JPS6010438B2 - protection gap device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealed protective gap device using an electrically negative gas such as SF6 gas as an insulating medium.

In order to protect sealed electrical equipment using electrically negative gas such as SF6 gas as an insulating medium from abnormal voltages such as lightning surges, there are so-called lightning arresters, which are used as a type of lightning arrester. It is known to provide a closed protective gap device containing an electrically negative gas such as SF6 gas.

It is well known that, for example, in a conventional sealed protective gap device filled with SF6 gas, the discharge pressure varies in a complicated manner depending on the structure of the gap, the pressure of the filled gas, etc. Since the pressure is not structurally controlled, the higher the filled gas pressure and the more unequal the electric field, the greater the difference in the discharge pressure value due to the polarity of the applied voltage, that is, the positive polarity voltage on the charging side. The discharge pressure (
The difference between the negative polarity (positive polarity) and the discharge pressure (negative polarity) obtained when a negative polarity voltage is applied to the charging side becomes large, and the protective gap device often operates in response to overvoltage on one side. It has the disadvantage that it is difficult to protect the protected equipment from overvoltages of opposite polarity.

This shortcoming will be concretely illustrated by one experimental result.

The experiment was conducted by setting a pair of spherical electrodes with a diameter of 1 in a metal tank with an inner diameter of 1.2 and a gap length of 1. The electric field of this experimental sample has a ratio of average electric field strength to maximum electric field strength of 0.956, and is treated as an equal electric field in the atmosphere. FIG. 1 is a curve showing the lowest discharge pressure and discharge time obtained in an experiment using this experimental sample, in which the gas pressure of the enclosed SF6 was absolute 1 atm (hereinafter all gas pressures are expressed in absolute pressure). ) and shows the discharge characteristics at 6 atm. As is clear from Fig. 1, when the enclosed SF6 gas pressure is 1 atm, there is no polarity difference in the discharge pressure;
In the case of atmospheric pressure, the polarity difference appears to be about 10%. Such differences in gutter characteristics become more pronounced as the filled gas pressure increases and as the electric field becomes more unequal. Even when the filled gas pressure is 1 atm, increasing the gap length (increasing the unequal electric field) , a polarity difference appears. As mentioned above, even if there is a slight inequality in the electric field, which is treated as an equal electric field in the atmosphere, the discharge in an electrically negative gas such as SF6 gas becomes noticeable as the pressure of the filled gas increases. It has a very important characteristic of producing a polarity difference in the discharge value.

As shown in the experimental results shown in Figure 1, the method to eliminate the polarity difference in the discharge pressure in a closed protective gap device filled with an electrically beneficial gas such as SF6 gas is to minimize the inequality of the electric field in the gap. It is clear that this can be obtained by reducing the pressure to 1 atm and filling the gas pressure to, for example, 1 atm.

However, a protective gap device designed using this method has a shape similar to that of the sample used in the experiment shown in Figure 1, and has a minimum discharge pressure of 100 volts. Approximately 1" brushing is required, and this has no value at all as an industrial product. Also, SF
6. Gas-filled electrical equipment (that is, gas insulated equipment) generally has a structure in which a cylindrical conductor on the conductor side is placed coaxially within a cylindrical container at ground potential.

In such a coaxial structure, the electric field on the surface on the power supply side is always higher than the electric field on the inner surface of the cylindrical container on the ground side. in this way,
In devices with asymmetrical electric fields on the electrical side and the ground side, if the mechanism of starting discharge at dielectric breakdown is different, a polarity difference will inevitably occur in the discharge voltage.

Specifically, the breakdown electric field strength of high-pressure SF6 gas is affected by the condition of the negative electrode surface and the size of the surface area, and is lower than the theoretical value where positive and negative electrodes are equal. can be said to be lower than that of positive polarity. Therefore, if a protective gap device with a structure similar to the sealed gas pressure and electric field of the protected electrical equipment is designed, it is possible to show the same degree of gutter difference, so even if there is a polarity difference, it is sufficient for practical use. There may be a question as to whether it is possible to protect electrical equipment and eliminating the polarity difference itself has no practical significance.

The above question can be said to be correct within the above range.

However, electrical equipment sealed with SF6 gas, etc., can be used in cases where the container is made of glass pipe, disconnectors, disconnectors, busbars, transformers, and earthing switches where the equipment is configured in a metal grounding container. There are a large number of types, bushings, etc., and their structures, sealed gas pressures, etc. vary widely. In other words, although these devices have a withstand voltage value higher than a predetermined value, the polarity difference in the withstand voltage value, the time characteristic of the emitted air pressure, etc. will each have different values if the structure and the filled gas pressure are different. Therefore,
In order to ensure the practicality of these various electric devices, either alone or in combination, it is not preferable that there be a polarity difference in the discharge voltage of the protective gap device. Furthermore, the protection gap device according to the present invention is not limited to the protection of electrical equipment filled with SF6 gas or the like, and it can be said that this performance is made possible by eliminating the polarity difference between the discharge voltages.

In order to eliminate the polarity difference between discharge pressures, which is a drawback of the conventional protective gap device as described above, the present invention provides a compact and good discharge device that controls the electric field by setting an appropriate structure. The purpose of the present invention is to provide a protective gap device having the following characteristics.

Next, an embodiment of the present invention shown in the figures will be described in detail.

In FIG. 2, reference numeral 1 denotes a container of a closed type gas-insulated electric device, and an electrically negative gas such as SF6 gas is sealed inside the container 2. In FIG.

Reference numeral 3 denotes a conductor that connects the conductor section of the sealed gas insulated equipment and the protective gap device, and is integrally constructed with an insulating spacer 4 made of epoxy resin or the like.

5 is a metal container that houses the protective gap device; 6 is the container 5;
The inside 7 is filled with an electrically negative gas such as SF6 gas.

These containers are sealed using gaskets 11, 12 provided on the flanges 8, 9, 101 provided on the containers 1, 5.
, 13 by screwing in bolts 14, 15 as shown. Reference numeral 16 denotes an electrode holding fitting which has a threaded portion at one end and a shape that can be connected to the conductor 3 at the end of the electrode, and is attached to the conductor 3 with a bolt 17 as shown, and a ball at the end of the electrode. A discharge pole 18 having a diameter of 10 arc◇, that is, a discharge pole on the side of power supply, is screwed and fixed.

A shield electrode 19 is made of a metal material and has a diameter of 27 mm and is fixed to the electrode holding fitting 17 with a bolt 20 so as to have the same potential as the discharge electrode 18.

As shown in the figure, 21 is a dew electrode mounting rod whose one end is integrally fixed to the lid 6 by welding or the like and has a threaded portion at the other end, and the threaded portion has a ball diameter of 10 mm. The discharge electrode 22, that is, the ground side discharge electrode is screwed and fixed.

The discharge electrodes 18 and 22 constitute a discharge gap 23 having a gap length of 6 mm. Container 5, lid 6, discharge electrode 22
etc. are grounded to the earth by a grounding wire 24. next,
The operation of the present invention will be explained.

The conductor 3 is always connected to the system voltage (ground voltage).

If an abnormal voltage such as a lightning surge enters from the conductor 3 side, the discharge gap 23 is discharged at a predetermined voltage, and the energy is discharged to the ground. Protect equipment insulation.

Next, the structure of the protective gap device and the method of controlling the electric field, which are the gist of the present invention, will be explained.

Figure 3 is a diagram showing the relationship between the distance between the electrodes and the electric field strength in the sphere-to-sphere discharge gap with a gap length of 6 times, and the vertical axis is the electric field E/Emax normalized by the maximum electric field Emax. For example, in FIG. 2, the curve 25 corresponds to the shield electrode 19.
This is the shape of the potential distribution that shows a general spherical gap with the spherical gap removed. That is, the electric field strength E18 of the 18 electrodes is
It becomes higher than the electric field strength E22 on the second side. This E18 and E2
2, by attaching a shield electrode 19 as shown in FIG. 2, or by attaching a shield electrode of any shape to the discharge electrode 22 to control the electric field, although not shown. E18 can optionally be greater than, equal to, or less than E22. science fiction
It is well known that discharge in 6 gas occurs when the electric field strength reaches the breakdown field strength of SF6 gas, but in the case of high pressure SF6 gas, the discharge occurs due to the surface condition and surface area of the negative electrode. , the breakdown electric field strength is affected and its value is lower than the theoretical value.

The reason for this is thought to be as follows. That is, when the electric field strength on the surface of the negative electrode increases, the work function of the negative electrode decreases due to the strong electric field, and electrons are emitted from the surface of the negative electrode. Since these electrons act as initial electrons that initiate dielectric breakdown in the SF6 gas space, the dielectric breakdown strength of the high pressure SF6 gas is determined by the electric field of the negative electrode. Figure 4 shows the relationship between the surface area S of the electrode and the breakdown electric field strength E based on the experimental results.
This relates to a gap between two flat plates made by Graphato whose surface has been treated to a height of about 0 m.

In general, it has been confirmed from a lot of experimental data that FIG. 4 follows the following equation. E=E. 10 (zu three;)fEd
．． ”...(・'Here, E is the electric field strength (kv/skin) Eo
is the minimum breakdown electric field [k v/ka] obtained when the electrode area is very large at that gas pressure, and is given by the following equation.

・ E.

=Ed×・10o. 355. po・7P is gas pressure [atm
] Ed is the theoretical breakdown electric field [kv/skin] of SF6 gas and is given by the following equation.

Ed = 8. m is a parameter of the Weibull distribution of the breakdown electric field. m = 7.4. So is a parameter of the Weibull distribution of the breakdown electric field. For example, in the case of a mirror-finished stainless steel electrode, o = 0. Hayabusa × p (1.15 p) In the case of a graphite electrode whose surface has been treated to a roughness of about 20 mm, the ratio is 240 × p (1.15 p).

Since the electric field strength on the electrode surface varies depending on its surface position, it is necessary to clarify what kind of surface area the above-mentioned surface area refers to.

The reason why the breakdown electric field strength decreases from the theoretical value as the surface area of the electrode increases or the surface becomes rougher can be explained by the increase in the number of weak points due to microprotrusions on the electrode surface. .

In addition, as the electric field strength on the negative electrode surface increases, weak points become smaller and smaller, such as minute protrusions, so the number of weak points is simply the number of structural weak points. Not, but
It is considered to be a function of the electric field strength on the electrode surface. The relationship between the electric field strength on the electrode surface and the surface area can be determined, for example, by calculating the electric field on the electrode surface using an electronic computer for the target gap, and calculating the electric field strength of the part where the electric field strength is higher than an arbitrary electric field strength E from the point of the maximum electric field Emax. The relationship between electric field strength and surface area can be determined using the area S leg obtained by integrating the electric field area. Figure 5 shows 1 Rune with a gap length of 6? Electric field E/Emax normalized by the S leg of the electrode on the lower side of the sphere-sphere gap and the maximum electric field Emax
The relationship is given as curve 27. On the other hand, since the number of weak points that reduce the breakdown electric field strength is a function of the electric field strength on the surface of the negative electrode as described above, the relationship between the density of weak points N[E} and the electric field strength E on the surface of the negative electrode is is shown as curve 28 in FIG.

In Fig. 5, the section price side for arbitrary electric field strength E and E ten-weizhou station strength - Bonito. It is expressed as manure.

As shown in FIG. 5, the negative sign is given so that as the electric field strength E increases, the area S leg decreases, that is, dS leg/dE becomes negative, so the area becomes positive. Similarly, from Fig. 6, if the average density of weak points in the interval between arbitrary electric field strength E and E+hime is N[E', the total number of weak points Nt is calculated as shown in equation {2). It is obtained by integrating the product of the area of each minute portion and the average density of weak points in that portion by the electric field strength.

Nt=-Misaki E'・d device. dE,. (2) Emax in formula (2) is the maximum electric field strength shown in FIGS. 5 and 6.

In addition, Equation '2} is the average density N (Emax) of weak points on the electrode surface in an equal electric field gap with the maximum electric field strength Emax and the equivalent area SeR such that the product thereof is equal to the equation {21]. As a product, it can be expressed as the '3' formula.

N(Emax)・Seff=-Misaki E). d basket・dE・・・・・・・．・[3' That is, the total number of weak points on the electrode surface with an arbitrary electric field shape can be replaced by an equal electric field (for example, parallel plate) electrode with an equivalent area $eff whose maximum electric field strength is equal, This Seff can be said to be the equivalent area when the above substitution is performed.

In addition, [2] is a function of the weak point density N [count] shown in the glue formula and Fig. 6, and the electric field strength, and from many experimental results, ME1 = input.

(principle) m--------[expressed in the form of 41. Here, E is the electric field strength [kv/skin], and Eo is the maximum breakdown electric field [kv/skin] obtained when the electrode area is very large at that gas pressure, which is given by the following equation.

・ E.

=Ed×・10o. 355. po. 7p is the gas pressure [at
m] Ed is the theoretical breakdown electric field [kv/arc] of SF6 gas and is given by the following equation.

Ed=89・P m is the parameter of the Weibull distribution of the breakdown electric field. m...7.4 Ino is the parameter of the Weibull distribution of the breakdown electric field. For example, in the case of a mirror-finished stainless steel electrode, ^o = 0. Umbrella × p (1.15 p) In the case of a graphite electrode whose surface has been treated to a roughness of approximately 20 mm, = 40 × p (1.15 p).

Figure 6 shows the week-to-week graphite electrode surface treated to a roughness of about ±20 rm in SF6 gas.
The relationship between the point density N legs and the electrode strength E is shown as an example. On the other hand, the relationship between the breakdown electric field strength E and the area S is
It is given by the '1} formula shown in Fig. 4, but in this case, if the gap with an arbitrary electrode shape and the maximum electric field strength are replaced by an equal electric field of Emax, the m formula becomes the formula ■Em fence = E.

Became 10th (Masho San;) City Ed---'51. here,【
2', Substitute the ■ expression into the glue expression, and between it and the '5} expression, E=Em
By solving the simultaneous equations with ax, S=Seff, the total number of weak points Nt, the equivalent electrode area SeH (or area S), and the maximum electric field strength Emax can be determined.

As mentioned above, dielectric breakdown in high-pressure SF6 gas is determined by the electric field on the negative electrode side, but when forming a discharge gap with a pair of electrodes, the negative electrode side differs depending on the polarity of the applied voltage, so the polarity effect is In order to eliminate this, it is necessary to equalize E for both electrodes according to the '3' formula.

The above concept is shown in FIG. 2 - an example will be described.

That is, in FIG. 2, the electric field strength is corrected by using a shield electrode 19 around the discharge electrode 18 on the lower side. The maximum electric field intensity generated at the ground side discharge electrode 22 is made larger than the maximum electric field intensity generated at the electrode 181 to obtain the relationship shown in FIG. In addition,
FIG. 7 is a diagram showing the relationship between the electric field strength on the electrode surface of the discharge poles 18 and 22 and the area exceeding the electric field strength, where the curve 29 is for the discharge pole 18 and the curve 30 is for the discharge pole. 22. Generally, the ground side electrode such as the discharge electrode 22 has the same potential as the container which is at the ground potential, so the surface electric field of the ground side electrode becomes steeper as it moves away from the tip of the discharge electrode 22 facing the discharge electrode 18. and the characteristic S'E
}' It has a small sloped groove as shown by curve 30 in FIG.
On the other hand, since the discharge electrode 18 on the charging side is surrounded by a container at ground potential, the surface electric field on the charging side does not decrease much even if it is separated from the tip of the discharge electrode 18 facing the discharge electrode 22. However, the characteristic S' house has the curve 29 in Figure 7, which is similar to the curve 29).

The total number of weak points of these two opposing electrodes is given by -', so in order to make the total number of weak points equal to each other in the gradient basket electrode, it is necessary to As shown in Figure 7, the ground side discharge electrode 22
It is necessary to configure it so that it has a maximum electric field Emax.

In this case, the maximum electric field strength Eop of the discharge poles on the charging side is:
Since it is smaller than Emax, the total number of weak points is (as shown in equation 21, -J).pN{E1 poisoning is also E.The reason why the integration range is Eop instead of Emax is because of this conspiracy side. The discharge electrode 18 has a voltage from Eop to Emax.
This is because there is no electric field strength up to In this way, the lake type N(Emax) SeH is
If the configuration is made so that the voltages and voltages are equal to each other, there will be no difference in the applied voltage depending on the gutter characteristics.

That is, from the formula, making the total number of weak points equal for both the discharge electrode 18 on the lightning side and the discharge electrode 22 on the ground side means that both electrodes have an equivalent area and an equal electric field with a maximum electric field force max is made. Therefore, a discharge gap device having no gutter effect can be obtained. Next, another embodiment shown in FIG. 8 will be described.

Components with the same reference numerals as those in FIG. 2 are the same or equivalent parts. In FIG. 8, 31 and 32 are spherical discharge electrodes that face each other and have a discharge gap 2 with a gap length of 6.
3, but the spherical diameter of the electrical discharge pole 31 on the conspiring side is 1
Ratio ◇, the spherical diameter of the ground side discharge electrode 32 is 6.6 cm.

In this way, by making the spherical radius of the discharge electrode 32 on the ground side smaller than the discharge electrode 31 on the power side, the electric field strength on the surface of the discharge electrode 31 on the power side can be weakened, and the surface of the discharge electrode 32 on the ground side can be reduced. It is possible to obtain a relationship similar to that shown in FIG. 7 by increasing the electric field intensity and making the maximum electric field intensity generated on the surface of the grounding side discharge electrodes 32 larger than the maximum electric field intensity generated on the power side discharge electrodes 31. Therefore, the container 5, the discharge gap 23, the discharge electrode 3
If the ground side discharge electrode 32 is configured with an appropriate spherical radius based on the relative relationship with the spherical radius of 1, the discharge electrode 3
N(Emax)・Sef on each electrode surface of 1 and 32
f can be made equal, and the polarity effect of the discharge voltage can be eliminated. In addition, in the embodiments shown in FIGS. 2 and 8, spherical electrodes are shown as discharge electrodes, but it is not necessarily necessary that the electrodes be spherical, and the gist of the present invention. Any shape can be used as long as the number of weak points on a given electrode surface is equalized.

As described above, according to the present invention, by controlling the electric field using the shape of the discharge electrode itself or the shield electrode, a structure that has no strange effects, that is, has good discharge characteristics, is simple.
An inexpensive protective gap device can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the discharge characteristics of a conventional discharge gap device, Fig. 2 is a sectional view showing an embodiment of the present invention, Fig. 3 is a diagram showing a general electric field distribution, and Fig. 4 is a diagram showing the discharge characteristics of a conventional discharge gap device. Diagrams showing the relationship between electrode surface area and breakdown electric field strength, Figures 5 and 7 are diagrams showing the relationship between electric field strength and the area exceeding the electric field strength, and Figure 6 is the electric field strength and average density of weak points. FIG. 8 is a cross-sectional view showing another embodiment. 5 is a container, 7 is an electrically charged gas such as SF6, 18,2
2, 31, and 32 are discharge electrodes, and 23 is a discharge gap. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 In an unequal electric field type protective gap device having a pair of energized side and ground side discharge electrodes arranged with a predetermined gap in a container filled with an insulating gas such as SF_6, the above ground side discharge electrode A protective gap device characterized in that the maximum electric field strength on the surface of the energizing side discharge electrode is made higher than the maximum electric field strength on the surface of the charging side discharge electrode, and the total number of weak points of both electrodes is made equal.