Surge voltage detection device

Abstract

To provide a surge voltage detection device that can detect surge voltages non-contact, has a relatively simple configuration, and has relatively low manufacturing and maintenance costs. [Solution] The surge voltage detection device 3 comprises an electric field detection unit 3C made of a conductor, which is positioned non-contact with the circuit to be detected for surge voltage and in which induced charges accumulate due to the electric field around the circuit; a detection voltage generation unit 3F which connects the electric field detection unit 3C to ground via resistors R31 and R32 and generates a detection voltage corresponding to the induced charge of the electric field detection unit 3C; and a positive polarity surge detection unit 3A and a negative polarity surge detection unit 3B connected to the detection voltage generation unit 3F. The positive polarity surge detection unit 3A comprises a comparator 3a1 to which a positive voltage threshold is set and the detection power is input, and a voltage signal output unit 3a2 connected to the comparator 3a1. The negative polarity surge detection unit 3B comprises a comparator 3b1 to which a negative voltage threshold is set and the detection voltage is input, and a voltage signal output unit 3b2 connected to the comparator 3b1.

Description

[Technical Field]

[0001] The present invention relates to a surge voltage detection device for detecting a surge voltage of a surge that has intruded into an electric system due to a lightning strike or the like. [Background Art]

[0002] In order to protect electrical equipment (load equipment) from surges such as lightning surges, a lightning-resistant transformer is interposed between an input power line and the load equipment (for example, Patent Document 1). Generally, a lightning-resistant transformer is mainly configured of an iron core, a primary winding on the primary side (input side) and a secondary winding on the secondary side (output side) wound around the iron core. The primary winding and the secondary winding are insulated from each other by an electrostatic shield or the like, whereby surges transitioning from the primary side to the secondary side are attenuated, and the load equipment is protected.

[0003] A lightning-resistant transformer operates such that the normally used power supply voltage is supplied to the secondary side (load equipment) according to the operating principle of the transformer, and abnormal overvoltage such as lightning surge is attenuated to suppress transition to the secondary side. Heretofore, there has been no means for easily confirming on site that a lightning-resistant transformer has operated to protect load equipment against surge intrusion, that is, that the lightning-resistant transformer has operated correctly. For example, in the case of an SPD (surge protector), the operation check of the SPD can be performed by detecting a surge current flowing through the SPD to a ground line with a surge counter or the like. However, in a lightning-resistant transformer, since a surge current flow unlike that in an SPD does not occur, operation check using a surge counter or the like cannot be performed. It is also conceivable to check the operation of the lightning-resistant transformer by measuring the primary side voltage (voltage to ground) of the lightning-resistant transformer with a voltage measuring device such as a voltage probe. In this case, however, the voltage measuring device is required to withstand the insulation performance of the lightning-resistant transformer (for example, a withstand voltage of 30 kV or more). This requires a large and extremely expensive voltage measuring device, which is not practical.

[0004] Furthermore, Patent Document 2 describes a device for detecting surge voltages of surges traveling along power transmission and distribution lines. The surge voltage detection device in Patent Document 2 uses a reflective electric field sensor to detect surge voltages non-contact. As shown in Figure 3 of the same document, this reflective electric field sensor is mainly composed of a branched interference optical waveguide formed on the surface of a substrate (11) such as lithium niobate, and a modulation electrode (13) formed near the branched interference optical waveguide. A micro-antenna (16) is formed integrally with the modulation electrode (13) on the surface of the substrate (11), and the transmission voltage and surge voltage on the power transmission and distribution lines are applied to the phase-shift optical waveguide (15) through the modulation electrode (13). This reflective electric field sensor can detect surge voltages with high accuracy, but its structure is complex, resulting in high manufacturing and maintenance costs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6119012 [Patent Document 2] Japanese Patent Application Publication No. 10-160779 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The objective of the present invention is to provide a surge voltage detection device that can detect surge voltages non-contact, has a relatively simple configuration, and has relatively low manufacturing and maintenance costs. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a surge voltage detection device comprising: an electric field detection unit made of a conductor, which is arranged non-contact with an electrical circuit to be detected for surge voltage, and which accumulates induced charges due to the electric field around the electrical circuit; and a surge voltage detection unit to which a detection voltage corresponding to the induced charge of the electric field detection unit is input, wherein the surge voltage detection unit is configured to operate based on the detection voltage when a surge voltage occurs in the electrical circuit and to output a voltage signal corresponding to the surge voltage. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a surge voltage detection device that can detect surge voltages non-contact, has a relatively simple configuration, and has relatively low manufacturing and maintenance costs. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram of a surge voltage detection device according to the first embodiment. [Figure 2] This diagram schematically shows examples of the shape and arrangement of the electric field detection unit. [Figure 3] This figure shows the waveform of a surge voltage (positive polarity) and the waveform of a voltage signal. [Figure 4] This figure shows the relationship between the magnitude of the surge voltage and the output time of the voltage signal. [Figure 5] This diagram shows the waveforms of a surge voltage (negative polarity) and a voltage signal. [Figure 6] This is a circuit diagram of a surge voltage detection device according to the second embodiment. [Figure 7] This figure shows the waveform of a surge voltage (positive polarity) and the waveform of a voltage signal. [Figure 8] This figure shows the relationship between the magnitude of the surge voltage and the output time of the voltage signal. [Figure 9] This diagram shows the waveforms of a surge voltage (negative polarity) and a voltage signal. [Figure 10] This is a circuit diagram of a surge voltage detection device according to a modified example of the second embodiment. [Figure 11] This is a circuit diagram of a surge voltage detection device according to the third embodiment. [Figure 12] This figure shows the waveform of a surge voltage (positive polarity) and the waveform of a voltage signal. [Figure 13] This diagram shows the waveforms of a surge voltage (negative polarity) and a voltage signal. [Figure 14] This is a circuit diagram of a surge voltage detection device according to a modified example of the third embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, a surge voltage detection device according to an embodiment of the present invention will be described with reference to the drawings. Surges include lightning surges and switching surges. The surge voltage detection device of this embodiment can be used to non-contactly detect the surge voltage of various surges that have entered power lines such as transmission lines and distribution lines and other electrical circuits. Here, we will describe the case in which the surge voltage of a lightning surge that has entered the electrical circuit on the primary side (input side) of a lightning-resistant transformer is detected.

[0011] Figure 1 is a circuit diagram showing a surge voltage detection device 1 according to the first embodiment. The surge voltage detection device 1 of this embodiment includes an electric field detection unit 1C1 and a positive surge detection unit 1A that detects positive surge voltages, and an electric field detection unit 1C2 and a negative surge detection unit 1B that detects negative surge voltages. The dashed-dot circle in the figure shows the configuration of the power supply E, where DC+ represents the positive side of the power supply E and DC- represents the negative side of the power supply E. The power supply E is a DC power supply and is configured by directly connecting two batteries, for example, two 1.5V dry cell batteries, and connecting the two batteries to ground.

[0012] The electric field detection unit 1C1 and the electric field detection unit 1C2 are each formed of a conductor (electric conductor), and are formed into an annular, plate-like, linear or other shape from, for example, a metal such as copper or a copper alloy, aluminum or an aluminum alloy, or an alloy of copper and aluminum, a conductive resin, a conductive ceramic, or other conductive materials, and are arranged in a non-contact manner with respect to an electric path to be detected. In this embodiment, the electric path to be detected is a primary-side electric path of a lightning-proof transformer to which a surge voltage is applied by a lightning surge, specifically an input power supply line or a primary winding on the primary side of the lightning-proof transformer, and particularly the input power supply line.

[0013] Figures 2(a) to 2(d) schematically show examples of the shapes and arrangement modes of the electric field detection unit 1C1 and the electric field detection unit 1C2. In the example shown in Fig. 2(a), the electric field detection unit 1C1 and the electric field detection unit 1C2 are each formed in a flat plate shape, and the electric field detection unit 1C1 and the electric field detection unit 1C2 are arranged such that one surface serving as the electric field detection surface of each of the electric field detection unit 1C1 and the electric field detection unit 1C2 faces the outer periphery of the input power line L with a predetermined gap therebetween. In the example shown in Fig. 2(b), the electric field detection unit 1C1 and the electric field detection unit 1C2 are each formed in an annular shape, and the electric field detection unit 1C1 and the electric field detection unit 1C2 are extrapolated to the input power line L such that the inner peripheral surfaces serving as the electric field detection surfaces of the electric field detection unit 1C1 and the electric field detection unit 1C2 face the input power line L with a predetermined gap therebetween. In the example shown in Fig. 2(c), compared with the example shown in Fig. 2(a), an electrostatic shield S1 is provided so as to cover the other surface opposite to the one surface serving as the electric field detection surface of the electric field detection unit 1C1 and the electric field detection unit 1C2. The electrostatic shield S1 is preferably grounded, more commonly grounded together with the lightning-proof transformer (connected to a ground terminal or the like of the lightning-proof transformer). Further, in the example shown in Fig. 2(d), compared with the example shown in Fig. 2(b), an electrostatic shield S2 is provided so as to cover the outer peripheral surface opposite to the inner peripheral surface serving as the electric field detection surface of the electric field detection unit 1C1 and the electric field detection unit 1C2. The electrostatic shield S2 is preferably grounded, more preferably commonly grounded together with the lightning-proof transformer. By providing the electrostatic shields S1 and S2, false detection caused by noise can be prevented. In this way, the positive surge detection unit 1A and the negative surge detection unit 1B are respectively connected to the surface opposite to the electric field detection surface (hereinafter referred to as "non-detection surface") of the electric field detection unit 1C1 and the electric field detection unit 1C2 arranged in a non-contact manner with respect to the input power line L.

[0014] The positive polarity surge detector 1A is mainly composed of a circuit element that conducts electrically when a positive voltage exceeding a predetermined value is applied, for example, an n-type field effect transistor (FET) 1a1, a power supply circuit 1a2 connected to a power supply E, a comparator 1a3 connected to the power supply circuit 1a2, and a voltage signal output unit 1a4 connected to the comparator 1a3.

[0015] The gate of the n-type field effect transistor 1a1 is connected to the non-detection surface of the electric field detector 1C1 via a resistor R1, and the source and the drain are connected to the power supply circuit 1a2. Further, the electric path between the gate of the n-type field effect transistor 1a1 and the resistor R1 is connected to the ground via a diode 1a5. The diode 1a5 functions to prevent positive induced charges accumulated on the non-detection surface of the electric field detector 1C1 from flowing to the ground side, and to release the gate leakage current of the n-type field effect transistor 1a1 to the ground side.

[0016] The power supply circuit 1a2 is composed of: an electric path extending from the positive electrode side of the power supply E to the drain of the n-type field effect transistor 1a1; an electric path extending from the source of the n-type field effect transistor 1a1 to the ground via resistors R2 and R3; an electric path extending from the positive electrode side of the power supply E to the collector of a transistor, for example, an npn-type transistor 1a21 via a resistor R4; an electric path extending from the emitter of the npn-type transistor 1a21 to the ground; and an electric path connecting the electric path between the resistors R2 and R3 and the base of the npn-type transistor 1a21.

[0017] The non-inverting input terminal of the comparator 1a3 is connected to the electric path between the collector of the npn-type transistor 1a21 and the resistor R4, the inverting input terminal is connected to a variable resistor 1a6, and the output terminal is connected to the voltage signal output unit 1a4. The positive and negative power supply terminals of the comparator 1a3 are connected to the positive electrode side and the negative electrode side of the power supply E, respectively. One end side of the variable resistor 1a6 is connected to the positive electrode side of the power supply E, and the other end side is connected to the ground. The variable resistor 1a6 can adjust the positive voltage threshold of the comparator 1a3 (the voltage input to the inverting input terminal) to a desired value.

[0018] The negative polarity surge detection unit 1B is mainly composed of a circuit element that conducts electrically when a negative voltage exceeding a predetermined value is applied, such as a p-type field-effect transistor (FET) 1b1, a power supply circuit 1b2 connected to the power supply E, a comparator 1b3 connected to the power supply circuit 1b2, and a voltage signal output unit 1b4 connected to the comparator 1b3.

[0019] The gate of the p-type field-effect transistor 1b1 is connected to the non-detecting surface of the field detection unit 1C2 via resistor R5, and its source and drain are connected to the power supply circuit 1b2. Furthermore, the circuit between the gate of the p-type field-effect transistor 1b1 and resistor R5 is connected to ground via diode 1b5 (in the opposite direction to diode 1a5). Diode 1b5 prevents the negative induced charge accumulated on the non-detecting surface of the field detection unit 1C2 from flowing to ground, and also allows the gate leakage current of the p-type field-effect transistor 1b1 to escape to ground.

[0020] The power supply circuit 1b2 consists of a circuit from the negative terminal side of the power supply E to the drain of the p-type field-effect transistor 1b1, a circuit from the source of the p-type field-effect transistor 1b1 to ground via resistors R6 and R7, a circuit from the negative terminal side of the power supply E to the collector of a transistor, such as a pnp-type transistor 1b21, via resistor R8, a circuit from the emitter of the pnp-type transistor 1b21 to ground, and a circuit connecting the circuit between resistors R6 and R7 to the base of the pnp-type transistor 1b21.

[0021] The inverting input terminal of comparator 1b3 is connected to the circuit between the collector of pnp transistor 1b21 and resistor R8, the non-inverting input terminal is connected to variable resistor 1b6, and the output terminal is connected to voltage signal output unit 1b4. The positive and negative power supply terminals of comparator 1b3 are connected to the positive and negative sides of power supply E, respectively. One end of variable resistor 1b6 is connected to the negative side of power supply E, and the other end is connected to ground. The negative voltage threshold of comparator 1b3 (the voltage input to the non-inverting input terminal) can be adjusted to a desired value using variable resistor 1b6.

[0022] The positive surge detection unit 1A and the negative surge detection unit 1B operate in the manner described below, depending on the polarity of the surge voltage generated in the input power line L.

[0023] For example, when a positive surge voltage is generated in the input power line L, electrostatic induction causes induced charges (negative induced charges) with the opposite polarity to the electric field around the input power line L to accumulate on the electric field detection surfaces of the electric field detection units 1C1 and 1C2, while polarization causes positive induced charges to accumulate on the non-detection surfaces of the electric field detection units 1C1 and 1C2. Then, due to the action of the positive induced charges accumulated on the non-detection surface of the electric field detection unit 1C1, resistor R1, and diode 1a5, a positive detection voltage corresponding to the accumulated positive induced charge is input to the gate of the n-type field-effect transistor 1a1 of the positive surge detection unit 1A. When this positive detection voltage exceeds the gate threshold voltage, the drain-source of the n-type field-effect transistor 1a1 conducts. As a result, the power supply circuit 1a2 of the positive surge detection unit 1A opens. On the other hand, due to the action of diode 1b5, no voltage is applied to the p-type field-effect transistor 1b1 of the negative polarity surge detection unit 1B, and since the p-type field-effect transistor 1b1 does not conduct under positive voltage, the power supply circuit 1b2 of the negative polarity surge detection unit 1B does not open.

[0024] In the above configuration, when the power supply circuit 1a2 of the positive polarity surge detection unit 1A is opened, a positive voltage from the power supply E is applied to the base of the npn transistor 1a21, causing the collector-emitter junction of the npn transistor 1a21 to conduct. As a result, the positive voltage from the power supply E is applied to the collector side of the npn transistor 1a21, and this positive voltage is input to the non-inverting input terminal of the comparator 1a3.

[0025] Comparator 1a3 compares the positive voltage input to the non-inverting input terminal with a positive voltage threshold (adjusted by variable resistor 1a6) input to the inverting input terminal, and outputs a digital signal (a signal such as "1" or "High" if the input voltage to the non-inverting input terminal exceeds the voltage threshold, and "0" or "Low" if it does not).

[0026] The voltage signal output unit 1b4 outputs a time-series voltage signal based on the digital signal output from the comparator 1a3.

[0027] Figure 3 shows the waveform of a positive surge voltage on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 1a4 of the positive surge detection unit 1A {Figure (b)}. The vertical axis represents voltage, and the horizontal axis represents time. DC+ and DC- on the vertical axis represent the voltage of the power supply E. When a positive surge voltage occurs on the input power line L, the positive surge detection unit 1A operates in the manner described above, and a voltage signal corresponding to the surge voltage is output from the voltage signal output unit 1a4. As shown in Figure (b), the waveform of this voltage signal is a pulse waveform that rises from approximately 0V to a voltage approximately equal to the power supply E voltage DC+. From this voltage signal, it is possible to detect that a positive surge voltage has occurred on the input power line L. Also, as schematically shown in Figure 4, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, the voltage signal from the voltage signal output unit 1a4 can be used to detect when a positive surge voltage has occurred on the input power line L, and to determine the magnitude level of the generated surge voltage (e.g., large, medium, small).

[0028] On the other hand, when a negative surge voltage is generated in the input power line L, electrostatic induction causes induced charges (positive induced charges) with the opposite polarity to the electric field around the input power line L to accumulate on the electric field detection surfaces of the electric field detection units 1C1 and 1C2, while polarization causes negative induced charges to accumulate on the non-detection surfaces of the electric field detection units 1C1 and 1C2. Then, due to the action of the negative induced charges accumulated on the non-detection surface of the electric field detection unit 1C2, resistor R5, and diode 1b5, a negative detection voltage corresponding to the accumulated negative induced charge is input to the gate of the p-type field-effect transistor 1b1 of the negative surge detection unit 1B. When this negative detection voltage exceeds the gate threshold voltage, the drain and source of the p-type field-effect transistor 1b1 conduct. As a result, the power supply circuit 1b2 of the negative surge detection unit 1B is opened. On the other hand, due to the action of diode 1a5, no voltage is applied to the n-type field-effect transistor 1a1 of the positive surge detection unit 1A, and since the n-type field-effect transistor 1a1 does not conduct under negative voltage, the power supply circuit 1a2 of the positive surge detection unit 1A does not open.

[0029] In the above configuration, when the power supply circuit 1b2 of the negative polarity surge detection unit 1B is opened, a negative voltage from the power supply E is applied to the base of the pnp transistor 1b21, causing the collector-emitter junction of the pnp transistor 1b21 to conduct. As a result, the negative voltage from the power supply E is applied to the collector side of the pnp transistor 1b21, and this negative voltage is input to the inverting input terminal of the comparator 1b3.

[0030] Comparator 1b3 compares the negative voltage input to the inverting input terminal with a negative voltage threshold (adjusted by variable resistor 1b6) input to the non-inverting input terminal, and outputs a digital signal (a signal such as "1" or "High" if the input voltage at the inverting input terminal exceeds the voltage threshold, and "0" or "Low" if it does not).

[0031] The voltage signal output unit 1b4 outputs a time-series voltage signal based on the digital signal output from the comparator 1b3.

[0032] Figure 5 shows the waveform of the surge voltage (negative polarity) on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 1b4 of the negative polarity surge detection unit 1B {Figure (b)}. The vertical axis is voltage, and the horizontal axis is time. DC+ and DC- on the vertical axis are the voltages of the power supply E. When a negative polarity surge voltage occurs on the power line L, the negative polarity surge detection unit 1B operates in the manner described above, and a voltage signal corresponding to the surge voltage is output from the voltage signal output unit 1b4. As shown in Figure (b), the waveform of this voltage signal is a pulse waveform that falls from approximately 0V to a voltage approximately equal to the power supply E voltage DC-. From this voltage signal, it is possible to detect that a negative polarity surge voltage has occurred on the input power line L. Although not shown in the figure, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, the voltage signal from the voltage signal output unit 1b4 can be used to detect when a negative surge voltage has occurred on the power line L, and to determine the magnitude level of the generated surge voltage (e.g., large, medium, small).

[0033] The information obtained from the voltage signal described above is stored in the memory of the operating unit of the surge voltage detection device and can be displayed on a display or other display device, or communicated to an external device via wired or wireless connection. The information stored may include the voltage signal in time series, the polarity of the surge voltage, the magnitude level of the surge voltage (indicated as large, medium, small, etc.), the time the surge voltage was detected, and the number of times the surge voltage was detected.

[0034] The surge voltage detection device 1 of this embodiment detects the surge voltage in the primary circuit of the lightning-protected transformer and, by comparing it with the status of the secondary side of the lightning-protected transformer (whether it was affected by the surge voltage, etc.), it is possible to confirm whether the lightning-protected transformer operated correctly in response to the intrusion of a lightning surge (generation of a surge voltage). Furthermore, since the surge voltage detection device 1 of this embodiment can determine the magnitude level of the generated surge voltage, for example, if a large lightning surge intrudes, maintenance of the lightning-protected transformer and load equipment can be performed, or depending on the frequency of lightning surge intrusions, it can be used as a guideline for replacing the lightning-protected transformer.

[0035] In this embodiment, the surge voltage detection device 1 can be placed not only in the primary circuit of the lightning protection transformer but also in circuits where surge voltages are not applied, such as the secondary circuit of the lightning protection transformer. By comparing the voltage signals from both circuits, false detections due to noise can be prevented, thereby improving the reliability of surge voltage detection.

[0036] In the surge voltage detection device 1 of this embodiment, the power supply E may be shared by the positive surge detection unit 1A and the negative surge detection unit 1B, or it may be provided separately for the positive surge detection unit 1A and the negative surge detection unit 1B. Instead of the power supply E, an AC power supply from a lightning protection transformer or a separately drawn DC or AC power supply may be used, converted to a voltage level suitable for circuit operation by a power conversion circuit or the like. Also, the npn type transistor 1a21 of the positive surge detection unit 1A and the pnp type transistor 1b21 of the negative surge detection unit 1B can be omitted. Furthermore, it is preferable that each ground of the surge voltage detection device 1 circuit (including the ground of the power supply E) be grounded in common with the lightning protection transformer, and the resistors R1 and R5 directly connected to the electric field detection units 1C1 and 1B1 are preferably high resistances of 100 to several hundred MΩ from the viewpoint of circuit protection.

[0037] The surge voltage detection device 1 of this embodiment can be widely used not only for detecting surge voltages in the primary circuit of a lightning protection transformer, but also for detecting surge voltages in any circuit where surge intrusion (generation of surge voltage) is expected.

[0038] Furthermore, when using the surge voltage detection device 1 of this embodiment for an electrical circuit where the intrusion of surges of either positive or negative polarity is expected, one of the following may be omitted depending on the polarity of the expected surge voltage: the electric field detection unit 1C1 and the positive surge detection unit 1A, or the electric field detection unit 1C2 and the negative surge detection unit 1B. In other words, the surge voltage detection device 1 of this embodiment can consist only of the electric field detection unit 1C1 and the positive surge detection unit 1A, or it can consist only of the electric field detection unit 1C2 and the negative surge detection unit 1B.

[0039] Figure 6 is a circuit diagram showing a surge voltage detection device 2 according to the second embodiment. The surge voltage detection device 2 of this embodiment also includes a positive surge detection unit 2A for detecting positive surge voltages and a negative surge detection unit 2B for detecting negative surge voltages. However, unlike the surge voltage detection device 1 of the first embodiment, a single electric field detection unit 2C is provided, which is shared by the positive surge detection unit 2A and the negative surge detection unit 2B. The electric field detection unit 2C is a conductor similar to the electric field detection units 1C1 and 1C2 of the surge voltage detection device 1 of the first embodiment, and is arranged in the same manner as the electric field detection units 1C1 and 1C1, without contact with the primary side input power line L of the lightning protection transformer. The electrostatic shield and the configuration of the power supply E shown in the dashed-dotted circle in the figure are also the same as those of the surge voltage detection device 1 of the first embodiment.

[0040] The non-detection surface of the electric field detection unit 2C is connected to ground via resistors R21 and R22. When a surge voltage occurs in the input power line L and induced charge accumulates on the non-detection surface of the electric field detection unit 2C, a voltage (voltage to ground) corresponding to the accumulated induced charge is generated in the circuit from the non-detection surface of the electric field detection unit 2C to ground via resistors R21 and R22. In this embodiment, the part that generates a detection voltage corresponding to the induced charge accumulated in the electric field detection unit 2C, the circuit from the non-detection surface of the electric field detection unit 2C to ground via resistors R21 and R22, is called the detection voltage generation unit 2F.

[0041] The positive surge detection unit 2A and the negative surge detection unit 2B are connected in parallel to the circuit between resistors R21 and R22 in the detection voltage generation unit 2F via an operational amplifier, such as a CMOS operational amplifier 2D (hereinafter simply referred to as "operational amplifier 2D").

[0042] The detection voltage generation unit 2F is connected to the non-inverting input terminal of the operational amplifier 2D, and the output circuit of the operational amplifier 2D is connected to the inverting input terminal of the operational amplifier 2D. The positive and negative power supply terminals of the operational amplifier 2D are connected to the positive and negative sides of the power supply E. This circuit including the operational amplifier 2D constitutes a voltage follower, reducing the output impedance and suppressing the voltage drop in the downstream positive surge detection unit 2A and negative surge detection unit 2B.

[0043] The positive polarity surge detection unit 2A is mainly composed of a comparator 2a1 connected to the output circuit of the operational amplifier 2D and a voltage signal output unit 2a2 connected to the comparator 2a1.

[0044] Comparator 2a1 is a hysteresis comparator with positive feedback, including resistor R23. The inverting input terminal of comparator 2a1 is connected to the output circuit of op-amp 2D, and the non-inverting input terminal is connected to the positive feedback circuit, which is connected to the variable resistor 2a3 via resistor R24. The output terminal of comparator 2a1 is connected to the voltage signal output section 2a2. The positive and negative power supply terminals of comparator 2a1 are connected to the positive and negative terminals of power supply E. The variable resistor 2a3 is connected to the positive terminal of power supply E and to ground, and the positive voltage threshold of comparator 2a1 (input voltage of the non-inverting input terminal) can be adjusted to a desired value using the variable resistor 2a3.

[0045] The negative polarity surge detection unit 2B is mainly composed of a comparator 2b1 connected to the output circuit of the operational amplifier 2D and a voltage signal output unit 2b2 connected to the comparator 2b1.

[0046] Comparator 2b1 is a hysteresis comparator with positive feedback, including resistor R25. The inverting input terminal of comparator 2b1 is connected to the output circuit of op-amp 2D, and the non-inverting input terminal is connected to the positive feedback circuit, which is connected to the variable resistor 2b3 via resistor R26. The output terminal of comparator 2b1 is connected to the voltage signal output section 2b2. The positive and negative power supply terminals of comparator 2b1 are connected to the positive and negative terminals of power supply E. The variable resistor 2b3 is connected to the negative terminal of power supply E and to ground, and the negative voltage threshold of comparator 2b1 (input voltage of the non-inverting input terminal) can be adjusted to a desired value using the variable resistor 2b3.

[0047] For example, when a positive surge voltage occurs in the input power line L, electrostatic induction causes induced charges (negative induced charges) with the opposite polarity to the electric field around the input power line L to accumulate on the electric field detection surface of the electric field detection unit 2C, while polarization causes positive induced charges to accumulate on the non-detection surface of the electric field detection unit 2C. Then, a positive detection voltage corresponding to the positive induced charges accumulated on the non-detection surface of the electric field detection unit 2C is generated in the detection voltage generation unit 2F. This positive detection voltage is input to the non-inverting input terminal of the operational amplifier 2D and output to the output circuit of the operational amplifier 2D. The positive detection voltage output from the operational amplifier 2D is applied to both the comparator 2a1 of the positive surge detection unit 2A and the comparator 2b1 of the negative surge detection unit 2B, but since a negative voltage threshold is set for comparator 2b1, comparator 2b1 does not output a digital signal.

[0048] When the positive detection voltage output from the operational amplifier 2D is input to the inverting input terminal of the comparator 2a1 of the positive polarity surge detection unit 2A, the comparator 2a1 compares the positive detection voltage input to the inverting input terminal with the positive voltage threshold (adjusted by the variable resistor 2a3) input to the non-inverting input terminal and outputs a digital signal.

[0049] The voltage signal output unit 2a2 outputs a time-series voltage signal based on the digital signal output from the comparator 2a1.

[0050] Figure 7 shows the waveform of the surge voltage (positive polarity) on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 2a2 of the positive polarity surge detection unit 2A {Figure (b)}. The vertical axis is voltage, and the horizontal axis is time. DC+ and DC- on the vertical axis are the voltages of the power supply E. As shown in Figure (b), the waveform of the voltage signal output from the voltage signal output unit 2a2 is a pulse waveform that falls from a voltage approximately equal to the voltage DC+ of the power supply E to approximately 0V, and from this voltage signal, it is possible to detect that a positive polarity surge voltage has occurred on the input power line L. Also, as shown in Figure 8, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, from the voltage signal of the voltage signal output unit 2a2, it is possible to detect that a positive polarity surge voltage has occurred on the power line L, and to determine the level of the magnitude of the generated surge voltage (e.g., large, medium, small).

[0051] On the other hand, when a negative surge voltage occurs in the input power line L, electrostatic induction causes induced charges (positive induced charges) with the opposite polarity to the electric field around the input power line L to accumulate on the electric field detection surface of the electric field detection unit 2C, and negative induced charges accumulate on the non-detection surface of the electric field detection unit 2C due to polarization. Then, a negative detection voltage corresponding to the negative induced charges accumulated on the non-detection surface of the electric field detection unit 2C is generated in the detection voltage generation unit 2F. This negative detection voltage is input to the non-inverting input terminal of the operational amplifier 2D and output to the output circuit of the operational amplifier 2D. The negative detection voltage output from the operational amplifier 2D is applied to both the comparator 2a1 of the positive surge detection unit 2A and the comparator 2b1 of the negative surge detection unit 2B, but since a positive voltage threshold is set for comparator 2a1, comparator 2a1 does not output a digital signal.

[0052] When the negative detection voltage output from the operational amplifier 2D is input to the inverting input terminal of the comparator 2b1 of the negative polarity surge detection unit 2B, the comparator 2b1 compares the negative detection voltage input to the inverting input terminal with the negative voltage threshold (adjusted by the variable resistor 2b3) input to the non-inverting input terminal and outputs a digital signal.

[0053] The voltage signal output unit 2b2 outputs a time-series voltage signal based on the digital signal output from the comparator 2b1.

[0054] Figure 9 shows the waveform of the surge voltage (negative polarity) on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 2b2 of the negative polarity surge detection unit 2B {Figure (b)}. The vertical axis is voltage, and the horizontal axis is time. DC+ and DC- on the vertical axis are the voltages of the power supply E. As shown in Figure (b), the waveform of the voltage signal output from the voltage signal output unit 2b2 is a pulse waveform that rises from approximately 0V to a voltage approximately equal to the power supply E voltage DC+. From this voltage signal, it is possible to detect that a negative polarity surge voltage has occurred on the input power line L. Although not shown in the figure, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, from the voltage signal of the voltage signal output unit 2b2, it is possible to detect that a negative polarity surge voltage has occurred on the power line L, and to determine the magnitude level of the generated surge voltage (e.g., large, medium, small).

[0055] Furthermore, as a method for determining the magnitude level of the surge voltage, a configuration can be made in which multiple sets of positive-polarity surge detection units 2A and negative-polarity surge detection units 2B are provided (two sets in the figure), as shown in the modified surge voltage detection device 2' in Figure 10, and mutually different positive voltage thresholds are set between the comparators 2a1 of the multiple positive-polarity surge detection units 2A, and mutually different negative voltage thresholds are set between the comparators 2b1 of the multiple negative-polarity surge detection units 2B. By selecting the detected power input to the comparators 2a1 and 2b1 within the voltage threshold range of each comparator 2a1 and 2b1 and outputting it to the voltage signal output units 2a2 and 2b2, the magnitude level of the generated surge voltage can be determined from the voltage signal output units 2a2 and 2b2 that output the voltage signals and the voltage thresholds of the comparators 2a1 and 2b1 corresponding to those voltage signal output units 2a2 and 2b2.

[0056] Other matters are the same as those described with respect to the surge voltage detection device 1 of the first embodiment.

[0057] Figure 11 is a circuit diagram showing a surge voltage detection device 3 according to a third embodiment. The surge voltage detection device 3 of this embodiment also includes a positive surge detection unit 3A for detecting positive surge voltages and a negative surge detection unit 3B for detecting negative surge voltages. However, unlike the surge voltage detection device 1 of the first embodiment, a single electric field detection unit 3C is provided, which is shared by the positive surge detection unit 3A and the negative surge detection unit 3B. The electric field detection unit 3C is a conductor similar to the electric field detection units 1C1 and 1C2 of the surge voltage detection device 1 of the first embodiment, and is arranged in a similar manner to the electric field detection units 1C1 and 1C2, without contact with the primary side input power line L of the lightning protection transformer. The electrostatic shield and the configuration of the power supply E shown in the dashed-dotted circle in the figure are also the same as those of the surge voltage detection device 1 of the first embodiment.

[0058] The non-detection surface of the electric field detection unit 3C is connected to ground via resistors R31 and R32. When a surge voltage is generated in the input power line L and induced charge accumulates on the non-detection surface of the electric field detection unit 3C, a voltage (voltage to ground) corresponding to the accumulated induced charge is generated in the circuit from the non-detection surface of the electric field detection unit 3C through resistors R31 and R32 to ground. In this embodiment, the part that generates a detection voltage corresponding to the induced charge accumulated in the electric field detection unit 3C, the circuit from the non-detection surface of the electric field detection unit 3C through resistors R31 and R32 to ground, is called the detection voltage generation unit 3F.

[0059] The positive surge detection unit 3A and the negative surge detection unit 3B are connected in parallel to the circuit between resistors R31 and R32 in the detection voltage generation unit 3F.

[0060] The positive polarity surge detection unit 3A is mainly composed of a comparator 3a1 connected to the detection voltage generation unit 3F and a voltage signal output unit 3a2 connected to the comparator 3a1.

[0061] Comparator 3a1 is a hysteresis comparator with positive feedback, including resistor R33. The inverting input terminal of comparator 3a1 is connected to the detection voltage generator 3F, and the non-inverting input terminal is connected to the positive feedback circuit, which is connected to the variable resistor 3a3 via resistor R34. The output terminal of comparator 3a1 is connected to the voltage signal output unit 3a2. The positive and negative power supply terminals of comparator 3a1 are connected to the positive and negative terminals of power supply E. The variable resistor 3a3 is connected to the positive terminal of power supply E and to ground, and the positive voltage threshold of comparator 3a1 (input voltage of the non-inverting input terminal) can be adjusted to a desired value using the variable resistor 3a3. A positive voltage is applied from power supply E to the circuit between comparator 3a1 and voltage signal output unit 3a2 via resistor R35.

[0062] The negative polarity surge detection unit 3B is mainly composed of a comparator 3b1 connected to the detection voltage generation unit 3F and a voltage signal output unit 3b3 connected to the comparator 3b1.

[0063] Comparator 3b1 is a hysteresis comparator with positive feedback, including resistor R36. The inverting input terminal of comparator 3b1 is connected to the detection voltage generator 3F, and the non-inverting input terminal is connected to the positive feedback circuit, which is connected to the variable resistor 3b3 via resistor R37. The output terminal of comparator 3b1 is connected to the voltage signal output unit 3b2. The positive and negative power supply terminals of comparator 3b1 are connected to the positive and negative terminals of power supply E. The variable resistor 3a3 is connected to the negative terminal of power supply E and to ground, and the variable resistor 3b3 allows the negative voltage threshold of comparator 3a1 (input voltage of the non-inverting input terminal) to be adjusted to a desired value. A positive voltage is applied from power supply E to the circuit between comparator 3b1 and the voltage signal output unit 3b2 via resistor R38.

[0064] For example, when a positive surge voltage occurs in the input power line L, electrostatic induction causes induced charges (negative induced charges) with the opposite polarity to the surrounding charges of the input power line L to accumulate on the electric field detection surface of the electric field detection unit 3C, while polarization causes positive induced charges to accumulate on the non-detection surface of the electric field detection unit 3C. Then, a positive detection voltage corresponding to the positive induced charges accumulated on the non-detection surface of the electric field detection unit 3C is generated in the detection voltage generation unit 3F. This positive detection voltage is applied to both the comparator 3a1 of the positive surge detection unit 3A and the comparator 3b1 of the negative surge detection unit 3B, but since a negative voltage threshold is set for comparator 3b1, comparator 3b1 does not output a digital signal.

[0065] When the above positive detection voltage is input to the inverting input terminal of the comparator 3a1 of the positive polarity surge detection unit 3A, the comparator 3a1 compares the positive detection voltage input to the inverting input terminal with the positive voltage threshold (adjusted by the variable resistor 3a3) input to the non-inverting input terminal and outputs a digital signal.

[0066] The voltage signal output unit 3a2 outputs a time-series voltage signal based on the digital signal output from the comparator 3a1.

[0067] Figure 12 shows the waveform of the surge voltage (positive polarity) on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 3a2 of the positive polarity surge detection unit 3A {Figure (b)}. The vertical axis is voltage, and the horizontal axis is time. DC+ and DC- on the vertical axis are the voltages of the power supply E. As shown in Figure (b), the waveform of the voltage signal output from the voltage signal output unit 3a2 is a pulse waveform that falls from a voltage approximately equal to the voltage DC+ of the power supply E to approximately 0V. From this voltage signal, it is possible to detect that a positive polarity surge voltage has occurred on the input power line L. Although not shown in the figure, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, from the voltage signal of the voltage signal output unit 3a2, it is possible to detect that a positive polarity surge voltage has occurred on the input power line L and to determine the magnitude level of the generated surge voltage.

[0068] On the other hand, when a negative surge occurs in the input power line L, electrostatic induction causes induced charges (positive induced charges) with the opposite polarity to the electric field around the input power line L to accumulate on the electric field detection surface of the electric field detection unit 3C, and negative induced charges accumulate on the non-detection surface of the electric field detection unit 3C due to polarization. Then, a negative detection voltage corresponding to the negative induced charges accumulated on the non-detection surface of the electric field detection unit 3C is generated in the detection voltage generation unit 3F. This negative detection voltage is applied to both the comparator 3a1 of the positive surge detection unit 3A and the comparator 3b1 of the negative surge detection unit 3B, but since a positive voltage threshold is set for comparator 3a1, comparator 3a1 does not output a digital signal.

[0069] When the above-mentioned negative detection voltage is input to the inverting input terminal of the comparator 3b1 of the negative polarity surge detection unit 3B, the comparator 3b1 compares the negative detection voltage input to the inverting input terminal with the negative voltage threshold (adjusted by the variable resistor 3b3) input to the non-inverting input terminal and outputs a digital signal.

[0070] The voltage signal output unit 3b2 outputs a time-series voltage signal based on the digital signal output from the comparator 3b1.

[0071] Figure 13 shows the waveform of the surge voltage (negative polarity) on the input power line L {Figure (a)} and the voltage signal output from the voltage signal output unit 3b2 of the negative polarity surge detection unit 3B {Figure (b)}. The vertical axis is voltage, and the horizontal axis is time. DC+ and DC- on the vertical axis are the voltages of the power supply E. As shown in Figure (b), the waveform of the voltage signal output from the signal output unit 3b2 is a pulse waveform that rises from approximately 0V to a voltage approximately equal to the power supply E voltage DC+. From this voltage signal, it is possible to detect that a negative polarity surge voltage has occurred on the input power line L. Although not shown in the figure, the output time (duration) of this voltage signal is proportional to the magnitude of the surge voltage. Therefore, from the voltage signal of the voltage signal output unit 3b2, it is possible to detect that a negative polarity surge voltage has occurred on the input power line L and to determine the magnitude level of the generated surge voltage.

[0072] Other matters are the same as those described for the surge voltage detection device 1 of the first embodiment and the voltage detection device 2 of the second embodiment.

[0073] Figure 14 is a circuit diagram of a surge voltage detection device 3' according to a modified example of the third embodiment. In this modified example of the surge voltage detection device 3', a capacitor C1 is connected in parallel to the resistor R32 of the detection power supply generation unit F. By connecting capacitor C1, it becomes possible to adjust the voltage waveform in the high-frequency range. The other configurations are the same as those of the surge voltage detection device 3 of the third embodiment, so redundant explanations are omitted.

[0074] In the surge voltage detection device 3 of the third embodiment and the modified surge voltage detection device 3', as a method for determining the magnitude level of the surge voltage, a configuration can be provided in which multiple sets of positive-polarity surge detection units 3A and negative-polarity surge detection units 3B are provided, similar to the surge voltage detection device 2' shown in Figure 10, and mutually different positive voltage thresholds are set between the comparators 3a1 of the multiple positive-polarity surge detection units 3A, and mutually different negative voltage thresholds are set between the comparators 3b1 of the multiple negative-polarity surge detection units 3B. [Explanation of Symbols]

[0075] 1. Surge voltage detection device 1A Positive polarity surge detection unit 1a1 n-type field-effect transistor 1a2 power circuit 1a3 Comparator 1a4 Voltage signal output section 1B Negative polarity surge detection unit 1b1 p-type field-effect transistor 1b2 power supply circuit 1b3 Comparator 1b4 Voltage signal output section 1C1 Electric field detection unit 1C2 Electric field detection unit 2. Surge voltage detection device 2A Positive Polarity Surge Detection Unit 2a1 Comparator 2a2 Voltage signal output section 2B Negative polarity surge detection unit 2b1 Comparator 2b2 Voltage signal output section 2C Electric Field Detection Unit 2D CMOS operational amplifier 2F Detection Voltage Generation Unit 3. Surge voltage detection device 3A Positive polarity surge detection unit 3a1 Comparator 3a2 Voltage signal output section 3B Negative polarity surge detection unit 3b1 Comparator 3b2 Voltage signal output section 3C Electric Field Detection Unit 3F Detection Voltage Generation Unit

Claims

1. An electric field detection unit made of a conductor, positioned non-contact with the circuit to be detected for surge voltage, and in which induced charges accumulate due to the electric field surrounding the circuit, The system includes a surge voltage detection unit to which a detection voltage corresponding to the induced charge of the electric field detection unit is input, The surge voltage detection unit comprises a circuit element that conducts electrically when the detected voltage exceeding a predetermined value is input, a power supply circuit connected to a power supply that generates a voltage from the power supply when the circuit element conducts, a comparator to which a voltage threshold is set and the voltage generated by the power supply circuit is input, and a voltage signal output unit connected to the comparator. A surge voltage detection device comprising: a comparator that compares a voltage input from the power supply circuit with a voltage threshold and outputs a predetermined signal to the voltage signal output unit, and the voltage signal output unit that outputs a voltage signal based on the signal output from the comparator.

2. The electric field detection unit consists of a first electric field detection unit and a second electric field detection unit. The surge voltage detection unit comprises a positive-polarity surge detection unit connected to the first electric field detection unit and a negative-polarity surge detection unit connected to the second electric field detection unit. The positive polarity surge detection unit comprises a first circuit element that conducts electrically when a positive detection voltage exceeding a predetermined value is input, a first power supply circuit connected to a power supply that generates a positive voltage from the power supply when the first circuit element conducts, a first comparator connected to the first power supply circuit and having a positive voltage threshold set, and a first voltage signal output unit connected to the first comparator. The surge voltage detection device according to claim 1, wherein the negative polarity surge detection unit comprises a second circuit element that conducts electrically when a negative detection voltage exceeding a predetermined value is input, a second power supply circuit connected to a power supply and which generates a negative voltage from the power supply when the second circuit element conducts, a second comparator connected to the second power supply circuit and which has a negative voltage threshold set, and a second voltage signal output unit connected to the second comparator.

3. An electric field detection unit made of a conductor, which is positioned in a non-contact manner with respect to the circuit to be detected for surge voltage, and which accumulates induced charges due to the electric field surrounding the circuit, The electric field detection unit is connected to ground via a resistor, and a detection voltage generation unit generates a detection voltage corresponding to the induced charge of the electric field detection unit, The system includes a surge voltage detection unit connected to the detection voltage generation unit, The surge voltage detection unit comprises a comparator to which a voltage threshold is set and the detected voltage generated by the detection voltage generation unit is input, and a voltage signal output unit connected to the comparator. A surge voltage detection device comprising: a comparator that compares the detected voltage input from the detection voltage generation unit with the voltage threshold and outputs a predetermined signal to the voltage signal output unit, and the voltage signal output unit that outputs a voltage signal based on the signal output from the comparator.

4. The surge voltage detection device according to claim 3, wherein an operational amplifier is interposed between the detection voltage generation unit and the surge voltage detection unit.

5. The surge voltage detection unit is composed of a positive-polarity surge detection unit and a negative-polarity surge detection unit connected to the detection voltage generation unit. The positive polarity surge detection unit comprises a first comparator to which a positive voltage threshold is set and the detected voltage generated by the detection voltage generation unit is input, and a first voltage signal output unit connected to the first comparator. The surge voltage detection device according to claim 3 or 4, wherein the negative polarity surge detection unit comprises a second comparator to which a negative voltage threshold is set and the detected voltage generated by the detection voltage generation unit is input, and a second voltage signal output unit connected to the second comparator.

6. The surge voltage detection device according to claim 5, comprising a plurality of sets of the positive surge detection unit and the negative surge detection unit, wherein the first comparator of the plurality of positive surge detection units in the plurality of sets is set to mutually different positive voltage thresholds, and the second comparator of the plurality of negative surge detection units in the plurality of sets is set to mutually different negative voltage thresholds.

7. The surge voltage detection device according to claim 1 or 3, wherein an electrostatic shield is provided on the side of the electric field detection unit opposite to the side facing the electric circuit.

8. The surge voltage detection device according to claim 1 or 3, wherein the circuit targeted for surge voltage detection is the primary side circuit of a lightning protection transformer.

Images