JPH11135345A - Transformer for meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transformer for meter which can be manufactured easily and whose transformation ratio is highly accurate. SOLUTION: A transformer is provided with an iron core 1, which is wound by a low-voltage winding 2 and a high-voltage winding 3 that is formed of a plurality of coaxial cylindrical coils 3a connected with each other in series and an insulation sheet 4 for insulating them; and a container 6 which is grounded and contains an insulation medium 7 having a dielectric ratio smaller than the insulation sheet 4. A distance between the end of the insulation sheet 4 on the inside of the high-voltage winding 3, and the end of the coil 3a on the outside of the high-voltage winding 3, is set to be larger than that between the insulation sheet 4 on the outside of the high- voltage winding 3 and the end of the coil 3a on the outside of the high-voltage winding 3, so that the number of cylindrical coils can be reduced, so as to obtain the required winding time and the device be made compact because of smaller outer diameter of the high-voltage winding 3, and further the combination of the cylindrical coil 3a is made tight and the leakage of magnetic flux is suppressed. Therefore, accurate transformation ratio can be obtained and the transformer can be manufactured easily because of simple structure of the coil 3a, realizing down-sizing and low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instrument transformer for accurately converting a high voltage to a low voltage for connection to a measuring instrument or a relay.

[0002]

2. Description of the Related Art An instrument transformer is a special transformer that converts a high voltage of several kV to several hundred kV into a low voltage and operates a display meter and a relay. Since the voltage on the low voltage side is about 100 V and the winding ratio is large, the high voltage winding has a large number of turns by connecting a plurality of cylindrical windings in series. Since the load connected to the low voltage side is extremely small and the winding ratio is large, only the exciting current flows through the high voltage winding. Therefore, a thin-film copper wire having a thin-film insulation on the surface is closely adhered to the high-voltage winding to form a cylindrical coil. In addition, the cylindrical coils of the high-voltage winding are also placed close to the minimum insulation distance in order to improve the coupling between the coils.

[0003] Such a conventional instrument transformer will be described with reference to FIG. A low-voltage winding 2 is wound around an iron core 1 for passing a magnetic flux, and a high-voltage winding 3 composed of a plurality of coaxial cylindrical coils connected in series outside the core and an insulation for insulating each cylindrical coil of the high-voltage winding 3 from each other. A sheet 4 is wound, and a high-voltage shield 5 for reducing an electric field is provided outside the high-voltage winding 3. These are placed in an electrically grounded metal container 6, and an insulating medium 7 having a lower dielectric constant than the insulating sheet 4 is sealed in the metal container 6. 8 is a high-voltage lead, and 9 is a low-voltage lead.

[0004] When a surge voltage such as a lightning impulse is applied to such an instrument transformer, the inductance of the cylindrical coils is large, and the capacitance between the cylindrical coils is large. It is inversely proportional to the distribution. The capacitance between each cylindrical coil is proportional to the diameter and length of the coil,
It is inversely proportional to the distance between adjacent coils. In order to suppress the electric field of each cylindrical coil and insulate efficiently, it is best to design the electric potential difference and the distance between each cylindrical coil to be uniform. For that purpose, it is necessary to make the capacitance between each coil the same, and the diameter Dn and the length Ln of each cylindrical coil are Dn × Ln = Const. ... (1) As a result, the cross section of the envelope connecting the ends of the cylindrical coil (high-voltage winding) 3 satisfying the expression (1) often has a curved shape as shown in FIG. In this figure, 1 is an iron core, 2 is a low voltage winding, 3 is a high voltage winding, 5 is a high voltage shield,
6 is a metal container, 7 is an insulating medium.

A high-voltage shield 5 is provided outside the high-voltage winding 3, and a contact between the high-voltage winding 3 and the high-voltage shield 5 is a contact with an insulating sheet that insulates the high-voltage winding 3 and a device is insulated. Electrical triple point of contact with the insulating medium 7
Since the electric field was concentrated, it was easy to become a weak point on insulation.

[0006]

As described above, the number of turns of each cylindrical coil is proportional to the coil length because the cylindrical coils are closely wound, so the number of turns of the high-voltage winding is the sum of the lengths of the respective cylindrical coils. Becomes When the potential difference of each cylindrical coil is designed to be uniform in order to bring each cylindrical coil close to each other, the cross section of the high-voltage winding becomes a curved shape as shown in FIG. Increasing the number does not increase the number of turns much. Therefore, when the voltage is increased and the number of turns of the high-voltage winding is increased, the number of cylindrical coils is increased, and the diameter of the high-voltage coil is greatly increased, so that the instrument transformer is enlarged. In addition, the increase in the number of cylindrical coils deteriorates the coupling with the low-voltage winding, and increases the error in the measured voltage.

Therefore, if the length of the cylindrical coil is increased in order to reduce the number of cylindrical coils, the length of the iron core also increases, and the transformer for the instrument becomes large. Further, since the width of the cylindrical coil is not constant and the rate of decrease thereof is not constant, the manufacturing process is complicated, and the number of steps for inspection and quality assurance is increased.

Therefore, the number of turns of the cylindrical coil can be increased by increasing the length of the cylindrical coil. To facilitate manufacture and inspection, the length of the cylindrical coil must be kept constant or the rate of decrease in length must be kept constant. do it. However, since the length of the cylindrical coil no longer satisfies the expression (1), the electric potential difference between the cylindrical coils is not constant, and the electric field becomes larger for the inner cylindrical coil.

Further, the contact between the high-voltage shield and the insulating sheet becomes an electrical triple point composed of the two and the insulating medium.
In particular, if the angle between the high-voltage shield and the insulating sheet is acute, this is a weak point in insulation. Therefore, it was necessary to cut the insulating sheet so that the insulating sheet and the high-voltage shield contacted at right angles. In addition, in order to reduce the electric field in the weak point, it is necessary to increase the size of the high-voltage coil to lower the electric field. However, there is a problem that the device becomes large and expensive.

The present invention (corresponding to claims 1 to 7) provides
The present invention has been made in view of the above circumstances, and an object thereof is to provide a transformer for an instrument which is easy to manufacture and can obtain a high-accuracy transformation ratio.

[0011]

In order to achieve the above object, a first aspect of the present invention is to provide an iron core for passing a magnetic flux, a high voltage winding comprising a plurality of coaxial cylindrical coils connected in series, An insulating sheet that insulates each of the cylindrical coils of the high-voltage winding from each other, a low-voltage winding that interlinks with the magnetic flux generated by the high-voltage winding, and an insulating medium having a dielectric constant smaller than the insulating sheet surrounding each of the windings. An instrument transformer comprising each of the windings and a grounded container for accommodating the insulating medium, wherein a distance between an insulating sheet end inside the high-voltage winding and a coil end inside the high-voltage winding is determined by the high-voltage winding The distance between the outer insulating sheet and the coil end on the outer side of the high-voltage winding is longer.

According to a second aspect of the present invention, in the instrument transformer according to the first aspect, a cross section of an envelope connecting the tips of the high-voltage windings is trapezoidal. Claim 3 of the present invention
The instrument transformer according to claim 1, wherein the cross section of the envelope connecting the tips of the high-voltage windings has a drum-like shape with a bulging center.

According to a fourth aspect of the present invention, there is provided an iron sheet for passing a magnetic flux, a high voltage winding composed of a plurality of coaxial cylindrical coils connected in series, and an insulating sheet for insulating the cylindrical coils of the high voltage winding from each other. A low-voltage winding interlinking with a magnetic flux generated by the high-voltage winding; an insulating medium surrounding each of the windings and having a dielectric constant smaller than that of the insulating sheet; and a grounding for accommodating the windings and the insulating medium. In the instrument transformer comprising a container, the distance between the insulating sheet end inside the high-voltage winding and the coil end inside the high-voltage winding is set to the distance between the insulating sheet outside the high-voltage winding and the coil end outside the high-voltage winding. It is characterized by being shorter than the distance.

A fifth aspect of the present invention is the instrument transformer according to the first aspect, wherein at least two or more cylindrical coils from the outermost cylindrical coil have the same axial length.

According to a sixth aspect of the present invention, in the instrument transformer according to the first or fourth aspect, at least two or more cylindrical coils from the innermost cylindrical coil have the same axial length. And

According to a seventh aspect of the present invention, there is provided an iron sheet for passing a magnetic flux, a high voltage winding composed of a plurality of coaxial cylindrical coils connected in series, and an insulating sheet for insulating the cylindrical coils of the high voltage winding from each other. A low-voltage winding interlinking with a magnetic flux generated by the high-voltage winding; an insulating medium surrounding each of the windings and having a dielectric constant smaller than that of the insulating sheet; and a grounding for accommodating the windings and the insulating medium. In the instrument transformer comprising a container, the dielectric constant of the insulating sheet between the cylindrical coils is changed.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a first embodiment (corresponding to claim 1) of the present invention. As shown in the figure, the instrument transformer of the present embodiment has a low voltage winding 2 on an iron core 1 for passing magnetic flux.
And a high-voltage winding 3 composed of a plurality of coaxial cylindrical coils 3a connected in series outside thereof, and an insulating sheet 4 for insulating each of the cylindrical coils 3a of the high-voltage winding 3 from each other. High voltage shield 5 to alleviate the electric field
Is provided. These are placed in an electrically grounded metal container 6, and an insulating medium 7 having a lower dielectric constant than the insulating sheet 4 is sealed in the metal container 6. 8 is a high voltage lead. Examples of the combination of the insulating sheet 4 and the insulating medium 7 include a combination of a polyester sheet and SF ₆ gas.

The cylindrical coils 3a are provided as close as possible to improve the coupling.
Are all the same, the outer cylindrical coil has a larger opposing surface area and a larger capacitance. Each cylindrical coil 3
Since the voltage sharing between a and c is inversely proportional to the capacitance, the inner cylindrical coil has a larger potential difference with the adjacent cylindrical coil 3a. Since the length of the insulating sheet 4 is the same in the conventional technology,
The equipotential lines are denser inward as shown in FIG. 11, and are sharply bent at the end of the cylindrical coil, and the electric field at the end of the cylindrical coil 3a is high, so that efficient insulation could not be performed and the equipment was enlarged. .

In this embodiment, the length between the end of the insulating sheet 4 on the inside and the end of the cylindrical coil 3a is made longer than that on the outside as shown in FIG. As shown in FIG. 2, the potential line is pushed out toward the insulating medium 7, and the electric field at the end of the cylindrical coil 3a is reduced, so that efficient insulation is possible.

As a result, the length of the outer cylindrical coil 3a can be made longer than before, so that the number of turns of the outer cylindrical coil 3a is large and the required number of turns can be obtained with a small number of cylindrical coils. By reducing the number of the cylindrical coils 3a, the diameter of the high-voltage winding 3 can be reduced, which contributes to downsizing of the device, and the coupling between the cylindrical coils 3a is improved, so that the error of the transformation ratio due to the leakage magnetic flux can be reduced. .

FIG. 3 is a sectional view of a second embodiment (corresponding to claim 2) of the present invention. As shown in the figure, the instrument transformer of the present embodiment is wound so that the length of the cylindrical coil 3a becomes shorter toward the outside. However, since the decreasing rate is constant, the cross section of the high-voltage winding 3 is trapezoidal. It is. Such a configuration is easy to manufacture and hard to make mistakes. The slope of the envelope connecting the ends of the insulating sheet 4 is greater than the inclination of the envelope 3b connecting the ends of the cylindrical coil 3a so that the distance from the end of each cylindrical coil 3a to the end of the insulating sheet 4 becomes longer toward the inner cylindrical coil 3a. I'm making it big.

Since the capacitance between the cylindrical coils 3a is proportional to the diameter and length of the cylindrical coil 3a, the voltage sharing of the cylindrical coil 3a is smallest at the center as shown in FIG.
The potential difference between the end cylindrical coils increases. Also, as in the first embodiment of FIG. 1, by making the insulating sheet 4 between the inner cylindrical coils longer than the other insulating sheets 4, the equipotential lines 10 when the lightning impulse voltage is applied are shown in FIG. As shown in (1), it can be extruded into the insulating medium 7 to prevent dielectric breakdown from the end of the cylindrical coil 3a. 9 is a low voltage lead.

According to this embodiment, the sum of the lengths of the cylindrical coils 3a can be made larger than in the conventional transformer for an instrument, and the high-voltage winding 3 is wound many times, so that the number of cylindrical coils 3a is reduced. be able to. Accordingly, the diameter of the high-voltage winding 3 can be reduced, which contributes to downsizing of the device, and the coupling between the cylindrical coils 3a is improved, so that the error in the transformation ratio due to the leakage magnetic flux can be reduced.

FIG. 5 is a sectional view of a third embodiment (corresponding to claim 3) of the present invention. As shown in the figure, in the instrument transformer of the present embodiment, the high-voltage winding 3 is sequentially longer from the inner cylindrical coil 3c to the central cylindrical coil 3d, and extends from the central cylindrical coil 3d to the outer cylindrical coil 3e. It is wound so that it becomes shorter sequentially. Therefore, the central cylindrical coil 3d
Is the longest. That is, each cylindrical coil is wound so that the cross section of the envelope connecting the tips of the high-voltage windings 3 has a drum shape with the center swelling. In addition, the center longest cylindrical coil 3d
Sheet 4 insulating the inner cylindrical coil 3c from the
Are all equal, and the length from the end of the cylindrical coil 3a to the end of the insulating sheet 4 is longer toward the inside.

In this embodiment, as shown in FIG. 13, the capacitance of the central cylindrical coil 3d is the largest, and the potential of the inner cylindrical coil 3c is large. The equipotential lines concentrate near the inner cylindrical coil 3c, but the inner cylindrical coil 3c
Since the intermediate cylindrical coil 3d is longer than the intermediate cylindrical coil 3d, it is bent so as to bypass the end of the intermediate cylindrical coil 3d, so that a gentle curve is drawn at the end of the inner cylindrical coil 3c.
The electric field at the c-edge is reduced. Furthermore, since the length from the end of the cylindrical coil 3c to the end of the insulating sheet 4 is longer inside,
The equipotential lines near the end of the inner cylindrical coil 3c are pushed out to the insulating medium 7, and the electric field at the end of the inner cylindrical coil 3c is further alleviated.

In the conventional instrument transformer, the length of the cylindrical coil 3a was gradually increased toward the innermost cylindrical coil in order to improve the potential distribution between the cylindrical coils 3a. Since the number of turns of the wire 3 is the sum of the lengths of the cylindrical coils 3a, a large number of cylindrical coils 3a were required to obtain a predetermined number of turns.

However, according to the present embodiment, the cylindrical coil 3
Since the average length of “a” becomes longer, the total number of cylindrical coils 3a decreases, which can contribute to downsizing of the device. Further, since the coupling between the cylindrical coils 3a is improved, the error in the transformation ratio due to the leakage magnetic flux can be reduced.

FIG. 6 is a sectional view of a fourth embodiment (corresponding to claim 4) of the present invention. As shown in the figure, in the instrument transformer of the present embodiment, a cylindrical coil 3 a
Is shortened from the inside to the outside so that the rate of decrease in length is greater than the rate of increase in diameter. The insulating sheets 4 that insulate the cylindrical coils 3a are all the same length, and the length from the end of the cylindrical coil 3a to the end of the insulating sheet 4 is longer as the outer cylindrical coil 3a is longer.

The capacitance between the cylindrical coils 3a is proportional to the diameter and the length. In this embodiment, the effect of the decrease in the length is greater than the effect of the increase in the diameter. That is, the capacitance between the inner cylindrical coils 3a is larger than the capacitance between the outer cylindrical coils 3a. Since the voltage sharing between the cylindrical coils 3a is inversely proportional to the capacitance, the potential difference between the outer cylindrical coils 3a is larger. Since the outer cylindrical coil 3a has a longer length between the end of each cylindrical coil 3a and the end of the insulating sheet 4, the equipotential lines are pushed out to the insulating medium 7 toward the outer cylindrical coil so that the end of the cylindrical coil 3a ends. , The electric field at the end of each cylindrical coil 3a becomes uniform.

The number of turns of the high-voltage winding 3 is determined by each cylindrical coil 3.
Although it is proportional to the sum of the lengths of a, the present embodiment can make the average length of the cylindrical coil longer than that of the conventional instrument transformer.
The number of cylindrical coils 3a for obtaining the required number of turns can be reduced, which contributes to the outer diameter of the high-voltage winding 3 and downsizing of the equipment. Can be smaller.

FIG. 7 is a sectional view of a fifth embodiment (corresponding to claim 5) of the present invention. As shown in the figure, in the instrument transformer of the present embodiment, a cylindrical coil 3 a
Are made shorter in order from the inside to the outside, but at least two cylindrical coils 3a from the outermost have the same length. The length of the insulating sheet 4 is at least the same as that of the two layers from the outside, and the length of the insulating sheet 4 is longer toward the inside.

Since the capacitance between the cylindrical coils 3a is proportional to the length and the diameter of the cylindrical coils 3a, the larger the diameter, the larger the capacitance when the length is the same. Since the voltage distribution between the cylindrical coils 3a is inversely proportional to the capacitance between the cylindrical coils 3a, the potential difference between the adjacent cylindrical coils 3a increases as the inner cylindrical coil 3a has a smaller capacitance.

In this embodiment, since the capacitance between the outermost cylindrical coils 3a is made larger than the capacitance between the other cylindrical coils 3a, the equipotential lines passing through the high-voltage winding 3 are located inside. The electric field near the insulating sheet 4 that is in contact with the high-voltage shield 5 becomes smaller. For this reason, even if the electrical triple point 11 formed by the high voltage shield 5, the insulating sheet 4 and the insulating medium 7 has a sharp wedge gap, the dielectric breakdown does not occur. The length of the iron core can be reduced because the size can be reduced to near. In addition, the size of the high-voltage winding 3 can be reduced to a size determined by the electric field at the end of each cylindrical coil 3a. Furthermore, since the length of the outermost cylindrical coil 3a can be increased, the number of turns can be increased, the number of cylindrical coils 3a can be reduced, and the error in the transformation ratio can be reduced.

FIG. 8 is a sectional view of a sixth embodiment (corresponding to claim 6) of the present invention. As shown in the figure, in the instrument transformer of the present embodiment, a cylindrical coil 3 a
Are made shorter in order from the inside to the outside, but at least two cylindrical coils 3a from the innermost have the same length. The insulating sheet 4 is sequentially longer from the outside to the inside, and if the length of the cylindrical coil 3a is the same, the cylindrical coil 3a
The length from the end of the insulating sheet 4 to the end of the insulating sheet 4 is longer as the inner cylindrical coil 3a is longer.

Since the capacitance between the cylindrical coils 3a is proportional to the length and the diameter of the cylindrical coils 3a, the larger the diameter, the larger the capacitance when the length is the same. The voltage distribution between the cylindrical coils 3a is inversely proportional to the capacitance between the cylindrical coils 3a.

In this embodiment, since the inner cylindrical coil 3a has the same length, the capacitance of the inner cylindrical coil 3a is small and the potential difference is large, but the distance between the end of the cylindrical coil 3a and the end of the insulating sheet 4 is large. Since the length is longer toward the inner side, the inner equipotential line is pushed out toward the insulating medium 7 and the electric field at the end of the inner cylindrical coil 3a does not increase. Since the lengths of at least two inner cylindrical coils 3a from the inside are the same, the cylindrical coils 3a
If the reduction rate of the length a is the same, the length of the cylindrical coil 3a other than the innermost is longer by at least one step, and the number of turns is several times longer than that of the cylindrical coil for one step.

The number of turns of the high-voltage winding 3 is proportional to the sum of the lengths of the cylindrical coils 3a. However, in the present embodiment, the required length is increased because the average length of the cylindrical coil 3a can be longer than that of the conventional transformer for an instrument. The number of cylindrical coils 3a for obtaining the number of times can be reduced,
This contributes to the reduction of the outer diameter of the high-voltage winding 3 and the size of the device, and the coupling between the cylindrical coils 3a is improved, so that the error in the transformation ratio due to the leakage magnetic flux can be reduced. Further, to obtain the same number of turns, the length of each cylindrical coil can be shortened, the length of the entire device can be reduced, and the cost can be reduced.

FIG. 9 is a sectional view of a seventh embodiment (corresponding to claim 7) of the present invention. As shown in the figure, in the instrument transformer of this embodiment, the high-voltage winding 3 is configured by connecting a number of cylindrical coils 3a having the same length in series. The insulating sheets 4 that insulate the respective cylindrical coils 3a have the same length, but the dielectric constant 4b of the inner insulating sheet 4 is larger than the dielectric constant 4c of the outer insulating sheet 4. Examples of the combination of the insulating sheets 4 include a combination of low dielectric constant kraft paper as the inner insulating sheet, a polyester film as the outer insulating sheet, and SF ₆ as the insulating medium 7. The length of the insulating sheet 4 may be increased toward the inside or toward the point where the dielectric constant is changed.

The capacitance between the cylindrical coils 3a connected in series is proportional to the length and diameter of the cylindrical coils, but also proportional to the dielectric constant of the insulating sheet 4 provided between the cylindrical coils 3a. Since the dielectric constant of the insulating sheet 4 is different between the inside and the outside, it is possible to make the capacitance between the inner cylindrical coils 3a closer to the capacitance between the outer cylindrical coils 3a even if the length of the cylindrical coils 3a is the same. As a result, the potential sharing in each of the cylindrical coils 3a becomes uniform, and insulation is achieved efficiently.

The number of turns of the high-voltage winding 3 is represented by the sum of the lengths of the cylindrical coils 3a. In this embodiment, since the average length of the cylindrical coil 3a can be made longer than that of the conventional instrument transformer, the required number of turns is large. The number of cylindrical coils for obtaining the number of times can be reduced, which contributes to the reduction of the outer diameter of the high-voltage winding 3 and the size of the equipment, and the coupling between the cylindrical coils 3a is improved, so that the error of the transformation ratio due to the leakage magnetic flux is reduced. Can be.

[0041]

As described above, the present invention (Claim 1)
Since the length of the cylindrical coil constituting the high-voltage winding can be increased without breaking the efficient insulating structure, the number of cylindrical coils that can obtain the required number of turns can be reduced. This contributes to the miniaturization of equipment by reducing the outer diameter of the high-voltage winding, and the coupling between the cylindrical coils is large,
Leakage magnetic flux is reduced, and a highly accurate transformation ratio can be obtained. Therefore, since the configuration of the cylindrical coil is simple, the manufacture is easy, and the size and cost of the device are reduced.

Further, in the instrument transformer according to the present invention (corresponding to claim 5), the electric triple point electric field formed by the high voltage shield, the insulating sheet and the insulating medium is alleviated, so that the insulating weak point is eliminated. In addition, the insulation is emphasized, and there is no need to provide an unnecessary insulation margin, and the size and cost of the device are reduced.

The instrument transformer according to the present invention (corresponding to claim 6) has a high-voltage winding composed of a plurality of cylindrical coils connected in series and an insulating sheet for insulating the cylindrical coils from each other. In an instrument transformer having a non-uniform surface area, an insulating sheet between cylindrical coils having a large potential difference is used as an insulating sheet having a large dielectric constant, so that the capacitance between the cylindrical coils increases, and a voltage shared between the cylindrical coils is increased. And the electric field is suppressed. As a result, the device becomes smaller and less expensive.

Further, in the transformer for an instrument according to the present invention (corresponding to claim 7), the capacitance between the cylindrical coils is controlled by suppressing the dielectric constant of an insulating sheet for insulating each cylindrical coil. Since the electric field at the end is reduced, the size and cost of the device are reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a view showing equipotential lines when a lightning impulse voltage is applied to the instrument transformer of FIG. 1;

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is a view showing equipotential lines when a lightning impulse voltage is applied to the instrument transformer of FIG. 3;

FIG. 5 is a sectional view of a third embodiment of the present invention.

FIG. 6 is a sectional view of a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a fifth embodiment of the present invention.

FIG. 8 is a sectional view of a sixth embodiment of the present invention.

FIG. 9 is a sectional view of a seventh embodiment of the present invention.

FIG. 10 is a cross-sectional view of a conventional instrument transformer.

FIG. 11 is a diagram showing equipotential lines when a lightning impulse voltage is applied to a conventional instrument transformer.

FIG. 12 is a cross-sectional view of a theoretical cylindrical coil configuration of an instrument transformer.

FIG. 13 is a characteristic diagram showing an example of a capacitance and a potential difference between each cylindrical coil of the instrument transformer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Iron core, 2 ... Low voltage winding, 3 ... High voltage winding, 3a ... Cylindrical coil, 3b ... Envelope connecting the tip of a cylindrical coil, 3c ... Inner cylindrical coil, 3d ... Central cylindrical coil, 3e ... Outer Cylindrical coil, 4 ... insulating sheet, 4a ... Envelope connecting the tip of the insulating sheet, 4b ... High dielectric constant insulating sheet, 4c ... Low dielectric constant insulating sheet, 5 ... High voltage shield, 6 ... Metal container, 7
... insulating medium, 8 ... high voltage lead, 9 ... low voltage lead, 10 ...
Equipotential lines, 11 ... electrical triple point.

Claims (7)

[Claims] 1. An iron core for passing a magnetic flux, a high voltage winding composed of a plurality of coaxial cylindrical coils connected in series, an insulating sheet for insulating the cylindrical coils of the high voltage winding from each other, and the high voltage winding A low-voltage winding interlinking with the magnetic flux generated by the winding, an insulating medium having a dielectric constant smaller than that of the insulating sheet surrounding each winding, and a grounded container containing the windings and the insulating medium. In the transformer, the distance between the insulating sheet end inside the high-voltage winding and the coil end inside the high-voltage winding is longer than the distance between the insulating sheet outside the high-voltage winding and the coil end outside the high-voltage winding. Instrument transformer. 2. The instrument transformer according to claim 1, wherein
An instrument transformer characterized in that the cross section of an envelope connecting the ends of each high-voltage winding is trapezoidal. 3. The transformer for an instrument according to claim 1, wherein
An instrument transformer characterized in that an envelope connecting the ends of each high-voltage winding has a drum-like shape with a bulging center. 4. An iron core for passing a magnetic flux, a high voltage winding composed of a plurality of coaxial cylindrical coils connected in series, an insulating sheet for insulating the cylindrical coils of the high voltage winding from each other, and the high voltage winding A low-voltage winding interlinking the magnetic flux generated by the winding, an insulating medium surrounding the windings and having a dielectric constant smaller than that of the insulating sheet, and a grounded container containing the windings and the insulating medium. In the transformer, the distance between the insulating sheet end inside the high-voltage winding and the coil end inside the high-voltage winding is shorter than the distance between the insulating sheet outside the high-voltage winding and the coil end outside the high-voltage winding. Instrument transformer. 5. The transformer for an instrument according to claim 1, wherein
A transformer for an instrument, wherein at least two or more cylindrical coils from the outermost cylindrical coil have the same axial length. 6. The transformer for an instrument according to claim 1, wherein at least two or more cylindrical coils from the innermost cylindrical coil have the same axial length. . 7. An iron core for passing a magnetic flux, a high-voltage winding composed of a plurality of coaxial cylindrical coils connected in series, an insulating sheet for insulating the cylindrical coils of the high-voltage winding from each other, and the high-voltage winding A low-voltage winding interlinking the magnetic flux generated by the winding, an insulating medium surrounding the windings and having a dielectric constant smaller than that of the insulating sheet, and a grounded container containing the windings and the insulating medium. A transformer for an instrument, wherein a dielectric constant of an insulating sheet between the cylindrical coils is changed in a transformer.