JPH0684614A - Electric machinery - Google Patents

Abstract

PURPOSE:To obtain an arrester construction having low protection level in which protection characteristics can be regulated easily while suppressing fluctuation thereof. CONSTITUTION:The arrester comprises zinc oxide elements 3a, 3b, semiconductor switches 4a, 4b and a voltage detector connected in parallel with a part of the zinc oxide elements, and a control circuit 6 for delivering firing signals to the semiconductor switches 4a, 4b for a predetermined time when the output from the voltage detector 5 exceeds a predetermined level. Since the semiconductor switches 4a, 4b are fired only upon intrusion of overvoltage, leak current can be suppressed for normal operating voltage and voltage level can be kept constant and regulated easily at the time of transition to overvoltage suppressing operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric device which suppresses a voltage caused by a surge, such as a lightning surge, which intrudes into a device connected in parallel with the lightning surge and improves reliability of insulation of the device. is there.

[0002]

2. Description of the Related Art FIG. 2 shows an equivalent circuit of a lightning arrester described in, for example, the Electrical Review April 1978 issue, FIG. 2a shows a lightning arrester with a gap, and FIG. 2b shows a lightning arrester without a gap.
In the figure, reference numeral 1 denotes a lightning arrester with a gap formed by connecting a plurality of characteristic elements 1a in series and a series gap 1b in series, and 2 is formed by connecting a plurality of zinc oxide type arrester elements 2a in series. A gapless arrester is shown.

Next, the operation of the conventional lightning arrester will be described. In the lightning arresters 1 and 2, the relationship between the voltage and current applied to the characteristic element 1a inside and the zinc oxide element 2a is the characteristic shown in FIG. 3 due to the non-linear resistance characteristic of the element. Even if is added, the overvoltage is suppressed to a level equal to or lower than the limit voltage level corresponding to each number. Therefore, as shown in FIG. 4, when the protected power device is connected in parallel with the lightning arrester 1 or 2, even if a dangerous surge overvoltage comes in, the lightning arrester has an overvoltage below a predetermined level due to the above characteristics. As a result, a dangerous surge does not enter the protected power device, and the insulation reliability is improved. The predetermined limiting voltage is determined by the number of elements inside the arrester. In addition, the operating voltage is always applied to the protected power device and is also applied to the lightning arrester, but in the lightning arrester with a gap, almost no current flows due to the series gap 1b, and the characteristic element 1a is protected by heat generation. Deterioration of characteristics and thermal stability is prevented. On the other hand, in the gapless lightning arrester 2, the number of zinc oxide elements is increased so that the leakage current is small at a constant operating voltage, and the constant operating voltage is selected to be a voltage lower than the limit voltage. Only current flows so that the heat generation does not deteriorate the protection characteristics and thermal stability.

[0004]

Since the conventional lightning arrester is constructed as described above, a lightning arrester with a gap requires a sufficient withstand voltage against a constant operating voltage. Therefore, it is necessary to stably discharge those gaps, and there is a limit to the protection performance due to the control of the discharge voltage of the series gaps, the time delay of discharge, and the like. Also, in the gapless arrester, the number of zinc oxide elements is determined and the value of the limiting voltage is determined because the heat generated by the leakage current due to the constant operating voltage must be within the allowable range. There was a problem that it was difficult to significantly reduce the level.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a lightning arrester structure capable of greatly reducing the protection level.

[0006]

An electric device according to the present invention detects a semiconductor switch connected in series with a part of a plurality of zinc oxide type arrester elements connected in series, and a voltage applied to the semiconductor switch. It is provided with a voltage detector and a control means for closing the semiconductor switch when the voltage detector exceeds a specified value.

[0007]

In the electric device according to the present invention, the semiconductor switch is closed only when the surge voltage enters, so that there is no gap discharge variation or discharge time delay, and the semiconductor element is extinguished with respect to the constant operating voltage. Therefore, it is possible to provide a lightning arrester with a low protection level, in which various characteristics are not deteriorated due to temperature rise.

[0008]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 3a and 3b are element groups in each of which a plurality of zinc oxide type arrester elements are connected in series.
The semiconductor switches 4a and 4b serially connected in parallel with a are connected in antiparallel, and the voltage detector 5 is connected in parallel with the semiconductor switches 4a and 4b. Reference numeral 6 is a control circuit which sends an ignition signal to all the thyristor elements constituting the semiconductor switches 4a and 4b for a certain period when the output of the detector 5 exceeds a certain level.

Next, the operation of the electric device according to the present invention will be described. The semiconductor switches 4a and 4b are in an extinguished state in a state where they are connected in parallel to a protected power device (not shown) and a constant operating voltage is applied to the arrester, and the output of the voltage detector 5 is the element group 3a. , 3b, a voltage obtained by dividing the operating voltage is applied. As described above, the number of elements and the limiting voltage of the elements are selected so that the leakage current of the element groups 3a and 3b has an impedance that does not cause a problem when the surge voltage does not enter. Next, when a surge voltage of a level that requires overvoltage suppression enters the protected power equipment, that is, the lightning arrester, the voltage detector 5
Output exceeds the specified value, and the control circuit 6 which receives the detection output of the voltage detector 5 sends an ignition signal to the semiconductor switches 4a and 4b for a certain period. When one of the semiconductor switches 4a and 4b fires, the element group 3a is short-circuited, the protection level of the entire lightning arrester is reduced to a level equivalent to that of the element group 3b, and a lightning arrester with a low protection level is obtained. When the ignition pulse sent to the semiconductor switches 4a and 4b is extinguished after a certain period of time and the current flowing through the semiconductor switch becomes small, the semiconductor switch 4a or 4b is extinguished and returns to the normal state.

Embodiment 2. Although the voltage detector 5 is provided in parallel with the semiconductor switches 4a and 4b in the first embodiment, the voltage detector 5 may detect the terminal voltage of the entire lightning arrester.

[0011]

As described above, according to the present invention, the semiconductor switch is provided in parallel with the element group, and the switch is ignited when a surge voltage invades, so that the switch is different from the conventional gap. The ignition level can be easily adjusted, variation in the ignition level is small, and a lightning arrester configuration with a low protection level can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional device.

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

FIG. 4 is a diagram showing an example of use of a lightning arrester.

[Explanation of symbols]

 3a, 3b zinc oxide type arrester element group 4a, 4b semiconductor switch 5 voltage detector 6 control circuit

Claims (2)

[Claims] 1. A lightning arrester in which a plurality of zinc oxide type arrester elements are connected in series, a semiconductor switch connected in parallel to a part of the zinc oxide type arrester element forming the arrester, and a voltage applied to the semiconductor switch. An electric device, comprising: an electric detector for detecting the electric shock; and a control circuit for closing the semiconductor switch when the voltage of the voltage detector exceeds a certain level. 2. The electric device according to claim 1, wherein one end of the semiconductor switch is set at or near the ground potential.