JP2573397B2 - Zinc oxide arrester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention relates to a zinc oxide arrester used for a distribution system and a transmission and transformation system.

(Prior Art) Conventionally, this type of lightning arrester mainly selects an operation starting voltage so as to have a sufficient life characteristic against an AC or DC operating voltage stress that is constantly applied, and a large current lightning impulse. Alternatively, the diameter of the zinc oxide element has been selected so as to withstand the switching surge rectangular wave current. Such international standards for zinc oxide surge arresters have been studied in various ways, mainly IEC, and are now coming together through many drafts.

In recent years, attention has been paid to the excellent protection performance and reliability of zinc oxide arresters, and movements to reduce system insulation level and improve reliability by actively utilizing these arresters are progressing worldwide. . For this reason, reliability beyond that required for conventional lightning arresters with gaps has been required, and verification of this has been incorporated into new standards. For example,
For lightning arresters applied to systems with insufficient lightning shielding such as distribution systems, the level of high current impulse withstand capability is raised, and immediately after the application of large current impulse, AC overvoltage is applied for a short time as a stability test. A test was added to verify that thermal runaway does not occur by applying operating voltage. This is due to the fact that the frequency of direct lightning strikes is relatively high in such systems.

(Problems to be Solved by the Invention) However, when the present inventors conducted tests on a conventional zinc oxide arrester according to the above-mentioned new standard proposal, the conventional arrester failed to withstand a large current impulse. However, in a subsequent stability test, it was found that thermal runaway occurred. Therefore, development of a zinc oxide surge arrester capable of sufficiently withstanding a stability test immediately after the application of a large current impulse has been desired.

The present invention has been proposed in order to solve the above-mentioned drawbacks, and an object of the present invention is to provide an efficient and highly reliable zinc oxide surge arrester that can sufficiently withstand a stability test immediately after application of a large current impulse. To provide.

[Constitution of the Invention] (Means for Solving the Problems) The zinc oxide surge arrester of the present invention has an element diameter such that the current density during a large-current impulse test is 5 KA / cm ² or more and 7 KA / cm ² or less. Characterized by using the above zinc oxide element.

(Operation) According to the present invention, a zinc oxide element having an element diameter such that the current density during a large-current impulse test is 7 KA / cm ² or less is used. Therefore, the operation start voltage is always maintained at a level higher than the maximum operation voltage. At the same time, a zinc oxide element having an element diameter such that the conduction current density during a large-current impulse test is 5 KA / cm ² or more is used. It is possible to contribute to scale-up.

Hereinafter, the circumstances that led to the invention will be described. First, the present inventors conducted various experiments, and found that the first rate between the decrease rate of the operation start voltage (here, 0.12 mA / cm ² ) after the application of two large current impulses and the current density of the impulse current was the first. It was found that there was a strong correlation as shown in the figure. In addition,
The experimental results shown in FIG. 1 are 32mm, 38mm, 41mm, 47mm, 65mm
Are obtained by applying an impulse current of 40 to 100 KA twice to an element having a diameter of The rate of change (decrease rate) shown in FIG. 1 indicates the average value of the rate of change of the same polarity and the rate of change of the opposite polarity. It is generally known that the application of an impulse current deteriorates the voltage-current characteristics in a low current region. That is, as shown in FIG.
Indicates the initial characteristics before the impulse current is applied, and the characteristic curve
b and c show the same and opposite polarities to the impulse current polarity after the application of the impulse current, respectively.
As is clear from the figure, when the impulse current is applied, the voltage-current characteristics particularly in the low current region are deteriorated.

By the way, in the conventional test method, since the application of the impulse current and the test of the stability were performed on another sample, the deterioration such as the decrease in the operation start voltage as shown in FIG. It did not affect stability testing.
However, in the new test method, the same sample is mainly used in accordance with the test sequence shown in Fig. 3 applied to distribution arresters or the test sequence shown in Fig. 4 applied to power arresters. Since the large current impulse application and the stability test are performed for the above, the influence of the leakage current due to the deterioration shown in FIG. 1 and the accompanying increase in heat generation appears. According to the experiments of the present inventors, the current density at the time of energizing a large current impulse is 7 KA / cm ^2, and if it is larger than this, the test shown in FIGS. 3 and 4 is rejected, If it is smaller than this, it was found to be acceptable.

The reason is presumed as follows. That is, as apparent from FIG. 1, the impulse current density was 4 KA / cm ²
Is about 20%. On the other hand, the rated voltage of the lightning arrester is usually around the operation start voltage in order to obtain the required protection characteristics.The maximum operating voltage is determined by the rise in the sound phase voltage at the time of a single-line ground fault, and is approximately 80 %. Therefore, if the operation start voltage drops by about 20% due to the application of a large current impulse, the operation start voltage becomes close to the maximum operation voltage, so that a considerable current flows due to the application of the operation voltage, and stability cannot be maintained. Can be Further, when the operation start voltage is reduced by 20% or more due to the application of the large current impulse (that is, when the impulse current density is 7 KA / cm ² or more), the operation start voltage becomes lower than the maximum operation voltage.
It is considered that a considerable amount of current leaks due to the application of the operating voltage, and the influence of heat generation and the like becomes significant. Further, as can be seen from FIG. 1, the gradient of the function between the impulse current density and the operation start voltage is 5 KA / cm ² compared to the case where the function is less than 5 KA / cm ^2.
The gradient in the case of 7 KA / cm ² or less is stronger. Therefore, in order to obtain a lightning arrester element whose element diameter is small to contribute to the downsizing of the lightning arrester itself and the rate of decrease of the operation start voltage can withstand the stability test, the operation of the impulse current density is started. The effect on the voltage drop rate is large, and the drop rate is within the range that can withstand the stability test at 5 KA / cm ²
It can be said that it is most efficient to select 7 KA / cm ² or less.

(Example) Hereinafter, the present invention will be specifically described based on examples.

First Embodiment In this embodiment, the present invention is applied to a distribution-type lightning arrester. The specification characteristics of the distribution arrester are as follows.

Rated voltage 30KV Maximum operating voltage 24KV Limiting voltage (5KA) 80KV Large current impulse withstand capability 4 / 10μs, 65KA Such a conventional lightning arrester for distribution uses a 32 mm diameter zinc oxide element. The test resulted in a thermal runaway and was rejected. This is because the impulse current density when applying a large current impulse exceeds 8.1 KA / mm and 7 KA / mm. Therefore, based on the gist of the present invention,
As a result of using a zinc oxide element having a diameter of 38 mm, the impulse current density at the time of applying a large current impulse could be 5.7 KA / mm, and the test passed.

Second Embodiment In this embodiment, the present invention is applied to an arrester for heavy duty power distribution. The specification characteristics of the heavy duty distribution lightning arrester are as follows.

Rated voltage 30KV Maximum operating voltage 24KV Limiting voltage (10KA) 80KV Large current impulse withstand 4 / 10μs, 100KA Such conventional lightning arrester for heavy duty power distribution uses zinc oxide element with 41mm diameter. The test resulted in a thermal runaway and was rejected. This is because the impulse current density when applying a large current impulse is 7.6 KA / cm ² 7 KA / c
This is because that beyond m ^2. Therefore, as a result of using a zinc oxide element having a diameter of 47 mm based on the gist of the present invention, the impulse current density at the time of applying a large current impulse could be 5.8 KA / cm ^2, and the test could be passed.

Third Embodiment This embodiment is a line discharge charge duty (switching surge) class 1
The present invention is applied to the lightning arrester of the above. The specification characteristics of this arrester are as follows.

Rated voltage 96KV Maximum operating voltage 77KV Limiting voltage (10KA) 259KV High current impulse withstand 4 / 10μs, 100KA Line discharge charge duty 2ms, 210A The conventional surge arrester of this class uses a 41mm diameter zinc oxide element. When the test shown in FIG. 4 was performed, thermal runaway occurred and the test was rejected. This impulse current density during high current impulse applied has exceeded the 7.6KA / cm ² and 7 kA / cm ^2, also line discharge charge responsibilities (switching surge) twice absorbed energy high-current impulse one This is because it is almost equal to the absorbed energy. Then, as a result of using a zinc oxide element having a diameter of 47 mm based on the gist of the present invention, the impulse current density at the time of applying a large current impulse was able to be 5.8 KA / cm ^2, and the test was successfully passed.

[Effects of the Invention] As described above, according to the present invention, a zinc oxide element having an element diameter such that an energizing current density in a large current impulse test is 5 KA / cm ² or more and 7 KA / cm ² or less is used. By configuring the zinc oxide surge arrester, a stability test immediately after the application of a large current impulse can be sufficiently endured, and a zinc oxide surge arrester having high efficiency and reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a rate of decrease in operation start voltage after application of a large current impulse, FIG. 2 is a diagram showing a change in voltage-current characteristics of a zinc oxide element after deterioration due to application of a large current impulse, and FIG.
The figure shows the test sequence for the power distribution arrester, and the fourth shows the test sequence for the power arrester.

Claims (1)

(57) [Claims] 1. A zinc oxide surge arrester characterized by using a zinc oxide element having an element diameter such that a current density during a large current impulse test is 5 KA / cm ² or more and 7 KA / cm ² or less. .