JPH02174104A - Current transformer - Google Patents

Abstract

PURPOSE:To obtain, in a stable state, a transformation ratio which is larger than a turn ratio by a method wherein a gap is formed in a primary-winding installation part of an iron core and a primary winding is inserted into this gap. CONSTITUTION:An amount of a magnetic flux interlinked with a secondary winding is dependent on a magnetomotive force of a primary winding and on an area ratio of the primary winding to the secondary winding. Then, a gap 15 is formed at a primary-winding installation part of an iron core 8; a primary winding 11 is inserted into the gap 15; the iron core is attached in such a way that an effective area in which its magnetic flux is interlinked with a secondary winding 12 is smaller than an area of the secondary winding 12. When an area ratio of the primary winding 11 to the secondary winding 12 is adjusted, a transformation ratio can be adjusted. Accordingly, an influence of an inductance component is small; a problem of a resistance temperature coefficient is not caused; when a spacer or the like is installed in the gap, the primary winding can be fixed easily to the iron core. Thereby, the transformation ratio which is larger than a turn ratio can be obtained in a stable state.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a current transformer.

[Conventional technology]

Recently, a type of wattmeter has been developed in which the output of a current transformer (CT) is processed by an electronic circuit. The current normally used in this electronic circuit is about several mA. Therefore, it is necessary to transform the current to about several mA in a current transformer and supply it to the electronic circuit, and the number of secondary turns tends to increase accordingly.

For example, if the n1 constant current is on the order of several A, the number of turns of the secondary winding may be around 1000 times, but if it is on the order of several mA, it is necessary to wind the secondary winding more than 20,000 times. There is a demand for a method to increase the metamorphic ratio.

Conventionally, there have been the following techniques as such.

First, in Fig. 11, 1 is a primary winding made of a rod-shaped conductor, 2 is a secondary winding, and the conductor making up the primary winding 1 is connected to a shunt circuit made of a conductor with a smaller resistance than this conductor. 3 are connected in parallel. This allows a part of the current supplied to the primary winding 1 to flow through the shunt circuit 3, thereby reducing the current flowing through the primary winding 1 by that much and increasing the transformation ratio. It's about making money.

However, this type has the disadvantage that the phase angle is large due to the large inductance component of the conductor constituting the primary winding 1, and the influence of the temperature coefficient of resistance is large.

Further, in FIG. 12, 4 is a primary core, 5 is a primary winding attached to this primary core 4, 6 is a secondary core, and 7 is a secondary winding attached to this secondary core 6. be. The primary core 4 has a cylindrical shape, and a magnetic field is generated by the primary core within its hollow portion. The secondary iron core 6 is rod-shaped,
The secondary winding 7 is inserted into the hollow portion of the primary core 4, thereby placing the secondary winding 7 within the magnetic field of the primary winding 5.

The secondary core 6 is held by the primary core 4 such that the axis of the secondary winding 7 forms an angle α with respect to the axis of the primary winding 5.

As a result, compared to the case where the primary winding 5 and the secondary winding 7 are arranged coaxially, this is (1/c).

The idea is to increase the metamorphic ratio by Sα).

However, in order to make accurate measurements, the secondary winding 7 must be fixed at an accurate angle of inclination, which makes the structure for fixing the secondary core 6 and bobbin complicated. There's a problem.

Although not shown, current transformers can be connected in cascade,
There is also a method of obtaining a small secondary current, but in this case, the secondary current of the - stage is large and cannot be compensated for by an electronic circuit, so there is a problem that the error becomes large, and a single current transformer is used to obtain a large secondary current. It is preferable to obtain metamorphic ratios.

[Problem to be solved by the invention]

As mentioned above, in conventional current transformers, in order to obtain a transformation ratio larger than the turns ratio, there is a problem that a stable transformation ratio cannot be obtained due to the phase angle, temperature coefficient, fixed structure of the windings, etc. There is.

The present invention has been made in view of the problems of the prior art, and its purpose is to provide a current transformer that can stably obtain a transformation ratio greater than the turns ratio. be.

[Means to solve the problem]

In the current transformer of the present invention, a gap is provided in the primary winding mounting portion of the iron core, and the effective area for linking the magnetic flux of the primary winding to the secondary winding is smaller than the area of the secondary winding. It was inserted into that gap.

[For production]

The amount of magnetic flux interlinking with the secondary winding depends on the magnetomotive force of the primary winding and the area ratio of the primary winding and the secondary winding.

According to the present invention, a gap is provided in the primary winding mounting portion of the iron core,
The primary winding is inserted into this gap, and the effective area for interlinking the magnetic flux with the secondary winding is smaller than the area of the secondary winding. Metamorphic ratio can be obtained.

In this way, the present invention has a structure in which the transformation ratio can be adjusted by adjusting the area ratio between the primary winding and the secondary winding, so the influence of the inductance component is small and there is no problem with the temperature coefficient of resistance. Moreover, by providing a spacer or the like in the gap, the primary winding can be easily fixed to the iron core, and a transformation ratio larger than the winding ratio can be obtained in a stable state [Example] The present invention will be described below. Examples will be described with reference to the drawings.

FIG. 1 is a front view of a current transformer according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■, and FIG. 3 is a cross-sectional view taken along the line ■-■. In addition, in FIG. 3, U is a symbol representing the direction of upward magnetic flux.

In these figures, 8 is an iron core made of MT cocoa, 11
The primary winding 12 attached to this iron core 8 is also a secondary winding.

The iron core 8 consists of an M-shaped part 9 and a T-shaped part 10, and the M-shaped part 9 and the T-shaped part 10 protrude at the center and the mutually opposing parts are used as secondary winding mounting parts 13 and 14. There is. The secondary winding 12 is divided into halves of the total number of windings and wound around these secondary winding mounting portions 13, 14 via bobbins (not shown).

The space between the secondary winding mounting part 13 and the secondary winding mounting part 14 is a mounting part for the primary winding 11, and this mounting part is constituted by a gap 15. A spacer 16 is inserted and fixed in this gap 15, and this spacer 16 is provided with a wire insertion hole 17 that penetrates from one side to the other side at the center in the front-rear direction.

The primary winding 11 consists of a wire which is passed through the wire insertion hole 17 of the spacer 16 and guided from each end to the front part of the spacer 16 to form a half part of the spacer 16. It is constructed by being wrapped around it.

As a result, all of the magnetic flux generated by the primary winding 11 interlinks with the secondary winding 12 in an ideal state, and the total area of the primary winding 11 becomes the effective area. is half smaller than the area of the secondary winding 12, so the transformation ratio is twice the turns ratio.

That is, the idea of this embodiment is to obtain a large transformation ratio by using a winding having a smaller area as the primary winding than the secondary winding.

Note that the spacer 16 may be integrated with the bobbin for the secondary winding 12.

FIG. 4 is a front view of a current transformer according to a second embodiment of the present invention, FIG. 5 is a sectional view taken along the line V-v in FIG. 4, and FIG. FIG.

In addition, in FIG. 6, U is an upward symbol, and D is a symbol representing a downward direction of magnetic flux, respectively.

In these figures, the feature of this second embodiment lies in the structure of the primary winding 11 and the structure of the spacer 16 accompanying this.

That is, the primary winding 11 consists of two winding parts 11A and 11B, and these winding parts 11A and IIB are wound around the spacer 16 so as to generate magnetic fluxes in mutually opposite directions, as shown in FIG. , this winding part 11
Since A and IIB cancel each other's magnetic flux, the effective area corresponds to the difference in area between the winding portions 11A and IIB.

As a result, the magnetic flux interlinking from the primary winding 11 to the secondary winding 12 becomes the difference between the magnetic fluxes generated by the winding parts 11A and IIB, and the winding ratio of the primary winding 11 and the secondary winding 12 is This means that a larger metamorphic ratio can be obtained.

The spacer 16 has two wire insertion holes 17A for inserting parts of each winding portion 11A and IIB.

17B is provided by shifting its position in the front-back direction.

In addition, when using such a structure, as shown in Fig. 7,
The spacer 16 is made thick, and the wire insertion hole 17A,
By shifting 17B in the front-rear direction and simultaneously in the thickness direction, high electrical insulation with the winding portion 11A11B is ensured.

FIG. 8 is a side view of a current transformer according to a third embodiment of the present invention, and FIG. 9 is a sectional view thereof taken along line IX-IX.

As shown in these figures, the present invention may use an iron core 18 made of a cut core. Reference numeral 19 and 20 are mounting portions for the secondary winding 12, and the secondary winding 12 is wound around this mounting portion in half of the total number of turns.

A gap 15 serving as a primary winding mounting portion is provided between the secondary winding mounting portion 19 and the secondary winding mounting portion 20, and a spacer 16 is inserted therein.

This spacer 16 has the same structure as that of the first embodiment, and the primary winding 11 is attached to this spacer 16 with the same structure as that of the first embodiment.

FIG. 10 shows an electronic circuit for compensating the output error of the current transformer of the present invention, which was developed by the inventor of the present invention and has been patented by the applicant of the present application (Japanese Patent Application No. 1983-
No. 276950).

In this figure, 21 is the current transformer of the present invention, 22 is its iron core, 23 is a primary winding, and 24 is a secondary winding.

One end of the secondary winding 24 is connected to an inverting input terminal of an operational amplifier 25, and the other end is connected to a non-inverting input terminal of the operational amplifier 25.

A first feedback impedance 26 is connected between the inverting input terminal and the output terminal of the operational amplifier 25.
A second feedback impedance 27 is connected between the non-inverting input terminal and the output terminal of.

A compensating impedance 28 is connected between the other end of the secondary winding 24 and the non-inverting input terminal of the operational amplifier 25,
A load 29 is connected between these connection points and earth.

Here, the impedance of the first feedback impedance 26 is Zr1, the impedance of the second feedback impedance 12 is Z11, the impedance of the compensation impedance 13 is Zn%, and the secondary leakage impedance is 221. The condition for the voltage E to become zero is Zn/Zta=Z21/Zf.

Each impedance Zn, Zm is adjusted to satisfy this condition.
, Zf', the secondary induced voltage E can be made zero, the excitation current becomes zero, and the error can be compensated for.

The secondary current flows from the one end of the secondary winding 24 to the first impedance 26, to the output terminal of the operational amplifier 25, to the output terminal of the operational amplifier 25.
Through the power supply terminal 5 and its ground point, the current flows back through the load 29 to the other end of the secondary winding 24 . Therefore, the burden is 29
obtains the measured quantity from its secondary current.

Therefore, in this compensation circuit, since the load 29 extracts the measured amount as a current, even if the compensation voltage is excessive or insufficient due to changes in the secondary leakage impedance z21 depending on the operating temperature conditions, the measurement The accuracy is not affected by this.

〔Effect of the invention〕

As explained above, according to the present invention, a gap is provided in the primary winding installation part of the iron core, and the primary winding is inserted into this gap, thereby increasing the effective area for interlinking the magnetic flux with the secondary winding. Since it is attached to the core so that the area is smaller than the area of the secondary winding, a transformation ratio larger than the turns ratio can be obtained, and the transformation ratio can be adjusted by adjusting the area ratio of the primary winding and the secondary winding. Since it has an adjustable structure, the influence of the inductance component is small, and there is no problem with the temperature coefficient of resistance.Furthermore, by providing a spacer etc. in the air gap, the primary winding can be easily fixed to the iron core, and it can be maintained in a stable state. The effect is that a transformation ratio larger than the winding ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front view of a current transformer according to the first embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. 4 is a front view of a current transformer according to the second embodiment of the present invention, FIG. 5 is a sectional view taken along line V-V in FIG. 4, and FIG. - A sectional view taken along the Vl line, FIG. 7 is a front view of a modification of the spacer when using the primary winding shown in FIGS. 4 to 6, and FIG. 8 is a current transformation according to the third embodiment of the present invention. 9 is a cross-sectional view taken along line IX-IX, FIG. 10 is a circuit diagram of a preferred error compensation circuit used in the current transformer of the present invention, and FIG. 11 is a conventional circuit diagram using a shunt circuit. An explanatory diagram of an example, FIG. 12 is an explanatory diagram of a conventional example using a structure in which the secondary winding is held at an angle with respect to the primary winding. 8... Iron core (MT cocoa, 11... Primary winding, 11
A, IIB...Winding portion that generates magnetic flux in mutually opposite directions, 12...Secondary winding, 15...Gap, 16...Spacer, 17.17A, 17B...Wire insertion Hole, 1
8... Iron core (cut core). 8 chickens and 10 illustrations

Claims (1)

[Claims] An air gap is provided as the primary winding mounting portion of the iron core to which the primary winding and the secondary winding are mounted, and the primary winding has an effective area that links the magnetic flux to the secondary winding. A current transformer, characterized in that the current transformer is inserted into the gap so that the area is smaller than the area of the next winding.