JPH04308678A - Protector against thunder surge - Google Patents

Abstract

PURPOSE:To exactly find the replacement timing by detecting the deterioration of a varistor quantitatively and accurately. CONSTITUTION:When a thunder surge impulse is induced in a power system 1a, a surge current flows to the varistor 3 inside a protector 2. If this exceeds the specified current I0, the voltage across the varistor 3 tops the limited voltage V0, and the detection signal of a voltage detector 4 reaches a reference voltage signal b. Hereby, surge detection signals are output from a comparator 5, and those are countered with a counter 6. The counter 6 counts the detection signals c, and counts in up by one count. By repetition of this, if the counter of any phase out of three phases reaches the life limit, it judges that as the deterioration of the varistor 3, and outputs a varistor deterioration signal d. The signal d is sent to a display and an alarm. Even if small energy of thunder surges are applied several times and the varistor deteriorates, since the deterioration can be detected quantitatively, one can find proper replacement timing of the varistor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightning surge protection device in which a varistor is connected as a lightning surge absorbing means to the input end of an electrical circuit to be protected.

0002

2. Description of the Related Art A protection device such as a lightning arrester is used as a protection device for protecting an electric circuit connected to a power system from lightning surges. This type of protection device uses a protective gap that utilizes an air discharge, a zinc oxide varistor (non-linear resistance element), or the like as a surge absorbing element.

[0003] Considering the miniaturization, cost reduction, and impulse response of such a protection device, it is advantageous to use a varistor as the surge absorption element, and varistors are currently widely used. However, mainly from the perspective of cost reduction, devices are generally not equipped to detect damage or deterioration of varistors. Not only is it impossible to know, but even if damage or deterioration that requires replacement has actually occurred, it cannot be known, so lightning surges may be induced after damage or deterioration has occurred. If this occurs, the lightning surge may be directly applied to the electrical circuit. In such a situation, even though a lightning surge protection device is provided, devices in the electric circuit cannot be protected from lightning surges, resulting in damage to them.

0004

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lightning surge protection device that is equipped with a means for detecting deterioration of a varistor and knowing the exact time to replace it.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the lightning surge protection device of the present invention includes a varistor connected as a lightning surge absorbing means to the input end of an electric circuit to be protected, and a terminal of this varistor. a voltage detection means for detecting voltage; a comparison means for comparing the voltage detected by the voltage detection means with a predetermined threshold voltage; and outputting a surge detection signal when the former exceeds the latter; The device includes a counter that counts the number of times a surge detection signal is generated from the means, and outputs a deterioration detection signal indicating the life limit of the varistor when the count value reaches a predetermined life limit.

[0006]

[Operation] Varistors have various characteristics depending on the materials used, and for example, they have voltage versus current characteristics as shown in FIG. In FIG. 4, the rated voltage of the circuit corresponds to the initial rise portion of the characteristic line. When a large current I0 due to a lightning surge flows through the varistor, a voltage V0 corresponding to the current is generated across the varistor. In addition, the surge current and surge wave tail length as shown in Figure 5 (Figure 6
) There is a surge life characteristic based on the relationship.

From the surge life characteristics shown in FIG.
The remaining life of the varistor can be determined based on the value of the surge current that actually flows and the wave tail length of the surge current. Based on this principle, the varistor voltage due to the actually applied lightning surge is detected, compared with a threshold value such as the limiting voltage Vs in the varistor operating region, and the number of times the former exceeds the latter is counted. When the varistor reaches a predetermined value determined from FIG. 5, that is, the life limit, it is assumed that the life of the varistor has come to an end, and a deterioration detection signal is generated. Note that by determining the deterioration state of the varistor based on the voltage across the varistor, which is easy to detect, the equipment configuration of the detection end can be simplified.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a block diagram illustrating a lightning surge protection device constructed in accordance with one embodiment of the present invention.

The lightning surge protection device shown in FIG. 1 includes a commercial power source 1, a power system 1a connected to the commercial power source 1, and a lightning surge absorber 2 connected to the power system 1a. The lightning surge absorption device 2 includes a zinc oxide type nonlinear resistance element (
barista) 3.

The voltage versus current characteristic of the varistor 3 is as shown in FIG.
When a current I0 flows through the varistor 3, a corresponding voltage V0 is generated across the varistor 3. Figure 5 shows the surge life characteristics of the varistor 3. By specifying the surge current and wave tail length (Figure 6) applied to the varistor 3, the remaining life of the varistor 3 can be determined by determining how many lightning surges will occur in the future. It shows the lifespan limit of whether it can withstand the application of impulses. FIG. 6 shows a standard waveform of a lightning surge impulse (current), in which e represents the standard wavefront length, f represents the standard wavetail length, and g represents the wave height value.

In FIG. 1, the voltage across the varistor 3 is detected for each phase by a voltage detector 4, and its detection signal a is introduced into a comparison input terminal of a comparator 5. A reference voltage signal b corresponding to the limit voltage V0 of the varistor 3 (see FIG. 5) is introduced into the reference input terminal of the comparator 5. Comparator 5
compares signals a and b separately for each phase, and when a≧b,
That is, when the varistor voltage exceeds the limit voltage V0, the surge detection signal c is output. This surge detection signal c
is counted separately for each phase by the counter 6. When the count content of the counter 6 reaches the life limit set in advance according to FIGS. 4, 6, and 5, the counter 6 outputs a deterioration detection signal d indicating the life limit of the varistor.

When a relatively small energy lightning surge impulse is induced into the power system 1a, a lightning surge current flows through the varistor 3 in the lightning surge protection device 2. When this surge current exceeds the surge current I0 defined in FIG. 5, the voltage appearing across the varistor 3 exceeds the limit voltage V0,
The detection signal a of the voltage detector 4 reaches the reference voltage signal b. As a result, the comparator 5 outputs the surge detection signal c,
It is counted by counter 6. counter 6
counts the surge detection signal c and increments by one. By repeating this process, when the counter of any one of the three phases reaches its life limit, it is determined that the varistor 3 has deteriorated, and a varistor deterioration detection signal d is output. This deterioration detection signal d is used, for example, to display on a display device (not shown) or to sound an alarm.

According to the above embodiment, even if the varistor 3 deteriorates due to the application of lightning surges of relatively low energy such as induced lightning several times, the deterioration can be quantitatively detected. , it is possible to appropriately notify when it is time to replace the lightning surge protection device or varistor.

FIG. 2 shows another embodiment of the invention. In the figure, the same reference numerals as in FIG. 1 indicate the same members, and the explanation thereof will be omitted. In this embodiment, an AND gate 8 is provided between the comparator 5 and the counter 6 for each phase. In AND gate 8, comparator 5
The surge detection signal c from the clock generator 7 is used as a gate control signal, and while the gate of the AND gate 8 is opened by the surge detection signal c, the clock pulse h generated by the clock generator 7 passes through the AND gate 8 and controls the counter. 9
is input and counted. The counter 9 consists of two cascade-connected unit counters. In the counter 9, the counter at the previous stage has a lightning surge impulse (current) that is greater than the current I0 corresponding to the limit voltage V0, and therefore, while the surge detection signal c is being generated, the lightning surge impulse (current) is detected through the AND gate 8. When the clock pulse h is input, the counter continues to count up, and every time the count reaches a value corresponding to a time equivalent to 20 μs, an output pulse is generated to cause the subsequent counter to count up. The output of the subsequent counter becomes the output signal of the counter 9, that is, the varistor deterioration detection signal d.

In this embodiment, the wave tail length f of the applied lightning surge impulse (current) is long, and therefore 1
If the amount of energy per session is large, the amount of energy can be taken into account. That is, as shown in FIG. 3, the embodiment is the same as the embodiment shown in FIG. 1 up to the point where the surge detection signal c is output. Assuming that a surge impulse current due to induced lightning flows through the power system 1a, the surge detection signal c is continuously output while the surge current exceeds the surge current I0 defined in FIG. During this period, the clock pulse h input to the counter 9 via the AND gate 8 is counted by the counter at the previous stage of the counter 9. In the above specific example, the front stage counter is 20μ
Output pulse every s. Therefore, this embodiment is no different from the embodiment of FIG. 1 when the wave tail length f is less than 40 μs. When the count content of the counter subsequent to the counter 6 reaches the above-mentioned life limit, the varistor deterioration detection signal d is output.

According to the embodiment shown in FIG. 2, regardless of the magnitude and waveform of the surge current, the count-up continues at predetermined time intervals as long as the surge current exceeds the surge current I0 defined in FIG. Since the group of straight lines representing the relationship between the surge current and the surge wave tail length of the characteristic No. 5 is revised upward, that is, the life limit is revised to a smaller value, deterioration detection can be performed with even higher accuracy.

[0018]

According to the present invention, deterioration of a varistor provided as a lightning surge absorbing means can be detected quantitatively and with high precision. Therefore, it is possible to notify maintenance personnel at an appropriate time that it is time to replace a deteriorated varistor, and to take prompt preventive action before a situation such as equipment damage occurs. Furthermore, unnecessary work when replacing the varistor can be eliminated, and maintenance work can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a lightning surge protection device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a lightning surge protection device according to another embodiment of the present invention.

FIG. 3 is a time chart for explaining the operation of a counter in the lightning surge protection device according to the embodiment of FIG. 2;

FIG. 4 is a characteristic diagram showing voltage versus current characteristics of a varistor used in a lightning surge protection device.

FIG. 5 is a characteristic diagram showing the surge life characteristics of the varistor shown in FIG. 4;

FIG. 6 is a diagram showing an impulse standard waveform of lightning surge current.

[Explanation of symbols]

1 Commercial power supply 1a Power system 2 Lightning surge absorption device 3 Varistor (non-linear resistance element) 4 Voltage detector 5 Comparator 6 Counter 7 Clock generator 8 AND gate 9 Counter

Claims (2)

[Claims] Claims 1: A varistor connected as a lightning surge absorption means to an input terminal of an electric circuit to be protected; a voltage detection means for detecting the terminal voltage of the varistor; and a voltage detected by the voltage detection means that is predetermined. a comparison means for outputting a surge detection signal when the former exceeds the latter, and a comparison means for counting the number of times the surge detection signal is generated from this comparison means, the count value being a predetermined value. A lightning surge protection device comprising: a counter that outputs a deterioration detection signal to notify the life limit of the varistor when the life limit has been reached. 2. The counter includes means for monitoring the time during which the voltage detected by the voltage detection means exceeds the predetermined threshold voltage and counting up every time a predetermined time elapses; The lightning surge protection device according to claim 1, further comprising means for modifying the life limit to a smaller value depending on the degree of count-up.