WO2001020345A2

WO2001020345A2 - Alternating current measuring apparatus

Info

Publication number: WO2001020345A2
Application number: PCT/KR2000/001027
Authority: WO
Inventors: Wi Yeng Choi; Yeo Yong Yoon
Original assignee: Wi Yeng Choi; Yeo Yong Yoon
Priority date: 1999-09-11
Filing date: 2000-09-08
Publication date: 2001-03-22
Also published as: WO2001020345A3; AU7041300A

Abstract

An alternating current measuring apparatus according to the present invention comprises: a centrally hollowed pipe which accommodates time-variant magnetic flux building up in a circular fashion around a conductor live with an alternating current to be measured; a coil which is supported by said centrally hollowed pipe, and inside which is generated an induced electromotive voltage caused by time-variant magnetic flux accommodated inside said centrally hollowed pipe; a cover which wraps up the outer surface of said coil to shield said coil and shuts off electromagnetic disturbance externally originating from the outside; a detachable fixing means for fastening each end of said cover; and a calculator for integrating the value of the induced electromotive voltage generated inside the coil so as to compute the alternating current running through the conductor to be measured.

Description

ALTERNATING CURRENT MEASURING APPARATUS

Technical Field

The present invention relates to an alternating current measuring apparatus, and more particularly to an alternating current measuring apparatus that measures a voltage induced by alternating current passing through the conductor to be measured and computes the alternating current from the measured voltage .

Background Art Conventionally, in measuring an electric current, a current transformer was employed which makes it possible to measure the primary current by sensing the secondary current (12), in which primary and secondary coils are spooled on a centrally hollowed iron core as shown in FIG. 1. Here, the primary and secondary current are expressed as II and 12, respectively, and the number of windings as Nl and N2, respectively. The value of primary current (II) is computed by means of the equation I1=(N2/N1) x 12, where secondary current (12) is measured by the current transformer.

However, since this current transformer is composed of the primary circuit, iron cores, the secondary circuit, insulating materials, supports, and the like, it results in high costs for manufacturing. Further, a saturation phenomenon of iron cores in addition to the problem of the second output being non-linear results in a narrow range of measurement. On the other hand, since the current transformer is a kind of source of the current, it runs the risk of generating a high electric voltage when opening the secondary circuit. Moreover, since it includes the primary current used in a load, when the insulating material is degraded, it most likely leads to a systems malfunction. And the Japanese laid-open patent No. 6-213937 discloses a sensor that measures the electric current by sensing an electric voltage sustained by the coils spooled around a ring-shaped conductor plate core positioned centering around the conductor to be measured. However, this sensor is also subject to narrow range of measurement due to the saturation phenomenon of the core of the conductor plate, and poses a problem due to a non-linear output of the voltage value.

The U.S. patent No. 5.642.041 discloses an alternating current sensor that senses alternating current generated from the changes in a magnetic flux existing in the air-core. This sensor comprises three conductor plates which electrically connect the electric current to be measured, and coils having cores of non- magnetic substance, the coils being inserted in the interior thoroughfare formed by means of the three conductor plates .

However, the U.S. patent poses a problem of having to connect electrically the live conductor to be measured with the conductor plate.

Disclosure of the Invention

The object of the present invention is to provide an alternating current measuring apparatus capable of measuring the value of the current covering a wide range and with a high degree of precision as a result of the linear output.

Another object of the present invention is to provide an alternating current measuring apparatus capable of measuring the current without electrically and directly connecting with the conductor to be measured.

Still another object of the present invention is to provide an alternating current measuring apparatus that is so adaptable as to be adjusted in size, tailored to a wide variety of shapes and types of the conductor to be measured.

A further object of the present invention is to provide an alternating current measuring apparatus capable of minimizing the electromagnetic effects externally originating except for the conductor to be measured. In order to attain the objects, the alternating current measuring apparatus according to the present invention comprises: a centrally hollowed pipe which accommodates time- variant magnetic flux building up in a circular fashion around a conductor live with an alternating current to be measured; a coil which is supported by said centrally hollowed pipe, and inside which is generated an induced electromotive voltage caused by time-variant magnetic flux accommodated inside said centrally hollowed pipe; a cover which wraps up the outer surface of said coil to shield said coil and shuts off electromagnetic disturbance externally originating from the outside; a detachable fixing means for fastening each end of said cover; and a calculator for integrating the value of the induced electromotive voltage generated inside the coil so as to compute the alternating current running through the conductor to be measured.

Here, said centrally hollowed pipe is square or round in shape. And said centrally hollowed pipe comprises a plurality of bobbins and coupling joints that structurally and electrically connect the bobbins.

Brief Description of the Drawings Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:

Fig. 1 is a schematic view of a conventional alternating current measuring apparatus; Fig. 2 is a schematic perspective view of a preferred embodiment of the present invention;

Fig. 3 is an exploded perspective view of a preferred embodiment of the present invention shown in Fig. 2; Fig. 4 is a cross-sectional view taken along line IV-IV of Fig. 3;

Fig. 5 is a cross-sectional view, similar to Fig. 4, of an alternate embodiment of the present invention;

Fig. 6 is a block diagram of calculator used in the present invention;

Fig. 7 is a schematic perspective view of another preferred embodiment of the present invention;

Fig. 8 is a partially cutaway perspective view of magnetic flux nodes illustrated in Fig. 7;

Best Mode for Carrying Out the Invention

Before going any further, it is to be noted that any terms or words used in the present specifications and claims should not be taken in a limited way and interpreted ordinarily and lexicographically, but interpreted in the sense and concept that go with the technical thoughts of the present invention, based on the principle that an inventor is authorized to define a term appropriately in order to explain his or her invention in the best possible way. Accordingly, the embodiment described in the specifications herein and the composition illustrated in the drawings herein are nothing more than an embodiment deemed most desirable, and do not represent the whole technical thoughts of the present invention, allowing for the possibility of a variety of equivalents that can replace the embodiments provided herein and variant examples being in existence at the time of the application for patent being submitted.

Detailed accounts of desirable embodiments follow with reference to the drawings attached herewith:

Embodiment 1

As illustrated in FIG. 2, the alternating current measuring apparatus according to the present invention comprises a substantially ring-shaped measuring component 190 positioned around a conductor 110 live with alternating current (I) to be measured and a calculator 310 that computes the value of an alternating current by using a value of induced electromotive voltage. The measuring component 190 comprises a centrally hollowed pipe 128, a coil 127 supported by the hollowed pipe, a cover 120 covering the coil, a detachable fixing for fastening each end of the cover 120.

The centrally hollowed pipe 128, which is hollowed in the inside, may be square in shape so that an air-core can be formed in the inside as illustrated in FIG. 4. The centrally hollowed pipe 128 may also be round in shape with a cross section as illustrated in FIG. 5. The centrally hollowed pipe 128,228, made of flexible synthetic resin, is easily bent in a ring shape as illustrated in FIG. 2.

The coil 127,227 is designed to wrap up continuously the surface of the outer periphery of the centrally hollowed pipe 128,228. Accordingly, the coil 127,227 constitutes an air-core instead of a magnetic core along with the centrally hollowed pipe 128,228, with magnetic flux forming in an alternating manner inside the air-core. The coil 127,227 may preferably be a copper wire .

The cover 120,220, adopted to cover the outside of the coil 127,227 which wraps up the centrally hollowed pipe 128, 228, shuts off electromagnetic disturbance externally originating from the outside of the air-core. The cover 120,220 may preferably be a flexible synthetic resin provided with a metallic thin film 125,225 located inside, so that it may easily be bent in a ring shape. The cover 120,220 may also be made of flexible metallic materials that will shut off electromagnetic disturbance externally originating. In the case of 3-phase in particular, where each phase affects the adjacent phase, metallic thin films 125,225 may preferably cover the surface of the outside periphery of the coil 128,228 as illustrated in FIG. 4 or FIG. 5.

After the measuring component is bent from a linear shape in FIG. 3 into a ring shaped form in FIG. 2, the fixing means 131 is used to fasten the measuring component that has been bent. A plate 129 is provided at one end of the cover 120, and fixing holes 130 are formed on top of the plate 129. An opening 126 is provided at the other end of the cover 120, and fixing protrusions 122 are formed on the cover 120 in front of the outlet 126. Accordingly, after the measuring component 190 in a linear shape is bent in a ring shape so that the conductor to be measured may be included in the center, the fastening plate 129 is inserted into the opening 126, a fixing hole 130 is fitted onto the fixing protrusion 122, and then the fixing means 131 is fastened by a nut, for example .

The calculator 310 computes the value of the current based on the induced electromotive voltage generated inside the coil 127,227. In case the alternating current (I) runs through the conductor 110, a time-variant magnetic flux ψ forms around the conductor 110 in a concentric circle. This time-variant magnetic flux ψ is accommodated in the interior of the air-core coil formed in the inside of the centrally hollowed pipe 120,220 and the coil 127,227. According to the electromagnetic inductive law, the magnetic flux ψ results in an induced electromotive V_DET which is extended by a lead wire 123.

The Ampere's law is expressed as:

, which gives the relationship between an electric current (I) and a magnetic field (B) caused by the current (I) at a distance (r) , where μ is permeability. The integral of Eq. (1) along the periphery of the circle with a radius (r) results in

B=^ ....Eq.(2)

On the other hand, since the induced electromotive force corresponds to a voltage V_DEτ induced inside the air-core coil, the Faraday's law is expressed as:

, and a magnetic flux is given by its definition as follows : ψ= B.dA...Eq.(4) Combining the above Eqs.(l) through (4), it follows :

V_DEr= jB.dA=-₇l/^= /^d ...E_q,5)

Where p =μ _rμ _c, μ _r is a relative permeability, μ ₀ is a vacuum permeability (=4π xlO^-7) , and A is a cross section area vertical with the magnetic field.

Expression of Eq. (5) in terms of the alternating current would result in:

Accordingly, when the induced electromotive voltage V_DET induced by the coil 127,227 has been measured, the calculator 310 can compute the current (I) running through the conductor 110 by means of the Eq. (6) .

The calculator 310 computes the value of alternating current (I) of the conductor 110 by using the data such as μ _r, μ _{o r} r, and A stored in the memory 340. That is, a CPU 330 converts the induced electromotive voltage V_DET to a digital value by means of alternating/direct converter 320, uses the data stored in the memory 340, computes the value of alternating current (I), and displays the value on the display unit 350. The calculator 310 may also constitute an analog circuit as well as a digital circuit illustrated in FIG. 6. The alternating current measuring apparatus according to the present invention may operate as follows :

After the flexible measuring component 190 is bent around the live conductor to be measured 110 in a ring shape, the fixing means 131 is used for fastening the measuring component 190. When an induced electromotive voltage has been generated on the coil 127,227 by the time-variant magnetic flux inside the air-core coil, and the conductor 110 has come to the ring-shaped center, the calculator 310 computes the value of the alternating current (I) based on the electromotive voltage measured, and displays the value of the alternating current.

Embodiment 2

FIG. 7, which represents another embodiment of the alternating current measuring apparatus according to the present invention, is basically the same as the embodiment 1, except for a measuring component 720. The measuring component 720 comprises a plurality of magnetic flux nodes 724 with a coil 722 spooled around, which are connected together by couplings.

FIG. 8 illustrates the composition of the magnetic flux nodes 724. The magnetic flux nodes 724 comprises a bobbin 723 which is made of an insulating material and is centrally hollowed in shape, and the coil 722 spooled on the surface of the periphery of the bobbin 723.

A projected bump 723a is formed at both ends of the bobbin 723. The projected bumps of the adjacent bobbin 723a are combined together by the coupling pin 726, which is a conductor, enabling a number of bobbins to be connected continuously in a ring shape. The coupling pin 726 combines together each face of the projected bump 723a formed on the adjacent bobbin 723, which results in the connection of each of the magnetic flux nodes. The bobbins 723 connected to each other this way are transformed flexibly, making a ring shape as a whole. It is desirable that coupling pin 726 is made of a highly elastic material so that adjacent projected bumps 723a may be tightly combined. When magnetic flux nodes 724 are additionally added or removed in this manner, the length of the measuring component 720 is appropriately adjusted, depending upon the size and shape of the conductor to be measured. The end of the coil 722 spooled around the bobbin 723 is connected with the projected bump 723a, which is a conductor, bobbins 723 are connected electrically with each other by the coupling pin 726. Continuously connected magnetic flux nodes in a ring shape forms the air-core coil as illustrated in embodiment 1. On the other hand, a shielding tape 725 is attached on the periphery of the magnetic flux node 724 with coils spooled around, minimizing the effects of electromagnetic disturbance externally originating from the outside on the coil 722. And as illustrated in FIG. 7, each end of the cover 716 is combined together by the fixing means 714. The coils 722 on the magnetic flux node 724 located at each end of the cover 716 are extended by the lead wire 123 and are connected to the calculator 310. Except for foregoing differences, embodiment 2 is basically the same as embodiment 1 in terms of technical principle, composition, operation and effects.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Since the alternating current measuring apparatus according to the present invention employs air-core coils, unlike the conventional current measuring apparatus employing iron core, it prevents saturation phenomenon caused by iron cores, making it possible to produce linear output, to measure the value of the current in a wide range, to ensure high precision in measurement. Minimization of externally originating electromagnetic effects also results in high precision in measurement .

Furthermore, the alternating current measuring apparatus according to the present invention enables the measurement of the electric current to be made easily without directly connecting electrically with the conductor to be measured, and makes it possible to adjust the size appropriately, tailored to a variety of shapes of the conductor to be measured.

Claims

I /We claim:

1. An alternating current measuring apparatus comprising: a centrally hollowed pipe which accommodates time- variant magnetic flux building up in a circular fashion around a conductor live with an alternating current to be measured; a coil which is supported by said centrally hollowed pipe, and inside which is generated an induced electromotive voltage caused by time-variant magnetic flux accommodated inside said centrally hollowed pipe; a cover which wraps up the outer surface of said coil to shield said coil and shuts off electromagnetic disturbance externally originating from the outside; a detachable fixing means for fastening each end of said cover; and a calculator for integrating the value of the induced electromotive voltage generated inside the coil so as to compute the alternating current running through the conductor to be measured.

2. The alternating current measuring apparatus as claimed in claim 1, wherein said centrally hollowed pipe is square or round in shape.

3. The alternating current measuring apparatus as claimed in claim 1, wherein said centrally hollowed pipe comprises a plurality of bobbins and coupling joints that structurally and electrically connect the bobbins.

4. The alternating current measuring apparatus as claimed in any one of claims 1 through 3, wherein said cover is made of flexible synthetic resin provided with metallic thin film inside therein.

5. The alternating current measuring apparatus as claimed in any one of claims 1 through 3, wherein said fixing means comprises a protrusion and a hole through which the protrusion is inserted.