JPH0138872Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a lightning arrester for instantaneously protecting an electric circuit from abnormal voltage.

Conventionally, there has been a device of this type as shown in FIG.

In the figure, 1 is a grounded tank, and the interior 2 of this grounded tank 1 is a gas having high dielectric strength, for example.
The space 3 filled with SF ₆ is a resistor having excellent non-linear characteristics, and is constructed by sequentially stacking resistors 3a, 3b, . 4 is a conductor serving as a high-voltage side lead wire, and 5 is an insulating spacer that supports the lead wire 4.

Next, the operation will be explained. The lead wire 4 is connected to a high voltage terminal of the equipment to be protected, and a surge caused by lightning or the like is short-circuited to the ground through the resistor 3. An example of the voltage-current characteristics of the zinc oxide sintered element used as the resistor 3 is shown in FIG. With such a wide range of constant voltage characteristics,
The increase in terminal voltage due to the above-mentioned surge can be suppressed to a low level. The solid line in Figure 2 shows the characteristics against DC or large current surges, but when AC voltage is applied to such an element, the voltage-current characteristics are as shown by the broken line in Figure 2, considering the peak values of both current and voltage. However, in the small current region, it differs from that for DC voltage. This is because the element has capacitance, and is a characteristic common to other nonlinear resistors including zinc oxide sintered elements. For AC voltages that are higher than a certain level, the voltage-current characteristics are the same as those for DC. In other words, in FIG. 2, when the voltage is above V ₀ , both AC and DC curves are approximately the same, but when below V ₀ , the two curves diverge.
In a zinc oxide sintered element, the current value for this V ₀ is usually 1 mA or more. However, in an AC lightning arrester, AC line voltage is always applied to the nonlinear resistor. This normal ground voltage is selected to be a voltage lower than V ₀ , for example, the level shown as Vp in FIG. 2, in view of the lifetime of the device, which will be described later.

For such low alternating voltages, the device behaves almost as a perfect capacitor, causing the following problems.

In the structure shown in Figure 1, non-linear element 3 and tank 1
There is a stray capacitance between them, and taking this into consideration, voltage sharing by the non-linear resistor can be discussed using an equivalent circuit as shown in FIG. 3 for low AC voltages such as the above-mentioned normal ground voltage.

In Figure 3, H is the total length of the nonlinear resistor,
is the distance from the high voltage end to the point being considered, dX is the differential distance for the following differential calculation, K/dX
is the capacitance of the element with length dX, and CdX is the length
The capacitance that the dX part has between it and the tank, and
V(X) is the potential of the non-linear resistor at point X relative to the total voltage V. There is a relationship between these: V(X)CdX = d/dX [(dV(X)/dX) ・(dX)・(K/dX)] dX, and C and K are constant regardless of X. If we think about this and rearrange this, we get dV(X)/dX ² =(C/K)・V(X). Solving this under the boundary conditions V(0)=V, V(H)=0 gives V(X)=V{sinh[(√)
・(H-K)]/sinh[(√)・H]} is found. The potential distribution V(X) of this resistor is the fourth
The shape is as shown by the solid line in Figure a, which is different from the linear potential distribution shown by the broken line. As can be seen from the above equation, the deviation from the linear potential distribution increases as the length of the resistor increases.

As a result, the electric field inside the resistor E(X) = |dV
(X)/dX| becomes extremely non-uniform as shown by the solid line in FIG. 4b. The maximum electric field is on the high voltage side (X = 0)
The electric field E _nax at that point is extremely high compared to the average electric field E _av . Under such circumstances, the portion of the nonlinear resistor close to the high voltage side is in an overvoltage state than the level of the normal ground voltage V _p shown in FIG. 2. If such an overvoltage is constantly applied to an element, the element generally deteriorates electrically.
FIG. 5 is an example of a voltage-life curve of a zinc oxide element. As the voltage approaches V ₀ , the lifespan rapidly shortens.

In the structure shown in FIG. 1, it is shown that more voltage is applied to the elements at the top (FIG. 4).

Therefore, the conventional construction method has the disadvantage that the normal ground voltage is biased toward the high voltage side, and the nonlinear resistor in that area rapidly deteriorates.

This idea was made in consideration of the above points, and by devising the arrangement of the non-linear resistors, the voltage distribution of the non-linear resistors is equalized and high-performance abnormal voltage protection without deterioration is achieved. The purpose is to provide equipment.

FIG. 6 is a diagram showing an embodiment of this invention. In this Fig. 6, 1 is a grounded tank, the interior 2 of this grounded tank 1 is a space filled with a gas having high dielectric strength, such as SF ₆ , 4 is a conductor that serves as a high voltage side lead wire, and 5 is a lead. This is an insulating spacer that supports the wire 4.

Reference numeral 6 indicates an electrode arranged along the axial direction of the grounded tank 1, and reference numeral 7 indicates a plurality of pipes made of an insulating material.

FIG. 7 is a plan view seen from the direction of the arrow A-A in FIG. 6.

Here, the total length when nonlinear resistors are stacked in series is L, the potentials of arbitrary different equipotential surfaces between the electrode 6 and the ground tank 1 are E ₁ , E ₂ , and the potential of the electrode 6 is E ₀ , if a nonlinear resistor with a height of L・(|E ₁ − _{E 2} |/E ₀ ) can be installed in the space between the equipotential surfaces of E ₁ and E ₂ , the electrode 6 and the ground tank 1
Equal voltage division of the nonlinear resistor becomes possible without disturbing the potential distribution.

Note that the potential distribution illustrated in FIG. 6 can be easily obtained by electric field calculation using a computer.

FIG. 8 shows the internal arrangement of FIG. 6 as a bird's eye view. In FIG. 8, a plurality of stages (three stages in this example) of non-linear resistors 9 are arranged inside each insulating pipe 7 with insulating spacers 10 in between.

The non-linear resistor 9a closest to the electrode 6 is first connected to the high voltage side lead wire 4 on the electrode 6 side by the lead wire 11a.
is connected to the non-linear resistor 9b via the lead wire 8a, and then to the next non-linear resistor 9c via the lead wire 8b. below,
Such a connection is made in series up to the non-linear resistor 9x, which is grounded through the lead wire 11b.

In FIG. 8A, a plurality of non-linear resistors 9c to 9 are attached to the insulating pipe 7 at the right end in FIG.
A cross-sectional view shows an example in which x is housed with an insulating spacer 10 interposed therebetween. This 8th A
In the figure, looking at the nonlinear resistor 9c,
Terminal plates 14, 14 are provided at both ends, and a lead wire 8 is connected to the terminal plate 14 on the upper side.
b refers to the non-linear resistor housed in the insulated pipe adjacent to the left in FIG. 8, which is marked with the symbol 9b, that is, the one immediately above the non-linear resistor 9c. The lead wire connected to the terminal plate 14 on the lower side is connected directly below the non-linear resistor 9c among the non-linear resistors housed in the insulated pipe adjacent to the right side. connected to something. Thereafter, the same connection relationship is maintained, and the high voltage side lead wire 4 continues to the electrode 6.
From, for example, a cylindrical metal container 1 such as a grounded tank
All nonlinear resistors are electrically connected in series in a spiral toward the ground point. In addition, in this FIG. 8A, 17 is the insulating pipe 7.
A coil spring 15 is provided between the metal cap 17 on the upper side and the protective plate 16 on the upper side of the insulating spacer 10, The mutual positional relationship of the non-linear resistors is defined.

FIG. 9 shows a conceptual diagram in which non-linear resistors are arranged in series in a spiral manner.

In FIG. 6, the potential distribution between the electrode 6 and the grounded tank 1 is indicated by a broken line 12. In this invention, each non-linear resistor 9 in FIG.
The shared voltage of a, 9b, 9c, ..., 9x is the 6th
It is arranged so as to match the potential approximately equal to the potential distribution in the figure. Therefore, by doing this, the voltages shared by each of the plurality of nonlinear resistors under constant alternating current voltage become approximately equal to each other, and therefore, for some nonlinear resistors, Therefore, a long-life and highly reliable abnormal voltage protection device can be obtained.

FIG. 10 shows another embodiment of this invention. In this FIG. 10, a conductor 12 is used in place of the electrode 6 in FIG.
Moreover, 13a and 13b are tanks of gas insulated busbars.

FIG. 11 is a graph diagram for explaining the operation of the embodiment of this invention. In the graph of FIG. 11, the horizontal axis indicates the number of the nonlinear resistor used in assembling the device, and the vertical axis indicates the maximum potential of 100 %, which is the potential distribution when the ground potential is 0%. A thin solid line 11A indicates an ideal voltage sharing curve. Dotted line 1
1B shows a voltage sharing curve according to an embodiment of the invention. Further, a thick solid line 11C indicates a voltage sharing curve according to the conventional example. This will be explained below with reference to FIG. 11.

First, the device according to the embodiment of this invention shown in FIG. 8 was assembled using 12 nonlinear resistors made of zinc oxide elements for 500 kV. The non-linear resistor 9a closest to the highest potential is designated as No. 1, and the non-linear resistor 9x closest to the ground potential is designated as No. 12. The potential of the thus assembled example device was measured on the ground side of each non-linear resistor. The measurement results are shown by thick solid line 11C in FIG.

Next, the conventional device shown in FIG. 1 was assembled using 12 nonlinear resistors made of zinc oxide elements for 500 kV. Then, the non-linear resistor 3a on the side closest to the highest potential is set as No. 1,
The nonlinear resistors 3x on the side closest to the ground potential were numbered sequentially below, and the nonlinear resistor 3x was designated as No. 12. Potential measurements similar to those of the above-mentioned embodiment device were also performed on this conventional device. The measurement results are shown by dotted line 11B in FIG.

As can be seen from FIG. 11, by adopting the configuration of the embodiment of this invention, it is possible to realize almost uniform voltage sharing, which is extremely close to the ideal voltage sharing compared to the conventional example. was completed.

[Brief explanation of the drawing]

FIG. 1 is an illustrative diagram of a conventional abnormal voltage protection device,
FIG. 2 is an illustrative diagram of voltage-current characteristics of a zinc oxide sintered element used as a resistor in such a device, and FIG. 3 is an equivalent circuit diagram of the device shown in FIG. 1.
FIG. 4 is a diagram illustrating the potential distribution situation in the device shown in FIG. FIG. 7 is a cross-sectional view of the device shown in FIG. 6 when viewed from the A-A side, FIG. 8 is a bird's-eye view of the device shown in FIG. 6, and FIG. 8A is a cross-sectional view of the device shown in FIG. FIG. 9 is a conceptual diagram showing the connection mode of the non-linear resistor; FIG. 10 is a configuration diagram showing another embodiment of the invention; FIG.
The figure is a graph diagram for explaining the operation of the embodiment of this invention. 1 is a metal container, 6 is an electrode, 7 is an insulated pipe, 9
a,...,9x are nonlinear resistors.

Claims (1)

[Scope of utility model registration request] A grounded cylindrical metal container, an electrode arranged concentrically with the cylindrical metal container and connected to a high voltage side conductor, and radially arranged from the electrode toward the inner bottom surface of the cylindrical metal container. an abnormal voltage protection device comprising a plurality of insulated pipes, and a plurality of nonlinear resistors housed in each of the insulated pipes at a predetermined interval from each other, the plurality of nonlinear resistors The body sequentially selects equipotential surfaces, which have the same number of different equipotential surfaces as the nonlinear resistors, and which are different from each other between the potential of the electrode and the ground potential of the cylindrical metal container, one by one from the side closest to the electrode. The plurality of non-linear resistors are electrically connected in series from the electrode to the ground point of the cylindrical metal container. Abnormal voltage protection device.