JP2549149B2 - Surge protection circuit - Google Patents

Description

The present invention relates to a surge protection circuit for indoor and outdoor electronic devices exposed to lightning surges.

(Prior Art) Outdoor equipment that draws in power through a pole transformer of a distribution line is usually equipped with a surge protection circuit in its power input circuit in order to prevent damage due to a lightning surge.

This surge protection circuit suppresses an impulse type lightning surge to a low voltage and thereby protects an electronic circuit connected thereafter. The conventional surge protection circuit has a structure as shown in FIG.

Insert the surge protection circuit 11 between the power lines A and B drawn from the pole transformer 2 of the distribution line, and then insert the surge protection circuits 12 and 13 between the power lines A and B and the frame ground FG of the outdoor device 1. are doing.

The surge protection circuits 12 and 13 are usually two pole pole transformers.
Since the second side is provided with the second type grounding E1, it seems that it is not necessary because the terminals B and FG of the outdoor device 1 are at the same potential in a normal state. However, the lightning surge current is grounded at E1
When it flows to the ground, a voltage drop occurs due to the grounding resistance of the second type grounding and the inductance of the grounding wire, and this voltage appears as a ground-to-ground surge voltage between the power supply lines A, B and FG of the outdoor equipment 1, so it is suppressed. In order to do so, surge protection circuits 12 and 13 are necessary.

(Problems to be Solved by the Invention) The conventional surge protection circuits 11, 12, and 13 shown in FIG. 3 are composed of various surge absorbing elements as shown in FIG.
It has the following advantages and disadvantages.

(A) is an arrester with a gap (hereafter called an arrester)
Thus, it has the characteristics shown by the one-dot chain line E _O in FIG.

As can be seen from the characteristic curve, the limiting voltage (E _O ) when discharged
Is low, the impulse discharge start voltage (E _S) is a feature that high.

Further, if the voltage is constantly applied, a follow current is likely to occur when discharged.

(B) is a gapless arrester (hereinafter referred to as a varistor) which is a non-linear element and has characteristics as shown by the dotted line e _O in FIG.

As can be seen from the characteristic curve, the limiting voltage at the beginning of applying the lightning impulse voltage (e) is low, but the limiting voltage becomes high as the current increases due to the entry of the lightning impulse voltage.

In addition, the characteristics of the varistor itself tend to deteriorate due to the flow of current.

Further, if it is used in a state where a voltage is always applied, there is a concern that the characteristics may be deteriorated due to a leakage current.

(C) is a combination of an arrester and a varistor in series. Since the impulse discharge starting voltage is determined by the characteristics of the arrester and the limiting voltage is determined by the characteristics of the varistor, in terms of suppressing lightning surge as much as possible (a), Inferior to (b).

In consideration of the above advantages and disadvantages, recently, ● Even if the device is always used with voltage applied, the leakage current of the varistor is blocked by the arrester, so deterioration of varistor characteristics due to leakage current can be prevented.

● Since the follower of the arrester is cut off by the varistor, it has excellent follow-current prevention characteristics.

In particular, the method (c) tends to be often used.

However, when the method of FIG. 4 (c) is adopted for the surge protection circuits 11, 12, and 13 of FIG. 3, the surge protection circuits 11 and 12 are circuits to which a constant voltage is applied. , It is very effective from the viewpoint of preventing the characteristic deterioration of the varistor, but with regard to the surge protection circuit 13, the B and FG are always at the same potential, and the follow current at the time of discharge does not occur, so the method of FIG. 4 (c) is adopted. There is no merit to do.

Further, as shown in FIG. 3, the surge protection circuits are three sets for the input power source to the outdoor equipment, and the equipment installed on the pole of the distribution line needs to be miniaturized. Therefore, considering the downsizing of the surge protection circuit, an arrester of the type shown in FIG. 4 (a) may be used, but it has a drawback that the impulse discharge starting voltage is high.

To suppress lightning surges as much as possible, see Fig. 4 (b).
Although the method may be adopted, there is a drawback that the varistor having a large withstanding capacity is required because the characteristics are easily deteriorated by the lightning surge current as described above, and the shape is large.

Therefore, the present invention provides a surge protection circuit that can be miniaturized and has good surge suppression performance and is less likely to cause characteristic deterioration as surge protection between the frame ground of an indoor / outdoor electronic device and the ground side of an input power supply. To aim.

[Structure of Invention]

(Means for Solving the Problem) According to the present invention, a surge protection circuit in which a varistor and an arrester are combined in series requires three sets per one input power source, as shown in FIG. And barista 14
Connect b'in series, connect one side of the varistor 14b 'to the ungrounded side A of the input power supply, connect one pole of the 3-pole arrester 14a' to the grounded side B of the input power supply, and connect the other pole to the frame ground FG of the outdoor device 1.
To the ground side B of the input power supply and the frame ground FG of the outdoor equipment 1
It is configured so that two sets of surge protection circuits can be inserted by inserting between them.

(Operation) With the configuration as shown in Fig. 1, it is effective for surge protection even if a lightning surge enters between the lines of the input power source or between the input power source and the ground. is there.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which 2 is a pole transformer, E ₁ is a secondary side grounding of the pole transformer secondary side, 1 is an outdoor device, and 10 is protection from lightning surge. Electronic circuit, A is the non-grounded side of the pole transformer, B is the grounded side of the pole transformer, FG is the frame ground of the outdoor equipment 1, and 14 'is the surge protection circuit.
a'is a 3-pole arrester, 14b 'is a varistor, and 13 is a conventional surge protection circuit (gap arrestor, gapless varistor, or series circuit of gap arrester and gapless varistor as shown in Fig. 4).
In the surge protection circuit 14 ', the intermediate pole of the three-pole arrester 14a' and the varistor 14b 'are connected in series, and the other end of the varistor is connected to the ungrounded side A of the power source and one pole of the three-pole arrester 14a' is connected to the grounded side B of the power source. Configure to connect the other pole to the frame ground FG of the outdoor equipment.

When a lightning surge from the outside enters between the A and B lines of the input power supply, the circuit connecting the B side of the varistor 14b 'and the three-pole arrester 14a' discharges and suppresses the voltage between A and b. If the lightning surge has entered between the transformer 2 Toko of the secondary side ground E ₁ Matahashira, the voltage between the discharge and A-E ₁ in the circuit of the FG side connection of the varistor 14b 'and 3-pole arrester 14a' Suppress.

Lightning surge current flows to the secondary side grounding E ₁ of pole transformer 2, and if surge voltage occurs between B and FG, surge protection circuit 13
It discharges at and suppresses the voltage.

At this time, if the intrusion surge is steep and the discharge voltage in the surge protection circuit 13 is high, the 3-pole arrester will also discharge, but the lightning surge is transient and B and FG will immediately be at the same potential, so continuous current interruption will occur without problems. It is something that will be done.

As described above, according to the present embodiment, two sets of surge protection circuits have the same surge protection performance as the conventional one, which is useful for downsizing outdoor equipment, and at the same time, reliability is improved because the number of parts is small. is there.

In the contents described above, the surge protection circuit for the outdoor equipment has been described, but the surge protection circuit for the indoor equipment can also be used. Further, in FIG. 1, when it is sufficient to suppress the discharge of the 3-pole arrester between B and FG, the surge protection circuit 13 is unnecessary.

〔The invention's effect〕

According to the present invention, it is possible to obtain a surge protection circuit which has a small size and good surge suppression performance.

[Brief description of drawings]

FIG. 1 is a block diagram of an outdoor device equipped with the surge protection circuit of the present invention, FIG. 2 is a characteristic diagram of each surge absorbing element, FIG. 3 is a block diagram of an outdoor device equipped with a conventional surge protection circuit, and FIG. FIG. 4 is a configuration diagram of a conventional surge protection element. 1 …… Outdoor (inside) equipment, 2 …… Pole transformer 10 …… Electric circuit 11 to 14,14 ′ …… Surge protection circuit 14a, 14a ′ …… Arrester, 14b, 14b ′ …… Varistor e …… Lightning Impulse voltage curve (lightning surge voltage) E _S …… arrester impulse discharge start voltage E _a …… arrester discharge start voltage e _o …… arrester limit voltage curve e _o …… varistor limit voltage curve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Harada 66-2 Horikawa-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Engineering Co., Ltd. (56) Bibliography Sho 63-105428 (JP, U) JP 61 -47050 (JP, B2)

Claims (1)

(57) [Claims] 1. In a surge protection circuit provided in a device using a power supply whose one wire is grounded as an input power supply, one end of a gapless varistor of a non-linear element is connected to the non-grounded side of the input power supply, and another gapless varistor is connected. An intermediate pole of a 3-pole arrester with a gap is connected to an end, one pole of the 3-pole arrester with a gap is connected to the ground side of the input power source, and the other end of the 3-pole arrester with a gap is used as a frame ground of the device. From a first surge protection circuit to be connected, and a second surge protection circuit to which a gap arrester, a gapless varistor, or a series circuit of a gap arrester and a gapless varistor is connected between the ground side of the input power source and the frame ground. Surge protection circuit characterized by