JPH088186B2 - Current transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current transformer.

[Conventional technology]

Recently, a method of processing the output of a current transformer (CT) with an electronic circuit has also been developed for a power meter. The current normally used in this electronic circuit is about several mA. Therefore, in the current transformer, it is necessary to transform the current to about several mA and supply it to the electronic circuit, and the number of secondary turns tends to increase accordingly.

For example, if the measured current is on the order of several A, the number of turns of the secondary winding may be about 1000, but if it is on the order of several mA, it is necessary to wind the secondary winding more than 20000 times, and the number of turns is small. The advent of methods to increase the ratio is desired.

Conventionally, there are the following as such techniques.

First, in FIG. 11, 1 is a primary winding made of a rod-shaped conductor, 2 is a secondary winding, and a conductor forming the primary winding 1 has a shunt circuit having a resistance smaller than that of the conductor. 3 are connected in parallel.

As a result, in this device, a part of the current supplied to the primary winding 1 is made to flow in the shunt circuit 3, and the current made to flow in the primary winding 1 is reduced by that amount, and the transformation ratio is increased.

However, this one has the drawback that the phase angle is large due to the large inductance component of the conductor forming the primary winding 1, and that the temperature coefficient of resistance has a large influence.

Further, in FIG. 12, 4 is a primary core, 5 is a primary winding mounted on the primary core 4, 6 is a secondary core, and 7 is a secondary winding mounted on the secondary core 6. is there. The primary iron core 4 has a cylindrical shape, and a magnetic field is generated in the hollow portion by the primary iron core. The secondary iron core 6 has a rod shape,
It is inserted into the hollow portion of the primary core 4 so that the secondary winding 7 is arranged in the magnetic field of the primary winding 5.

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

As a result, this is intended to increase the transformation ratio by (1 / cos α) as compared with the case where the primary winding 5 and the secondary winding 7 are coaxially arranged.

However, this is
There is a problem that the secondary winding 7 must be fixed with the inclination angle being correct, which complicates the structure for fixing the secondary iron core 6 and the bobbin.

Although not shown, there is also a method of connecting a current transformer in a cascade to obtain a small secondary current, but in this case, the secondary current at the first break is large and cannot be compensated by an electronic circuit. There is a problem that the error becomes large, and it is desirable to obtain a large transformation ratio with one current transformer.

[Problems to be Solved by the Invention]

As described above, in the conventional current transformer, when obtaining a transformation ratio larger than the turns ratio, a stable transformation ratio cannot be obtained due to the phase angle, temperature coefficient, winding fixing structure, etc. There is.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a current transformer that can stably obtain a transformation ratio larger than the turns ratio. is there.

[Means for solving the problem]

In the current transformer of the present invention, an air gap is provided in the primary winding mounting portion of the iron core, and the effective area for interlinking the magnetic flux with the primary winding is smaller than the area of the secondary winding. It was inserted in the space like this.

[Action]

The amount of magnetic flux linked to the secondary winding is the magnetomotive force of the primary winding,
And the area ratio between the primary winding and the secondary winding.

According to the present invention, an air gap is provided in the primary winding mounting portion of the iron core, and the primary winding is inserted into this air gap so that the effective area for interlinking the magnetic flux with the secondary winding is Since it was mounted on the iron core so as to be smaller than the area, it is possible to obtain a transformation ratio larger than the turns ratio.

As described above, 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 that the influence of the inductance component is small and there is no problem of the temperature coefficient of resistance. Moreover, the primary winding can be easily fixed to the iron core by providing a spacer or the like in the gap,
In a stable state, a transformation ratio larger than the winding ratio can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view of a current transformer according to a first embodiment of the present invention,
2 is a sectional view taken along line II-II, and FIG. 3 is III-III.
It is sectional drawing which follows the line. In FIG. 3, U is a symbol indicating the direction of upward magnetic flux.

In these figures, 8 is an iron core made of an MT core, 11 is a primary winding 12 mounted on the iron core 8 and is a secondary winding.

The iron core 8 is composed of an M-shaped portion 9 and a T-shaped portion 10, and the M-shaped portion 9 and the T-shaped portion 10 project at their central portions and are opposed to each other as secondary winding mounting portions 13 and 14. There is. The secondary winding 12 is divided into half parts of the total number of turns around the secondary winding mounting parts 13 and 14 and wound around bobbins (not shown).

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

The primary winding 11 is composed of a single wire, which is passed through the wire insertion hole 17 of the spacer 16 and guided to the front portion of the spacer 16 from each end thereof so that the half portion of the spacer 16 is covered. It is composed by being wrapped.

As a result, the magnetic fluxes generated on one side and the other side of the gap 15 where the primary winding 11 passes are the opposite directions, and the difference (effective area) between the areas on each side of the gap 15 is two. The interlinkage magnetic flux of the next winding 12 is obtained, and a transformation ratio larger than the turn ratio is obtained.

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 VV of FIG. 4, and FIG.
It is sectional drawing which follows the VI-VI line of a figure. In FIG. 6, U
Is a symbol indicating upward and D is a symbol indicating downward, respectively.

In these drawings, the feature of the second embodiment lies in the structure of the primary winding 11 and the structure of the spacer 16 associated therewith.

That is, the primary winding 11 is composed of two winding portions 11A and 11B, and these winding portions 11A and 11B are wound around the spacer 16 so as to generate magnetic flux in opposite directions as shown in FIG. , The winding parts 11A and 11B cancel out the magnetic flux, so the effective area is
Equivalent to the area difference of B.

As a result, the magnetic flux that links the primary winding 11 to the secondary winding 12 becomes the difference between the magnetic fluxes generated by the winding portions 11A and 11B, and the winding ratio between the primary winding 11 and the secondary winding 12 is increased. It is possible to obtain a larger metamorphic ratio.

Two wire insertion holes 17A and 17B are provided in the spacer 16 so as to insert a part of each winding portion 11A and 11B, and the positions are shifted in the front-rear direction.

In the case of such a structure, as shown in FIG. 7, the spacer 16 is thick and the wire insertion holes 17A, 17
By shifting B in the front-back direction and at the same time shifting it in the thickness direction, high electrical insulation with the winding portions 11A11B is secured.

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

As shown in these figures, the present invention may use an iron core 18 made of a cut core. Numerals 19 and 20 are mounting parts for the secondary winding 12, and the secondary winding 12 is wound around the mounting part divided into half of the total number of turns.

The void 15 that serves as the primary winding mounting part is
It is provided between 19 and the secondary winding mounting portion 20, and the spacer 16 is inserted therein.

The spacer 16 has the same structure as that of the first embodiment, and the primary winding 11 is mounted on the 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 applied for a patent by the applicant of the present application (Japanese Patent Application No. 63-27).
No. 6950).

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

The inverting input terminal of the operational amplifier 25 is connected to one end of the secondary winding 24, and the non-inverting input terminal of the operational amplifier 25 is connected to the other end thereof.

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

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, and a load 29 is connected between these connection points and the ground.

Here, the impedance of the first feedback impedance 26 is Zf, the impedance of the second feedback impedance 12 is Zm, the impedance of the compensation impedance 13 is Zn,
When the secondary leakage impedance is Z21, the condition that the secondary induced voltage E of the current transformer 21 becomes zero is Zn / Zm = Z21 / Zf.

In order to satisfy this condition, each impedance Zn, Zm, Zf
By setting, the secondary induced voltage E can be made zero, the exciting current becomes zero, and the error can be compensated.

The secondary current passes from the above-mentioned one end of the secondary winding 24, the first impedance 26, the output terminal of the operational amplifier 25, the power supply terminal of the amplifier 25, the ground point thereof, and the load 29 to the secondary winding 24.
Reflux to the other end of. Thus, the burden 29 derives the measured quantity from its secondary current.

For this reason, in this compensation circuit, since the load 29 takes out the measured amount as a current, even if the secondary leakage impedance Z21 changes due to operating temperature conditions, even if the compensation voltage becomes excessive or insufficient, measurement is performed. The accuracy is not affected by this.

〔The invention's effect〕

As described above, according to the present invention, a void is provided in the primary winding mounting portion of the iron core, and the primary winding is inserted into this void, so that the effective area for linking the magnetic flux with the secondary winding is increased. Since the iron core was installed so that it was smaller than the area of the secondary winding, a transformation ratio larger than the turns ratio was obtained, and the transformation ratio was adjusted by adjusting the area ratio between the primary winding and the secondary winding. Since the structure is adjustable, the influence of the inductance component is small, there is no problem of the temperature coefficient of resistance, and the primary winding can be easily fixed to the iron core by providing a spacer etc. in the air gap, and in a stable state. This has an effect that a transformation ratio larger than the winding ratio can be obtained.

[Brief description of drawings]

1 is a front view of a current transformer according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is taken along line III-III of FIG. 4 is a front view of a current transformer according to a second embodiment of the present invention, FIG. 5 is a cross-sectional view taken along the line VV of FIG. 4, and FIG. 6 is VI of FIG. -A cross-sectional view along line VI,
FIG. 7 is a front view of a modification of the spacer when the primary winding of FIGS. 4 to 6 is used, FIG. 8 is a side view of the current transformer according to the third embodiment of the present invention, and FIG. Is a sectional view taken along the line IX-IX, FIG. 10 is a circuit diagram of a suitable error compensation circuit used in the current transformer of the present invention, FIG. 11 is an explanatory view of a conventional example using a shunt circuit, and FIG. FIG. 6 is an explanatory diagram of a conventional example using a structure in which a secondary winding is inclined and held with respect to a primary winding. 8 ... Iron core (MT core), 11 ... Primary winding, 11A, 11B ... Winding parts that generate mutually opposite magnetic flux, 12 ... Secondary winding, 15 ... Air gap, 16 ... Spacer, 17, 17A, 17B ... Wire insertion hole, 18 ... Iron core (cut core).

Claims (1)

[Claims] 1. An air gap is provided as the primary winding mounting portion of an iron core in which a primary winding and a secondary winding are mounted, and the primary winding links the magnetic flux to the secondary winding. A current transformer, characterized in that the current transformer is inserted into the air gap so that the effective area is smaller than the area of the secondary winding.