JP2013187215A - Capacitance potential divider - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance potential divider capable of suppressing a change in a division ratio due to temperature, improving reliability, and improving assemblability.SOLUTION: A high-voltage conductor and an intermediate electrode are formed of the same metallic material. A coefficient of linear expansion β[K] of the metallic material that forms the high-voltage conductor and the intermediate electrode in a first capacitor, and a temperature coefficient γ[K] being a rate in which capacitance changes with respect to temperature in a second capacitor satisfy the formula (A).

Description

  Embodiments described herein relate generally to a capacitive voltage divider.

  In a gas insulated switchgear, an instrument transformer is used to measure the voltage value of a high voltage conductor. As a voltage transformer, devices such as a capacitive voltage divider (capacitor-type voltage transformer (CVT)) are used in addition to a wound-type gas insulated voltage transformer (VT (Voltage Transformer)).

  The capacitive voltage divider divides a high voltage using a plurality of capacitors connected in series. (For example, refer to Patent Document 1).

  For example, in the capacity voltage divider, the first capacitor is formed between the high-voltage conductor and the intermediate electrode inside the conductive container filled with the insulating gas, and the electrostatic capacity is outside the conductive container. A large second capacitor is provided in series with the first capacitor. With this configuration, the capacity voltage divider is reduced in size and weight. The capacitive voltage divider as described above is used, for example, in amplifier-type instrument transformers (amplifier PD (Potential Device)) and optical application instrument transformers (optical PD).

JP 2004-128304 A

  However, in the capacitive voltage divider, the voltage division ratio may change as the temperature changes. For this reason, the reliability of the capacitive voltage divider may be reduced. Moreover, in order to overcome this, it is necessary to make the capacitive voltage divider a complicated structure, and assemblability may be reduced.

  Therefore, the problem to be solved by the present invention is to provide a capacitive voltage divider that suppresses changes in the voltage division ratio due to temperature, increases reliability, and is easy to assemble.

In the capacitive voltage divider of this embodiment, an insulating gas is sealed inside a grounded conductive container. A high voltage conductor is provided inside the conductive container. An intermediate electrode is provided inside the conductive container so as to form a first capacitor with the high voltage conductor. A second capacitor is provided outside the conductive container so that one end is connected to the intermediate electrode and the other end is connected to the ground potential. Here, the high voltage conductor and the intermediate electrode are formed of the same metal material. The linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high-voltage conductor and the intermediate electrode in the first capacitor, and the temperature coefficient that is the rate at which the capacitance changes with respect to the temperature in the second capacitor γ [K ⁻¹ ] satisfies the following formula (A).

  According to the present invention, it is possible to provide a capacitive voltage divider that suppresses changes in the voltage division ratio due to temperature, improves reliability, and is easy to assemble.

FIG. 1 is a cross-sectional view of the capacitive voltage divider according to the first embodiment viewed from the side. FIG. 2 is a cross-sectional view of the capacitive voltage divider according to the first embodiment viewed from the front. FIG. 3 is a circuit diagram of the capacitive voltage divider according to the first embodiment. FIG. 4 is a diagram illustrating the relationship between the capacitance of the second capacitor 42C and the temperature in the capacitive voltage divider according to the first embodiment. FIG. 5 is an equivalent circuit of the capacitive voltage divider according to the first embodiment. FIG. 6 is a diagram illustrating a phase angle error in the capacitive voltage divider according to the first embodiment. FIG. 7 is a cross-sectional view of the capacitive voltage divider according to the second embodiment viewed from the side.

  Embodiments will be described with reference to the drawings.

<First Embodiment>
[A] Configuration FIGS. 1, 2, and 3 are diagrams illustrating a capacitive voltage divider according to the first embodiment. Here, FIG. 1 is a sectional view of the capacitive voltage divider according to the first embodiment viewed from the side. FIG. 2 is a cross-sectional view of the capacitive voltage divider according to the first embodiment viewed from the front. FIG. 3 is a circuit diagram of the capacitive voltage divider according to the first embodiment.

  As shown in FIGS. 1 and 2, the capacitive voltage divider 1 includes a conductive container 11, a high voltage conductor 21, and an intermediate electrode 31. The capacitive voltage divider 1 is provided with a first capacitor 41C (main capacitor) including a high voltage conductor 21 and an intermediate electrode 31, and a second capacitor 42C (voltage dividing capacitor). As shown in FIG. 3, in the voltage divider 1, a first capacitor 41C and a second capacitor 42C are connected in series, and a high voltage is generated by the first capacitor 41C and the second capacitor 42C. The voltage V1 of the conductor 21 is output as the divided voltage V2.

  Below, each part which comprises the capacity | capacitance voltage divider 1 is demonstrated sequentially.

As shown in FIGS. 1 and 2, the conductive container 11 has a cylindrical shape. The conductive container 11 has therein a storage space extending in the axial direction (here, the horizontal direction), and an insulating gas is sealed in the storage space. As the insulating gas, for example, a gas such as SF ₆ is enclosed. The conductive container 11 is made of a conductive material such as metal and is grounded. The conductive container 11 includes a first container member 11A and a second container member 11B.

  As shown in FIG. 1, in the conductive container 11, each of the first container member 11 </ b> A and the second container member 11 </ b> B is a tubular body, and is aligned so that the central axes thereof coincide with each other in the axial direction. Yes. Each of the first container member 11A and the second container member 11B is provided so that the flanges 11Fa and 11Fb protrude outward at the ends. In each of the first container member 11A and the second container member 11B, the flanges 11Fa and 11Fb are opposed to each other, and the flanges 11Fa and 11Fb are connected to each other using a fastening member such as a bolt. . In addition, a ring-shaped flange 61 (insulating rod support member) is interposed between the pair of opposed flanges 11Fa and 11Fb. Here, the first container member 11A has a larger inner diameter than the ring-shaped flange 61, and the second container member 11B has the same inner diameter as the ring-shaped flange 61.

  As shown in FIGS. 1 and 2, the high voltage conductor 21 has a cylindrical shape. The high-voltage conductor 21 is a rod-shaped line conductor, and is disposed so as to extend in the axial direction of the conductive container 11 in the accommodating space of the conductive container 11. Here, the central axis of the high voltage conductor 21 is provided so as to coincide with the central axis of the conductive container 11. The high voltage conductor 21 is formed using a metal material.

  As shown in FIGS. 1 and 2, the intermediate electrode 31 has a cylindrical shape, and a flange 31 </ b> F is formed so as to protrude outward at an end portion in the axial direction. The intermediate electrode 31 is a tubular body, and is disposed so as to surround the high voltage conductor 21 in the accommodation space of the conductive container 11. Here, the central axis of the intermediate electrode 31 is provided so as to coincide with the central axis of the conductive container 11.

  As shown in FIGS. 1 to 3, the intermediate electrode 31 and the high voltage conductor 21 constitute a first capacitor 41 </ b> C. That is, the first capacitor 41 </ b> C is configured by using the intermediate electrode 31 and the high voltage conductor 21 as a pair of electrodes, and an insulating gas interposed between the intermediate electrode 31 and the high voltage conductor 21 as a dielectric.

  In the present embodiment, the intermediate electrode 31 is formed using the same metal material as that of the high voltage conductor 21.

  In the present embodiment, the intermediate electrode 31 is fixed in the accommodating space of the conductive container 11 by a plurality of insulating rods 51 as shown in FIGS. As shown in FIG. 1, the plurality of insulating rods 51 are rod-shaped bodies, and one end thereof is supported by a ring-shaped flange 61 so as to extend in the axial direction in the accommodation space of the conductive container 11. ing. And the flange 31F of the intermediate electrode 31 is being fixed to the some insulation rod 51 using fastening members, such as a volt | bolt, in the other edge part.

  In the present embodiment, the insulating rod 51 is formed using, for example, an epoxy resin filled with alumina.

  As shown in FIGS. 1 and 2, the second capacitor 42 </ b> C is installed outside the conductive container 11. One terminal of the second capacitor 42 </ b> C is electrically connected to the intermediate electrode 31 via the sealing terminal 91. The other terminal of the second capacitor 42C is electrically connected to the ground potential.

Although details will be described later, in the present embodiment, the second capacitor 42C has a temperature coefficient γ [K ⁻¹ ], which is a rate at which the capacitance changes with respect to temperature, in the high voltage conductor 21 and the intermediate electrode 31. ^Is substantially the same as the linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the material. Specifically, the linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high voltage conductor 21 and the intermediate electrode 31 and the temperature coefficient γ [K ⁻¹ ] of the second capacitor 42C are expressed by the following formula ( It is configured to satisfy the relationship of A)

  As the second capacitor 42C, for example, a plurality of mica capacitors using mica (mica) as a dielectric is installed.

  Further, in the present embodiment, each of the second capacitor 42 </ b> C and the sealing terminal 91 is accommodated in the accommodating space of the sealed container 71 disposed outside the conductive container 11. And in the accommodation space of the airtight container 71, the desiccant 81 which absorbs a water | moisture content is further accommodated. For example, silica gel is used as the desiccant 81.

[B] Summary As described above, the capacitive voltage divider 1 of the present embodiment includes the linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high-voltage conductor 21 and the intermediate electrode 31, and the second capacitor 42C. The temperature coefficient γ [K ⁻¹ ] is substantially the same and satisfies the relationship of the above-described formula (A). For this reason, this embodiment can suppress the change of the partial pressure ratio by temperature, and can improve reliability.

  Hereinafter, the reason why the change in the partial pressure ratio due to temperature can be suppressed in the present embodiment will be described.

  In the capacitive voltage divider 1, the relationship of the formula (1) is established between the voltage V1 of the high voltage conductor 21 and the divided voltage V2 (see FIGS. 1 and 3). Here, C1 is the capacitance of the first capacitor 41C, and C2 is the capacitance of the second capacitor 42C. When the capacitance C1 of the first capacitor 41C is small enough to be negligible with respect to the capacitance C2 of the second capacitor 42C (C1 << C2), it can be approximated to the equation (1a). .

  The capacitance C1 of the first capacitor 41C is expressed by the following equation (2) when the temperature difference Δt [K] changed from the reference temperature is taken into consideration.

Each parameter in the above formula is as follows (hereinafter the same).
ε: dielectric constant of insulating gas a: radius [m] of high-voltage conductor 21 (see FIG. 1)
b: Radius [m] of the intermediate electrode 31 (see FIG. 1)
L: Length in the axial direction [m] of the intermediate electrode 31 (see FIG. 1)
α: Linear expansion coefficient [K ⁻¹ ] of the material constituting the high voltage conductor 21
β: linear expansion coefficient [K ⁻¹ ] of the material constituting the intermediate electrode 31
a ₀ : radius [m] of the high-voltage conductor 21 at the reference temperature
b ₀ : radius [m] of the intermediate electrode 31 at the reference temperature
L ₀ : length in the axial direction of the intermediate electrode 31 at the reference temperature [m]
Δt: Temperature difference from the reference temperature [K]

In the present embodiment, the high voltage conductor 21 and the intermediate electrode 31 are formed of the same metal material, and the linear expansion coefficients of the high voltage conductor 21 and the intermediate electrode 31 are equal. For this reason. Since α = β holds, the equation (2) becomes the following equation (2a). As can be seen, the temperature characteristic of the capacitance C1 of the first capacitor 41C is determined by the linear expansion coefficient β of the metal material constituting the high voltage conductor 21 and the intermediate electrode 31. When the metal material is aluminum, β = 23.1 × 10 ⁻⁶ [K ⁻¹ ], and when the metal material is copper, β = 16.5 × 10 ⁻⁶ [K ⁻¹ ] (Science Chronology) (Quoted from).

  On the other hand, the capacitance C2 of the second capacitor 42C (mica capacitor) is expressed by the following equation (3).

Each factor in the above formula is shown as follows.
C2 ₀ : Capacitance at reference temperature γ: Temperature coefficient of second capacitor 42C (mica capacitor) (rate at which capacitance changes with temperature)

  For this reason, the voltage division ratio V2 / V1 is represented by the following formula (4) from the above formulas (1a), (2a), and (3).

  Since the relationship 1 / (1 + x) ≈1-x is established when x << 1, the following equation (4a) is derived.

Therefore, as can be seen from the above relationship, the linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high voltage conductor 21 and the intermediate electrode 31 and the temperature coefficient γ [K ⁻¹ ] of the second capacitor 42C. Are substantially the same, the temperature change of the partial pressure ratio is small. That is, the voltage dividing ratio (V2 / V1) changes as the capacitance of the first capacitor 41C changes as the temperature changes, and the capacitance of the second capacitor 42C also changes as the temperature changes. Can be suppressed by changing.

As described above, the linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high-voltage conductor 21 and the intermediate electrode 31 and the temperature coefficient γ [K ⁻¹ ] of the second capacitor 42C are expressed by the following equations: It is preferable to satisfy the relationship (A). Since the voltage error specified in the capacitive voltage divider is 1% (0.01), it is sufficient to allow an error due to a temperature change up to 1/20 (0.01 ÷ 20 = 0.005). It is believed that there is. It can be assumed that the temperature changes from the reference temperature to about 50K. For this reason, it is preferable that the difference value between β and γ is less than 10 ⁻⁵ (0.005 ÷ 50 = 10 ⁻⁵ ) as in the following equation.

  FIG. 4 is a diagram illustrating the relationship between the capacitance of the second capacitor 42C and the temperature in the capacitive voltage divider according to the first embodiment. In FIG. 4, the vertical axis represents the rate of change H (%) of the capacitance, and shows the ratio when the capacitance at the reference temperature (20 ° C.) is used as a reference. The horizontal axis is the temperature T (° C.). Here, the measured value is shown when the second capacitor 42C is a mica capacitor.

As shown in FIG. 4, when the second capacitor 42C is a mica capacitor, the temperature coefficient γ is 18.7 × 10 ⁻⁶ [K ⁻¹ ]. The linear expansion coefficient β of the metal material constituting the high voltage conductor 21 and the intermediate electrode 31 is β = 23.1 × 10 ⁻⁶ [1 / k] when the metal material is aluminum. Therefore, the difference value between β and γ is 4.4 × 10 ⁻⁶ [K ⁻¹ ].

  Therefore, the temperature change of the partial pressure ratio can be sufficiently reduced to satisfy the above-described formula (A).

  In the present embodiment, the second capacitor 42 </ b> C is housed in the housing space of the sealed container 71 disposed outside the conductive container 11. A desiccant 81 is accommodated in the accommodating space of the sealed container 71. Therefore, in this embodiment, the phase angle error can be reduced.

  The reason why the phase angle error can be reduced in the present embodiment will be described below.

  The influence of the phase difference (phase angle error) between the voltage V1 applied to the high voltage conductor 21 and the divided voltage V2 is expressed by the following equation (5). Each factor in this equation is as follows, and the angular frequency ω is expressed by the following equation (6).

R2: insulation resistance value of the second capacitor 42C ω: angular frequency f: frequency

  FIG. 5 is an equivalent circuit of the capacitive voltage divider according to the first embodiment. As shown in FIG. 5, the insulation resistance value R2 of the second capacitor 42C is added to the circuit diagram of FIG. The insulation resistance value R1 (not shown) of the first capacitor 41C is not affected because it is in the insulating gas, and can be omitted in the equivalent circuit.

  FIG. 6 is a diagram illustrating a phase angle error in the capacitive voltage divider according to the first embodiment. In FIG. 6, the vertical axis represents the phase difference error, and the horizontal axis represents the insulation resistance value R2 of the second capacitor 42C (mica capacitor). Here, the results in the case of the voltage division ratio (V2 / V1) = 1/2500, C1 = 20 pF, C2 = 50000 pF, and f = 50 Hz are shown by a thick solid line. FIG. 6 also shows the upper limit value of the phase angle error for each class defined by IEC, JIS, and JEC.

  As shown in FIG. 6, when the insulation resistance value R2 of the second capacitor 42C decreases, the phase angle error increases. The insulation resistance value R2 of the second capacitor 42C rapidly decreases due to moisture and dust, so that the phase angle error increases.

  However, in the present embodiment, since the second capacitor 42C is accommodated in the accommodating space of the sealed container 71, the sealed container 71 can prevent dust from entering the second capacitor 42C from the surroundings. Further, since the desiccant 81 is accommodated in the accommodation space of the sealed container 71, the desiccant 81 can absorb moisture from the second capacitor 42C. Therefore, in this embodiment, the occurrence of a phase angle error can be suppressed and reliability can be ensured over a long period of time.

  In this embodiment, the insulating rod 51 is attached to the ring-shaped flange 61 (insulating rod support member) so as to be parallel to the axial direction of the high-voltage conductor 21. For this reason, outside the conductive container 11, after the insulating rod 51 is assembled to the ring-shaped flange 61 with high accuracy, the insulating rod 51 can be inserted into the conductive container 11 and fixed to the flange 61. Therefore, attachment work can be facilitated.

Further, in this embodiment, the insulating rod 51 is formed using an alumina-filled epoxy resin. For this reason, reliability can be improved. The reason for this will be described. When SF ₆ gas having excellent insulating properties is used as the insulating gas, for example, when an electrical short circuit occurs between the grounded conductive container 11 and the high voltage conductor 21, a corrosive gas such as HF is used as a decomposition gas. Will occur. However, epoxy resin filled with alumina is less likely to be corroded by corrosive gas than other materials. Therefore, as described above, this embodiment can be used for a long time and can improve reliability.

Second Embodiment
[A] Configuration FIG. 7 is a cross-sectional view of a capacitive voltage divider according to the second embodiment as viewed from the side.

  In this embodiment, as shown in FIG. 7, the form of the conductive container 11 is different from that of the first embodiment. The present embodiment is the same as that of the first embodiment except for this point and points related thereto. For this reason, in this embodiment, the description which overlaps with this embodiment is abbreviate | omitted suitably.

  As shown in FIG. 7, the present embodiment includes a disk-shaped flange 11Bb (insulating bar support member), and the disk-shaped flange 11Bb is provided on the flange 11Fa provided at the end of the conductive container 11. is set up. An insulating rod 51 is attached to the disk-shaped flange 11Bb. In this portion, the end of the high voltage conductor 21 is located. As in the case of the first embodiment, a first capacitor 41C is formed, and a second capacitor 42C is provided.

[B] Summary As described above, the capacitive voltage divider 1b of the present embodiment can form the first capacitor 41C and the second capacitor 42C at the end of the high-voltage conductor 21. Here, as in the case of the first embodiment, the linear expansion coefficient β of the metal material constituting the high voltage conductor 21 and the intermediate electrode 31 and the temperature coefficient γ of the second capacitor 42C are substantially the same. Further, the insulating rod 51 is attached to the disc-shaped flange 11Bb (insulating rod support member), and the disc-shaped flange 11Bb (insulating rod support member) is installed at the end of the conductive container 11.

  Therefore, as in the case of the first embodiment, this embodiment can suppress a change in the partial pressure ratio due to temperature, improve reliability, and improve assembly.

<Others>
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Capacitance voltage divider, 1b ... Capacitance voltage divider, 11 ... Conductive container, 11A ... 1st container member, 11B ... 2nd container member, 11Bb ... Flange, 11Fa, 11Fb ... Flange, 21 ... High voltage conductor, 31 ... Intermediate electrode, 31F ... Flange, 41C ... First capacitor, 42C ... Second capacitor, 51 ... Insulating rod, 61 ... Flange, 71 ... Sealed container, 81 ... Desiccant, 91 ... Sealed terminal

Claims (8)

Insulating gas sealed inside and grounded conductive container;
A high-voltage conductor provided inside the conductive container;
An intermediate electrode provided so as to form a first capacitor with the high-voltage conductor inside the conductive container;
A second capacitor having one end connected to the intermediate electrode and the other end connected to a ground potential outside the conductive container;
The high voltage conductor and the intermediate electrode are formed of the same metal material,
The linear expansion coefficient β [K ⁻¹ ] of the metal material constituting the high-voltage conductor and the intermediate electrode in the first capacitor, and the temperature that is the rate at which the capacitance changes with respect to the temperature in the second capacitor The coefficient γ [K ⁻¹ ] satisfies the following formula (A):
Capacitance voltage divider.

An insulating rod for supporting the intermediate electrode inside the conductive container;
The insulating rod is provided so as to extend parallel to the axial direction in which the high-voltage conductor extends,
The capacitive voltage divider according to claim 1. The second capacitor is a mica capacitor,
The capacitive voltage divider according to claim 1 or 2. A sealed container installed outside the conductive container,
The second capacitor is housed in the sealed container,
The capacitive voltage divider according to any one of claims 1 to 3. The capacity divider according to claim 4, wherein the sealed container contains a desiccant that absorbs moisture. The insulating rod is formed using an epoxy resin filled with alumina,
The capacitive voltage divider according to claim 2. An insulating rod support member on which the insulating rod is installed,
The conductive container has a first container member and a second container member,
The insulating rod support member is provided between the first container member and the second container member,
The capacity voltage divider according to any one of claims 1 to 6. An insulating rod support member on which the insulating rod is installed,
The insulating rod support member is installed at an end of the conductive container,
The capacity voltage divider according to any one of claims 1 to 6.

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