KR100322175B1 - Insulation and gas-insulated high voltage devices with insulation - Google Patents

Abstract

The gas insulated high voltage electrical apparatus has a tank (1) filled with an insulated gas such as SF ₆ , a high voltage conductor (2, 10, 12) inside the container and a red smoke (3, 4, 20, 30) connected to the conductor, have. The insulator is composed of an insulator body having a thin film of electrically conductive or semiconducting material on the exposed surface of the insulator gas. The thin film disperses the charge that tends to charge on the insulator surface and has a surface resistivity less than that of the same thickness thin film formed of the insulator material of the insulator body. The thin film is typically 10 ⁸ ~ 5 x 10 ¹⁶ Ω has a surface resistivity in a thickness of less than 1㎛. It has, for example, used are oxides, such as metal and the _{Cu 2 O, Cr 2 O 3} , Fe 2 O 3 , such as Cu, Cr, Al, Fe.

Description

Insulation and gas insulated high voltage equipment with insulation

The present invention relates to a device comprising an insulator and an insulator for a gas insulated high voltage electric device, and in particular, to a container filled with an insulating gas such as SF _6, and a conductor to which a direct current potential is applied, for example, to support a conductor. To a device having an insulator connected thereto.

Surface discharge or surface flashover, which is one of the insulating properties in gas insulator, has a big difference between AC and DC voltage. The characteristics of direct-current surface discharges in gases are described in detail in, for example, Technical Report (Part II) 397, pp. 17-23, "DC Insulation of Gas-Insulated Switchgear" (December 1991). In this example, it is also reported that the insulating properties of the insulator under the direct current voltage state are affected by the charging of the insulator surface, and the surface breakdown voltage of the insulator is changed by the amount of charge charge. An example is shown in FIG. 4 of the drawings attached to this specification, indicating that the breakdown voltage tends to decrease when the amount of charged charge increases.

As a countermeasure of the conventional problem, as shown in the literature, when selecting an insulator shape, a method (for example, making wrinkles on the surface of the insulator) has been performed in a form that is not easily charged.

Charge accumulation on the surface of an insulator can be caused by one of several causes, specifically conduction at the insulator, conduction at the insulator surface, dust or other particles of the device in contact with the insulator surface, ions from gas molecules of the device. The inventors claim that this is due to the production of and the ionization by spacecraft or X-rays. In particular, in the vacuum switch, there is a problem of impact on the surface of the insulator due to electrons emitted from the cathode causing secondary electron emission from the surface of the insulator. This is not a major problem for gas-filled devices, and the energy of electrons released to some extent is greatly reduced, for example by ionization of gas molecules. Therefore, no secondary electrons are generated.

As mentioned above, the countermeasure against the problem lies in the surface shape of the insulator for increasing the surface passage length. Other measures presented make the insulator convexly curved surface with the intention of matching the electric field lines to reduce the surface impact by electrons or other charged particles. Another alternative presented is to treat the insulator surface by water jet wear.

Reducing the surface flashover of an insulator in vacuum by the use of cuprous oxide (Cu ₂ O) or chromium oxide (Cr ₂ O ₃ ) covering the surface of the insulator by two researchers (Cross and Sudarshan). (Electrical Insulation Award IEEE Report EI-9, No. 4, December 1974, pp. 146–150, and EI-11, No. 1, March 1976, pp. 32–35). It has been found that the coating of nitrous oxide in the state can eliminate the control effects observed in the case of insulators which are not coated under direct and alternating voltage. The regulating effect gradually increases the insulator flashover voltage with the number of flashovers applied. In this case the Cu ₂ O coating does not cause an increase in flashover voltage after conditioning. In the case of chromium oxide coatings, the flashover voltage increases considerably and the control effect decreases due to the use of chromium oxide layers. Kros and the authors argue that the removal of positive surface charges has had these effects because the coating significantly reduced the secondary electron emission of the insulator surface. As a result of the secondary electron emission, it is clearly shown that it is associated with charges that charge very quickly on the insulator surface. It is also associated with avoiding the resistive thermal effects of insulators, which results in coatings with high resistances associated with low secondary electron coefficients. In cuprous oxide, a coating thickness of 20-200 nm is made by coating the insulator with copper by vacuum deposition and then heated in a suture tube. In the case of chromium oxide it is deposited from an aqueous solution.

As above, the secondary electron emission is not a problem in the gas station system. The increase in charge on the insulator surface is much less in a gas insulation system (a matter of hours) than in a vacuum system (a few minutes) and the electrons from the cathode because the electron energy is much lower by an insulating gas such as SF _6. Collision is not a problem. Therefore, the proposals by Cross and Sudashan are not explicitly applied in gas insulation systems. Cross and Sudashan insist that it is impossible to remove them as quickly as they form conductive charges. This is because the required current causes severe heating of the surface in vacuum.

It is an object of the present invention to provide an insulator for a gas insulated high voltage electrical device, wherein the problem of reducing surface flashover by charge charges on the surface of the insulator is reduced or eliminated. It is also another object to provide a gas insulated high voltage electrical device having such an insulator.

The inventors of the present invention find that coatings with reduced resistivity compared to the material of an insulator in gas insulated high voltage devices successfully dissipate a charge that tends to charge on the insulator surface without increasing the resistive current flow. The coatings used in the present invention are suitable for coatings invented by Cross and Sudashan, but they are, for example, filled with insulating gas rather than air, and conduction of charge rather than secondary electron emission prevention in other devices. It is importantly used in devices with different functions.

This invention shows the use of smaller insulators that exhibit a flashover voltage increase in the range of, for example, 20-40% and have a flashover voltage, such as insulators of the prior art. Various advantages of the present invention or embodiments thereof are described below.

In one aspect of the present invention, an insulator for a gas insulated high voltage electric device having an insulator of an insulating material is shown. The insulator has at least a portion of a thin film of electrically conductive or semiconducting material to dissipate the electrical charge on the object. The surface resistivity of the thin film is generally less than the surface resistivity of the thin film with the same thickness made of the insulator's insulator, for example up to 1/10 of its later value. The thin film preferably has a surface resistivity in the range of 10 ^{8 to} 5 x 10 ¹⁶ Ω. As the epoxy resin insulator, a surface resistivity of 10 ³ to 3 x 10 ¹⁶ Ω was obtained, but low values such as 10 ⁸ to 10 ¹² Ω are also suitable. The thickness of the thin film is preferably less than 1 µm, more preferably in the range of 20 to 200 nm.

The thin film is used as a suitable insulator having surface resistance in the range of 10 ¹⁴ to 10 ¹⁶ Ω.

In order to make an effective conductive path for electric charge distribution, a thin film on the surface of the insulator is in contact with an electrode or other conductor on one or both sides of the insulator.

In principle, a suitable conductive or semiconducting material can make a surface thin film on an insulator, which should be able to adhere appropriately to the surface and provide the desired surface resistance shown above. Preferred methods of thin film formation are, for example, chemical vapor deposition, physical vapor deposition, sputtering and vacuum deposition. The thin film is preferably uniformly attached to all parts exposed to the insulating gas of the gas insulating device.

The charge dispersing thin film used in the present invention has functions to allow surface charge to pass along the insulator, whereby the charge is dispersed. Moreover, the thin film tends to increase the uniformity of the surface resistance of the insulator, and in particular has the advantage that the charge does not accumulate in one place. The coating also has another advantage of reducing the tendency of external metal particles to stick to the insulator surface causing flashover due to its conductivity. If charged metal particles adhere to the surface of the insulator, the charge is quickly dispersed by the thin film, causing the particles to drop quickly and no longer be held back by electrostatic attraction.

There are also advantages such as ease of transportation and handling of the insulator by hand, which makes it easier to handle and less contaminated on the insulator surface. In the past, it was considered impossible to treat such insulators by hand in gas insulation systems. A bigger advantage is the increased safety while continuing to perform personally. In spite of the rapid dissipation of the charge on the insulator, in the prior art, surface charges remain in the insulator for a long period of time, and even for several days, creating the risk of requiring personnel for maintenance.

Methods such as the application of thin films comprising insulator contact with water and the deposition of chromium oxide in the solutions presented by Cross and Sudashan are undesirable. And even if a small amount of remaining water remains on or in the insulator, this water evaporates inside the gas insulated tank. SF ₆ also partially decomposes, for example, on the obstruction of such a device, and the result of the decomposition reactions constituting water results in corrosive HF.

Preferred coating thin film materials of the present invention are Cu, Cr, Al, Fe, cuprous oxide, chromium oxide, and ferric oxide (Fe ₂ O ₃ ).

It is known that gas insulated high voltage electrical systems use insulators made of synthetic resins, in particular epoxy resins. Epoxy resins comprise a specific filler in such alumina, and according to the invention the use of such resins is preferred. The thin film used in the present invention presents a particular advantage in this case, since this filled epoxy resin is uneven in its surface resistance by the filler particles. The applied thin film improves the uniformity of surface resistivity. In addition, the regulation (e.g. application of the flashover number to improve the flashover voltage), in which state reduction is described as an advantage by Sudashan and Cross, does not require an epoxy resin insulator and is very disadvantageous. It is necessary for the control effect because flashover melts the epoxy resin material. On the other hand, if a flashover occurs while the insulator of the present invention is used, the surface thin film tends to protect the epoxy resin from the effects of the flashover.

According to another aspect of the present invention, there is provided a high voltage conductor inside the container filled with insulating gas and an insulator connected to the conductor. The insulator has an insulator made of an insulator material having a thin film of material selected from electrically conductive and semiconducting materials on at least one portion of the surface exposed to the insulating gas. The thin film has a smaller surface resistivity than that of thin films of the same thickness made of an insulator insulator. In another aspect of the invention, there is provided a container filled with an insulating gas, a high voltage conductor in the container, and an insulator connected to the conductor, wherein the insulator is made of a material having electrical conductivity on at least a portion of the surface exposed to the insulating gas. With a thin film, a gas insulated high voltage electrical device suitable for conducting the thin film conductively dissipates the charge accumulated in the insulating material can be seen.

The invention can be used in particular in gas insulated high voltage electrical devices in which a direct current voltage is applied to the conductor, in particular a high voltage of 500 kv or more.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the scope of the present invention is not limited thereto.

The gas insulator of FIG. 1 includes a sealed ground tank 1, a conductor 2, a blocking device 50 including a movable electrode 12, a support conductor 11 for the movable electrode 12, and a fixed electrode 10. It consists of. The various insulators are provided with such high voltage conductor parts, in particular gas compartments defining the insulating spacers 3, conductor supporting post-shaped spacers 4, insulating supporting tubes 20 for supporting the conductors 11, and operating units 35 in an insulating manner. And an insulating operation rod 30 for driving the movable electrode 12 connected thereto. In general, this is a conventional configuration, and the insulating gas is SF ₆ under the pressure filled in the tank 1 in a conventional method.

In the gas insulation device having the device described above, the insulator according to the present invention is used as each of the insulation spacer 3, the post spacer 4, the insulation support tube 20 and the insulation operation rod 30, A thin film of sputtered metal or oxide is formed on at least the entire surface of one or a plurality of these insulators in contact with the insulator gas.

The post spacer 4 used in this gas insulator is shown in detail in FIG. The post spacer 4 is provided with an epoxy resin main body 40 including alumina filler particles and a post spacer 4 and provided in an end surface facing the epoxy resin main body 40 for the purpose of reducing electric field strength. Electrodes 41 are provided. The thin film 45 is formed on the surface of the resin main body 40 by evaporation or sputtering of the deceleration particles. The thin film 45 is connected to the electrodes 41 on both electrical sides of the insulator. The thickness t of the thin film 45 depends on the required insulation resistance value, but in order to achieve the effects and advantages of the present invention, it is preferable to select from approximately 20 to 200 nm. The surface resistivity of the thin film is generally smaller than the surface resistivity of the thin film (of the same thickness) equivalent to the epoxy-based material of the body 40.

Preferred materials for thin film 45 are Cu, Cr, Al or Fe and oxides Cu ₂ O, Cr ₂ O ₃ and Fe ₂ O ₃ .

3 conceptually illustrates the surface resistivity of the spacer and the amount of charge on the surface of the spacer. Compared to the normal uncoated spacer A having a surface resistance value of 10 ¹⁴ to 10 ¹⁶ Ω, the surface resistivity value of the spacer B according to the present invention is lowered to 10 ⁸ to 10 ¹² Ω. This reduces the charge on the surface of the insulator. In one embodiment of the present invention, it is possible to improve the liquid level resistance voltage value for DC voltage by 20 to 40%.

Incidentally, since the insulator having the surface thin film is greatly different from the insulators not dealt with in the surface resistivity, the surface color of the former and the latter insulators is preferably made differently to visually distinguish.

According to the present invention described above, it is possible to increase the internal pressure of the insulator. As a result, it is possible to increase the insulation reliability of the gas insulator and also reduce the size and weight of the device.

One of the methods for forming a thin film on an insulator surface by sputtering is described next.

Epoxy resin insulators are placed at regular intervals between the high voltage electrode and the ground electrode made of copper. And they are sealed in a vacuum chamber filled with argon at low pressure after bleeding air. Half-wave rectified 50 Hz alternating voltage is applied between the electrodes. By discharging between the high voltage electrode and the ground electrode, Ar ions collide with the high voltage electrode to sputter metallic copper. The sputtered copper then accumulates in the epoxy resin sample and forms a thin copper film. The sputtering state for forming the sputter thin film on the epoxy resin sample is as follows:

Voltage supply 2000V

Current 12mA

Argon Gas Pressure Approx.0.04 Torr

10 minutes sputtering time

To obtain a thin film of uniform thickness, the epoxy resin sample was rotated approximately 30 times per minute. The surface resistivity of the epoxy resin specimen having the sputter thin film thus formed was approximately 1 × 10 ¹⁵ Ω, and the resistivity of the raw epoxy resin specimen was 5 × 10 ¹⁶ Ω, so that the value was 1/50 by the sputter thin film. It is reduced.

Furthermore, if the pressure of Ar is changed in the range of 0.02 to 0.05 Torr with the applied voltage at 2000 V, the thickness of the sputtered thin film can be changed so that the surface resistivity is in the range of 3 x 10 ^{16 to} 1 x 10 ¹³ Ω, for example. desirable.

On the epoxy resin specimen of 40 mm length and 50 mm diameter, a sputtered copper thin film is formed by the above-described method so that the surface resistivity is reduced. In this case, the surface resistivity is reduced to about 2 × 10 ¹⁶ to about 3 × 10 ¹⁴ Ω.

After prestressing at 200kV dc, the polarity of the insulator was changed and the flashover voltage measured was 450kV. The flashover voltage for pure epoxy resin specimens without compressive stress (without changing polarity) was 380 kV. The internal pressure is increased by about 20% by the Cu thin film as compared to the case of pure specimens with no change in polarity. And so far it is generally believed that inversion of polarity reduces the flashover voltage. However, the formation of sputtered thin films prevents this reduction.

The structure of the epoxy resin body under such flashover inspection is shown in FIG. The epoxy resin body 40 has one aluminum electrode 41 inserted therebetween and is located between the electrodes 42. The main body 40 is a cylinder of 40 mm in height and 50 mm in diameter, and the electrode 41 is 15 mm in height and 40 mm in diameter.

A preferred method of measuring the surface resistivity of an insulator is shown in FIG. 6 with or without the conductive thin film provided by the present invention.

Three copper tapes 46 having a width of 5 mm are wound around the sample at intervals of 5 mm, as shown in FIG. 1, and are connected to a circuit including the illustrated 500 V DC voltage source and an ammeter. The upper and lower copper tapes 46 serve as guard electrodes and the central copper tapes 46 serve as high voltage electrodes. The sample is then placed in a shield box at 20 ° C. After 1 to 2 minutes, a voltage is applied and after 2 minutes the readings are read, from which the surface resistivity is calculated.

1 is a cross-sectional view of a gas insulator device showing a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of a columnar spacer forming an insulator showing an embodiment of the invention implemented in the apparatus of FIG. 1;

3 is a graph showing an example of the effects of the present invention;

4 is a graph showing flashover voltage reduction with increasing charge amount on an insulator surface;

5 is an explanatory diagram of an insulator under the flashover test;

6 is a diagram of the surface resistance measurement method.

Claims (10)

In gas insulated high voltage electrical equipment, A container 1 filled with insulating gas; An insulator (3, 4, 20, 30) having a high voltage conductor (2, 10, 12) inside the container (1) and an insulator body (40) connected to the conductor to support the conductor, A portion of the surface of the body 40 exposed to the insulating gas has an electrical conductivity that conducts and dissipates the electrical charge accumulated on the insulating material while avoiding severe resistive heating of the insulating material 3, 4, 20, 30. Gas insulation high voltage electrical apparatus, characterized in that there is a thin film 45 made of a material having a. The method of claim 1, The thin film 45 is a gas insulated high voltage electrical apparatus, characterized in that the surface resistivity is smaller than the surface resistivity of the thin film having the same thickness formed of the insulating material constituting the insulator body. The method according to claim 1 or 2, Part of the insulator material of the insulator body (40) is a gas insulated high voltage electrical apparatus, characterized in that the resin. The method of claim 3, wherein Part of the insulator material of the insulator body (40) is an epoxy resin and optionally comprises a filler. The method according to any one of claims 1, 2 or 4, Gas insulation high voltage electrical apparatus, characterized in that the thin film (45) has a thickness less than 1㎛. The method of claim 5, And wherein said thin film 45 has a thickness in the range of 20-200 nm. The method according to any one of claims 1, 2, 4 or 6, Gas insulation high voltage electrical apparatus, characterized in that the thin film 45 has a surface resistance in the range of 10 ⁸ ~ 5 × 10 ¹⁶ Ω. The method according to any one of claims 1, 2, 4 or 6, Gas insulator high voltage electrical apparatus, characterized in that the insulator body (40) has a surface resistance in the range 10 ¹⁴ ~ 10 ¹⁸ Ω. The method according to any one of claims 1, 2, 4 or 6, The material of the thin film 45 is Cu, Cr, Al, Fe, Cu ₂ O, Cr ₂ O ₃ And Fe ₂ O _{3 The} gas insulated high-voltage electric device, characterized in that. The method of claim 1, Gas insulation high voltage electrical apparatus, characterized in that the insulation gas is SF ₆ .