JP7633715B2 - Surge Protection Circuit - Google Patents

Description

This invention particularly relates to surge protection circuits for protecting electrical equipment from abnormal increases in current or voltage.

A conventional surge protection circuit 100 is an electric circuit that is incorporated into a lightning arrester that is installed as shown in FIG. 3(a). The surge protection circuit 100 is connected in parallel to the power input line 200. That is, as shown in FIG. 3(b), the surge protection circuit 100 includes a varistor 300 and a gas arrester 400, or an equivalent circuit, that are arranged on the L-N connection line that connects the non-grounded electric wire L and the grounded electric wire N. As a result, even after the varistor 300 is destroyed or broken down by the application of a surge and the function of the surge protection circuit 100 is impaired, electricity can still flow between the main power source and the electric device, making it difficult to protect the electric device from the surge.

Japanese Patent Application Publication No. 11-97215 JP 2020-38861 A

To solve the above problem, Patent Document 1 (JP Patent Publication No. 11-97215) discloses a protection device that includes a varistor and a thermistor arranged adjacent to the varistor. In the device described in Patent Document 1, the thermistor detects that the varistor has reached an abnormally high temperature state, thereby interrupting the current. Furthermore, Patent Document 2 (JP Patent Publication No. 2020-38861) discloses a lightning arrester that includes a varistor and a thermal fuse arranged adjacent to the varistor. Patent Document 2 discloses that the thermal fuse is melted by the heat generated by the varistor when it is destroyed, thereby interrupting the current.

Both Patent Document 1 and Patent Document 2 use the heat generated by the destruction of a varistor when a surge is applied to cut off the circuit. However, a varistor is larger than a thermistor or a thermal fuse, and destruction of the varistor occurs instantly at any position on the varistor's surface. As a result, there are cases where the abnormally high temperature cannot be detected accurately, for example, when the varistor destruction occurs on the side not in contact with the thermistor or thermal fuse. In other words, there are cases where the current is not cut off even if the varistor is destroyed.

The present invention has been made to solve the above problems, and its purpose is to provide a surge protection circuit that can reliably cut off current when a varistor fails due to the application of a surge.

The surge protection circuit according to this embodiment includes a power input line having a non-grounded electric wire (L) and a grounded electric wire (N), a first varistor that is arranged in an L-N connection line that connects the non-grounded electric wire and the grounded electric wire and absorbs surges, and a first fault detection means that is arranged in the L-N connection line in series with the first varistor and cuts off the current to at least one of the non-grounded electric wire and the grounded electric wire in response to a current flowing in the L-N connection line due to a fault in the first varistor.

Preferably, the first fault detection means includes a first resistor disposed in the L-N connection line and generating heat in response to the flow of current, and a first temperature fuse disposed in the middle of at least one of the non-grounded electric wire and the grounded electric wire, disposed in close proximity to the first resistor, and melting in response to the heat temperature of the first resistor exceeding a set value.

Preferably, the power input line includes an earth wire (G). In this case, the surge protection circuit of this embodiment includes a second varistor that is arranged in the L-G connection line that connects the non-grounded electric wire and the earth wire and absorbs surges, a first gas arrester that is arranged in the L-G connection line in a series relationship with the second varistor, and a second fault detection means that is arranged in a first branch line that branches off between the second varistor and the first gas arrester on the L-G connection line and connects to the grounded electric wire, and that cuts off the current flowing through the non-grounded electric wire in response to a current flowing through the L-G connection line and the first branch line due to a fault in the second varistor.

Preferably, the second fault detection means includes a second resistor disposed in the first branch line and generating heat in response to the flow of current, and a second temperature fuse disposed midway along the non-grounded electric wire and adjacent to the second resistor, which melts in response to the heat generated by the second resistor exceeding a set value.

When the power input line includes an earth wire (G), another embodiment of the surge protection circuit includes a third varistor that is arranged in the N-G connection line connecting the grounded electric wire and the earth wire and absorbs surges, a second gas arrester that is arranged in the N-G connection line in a series relationship with the third varistor, and a third fault detection means that is arranged in a second branch line that branches off between the third varistor and the second gas arrester on the N-G connection line and connects to the non-grounded electric wire, and that cuts off the current flowing through the N-G connection line and the second branch line due to a fault in the third varistor.

Preferably, the third fault detection means includes a third resistor disposed in the second branch line and generating heat in response to the flow of current, and a third temperature fuse disposed midway along the ground side electric wire and adjacent to the third resistor, which melts in response to the temperature of the third resistor exceeding a set value.

A surge protection circuit according to another embodiment of the present invention includes a power input line including a non-grounded electric wire (L), a grounded electric wire (N), and an earth wire (G), a varistor arranged on an earth connection line connecting either the grounded electric wire or the non-grounded electric wire to the earth wire and absorbing a surge, a gas arrester arranged on the earth connection line in a series relationship with the varistor, and a fault detection means arranged on a branch line that branches off between the varistor and the gas arrester on the earth connection line and is connected to the other of the grounded electric wire or the non-grounded electric wire, and that cuts off the current flowing through either the grounded electric wire or the non-grounded electric wire in response to a current flowing through the earth connection line and the branch line due to a fault in the varistor.

A surge protection circuit according to another embodiment is incorporated into a three-phase AC circuit having three input lines. The surge protection circuit includes a varistor that is disposed on a connection line that connects any two input lines and absorbs surges, and a fault detection means that is disposed on the connection line in series with the varistor and that cuts off the current to one or the other input line in response to a current flowing through the connection line due to a fault in the varistor.

A surge protection circuit incorporated in a three-phase AC circuit having three input lines (L1, L2, L3) and an earth wire (G) comprises a varistor that is arranged on an earth connection line connecting one of any two input lines to the earth wire and absorbs surges, a gas arrester that is arranged on the earth connection line in a series relationship with the varistor, and a fault detection means that is arranged on a branch line that branches off between the varistor and the gas arrester on the earth connection line and is connected to the other of any two input lines, and that cuts off the current to one or the other of the input lines in response to a current flowing through the earth connection line and the branch line due to a fault in the varistor.

According to the present invention, when a varistor fails due to a surge, it is possible to reliably cut off current and protect electrical equipment.

1A and 1B are diagrams showing a surge protection circuit according to an embodiment of the present invention, in which FIG. 1A is a schematic diagram and FIG. FIG. 13 is a circuit diagram showing a surge protection circuit according to another embodiment. 1A and 1B are diagrams illustrating a conventional surge protection circuit, in which FIG. 1A is a schematic diagram and FIG.

(About the composition)
The surge protection circuit of this embodiment will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated. Also, the configurations labeled "first", "second" and "third" basically have the same or similar performance, and the description of the configuration labeled "second" and subsequent components will not be repeated.

Figure 1 is a diagram showing a surge protection circuit 1 according to this embodiment. Figure 1(a) is a schematic diagram showing that the surge protection circuit 1 according to this embodiment is installed between a main power source and an electrical device. Figure 1(b) is a circuit diagram showing the electrical circuit within the dotted line in Figure 1(a) extracted.

The surge protection circuit 1 includes a power input line 2. The power input line 2 includes a non-grounded electric wire L, a grounded electric wire N, and an earth wire G. The power input line 2 is a line that electrically connects a main power source and an electrical device. Note that, although an example in which an earth wire G is provided is described in this embodiment, providing this is not essential.

The surge protection circuit 1 according to this embodiment includes an L-N connection line 3 that connects the non-grounded electric wire L and the grounded electric wire N. The surge protection circuit 1 includes a first varistor 32 that is disposed on the L-N connection line 3 and absorbs surges, and a first fault detection means 31 that is disposed on the L-N connection line 3 in series with the first varistor 32 and that cuts off the current to at least one of the non-grounded electric wire L and the grounded electric wire N in response to a current flowing through the L-N connection line 3 due to a fault in the first varistor 32.

On the L-N connection line 3, the first varistor 32 is provided on the non-grounded electric wire L side, and the first fault detection means 31 is provided on the grounded electric wire N side. During normal energization, the impedance of the first varistor 32 is high, so that a current flows on the non-grounded electric wire L toward the electric device, and does not flow to the L-N connection line 3 side. If a surge is applied here and the first varistor 32 breaks down, the impedance of the first varistor 32 drops, so that a current flows into the L-N connection line 3. Note that a varistor failure is a state in which the function of the varistor is reduced or lost. In this embodiment, on the L-N connection line 3, the first varistor 32 is provided on the non-grounded electric wire L side, and the first fault detection means 31 is provided on the grounded electric wire N side, but these arrangements may be reversed. That is, the first varistor 32 is provided on the grounded electric wire N side, and the first fault detection means 31 is provided on the grounded electric wire N side.
may be arranged on the non-grounded electric wire L side.

In this embodiment, when a current flows into the L-N connection line 3, the first fault detection means 31 detects this and cuts off the current flow to the non-grounded electric wire L. The first fault detection means 31 may be any means that cuts off the current flow to the power input line 2. In this embodiment, the first fault detection means 31 includes a first resistor 33 that is disposed on the L-N connection line 3 and generates heat in response to the current flow, and a first temperature fuse 34 that is disposed midway on at least one of the non-grounded electric wire L and the grounded electric wire N, is disposed in close proximity to the first resistor 33, and melts down in response to the heat temperature of the first resistor 33 exceeding a set value.

The first resistor 33 generates heat when electricity is applied to the L-N connection line 3. That is, the first resistor 33 does not generate heat when electricity is normally applied, but generates heat when the first varistor 32 breaks down due to the application of a surge and current flows through the L-N connection line 3. From the viewpoint of cutting off the current to the non-grounded electric wire L as quickly as possible, it is preferable to use a first resistor 33 that heats up to 100°C or more in a few to several tens of seconds.

The first temperature fuse 34 in this embodiment is provided at a midpoint on the non-grounded electric wire L. The first temperature fuse 34 and the first resistor 33 are positioned close to each other. "Close" here typically means that at least a portion of the first temperature fuse 34 and the first resistor 33 are in contact, and the first temperature fuse 34 is positioned in a position where it can be sufficiently affected by the temperature of the first resistor 33. This allows the first temperature fuse 34 to melt down due to the heat emitted from the first resistor 33. From the viewpoint of practicality, it is preferable to use a first temperature fuse 34 that melts down at 100°C or higher.

The first resistor 33 and the first temperature fuse 34 may be bound together with tape or the like and tightly attached to each other in order to ensure that they melt.

The surge protection circuit 1 according to this embodiment includes an L-G connection line 4. In this case, the surge protection circuit 1 includes a second varistor 42 that is disposed on the L-G connection line 4 connecting the non-grounded electric wire L and the earth wire G and absorbs surges, and a first gas arrester 45 that is disposed on the L-G connection line in series with the second varistor 42. The surge protection circuit 1 also includes a second fault detection means 41 that is disposed on a first branch line 40 that branches off between the second varistor 42 and the first gas arrester 45 on the L-G connection line 4 and is connected to the grounded electric wire N.

On the L-G connection line 4, the second varistor 42 is provided on the non-grounded electric wire L side, and the first gas arrester 45 is provided on the earth wire G side. During normal energization, the impedance of the second varistor 42 and the first gas arrester 45 is high, so that current flows to the non-grounded electric wire L and does not flow to the L-G connection line 4 side. When a surge is applied here, the second varistor 42 absorbs the surge by changing its impedance, and the first gas arrester 45 absorbs the surge by discharging. When the second varistor 42 breaks down due to the application of a surge, the impedance of the second varistor 42 decreases, and the impedance of the first gas arrester 45 is high, so that a current flows into the L-G connection line 4 and the first branch line 40. A second resistor 43 is provided on the first branch line 40, and the second fault detection means 41 functions when a current flows through the first branch line 40.

When a surge is applied to the L-G connection line 4 and the second varistor 42 fails, the second fault detection means 41 cuts off the current flow to the non-grounded electric wire L. The second fault detection means 41 of this embodiment includes a second resistor 43 that is disposed in the first branch line 40 and generates heat in response to a current flow, and a second temperature fuse 44 that is provided midway along the non-grounded electric wire L and disposed in close proximity to the second resistor 43, and melts in response to the heat temperature of the second resistor 43 exceeding a set value.

The second resistor 43 generates heat when a current flows into the first branch line 40. Because the first gas arrester 45 has a high impedance, almost no current flows to the earth wire G side. In other words, the current that flows into the L-G connection line 4 after the second varistor 42 is destroyed does not flow to the earth wire G, but flows to the first branch line 40, which is why the second resistor 43 generates heat reliably and melts the thermal fuse 44.

The surge protection circuit 1 according to this embodiment includes an N-G connection line 5. In this case, the surge protection circuit 1 includes a third varistor 52 that is disposed on the N-G connection line 5 that connects the grounded electric wire N and the earth wire G and absorbs surges, and a second gas arrester 55 that is disposed on the N-G connection line 5 in series with the third varistor 52. The surge protection circuit 1 also includes a third fault detection means 51 that is disposed on a second branch line 50 that branches off from between the third varistor 52 and the second gas arrester 55 on the N-G connection line 5 and is connected to the non-grounded electric wire L.

On the N-G connection line 5, the third varistor 52 is provided on the ground side electric wire N side, and the second gas arrester 55 is provided on the earth wire G side. During normal energization, the impedance of the third varistor 52 and the second gas arrester 55 is high, so that current flows to the ground side electric wire N and does not flow to the N-G connection line 5 side. When a surge is applied here, the third varistor 52 absorbs the surge by changing its impedance, and the second gas arrester 55 absorbs the surge by discharging. When the third varistor 52 breaks down due to the application of a surge, the impedance of the third varistor 52 decreases, and the impedance of the second gas arrester 55 is high, so that a current flows into the N-G connection line 5 and the second branch line 50. A third resistor 53 is provided on the second branch line 50, and the third fault detection means 51 functions when a current flows through the second branch line 50.

The third fault detection means 51 cuts off the current to the ground wire N when a surge is applied to the N-G connection line 5 and the third varistor 52 fails. The third fault detection means 51 in this embodiment includes a third resistor 53 that is disposed in the second branch line 50 and generates heat in response to the current flowing through it, and a third temperature fuse 54 that is provided midway along the ground wire N and disposed close to the third resistor 53, and melts in response to the heat temperature of the third resistor 53 exceeding a set value.

The third resistor 53 generates heat when current flows into the second branch line 50. Because the second gas arrester 55 has high impedance, almost no current flows to the earth wire G side. In other words, the current that flows into the N-G connection line 5 after the third varistor 52 is destroyed does not flow to the earth wire G, but flows to the second branch line 50, which is why the third resistor 53 reliably generates heat and melts the third temperature fuse 54.

(About the effects)
A first gas arrester 45 is provided on the L-G connection line 4, and a second gas arrester 55 is provided on the N-G connection line 5. Here, the first and second gas arresters 45, 55 have the characteristic of not conducting electricity due to high impedance at the voltage during normal current supply. That is, the first and second gas arresters 45, 55 function to make the current flowing into the L-G connection line 4 and the N-G connection line 5 flow to the first and second branch lines 40, 50. This allows current to flow between L-N. Therefore, the current flow between L-N after the varistor breaks down is carried out via the first and second branch lines 40, 50. The second and third resistors 43, 53 provided on the first and second branch lines 40, 50 are heated by the current flowing through the branch lines 40, 50. This allows the second and third temperature fuses 44, 54 to be surely melted.

The surge protection circuit 1 according to this embodiment ensures that power to the electrical device is cut off, making it easy to recognize the failure. In addition, since the electrical device will not continue to be used after the varistor has failed, damage caused by the next surge can be prevented.

Conventional surge protection circuits detect heat generation from a varistor when the shape of the varistor is destroyed and the heat sensing is unstable. The surge protection circuit of this embodiment differs from this conventional configuration in that the current passing through a destroyed or broken varistor causes the resistor to heat up, and the heat generated by this resistor reliably melts the thermal fuse and cuts off the power input line.

The surge protection circuit 1 of this embodiment only needs to have at least one fault detection means. However, if it has two or more, particularly the second and third fault detection means 41, 51, further effects can be obtained. When a surge is applied to the power input line 2, a surge current also flows through the first branch line 40 and the second branch line 50. As a result, the surge protection circuit 1 of this embodiment forms three parallel circuits connecting L-N, and the varistors and/or gas arresters provided on the L-N connection line 3, the L-G connection line 4, and the N-G connection line 5 can absorb the distributed surge. In other words, the surge protection circuit 1 of this embodiment can improve the surge tolerance.

In the above explanation, the surge protection circuit 1 of this embodiment is described as having an L-N connection line 3, an L-G connection line 4, and an N-G connection line 5, but the effects of the present invention can be achieved simply by providing a fault detection means in any one of these connection lines. Therefore, the surge protection circuit 1 in another embodiment of the present invention includes a power input line 2 having a non-grounded electric wire (L), a grounded electric wire (N), and an earth wire (G), a varistor 42, 52 that is arranged on the earth connection line 4, 5 that connects either the grounded electric wire or the non-grounded electric wire to the earth wire and absorbs surges, a gas arrester 45, 55 that is arranged on the earth connection line 4, 5 in a series relationship with the varistor 42, 52, and a fault detection means 41, 51 that is arranged on the branch line 40, 50 that branches off from between the varistor 42, 52 and the gas arrester 45, 55 on the earth connection line 4, 5 and is connected to the other of the grounded electric wire L or the non-grounded electric wire N, and that cuts off the current flowing through either the grounded electric wire N or the non-grounded electric wire L in response to the current flowing through the earth connection line 4, 5 and the branch line 40, 50 due to a fault in the varistor 42, 52.

(Other embodiments)
Next, a surge protection circuit 1A according to another embodiment will be described with reference to Fig. 2. The surge protection circuit 1 according to the present invention is adopted in a single-phase AC electric circuit, but the surge protection circuit 1A according to another embodiment is a surge protection circuit 1A adopted in a three-phase AC electric circuit. A three-phase AC circuit is essentially a combination of three single-phase AC circuits, and the surge protection circuit 1 for a single-phase AC circuit described above can also be applied to a three-phase AC circuit.

The varistors and fault detection means of the surge protection circuit 1A shown in Fig. 2 are provided between any two of the three input lines L1, L2, and L3. That is, varistors 32A, 42A, and 52A that absorb surges and fault detection means 31A, 41A, and 51A are provided on the L1-L2 connection line 3A, the L2-L3 connection line 4A, and the L3-L1 connection line 5A, respectively. A current flows in each connection line 3A, 4A, and 5A due to a fault in each varistor 32A, 42A, and 52A. In response to the flow of the current, the fault detection means 31A, 41A, and 51A cut off the current to one input line or the other input line.

The fault detection means 31A, 41A, 51A includes resistors 33A, 43A, 53A that generate heat in response to the flow of current through the connection lines 3A, 4A, 5A, and includes temperature fuses 34A, 44A, 54A that are provided midway along one or the other of any two input lines, are positioned close to the resistors 33A, 43A, 53A, and melt down in response to the heat generated by the resistors 33A, 43A, 53A exceeding a set value.

When the power input line 2A includes an earth wire G, the surge protection circuit 1A may have an L1-G connection line 6A, an L2-G connection line 7A, and an L3-G connection line 8A, and a varistor 62A, 72A, 82A and a gas arrester 65A, 75A, 85A may be provided on each of the earth connection lines 6A, 7A, 8A. Even in this case, when a current flows through the branch lines 60A, 70A, 80A that branch out from between the varistors 62A, 72A, 82A and the gas arresters 65A, 75A, 85A of the earth connection lines 6A, 7A, 8A and connect to the corresponding lines of the power input line 2A, the fault detection means 61A, 71A, 81A cuts off the current.

The fault detection means 61A, 71A, 81A includes resistors 63A, 73A, 83A that generate heat in response to the flow of current on the branch lines 60A, 70A, 80A, and thermal fuses 64A, 74A, 84A that are provided midway along one or the other of the power input lines, positioned close to the resistors 63A, 73A, 83A, and that melt when the temperature of the resistors 63A, 73A, 83A exceeds a set value.

The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims rather than the above description, and it is intended to include all modifications within the scope and meaning equivalent to the claims.

1 surge protection circuit, 2 power input line, 3 L-N connection line, 4 L-G connection line, 5 N-G connection line, 31 first fault detection means, 32 first varistor, 33 first resistor, 34 first thermal fuse, 40 first branch line, 41 second fault detection means, 42 second varistor, 43 second resistor, 44 second thermal fuse, 45 first gas arrester, 50 second branch line, 51 third fault detection means, 52 third varistor, 53 third resistor, 54 third thermal fuse, 55 second gas arrester, 1A surge protection circuit, 2A power input line, 3A L1-L2 connection line, 4A L2-L3 connection line, 5A L3-L1 connection line, 6A L1-G connection line, 7A L2-G connection line, 8A L3-G connection line, 60A, 70A, 80A Branch line, 31A, 41A, 51A, 61A, 71A, 81A Fault detection means, 32A, 42A, 52A, 62A, 72A, 82A Varistor, 33A, 43A, 53A, 63A, 73A, 83A Resistor, 34A, 44A, 54A, 64A, 74A, 84A Thermal fuse, 65A, 75A, 85A
Gas arrester.

Claims (8)

A power input line including a non-grounded electric wire (L), a grounded electric wire (N), and a ground wire (G);
An L-G connection line that connects the non-grounded electric wire and the earth wire;
a first varistor disposed on the LG connection line;
a first gas arrester disposed in the LG connection line in series with the first varistor;
a first branch line that branches off from between the first varistor and the first gas arrestor on the LG connection line and is connected to the ground side electric wire ;
a first fault detection means arranged in the first branch line and cutting off current flow in the non-grounded electric wire in response to a failure of the first varistor causing a current to flow in the first branch line . The surge protection circuit comprises:
An NG connection line that connects the ground side electric wire and the earth wire;
A second varistor disposed on the NG connection line;
a second gas arrester disposed in the N-G connection line in series with the second varistor;
A second branch line that branches off from between the second varistor and the second gas arrester on the N-G connection line and is connected to the non-grounded electric wire ;
2. The surge protection circuit according to claim 1, further comprising: a second fault detection means arranged in the second branch line and cutting off current flow to the ground side electric wire in response to a current flowing in the second branch line due to a fault in the second varistor. 2. The surge protection circuit of claim 1 , wherein the first fault detection means comprises a resistor disposed in the first branch line. 3. The surge protection circuit of claim 2, wherein the second fault detection means comprises a resistor disposed in the second branch line. An L-N connection line that connects the non-grounded electric wire and the grounded electric wire;
3. The surge protection circuit of claim 1, further comprising a varistor disposed on the LN connection line. A surge protection circuit to be incorporated in a three-phase AC circuit having three input lines (L1, L2, L3) and a ground wire (G),
an earth connection line connecting one of any two input lines to an earth line;
a varistor disposed in the earth connection line;
a gas arrester disposed in the earth connection line in series with the varistor;
a branch line that branches off from between the varistor and the gas arrester on the earth connection line and is connected to the other of any two input lines ;
a failure detection means arranged in the branch line for cutting off current flow to the one input line in response to a current flowing through the branch line due to a failure of the varistor. 7. The surge protection circuit of claim 6, wherein the fault detection means comprises a resistor disposed in the branch line. an input line connection line connecting any two input lines;
7. The surge protection circuit of claim 6, further comprising a varistor disposed in the input inter-line connection line.

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