JPH0577165B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zinc oxide lightning arrester, and particularly to a lightning arrester in which a non-linear resistance element housed inside the lightning arrester is arranged in a unique manner.

[Conventional technology]

Lightning arresters control abnormal voltages that occur in power grids and prevent insulation breakdown accidents in various protected devices connected to the grid. In general, lightning arresters discharge current when a certain overvoltage level is reached, and do not operate at a certain voltage level such as normal operating voltage, exhibiting characteristics similar to ordinary insulators.

Zinc oxide type lightning arresters are currently the mainstream type of lightning arrester, and a typical example thereof will be described. FIG. 3 is a side sectional view showing an insulator-shaped zinc oxide type lightning arrester. In the figure, 1 is an insulator tube container having flanges 2 at both ends thereof.
Reference numeral 3 denotes a non-linear resistance element column constructed by connecting a plurality of non-linear resistance elements 31 to 3n in series, each consisting of a sintered body of a metal oxide containing zinc oxide as a main component. This non-linear resistance element column 3 is fixed to the sealing lid 5 via a spring 4 with spring pressure.

Next, the operation will be explained. When an abnormal voltage such as a lightning surge hits the lightning arrester shown in FIG. Surge current is applied to suppress overvoltage below a certain level. On the other hand, after the abnormal voltage is suppressed, the resistance of the non-linear resistance element pillar 3 becomes very high, so that the non-linear resistance element pillar 3 exhibits characteristics close to those of a normal insulator. For such normal continuous operating voltages, the voltage distribution within the lightning arrester will affect the energized life and thermal stability of the lightning arrester.
This characteristic will be explained below using figures.

FIG. 4 is a circuit diagram showing an equivalent circuit of the lightning arrester shown in FIG. 3, and for the sake of simplicity, shows a case where the nonlinear resistance element column 3 is composed of four nonlinear resistance elements 31 to 34. and Ce ₁ to _{Ce 4} are the nonlinear resistance and capacitance of each nonlinear resistance element 31, 32, 32, and 34, respectively, and Cs ₁ to Cs ₃ are the ground stray capacitances. Although it depends on the shape and size of the non-lightning device, roughly speaking, for lightning protection devices with a system voltage of 154 kV or higher, the parallel capacitance value of the stray capacitances Cs ₁ to Cs ₃ to the ground is equal to the capacitance Ce ₁ of each non-linear resistance element. ~ larger than the series capacitance value of Ce ₄ . Furthermore, at normal continuous operating voltages, the capacitive reactance due to the capacitance of each nonlinear resistance element is smaller than the resistance of each nonlinear resistance element, and is approximately several percent to about 20%. Therefore, under normal continuous operating voltage,
Under the influence of the ground stray capacitances Cs ₁ to Cs ₃ , voltage sharing among the nonlinear resistance element pillars 3 becomes unequal. That is, the fourth
As can be seen from the equivalent circuit in the figure, if the current flowing through each non-linear resistance element is Ie ₁ to Ie ₄ , the higher the voltage side, the larger the current Ie flowing through the non-linear resistance element, and the resulting voltage drop becomes larger. .

FIGS. 5a and 5b show the potential distribution characteristics of the nonlinear resistance element column 3 and the voltage characteristics per element of the lightning arrester shown in FIG. 3, respectively. The broken line shows the case where the voltage distribution obtained when there is no stray capacitance to ground Cs ₁ to Cs ₃ is equal, and it can be seen from Figure 5b that the voltages applied to each nonlinear resistance element at continuous operating voltage are equal. I understand. However, if stray capacitance to ground is included, the broken line curve becomes a solid line curve with unequal voltage distribution, and as can be seen from Figure 5b, a higher voltage is applied to the nonlinear resistance element on the high voltage side than to the other nonlinear resistance elements. Become a part of it.

[Problem that the invention seeks to solve]

In this way, if the voltage distribution of the lightning arrester is unequal, a voltage higher than the set value will be applied to some non-linear resistance elements, causing significant deterioration of the non-linear resistance elements in these parts. As a result, there was a possibility that the energized life of the entire lightning arrester would be shortened and the thermal stability would be deteriorated. For this reason, lightning arresters with large ratings require the addition of voltage dividing capacitors for voltage sharing uniformity and large voltage dividing shields, resulting in large and expensive devices. .

The present invention was made to solve these problems, and an object of the present invention is to obtain a lightning arrester in which each nonlinear resistance element shares a uniform voltage.

[Means for solving problems]

In the lightning arrester according to the present invention, a nonlinear resistance element having a large ratio V _NnA /Zc is arranged on the high voltage side.

[Effect]

In this invention, by arranging nonlinear resistance elements with a large ratio V _NnA /Zc on the high voltage side and arranging them in order from the high voltage side to the ground side, the voltage sharing of the lightning arrester becomes equal.

〔Example〕

The concept of this invention will be explained below with reference to the drawings. FIG. 2 is a diagram showing voltage-current (VI) characteristics of each non-linear resistance element. In order to correspond to the lightning arrester series gap, a starting voltage is set, which refers to the voltage at a current of NmA (using a typical current of 1 to 3 mA). This V-I characteristic has a wide current range, especially from NmA to 10KA.
It exhibits excellent nonlinearity with little voltage change, and in this region, almost the same stable V-I curve can be obtained even when a large number of nonlinear resistance elements are manufactured. On the other hand, V- in the small current region below NmA
The I characteristic does not show much nonlinearity, and when mass-producing devices, there is a large variation as shown by the diagonal lines in the figure, which is about ±20% maximum for the same voltage.
There are degrees.

On the other hand, the life of the non-linear resistance element when applied with electricity depends on the ratio of the continuous operating voltage and the operation start voltage shown in the figure, that is, the application rate P. Generally, it is said that if the charging rate P increases by 10%, the charging life will be shortened by about one order of magnitude, so it is important to eliminate the inequality in the voltage distribution of the lightning arrester and use it at a constant average charging rate. It is a way to increase lifespan.

The present invention utilizes such characteristics possessed by non-linear resistance elements. First, the operation start voltage V _NnA of each nonlinear resistance element is measured. Next, the leakage current is measured at a predetermined voltage, in this case the continuous operating voltage for each nonlinear resistance element (the average value obtained by dividing the continuous operating voltage of the lightning arrester by the total number of operating elements). And from the ratio of both, the impedance Zc
seek. Zc obtained in this way and the above
Furthermore, the ratio V _NnA /Zc is determined from V _NnA as follows.

Here, the ratio V _NnA /Zc is an index that determines the application of the nonlinear resistance element, and the idea of the present invention is that the element having a larger value is placed at a location with a higher charge rate.

The derivation of this ratio will be explained below. When a continuous working voltage (P×V _NnA ) is applied to a nonlinear resistance element with an operation start voltage V _NnA and an impedance Zc,
When the current flowing through the non-linear resistance element is Ie, the following relationship holds true.

P・V _NnA /Zc=Ie When P is transferred, P・V _NnA /Zc=1/P・Ie Here, in order to make the charge rate P of each nonlinear resistance element of the lightning arrester constant, P= Assuming that it is constant, it is necessary to satisfy the following equation.

V _NnA /Zc∝Ie As mentioned in the equivalent circuit in Figure 4, a larger leakage current Ie flows through the nonlinear resistance element on the high voltage side with a high voltage share than other nonlinear resistance elements, so from the above equation, In areas where the voltage sharing is large,
If a nonlinear resistance element with a large V _NnA /Zc is placed,
It is possible to satisfy the above formula.

The structure of the lightning arrester according to the present invention is as follows:
It is exactly the same as the one in the figure, and the effect of suppressing abnormal voltages such as lightning surges does not change at all.

Next, the voltage sharing characteristics of the lightning arrester according to the present invention at normal continuous operating voltage will be explained. FIGS. 1a and 1b show examples of the voltage sharing characteristics of the nonlinear resistance element pillar 3 according to the present invention, which are the voltage distribution characteristics and the voltage characteristics per element, respectively. The solid line in the diagram shows the ratio from the high voltage side to the ground side.
This is the case where the nonlinear resistance elements are arranged in order from the highest value of V _NnA /Zc.
Compared to the case of , the voltage applied to the non-linear resistance element on the high voltage side is significantly smaller, and exhibits characteristics close to the case of equal voltage sharing as shown by the broken line.

Further, as another embodiment, the same effect can be obtained by using the capacitive reactance 1/ωCe of the nonlinear resistance element in place of the above-mentioned Zc. This means that the resistance of the non-linear resistance element is 1/1 at around the normal continuous operating voltage.
This is because it is sufficiently larger than ωCe and can be ignored.

〔Effect of the invention〕

As explained above, by arranging a non-linear resistance element with a large ratio V _NnA /Zc on the high voltage side of the lightning arrester, the voltage distribution of the lightning arrester becomes equal, and some high-voltage There is no possibility that the linear resistance element will be significantly deteriorated by the application of electricity. This not only extends the life of the entire lightning arrester, but also improves its thermal stability.In a lightning arrester with a large rating, it is possible to use a voltage dividing capacitor with a smaller capacity to equalize the voltage distribution. It can be made into
This has the effect of requiring only a small partial pressure shield.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the voltage distribution characteristic a of the nonlinear resistance element column and the voltage characteristic b per element in the lightning arrester according to the present invention, and FIG. 2 is a diagram showing the voltage-current (V- I) A diagram showing the characteristics, Figure 3 is a side sectional view showing the lightning arrester currently in use, Figure 4 is the
FIG. 5 is a circuit diagram showing an equivalent circuit of the lightning arrester shown in the figure, and FIG. 5 is a diagram showing voltage distribution characteristics a of a nonlinear resistance element column and voltage characteristics b per element in a conventional lightning arrester. In the figure, 3 is a non-linear resistance element column, 31 to 3
n is the nonlinear resistance element, V _NnA is the operation start voltage of the nonlinear resistance element, and Zc is the impedance of the nonlinear resistance element. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a lightning arrester equipped with a non-linear resistance element column configured by serially connecting a plurality of non-linear resistance elements made of a metal oxide whose main component is zinc oxide, for each non-linear resistance element: , measured starting voltage
Determine the impedance Zc from V _NnA and the leakage current measured at a given voltage, and calculate the impedance Zc from these V _NnA and
A lightning arrester characterized in that a ratio V _NnA /Zc is further determined from Zc, and a nonlinear resistance element having a large ratio is arranged on the high voltage side of the lightning arrester. 2 Ratio from the high voltage side of the lightning arrester to the ground side.
2. The lightning arrester according to claim 1, wherein the nonlinear resistance elements are arranged in order from the highest value of V _NnA /Zc. 3. The lightning arrester according to claim 1 or 2, wherein the predetermined voltage for measuring leakage current is a continuous operating voltage. 4. The lightning arrester according to claim 1 or 2, characterized in that the capacitive reactance 1/ωCe of the nonlinear resistance element is used in place of Zc.