JPH11220816A - Insulation switching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a gas insulation switching device where a plurality of lightening arresters are installed and to reduce its price. SOLUTION: A standard operation duty lightening arrester is applied to a lightening arrester 4 for transmission line being installed at a connection terminal with an overhead line 2, and a light operation duty lightening arrester where the limitation voltage value is set higher than the limitation voltage characteristics of the standard operation duty lightening arrester is applied to a lightening arrester 26 for transformer being installed at a connection terminal with a transformer 3, thus securing the withstand voltage protection of each equipment and at the same time setting one portion of the lightening arrester to the light operation duty arrester for miniaturization and hence miniaturizing a gas insulation switching device and reducing price.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas insulated switchgear installed between a transmission line and a transformer in the field of power generation and transformation of a power system, and more particularly to a surge protection technique using a lightning arrester.

[0002]

FIG. 13 shows, for example, Mitsubishi Electric Technical Report Vol.
53 No. 2, 1979, p. 172 to 176 "50
A single-line diagram showing a conventional gas-insulated switchgear as an electric station such as a power station or a substation to which a lightning arrester described in “Mitsubishi zinc oxide arrester <MOA> for 0 kV” is applied, FIG. 14 is a side view thereof, and FIG. Is a plan view thereof. In the figure, 1 is a gas insulated switchgear, 2 is an overhead line as a transmission line, 3 is a transformer, 4a and 4b are main buses, 5 is an air bushing, 6 is a gas oil bushing, 7 and 8 are branch buses, 9 is a circuit breaker for a transmission line, 10 is a circuit breaker for a transformer, 11 is a main bus-side disconnector for a transmission line, 12 is a main bus-side disconnector for a transformer, 13
Is a transmission line disconnector, 14 is a transmission line lightning arrester, and 15 is a transformer lightning arrester.

Next, a description will be given mainly of a surge protection operation performed by an arrester. Since the entire gas insulated switchgear 1 is housed in a grounded container (tank), the surge voltage generating sources include lightning surge due to lightning strike from the overhead line 2 and switching of the circuit breaker 9 for the transmission line. The accompanying switching surge is the center. For example, in the case of the 500 kV class, the lightning surge withstand voltage value of the gas insulated switchgear 1 is 1550 kV, and the transformer lightning surge withstand voltage value is 1300 kV. For this reason,
Usually, a lightning arrester 14 for a transmission line is installed at a connection end with each overhead line 2 and a lightning arrester 15 for a transformer is installed at a connection end with the transformer 3 to insulate each device from the lightning surge and the switching surge described above. Is protected.

In this case, the two lightning arresters 14 and 15 are:
A standard operation duty lightning arrester having a limited voltage characteristic (limited voltage of 870 kV or less) based on a standard specification based on the Institute of Electrical Engineers of Japan Standardization Committee JEC-2372 "Gas insulated tank type lightning arrester" is adopted.

FIG. 16 is a sectional view showing a schematic structure of the standard operation duty lightning arrester. In the figure, 16 is a container, 1
7 is a zinc oxide element, 18 is an intermediate shield, 19 is a shield, 20 is an insulator, 21 is a ground side shield, 22 is a mounting bracket, 23 is an insulating spacer, 24 is a conductor, and 25 is a control box. The structure of the gas insulated tank arrester is as described above.However, in the case of the standard operation duty arrester, the energy due to the switching surge must be absorbed and suppressed to the limit voltage according to the standard specifications. In particular, in the case of the 500 kV class, the size becomes considerably large in addition to the necessity of sandwiching a metal plate for increasing the heat capacity.
As a result, the height h of the container 16 serving as the outer shape as an arrester is
_{Both 1} and the diameter d ₁ are large numerical values.

[0006]

As described above, the conventional gas insulated switchgear is provided with a plurality of lightning arresters 14 and 15 and each of the switchgears 9 and 10, etc., the main buses 4a and 4b, and the transformer 3 Is protected from lightning surges and switching surges. However, since each of the lightning arresters 14 and 15 has the same standard operation duty, as shown in FIG. Become Accordingly, the arrester 14 and 15, becomes a structure defer independently, for example, as shown in FIG. 14, the distance w ₁ between the centers of the main bus 4b of the transformer 3 becomes particularly large However, there is a problem that the gas insulated switchgear 1 is increased in size and cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a gas-insulated switchgear which is economical and can be downsized.

[0008]

According to a first aspect of the present invention, there is provided an insulated switchgear which is interposed between a transmission line and a transformer, includes a switchgear, a plurality of lightning arresters, and connection means for electrically connecting these devices. In the insulated switchgear, the lightning arrester installed at the connection end with the transmission line is a standard operation duty lightning arrester having a limited voltage characteristic according to a standard specification. Is a light duty duty lightning arrester in which the limiting voltage value is set higher than the limiting voltage characteristic of the standard duty duty lightning arrester.

According to a second aspect of the present invention, in the insulated switchgear according to the first aspect, when a bus is provided between a connection end with the transmission line and a connection end with the transformer, the connection end with the transformer is provided. And a light duty lightning arrester installed on the bus.

According to a third aspect of the present invention, there is provided an insulated switchgear according to the first or second aspect, further comprising a disconnector connected to a connection end to a transmission line via a branch bus. A light duty duty lightning arrester is installed at the connection with the disconnector.

According to a fourth aspect of the present invention, there is provided an insulated switchgear according to any one of the first to third aspects, wherein, when a transformer is connected via a cable, a light-acting lightning arrester is installed at at least one end of the cable. Things.

According to a fifth aspect of the present invention, there is provided an insulated switchgear according to any one of the first to fourth aspects, wherein the light-operation duty lightning arrester is installed at the connection end with the transformer. It was housed in the container of the vessel.

According to a sixth aspect of the present invention, there is provided an insulated switchgear according to any one of the first to fifth aspects, wherein the light-acting lightning arrester is different from the lightning-arrival lightning element of the standard operating duty lightning arrester. % Or less.

According to a seventh aspect of the present invention, there is provided an insulated switchgear interposed between a transmission line and a transformer, wherein the switchgear, a plurality of lightning arresters, and connection means for electrically connecting these devices are provided in a grounded container. In the insulated switchgear, the withstand voltage characteristic of one or both of the switchgear and the transformer is set lower than the withstand voltage characteristic according to the standard specification.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 The present invention focuses on installing a plurality of lightning arresters for surge protection of a gas insulated switchgear, and focusing on a difference in operation responsibilities of each lightning arrester,
The overall size and price have been reduced, and specific examples thereof will be described sequentially from the first embodiment.

FIG. 1 is a single line diagram showing a gas insulated switchgear according to Embodiment 1 of the present invention, and FIG. 2 is a side view thereof. In the figure, reference numeral 1 denotes a gas insulated switchgear which is interposed between an overhead line 2 as a transmission line and a transformer 3 and houses each device described below in a grounded container (tank).
Reference numerals a and 4b denote main buses, which can be connected to main buses of adjacent gas insulated switchgears. Reference numeral 5 denotes an aerial bushing for connecting to the overhead line 2, and reference numeral 6 denotes a gas oil bushing for connecting to the transformer 3.

Reference numerals 7 and 8 denote branch buses required in connection with the installation position of the air bushing 5 and the transformer 3 and the like, and 9 denotes a transmission line for opening and closing the connection between the overhead line 2 and the main buses 4a and 4b. A circuit breaker 10, a transformer circuit breaker for opening and closing the connection between the main buses 4a, 4b and the transformer 3, a main line side disconnector 11 for a transmission line, a main line disconnector 12 for a transformer, and a line breaker 13 It is a disconnector for transmission line. Reference numeral 14 denotes a lightning arrester for a transmission line installed at a connection end with the overhead line 2, to which the standard operation duty lightning arrester described above is applied. Reference numeral 26 denotes a lightning arrester for a transformer installed at the connection end with the transformer 3, to which a light duty lightning arrester is applied. Here, the light duty lightning arrester is a lightning arrester in which the limiting voltage value is set higher than the limiting voltage characteristic of the standard operating duty lightning arrester.

That is, since the lightning arrester 14 for the transmission line is installed at the connection end with the overhead wire 2 through which the lightning surge enters, the limiting voltage characteristics must satisfy those of the standard operation duty lightning arrester. However, as for the lightning arrester 26 for the transformer, the lightning arrester 14 for the transmission line is installed, and taking into account that the surge protection operation associated with the limited voltage characteristic, which is the standard operation responsibility, is taken into consideration, the standard operation is not always required. There is no need to apply duty arresters. Since a plurality of lightning arresters are connected in parallel, the discharge current during operation of the lightning arrester due to surge intrusion is distributed to the multiple lightning arresters, and the discharge current of each individual lightning arrester is reduced. is there.

FIG. 3 shows the voltage-current characteristics of the zinc oxide elements having different operation responsibilities. The lower curve shows the characteristics of the zinc oxide element for the standard operation lightning arrester, and the upper curve shows the zinc oxide element for the light operation duty lightning arrester. It is a characteristic. As shown in the figure, the current values a ₁ and a _{2 of} both characteristics corresponding to the element voltage 相当 corresponding to the limit voltage of the surge arrester are different (a ₂ <a ₁ ). In other words,
For the same current, the limiting voltage value of the light duty lightning arrester is higher than that of the standard duty lightning arrester.

Specifically, the extent to which the operation duty of the lightning arrester 26 for the transformer is reduced from that of the lightning arrester 14 for the transmission line, which is the standard operation duty lightning arrester, is described in detail in the gas-insulated switchgear 1 shown in FIGS. It will be decided by conducting circuit simulation etc. based on dimensional specifications, but it will be determined from the viewpoint of general specifications and effective reduction of lightning arresters by reducing operation duty as a result, the current value a ₂ shown in FIG. 3 it was concluded that should be less than 40% of the current value a _1. That is, the current value corresponding to the specified limited voltage of the lightly operated lightning arrester is set to 40% or less of that of the standard operationly duty lightning arrester.

In this case, the light duty surge arrester has almost no energy absorption duty for switching surge required for the standard duty lightning arrester, only the light duty surge energy absorption duty is required, and the heat duty of the light duty duty lightning arrester is standard. It is one-tenth or one-tenth of an operation duty lightning arrester.

The lightening of the lightning arrester can be greatly reduced by reducing the above-mentioned operation duty. FIG. 4 is a cross-sectional view showing the schematic structure of the light duty duty lightning arrester. In the figure, 2
7 is a container, 28 is a zinc oxide element stacked linearly, 2
9 is a ground terminal, 30 is an insulator, 31 is a zinc oxide element 28
, 32 is a metal plate, 33 is a spring conductor, 3
4 is a shield, 35 is a conductor, 36 is an insulating spacer, 37
Is a mounting bracket. Since the detailed configuration of the arrester itself is not the subject of the present application, a detailed description will be omitted. However, as a result of the reduced duty of operation, each zinc oxide element has a significantly larger size than that of the standard surge arrester described in FIG. Down to
The height of the height the outer shape of the overall arrester h ₂ and a diameter d ₂ is the standard operating duty arrester h _1, and the diameter d ₁ (FIG. 16
See)).

As a result, the lightning arrester 26 for the transformer employing the light duty lightning arrester does not need to have a structure (see FIG. 14) which is independently installed like the conventional lightning arrester 15 for the transformer, as shown in FIG. , Can be directly connected to a lower portion of a container for accommodating the branch bus 8, and electrically connected to the branch bus 8 via an insulating spacer 36. Therefore, the floor area of this portion is greatly reduced, and as shown in FIG. 2, the distance w ₂ between the center of the transformer 3 and the center of the main bus 4b is reduced.
Is significantly shorter than the conventional distance w ₁ (see FIG. 14),
The price as the gas insulated switchgear 1 is also reduced.

FIG. 5 shows an example of a structure of a light duty lightning arrester different from that of FIG. 4. By arranging zinc oxide elements electrically connected in series also in the radial direction, the height of the lightning arrester can be reduced particularly. It is intended. In the figure, 38 is a container,
39 is a zinc oxide element, 40 is an intermediate shield, 41 is a ground terminal, 42 is an insulator, 43 is a shield, 44 is a conductor,
5 is an insulating spacer, and 46 is a mounting bracket. in this case,
In particular, the height of the zinc oxide element 39 is reduced and the diameter of the zinc oxide element 39 is increased.
Height h ₃ is decreased (h ₃ <h _2), diameter d ₃ is increased (d _3> d _2). Which of the light duty duty lightning arresters shown in FIGS. 4 and 5 is applied may be arbitrarily selected from the installation position, the relation with peripheral devices, and the like.

Although FIGS. 1 and 2 show a case where the overhead line 2 is connected as a transmission line, the present invention can be similarly applied to a case where a cable is connected, and the same effect can be obtained. To play. Also, the transformer 3 is an oil-filled transformer,
A gas-insulated transformer may be used.

Embodiment 2 FIG. FIG. 6 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 2 of the present invention, and FIG. 7 is a plan view thereof. Hereinafter, points different from the first embodiment will be mainly described. Here, the following two types of lightning arresters are additionally installed. That is, the main bus side arrester 47 for the transmission line and the main bus side arrester 48 for the transformer. The light duty duty lightning arrester described above is applied to each of these lightning arresters.

The main buses 4a and 4b may be open ends on the circuit depending on the open / close operation of the disconnectors 11 and 12. When a surge enters under such conditions, a so-called surge traveling wave reflection is generated. Due to the phenomenon, the main buses 4a, 4a, 4
At b, a high voltage can be generated. The transmission line main bus arrester 47 and the transformer main bus arrester 48 shown in FIG. 6 effectively suppress this high voltage. Here, the lightning duty lightning arresters can be applied to these additional lightning arresters 47 and 48 because the standard operation duty lightning arresters are connected to the connection end with the overhead line 2 as described in the first embodiment. It is assumed that the power line arrester 14 is installed.

Although it is necessary to determine the degree to which the operation duty of the lightning arresters 47 and 48 is to be specifically reduced by performing a circuit simulation or the like based on the specifications of the configuration shown in FIG. As shown in FIG. 7, these lightning arresters 47 and 48 may have a simple and compact structure that is directly connected to a container above the main buses 4a and 4b, respectively. It becomes possible. Accordingly, the distance w ₃ between the centers of the main bus 4b of the transformer 3 can be kept almost the same value as the distance w ₂ of the first embodiment without the arrester 47 and 48.

As shown in FIG. 6, when installing a plurality of lightning arresters over the entire gas insulated switchgear 1,
With the surge voltage suppression function synergistically, the voltage rise of each part at the time of surge intrusion can be suppressed to a considerably low value. When viewed from the protected device, the withstand voltage value can be reduced below the standard value. For example, 5
The withstand voltage value of the 00 kV transformer is reduced to 1175 kV from the withstand voltage value of 1300 kV according to the standard specification.
Circuit simulation results indicate that the withstand voltage value of the 50 kV gas insulated switchgear can be reduced to 1300 kV from the withstand voltage value of 1550 kV according to the standard specification. In this case, the outer shape and price of these protected devices can be reduced accordingly.

Embodiment 3 FIG. 8 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 3 of the present invention, and FIG. 9 is a side view thereof. Hereinafter, the points different from the above embodiment will be mainly described. Here, for example, a branch bus 49 having a length of 20 m or more is provided, for example, in relation to the relationship with the drawing position of the overhead bus 2, and the disconnector 1 of the branch bus 49 is provided.
A lightning arrester 50 for branch buses is installed at the three side ends. The light-duty lightning arrester described above is applied to the branch bus arrester 50.

If a branch bus having a length exceeding about 20 m is present, a high voltage may be generated at this portion due to the reflection of a so-called surge traveling wave. Suppress to protect surrounding switchgear from overvoltage. In this case, a light-duty lightning arrester that can be downsized is applied to the branch bus arrester 50.
As shown in the figure, the lightning arrester for branch bus 50 can adopt a simple and small structure directly connected to the container accommodating the branch bus 49. By additionally installing the lightning arrester 50, the installation area of the gas insulated switchgear 1 can be reduced. It hardly increases.

As described in the second embodiment, focusing on the synergistic effect of the voltage suppressing function by installing a plurality of lightning arresters in a grounded container connected continuously and relatively close to each other, the transformer 3 It is also possible to pursue a reduction in the size and the price by lowering the withstand voltage value such as the standard specification.

Embodiment 4 FIG. FIG. 10 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 4 of the present invention.
Is a side view of the transformer 3. The lightning arrester for light operation is applied as well as the lightning arrester 26A for the transformer. Here, the lightning arrester 26A for the transformer is housed in the container of the transformer 3. Since it is a light duty, the lightning arrester can be made small,
The accommodation of the transformer 3 in the container can be realized relatively easily.

Further, the connection position of the transformer lightning arrester 26A is closer to the transformer 3 itself, which is most effective in reducing the withstand voltage value of the transformer 3. The transformer lightning arrester 26A is arranged in insulating oil when the transformer 3 is an oil-filled type, and in insulating gas when the transformer 3 is a gas-insulated type.
Of course, by using the insulating spacer, it may be housed in a space separate from the insulating oil or the insulating gas of the transformer, though it is inside the container of the transformer 3.

Embodiment 5 FIG. FIG. 12 is a single line diagram of a gas insulated switchgear according to Embodiment 5 of the present invention. Here, the transformer 3 is connected via a cable. In the figure, 52 is a cable, 53 and 54 are cable heads, 51 is a cable end lightning arrester provided at the connection end with the cable head 53, and here a light duty duty lightning arrester is applied. 26B is a transformer lightning arrester installed at the connection end with the transformer 3, to which a light duty duty lightning arrester is similarly applied. Thereby, not only each switching device in the gas insulated switchgear 1 but also the cable 52 and the transformer 3 are suppressed in surge voltage below their withstand voltage value, and reliable insulation protection is achieved.

However, if the cable 52 is particularly long, the energy absorption due to the switching surge of the cable portion becomes large. Therefore, either the cable end lightning arrester 51 or the transformer lightning arrester 26B is used as the standard operation duty lightning arrester. There is a need to. Further, the lightning arrester 26B for the transformer installed on the transformer 3 side may be arranged in the elephant part for accommodating the cable head 54 of the transformer 3, and is accommodated in the container of the transformer 3 as shown in FIG. You may make it.

In each of the above embodiments, a lightning arrester using a zinc oxide element has been described, but the present invention is not necessarily limited to this.
The present invention is similarly applicable to a lightning arrester of a type in which a discharge gap and a characteristic element are connected in series, and has the same effect.

[0038]

As described above, the insulated switchgear according to the first aspect is interposed between the power transmission line and the transformer, and is configured to electrically connect the switchgear, the plurality of arresters, and each of these devices. In the insulated switchgear that is housed in a grounded container, among the plurality of lightning arresters, the lightning arrester installed at the connection end with the transmission line is a standard operation duty lightning arrester having a limited voltage characteristic according to standard specifications, and The lightning arrester is a light duty lightning arrester with a limiting voltage value set higher than the limiting voltage characteristics of the standard operating duty lightning arrester, so that the withstand voltage protection of each device can be secured and a part of the lightning arrester is used as a light duty duty lightning arrester. The size is reduced, and the size and the price of the gas insulated switchgear are reduced.

Further, in the insulation switching device according to the present invention, when a bus is provided between the connection end to the transmission line and the connection end to the transformer, the connection end to the transformer and the bus are connected to each other. Since the light duty duty lightning arrester is installed, it is possible to reliably suppress the voltage of the bus, which becomes an open end and in which the surge voltage is liable to increase, without a significant increase in size and cost.

Further, when the insulated switchgear according to the third aspect includes a disconnector connected to a connection end to a transmission line via a branch bus, a connection between the connection end to the transformer and the disconnector is provided. Since the lightning duty lightning arrester is installed in the power supply unit, the voltage of the branch bus which becomes an open end and in which the surge voltage tends to increase can be surely suppressed without a significant increase in size and price.

Further, in the insulated switchgear according to claim 4, when a transformer is connected via a cable, a light-acting lightning arrester is installed at at least one end of the cable.
The withstand voltage protection of the cable portion can be realized at a relatively small size and at a low price.

According to a fifth aspect of the present invention, in the case where a light duty lightning arrester is installed at a connection end with the transformer, the light duty lightning arrester is housed in a container of the transformer. The withstand voltage protection of the device is more reliably performed.

Also, in the insulated switchgear according to claim 6, since the lightning duty lightning arrester has a current value corresponding to a prescribed limit voltage of 40% or less of that of the standard operating duty lightning arrester, the light duty duty lightning arrester is provided. The actual benefits of miniaturization and cost reduction of the standard operation duty lightning arrester will be remarkable.

According to a seventh aspect of the present invention, there is provided an insulated switchgear which is interposed between a transmission line and a transformer, and includes a switchgear, a plurality of lightning arresters, and connection means for electrically connecting these devices in a grounded container. In the insulated switchgear housed in the switchgear, the withstand voltage characteristic of one or both of the switchgear and the transformer is set lower than the withstand voltage characteristic according to the standard specification. By effectively utilizing the synergistic effect of the voltage suppression function, it is possible to reduce the size and cost of switchgear and the like.

[Brief description of the drawings]

FIG. 1 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 1 of the present invention.

FIG. 2 is a side view showing the gas insulated switchgear of FIG.

FIG. 3 is a diagram showing voltage-current characteristics of a zinc oxide element.

FIG. 4 is a cross-sectional view showing a schematic structure of a light-operation duty lightning arrester.

FIG. 5 is a cross-sectional view showing a schematic structure of a light duty duty lightning arrester different from FIG. 4;

FIG. 6 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 2 of the present invention.

FIG. 7 is a plan view showing the gas insulated switchgear of FIG. 6;

FIG. 8 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 3 of the present invention.

FIG. 9 is a side view showing the gas insulated switchgear of FIG. 8;

FIG. 10 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 3 of the present invention.

11 is a side view showing the transformer 3 of FIG.

FIG. 12 is a single-line diagram showing a gas-insulated switchgear according to Embodiment 5 of the present invention.

FIG. 13 is a single line diagram showing a conventional gas insulated switchgear.

FIG. 14 is a side view showing the gas insulated switchgear of FIG.

FIG. 15 is a plan view showing the gas insulated switchgear of FIG.

FIG. 16 is a sectional view showing a schematic structure of a standard operation duty lightning arrester.

[Explanation of symbols]

1 gas-insulated switchgear, 2 overhead wires, 3 transformers, 4
a, 4b main bus, 9 breaker for transmission line, 10 breaker for transformer, 11 disconnector for main bus side for transmission line, 12
Main bus-side disconnector for transformer, 13 Power line disconnector, 1
4 Lightning arresters for transmission lines, 26, 26A, 26B Lightning arresters for transformers, 47 Lightning arresters for main buses for transmission lines, 48 Lightning arresters for main buses for transformers, 49 branch busbars, 50 lightning arresters for branch busbars, 51 cable lightning arresters, 52 cables.

Claims (7)

[Claims] 1. An insulated switchgear interposed between a transmission line and a transformer, wherein a switchgear, a plurality of lightning arresters, and connection means for electrically connecting these devices are housed in a grounded container. Among the plurality of lightning arresters, the lightning arrester installed at the connection end with the transmission line is a standard operation duty lightning arrester having a limiting voltage characteristic according to a standard specification, and the other lightning arrester is a limiting voltage according to the limiting voltage characteristic of the standard operation duty lightning arrester. An insulated switchgear characterized by a light duty lightning arrester with a high value set. 2. When a bus is provided between a connection end to a transmission line and a connection end to a transformer, a light duty lightning arrester is installed at the connection end to the transformer and the bus. The insulated switchgear according to claim 1. 3. When a disconnector connected to a connection end to a transmission line via a branch bus is provided, a light duty lightning arrester is installed at a connection end to the transformer and a connection portion to the disconnector. The insulated switchgear according to claim 1 or 2, wherein: 4. The insulated switchgear according to claim 1, wherein when a transformer is connected via a cable, a light duty lightning arrester is installed at at least one end of the cable. 5. The light-acting lightning arrester installed at the connection end with a transformer, wherein the light-acting lightning arrester is housed in a container of the transformer. An insulated switchgear according to any of the preceding claims. 6. A light duty lightning arrester having a current value corresponding to a prescribed limit voltage of 40% of that of a standard lightning arrester.
The insulated switchgear according to any one of claims 1 to 5, wherein: 7. An insulated switchgear interposed between a transmission line and a transformer, wherein a switchgear, a plurality of lightning arresters, and connection means for electrically connecting these devices are housed in a grounded container. An insulated switchgear, wherein the withstand voltage characteristic of one or both of the switchgear and the transformer is set lower than the withstand voltage characteristic according to the standard specification.