TW201944084A - Electric leakage detection apparatus and leakage breaker - Google Patents

Abstract

An electric leakage detection apparatus comprises a zero-phase-sequence current transformer (ZCT) (10), a clamping circuit (20), a voltage conversion circuit (30), a low-pass filter (40), and a leakage determination circuit (50). The clamping circuit (20) limits a voltage (Vz) between secondary side terminals (13, 14) of the ZCT (10) below a clamping voltage. The voltage conversion circuit (30) is connected in parallel with the clamping circuit (20), and converts an output current (Iz) from the ZCT (10) into a voltage (Vch). The leakage determination circuit (50) determines whether leakage occurs or not according to a voltage (Vin) output from the low-pass filter (40). The voltage conversion circuit (30) includes a voltage conversion element (31) converting the output current (Iz) from the ZCT (10) into the voltage (Vch), and a series circuit connected in series with a resistance adjustable element (32) adjusting the resistance of the voltage conversion circuit (30).

Description

   Leakage detection device and earth leakage circuit breaker   

The present invention relates to a leakage detection device and a leakage circuit breaker that determine that a leakage has occurred in a circuit.

Conventionally, earth leakage circuit breakers are provided with a zero phase current detector that detects the zero phase current of the circuit, a voltage conversion circuit that converts the secondary side current of the zero phase current to a voltage, and a high frequency of the converted voltage A low-pass filter that removes components, and a leakage determination circuit that determines whether a circuit is leaking based on a voltage output from the low-pass filter.

Regarding such an earth leakage circuit breaker, Patent Document 1 discloses that a clamping circuit is provided to limit the voltage between the terminals of the secondary side of the zero-phase inverter to below the clamping voltage so that the voltage does not exceed the voltage due to a lightning surge. In the case of a single short-term overcurrent caused by a wave or the like, the technology exceeds the withstand voltage of electronic components arranged on the secondary side of the zero phase current transformer.

    [Previous Technical Literature]         [Patent Literature]    

(Patent Document 1) Japanese Patent Laid-Open No. 2006-148990

However, in the above-mentioned prior art, since the clamp circuit and the low-pass filter are connected in parallel, the maximum value of the voltage input to the leakage determination circuit via the low-pass filter is specified by the clamp voltage of the clamp circuit. Since the clamping voltage is specified by the forward voltage of the diodes constituting the clamping circuit, the clamping voltage cannot be reduced to a value smaller than the forward voltage of the diodes. Therefore, even when a Schottky barrier diode with a low forward voltage is used, it is difficult to make the maximum value of the voltage input to the leakage determination circuit 100, for example, 100 [mV]. As described above, the aforementioned prior art has a problem that the maximum value of the voltage input to the leakage determination circuit cannot be adjusted independently of the clamping voltage, and it is difficult to reduce the maximum value of the voltage input to the leakage determination circuit.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to obtain a leakage detection device capable of adjusting a maximum value of a voltage input to a leakage determination circuit independently of a clamping voltage.

In order to solve the above-mentioned problems and achieve the purpose of the present invention, the leakage detection device of the present invention is provided with a zero-phase current transformer, a clamp circuit, a voltage conversion circuit, a low-pass filter, and a leakage determination circuit. The zero phase current transformer detects the zero-phase current flowing to the circuit. The clamp circuit limits the voltage between the secondary terminals of the zero-phase inverter to below the clamp voltage. The voltage conversion circuit is connected in parallel with the clamp circuit, and converts the output current of the zero-phase converter into a voltage. The low-pass filter removes the high-frequency components of the voltage converted by the voltage conversion circuit, and outputs the voltage after removing the high-frequency components. The leakage detection circuit determines whether the circuit is leaking based on the voltage output by the low-pass filter. The voltage conversion circuit is a series circuit including a voltage conversion element that converts the output current of the zero-phase inverter to a voltage and outputs the converted voltage to a low-pass filter, and a series connection with an impedance adjustment element that adjusts the impedance of the voltage conversion circuit.

According to the present invention, there is an effect that the maximum value of the voltage input to the leakage determination circuit can be adjusted independently of the clamping voltage.

1,1A‧‧‧Leakage circuit breaker

2‧‧‧circuit

3‧‧‧ opening and closing department

3 ₁ , 3 ₂ ‧‧‧ open and close contacts

4,4A‧‧‧Leakage detection department

5‧‧‧trip device

6 ₁ , 6 ₂ ‧‧‧ Power side connection terminal

7 ₁ , 7 ₂ ‧‧‧ load side connection terminal

8 ₁ , 8 ₂ ‧‧‧ conductor

10‧‧‧Zero Phase Comparator

11‧‧‧ Ring Core

12‧‧‧ secondary winding

13,14‧‧‧Secondary terminal

20‧‧‧Clamp circuit

21,22‧‧‧diodes

30,30A‧‧‧Voltage Conversion Circuit

31‧‧‧Voltage Conversion Element

32,32A‧‧‧Impedance adjusting element

40‧‧‧low-pass filter

50‧‧‧Leakage determination circuit

Iz‧‧‧Output current

Vch, Vin, Vz‧‧‧ Voltage

Vleak‧‧‧Leakage determination threshold

T2‧‧‧

T1‧‧‧ cycle

Sleak‧‧‧Leakage Detection Signal

Vclamp‧‧‧Clamping voltage

Fig. 1 is a diagram showing a configuration example of an earth leakage circuit breaker according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of the relationship among the clamping voltage, the leakage judgment threshold, the voltage between the secondary terminals, and the voltage converted by the voltage conversion circuit in the first embodiment.

Fig. 3 is a diagram for explaining the operation of the leakage detection unit in the first embodiment.

Fig. 4 is a diagram showing a configuration example of an earth leakage circuit breaker according to a second embodiment of the present invention.

Hereinafter, a leakage detection device and a leakage circuit breaker according to an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

    Embodiment 1.    

Fig. 1 is a diagram showing a configuration example of an earth leakage circuit breaker according to a first embodiment of the present invention. As shown in FIG. 1, the earth leakage circuit breaker 1 according to the first embodiment includes: an opening and closing unit 3 that opens and closes the circuit 2; an earth leakage detection unit 4 that detects a leakage current flowing to the circuit 2; and an earth leakage detection unit 4 When a leakage is detected, the trip device 5 of the opening / closing section 3 is controlled. The leakage detection unit 4 is an example of a leakage detection device.

The opening / closing section 3 has opening / closing contacts 3 ₁ , 3 ₂ for opening and closing the circuit ₂ . Each of the opening and closing contacts 3 ₁ and 3 ₂ has a fixed contact (not shown) and a movable contact (not shown). In the switching contacts _31, the fixed contact is in contact with the movable contact, causes the power supply side connector ₈₁ electrically connected to terminal ₇₁ through a conductor ₆₁ connected to a load side terminal. Further, the switching contacts ₃₂ contact the fixed contact and the movable contact, is connected to the power source side terminal ₆₂ and the load side connecting terminal ₇₂₈₂ is electrically connected through a conductor. Thereby, the current will flow to the circuit 2 and the earth leakage circuit breaker 1 is in an on state at this time.

Further, in each of the switching contacts _{31, 32,} the fixed contact and the movable contact spaced to open and close the contacts _{31, 32} is turned off, cutting off the connection terminals _{61, 62} and the power source side load Electrical connection of the side connection terminals 7 ₁ , 7 ₂ . Thereby, the current of the circuit 2 is cut off and the earth leakage circuit breaker 1 is in an off state at this time. In the example shown in FIG. 1, circuit 2 grounds one of the three phases, R phase, S phase, and T phase, which is not shown in the figure, but it may be R phase, S phase, and T phase. Are not grounded. In this case, the opening and closing section 3 is provided with three opening and closing contacts.

The leakage detection unit 4 is provided with a zero current transformer 10, a clamp circuit 20, a voltage conversion circuit 30, a low-pass filter 40, and a leakage determination circuit 50.

The zero-phase comparator 10 detects a zero-phase current flowing to the circuit 2. The zero-phase current transformer 10 includes a ring-shaped iron core 11 passed by or wound on the conductors 8 ₁ , 8 ₂ , and a secondary winding 12 wound on the ring-shaped iron core 11. At both ends of the secondary winding 12, secondary-side terminals 13 and 14 are provided. From the secondary-side terminals 13 and 14, a current Iz indicating a detection result of the zero-phase current by the zero phase current transformer 10 is output. Hereinafter, the current Iz may be referred to as an output current Iz.

The clamp circuit 20 is connected between the secondary-side terminals 13 and 14 of the zero-phase inverter 10, and the voltage Vz between the secondary-side terminals 13 and 14 is equal to or lower than the clamp voltage Vclamp. In the example shown in FIG. 1, the clamp circuit 20 includes two diodes 21 and 22 connected in antiparallel. Thereby, the voltage Vz between the secondary terminals 13 and 14 is suppressed to the forward voltage of the diodes 21 and 22 or less. In this way, the clamp circuit 20 operates with the forward voltage of the diodes 21 and 22 as the clamp voltage Vclamp.

The voltage conversion circuit 30 includes a voltage conversion element 31 that converts the output current Iz of the zero phase inverter 10 into a voltage Vch, and an impedance adjustment element 32 that adjusts the impedance Z of the voltage conversion circuit 30. The voltage conversion element 31 and the impedance adjustment element 32 are connected in series. The series circuit of the voltage conversion element 31 and the impedance adjustment element 32 is connected in parallel with the clamp circuit 20. The voltage conversion circuit 30 will be described later.

The low-pass filter 40 removes high-frequency components of the voltage Vch output from the voltage conversion circuit 30. The high-frequency component of the voltage Vch is a frequency component higher than the frequency of the leakage current to be detected by the leakage detection unit 4. The cut-off frequency of the low-pass filter 40 is set to a frequency higher than the frequency of the leakage current to avoid removing the frequency component of the leakage current.

The leakage detection circuit 50 determines whether there is a leakage in the circuit 2 based on the voltage Vin output from the low-pass filter 40. Specifically, the leakage determination circuit 50 compares the instantaneous value of the voltage Vin output from the low-pass filter 40 with the leakage determination threshold Vleak at a predetermined period T1. If the instantaneous value of the voltage Vin exceeds the leakage determination threshold Vleak for a preset period T2, it is determined that a leakage has occurred in the circuit 2 and the leakage detection signal Sleak at an active level is output to the trip.装置 5。 Device 5. The period T1 is, for example, 1 [ms], and the period T2 is, for example, 3 [ms].

When the leakage detection circuit 50 determines that a leakage has occurred in the circuit 2, it outputs a leakage detection signal Sleak at a valid level to the trip device 5. The effective level leakage detection signal Sleak is, for example, a High level signal.

When the trip device 5 receives the leakage detection signal Sleak at a valid level output from the leakage detection section 4, the fixed contact and the movable contact in the contact state of the opening and closing section 3 are separated, and the circuit 2 is turned off to cause The earth leakage breaker 1 is turned off. The opening-closing section 3 has an opening-closing mechanism (not shown) for moving the movable contact, and the tripping device 5 can separate the fixed contact and the movable contact in the contact state by acting on the opening-closing mechanism.

In addition, if the instantaneous value of the voltage Vin does not exceed the leakage determination threshold Vleak for more than a preset period T2, the leakage determination circuit 50 determines that no leakage has occurred in the circuit 2, and does not output a leakage detection signal Sleak at a valid level. To the trip device 5. In this case, the fixed contact and the movable contact of the opening / closing section 3 are maintained in a contact state, and the earth leakage circuit breaker 1 is maintained in a conducting state.

Next, the voltage conversion circuit 30 will be described in more detail. Hereinafter, for convenience of explanation, the “single-time short-term overcurrent caused by a lightning surge or the like” may be simply referred to as a “lightning surge current”. As described above, the voltage conversion circuit 30 includes, in addition to the voltage conversion element 31 that converts the output current Iz of the zero phase inverter 10 to a voltage Vch, an impedance adjustment element 32 that adjusts the impedance Z of the voltage conversion circuit 30.

The smaller the impedance Z of the voltage conversion circuit 30 is, the smaller the voltage generated between the secondary terminals 13 and 14 due to the lightning surge current is, and the smaller the ratio of being clamped by the clamp circuit 20 is. When the ratio of the clamped by the clamp circuit 20 becomes smaller, the possibility of malfunction of the earth leakage breaker 1 due to lightning surge current becomes higher.

Therefore, the earth leakage circuit breaker 1 uses the impedance adjustment element 32 to adjust the impedance Z of the voltage conversion circuit 30 so that the voltage generated between the secondary terminals 13 and 14 due to the lightning surge current is clamped by the clamp circuit 20.

Here, the impedance Z of the voltage conversion circuit 30 and the clamp voltage Vclamp of the clamp circuit 20 will be specifically described. The voltage conversion element 31 of the voltage conversion circuit 30 is a resistor having a resistance value Rf, and the impedance adjusting element 32 is a resistor having a resistance value Radj.

When the leakage detection unit 4 does not include the clamp circuit 20 and the impedance adjustment element 32, the voltage Vz between the secondary terminals 13 and 14 can be expressed by the following formula (1).

Vz = Iz × Rf ... (1)

In the case where the leakage detection unit 4 does not include the clamp circuit 20 but the impedance adjustment element 32, the voltage Vz between the secondary terminals 13 and 14 can be expressed by the following formula (2).

Vz = Iz × (Rf + Radj) ... (2)

The impedance of the secondary winding 12 of the zero-comparator 10 is smaller than that of the impedance Z of the voltage conversion circuit 30. Therefore, the magnitude of the output current Iz of the zero-to-inverter 10 does not substantially change even if the magnitude of the impedance Z of the voltage conversion circuit 30 changes.

Therefore, the impedance conversion element 32 is provided in the voltage conversion circuit 30, and a voltage that is (Rf + Radj) / Rf times can be generated between the secondary-side terminals 13, 14 compared with the case where the impedance adjustment element 32 is not provided. Therefore, the ratio of the components which are clamped by the clamp circuit 20 among the components generated on the secondary side of the zero phase current transformer 10 due to the components of the lightning surge current can be increased.

The impedance Z of the voltage conversion circuit 30 can be expressed by the following formula (3), and the voltage Vch output from the voltage conversion circuit 30 to the low-pass filter 40 can be expressed by the following formula (4).

Z = Rf + Radj ... (3)

Vch = Rf / (Rf + Radj) × Vz ... (4)

Therefore, by appropriately adjusting the resistance value Radj of the impedance adjustment element 32 and the resistance value Rf of the voltage conversion element 31, the voltage Vch output from the voltage conversion circuit 30 can be adjusted to an arbitrary value smaller than the clamping voltage Vclamp of the clamping circuit 20. value. For example, by setting the voltage Vch output to the low-pass filter 40 to 100 [mV] or less, the voltage Vin input to the leakage determination circuit 50 can be 100 [mV] or less. In this way, the leakage detection unit 4 can adjust the maximum value of the voltage Vin input to the leakage determination circuit 50 independently of the clamp voltage Vclamp.

However, if the impedance Z of the voltage conversion circuit 30 is too large, the voltage Vz generated between the secondary terminals 13, 14 due to the minimum leakage current to be detected by the leakage detection unit 4 becomes larger than the clamp voltage Vclamp. Therefore, the leakage determination circuit 50 cannot determine whether it is a leakage. Therefore, the condition for the upper limit value of the impedance Z of the voltage conversion circuit 30 to be satisfied is that the voltage Vz generated between the secondary terminals 13, 14 by the minimum leakage current to be detected by the leakage detection unit 4 must be clamped. Voltage below the bit voltage Vclamp.

Here, the peak value of the output current Iz of the secondary terminals 13 and 14 due to the minimum leakage current to be detected by the leakage detection unit 4 is denoted as Iz_trip, and the clamping voltage Vclamp must satisfy the following formula (5) . The so-called minimum leakage current refers to the lower limit value of the leakage current to be detected by the leakage detection section 4. When the leakage current flowing to the circuit 2 is above the minimum leakage current, the leakage detection section 4 Leakage detected.

Vclamp ≧ Iz_trip × (Rf + Radj) ... (5)

In addition, the leakage determination threshold value Vleak of the leakage determination circuit 50 must satisfy the following formula (6).

Vleak = Rf × Iz_trip ... (6)

Therefore, the resistance value Radj of the impedance adjustment element 32 can be expressed as the following formula (7).

Radj ≦ (Vclamp-Vleak) / Iz_trip ... (7)

The leakage determination circuit 50 determines whether the leakage occurs based on whether the instantaneous value of the voltage Vin is greater than or equal to the leakage determination threshold Vleak, so it does not matter to what extent the instantaneous value of the voltage Vin exceeds the leakage determination threshold Vleak. Therefore, the maximum value Radjmax of the resistance value Radj can be expressed as the following formula (8).

Radjmax = (Vclamp-Vleak) / Iz_trip ... (8)

Here, it is assumed that Vclamp = 1 [V], Vleak = 100 [mV], and Iz_trip = 200 [μA]. In this case, Radjmax = 4.5 [kΩ] can be calculated from the above formula (8). In addition, Rf = 0.5 [kΩ] can be calculated from the above formula (6).

FIG. 2 is a diagram showing an example of the relationship between the clamping voltage, the leakage judgment threshold, the voltage between the secondary terminals, and the voltage converted by the voltage conversion circuit in the first embodiment, and shows the judgment by the leakage judgment circuit 50 An example of a case where the leakage current having the minimum leakage current flows to the circuit 2.

In the example shown in FIG. 2, the peak value of the voltage Vz between the secondary terminals 13 and 14 is the same as the clamp voltage Vclamp. The peak value of the voltage Vch output from the voltage conversion circuit 30 is the same as the leakage determination threshold value Vleak. Since the cut-off frequency of the low-pass filter 40 is set higher than the frequency of the leakage current, the peak value of the voltage Vin output from the low-pass filter 40 is the same as the peak value of the voltage Vch output from the voltage conversion circuit 30.

Therefore, while the peak value of the voltage Vz between the secondary terminals 13, 14 is higher than the clamp voltage Vclamp, the peak value of the voltage Vin output from the low-pass filter 40 is the same as the leakage determination threshold value Vleak. Therefore, if the period in which the peak value of the voltage Vz between the secondary terminals 13 and 14 is higher than the clamp voltage Vclamp continues for the period T2 or more, the leakage determination circuit 50 determines that a leakage has occurred in the circuit 2.

The same applies when a lightning surge is applied to circuit 2. The peak value of the voltage Vz between the secondary terminals 13, 14 is the same as the clamp voltage Vclamp. The peak value of the voltage Vch output from the voltage conversion circuit 30 is equal to the leakage determination threshold. Vleak is the same. The voltage Vch output from the voltage conversion circuit 30 is input to the low-pass filter 40.

Since the cut-off frequency of the low-pass filter 40 is lower than the frequency of the lightning surge current, the low-pass filter 40 reduces the voltage component generated by the lightning surge current. Therefore, the peak value of the voltage Vin output from the low-pass filter 40 is lower than the peak value of the voltage Vch output from the voltage conversion circuit 30. Therefore, the leakage determination circuit 50 does not determine that a leakage has occurred in the circuit 2. Therefore, the leakage detection unit 4 can increase the ratio of the voltage component due to the lightning surge current to the voltage Vin, that is, the S / N ratio (Signal-to-Noise Ratio).

FIG. 3 is a diagram for explaining the operation of the leakage detection unit of the first embodiment, and shows an example when a lightning surge is applied to the circuit 2 in which a leakage current of a magnitude that the existing leakage determination circuit 50 does not determine is a leakage current. .

As shown in FIG. 3, when a lightning surge current is applied to the circuit 2 where the leakage current flows, a current obtained by superimposing the lightning surge component on the leakage current flows to the circuit 2. At this time, the output current Iz having the waveform shown in FIG. 3 is output from the zero-phase inverter 10.

A voltage is generated at both ends of the voltage conversion circuit 30 due to the output current Iz of the zero-phase converter 10, and a voltage exceeding the clamping voltage Vclamp of the clamping circuit 20 is clamped by the clamping circuit 20. Therefore, the voltage Vz between the secondary terminals 13, 14 will have a waveform as shown in FIG.

The voltage conversion circuit 30 outputs the voltage of the voltage conversion element 31 generated by the output current Iz, that is, the voltage Vch to the low-pass filter 40. The low-pass filter 40 removes high-frequency components of the voltage Vch output from the voltage conversion circuit 30, so the voltage Vin of the waveform shown in FIG. 3 is input from the low-pass filter 40 to the leakage determination circuit 50.

In the example shown in FIG. 3, since the voltage Vin output from the low-pass filter 40 is smaller than the leakage determination threshold value Vleak, the leakage determination circuit 50 does not determine that there is leakage. As described above, when a lightning surge current is applied to the circuit 2, the leakage determination circuit 50 does not determine that there is a leakage, and does not malfunction due to the lightning surge current of the circuit 2.

As described above, the leakage detection section 4 of the leakage circuit breaker 1 of the first embodiment includes the zero-phase current transformer 10, the clamp circuit 20, the voltage conversion circuit 30, the low-pass filter 40, and the leakage determination circuit 50. The zero phase comparator 10 detects a zero-phase current flowing to the circuit 2. The clamp circuit 20 limits the voltage Vz between the secondary terminals 13 and 14 of the zero phase comparator 10 to below the clamp voltage Vclamp. The voltage conversion circuit 30 is connected in parallel with the clamp circuit 20, and converts the output current Iz of the zero phase inverter 10 into a voltage Vch. The low-pass filter 40 removes high-frequency components of the voltage Vch converted by the voltage conversion circuit 30 and outputs a voltage Vin after removing high-frequency components from the voltage Vch. The leakage detection circuit 50 determines whether or not the circuit 2 has a leakage based on the voltage Vin output from the low-pass filter 40. The voltage conversion circuit 30 has a voltage conversion element 31 that converts the output current Iz of the zero phase comparator 10 into a voltage Vch, and outputs the converted voltage Vch to the low-pass filter 40, and an impedance that adjusts the impedance of the voltage conversion circuit 30. The series circuit of the adjusting element 32 is connected in series.

Therefore, the voltage Vin input to the leakage determination circuit 50 can be adjusted independently of the clamp voltage Vclamp of the clamp circuit 20. Therefore, even if the leakage determination threshold value Vleak of the leakage determination circuit 50 is lower than the clamp voltage Vclamp, for example, the leakage determination circuit 50 can be prevented from malfunctioning due to a single-time overcurrent such as a lightning surge current. For example, when the diodes 21 and 22 of the clamp circuit 20 are general diodes, the clamp voltage Vclamp is 0.7 to 1 [V]. When the diodes 21 and 22 are Schottky barrier diodes, the clamping voltage Vclamp is, for example, 0.3 [V]. Therefore, it is difficult to set the clamp voltage Vclamp to 100 [mV]. In the absence of the impedance adjustment element 32, the voltage Vin input to the leakage determination circuit 50 due to a lightning surge current exceeds 100 [mV]. At this time, if the leakage determination threshold value Vleak of the leakage determination circuit 50 is 100 [mV], the leakage determination circuit 50 incorrectly determines the lightning surge current as the leakage current. On the other hand, since the leakage detection unit 4 of the earth leakage circuit breaker 1 of the embodiment 1 has the impedance adjusting element 32, even if the value of the clamp voltage Vclamp is not adjusted, it can easily match the leakage determination threshold value Vleak of the leakage determination circuit 50. The maximum value of the voltage Vin input to the leakage determination circuit 50 is adjusted. Therefore, even when the leakage detection threshold Vleak is, for example, 100 [mV], the leakage detection unit 4 can prevent erroneous detection.

The impedance adjusting element 32 includes a resistor. Therefore, the voltage Vch output from the voltage conversion circuit 30 can be adjusted regardless of the frequency. Therefore, the voltage conversion circuit 30 can be adjusted regardless of the frequency.

The leakage determination circuit 50 determines that the circuit 2 is leaking when the instantaneous value of the voltage Vin output from the low-pass filter 40 is equal to or higher than the leakage determination threshold Vleak for a predetermined period T2 or more. Therefore, compared with the case where the circuit 2 determines that there is a leakage, for example, when the voltage Vin output from the low-pass filter 40 exceeds a positive threshold and exceeds a negative threshold, it is possible to detect that a leakage has occurred in the circuit 2 at high speed.

    Embodiment 2.    

The first embodiment is different from the first embodiment in that the impedance adjustment element is constituted by using a resistor, and the second embodiment is that the impedance adjustment element is constituted by using an inductor. Hereinafter, the constituent elements having the same functions as those of the first embodiment will be designated by the same reference numerals, and descriptions thereof will be omitted. Only the differences from the earth leakage circuit breaker 1 of the first embodiment will be described.

Fig. 4 is a diagram showing a configuration example of a leakage circuit breaker according to a second embodiment of the present invention. As shown in FIG. 4, the earth leakage circuit breaker 1A of the second embodiment is provided with an opening and closing section 3, a leakage detection section 4A, and a trip device 5. The leakage detection unit 4A is provided with a zero phase current transformer 10, a clamp circuit 20, a voltage conversion circuit 30A, a low-pass filter 40, and a leakage determination circuit 50.

The voltage conversion circuit 30A includes a voltage conversion element 31 and an impedance adjustment element 32A. The voltage conversion element 31 is a resistor having a resistance value Rf, and the impedance adjusting element 32A is an inductor having an inductance value L.

The impedance Z of the voltage conversion circuit 30A can be expressed by the following formula (10), and the voltage Vch output by the voltage conversion circuit 30A can be expressed by the following formula (11).

Therefore, by appropriately adjusting the inductance value L of the impedance adjustment element 32A and the resistance value Rf of the voltage conversion element 31, the voltage Vch output from the voltage conversion circuit 30A can be adjusted to be smaller than the clamping voltage Vclamp of the clamp circuit 20. Arbitrary value. For example, it can be set to a small value that enables the voltage Vin input to the leakage determination circuit 50 to be 100 mV or less.

In addition, the peak value of the output current Iz of the secondary terminals 13 and 14 due to the minimum leakage current to be detected by the leakage detection unit 4A is denoted as Iz_trip, and the clamping voltage Vclamp must satisfy the following formula (12).

The leakage determination threshold value Vleak of the leakage determination circuit 50 must satisfy the following formula (13).

Vleak ≧ Rf × Iz_trip ... (13)

Therefore, the inductance value L of the impedance adjustment element 32A can be expressed by the following formula (14).

The leakage detection circuit 50 determines whether there is a leakage based on whether the instantaneous value of the voltage Vin is equal to or higher than the leakage determination threshold Vleak, and therefore does not use a value exceeding the leakage determination threshold Vleak for processing. Therefore, the maximum value Lmax of the inductance value L can be expressed by the following formula (15).

Here, it is assumed that Vclamp = 1 [V], Iz_trip = 200 [μA], ω = 2πf, f = 50 [Hz], and Rf = 500 [Ω]. In this case, Lmax = 15.8 [H] can be calculated from the above formula (15).

The frequency of the lightning surge current is higher than the frequency of the leakage current. Therefore, "ω" in the above formula (15) can be set to a frequency higher than the frequency of the leakage current. For example, when the frequency of the lightning surge current is known, "ω" in the above formula (15) may be the frequency of the lightning surge current. For example, when the frequency of the lightning surge current is 100 [kHz], by setting ω = 100 [kHz] in the above formula (15), Lmax = 7.9 [mH] can be calculated. Therefore, the voltage Vin input to the leakage determination circuit 50 can be limited in the frequency range of the high-frequency component of the output current Iz and lower than the cut-off frequency of the low-pass filter 40, for example.

In the leakage detection section 4A of the leakage circuit breaker 1A of the second embodiment, the impedance adjustment element 32A includes an inductance. Therefore, compared with the impedance of the impedance adjustment element 32A when a leakage current flows to the circuit 2, the impedance of the impedance adjustment element 32A when a lightning surge current flows to the circuit 2 is larger. Therefore, when a lightning surge current flows to the circuit 2, the voltage Vin input to the leakage determination circuit 50 can be made significantly smaller than the leakage determination threshold Vleak, and it is possible to suppress the leakage determination circuit 50 from making erroneous determinations with good accuracy.

The capacitor elements may be connected in parallel or in series to the impedance adjusting elements 32 and 32A in the first and second embodiments. Thereby, when a high-frequency current such as a lightning surge current flows to the circuit 2, the voltage Vin input to the leakage determination circuit 50 can be made smaller than that when the leakage current flows to the circuit 2. In addition, the voltage conversion element 31 in the first embodiment is constituted by a resistor, but the voltage conversion element 31 may be constituted by an element in which a resistor and an inductor are connected in series. The adjustment of the impedance adjustment elements 32 and 32A is an example, and the adjustment of the impedance adjustment elements 32 and 32A is not limited to the above example.

The structure disclosed in the above embodiment shows an example of the content of the present invention. The present invention is not limited to this, and can be combined with other known technologies, and can be configured without departing from the gist of the present invention. Some omissions and changes. The earth leakage detection section 4, 4A can be used for equipment or devices other than earth leakage circuit breakers 1, 1A. For example, the leakage detection units 4, 4A can be used for a leakage monitoring device, a leakage relay (relay), and other measuring devices.

Claims (5)

    A leakage detection device comprising: a zero-phase current transformer that detects a zero-phase current flowing to a circuit; and a clamping circuit that limits a voltage between the secondary-side terminals of the zero-phase current transformer below a clamping voltage; The voltage conversion circuit is connected in parallel with the clamp circuit to convert the output current of the zero phase current transformer into a voltage; the low-pass filter removes the high frequency components of the voltage obtained by the voltage conversion circuit and outputs the foregoing A voltage after the high-frequency component is removed; and a leakage determination circuit that determines whether the circuit is leaking based on the voltage output from the low-pass filter; the voltage conversion circuit includes a series circuit that compares the output of the zero-to-zero converter A circuit in which a current is converted into the voltage and the converted voltage is output to a voltage conversion element of the low-pass filter and an impedance adjustment element that adjusts the impedance of the voltage conversion circuit.         The leakage detection device according to item 1 of the scope of patent application, wherein the impedance adjusting element includes a resistor.         The leakage detection device according to item 1 of the scope of patent application, wherein the impedance adjusting element includes an inductor.         The leakage detection device according to any one of claims 1 to 3, wherein the leakage determination circuit continues to reach a preset value in a state where the instantaneous value of the voltage output by the low-pass filter is above a threshold value. For the period above, it is judged that the aforementioned circuit has a leakage.         An earth leakage circuit breaker includes: the earth leakage detection device according to any one of claims 1 to 3; an opening and closing unit that opens and closes the circuit; and a trip device that determines that the circuit has In the case of leakage, the aforementioned opening / closing section shuts down the aforementioned circuit.