JPH0344483B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Heat of the Invention] The present invention uses sulfur hexafluoride gas (hereinafter _SF6 ) as an insulating gas in a box housing electrical equipment or conductors.
This invention relates to a gas insulating device that encloses gas (abbreviated as “gas”).

[Technical background of the invention and its problems]

Generally, main circuit devices such as closed switchboard edges, disconnectors, disconnectors, busbars connected thereto, monitoring and control equipment, etc. are housed in a metal box, and this box is grounded.

If the main circuit is three-phase, a barrier made of an insulating material is inserted between the phases of the main circuit equipment to reinforce the insulation between the phases, thereby reducing the overall distance. We are trying to reduce the number of people. However, the basic insulation in closed switchboards is mainly air insulation using air, and in this air insulation, the dielectric strength in an unequal electric field is generally 6 [KV/cm].
Because of this, many closed switchboards with a rated voltage of 30 [KV] or less only have air insulation.

Using such air insulation, the rated voltage is 60 [KV]
In order to manufacture a similar closed power distribution board, the main circuit equipment had to be insulated and the insulation distance between the phases had to be further increased, making the entire power distribution board larger.

On the other hand, in recent years, in order to cope with land shortages and increasing population density, there has been a strong desire for a small closed switchboard with excellent insulation strength.

As one way to solve this problem, electrical equipment in which SF ₆ gas as an insulating medium is sealed in a box is often used in substations and the like, and such electrical equipment is generally referred to as gas insulated equipment or gas insulated equipment.

As is well known, _SF6 gas is colorless and odorless, and its dielectric strength is approximately 2 to 3 times higher than that of air.
By using SF ₆ gas as an insulating medium, it becomes possible to downsize closed switchboards and the like.

However, this SF ₆ gas has a strong electric field dependence, and its dielectric strength in an unequal electric field is significantly lower than that in an even electric field. Therefore, the radius of curvature of the main circuit conductor, etc. must be made as large as possible to approximate a uniform electric field. For this reason, it takes a lot of effort to make the main circuit conductors and the like round when manufacturing them, which is one of the reasons for the increase in the price of the entire device.

On the other hand, in order to seal pure SF ₆ gas inside the box, the inside of the box must be degassed to create a high vacuum state.
Next, a method is adopted in which SF ₆ gas is sealed and the pressure is increased to a specified pressure. For this reason, the box body was required to have the strength to withstand high vacuum, and the thickness of the box wall had to be increased.

In addition, the gas pressure of a typical gas insulation device is 0.3
In many cases, the pressure is ~0.6 [MPa], and there are strict legal regulations for pressure vessels, and it was necessary to make the box wall thickness sufficiently large to meet these regulations.

However, since the box body of gas insulating equipment must be strong and also increase in weight, the means of transportation becomes large-scale and installation is also difficult. Furthermore, there is a strong demand for lower prices and shorter construction times. In some ways, this is a reversal of the recent trend.

[Purpose of the invention]

The present invention was made in consideration of the above circumstances, and
By appropriately selecting the concentration and gas pressure of SF ₆ gas, it is possible to reduce the weight of the box and simplify the gas filling work without significantly reducing the dielectric strength, and it is also possible to reduce the cost. The purpose is to provide inexpensive gas insulation equipment.

[Summary of the invention]

In order to achieve this object, the present invention stores electrical equipment or conductors in a hermetically sealed box so that the electric field utilization factor is 0.4 or less, and sulfur hexafluoride gas and air are mixed inside the box. At the same time, the mixed gas is filled with a sulfur hexafluoride gas concentration of approximately 60 [%] or more, and the total pressure is approximately 0.10 to 0.2.
It is characterized by being maintained within the range of [MPa].

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing the configuration of a gas insulating cubicle as a gas insulating device according to the present invention. So there are 4 rooms A,
It is divided into rooms B, _C1 , _{and C2} (hereinafter referred to as room A, room B, room _C1 , and room _C2 ), and a cable head 11 for connecting a power transmission line (not shown) is located on the wall of room B. It penetrates through the container 1 and is attached substantially perpendicularly to the installation surface of the container 1. This cable head 11 is the same B
It is connected to a disconnector 15 provided in the A room via a transformer 12, a disconnector 13, and a through current transformer 14 provided in the room. Note that the disconnector 13 and the shingle breaker 15 are connected to each other by a power supply side main circuit bus bar 16 that passes through an insulating spacer 18 supported by the partition plate 2 and is arranged horizontally.

In addition, on the load side of the breaker 15, a load-side main circuit bus 17 for two circuits passes through another insulating spacer 18 supported by the partition plate 2, and is placed horizontally into the _C1 room. While this is connected to the disconnect switch 13 of the C ₁ room, it is also connected to the disconnect switch 13 of the C ₂ room through another insulating spacer 18 supported by the partition plate 4. There is.

Although the details of the disconnector 13 are not shown here, the disconnector 13 includes a fixed electrode and a movable electrode that is disposed opposite to the fixed electrode and is movable in the horizontal direction. A movable current collector moves horizontally to open and close the main circuit. These fixed electrodes and movable electrodes are connected to the container 1 or the partition plates 3 and 4, respectively.
In contrast, the container 1 is held via an insulator having a predetermined dielectric strength, and the container 1 itself is grounded. Further, a grounding device 19 is provided on the upper wall of the B room.

The insulating cubicle shown in FIG.
For equipment and main circuit busbars etc. stored in
It does not necessarily have a rounded shape with a large radius of curvature; in particular, the radius of curvature of the ends of the main circuit busbar and their connection parts remains small, and therefore the configuration is such that unequal electric fields are likely to be formed. .

In addition, the inside of the container 1 is made of a mixed gas of SF ₆ gas and air, and the best condition is a mixture ratio of approximately 9:1 and a gas pressure of approximately 0.12 [MPa]. Gas is sealed.

Note that the method of filling the insulating gas is a replacement method that utilizes the difference in specific gravity between SF ₆ gas and air.
That is, since the specific gravity of SF ₆ gas is 5.10 [Electrical Engineering Handbook, edited by the Institute of Electrical Engineers of Japan], SF ₆ gas is gradually poured from the bottom of container 1, and a valve (not shown) provided on the top wall of container 1 is opened. In this way, the air is pushed out, and when the air is almost gone, the valve is closed to raise the gas pressure to a predetermined level.

Therefore, when filling the container 1 with SF ₆ gas, it was necessary to create a vacuum state with the conventional device, but with this method, there is no need to create a vacuum state, and moreover, the gas pressure is also reduced. The best condition is 0.12 [MPa], and since the container is sealed close to this value, the container wall can also be made of thin plate material.

In addition, since the purity of SF ₆ gas is not 100%, but the best is 90%, it can be said to be easier to handle.

Secondly, no active measures were taken to bring the electrical equipment and conductors stored in container 1 closer to an equal electric field, and SF ₆ was used as an insulating gas.
The reasons for mixing gas and air at a ratio of approximately 9:1 and for keeping the gas pressure close to 0.12 [MPa] will be explained based on an experimental example conducted by the inventors.

[Experimental Example 1] First, as shown in Fig. 2a, a ball electrode 21 made of a copper alloy and a flat plate electrode 22 are placed facing each other in a high-pressure tank with the electrode spacing l (hereinafter also referred to as gap) being varied. A gas mixture of SF ₆ gas and air at a ratio of 9:1 is sealed in this high-pressure tank, while a pair of spherical electrodes made of copper alloy are placed inside the high-pressure tank, as shown in Figure 2b. 21 was placed in a high-pressure gas tank in the same atmosphere as described above with the gap l being varied.

Here, the radius of curvature r of the spherical electrode 21 and the gap l
The electric field inequality coefficient f is naturally determined by the relationship between . In other words, if the inequality coefficient is f, the maximum electric field strength is E _Max , and the average electric field strength is E _ave , then there is a relationship of f = E _Max / E _ave ...(1), so when r≫l, the electric field is close to an equal electric field. ,
The inequality coefficient f becomes f≒1. Conversely, when r<<l, the electric field becomes unequal, and the inequality coefficient f takes a value of 1 or more.

This inequality coefficient f can be determined with high precision using the recently announced electric field calculation method (IEEJ Technical Report No. 98, Recent Electric Field Calculation Method).
Generally, the following formula f=0.9・r+l/r...(2) is used for Figure 2a, and the following formula f=0.9・r+l/2/r...(2) is used for Figure 2b. 3) is used.

Here, the electric field utilization rate U may be used instead of the inequality coefficient f, and the relationship between the electric field utilization rate U and the inequality coefficient f is expressed by the following equation.

U=1/f...(4) Figure 3 is a diagram depicting the relationship between gas pressure and flashover voltage between electrodes, using electric field utilization factor U as a parameter, according to experimental values. This is the power over voltage expressed as a percentage.

In the figure, as the electric field utilization factor U increases, the flashover voltage increases and at the same time increases in proportion to the gas pressure.
In the range of 0.40, the flashover voltage peaks at a gas pressure of 0.12 [MPa], and then decreases to 0.3
It gradually decreases as it approaches [MPa], and this 0.3
When it exceeds [MPa], it rises slowly again.

In other words, in an uneven electric field, the flashover voltage reaches its maximum at a gas pressure of 0.12 [MPa] in a region where the electric field utilization rate is low, meaning that it has excellent dielectric strength.

Furthermore, even if the gas pressure is further increased,
The area with dielectric strength equivalent to 0.12 [MPa] is 0.5
[MPa], it can be seen that practically setting the gas pressure to 0.12 [MPa] is most effective in terms of dielectric strength.

[Experimental Example 2] Figure 4 shows the electric field when electrodes 21 and 22 similar to those described above are placed in a high-pressure tank, the gap l and the radius of curvature r are varied, and the concentration of SF ₆ gas is varied. Using the utilization rate U as a parameter
FIG. 3 is a diagram depicting the relationship between SF ₆ gas concentration and flashover voltage according to experimental values. In this case, the gas pressure was maintained at 0.12 [MPa].

In the figure, in the region where the field utilization factor U is 0.40 or less, the flashover voltage becomes a parabolic curve with the maximum value when the SF ₆ gas concentration is 90%, and in the region where the field utilization factor U is 0.41 or more, the SF 6 gas concentration becomes 90%. It can be seen that the characteristic curve shows that the flashover voltage also decreases in proportion to the decrease in the ₆ gas concentration.

In other words, in an unequal electric field, the _SF6 gas concentration can be reduced to 90%.
By doing so, the dielectric strength can be maximized.

As is clear from the two experimental examples mentioned above,
The condition under which the mixed gas of SF ₆ gas and air contributes most to the improvement of dielectric strength is that the electric field utilization factor U is 0.40.
gas pressure is 0.12 [MPa], and SF ₆ gas concentration is 90%.

One reason for the maximum dielectric strength under these conditions is that the so-called secondary ionization effect, such as electron emission σ _p from the electrode metal surface, is suppressed under the above conditions, which increases the discharge withstand voltage. It is considered that

However, for equipment with an electric field utilization factor U of 0.4 or less, the above conditions are the best, but the gas pressure is 0.1 to 0.2 [MPa] and the SF ₆ gas concentration is
Since there is no significant drop in flashover voltage even when the voltage is maintained in the range of 60 to 100%, there is almost no problem in practical terms.
Taking into consideration the fact that it is difficult to define the SF ₆ gas concentration strictly,
It is considered optimal to keep the dielectric strength within the above range assuming conditions that maximize the dielectric strength.

In the above embodiment, a gas insulated cubicle was explained, but other examples include gas insulated vacuum shields in which a vacuum valve is housed in an insulated container, a closed busbar, etc., and other devices with an unequal electric field utilization rate U of 0.40 or less. Of course, it can also be applied to gas insulated equipment that has an electric field.

〔Effect of the invention〕

As is clear from the above explanation, according to the gas insulating device of the present invention, the concentration of SF ₆ gas does not necessarily have to be reduced.
Since it does not need to be 100% and the gas pressure is low, the gas filling work can be significantly simplified.
In conjunction with this, the plate constituting the box body can also be made thin and the weight of the entire device can be significantly reduced, which is an excellent effect.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the gas insulating device according to the present invention, and Figs. 2 a and b show the shapes of the main elements of the experimental equipment used to determine the insulating gas concentration of the same embodiment. The side view, FIGS. 3 and 4 are characteristic diagrams showing experimental results using this experimental device. 1... Container, 2, 3, 4... Partition plate, 11...
Cable head, 12...Transformer, 13...Disconnector, 14...Through current transformer, 15...Shin breaker,
16, 17... Main circuit bus bar, 18... Insulating spacer, 19... Grounding device, 21... Ball electrode, 22...
...Plant electrode.

Claims (1)

[Claims] 1. An electric device or a conductor is housed in a sealed box so that the electric field utilization factor is 0.4 or less, and a mixed gas of sulfur hexafluoride gas and air is placed inside the box. A gas insulating device characterized in that the sulfur hexafluoride gas concentration of the mixed gas is maintained at approximately 60 [%] or more and the total pressure is maintained within the range of approximately 0.10 to 0.2 [MPa]. 2 Set the sulfur hexafluoride gas concentration of the mixed gas to 90
[%] and the pressure of this mixed gas is maintained at 0.12 [MPa].