EP2996121A1

EP2996121A1 - Improved current transformer shield for an electronic watt-hour meter

Info

Publication number: EP2996121A1
Application number: EP14184053.8A
Authority: EP
Inventors: Emre SARI; Mükremin SARI
Original assignee: Core Elektronik Ticaret Ve Sanayi Ltd Sti
Current assignee: Core Elektronik Ticaret Ve Sanayi Ltd Sti
Priority date: 2014-09-09
Filing date: 2014-09-09
Publication date: 2016-03-16

Abstract

The present invention relates to a watt-hour meter (1) for measuring usage of electricity, said watt-hour meter (1) comprising at least one current transformer (2) having a magnetic core (2) encircling a line conductor (4) and through the windings of which a current flow is induced in response to a magnetic field being induced by a current flow through said line conductor (4), said watt-hour meter (1) further comprising a magnetic shield (6) for shielding said at least one current transformer (2) against external magnetic fields.

Description

Technical Field of the Present Invention

The present invention relates to an improved current transformer shield, said current transformer having a toroidally shaped core and as well as toroidal windings.

Background of the Present Invention

As is known, watt-hour meters serve to the purpose of measuring usage of electricity. An electronic watt-hour meter may typically include at least one current transformer, conventionally effective in measuring and calculating usage of electricity.
A current transformer typically functions such that a current flow is induced through the windings of said current transformer in response to a magnetic field being in turn induced by a current flow through a line conductor. To this end, the amount of current and accordingly the energy drawn by a load can be determined depending on the specific number of turns in said current transformer. In this regard, the signal from said current transformer may be fed to a high gain differential amplifier, whose output being in turn fed to a feedback winding so as to measure the amount of energy being drawn.
More particularly, such a current transformer has a core of magnetic material encircling the line conductor. An alternating magnetic flux from the line conductor current is induced in the current transformer core, inducing a voltage in the windings of the current transformer.
A prior art publication in the technical field of the present invention may be referred to as EP2458599 among others, the document disclosing an electronic watt-hour meter; a current transformer operatively coupled to the electronic watt-hour meter; a first shield on a first side of the current transformer; and a second shield on a second side of the current transformer, wherein the second side is substantially parallel to the first side, wherein the first shield and the second shield each include a substantially magnetically permeable and conductive metal.
The present invention distinguishes over WO2010063760A1 in that it provides magnetic flux paths which function in the manner to create shielding against external magnets as defined by the characterizing features given in Claim 1.

Objects of the Present Invention

Primary object of the present invention is hence to provide a watt-hour meter which is effectively shielded against external magnetic fields, including the case of two external magnets creating a stronger magnetic field to falsify watt-hour meter indications.

Brief Description of the Figures of the Present Invention

Accompanying drawings are given solely for the purpose of exemplifying a watt-hour meter, whose advantages over prior art were outlined above and will be explained in brief hereinafter.
The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said claims without recourse to the technical disclosure in the description of the present invention.

Fig. 1 demonstrates a general perspective view of a three-phase watt-hour meter according to a first alternative embodiment of the present invention.
Fig. 2 demonstrates a general perspective view of the watt-hour meter according to a second alternative embodiment of the present invention.
Fig. 3 demonstrates a general perspective view of a three-phase watt-hour meter according to a third alternative embodiment of the present invention.
Fig. 4 demonstrates another general perspective view of the three-phase watt-hour meter according to the fourth alternative embodiment of the present invention.

Detailed Description of the Present Invention

The following numerals are assigned to different parts demonstrated in the drawings:

1) Watt-hour meter
2) Current transformer
3) Magnetic core
4) Line conductor
5) Line conductor terminals
6) Magnetic shield
7) Magnetic shield body
8) Elliptical halves
9) Minor axis notch
10) Insulation housing
11) Centering ears
12) Perimetric flux path member
13) Central confining member
14) Magnetic shield opening
15) Intermediate flux path member
16) Magnetically permeable plate

The present invention relates to a watt-hour meter (1) comprising a core of magnetic material (magnetic core, 2) encircling a line conductor (4). An alternating magnetic flux from the line conductor (4) current between the terminals thereof (line conductor terminals, 5) is induced in the current transformer (2) core, inducing a voltage in the windings (not shown) of the current transformer (2).
In accordance with the invention, a magnetic shield is proposed (6), said shield having a body (magnetic shield body, 7) having perimetric and/or intermediate flux path members (respectively 12 and 15). According to the first alternative embodiment of the present invention, the watt-hour meter (1) comprises at least one current transformer (2) placeable in the magnetic shield (6) having a body (magnetic shield body, 7) with a cross-section in the form of two elliptical halves (8) separated by the shorter diameter of the elliptical profile cross-section. Two minor axis notches (9) are provided to accommodate centering ears (11) of insulation housings (10) as delineated hereinafter.
The magnetic shield body (7) in the form of two elliptical halves separated by said minor axis notches (9) according to the invention provides that two air regions are created inside each magnetic shield body (7) below and above a respective insulation housing (10). This is advantageous in that magnetic flux lines generated by external magnets used in a fraudulent attempt tend to travel along perimetric flux path members (12) instead of the magnetic core (3) of the current transformer (2). Therefore, the elliptical structure creating two air regions provides the desired effect even in the case of two external magnets enclosing the magnetic core (2) at two sides thereof.
To this end, in the case where two external magnets are used such that the magnetic core (2) lies between the poles of two magnets, said perimetric flux path members (12) will serve as parts of the magnetic shield body (7) along which magnetic flux lines travel and the inner space of the magnetic shield body (7) containing the current transformer (2) along with the two air regions will be magnetically less permeable. In the case of a three-phase watt-hour meter as depicted in Fig. 1, intermediate flux path members (15) together with said perimetric flux path members (12) will carry magnetic flux and protect the magnetic current transformer's (2) magnetic core (3).
In accordance with the present invention, said insulation housings (10) advantageously accommodate the current transformers (2) such that an insulation material such as for instance epoxy resin or polyurethane is injected inside said insulation housings (10), which therefore serve as a mold containing the insulation material as well as the current transformer (2). Insulation housings (10) therefore substantially reduce production time as the housing itself is also used as mold containing the insulation material. Another advantage of the insulation housings (10) lies in that two centering ears (11) of the housings act as a centering and aligning means in cooperation with said minor axis notches (9). The appropriate positioning of the current transformers (2) inside said housings is therefore ensured. The depthwise length of the minor axis notches (9) is limited so that magnetic flux paths along intermediate or perimetric flux path members (15, 12) are not interrupted. The length of the minor axis notches (9) is preferably less than half of the total dimension of the magnetic shield body (7) at the same line.
Further, the invention provides that a magnetically permeable plate (16) is provided to be attached to at least one magnetic shield body (7) so as to cover the same from behind at the opposite side of the openings through which said insulation housings (10) are introduced into said magnetic shield bodies (7) such that an additional magnetic flux path is created. The magnetically permeable plate (16) may additionally be provided (not shown) in between two neighboring intermediate flux path members (15) so as to strengthen the intermediate flux line and compensate the permeability loss caused by said minor axis notches (9).
In accordance with an alternative embodiment of the invention as demonstrated in Fig. 2, the insulation housing (10) containing the current transformer (2) is placed inside a magnetic shield (6) having two lateral confining members also acting as perimetric flux path members (12). Further, a central confining member (13) according to an alternative embodiment of the invention is used in the case more than one current transformer (2) is to be shielded (Fig. 3).
In accordance with a fourth alternative embodiment of the present invention, a magnetic shield body (7) having magnetic shield openings (14) is used to provide shielding. To this end, said magnetic shield body (7) is provided with intermediate flux path members (15) together with perimetric flux path members (12) so as to create paths of least resistance for the lines of magnetic flux. According to this alternative embodiment being demonstrated in Fig. 4, the magnetic shield openings (14) serve to the purpose of inserting the current transformers (2) inside the magnetic shield body (7). Although said magnetic shield openings (14) do have circular contours in Fig. 4, they can be elliptical to provide the effects as delineated in association with the first alternative embodiment demonstrated in Fig. 1.
In a nutshell, the present invention proposes a watt-hour meter (1) for measuring usage of electricity, said watt-hour meter (1) comprising at least one current transformer (2) having a magnetic core (2) encircling a line conductor (4) and through the windings of which a current flow is induced in response to a magnetic field being induced by a current flow through said line conductor (4), said watt-hour meter (1) further comprising a magnetic shield (6) for shielding said at least one current transformer (2) against external magnetic fields.
In an embodiment of the present invention, said at least one current transformer (2) is placeable inside a magnetic shield (6) having a magnetic shield body (7), said magnetic shield body (7) having at least one perimetric flux path member (12) creating a path of least resistance for the lines of magnetic flux.
In a further embodiment of the present invention, said magnetic shield body (7) has a cross-sectional profile with two elliptical halves (8) being separated by the conjugate diameter of the elliptical profile cross-section.
In a still further embodiment of the present invention, two minor axis notches (9) are provided at two ends of the conjugate diameter of the elliptical profile cross-section.
In a yet still further embodiment of the present invention, said two air regions are created inside each magnetic shield body (7) below and above a respective current transformer (2).
In a yet still further embodiment of the present invention, an insulation housing (10) accommodates one current transformer (2) such that an insulation material is injectable inside said insulation housing (10).
In a yet still further embodiment of the present invention, insulation housing (10) constitutes a mold containing the insulation material as well as the current transformer (2).
In a yet still further embodiment of the present invention, said insulation housing (10) has two centering ears (11) for centering and aligning a current transformer (2) in cooperation with said minor axis notches (9).
In a yet still further embodiment of the present invention, said two air regions are created inside each magnetic shield body (7) below and above a respective insulation housing (10).
In a yet still further embodiment of the present invention, said minor axis notches (9) receive and accommodate centering ears (11) of the insulation housings (10).
In a yet still further embodiment of the present invention, length of the minor axis notches (9) is preferably less than half of the total dimension of the magnetic shield body (7) at the same line.
In a yet still further embodiment of the present invention, said magnetic shield body (7) has at least one intermediate flux path member (15) in the case of more than one current transformers (2), said intermediate flux path member (15) creating a path of least resistance for the lines of magnetic flux.
In a yet still further embodiment of the present invention, a magnetically permeable plate (16) is provided to be attached to at least one magnetic shield body (7) so as to cover the same from behind at the opposite side of an opening through which said current transformer (2) is introducible into said magnetic shield body (7).
In a yet still further embodiment of the present invention, a magnetically permeable plate (16) is provided in between two neighboring intermediate flux path members (15) so as to strengthen the intermediate flux line.
In a yet still further embodiment of the present invention, said magnetic shield body (7) comprises two lateral confining members in the form of perimetric flux path members (12) and a central confining member (13) in between the latter two perimetric flux path members (12).
In a yet still further embodiment of the present invention, said magnetic shield body (7) has magnetic shield openings (14) for insertion of current transformers (2).
The present invention therefore ensures that a fraudulent attempt in order for interfering with the operation of the watt-hour meter is effectively avoided by way of providing alternative magnetic flux lines and the current transformer (2) being encircled by air regions as well as a polymer-based insulation housing (10) provides a magnetically less permeable path.

Claims

A watt-hour meter (1) for measuring usage of electricity, said watt-hour meter (1) comprising at least one current transformer (2) having a magnetic core (2) encircling a line conductor (4) and through the windings of which a current flow is induced in response to a magnetic field being induced by a current flow through said line conductor (4), said watt-hour meter (1) further comprising a magnetic shield (6) for shielding said at least one current transformer (2) against external magnetic fields characterized in that;
said at least one current transformer (2) is placeable inside a magnetic shield (6) having a magnetic shield body (7), said magnetic shield body (7) having at least one perimetric flux path member (12) creating a path of least resistance for the lines of magnetic flux.
A watt-hour meter (1) as set forth in Claim 1, characterized in that said magnetic shield body (7) has a cross-sectional profile with two elliptical halves (8) being separated by the conjugate diameter of the elliptical profile cross-section.
A watt-hour meter (1) as set forth in Claim 2, characterized in that two minor axis notches (9) are provided at two ends of the conjugate diameter of the elliptical profile cross-section.
A watt-hour meter (1) as set forth in Claim 2 or 3, characterized in that said two air regions are created inside each magnetic shield body (7) below and above a respective current transformer (2).
A watt-hour meter (1) as set forth in Claim 1, 2, 3 or 4, characterized in that an insulation housing (10) accommodates one current transformer (2) such that an insulation material is injectable inside said insulation housing (10).
A watt-hour meter (1) as set forth in Claim 5, characterized in that insulation housing (10) constitutes a mold containing an insulation material as well as the current transformer (2).
A watt-hour meter (1) as set forth in Claim 3 and 5, characterized in that said insulation housing (10) has two centering ears (11) for centering and aligning a current transformer (2) in cooperation with said minor axis notches (9).
A watt-hour meter (1) as set forth in Claim 2 and 5, characterized in that said two air regions are created inside each magnetic shield body (7) below and above a respective insulation housing (10).
A watt-hour meter (1) as set forth in Claim 7, characterized in that said minor axis notches (9) receive and accommodate centering ears (11) of the insulation housings (10).
A watt-hour meter (1) as set forth in Claim 3, characterized in that length of the minor axis notches (9) is preferably less than half of the total dimension of the magnetic shield body (7) at the same line.
A watt-hour meter (1) as set forth in Claim 1, characterized in that said magnetic shield body (7) has at least one intermediate flux path member (15) in the case of more than one current transformers (2), said intermediate flux path member (15) creating a path of least resistance for the lines of magnetic flux.
A watt-hour meter (1) as set forth in Claim 1, characterized in that a magnetically permeable plate (16) is provided to be attached to at least one magnetic shield body (7) so as to cover the same from behind at the opposite side of an opening through which said current transformer (2) is introducible into said magnetic shield body (7).
A watt-hour meter (1) as set forth in Claim 11, characterized in that a magnetically permeable plate (16) is provided in between two neighboring intermediate flux path members (15) so as to strengthen the intermediate flux line.
A watt-hour meter (1) as set forth in Claim 1, characterized in that said magnetic shield body (7) comprises two lateral confining members in the form of perimetric flux path members (12) and a central confining member (13) in between the latter two perimetric flux path members (12).
A watt-hour meter (1) as set forth in Claim 11, characterized in that said magnetic shield body (7) has magnetic shield openings (14) for insertion of current transformers (2).