Lightning arrester operation detector and method

Abstract

Provided is a lightning arrester operation detector capable of exhibiting required withstand voltage performance without increasing a physical size. The lightning arrester operation detector according to an embodiment is provided with: a nonlinear resistance unit capable of generating an inter-terminal voltage of a prescribed voltage or less by receiving a discharge current of a lightning arrester; a protection resistor for limiting a current flowing by the inter-terminal voltage; a light emission unit for generating, on the basis of a current flowing through the protection resistor, an optical signal corresponding to said current; and a phototransistor unit for generating a pulse signal corresponding to the operation of the lightning arrester on the basis of the optical signal.

Description

Lightning arrester operation detector, method

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a lightning arrester operation detector and method for detecting the operation of a lightning arrester.

[0002] A lightning arrester is a type of equipment that protects substation equipment. Lightning arresters reduce overvoltages that occur in power systems due to lightning strikes, ground faults, switchgear operation, etc., and maintain the insulation of substation equipment. Lightning arresters are installed in various locations in power systems and contribute to the stable transmission of electricity.

[0003] Surge arresters may be equipped with a discharge frequency meter, which is a device that measures the number of times overvoltage occurs in a power system, etc. Operators of substation equipment (such as electric power companies) can know the operating status of the surge arrester from the measurement results of the discharge frequency meter.

[0004] The discharge frequency meter is connected directly between the earth terminal of the surge arrester and the ground. The discharge frequency meter detects the discharge current (hereinafter referred to as "discharge current") that flows through the surge arrester when an overvoltage occurs. The number of overvoltage occurrences serves as a guide for determining the overvoltage occurrence conditions in the surrounding area in the surge arrester's installation environment, estimating the short-circuit current flow path in the event of a short-circuit accident, and judging the surge arrester's lifespan. This information is important for operators of substation equipment.

[0005] The discharge frequency meter includes a lightning arrester operation detector that detects the discharge current of the lightning arrester. Conventional lightning arrester operation detectors have, for example, a parallel-connected capacitor, nonlinear resistor, and counter. That is, conventional lightning arrester operation detectors detect (count) the operation of the lightning arrester by charging the capacitor with the voltage drop caused by the discharge current flowing through the nonlinear resistor, and discharging the energy stored in the capacitor to the frequency meter.

[0006] Alternatively, conventional surge arrester operation detectors have a current transformer with a grounding wire passing through it, and the output of the current transformer is converted into a DC signal by a rectifier, and surge arrester operation is detected based on the DC signal.

[0007] Japanese Utility Model Publication No. 1-009106, Japanese Patent Application Laid-Open No. 63-190305

[0008] As described above, conventional surge arrester operation detectors use capacitors or current transformers to detect surge arrester operation. However, because capacitors and current transformers require a certain capacitance and voltage resistance to withstand the voltage generated by the discharge current, the surge arrester operation detectors are inevitably large in physical size.

[0009] An object of the embodiments of the present invention is to provide a lightning arrester operation detector and method that can exhibit required voltage resistance performance without increasing the physical size.

[0010] The lightning arrester operation detector of the embodiment includes a nonlinear resistance unit capable of generating a terminal-to-terminal voltage equal to or lower than a predetermined voltage upon receiving a discharge current from the lightning arrester, a protective resistor that limits the current that flows due to the terminal-to-terminal voltage, a light-emitting unit that generates an optical signal corresponding to the current based on the current flowing through the protective resistor, and a phototransistor unit that generates a pulse signal corresponding to the operation of the lightning arrester based on the optical signal.

[0011] Fig. 1 is a circuit diagram showing a configuration example of a lightning arrester operation detector of a first embodiment. Fig. 2 is a diagram explaining a limiting voltage of a zinc oxide element 10 of the lightning arrester operation detector of the first embodiment. Fig. 3 is a circuit diagram showing the configuration of a lightning arrester operation detector according to a comparative example. Fig. 4 is a circuit diagram showing a configuration example of a lightning arrester operation detector of a second embodiment. Fig. 5 is a circuit diagram showing a configuration example of a lightning arrester operation detector of a third embodiment.

[0012] (First embodiment) A lightning arrester operation detector according to an embodiment will be described in detail below with reference to the drawings. Fig. 1 is a circuit diagram showing an example of the configuration of a lightning arrester operation detector according to the first embodiment. Fig. 2 is a diagram illustrating the limiting voltage of a zinc oxide element 10 of the lightning arrester operation detector according to the first embodiment. As shown in Fig. 1, the lightning arrester operation detector 1 according to this embodiment includes a zinc oxide element 10, a photocoupler 20, a protective resistor R1, and a load resistor R2.

[0013] The zinc oxide element 10 (ZnO element) is a resistor (nonlinear resistance section) with nonlinear resistance characteristics. FIG. 2 shows the relationship between the terminal voltage V and the current I in the zinc oxide element 10. As shown in FIG. 2, the zinc oxide element 10 has a nonlinear current-voltage characteristic. That is, the zinc oxide element 10 has a high resistance value and almost no current I flows until the terminal voltage V reaches the clamping voltage Ea. On the other hand, once the terminal voltage V reaches the clamping voltage Ea, a large current I suddenly flows. That is, the zinc oxide element 10 receives the discharge current of the lightning arrester LA and generates a terminal voltage equal to or less than the clamping voltage Ea. Therefore, the zinc oxide element 10 can absorb surge voltages exceeding the clamping voltage Ea.

[0014] Although in this embodiment a zinc oxide element is used as the nonlinear resistance section, the present invention is not limited to this and any other element may be used as long as it is a nonlinear resistance element having a nonlinear current-voltage characteristic with a clamping voltage Ea.

[0015] The lightning arrester LA is a device that protects electric power equipment and the like from transient abnormally high voltages. That is, the lightning arrester LA is a device that is the detection target of the lightning arrester operation detector 1 of the embodiment. The lightning arrester LA has a function of protecting the protected equipment by bypassing the protected equipment when a surge current is received.

[0016] In the lightning arrester operation detector 1 of this embodiment, the ground terminal a of the lightning arrester LA is connected to one terminal of the zinc oxide element 10. The other terminal of the zinc oxide element 10 is connected to the ground GND. In other words, the surge voltage generated in the lightning arrester LA is applied to both terminals of the zinc oxide element 10.

[0017] The photocoupler 20 is an element that can transmit signals by internally converting electrical signals into light and then converting the light into electrical signals. As shown in Figure 1, the photocoupler 20 is configured by combining a light-emitting diode unit (light-emitting unit) having terminals D1 and D2 with a phototransistor unit having a terminal Qc corresponding to the collector and a terminal Qe corresponding to the emitter. That is, when a current flows through the terminals D1 and D2, a current is controlled to flow between the terminals Qc and Qe via an optical signal.

[0018] Terminal D1 of the light-emitting diode part of the photocoupler 20 is connected via a protective resistor R1 to the connection point between the ground terminal a of the lightning arrester LA and one terminal of the zinc oxide element 10. On the other hand, terminal D2 of the light-emitting diode part of the photocoupler 20 is connected to the connection point between the other terminal of the zinc oxide element 10 and ground GND. In other words, the voltage between the terminals of the zinc oxide element 10 is applied between terminals D1 and D2 via the protective resistor R1.

[0019] The light-emitting diode portion of the photocoupler 20 of the embodiment has a configuration in which two diode elements, each with its anode and cathode connected in reverse, are connected in parallel. In other words, the photocoupler 20 has the characteristic of not restricting the polarity of the input current that flows in.

[0020] The photocoupler 20 shown in Figure 1 is equipped with two diode elements with their anodes and cathodes connected in reverse parallel to support AC input, but this is not limited to this. A photocoupler equipped with a single unidirectional diode element that supports only DC input can also achieve the same function. In this case, terminal D1 can be the anode of the diode element, and terminal D2 can be the cathode of the diode element.

[0021] A terminal Qc corresponding to the collector of the phototransistor of the photocoupler 20 is connected to a DC voltage source VCC, and a terminal Qe corresponding to the emitter is connected to ground GND via a load resistor R2. A detection output out is connected to the connection point of terminal Qe and the load resistor R2. That is, when the transistor of the photocoupler 20 is turned on, a voltage corresponding to the voltage drop across the load resistor R2 is output to the detection output out.

[0022] Although the lightning arrester operation detector 1 of this embodiment uses a photocoupler 20 to detect the operation of the lightning arrester LA, this is not limited to this. That is, as long as there is a light-emitting diode unit that converts the voltage between the terminals of the zinc oxide element 10 serving as a nonlinear resistance element into an optical signal and a phototransistor unit that is driven by the converted optical signal, the detector does not need to be a single photocoupler. That is, the detector may be realized by other components as long as it can convert the detection of the operation of the lightning arrester LA into a signal of another medium, such as light, and obtain a pulse signal or the like from the converted signal of another medium. This configuration allows the circuit portion to which the surge voltage is applied to be safely separated from the circuit portion that outputs the pulse signal.

[0023] The protective resistor R1 is a resistor that protects the light-emitting diode portion of the photocoupler 20. Since the voltage across the zinc oxide element 10 generally rises up to a limiting voltage Ea at which a large current I starts to flow, the resistance value of the protective resistor R1 is set to a resistance value that limits the current that flows due to the voltage across the zinc oxide element 10 to a level that does not destroy the light-emitting diode portion of the photocoupler 20. One terminal of the protective resistor R1 is connected to the connection point between the ground terminal of the lightning arrester LA and one terminal of the zinc oxide element 10. The other terminal of the protective resistor R1 is connected to terminal D1 of the light-emitting diode portion of the photocoupler 20 (the anode terminal if the light-emitting diode portion is a unipolar diode element).

[0024] The load resistor R2 is a resistor that generates a voltage at the output out of the photocoupler 20. One terminal of the load resistor R2 is connected to the terminal Qe of the phototransistor part of the photocoupler 20, and the other terminal is connected to the ground GND.

[0025] As shown in Figure 1, the lightning arrester operation detector 1 of this embodiment comprises a zinc oxide element 10, a protective resistor R1 connected in series, and a photocoupler 20 connected in parallel. One terminal of the zinc oxide element 10 is connected to the ground terminal a of the lightning arrester LA, and the other terminal is connected to ground GND. The photocoupler 20 electrically insulates the circuit of the lightning arrester LA to which the discharge voltage is applied from the circuit of the detection output (out) that outputs a pulse signal. A DC voltage source is connected to the collector of the phototransistor part of the photocoupler 20, and the output (out) and one end of a load resistor R2 are connected to the emitter. The other end of the load resistor R2 is connected to ground GND.

[0026] (Operation of First Embodiment) Next, the operation of the lightning arrester operation detector 1 of this embodiment will be described.

[0027] When the lightning arrester LA operates and a discharge current is generated, the discharge current flows through the zinc oxide element 10. The terminal voltage generated between both terminals of the zinc oxide element 10 is determined by, for example, the current-voltage characteristics of the zinc oxide element 10 shown in Figure 2. If the terminal voltage of the zinc oxide element 10 is less than the limit voltage, the zinc oxide element 10 exhibits a high resistance value, and the terminal voltage of the zinc oxide element 10 is applied to the protective resistor R1 and the light-emitting diode element of the photocoupler 20.

[0028] When the voltage applied to the zinc oxide element 10 reaches the limiting voltage, the zinc oxide element 10 suddenly starts to pass a large current. That is, the voltage between the terminals of the zinc oxide element 10 generates a pulse signal with the limiting voltage as its upper limit.

[0029] When a voltage between the terminals of the zinc oxide element 10 is applied to one end of the protective resistor R1, a current flows to ground GND via the protective resistor R1 and the light-emitting diode portion of the photocoupler 20. The maximum current that flows at this time is determined by the clamping voltage Ea and the protective resistor R1. When this current exceeds the operation start threshold of the photocoupler 20, the phototransistor portion of the photocoupler 20 enters an operating state (ON). In other words, the phototransistor portion of the photocoupler 20 can be controlled by a pulse signal of the voltage between the terminals of the zinc oxide element 10.

[0030] When the phototransistor unit of the photocoupler 20 is turned on, a current flows through the load resistor R2 connected to the terminal Qe (emitter side of the transistor) of the phototransistor unit of the photocoupler 20. As a result, a voltage drop across the load resistor R2 causes a positive logic voltage pulse signal to be output at the output (out). This pulse signal corresponds to the pulse signal of the voltage across the zinc oxide element 10. That is, the photocoupler 20 outputs a pulse signal corresponding to the operation of the lightning arrester LA based on the current flowing from the protective resistor R1 to the light-emitting diode unit of the photocoupler 20. The phototransistor unit of the photocoupler 20 controls the output of the pulse signal. The light-emitting diode unit of the photocoupler 20 drives the phototransistor unit of the photocoupler 20 based on the current flowing from the protective resistor R1. By counting this pulse signal, it is possible to measure the number of times the lightning arrester LA has operated.

[0031] The output duration of the pulse signal appearing at the output Out is roughly linked to the duration of the clamping voltage of the zinc oxide element 10. When a standard lightning impulse current flows, its duration is approximately several tens of μs.

[0032] In this way, in the lightning arrester operation detector of this embodiment, the zinc oxide element 10 passes a discharge current and at the same time converts the current into a voltage signal, and the photocoupler 20 transmits (outputs) a pulse signal based on the voltage signal.

[0033] Here, a comparison between the lightning arrester operation detector according to the comparative example shown in FIG. 3 and the lightning arrester operation detector according to the embodiment will be described.

[0034] Fig. 3 is a circuit diagram showing the configuration of a lightning arrester operation detector according to a comparative example. The lightning arrester operation detector 5 shown in Fig. 3 has a configuration in which a zinc oxide element 10, a capacitor C, and a relay RY1 are connected in parallel. One terminal of the zinc oxide element 10 is connected to the ground terminal of the lightning arrester LA, and the other terminal is connected to ground GND.

[0035] Next, the operation of the lightning arrester operation detector 5 according to the comparative example will be described. When the lightning arrester LA operates and a discharge current is generated, the discharge current flows through the zinc oxide element 10. The terminal voltage generated between both terminals of the zinc oxide element 10 is determined by the current-voltage characteristics of the zinc oxide element 10 shown in Figure 2, for example. When the terminal voltage of the zinc oxide element 10 is less than the limit voltage, the zinc oxide element 10 exhibits a high resistance value, and therefore the capacitor C is charged by the terminal voltage of the zinc oxide element 10.

[0036] When the voltage applied to the zinc oxide element 10 reaches the limit voltage, the zinc oxide element 10 suddenly starts to pass a large current. The capacitor C drives the relay RY1 with the voltage that has been charged up to that point. As a result, the relay output RY1out provides a driving output.

[0037] The lightning arrester operation detector 5 of the comparative example provides a drive output for the relay RY1, which is driven by the charging voltage of the capacitor C. Therefore, the capacitance value of the capacitor C that drives the relay RY1 is important. That is, the important factors for the capacitor C are the voltage resistance that can withstand the limiting voltage of the zinc oxide element 10 and the capacity that can drive the relay RY1. The capacitor C that satisfies these requirements must be of a considerable size.

[0038] On the other hand, the lightning arrester operation detector 1 of the embodiment does not use the charging voltage of the capacitor, but controls the output of the photocoupler 20 based on the limiting voltage of the zinc oxide element 10. In other words, it is possible to detect the operation of the lightning arrester with sufficient sensitivity without requiring components such as a large capacitor or a relay with a driving mechanism.

[0039] As described above, according to the lightning arrester operation detector 1 of this embodiment, no capacitor, current transformer, or relay is required to detect the operation of the lightning arrester, so the volume required for operation detection can be reduced.

[0040] Furthermore, since the discharge current when a standard lightning impulse enters is generally several tens of kA, it is necessary to take measures against overvoltage that can cope with the discharge current flowing through the circuit elements connected in series to the ground line. In the comparative example, for example, it is necessary to take measures against the withstand voltage of the capacitor C.

[0041] However, the lightning arrester operation detector 1 of the embodiment utilizes the current compression characteristics that limit the voltage generated across the zinc oxide element to approximately several tens to several hundreds of volts, so there is no need to add any special components for overvoltage protection, which contributes to reducing the required volume.

[0042] Second Embodiment Next, a lightning arrester operation detector of a second embodiment will be described in detail. Fig. 4 is a circuit diagram showing an example of the configuration of a lightning arrester operation detector 2 of the second embodiment. The lightning arrester operation detector 2 of the second embodiment is obtained by modifying the output circuit of the photocoupler 20 in the lightning arrester operation detector 1 of the first embodiment. In the following description, elements common to the first embodiment are designated by the same reference numerals, and duplicated description will be omitted.

[0043] 4, the lightning arrester operation detector 2 of this embodiment includes, instead of the load resistor R2 of the first embodiment, a load resistor R3 having one terminal connected to the terminal Qc of the phototransistor part of the photocoupler 20 and the other terminal connected to the DC voltage source VCC. The terminal Qe of the phototransistor part of the photocoupler 20 is directly connected to ground GND.

[0044] Furthermore, the lightning arrester operation detector 2 of the second embodiment includes a monostable multivibrator 30 whose input terminal is connected to the terminal Qc of the phototransistor part of the photocoupler 20, instead of the output terminal Out of the first embodiment. The output terminal of the monostable multivibrator 30 is connected to the base of the transistor Q1 via a load resistor R4. The collector and emitter of the transistor Q1 are connected to the input terminals of the digital counter 40.

[0045] The monostable multivibrator 30 is an electronic circuit that implements two states, one of which is stable and the other of which is unstable. For example, when a voltage signal is input, the monostable multivibrator 30 has the function of outputting a voltage signal of a certain duration. In other words, it has the function of expanding the duration of the input pulse signal. The monostable multivibrator 30 also has the function of preventing chattering.

[0046] The digital counter 40 is an electronic circuit that counts the number of input pulse signals.

[0047] As shown in Figure 4, the lightning arrester operation detector 2 of this embodiment outputs a pulse signal from terminal Qc of the phototransistor unit of photocoupler 20. When the phototransistor unit of photocoupler 20 is in the off state, terminal Qc is at the potential of the DC voltage source VCC, and when it is in the on state, terminal Qc is at ground potential. That is, the operation of lightning arrester LA is transmitted to terminal Qc as a negative logic pulse signal. The negative logic pulse signal appearing at terminal Qc is input to the input terminal of monostable multivibrator 30.

[0048] The monostable multivibrator 30 extends the pulse duration of the input negative logic pulse signal, which serves to reduce the error in counting the pulse signal by the digital counter 40.

[0049] The pulse signal (stretched pulse signal) output from the monostable multivibrator 30 is amplified in amplitude by the load resistor R4 and the transistor Q1 and input to the input terminal of the digital counter 40.

[0050] In the lightning arrester operation detector 2 of this embodiment, the monostable multivibrator 30 generates an expanded pulse signal by expanding the pulse width of the output pulse signal of the photocoupler 20, and the transistor Q1 amplifies the amplitude of the expanded pulse signal, and the digital counter 40 counts the number of pulses from this expanded pulse signal. As a result, even when using a digital counter 40 that requires a duration of about milliseconds to operate, for example, it is possible to reliably detect the operation of the lightning arrester LA.

[0051] Third Embodiment Next, a lightning arrester operation detector according to a third embodiment will be described in detail. Fig. 5 is a circuit diagram showing an example of the configuration of a lightning arrester operation detector 3 according to the third embodiment. In the lightning arrester operation detector 3 according to the third embodiment, the output of the transistor Q1 in the lightning arrester operation detector 2 according to the second embodiment is changed from the digital counter 40 to a relay RY2. In the following description, elements common to those in the second embodiment are designated by the same reference numerals, and duplicated description will be omitted.

[0052] As shown in Figure 5, in the lightning arrester operation detector 3 of this embodiment, the collector of the transistor Q1 of the second embodiment is connected to one input terminal Ri1 of a relay RY2, and the other input terminal Ri2 of the relay RY2 is connected to one terminal of a load resistor R5. The other terminal of the load resistor R5 is connected to a DC voltage source VCC. When current flows through its input terminals Ri1 and Ri2, the relay RY2 turns on the relay output RY2out. The emitter of the transistor Q1 is directly connected to ground GND.

[0053] As shown in Figure 5, the lightning arrester operation detector 3 of this embodiment outputs a pulse signal from terminal Qc of the phototransistor unit of photocoupler 20. When the phototransistor unit of photocoupler 20 is in the OFF state, terminal Qc is at the potential of DC voltage source VCC, and when it is in the ON state, terminal Qc is at ground potential. That is, the operation of lightning arrester LA is indicated by a negative logic pulse signal output to terminal Qc. The negative logic pulse signal appearing at terminal Qc is input to the input terminal of monostable multivibrator 30.

[0054] The monostable multivibrator 30 extends the pulse duration of the negative logic pulse signal that is input to it. The pulse signal (extended pulse signal) output from the monostable multivibrator 30 is input to the load resistor R4 and the base of the transistor Q1.

[0055] The negative logic stretched pulse signal input to the base of transistor Q1 drives transistor Q1 to control the on / off of relay RY2. That is, when the potential of the stretched pulse signal input to the base of transistor Q1 is a logical value "1" (or a logical value "H"), transistor Q1 is turned on and relay RY2 is turned on. On the other hand, when the potential of the stretched pulse signal input to the base of transistor Q1 is a logical value "0" (or a logical value "L"), transistor Q1 is turned off and relay RY2 is turned off. Relay RY2 provides an open / close output from relay output RY2out in accordance with the current flowing through input terminals Ri1 and Ri2.

[0056] According to the lightning arrester operation detector 3 of this embodiment, the relay RY2 is driven by the detection output of the operation of the lightning arrester LA, so that any device can be notified of the operation of the lightning arrester LA. Furthermore, according to the lightning arrester operation detector 3 of this embodiment, the relay RY2 that provides the output is driven by the DC voltage source VCC, so that a relay device that is smaller in size than the relay RY1 of the comparative example that is driven by the capacitor C charged by the discharge current can be used.

[0057] Although several embodiments of the present invention have been described, they are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0058] 1 to 3, 5...Lightning arrester operation detector 10...Zinc oxide element 20...Photocoupler 30...Monostable multivibrator 40...Digital counter C...Capacitor D1, D2...Terminal GND...Ground LA...Lightning arrester Out...Output terminal Q1...Transistor R1...Protective resistor R2 to R5...Load resistors Ri1, Ri2...Input terminals RY1, RY2...Relay RY1out, RY2out...Relay output VCC...DC voltage source out...Output

Claims

1. A lightning arrester operation detector comprising: a nonlinear resistance unit capable of generating a terminal voltage equal to or lower than a predetermined voltage upon receiving a discharge current from a lightning arrester; a protective resistor that limits the current that flows due to the terminal voltage; a light emitting unit that generates an optical signal corresponding to the current flowing through the protective resistor based on the current; and a phototransistor unit that generates a pulse signal corresponding to the operation of the lightning arrester based on the optical signal.

2. The lightning arrester operation detector according to claim 1, further comprising a photocoupler having said light emitting diode section and said phototransistor section.

3. The surge arrester operation detector according to claim 1, wherein the nonlinear resistance section has a zinc oxide element with the predetermined voltage as a limit voltage.

4. The lightning arrester operation detector according to claim 1, wherein said light emitting section has a plurality of light emitting diode elements connected in parallel with opposite polarities.

5. The lightning arrester operation detector according to claim 1, further comprising a load resistor for generating a pulse voltage based on said pulse signal.

6. The lightning arrester operation detector according to claim 1, further comprising: a monostable multivibrator that outputs an expanded pulse signal in which the pulse width of the pulse signal is expanded based on the pulse signal; and a digital counter that counts the number of pulses of the expanded pulse signal output from the monostable multivibrator.

7. The lightning arrester operation detector according to claim 1, further comprising: a monostable multivibrator that outputs an expanded pulse signal in which the pulse width of the pulse signal is expanded based on the pulse signal; and a relay that is driven based on the expanded pulse signal output from the monostable multivibrator.

8. A method for detecting the operation of a lightning arrester, comprising: receiving the discharge current of the lightning arrester through a non-linear resistor capable of generating a voltage between its terminals equal to or less than a predetermined voltage; limiting the current generated by the voltage between its terminals through a protective resistor; generating an optical signal corresponding to the current flowing through the protective resistor through a light-emitting diode; and generating a pulse signal corresponding to the operation of the lightning arrester through a phototransistor based on the optical signal.

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