Surge protection circuit for DC power distribution

Abstract

To provide a surge protection circuit for DC power distribution which can handle large currents and suppress follow currents.SOLUTION: In a surge protection circuit for DC power distribution 1 provided between a positive electrode terminal 31 and a negative electrode terminal 32, a gas discharge tube GDT12 is provided in series on a first current path 11 connecting the positive electrode terminal 31 and the negative electrode terminal 32, and a second current path 13 is provided in parallel with the first current path 11. A capacitor C14 and a semiconductor element 15, which is a thyristor, are provided in series on the second current path 13, a resistor R16 is provided in parallel with the capacitor C14, a current sensor 18 is connected to the first current path 11, and the output terminal of the current sensor 18 is connected to the semiconductor element 15 via a delay circuit in which a coil L19 and a capacitor C20 are connected in series.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surge protection circuit using an SPD (Surge protective device) that protects equipment and devices from sudden large currents and voltages such as lightning.

Background Art

[0002] Conventionally, there has been a surge protection circuit using an SPD that protects equipment and devices from sudden large currents and voltages (≈surges) such as lightning.

[0003] Among surge protection circuits, there are those using a gas discharge tube (GDT) and those using a zinc oxide varistor (MOV).

[0004] For example, Patent Document 1 discloses a configuration in which a temperature fuse that opens due to heat generated by varistor deterioration is integrally assembled to a zinc oxide varistor in order to prevent smoke and fire caused by thermal runaway of the zinc oxide varistor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] However, the above-described surge protection circuit using a gas discharge tube can be small and handle large currents, but in the case of a DC circuit, the discharge (arc) continues to flow, resulting in circuit destruction or the like. Note that "follow current" refers to a phenomenon in which, after the surge has subsided, the discharge is maintained by the main power supply voltage of the device and the arc discharge in the gas discharge tube, and current continues to flow through the circuit. In an AC power supply (circuit), 0 V is reached due to the zero cross, but in a DC power supply (circuit), 0 V is not reached, so a follow current countermeasure is required.

[0007] On the one hand, in a surge protection circuit using a zinc oxide varistor, no follow current is generated, but its shape is large and it is not suitable for large currents. Also, the device itself is expensive.

[0008] Therefore, in order to address the above problems, it is an object of the present invention to provide a surge protection circuit for DC power distribution that can handle large currents and suppress follow current.

Means for Solving the Problems

[0009] To achieve the above object, the invention according to claim 1 is A surge protection circuit for DC power distribution provided between a positive terminal and a negative terminal, A gas discharge tube is provided in series on a first current path connecting the positive terminal and the negative terminal, A second current path is provided in parallel with the first current path, A capacitor and a semiconductor element are provided in series on the second current path, The semiconductor device is a thyristor, FET, bipolar transistor, IGBT, or triac, and A resistor is provided in parallel with the capacitor, A current sensor is connected to the first current path, and an output terminal of the current sensor is connected to the semiconductor element via a delay circuit, forming a surge protection circuit for DC power distribution.

[0010] Also, the invention according to claim 2 is A surge protection circuit for DC power distribution provided between a positive terminal, or between a negative terminal and a reference potential point, A gas discharge tube is provided in series on a first current path connecting the positive terminal, or the negative terminal and the reference potential point, A second current path is provided in parallel with the first current path, A capacitor and a semiconductor element are provided in series on the second current path, The semiconductor device is a thyristor, FET, bipolar transistor, IGBT, or triac, and A resistor is provided in parallel with the capacitor, A current sensor is connected to the first current path, and an output terminal of the current sensor is connected to the semiconductor element via a delay circuit, thereby forming a surge protection circuit for DC power distribution.

[0011] Further, the invention according to claim 3 is The surge protection circuit for DC power distribution according to claim 1 or 2, wherein the current sensor is a current sensor using a Hall element.

[0012] Further, the invention according to claim 4 is The surge protection circuit for DC power distribution according to any one of claims 1 to 3, wherein the delay circuit is an LC circuit in which a coil L and a capacitor C are connected in series.

[0013] Further, the invention according to claim 5 is The surge protection circuit for DC power distribution according to any one of claims 1 to 3, wherein the delay circuit is an RC circuit in which a resistor R and a capacitor C are connected in series.

Advantages of the Invention

[0015] According to the present invention, a gas discharge tube that can handle small size, low cost, and large current while suppressing follow current can be used in a surge protection circuit for a DC power distribution system. Further, in the present invention, since the component that deteriorates over time is only the gas discharge tube, the running cost can be reduced.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] (Embodiment Example 1) Hereinafter, Embodiment Example 1 according to the present invention will be described in detail with reference to the accompanying drawings. However, the components described in this embodiment example are merely examples, and are not intended to limit the scope of the present invention thereto. Note that the surge protection circuit 1 of Embodiment Example 1 according to the present invention is provided to protect equipment and devices receiving DC power distribution from large currents and large voltages such as lightning.

[0018] <Configuration of Surge Protection Circuit 1 for DC Power Distribution> The surge protection circuit 1 for DC power distribution of Embodiment Example 1 is provided between a positive electrode terminal 31 and a negative electrode terminal 32 to which the main power supply voltage of the device is applied.

[0019] A gas discharge tube GDT12 is provided in series on a first current path 11 connecting the positive electrode terminal 31 and the negative electrode terminal 32.

[0020] The gas discharge tube GDT12 has a structure in which gas is enclosed in an insulator container 122 with electrodes 121 facing each other, and operates depending on the applied voltage. That is, even when a voltage lower than the threshold value is applied between the electrodes 121, a state of high impedance is maintained, and no current flows between the electrodes 121. On the other hand, when a voltage equal to or higher than the threshold value (such as an abnormal high voltage and high current (surge) suddenly generated by lightning or the like) is applied between the electrodes 121, the enclosed gas is ionized, an arc discharge occurs between the electrodes 121, and current flows to the ground side (in Embodiment Example 1, the negative electrode terminal 32).

[0021] A second current path 13 is provided in parallel with the first current path 11. On the second current path 13, a capacitor C14, a semiconductor element 15 are provided in series in descending order of potential. Also, a resistor R16 is provided in parallel with the capacitor C14. Specifically, a third current path 17 is provided in parallel with the second current path 13, and a resistor R16 is provided in series on the third current path 17.

[0022] The resistor R16 provided in parallel with the capacitor C14 is for consuming (discharging) the electric charge stored in the capacitor C14, and is, for example, a 1M (mega) Ω resistor. On the other hand, if a resistor R16 with too large a resistance value is used, the electric charge stored in the capacitor C14 cannot be completely consumed (discharged) by the time of the next lightning strike, and the arc discharge of the gas discharge tube GDT12 cannot be extinguished.

[0023] A current sensor 18 is connected at a position where the potential is lower than that of the gas discharge tube GDT12 on the first current path 11. And there are two current paths for outputting the current input to the current sensor 18. One of them, the fourth current path 21, is connected to the semiconductor element 15 via a delay circuit in which a coil L19 and a capacitor C20 are connected in series. In the surge protection circuit 1 for DC power distribution of the first embodiment of this example, although the configuration in which the current sensor 18 is connected to the first current path 11 at a position where the potential is lower than that of the gas discharge tube GDT12 is shown, it is not limited to this configuration. The current sensor 18 may be configured to be connected to the first current path 11 at a position where the potential is higher than that of the gas discharge tube GDT12, or at the same potential position.

[0024] The current sensor 18 is, for example, a current sensor using a Hall element, and converts the magnetic field generated around the current flowing through the first current path 11 into a voltage by the Hall effect related to the Hall element and outputs it. The output voltage is proportional to the current input to the current sensor 18.

[0025] In addition, in the first exemplary embodiment, a configuration using a Hall element type current sensor as the current sensor 18 is shown. However, the configuration is not limited to this. For example, as the current sensor 18, a configuration using an AC CT (alternating current current transformer), a configuration using a DC CT (direct current current transformer), or a configuration using a shunt resistor may be employed. Note that, as the shunt resistor, one having a resistance value as low as possible, for example, several m (milli) Ω is used. Therefore, since the value of the voltage across the shunt resistor becomes small, an operational amplifier or the like that can amplify the voltage is provided together with the shunt resistor. The operational amplifier or the like detects the voltage of the shunt resistor and amplifies and outputs the voltage. Alternatively, when the voltage generated across the shunt resistor is large, a configuration using only the shunt resistor without using an operational amplifier or the like may be employed.

[0026] The delay circuit in which the coil L19 and the capacitor C20 are connected in series serves to delay (delay) the voltage output from the current sensor 18 in terms of time.

[0027] If the voltage output from the current sensor 18 is delayed too much (= the delay time is long), the time for current to flow through the gas discharge tube GDT12 on the first current path 11 becomes long, and it may be damaged due to overload. On the other hand, if the delay is insufficient (the delay time is short), the surge cannot be completely removed.

[0028] Therefore, the coil L19 and the capacitor C20 are used such that the time constant of the delay circuit in which the coil L19 and the capacitor C20 are connected in series (= an amount representing the speed of change from the transient state to the steady state, the delay time) becomes, for example, 60 to 100 μ (micro) sec. If a coil having an inductance of 1 mH (= 1 millihenry) is used as the coil L19 and a capacitor having a capacitance of 0.1 μF (= 0.1 microfarad) is used as the capacitor C20, the time constant becomes 100 μ (micro) sec.

[0029] In the first exemplary embodiment, a configuration using an LC circuit in which coil L19 and capacitor C20 are connected in series is shown as the delay circuit. However, the delay circuit is not limited to this configuration as long as its time constant is, for example, 60 to 100 μ (micro) sec. For example, a configuration using an RC circuit in which resistor R and capacitor C are connected in series may be used, or a configuration using a circuit in which a reactor and capacitor C are connected in series may be used. In the case of a configuration using an RC circuit, for example, if a resistor with a resistance value of 1 KΩ (= 1 kiloohm) is used as resistor R and a capacitor with a capacitance of 0.1 μF (= 0.1 microfarad) is used as capacitor C, the time constant will be 100 μ (micro) sec.

[0030] Also, in the first exemplary embodiment, semiconductor element 15 is a thyristor. The output terminal of current sensor 18 (the fourth current path 21) is connected to the gate of this thyristor (labeled "G" in FIG. 1). Note that on the second current path 13, the anode of semiconductor element 15 (labeled "A" in FIG. 1) is connected to capacitor 14.

[0031] Note that in the first exemplary embodiment, a configuration using a thyristor as semiconductor element 15 is shown, but the configuration is not limited to this. For example, instead of a thyristor, a configuration using an FET (field effect transistor), bipolar transistor, IGBT , triac may be used. In that case, the output terminal of current sensor 18 is connected to the gate of this FET, the base of the bipolar transistor, IGBT the gate of, or the gate of the triac. Also, the drain of the FET (in the case of an N-channel), the collector of the bipolar transistor, IGBT the collector of, or any main terminal of the triac is connected to capacitor C14.

[0032] Also, a fifth current path 22, which is the other side of the current path that outputs the current input to the current sensor 18, is connected to the second current path 13 at a position where the potential is lower than that of the cathode of the semiconductor element 15, which is a thyristor (displayed as "K" in FIG. 1).

[0033] A diode 24 is provided on a sixth current path 23 that connects between the connection point of the capacitor C20 on the fourth current path 21 and the connection point of the semiconductor element 15, and between the connection point of the capacitor C20 on the fifth current path 22 and the connection point of the second current path 13, with the direction of the fourth current path 21 as the cathode. This diode 24 is for protecting the semiconductor element 15 from sudden voltage and current. Specifically, in the first exemplary embodiment of the present invention, it is for preventing a reverse current from flowing from the cathode to the gate so that a reverse voltage is not applied from the cathode side (displayed as "K" in FIG. 1) of the semiconductor element 15, which is a thyristor.

[0034] The second current path 13 is connected to the first current path 11 at a position where the potential is lower than the position where the current sensor 18 is connected.

[0035] <Operation of the Surge Protection Circuit 1 for DC Power Distribution> Next, the operation of the surge protection circuit 1 for DC power distribution according to the first exemplary embodiment of the present invention will be described with reference to FIGS. 2 to 4.

[0036] When a surge suddenly occurs due to lightning or the like and a voltage equal to or higher than the threshold value is applied between the electrodes 121 of the gas discharge tube GDT12, as shown in FIG. 2, the gas enclosed in the insulator container 122 is ionized, an arc discharge occurs between the electrodes 121, and current flows from the positive terminal 31 to the negative terminal 32, which is the ground side.

[0037] When a current flows through the first current path 11 due to a surge, as shown in FIG. 3, the current sensor 18 converts the current into a voltage and outputs it. However, since a delay circuit in which the coil L19 and the capacitor C20 are connected in series is connected to the current sensor 18, the voltage is output to the gate of the semiconductor element 15, which is a thyristor, with a delay. The semiconductor element 15 to which a voltage is applied to the gate becomes in the ON state (the anode and the cathode are conductive).

[0038] As a result, as shown in FIG. 4, the voltage between the electrodes 121 of the gas discharge tube GDT12 related to the first current path 11 becomes 0 V by forming a parallel circuit with the capacitor C14 related to the second current path 13. When the voltage between the electrodes 121 becomes 0 V, the follow current based on the arc discharge disappears (= arc extinction).

[0039] After that, as shown in FIG. 5, even when a voltage is applied from the main power supply, since no current flows between the electrodes 121 of the gas discharge tube GDT12, no current flows through the first current path 11. However, since the semiconductor element 15 is in the ON state, current flows through the second current path 13 and the capacitor C14 is charged.

[0040] Then, as shown in FIG. 6, when the charging of the capacitor C14 is completed, the semiconductor element 15 becomes in the OFF state (the anode and the cathode are in a non-conductive state). The charge stored in the capacitor C14 is consumed (discharged) by the resistor R16 provided in parallel.

[0041] In this way, while suppressing the follow current, the gas discharge tube GDT12 that is small, inexpensive, and can handle a large current can be used in the surge protection circuit for DC power distribution. Further, in the surge protection circuit 1 for DC power distribution according to the first embodiment example, since the component that deteriorates over time is only the gas discharge tube GDT12, the running cost can be reduced.

[0042] In addition, in the first exemplary embodiment, a configuration is shown in which a surge protection circuit 1 for DC power distribution is provided between lines. However, the present invention is not limited to this configuration. As shown in FIG. 7, a configuration in which a surge protection circuit 1 for DC power distribution is provided between the ground (positive electrode or negative electrode and the reference potential point) may also be adopted.

[0043] However, it goes without saying that when providing the surge protection circuit 1 for DC power distribution between the ground, fine changes such as the orientation of the elements and the addition or deletion of elements may be required.

[0044] For example, when a thyristor is used as the semiconductor element 15, when the surge protection circuit for DC power distribution according to the present invention is provided between the ground of the positive electrode and the reference potential point, the configuration shown in FIG. 7 can be used as it is. However, in order to exhibit the function of the present invention not only between the ground of the positive electrode and the reference potential point but also between the ground of the negative electrode and the reference potential point, it is necessary to add a thyristor in the opposite direction to the thyristor related to the semiconductor element 15 on the circuit.

[0045] In addition, when a triac is used as the semiconductor element 15, the configuration shown in FIG. 7 can be used as it is whether it is between the ground of the positive electrode and the reference potential point or between the ground of the negative electrode and the reference potential point. However, it is not necessary to provide the diode 24.

Explanation of Reference Numerals

[0046] 1: Surge protection circuit for DC power distribution, 11: First current path, 12: Gas discharge tube GDT, 121: Electrode, 122: Insulator container, 13: Second current path, 14: Capacitor C, 15: Semiconductor element, 16: Resistor R, 17: Third current path, 18: Current sensor, 19: Coil L, 20: Capacitor C, 21: Fourth current path, 22: Fifth current path, 23: Sixth current path, 24: Diode, 31: Positive terminal, 32: Negative terminal

Claims

1. A surge protection circuit for DC power distribution provided between a positive terminal and a negative terminal, wherein a gas discharge tube is provided in series on a first current path connecting the positive terminal and the negative terminal, a second current path is provided in parallel with the first current path, a capacitor and a semiconductor element are provided in series on the second current path, the semiconductor element is a thyristor, FET, bipolar transistor, IGBT, or triac, a resistor is provided in parallel with the capacitor, a current sensor is connected to the first current path, and an output terminal of the current sensor is connected to the semiconductor element via a delay circuit, characterized in that it is a surge protection circuit for DC power distribution.

2. A surge protection circuit for DC power distribution provided between a positive terminal or a negative terminal and a reference potential point, wherein a gas discharge tube is provided in series on a first current path connecting the positive terminal or the negative terminal and the reference potential point, a second current path is provided in parallel with the first current path, a capacitor and a semiconductor element are provided in series on the second current path, the semiconductor element is a thyristor, FET, bipolar transistor, IGBT, or triac, a resistor is provided in parallel with the capacitor, a current sensor is connected to the first current path, and an output terminal of the current sensor is connected to the semiconductor element via a delay circuit, characterized in that it is a surge protection circuit for DC power distribution.

3. The surge protection circuit for DC power distribution according to claim 1 or 2, characterized in that the current sensor is a current sensor using a Hall element.

4. The surge protection circuit for DC power distribution according to any one of claims 1 to 3, characterized in that the delay circuit is an LC circuit in which a coil L and a capacitor C are connected in series.

5. The surge protection circuit for DC power distribution according to any one of claims 1 to 3, characterized in that the delay circuit is an RC circuit in which a resistor R and a capacitor C are connected in series.

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