US3617967A

US3617967A - Current transformer having primary side switchable to different measuring ranges

Info

Publication number: US3617967A
Application number: US28462A
Authority: US
Inventors: Werner Mitrach
Original assignee: Electromagnetic Industries Inc
Current assignee: Electromagnetic Industries Inc
Priority date: 1970-04-14
Filing date: 1970-04-14
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02

Abstract

A current transformer has a pair of input terminals and a primary side which is switchable to different measuring ranges, the current transformer having two or four primary winding sections whose ends are connected to switching terminals disposed in a transformer head having a pair of spaced partitions. By means of the switching terminals, two primary winding sections may be connected selectively either in parallel or in series, or four primary winding sections may be connectable selectively in parallel, series-parallel, or series. The switching terminals are arranged in pairs each including a first terminal and a second terminal, with the first terminals being arranged in one or more rows on one of the partitions and the second terminals being arranged in one or more rows on the other of the partitions. Each end of each winding section is connected to a respective one of the pairs of switching terminals, including a respective first and a respective second terminal.

Description

United States Patent Primary ExaminerThomas J. Kozma Attorney-McGlew and Toren ABSTRACT: A current transformer has a pair of input terminals and a primary side which is switchable to different measuring ranges, the current transformer having two or four primary winding sections whose ends are connected to switching terminals disposed in a transformer head having a pair of spaced partitions. By means of the switching terminals, two primary winding sections may be connected selectively either in parallel or in series, or four primary winding sections may be connectable selectively in parallel, series-parallel, or series. The switching terminals are arranged in pairs each including a first terminal and a second terminal, with the first terminals being arranged in one or more rows on one of the partitions and the second terminals being arranged in one or more rows on the other of the partitions. Each end ofeach winding section is connected to a respective one of the pairs of switching terminals, including a respective first and a respective second terminal.

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E; Ib I v m) .INVENTOR WERNER MITRACH ATTORNEYS CURRENT TRANSFORMER HAVING PRIMARY SIDE SWITCI'IABLE TO DIFFERENT MEASURING RANGES BACKGROUND OF THE INVENTION In current transformers which are switchable to different measuring ranges on the primary side, the required switching device, which is subjected to a high potential, is usually mounted in the head of the current transformer housing- In a known arrangement, the terminals required for the range switching are arranged externally on the surface of the housing of the transfer head.

For current transformers which areswitchable, on the primary side, in the ratio 1:2, the switching terminals usually are arranged side-by-side in a common plane. Forcurrent transformers switchable in the ratio l:2:4, the switching terminals may be arranged in two planes, with four terminals in each terminal row, or in three planes, also with four terminals ineach terminal row. The eight-terminal arrangement offersthe advantage of a smaller number of circuit elements, but it has the disadvantage that individual switching terminals or contact studs are traversed by an especially high percentage of the total current on the primary side, so that their cross-sectional area must be correspondingly large. On the other hand, the IZ-terminal arrangementoffers the advantage of a uniformly low-current load on all switching terminals andcontact studs. A disadvantage, however, is the greater number of.circuit.ele ments.

To simplify the production of the switching device, all the terminals may be constructed with the samedimension and, in particular, with the same diameter. The diameter of the terminals should be rated for the maximum current load occur ring in the various switching positions. This results in a specific height of the connecting or switching head for the various primary nominal current ranges, if the switching head is designed in an optimum manner, that is, of a size only large enough that the switching device can just barely be accommodated. The advantage of optimum switching head design is thus obtained at the price of the disadvantage of a great number of types, and hence a high cost of the stock, which must be maintained in inventory.

SUMMARY OF THE INVENTION This invention relates to current transformers switchable, on the primary side, to different measuring ranges and, more particularly, to such a current transformer in which the switching device, on the primary side, has a design such that fewer types of switching heads are needed while the advantages of optimum switching head design are maintained.

The invention is thus directed to a current transformer switchable to different measuring ranges on the primary side, and having two or four primary winding sections whose ends are connected to switching terminals disposed in the transformer head, and with which the primary winding sections are switchable selectively in parallel or in series, with two winding sections, or in parallel, series-parallel, or series, with four winding sections. In accordance with the invention, each end of a primary winding section is connected to a pair of switching terminals, and the switching terminals of each pair are arranged on two spaced partitions of the transformer housing head in such a way that one terminal of each pair is disposed on one partition and the other terminal of each pair on the other partition.

This doubling of the switching terminals results in various advantages, which will be described more fully hereinafter. However, the larger number of switching terminals does not require additional space, because the switching heads are usually designed in a symmetrical manner, for reasons for simplifying manufacture. In particular, the recess for the switching device usually is provided in duplicate, for the mentioned reasons of symmetry as well as for reasons of displacement of insulating material, the recesses being provided on two opposite partitions of the transformer switching head.

With thearrangement of the switching terminals in accordance with the invention, their current load can be greatly reduced or, at equal current load, the maximum permissible current can be greatly increased, so that switching heads of the same dimensions can, if desired, be used for different nominal current ranges. This greatly decreases the amount of stock which must be maintained in inventory. A further characteristic feature of the invention u that, due to the symmetrical'arrangement of the switching terminals in the switching head, or in the current transformer head, the occurring current forces are distributed evenly over two halves of the current transformer head. Thereby, a unilateral load, which is'dangerous in particular in the case of shock stresses, is avoided.

In a variation of the invention, the terminals of eachpair of switching terminals are electrically interconnected, and the ends of the primary winding sections are connected to'the center ofthe electrical connections ofeach pair of terminals.

With this circuit arrangement, all the switching terminals and w contact studs are loaded, in all switching positions occurring tion embodying the invention,-in casethe primary winding sections are formedby partial or sectional conductors, only the switching terminals of the pairs located atthe ends of the two terminal rows are electrically interconnected with each other and with one end of the partial conductors of one or the other primary winding section, while the other end of the partial conductors'of both primary winding sections is connected to a terminal pair lying between the ends of 'the rows. There is again obtained, for all switching positions, a reduction of the current flowingthrough the switching terminals, and which amounts to 50 percent for the outer terminal pairs under the higher load and 25 percent for the inner terminal pairs under a smaller load. If the outer terminals are designed, at the same time, as switching'and junction points, in such a way that onehalf of the current component coming from an input terminal flows to the connected winding and the other half into the connected contact stud, thereis obtained a uniform current load of all switching terminals with one-fourth of the current flowing through the primary junction or input terminals. With this current dividing circuit, there is thus obtained also, with a 1:2 switching-device with 2X4 switching terminals, the same advantage with respect to the current loading of the'terminals as with the known l:2:4 switching devices requiring l2 terminals.

An object of the invention is to provide an improved switching terminal arrangement for a current transformer whose primary side is switchable to different measuring ranges.

Another object of the invention is to provide such a switching arrangement in which the current load on the switching terminals is substantially reduced.

A further object of the invention is to provide such a switching arrangement in which a minimum number of switching or transformer heads need be maintainedin stock.

Another object of the invention is to provide such a switlching arrangement which is simple, economical, and versati e.

For an understanding of the principles of the invention, reference is made to the following description of typical embodirnents thereof as illustrated in the accompanying drawings.

3 BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIGS. 1 and 2 are schematic wiring diagrams of switching arrangements embodying the invention, for a current transformer switchable, on the primary side, in the ratio 1:2;

FIGS. 3 and 4 are schematic wiring diagrams illustrating two switching arrangements, embodying the invention, for a current transformer switchable, on the primary side, in the ratio l :2:4 with 2 l2 switching terminals;

FIGS. 5 and 6 are schematic wiring diagrams of two switching arrangements embodying the invention for a current transformer with 2X8 switching terminals and switchable, on the primary side, in the ratio 1:2:4; I

FIG. 7 is a plan view, partly in section, of a switching head mounting a switching arrangement embodying the invention and usable for primary-side switching in the ratio l :2;

FIG. 8 is a sectional view taken on the line 8-8 of Fig. 7; and

FIG. 9 is a sectional view taken on the line 9-9 of Fig. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Fig. l, 8 switching terminals 1-8 are aligned in two terminal rows I and II. The terminals of each switching terminal pair 1-2,3-4, 5-6, and 7-8 are electrically interconnected by respective electrically conductive connections 9-12. The ends of the primary winding sections 13 and 14 are connected to the centers of the conductive connections -12 of each pair of switching terminals. The current transformer has primary input terminals K and L, which are connected to the centers of connections 9 and 12, respectively, of the terminal pairs 1-2 and 7-8 at the enos of the two terminal rows I and II. By means ofcontact studs or connector elements 15-18, the two primary winding sections 13 and 14 can be connected in parallel, as shown in solid lines, or in series, as shown in broken lines.

As can be seen, all the switching terminals I-8 and all the connecting elements 15-18, in both the series and parallel arrangements, are loaded with only one-fourth of the current flowing through the primary input terminals K and L. For electrical reasons, two of the connector elements 15, 16 or 17, 18 actually would be unnecessary for the series connection. However, in order to obtain a uniform terminal load, the circuit is arranged as shown. It would also be possible to connect the ends ofthe primary winding sections 13 and 14 directly to one terminal ofthe associated terminalpair 1-1, 3-4, 5-6, or 7-8. However, considered from a uniform current loading on the terminals, the illustrated central connection is more favorable.

In Fig. 2, the two terminal rows are again designated I and II, the eight switching terminals are indicated at 1-8, the connecting elements at 15-18 and the primary input terminals at K and L. The electrical interconnections of the terminals of the pairs 1-2 and 7-8 at the ends of the terminal rows I and II are designated 9 and 12. The primary winding sections are formed by partial or sectional conductors l3a-l3b and l4a-14, respectively. First ends of the partial conductors 13a, 13b and 14a, 14b are connected to the external switching terminals 1, 2 and 7, 8 respectively, and the other ends of the partial or sectional conductors are connected to the intermediate switching terminals 3-6. Thus, in the same manner as in Fig. 1, only two primary winding sections are provided, except that each primary winding section is composed of at least two partial conductors which are connected as illustrated. As compared with the embodiment of the invention shown in Fig. l, the expense for active conductor material thus is not increased.

The partial conductors of each primary winding section need not be arranged in spaced relation to each other, as illustrated in Fig. 2, but can be wound conjointly and simultaneously. As in Fig. l, the parallel connection is shown in solid lines and the series connection is broken lines. Also, as can be seen from Fig. 2, the highest current load, in a parallel connection, occurs at the external terminal pairs 1, 2 and 7, 8, which are loaded with one-half of the current flowing through the primary input terminals K and L. As has been mentioned, however, a uniform current load on all switching terminals can be attained with only one-fourth of the current flowing through the primary input terminals K and L, if the external terminals 1, 2 and 7, 8 are simultaneously designed as switching tenninals and as junction points. In order to secure a favorable current distribution, the primary input terminals K and L are again connected to the midpoints or centers of the connections 9 and 12, respectively, between the terminal pairs, 1,2 and 7, 8.

Fig. 3 illustrates a switching arrangement for a current transformer, embodying the invention, switchable on the primary side of the ratio 1:224 with 2X12 switching terminals and with four primary winding sections each comprising two partial conductors. The series connection of the primary winding sections is illustrated and the parallel connection, as well as the series-parallel connection, can be established in a known manner by corresponding arrangement of the connecting elements or contact studs.

Switching terminals 21-44 are arranged on opposite partitions of the transformer head, in three terminal rows la, Ila, Illa and lb, llb,IIlb, respectively, each row including four aligned terminals in adjacent relation. The switching terminals 21, 29, 37 and 27, 35, 43, or, respectively, 22, 30, 38 and 28, 36, 44, positioned at the ends of the terminal rows, are electrically interconnected by electrically conductive connections 45-48 and 49-52. The primary input terminals K and L are connected to central switching terminals 29, 30 and 35, 36, respectively, and the illustrated circuit connections can be established by means of the connecting elements or contact studs 53-64.

In common with the primary input terminals K and L, one end of the two outer of the four primary winding sections formed by partial conductors 650-651), 660-6617, 67a-67band 680-68 is connected to the central of the external switching terminals 29, 30 and 35,36. It is thus attained that, also in the parallel connection and the series-parallel connection, at the most only one-fourth of the current flowing through the primary input terminals K and L flows through each switching terminal 21-24, so that all of the switching terminals are loaded at the most with one-fourth of the primary input current. The other ends of the two outer partial conductors 65a, 65b and 68a, 68 b, and the inner partial conductors 66a, 66b and 67a, 67bare connected to the intermediate terminals 23, 31,39, 25, 33,41, and 24, 32, 40, or 26, 34, 42, respectively.

Fig. 4 illustrates a switching arrangement similar to that shown in Fig. l, with four primary winding sections consisting of compact conductors, or consisting of parts of conductors, but in which no use is made of the partial conductor connection, as in Fig. 3. Identical parts are designated with the same reference symbols as in Fig. 3, and the series-parallel connection is illustrated in Fig. 4.

The primary winding sections 65-68 are connected to the centers of the electrically conductive connections 69-76 which interconnect the various terminal pairs of switching terminals. The primary input terminals K and L likewise are connected to the centers of the external connections 72 and 76, respectively. In the arrangements shown in Fig. 4, the switching terminals also carry, in all switching positions, only one-fourth of the current flowing in the primary input terminals K and L if the connections to the external terminals 37, 29, 2] or 22, 30, 38 or 43, 35, 27 or 28, 36, 44 correspondingly designed.

FIG. 5 illustrates a switching arrangement for a current transformer, switchable on the primary side of the ratio 1:2:4with 2X8 switching tenninals and 4 primary windings sections, each formed of partial conductors. the Parallel connection of the primary winding sections being illustrated. The series and series-parallel connection can be established by corresponding arrangement of the contact studs or connecting elements in a known manner.

Switching terminals 81-96 are arranged on two opposite partitions of the switching or transformer head and in two mutually spaced terminal rows la,lla and lb, llb, each including four terminals arranged in a row in adjacent spaced relation. Terminals 81, 82 and 95, 96 at the ends of the terminal rows la, Ila and 1b, llb are electrically interconnected by electrically conductive connections 97 and 98, respectively. The primary input terminals K and L are connected to the centers of the respective connections 97 and 98 and, by means of contact studs or connector elements 99-110, the several interconnections of the primary winding sections can be established.

The primary winding sections formed by partial conductors Illa-111b, ll2a-l12b, ll3a-113b and 1140-1141: are connected with a terminal of an upper terminal row and with a terminal of adjacent lower terminal row. In a known circuit arrangement, without doubling of the switching terminals in accordance with the invention, in a parallel connection, the switching terminals 81 and 95 connected with the primary input terminals K and L, respectively, carry the highest current, which is three-fourths of the current flowing in the primary input terminals. The other terminals carry a smaller percentage of the current, namely two-fourths or, respectively, one-fourth of the primary input current. By contrast, in the arrangement embodying the invention, the current component flowing in the switching terminal is reduced to one-half. Thus, in this arrangement also, twice the current flow in the primary input terminals at a given current loading of the switching terminal is made possible.

Fig. 6 illustrates a switching arrangement similar to that shown in Fig. 5, but with four primary winding sections consisting of compact conductors, or with primary winding sections consisting of partial conductors, and where, however, no use is made of the partial conductor circuit as illustrated in Fig. 5. Identical parts are indicated with the same reference symbols as in Fig. 5, and the connection illustrated is the series-parallel connection.

Each of the four primary winding sections 111-114 is connected to the center of the conductive connections 115-112 of the individual terminal pairs 81-82, 83-84, 85-86, 87-88, 89-90, 91-92, 93-94 and 95-96. The primary input terminals K and L are connected to the centers of the connections 115 and 122, respectively, of the external switching terminal pairs 81-82 and 95-96.By means of the connection elements or contact studs 99-110, the desired circuit connections can be established. Also in this circuit arrangement, twice the current flow can be permitted in the primary input terminals K and L, as compared with a circuit arrangement without the doubling of the switching terminals, according to the invention, and without exceeding the permissible current loading of the terminals.

Figs, 7, 8 and 9 illustrate a switching or transformer head with the connections in accordance with the schematic wiring diagram of Fig. l, the same elements being provided with the same reference symbols as in Fig. 1.

Referring to Figs. 7, 8 and 9, the two switching terminal rows land 11, comprising switching pins or switching terminals 1, 3, 5, 7 and 2, 4, 6, 8 are arranged in pocket type recesses 123, 124, respectively, on opposite partitions 125, 126 respectively of the transformer or switching head 127. The connections between the switching terminal pairs 1-2, 3-4, 5-6, and 7-8 are indicated at 9-12. The junctions of the primary winding sections 13 and 14 are provided in the manner described with respect of Fig. 1. The switching terminals of each terminal row i and I1 are arranged in aligned and adjacent spaced relation, as illustrated in Fig. 8.

Advantageously, switching terminals 1, 3, 5, 7 and 2, 4, 6, 8, arranged in adjacent relation, are positioned at the level of the axes of the primary input terminals K and L, as will be clear from Figs. 8 and 9. Thus, the connections with the primary input terminals can be produced without bends. In addition, it is advantageous to connect the two primary input terminals to the centers of the conductive connections of the two switching terminal pairs lying at the ends of the two terminal rows.

Thereby, there is obtained a symmetrical current distribution in the switching terminals and in the primary winding sections.

The invention switching arrangement permits a current flow up to twice the current strength of the total current flowing through the primary input terminals, as compared with a conventional switching arrangement without doubling of the switching terminals. There is thereby obtained uniform lead-in and circuit elements for a large nominal current range, thus permitting rational production. At the same time, the casting molds or pattern arrangements for the switching or transformer head can be standardized. Due to the division of current, smaller conductor cross sections can be used, so that installation is facilitated. Moreover, if use is made of the current doubling in the primary input terminals, extremely large winding cross sectionsof the primary winding sections, such as fiat bars bent in U shape, round conductors, or pipes or tubes, can be connected conveniently without bends or additional means, on the one hand to the primary input terminals and, on the other hand, to the connections extending between the switching terminals. The mechanical stresses on the transformer head, exerted by dynamic forces in particular when shock currents occur, is rendered uniform.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In a current transformer having a pair of primary winding input terminals and whose primary side is switchable to different measuring ranges, and having at least two primary winding sections whose ends are connected to switching terminals disposed in a transformer housing head, having a pair of spaced partitions, for connection of two primary winding sections selectively in parallel or in series, or for connection of four primary winding sections selectively in parallel, seriesparallel, or series, the improvement comprising, in combination, said switching terminals being arranged in pairs each including a first terminal and a second terminal; said first terminals being arranged on one of said partitions and said second terminals being arranged on the other of said partitions; and meansconnecting each end of each winding section to a respective one of said pairs of switching terminals including a respective first and a respective second terminal.

2. In a current transformer, the improvement claimed in claim 1, in which said current transformer includes two primary winding sections; said switching terminals comprising four first switching terminals arranged in laterally adjacent spaced relation in a first row on one partition, and four second switching terminals arranged in laterally adjacent spaced relation in a second row on the other partition; each primary input terminal being connected to a respective pair of first and second switching terminals at the ends of said rows.

3. In a current transformer, the improvement claimed in claim 2, in which said two rows are in a common place including the axes of said primary input terminals.

4. In a current transformer, the improvement claimed in claim 1, including electric conductors connecting each first terminal to a respective second terminal; the ends of said primary winding sections being connected to the centers of said electric conductors.

5. In a current transformer, the improvement claimed in claim 1, in which each primary winding section is formed by partial conductors; said first switching terminals being arranged in adjacent spaced relation in a first row on one of said partitions, and said second switching terminals being arranged in spaced adjacent relation in a second row on the other of said partitions; respective electric conductors connecting the first switching terminals at the ends of said first row to the second switching terminals at the ends of said second row; said thus interconnected first and second switching tenninals constituting end switching terminals; means connecting one end of each partial conductor to a respective end switching terminal; and means connecting the opposite end of each partial conductor to a respective switching terminalintermediate said end switching terminals.

6. In a current transformer, the improvement claimed in claim 4, in which said primary input terminals are connected, respectively, to the electric conductors interconnecting the switching terminals at the opposite ends of said two rows.

7. In a current transformer, the improvement claimed in claim 5, in which each primary input terminal is connected to a respective one of said electric conductors.

8. In a current transformer, the improvement claimed in claim 1, in which said current transformer comprises four primary winding sections; said switching terminals including three rows of first switching terminals, each including four first switching terminals, arranged in superposed planes on one of said partitions, and three rows of second switching terminals each including four second second switching terminals arranged in said superposed planes on the other of said partitions.

9. [n a current transformer, the improvement claimed in claim 1, in which said current transformer includes four primary winding sections; said switching terminals including two first rows of first switching terminals, each including four first switching terminals, arranged on one of said partitions, and two second rows of second switching terminals, each including four second switching terminals, arranged on the other of said partitions; each first row lying in a common plane with each second row, which planes are superposed; the terminals in each first row being offset from the terminals in the other first row, and the terminals in each second row being offset from the terminals in the other second row.

10. In a current transformer, the improvement claimed in claim 9, in which the terminals in each second row are aligned with the terminals in the first row which is in the same plane with the second row.

Claims

1. In a current transformer having a pair of primary winding input terminals and whose primary side is switchable to different measuring ranges, and having at least two primary winding sections whose ends are connected to switching terminals disposed in a transformer housing head, having a pair of spaced partitions, for connection of two primary winding sections selectively in parallel or in series, or for connection of four primary winding sections selectively in parallel, seriesparallel, or series, the improvement comprising, in combination, said switching terminals being arranged in pairs each including a first terminal and a second terminal; said first terminals being arranged on one of said partitions and said second terminals being arranged on the other of said partitions; and means connecting each end of each winding section to a respective one of said pairs of switching terminals including a respective first and a respective second terminal.

5. In a current transformer, the improvement claimed in claim 1, in which each primary winding section is formed by partial conductors; said first switching terminals being arranged in adjacent spaced relation in a first row on one of said partitions, and said second switching terminals being arranged in spaced adjacent relation in a second row on the other of said partitions; respective electric conductors connecting the first switching terminals at the ends of said first row to the second switching terminals at the ends of said second row; said thus interconnected first and second switching terminals constituting end switching terminals; means connecting one end of each partial conductor to a respective end switching terminal; and means connecting the opposite end of each partial conductor to a respective switching terminal intermediate said end switching terminals.

9. In a current transformer, the improvement claimed in claim 1, in which said current transformer includes four primary winding sections; said switching terminals including two first rows of first switching terminals, each including four first switching terminals, arranged on one of said partitions, and two second rows of second switching terminals, each including four second switching terminals, arranged on the other of said partitions; each first row lying in a common plane with each second row, which planes are superposed; the terminals in each first row being offset from the terminals in the other first row, and the terminals in each second row being offset from the terminals in the other second row.