUSI-HNG CURRENT FOREIGN PATENTS OR APPLICATIONS TRANSFORMER Inventors: Denji Tsubouchi; Susumu Ito, both of Yokohama; Eisuke Toyota, Hiratsuka;

Kenji Wada, Yamato, all of Japan Assignee: Co.,

Tokyo Shibaura Electric Kawasaki-shi, Japan Filed: Mar. 19, 1971 Appl. No.: 126,121

Ltd.,

Foreign Application Priority Data Mar. 31, 1970 Japan ..45/26883 References Cited UNITED STATES PATENTS AttorneyOblon, Fisher & Spivak [57] ABSTRACT A bushing current transformer is provided and includes an auxiliary current transfonner mounted on the top of a bushing. The primary andsecondary coils of the auxiliary current transformer are connected parallel to each other and in series to an electrical power line having a high voltage and carrying a high current therethrough. A conductive lead is connected to the secondary coil of the auxiliary current transformer and is conducted to the bottom of the bushing to thereby form a primary coil of a main current transformer which is positioned on the bottom of the bushing and then conducted upwards again through the bushing. With such an arrangement the size of the line conductor being introduced into the bottom of the bushing can be made smaller, since the current transformation ratio between the primary and secondary current transformer can be adjusted. Also, the current transformer can be standardized and thereby adapted for mass production due to the ability to fix the secondary current of the auxiliary current transformer at a constant amplitude.

6 Claims, 5 Drawing Figures coils of the auxiliary PAIENTEDJuu 6|972 3,668,513

SHEET 2 OF 2 1 UPRIGIIT'I'YIII BUSHING CURRENT TRANSFORMER BACKGROUND OF THE INVENTION 1. Field Of The Invention The present invention generally relates to an upright type bushing current transformer, and more particularly to a bushing current transformer which is adapted for mass production.

2. Description Of The Prior Art In the past, upright type bushing current transformers,

.which were employed in AC. electrical power circuits for measuring the current amplitude of the circuit, have generally bottom portion of an insulating tube or bushing and a conductor to be connected in series to a line conductor was conductedfrom the top of the bushing into the bottom portion thereof to form a primary coil of the transformer assembly and then conducted upwards again through the bushing. The bushing used in the upright type bushing current transformer for high voltage use was located relatively high in order to resist against the high line voltage present. As a consequence thereof, the aforesaid conductor being directed into the bushing had to be of a relatively long length. Moreover, when the bushing type current transformer was used for measuring large currents, the conductor was required to have a large cross-section in order to enable a large current to pass therethrough. Thus, the prior art type bushing current transformer was usually quite expensive. 7

In order to eliminate some of the aforesaid drawbacks, a prior art upright type bushing current transformer was developed which included a transformer assembly mounted on the insulating tube or bushing. In'this type of assembly, a conductor was connected in series to a line conductor and then merely extended through a window of aniro n core of the transformer assembly mounted on the top of the bushing. As such, the length of the conductor was reduced to a much shorter length. However, again while somewhat satisfactory, because the transformer assembly had a large weight, it was found that with the bushing current transformer mounted on top of the transformer assembly, the same was top heavy and therefore undesirable from an earthquake-proof point of view.

' SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new and improved unique bushing type current transfonner wherein the main current transformer thereof may be readily employed without changes being made thereto with electrical lines having different current ratings.

Another object of the present invention is to provide a new and improved unique upright type bushing current trans former wherein the same may be readily standardized and thereby reduce the manufacturing cost thereof.

Still another object of this invention is to provide a new and improved unique upright type bushing current transformer for measuring a line current having a large amplitude and wherein a conductive lead having a relatively small cross-section is directed into the bushing thereof to form a primary coil of a main current transformer located at a bottom portion of the bushing.

Yet one other object of the present invention is to provide a new and improved unique upright type bushing current transformer which is relatively immune to damage from earthquakes.

Briefly, in accordance with this invention, these and other objects are, in one aspect, attained by the provision of an auxiliary current transformer mounted on the top of an insulating tube or bushing. The primary and secondary coils of the auxiliary current transformer have conductors which extend through a window of an iron core. The primary and secondary coils are wound in opposite directions with respect to current flow therethrough and are further connected in parallel to each other. The parallelly connected primary and secondary coils of the auxiliary current transformer are then connected housing provided and is then conducted upwards through the bushing.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood from the following description when taken in connection with reference to the accompanying drawings, wherein:

FIG. 1 is a front sectional view, partly broken away, of a preferred embodiment of an upright type bushing transformer according to the present invention;

FIG. 2 is an equivalent circuit diagram of the bushing current transformer of FIG. 1;

FIG. 3 is an equivalent circuit diagram of the bushing current transformer of another and alternative embodiment of the present invention; I

FIG. 4 is a circuit diagram of the bushing current transformer of still another and alternative embodiment of the present invention; and,

FIG. 5 is a circuit diagram of one other alternative embodiment of the bushing current transformer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof,wherein an upright type bushing current transformer is generally shown with a reference numeral 10, and the same includes a bottom casing 11, a main current transformer 12 mounted therein, an upright insulating tube or'bushing 13 mounted on the casing 1 1, an auxiliary current transformer 14 removably mounted on the top of the upright bushing I3, and a housing 15 which sealingly encloses the auxiliary current transformer 14 therein.

The auxiliary current transformer 14 includes a conventionally wound iron core 16 having a window 17 through which a primary coil 18 extends. The opposite ends of the primary coil 18 extend through a pair of insulators l9 and 20 mounted on the side walls of the housing 15, and have a pair of

terminals

21 and 22 which are connected to the ends of electrical power lines (not shown). The auxiliary current transformer 14 also has a secondary coil 23 which is wound around the iron core 16 and the same has a pair of end terminals that are respectively connected to the opposite end portions of the primary coil 18. through

lead conductors

24 and 25 provided along the outside area of the window 17. Thus, it should be apparent that the primary and secondary coils l8 and 23 have been connected in parallel with each other.

Now let us assume, for example, that an electrical current flow is present during a half cycle of A. C. and flows from terminal 21 to terminal 22. It can be understood from FIG. 1 with respect to the direction of current flow, that the primary coil 18 extends through the window 17 of the core 16 from the left side to the right side, while the secondary coil 23 extends through the window 17 from the right side to the left side. Thus, it should be understood that the primary and

secondary coils

18 and 23 are wound around the core 16 in opposite directions to each other, and are connected in parallel. Also, it should be understood that the line currents flowing through the primary coil 18 and the

leads

24 and 25 will be in the same 'and respective primary and'secondary

coils

32 and 33 which are wound thereon. The iron core 31 is supported on the base of the casing 11 by an insulating support 35. The conductive lead 28 is directed downward through the bushing 13 and then wound around the core 31 through a window 34 provided in the core to thereby form the primary coil 32. The end of the primary coil 32 is then returned upward by the conductive lead 25 which also extends through the bushing 13.

The main current transformer assembly 12, which includes the core 31, the primary and

secondary coils

32 and 33 and the pairof lead.

conductors

28 and 25, may be molded in a resinous insulation 36.

It should be understood that a conventional condenser cone 40 is provided around the high

tension lead conductors

25 and 28, as well as the main transformer assembly 12, to thereby restrain the potential gradient.

While not shown, it should be apparent that a suitable insulating and cooling fluid, such, for example, as mineral oil and gaseous sulphur hexafluoride (SF,,) is filled within the casing II and the bushing 13.

The output from the secondary coil 33 of the main current transformer 12 is provided at a pair of

terminals

37 and 38 which are mounted on the'side of the casing 11, and the same may be employed to energize any suitable device such, for example, as meters, protecting relays and the like.

The equivalent circuit diagram of the upright bushing current transformer 10 of FIG. 1 is shown in FIG. 2.

From FIG. 2, it is clearly seen that the primary and secondary'coils 18 and 23 of the auxiliary current transformer 14 are connected in parallel with each other and in series with an electrical power line (not shown) through the

terminals

21 and 22. I

' Assuming now that the number of turns of the primary coil 18 of the auxiliary current transformer 10 is one turn, the number of turns of the secondary coil 23 is nine turns, and the amplitude of the rated current is 4,000 amperes, then a reduced current of 400 amperes will be-applied-through the secondary coil 23 and the remaining 3,600 amperes will be applied through the primary coil 18. Accordingly, the reduced current of 400 amperes will be applied through the primary coil 32 of the main current transformer 12 along the

lead conductors

28 and 25. In this case, a rated current, such as amperes, may be provided at the

terminals

37 and 38 of the secondary coil 33 of the main current transformer 12.

When, for example, the rated line current has an amplitude of 2,000 amperes, the intermediate tap 26 may be employed instead of the tap 27 in order to change the number of turns of the secondary coil 23 of the auxiliary current transformer 14 from the aforesaid value of nine turns to four turns. Thus, with such a change, it will be apparent that the current amplitude of the secondary coil 23 will have the same amplitude, namely, 400 amperes, but that the current amplitude of the primary coil 18 will have an amplitude of 1,600 amperes.

It will thus be apparent that according to the present invention a main current transformer 12 having the same rating may be readily employed with electrical power lines having-different current ratings.

It can be further seen that according to the present invention an auxiliary current transformer 14 can be easily altered to another rating without requiring any changes to the main current transformer assembly 12. Accordingly, a main current transformer assembly 12 having a given current rating, size and construction can be readily employed for use with power lines havingdifferent current ratings.

In accordance with the above, main current transformer assemblies, such as the transformer assembly 12, can be readily standardized with the attendant advantages of reduction in manufacturing cost of the upright type current transformers, since the same can be adapted for mass production.

Moreover, it can be seen that since the main current transformer 12 of the present invention is located at the bottom portion of the bushing 13 that the center of gravity of the upright type current transformer assembly 10 will be at a low position and thereby enable an effective resistance against earthquakes and the like.

It will be further apparent that in accordance with the present invention, since a reduced current can be supplied to the primary coil 32 of the main current transformer 12 through the

lead conductors

25 and 28 that the sectional areas of the

lead conductors

25 and 28, as well as that of the primary coil 32, can be effectively reduced and thereby save the quantity of copper or aluminum required for the same.

Referring now to FIG. 3, an alternative embodiment of the present invention is shown with the auxiliary current transformer 14 having a pair of secondary coils 230 and 330 each of which have the same number of turns. Thus, it is possible to employ the auxiliary transfonner 14 in two different ways by selecting either a series connection or a parallel connection of the pair of coils 230 and 330.

Referring now to FIG. 4, a further alternative embodiment of the present inventionis shown with an additional auxiliary current transformer having a primary coil and a secondary coil 430, similar to that-of FIG. 1, being connected in series with the secondary coil 23 of the auxiliary current transformer 14. Thus, the circuit of FIG. 4 may by employed for either providing a more reduced current at the

lead conductors

25 and 26, or for enabling measurement of a line current having an extremely high amplitude.

. Referring now to FIG. 5, one other alternative embodiment of the present invention is shown with an impedance element 39 being connected across the secondary coil 23 of the auxiliary current transformer 14 for enabling a fine adjustment of the current flowing therethrough to be made. The impedance element 39 may be either of the variable or fixed type, and may be connected across the primary coil 18 of the auxiliary current transformer 14.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An upright type bushing current transformer comprising:

a casing;

a main current transformer mounted in said casing and having an iron core with a primary and a secondary coil wound thereon:

an upright bushing mounted on said casing;

an auxiliary current transformer mounted on the top of said bushing and having an iron core with a primary and a secondary coil wound thereon, the windings being in opposite directions and said primary and secondary coils of said auxiliary current transformer being connected in parallel with each other and being connected in series to an electrical power line; and,

a conductive lead connected to said primary of said main transformer and said secondary of said auxiliary transformer and extending through said bushing for enabling energization of the primary coil of said main current transformer in accordance with the current of the secondary coil of said auxiliary current transformer. v

2. An upright type bushing current transformer according to claim 1, wherein said auxiliary current transformer is removably mounted on claim 1, wherein the topofsaid ushing said secondary coil of the auxiliary current transformer inp bushing cunenf "ansformer ifccol'dmg to cludes a second auxiliary current transformer connected claim 1, wherein said secondary coil of the auxiliary current i Series there;

transformer includes at least one intermediate tap for enabling 5 different current transformations to be realized.

4. An upright type bushing current transformer according to at least one of Said primary and Secondary cons of Said claim 1, wherein said secondary coil of the auxiliary current transformer innary current tansformer Includes an Impedance element eludes at least two coil elements which may be connected l0 :snnected therzlcross enabling a fine adjustment of either in series or in parallel. e current can ormanon to occur 5. An upright type bushing current transformer according to 6. An upright type bushing current transformer according to claim 1, wherein

Claims

1. An upright type bushing current transformer comprising: a casing; a main current transformer mounted in said casing and having an iron core with a primary and a secondary coil wound thereon: an upright bushing mounted on said casing; an auxiliary current transformer mounted on the top of said bushing and having an iron core with a primary and a secondary coil wound thereon, the windings being in opposite directions and said primary and secondary coils of said auxiliary current transformer being connected in parallel with each other and being connected in series to an electrical power line; and, a conductive lead connected to said primary of said main transformer and said secondary of said auxiliary transformer and extending through said bushing for enabling energization of the primary coil of said main current transformer in accordance with the current of the secondary coil of said auxiliary current transformer.

2. An upright type bushing current transformer according to claim 1, wherein said auxiliary current transformer is removably mounted on the top of said bushing.

3. An upright type bushing current transformer according to claim 1, wherein said secondary coil of the auxiliary current transformer includes at least one intermediate tap for enabling different current transformations to be realized.

4. An upright type bushing current transformer according to claim 1, wherein said secondary coil of the auxiliary current transformer includes at least two coil elements which may be connected either in series or in parallel.

5. An upright type bushing current transformer according to claim 1, wherein said secondary coil of the auxiliary current transformer includes a second auxiliary current transformer connected in series thereto.

6. An upright type bushing current transformer according to claim 1, wherein at least one of said primary and secondary coils of said auxiliary current transformer includes an impedance element connected thereacross for enabling a fine adjustment of the current transformation to occur.