US2892167A - Tubular bar current transformer - Google Patents

Description

June 23, 1959 H. RITZ TUBULAR BAR CURRENT TRANSFORMER Fil ed Dec. 7, 1953 United States Patent i TUBULAR BAR CURRENT TRANSFORMER Hans Ritz, Hamburg, Germany Application December 7, 1953, Serial No. 396,542

Claims priority, application Germany December 8, 1952 4 Claims. (Cl. 336-174) In order to provide a better picture of the loading of the various phases in the outlet of electrical switchgear, as well as to provide indispensable accurate measurements or metering for operating purposes, there is an increasing need to incorporate current transformers into electrical switchgear. In most cases this refers to indicative measurements, for which no particularly high degree of accuracy is required. Since the loading of current transformers of this type through the connection of one or a few instruments is very low, the current transformer can in such cases be constructed as a single-conductor transformer. This is true even for very small currents which can no longer be measured directly be measuring instruments, provided that dimensions of the highly permeable magnetic material used can be kept so small that the little space required enables these transformers to be incorporated without difiiculty into existing switchgear.

If the current transformer constructions heretofore used for such purposes are constructed as single conductor devices which permit low current flow, the dimensions of such devices will generally be too large. When using single-conductor transformers or wound transformers of the construction previously adopted, it is necessary to sever a current path, for example the copper rails or flexible cable lines, in order to be able to incorporate one of the hitherto customary current transformers. The use of hinged or conversion transformers has hitherto not been found generally possible on account of the excessive dimensions or cost, and because of the excessive amount of labor required for fitting.

The present invention proposes a way of building a very small current transformer excellently suited for such purposes. It proposes not to push the transformer, over the current conductors (bars or circular conductors) of the switchgear or to insert it in the lead after removal of a piece of the latter, as was previously done, but to insert the transformer in the line connection points. A tubular bar, corresponding to the very short axial length of the transformer and being dimensioned for the primary current, is incorporated as a tubular conductor or bushing around the connecting bolts existing at the line connection point. The tubular bar serves as the primary conductor of the current transformer.

The width of such transformers, when highly permeable material is used, can be kept smaller than the usual or standardised phase spacings. For example, for low voltage installations, while the axial length of such transformers can be made somewhat less than one quarter of the width measurement (flat disc), the transformers can be incorporated into all existing switchgear. No changes in an installation are required, provided that a rather long bolt or the like is used instead of the existing connecting bolts.

In its external shape this novel current transformer comprises a washer constructed as a current transformer and an internal current-conducting tubular rod. The axial dimensions both of the rod and of the washer are 2,892,167 Patented June 23, 1959 kept substantially smaller than the radial dimensions in order to achieve universal attachability to any existing connection points (contact points).

In many cases the capacity of these tubular rod current transformers is insufficient for low primary current strengths. In order to create a suitable transformer for such cases, a device is required which will be capable of incorporation within a small space in the same manner as the tubular bar-conductor transformer. It is proposed as another embodiment of the invention to construct the tubular bar current transformer as a tubular bar-wound current transformer.

The construction of the tubular bar transformer requires only small space for incorporation. With medium current strengths, encountered in normal use of these transformers the necessary power and the accuracy of measurement require a predetermined transformer diameter. An optimum diameter must be attained if the height of the transformer is not to be made too great.

For reasons of economy the smallest number of models of different dimensions must be produced. In practice cases occur in which the necessary incorporation space is not available in one direction. This is the case, for example, with bases of fuse elements, where the tubular bar transformers are screwed on to the connection straps. In particular, for low current strengths, a transformer of conventional construction would have to be built with a substantially smaller diameter, while its height would then be inconveniently great.

Accordingly, therefore, the present invention contemplates ingenious current transformer structure in which these drawbacks and deficiencies of prior art systems are eliminated.

Other objects, advantages and characteristic features of the present invention will become apparent upon consideration of the following detailed description of preferred embodiments of the invention taken in conjunction with the appended drawings in which:

Figures 1, 2, 2a, 3, 4, 5 and 6 are vertical sectional views of several embodiments of the tubular bar current transformer provided according to the principles of the present invention.

In Figure 1 there is shown a connecting bolt push-on current transformer in disc form having an internal tubular conductor. It consists of a small magnetic core 1, preferably an annular band core of highly permeable material, which after the application of the secondary insulation is surrounded by a secondary winding 2. The ends of secondary winding 2 are sent to secondary connection terminals, preferably as connection leads 3 which lead to a measuring instrument. In this core is disposed a fitting current-conducting tubular bar conductor piece 4 which is simply a current-conducting bush or sleeve. The internal diameter of the piece 4 is connected to the connecting bolts 5 used in the switchgear for the current contacts, the cross-section of which is dimensioned according to the primary current strengths. The ends of the current-conducting bush are constructed parallel to one another so that by means of the high pressure of the [fastening bolt or bolts 5 an excellent transfer of current is achieved.

In Figures 2 and 2a is shown another construction of a tubular bar current transformer in which the core 1 with the secondary winding 2 is surrounded by a housing 6a, 6b. The housing 6a, 6b is made of insulating material and is preferably divided into two parts which are held together centrally by a tubular rivet 7. The rivet 7 is dimensioned for the primary current in question, while for correspondingly high primary current strengths a current-conducting tubular bar 4, as illustrated in Figure 1, can be additionally received by the tubular rivet 7.

In the embodiment illustrated in Figure 2a the tubular bar 4a is made longer than that shown in Figure 1, and the parts are held together by a semi-tubular rivet 7a.

Moreover as illustrated in Figure 3, the parts of the transformer can' be held together conventionally by a peripherally disposed tubular rivet 8, the remaining construction being unchanged. For this purpose, flanges or attachments 6c, 6d, or the like are constructed on each of the housing parts 6a, 6b, the flange or attachment being embraced by a tubular rivet 8.

A construction is illustrated in Figure 4 in which the abovedescribed transformer parts either separately or together with the current-conducting tubular bar 4b, are cast together to form one body by the cast resin method. A semi-tubular rivet constructed integrally with the tubular bar 4b is provided.

In Figure 5 an embodiment having a housing 6 of insulating material is illustrated. In this figure an en larged contact surface of the ends of the tubular bar is also provided. The tubular bar and the hollow rivet are constructed in one piece.

In Figure 6 is illustrated an embodiment in which housing parts 9 and 10 consist of current-conducting material which have at their outer periphery an inter ruption 11, and for example at A or B or C have a contact point. The dimensions are such that the middle cross-section surrounding the fastening bolt is dimensioned for the primary current strengths in question.

When the housing is made of insulating material as well as when it is made of metal, there can be provided either on the outer periphery or on the entire periphery, pocket-like dovetail-shaped or otherwise shaped recesses. Thi permits the insertion of the lead-out bush or the removal of the secondary leads. If desired, the secondary connection terminals may be provided with insulation. Moreover, the data plates of the transformer, which in particular can be made of insulating material or other fastening means are indicated in Figures 2, 4, and 6 to 12.

Although the present invention has been shown and described in reference to specific embodiments, nevertheless various changes and modifications obvious to those skilled in the art are deemed to be Within the spirit, scope, and contemplation of the invention.

I claim:

1. For use with a connection point of a low voltage electrical installation, which includes two overlapping and spaced apart conductor bars connected by a fastening bolt, a current transformer comprising a primary conductor in the form of a tubular bar conductor piece mounted on the fastening bolt between the conductor bars and having opposing ends abutting the conductor bars, an annular core of magnetic permeable material mounted on the conductor piece and being of less axial extension than the conductor piece, a secondary winding wound on the core and an annular split casing of insulative material enclosing the core and circutnposed on the conductor piece and consisting of two annular shallow sections, and means securing the sections together around the core, wherein said securing means includes a tubular rivet disposed in the bore of the casing and having its ends secured over onto the sections and in which the tubular bar conductor piece is axially fitted.

2. For use with a connection point of a low voltage electrical installation, which includes two overlapping and spaced apart conductor bars connected by a fastening bolt, a current transformer comprising an annular core of magnetic permeable material of slight axial extension, a secondary winding wound on the core and having lead ends, a sectional insulative annular casing in which the core is housed, said casing consisting of two annular shallow members, and a tubular central rivet axially fitted in the center of the casing and holding the sections together, said rivet forming a primary conductor and being fitted on the fastening bolt of the connection point in the current lead of an installation.

3. For attachment to a connection point of a low voltage electrical installation, which includes two confronting and spaced apart conductor bars connected by a fastening bolt, a current transformer comprising an annular core of magnetic permeable material of slight axial extension, at secondary winding wound on the core and having lead ends, an insulative sectional annular casing in which the core is housed, said casing consisting of two annular shallow members, and a tubular central rivet axially fitted in the center of the casing and holding the section" together, and a tubular conductor sleeve axially fitted in the rivet and forming a primary conductor and fitted on the fastening bolt in the current lead of an installation.

4. A current transformer as claimed in claim 3, wherein said conductor sleeve has opposing parallel flat ends which extend axially beyond the core and abut the inner faces of the conductor bars.

References Cited in the file of this patent UNITED STATES PATENTS 687,141 Everest Nov. 19, 1901 826,283 Schmidt July 17, 1906 2,214,915 Wehrlin Sept. 17, 1940 2,327,774 Dickinson Aug. 24, 1943 2,592,721 Mott Apr. 15, 1952 2,618,689 Cook Nov. 18, 1952 FOREIGN PATENTS 576,371 Germany Apr. 27, 1933 614,865 Germany June 20, 1935

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