Leak current breaker and method

A leak current breaker is provided which includes a detector (10) to detect a leakage current from electric lines, a first removing unit (12) to convert the detected leakage current into a voltage and a voltage detector (14) to detect a voltage developed in electric lines A under testing, a second removing unit (16) to remove a harmonic component included in the voltage, a phase contrast detector (20) to detect a phase contrast from a signal waveform having the harmonic component removed, a frequency calculator (21) to calculate a frequency occurring on electric lines A on the basis of the signal waveform of the voltage having the harmonic component removed by the second removing unit (16), a phase angle calculator (22) to calculate a phase angle of the leakage current flowing through the electric lines A on the basis of the phase contrast and frequency, a root-mean-square value calculator (24) to calculate a root-mean-square value of the voltage having the harmonic component removed by the first removing unit (12), a calculator (27) to calculate a leakage current component Igr arising from an earth insulation resistance included in the leakage current flowing through the electric lines A on the basis of the root-mean-square value and phase angle of the leakage current, a judging unit (29) to judge whether the leakage current component Igr calculated by the calculator (27) has exceeded an arbitrary value, and a circuit breaker (30) to break the electric lines A on the basis of the judgment made by the judging unit (29).

TECHNICAL FIELD

The present invention relates to a leak current breaker and method for detecting a leakage current from an electric circuit under testing to interrupt the leakage current.

BACKGROUND ART

Everyday life is carried on without much awareness of electricity. Since electricity is widely used as a source of energy in various fields, such as information processing, communication, and the like, it is indispensable in modern life.

Since electrical energy is important and useful, any failure in appropriate management and use thereof will possibly result in accidents such as short circuit-caused fires, electrocution, etc.

For example, a leakage current that will possibly cause such a serious accident is deeply linked with poor insulation of a circuit or device through which an electric current flows. However, checking for a leakage current takes a very long time and needs a momentary interruption of the power supply, and the numerical value of electric current corresponding to poor insulation has to be measured by an insulation resistance tester.

These days computers are used widely in society. In intelligent buildings and factory automation (FA), computer systems are continuously running day and night. Such computer systems should be checked for any leakage current while continuing to operate, that is, without being turned off even for a very short time.

Therefore, the present highly sophisticated information society requires maintenance of an uninterruptible power supply system. On this account, the insulation management of circuits and devices, through which an electric current flows, has been shifted from the conventional method of checking for a leakage current by the insulation resistance tester with power interruption, to a leakage current measurement which can be done with no power interruption. For this insulation management, there has been proposed a variety of methods of keeping power supply during measurement of a leakage current by a leak current breaker, earth leakage fire alarm or the like (as in Japanese Unexamined Patent Application Publication No. 2001-215247 and 2002-98729).

Note here that the leakage currents (I) include a leakage current (Igc) caused by earth capacitance and leakage current (Igr) caused by an earth insulation resistance involved directly with an insulation resistance. Since the above-mentioned short circuit-caused fire arises from insulation resistance, if the leakage current (Igr) alone, that arises from the insulation resistance, can accurately be detected in a circuit, it is possible to check the insulation state of the circuit and thus prevent a catastrophe such as a short circuit-caused fire or the like.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In many factories, however, electrical devices are connected to each other by long electric lines. This large length of the electric lines will add to the earth capacitance, and thus the leakage current (Igc) arising from the earth capacitance will be correspondingly large.

Also, each of such electric devices has installed therein an inverter in which a power semiconductor device is applied. Since the inverter is used as a high-speed switch, a harmonic distortion current will inevitably occur as a sine-wave signal whose frequency is an integral multiple of 50 or 60 Hz which is the fundamental frequency of commercial power supplies. Since the harmonic distortion current contains a high frequency component, it will flow to the electric lines through the earth capacitance naturally distributed along the electric lines and increase the value of the leakage current (I).

Therefore, the leakage current (Igr) arising from the earth insulation resistance involved directly with the quality of the insulation will be adversely affected by the harmonic distortion current caused by the length of the electric lines, inverter, etc. and will thus become difficult to accurately detect.

Also, in electronic devices in which parts are installed with a high density, such as telephone, facsimile, printer, copier, etc., when leakage current is measured by the insulation resistance tester or the like to locate poor insulation, the electronic circuits will possibly be influenced by a test voltage which is applied. Therefore, since it is likely that such electronic devices will functionally be damaged, many of them cannot be tested for insulation resistance.

It is therefore desirable to overcome the above-mentioned drawbacks of the related art by providing a leak current breaker and method, for measuring a leakage current flowing through electric lines, mechanical facility or the like, and detecting only a leakage current (Igr) arising from an earth insulation resistance involved directly with the quality of an insulation, simply and safety, from outside without having to break the electric lines, mechanical facility or the like during detection of the leakage current, without any functional damage of devices connected to the electric lines under testing, and with interrupting only the electric lines under testing on the basis of the detected leakage current.

Means for Solving the Problems

According to the present invention, there is provided a leak current breaker including, according to the present invention, a leakage current detecting means for detecting a leakage current flowing through electric lines under testing, a converting means for converting the leakage current detected by the leakage current detecting means into a voltage, an amplifying means for amplifying the voltage output from the converting means, a first harmonic component removing means for removing a harmonic component from the voltage amplified by the amplifying means, a voltage detecting means for detecting a voltage developed on the electric lines under testing, a second harmonic component removing means for removing a harmonic component from the voltage detected by the voltage detecting means, a phase contrast detecting means for detecting a contrast in signal waveform between the voltage from which the harmonic component has been removed by the first harmonic component removing means and the voltage from which the harmonic component has been removed by the second harmonic component removing means, a frequency calculating means for calculating a frequency occurring on a voltage line on which the voltage has been detected by the voltage detecting means on the basis of the signal waveform of the voltage having the harmonic component removed by the second harmonic component removing means, a phase angle calculating means for calculating a phase angle of the leakage current flowing through the electric lines under testing on the basis of the phase contrast detected by the phase contrast detecting means and frequency calculated by the frequency calculating means, a root-mean-square value calculating means for calculating a root-mean-square value of the voltage having the harmonic component removed by the first harmonic component removing means, an earth insulation resistance-caused leakage current component calculating means for calculating a leakage current component arising from an earth insulation resistance included in the leakage current flowing through the electric lines under testing on the basis of the root-mean-square value calculated by the root-mean-square value calculating means and phase angle of the leakage current flowing through the electric lines under testing, calculated by the phase angle calculating means, a judging means for judging whether the leakage current component arising from the earth insulation resistance included in the leakage current flowing through the electric lines under testing and calculated by the earth insulation resistance-caused leakage current component calculating means has exceeded an arbitrary value, and a circuit breaking means for breaking the electric lines under testing on the basis of the judgment made by the judging means.

According to the present invention, there is also provided a leakage current interruption method including, according to the present invention, a leakage current detecting step of detecting a leakage current flowing through electric lines under testing, a converting step of converting the leakage current detected in the leakage current detecting step into a voltage, an amplifying step of amplifying the voltage output from the converting step, a first harmonic component removing step of removing a harmonic component from the voltage amplified in the amplifying step, a voltage detecting step of detecting a voltage developed on the electric lines under testing, a second harmonic component step of removing a harmonic component from the voltage detected in the voltage detecting step, a phase-contrast detecting step of detecting a contrast in signal waveform between the voltage from which the harmonic component has been removed in the first harmonic component removing step and the voltage from which the harmonic component has been removed in the second harmonic component removing step, a frequency calculating step of calculating a power frequency occurring on a voltage line on which the voltage has been detected in the voltage detecting step on the basis of the signal waveform of the voltage having the harmonic component removed in the second harmonic component removing step, a phase angle calculating step of calculating a phase angle of the leakage current flowing through the electric lines under testing on the basis of the phase contrast detected in the phase contrast detecting step and power frequency calculated in the frequency calculating step, a root-mean-square value calculating step of calculating a root-mean-square value of the voltage having the harmonic component removed in the first harmonic component removing step, an earth insulation resistance-caused leakage current component calculating step of calculating a leakage current component arising from an earth insulation resistance included in the leakage current flowing through the electric lines under testing on the basis of the root-mean-square value calculated in the root-mean-square value calculating step and phase angle of the leakage current flowing through the electric lines under testing, calculated in the phase angle calculating step, a judging step of judging whether the leakage current component arising from the earth insulation resistance included in the leakage current flowing through the electric lines under testing and calculated in the earth insulation resistance-caused leakage current component calculating step has exceeded an arbitrary value, and a breaking step of breaking the electric lines under testing on the basis of the judgment made in the judging step.

These objects and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the best mode for carrying out the present invention when taken in conjunction with the accompanying drawings.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below with respect to a leakage current interrupter as an embodiment thereof with reference to the accompanying drawings.

As shown inFIG. 1, the leakage current interrupter, generally indicated with a reference numeral1, includes a current transformer type sensor (will be referred to as “CT sensor” hereunder)10clamped to the entire electric lines A under testing to detect a leakage current I flowing through the electric lines A, an amplifier11to convert the leakage current I detected by the CT sensor10into a voltage and amplify the voltage V1resulting from the conversion (will be referred to as “converted voltage” hereunder), a low-pass filter12(will be referred to as “LPF” hereunder) to remove a harmonic component from the converted voltage V1after amplification, a full-wave rectifier13to rectify the converted voltage V1having the harmonic component removed by the LPF12, a voltage detector14to detect a voltage V2from a voltage line included in the electric lines A, a transformer15to change the voltage V2detected by the voltage detector14to a predetermined transformation ratio, a low-pass filter (will be referred to as “LPF” hereunder)16to remove a harmonic component from the voltage V2changed by the transformer15to have a predetermined value, a full-wave rectifier17to rectify the voltage V2from which the harmonic component has been removed by the LPF16, a comparator18to make a comparison between a signal waveform S1of the converted voltage V1having the harmonic component removed by the LPF12and a signal waveform S2of the voltage V2having the harmonic component removed by the LPF16, a calculator19to make a predetermined calculation on the basis of the result of comparison from the comparator18, a phase pulse width measuring unit20to measure the phase pulse width on the basis of the result of calculation from the calculator19, a power frequency measuring unit21to measure a power frequency occurring on the voltage line included in the electric lines A from a signal indicative of the voltage V2having the harmonic component removed by the LPF16, a phase angle calculator22to calculate the phase angle of the leakage current I flowing through the electric lines A from the phase pulse width measured by the phase pulse width measuring unit20and power frequency measured by the power frequency measuring unit21, an A-D converter23to convert the converted voltage V1rectified by the full-wave rectifier13into a digital signal, a root-mean-square value calculator24to calculate the root-mean-square value of the converted voltage V1converted by the A-D converter23into the digital signal, an A-D converter25to convert the voltage V2rectified by the full-wave rectifier17into a digital signal, a root-mean-square value calculator26to calculate the root-mean-square value of the voltage V2converted by the A-D converter25into the digital signal, a leakage current calculator27to calculate a leakage current Igr arising from an earth insulation resistance from the phase angle of the leakage current I calculated by the phase angle calculator22and root-mean-square value of the converted voltage V1calculated by the root-mean-square value calculator24, a resistance calculator28to calculate the value of the earth insulation resistance from the leakage current I calculated by the leakage current calculator27and root-mean-square value of the voltage V2calculated by the root-mean-square value calculator26, a judging unit29to judge whether the leakage current Igr calculated by the leakage current calculator27has exceeded an arbitrary value, a circuit breaker30to break the electric lines A on the basis of the result of judgment from the judging unit29, and a communication unit33to make communications with an external device. Similar to the conventional earth leakage breaker, the circuit breaker30has a breaking speed of approximately 2 cycles (0.04 sec with a power frequency of 50 Hz) to 5 cycles (0.1 sec with a power frequency of 50 Hz). Also, it should be noted that in the leakage current interrupter1according to the present invention, a block indicated with a letter B inFIG. 1is made as a chip to detect a root-mean-square value I0in the conventional leakage current breaker.

The above CT sensor10detects magnetism arising from a leakage current component flowing through the electric lines A under testing and produces a current from the detected magnetism. The CT sensor10supplies the amplifier11with the current thus produced as a leakage current I. It should be noted that the leakage current I produced by the CT sensor10comprises a leakage current Igc arising from an earth capacitance, and a leakage current Igr arising from an earth insulation resistance involved directly with an insulation resistance. It should also be noted that the leakage current Igc will increase corresponding to the length of the electric lines A and will also be increased due to a harmonic distortion current arising from an inverter, noise filter and the like, included in an electric device.

The amplifier11converts the leakage current I supplied from the CT sensor10into a voltage and amplifies the converted voltage V1up to a predetermined level. Also, in cases where the leakage current I supplied from the CT sensor10is 0 to 10 mA, the amplifier11amplifies the converted voltage V1in two steps. In cases where the leakage current I supplied from the CT sensor10is 10 to 300 mA, the amplifier11amplifies the converted voltage V1in a single step. The amplifier11supplies the converted voltage V1after amplification to the LPF12. The LPF12removes (filters out) a harmonic component from the converted voltage V1. The LPF12supplies the converted voltage V1having the harmonic component thus removed, to the full-wave rectifier13and comparator18. The full-wave rectifier13rectifies the supplied converted voltage V1, and supplies the converted voltage V1thus rectified to the A-D converter23.

The voltage detector14has a voltage probe thereof connected to the electric lines A under testing to detect a voltage developed on a voltage line included in the electric lines A. It should be noted that in cases where the electric lines A are of a three-phase three-wire system (delta connection type), the voltage detector14detects a voltage between R and T phases, outside of S phase (grounding). Also, in cases where the electric lines A are of a three-phase four-wire system (star connection type), the voltage detector14detects a voltage between phases, outside of the grounding wire. Also, in cases where the electric lines A are of a single-phase two-wire system, the voltage detector14detects a voltage between N and L phases.

The voltage detector14determines a reference point from the voltage V2detected from the electric lines A and supplies the voltage V2to the transformer15. For example, the voltage detector14determines, as the reference point, a point where the voltage V2detected from the electric lines A crosses zero (zero-cross point).

The transformer15changes the supplied voltage V2into a voltage of a predetermined value, and supplies the transformed voltage V to the LPF16. The transformer15changes the voltage V2to a transformation ratio of 20:1, for example. The LPF16removes a harmonic component from the supplied voltage V2. The LPF16supplies the voltage V2having the harmonic component removed to the full-wave rectifier17, comparator18and power frequency measuring unit21. The full-wave rectifier17rectifies the supplied voltage V2and supplies the rectified voltage V2to the A-D converter25.

The comparator18takes a zero-cross point of the converted voltage V1supplied from the LPF12and converts the voltage V1into a signal having a square wave, and supplies the square-wave signal to the calculator19. Also, the comparator18takes zero-cross point of the voltage V2supplied from the LPF16and converts it into a signal having a square wave, and supplies the square-wave signal to the calculator19.

The calculator19makes a predetermined calculation on the basis of the signal supplied from the comparator18and supplies the calculated signal to the phase pulse width measuring unit20. The calculator19is, for example, an EXOR (exclusive OR) circuit to make EXOR calculation of two square-wave signals from the comparator18.

The phase pulse width measuring unit20detects phase pulse widths of the converted voltages V1and V2on the basis of the result of calculation from the calculator19. The phase pulse width measuring unit20functions as will be explained below:

In case the electric lines A under testing are of a single-phase system, the phase angle θ of the leakage current Igr is 0 deg. and phase angle θ of the leakage current Igc is 90 deg. as shown inFIG. 2A. Therefore, the phase contrast between the leakage currents Igr and Igc is 90 deg. (¼ cycle). Also, in cases where the power is a three-phase one, the phase angle θ of the leakage current Igr is 60 deg. and phase angle θ of the leakage current Igc is 0 deg. as shown inFIG. 2B. Therefore, the phase contrast between the leakage currents Igr and Igc is 60 deg. (⅙ cycle). Thus, the phase pulse width measuring unit20is applicable to a phase pulse width of ¼ or less of one cycle so that it can measure a phase angle whether the power is a single-phase or three-phase one.

Therefore, the phase pulse width measuring unit20supplies the phase angle calculator22with a phase pulse width of less than ¼ of one cycle, calculated based on the result of calculation from the calculator19. It should be noted that in cases where the power frequency is 60 Hz, one cycle is 16.6 ms and thus the phase pulse width is 4.15 ms or less, and that in cases where the power frequency is 50 Hz, one cycle is 20 ms and thus the phase pulse width is 5 ms or less.

The power frequency measuring unit21measures a power frequency on the basis of the voltage V2supplied from the LPF16, and supplies the result of measurement to the phase angle calculator22. It should be noted that in cases where the electric lines A under testing are intended for a commercial power system, the result of measurement from the power frequency measuring unit21is 50 or 60 Hz. Also, the power frequency measuring unit21may be adapted to judge, based on the voltage V2supplied from the LPF16, whether the power frequency is 50 or 60 Hz.

The phase angle calculator22calculates, by an equation (1) given below, the phase angle θ of the leakage current I flowing through the electric lines A under testing on the basis of a phase pulse width W supplied from the phase pulse width measuring unit20and power frequency F supplied from the power frequency measuring unit21:
θ=360×W×F(1)

The phase angle calculator22supplies the calculated phase angle θ to the leakage current calculator27.

The A-D converter23converts the converted voltage V1supplied from the full-wave rectifier13into a digital signal and supplies the digital signal to the root-mean-square value calculator24. This root-mean-square value calculator24calculates, by an equation (2) given below, a root-mean-square value I0of the converted voltage V1on the basis of the signal supplied from the A-D converter23. It should be noted that the signal supplied to the root-mean-square value calculator24is taken as for convenience of explanation because it is based on the converted voltage V1resulting from conversion of the leakage current I flowing through the electric lines A under testing.
I0=I×(π/2)/√2

The root-mean-square value calculator24supplies the calculated root-mean-square value I0to the leakage current calculator27.

Also, the A-D converter25converts the rectified voltage V2supplied from the full-wave rectifier17into a digital signal, and supplies the digital signal to the root-mean-square value calculator26. This root-mean-square value calculator26calculates, by an equation (3) given below, a root-mean-square value V0of the voltage V2on the basis of the signal supplied from the A-D converter25:
V0=V×(π/2)/√2  (3)

The root-mean-square value calculator26supplies the calculated root-mean-square value V0to the resistance calculator28.

The leakage current calculator27calculates a leakage current Igr on the basis of the phase angle θ supplied from the phase angle calculator22and root-mean-square value I0supplied from the root-mean-square value calculator24, and supplies the calculated leakage current Igr to the resistance calculator28. It should be noted that in cases where the power is a single-phase one, the leakage current Igr is to be calculated using an equation (4) given below, and that in cases where the power is three-phase, the leakage current Igr is to be calculated using an equation (5) given below:
Igr=I0×cos θ  (4)
Igr=(I0×sin θ)/cos 30°  (5)

Note that the leakage current calculator27judges, based on a selected position of a rotary switch, whether the power is single-phase or three-phase.

The resistance calculator28calculates, by an equation (6) given below, a resistance Gr on the basis of the root-mean-square value V0supplied from the root-mean-square value calculator26and leakage current Igr supplied from the leakage current calculator27:
Gr=V0/Igr(6)

In cases where the leakage current Igr calculated by the leakage current calculator27exceeds an arbitrary value, the judging unit29generates a predetermined cutoff signal Scand supplies the cutoff signal Scthus generated to the circuit breaker30.

The circuit breaker30breaks the electric lines A under testing on the basis of the cutoff signal Scsupplied from the judging unit29. Also, the circuit breaker30is formed from a trigger coil TC and the like as shown inFIG. 3, and breaks the electric lines A on the basis of the cutoff signal Scsupplied from the judging unit29.

Also, the leakage current interrupter1may include a setting unit31to set an arbitrary value, and may be designed such that the judging unit29judges whether the leakage current Igr calculated by the leakage current calculator27has exceeded an arbitrary value set by the setting unit31. In this case, the setting unit31may be adapted to select a plurality of preset values by means of a rotary switch. Also, the values are set in steps of 10 mA.

Also, the leakage current interrupter1may include a recording unit32to record the leakage current Igr calculated by the leakage current calculator27. Since the recording unit32records the leakage current Igr calculated by the leakage current calculator27at every elapsed time interval, the user can know how the leakage current Igr changes as time proceeds.

For example, it is assumed that the user connects a monitor to the leakage current interrupter1via a communication connector to access data stored in the recording unit32. It should be noted that the leakage current interrupter1should be pre-assigned a unique ID number.

In this case, the monitor will read the root-mean-square value I0calculated by the root-mean-square value calculator24, leakage current Igr calculated by the leakage current calculator27, voltage V on the electric lines A detected by the voltage detector14, frequency measured by the power frequency measuring unit21and ID number of the leakage current interrupter1from the leakage current interrupter1via the communication connector. Also, the monitor has a round connector for connection to the communication unit33and has a disconnection preventive mechanism to prevent poor contact with the communication unit33.

When it is found from how the leakage current Igr has varied over time that the leakage current Igr has momentarily arrived at an arbitrary value, for example, with reference to data stored in the recording unit32, it is very likely that the leakage current has been caused by a device put into operation or already in operation when the leakage current Igr has arrived at the arbitrary value, which can be used as clues to locate the leakage.

Also, when it is found from how the leakage current Igr has varied over time that the leakage current Igr has gradually been increased, for example, a device possibly causing a leakage current can be located early by testing the device in operation.

The leakage current interrupter1constructed as above according to the present invention can operate even with the electric lines A of a three-phase system, for example, in the same manner as with a single-phase power. Here will be explained the principle of the leakage current interrupter1according to the present invention.

The CT sensor10clamps the electric lines A under testing, and detects waveforms between R and S phases, between S and T phases and between T and R phases, which are different by 120 deg. from each other as shown inFIG. 4A. It should be noted thatFIG. 4Ashows the waveforms for convenience of explanation but the waveforms detected by the CT sensor10are synthetic ones. The synthetic waveforms detected by the CT sensor10are supplied to the calculator19via the amplifier11, LPF12and comparator18.

Also, the voltage detector14has a voltage probe thereof connected between the R and T phases to detect a voltage between these R and T phases, and inverts the detected voltage as shown inFIG. 4B. The voltage detector14takes, as a reference point a, a point having zero-crossing with a predetermined point of the detected voltage. The voltage V2, whose reference point a is thus determined, is supplied to the calculator19via the transformer15, LPF16and comparator18.

For example, in cases where only the leakage current Igr occurs at the R phase of the electric lines A (the leakage current Igr will be referred to as “R-phase Igr” hereunder) and only the leakage current Igr occurs at the T phase (this leakage current Igr will be referred to as “T-phase Igr” hereunder), the R-phase Igr will have a phase contrast of 120 deg. in relation the reference point a while the T-phase Igr will have a phase contrast of 60 deg. in relation to the reference point a, as shown inFIG. 4C.

Also, in cases where only the leakage current Igc occurs at the R phase of the electric lines A (the leakage current Igc will be referred to as “R-phase Igc” hereunder) and only the leakage current Igc occurs at the T phase (this leakage current Igc will be referred to as “T-phase Igc” hereunder), a synthetic waveform of the R-phase Igc and T-phase Igc will have a phase contrast of 180 deg. (0 deg.) in relation the reference point a as shown inFIG. 4D.

Further, in cases where the leakage currents Igr and Igc occur at the R phase of the electric lines A under testing and also at the T phase, the synthetic waveform will be as shown inFIG. 4E.

Also, the above description is represented by a vector as follows. Since the electric lines A under testing are of the three-phase system, the vector is as shown inFIG. 5A. A voltage between the R and T phases is detected by the voltage detector14and the reference point a is determined from the detected voltage. The single-phase vector is as diagrammatically shown inFIG. 5B. It should be noted that the phase contrast between the R-phase Igr and reference point a is 60 deg. while the phase contrast between the T-phase Igr and reference point a is 120 deg.

Also, in cases where the electric lines A under testing are of the single-phase system, the R-phase Igc can be found at a point 90 deg. from the R-phase Igr and the T-phase Igc can be found at a point 90 deg. from the T-phase Igr because the phase contrast between the leakage currents Igr and Igc is 90 deg. as was described above with reference toFIG. 2A. Also, a synthetic vector Igc derived from the R-phase Igc and T-phase Igc can be found at a point 180 deg. (0 deg.) from the reference point a (as inFIG. 5C).

Therefore, in cases where only the R-phase Igr occurs in the electric lines A, for example, a synthetic vector derived from the R-phase Igr and Igc, that is, the leakage current I0flowing through the electric lines A, can be represented as shown inFIG. 5D. It should be noted that the aforementioned equation (5) can be derived to calculate the R-phase Igr as shown inFIG. 5D. Also, it should be noted that the phase contrast θ of the leakage current I0varies 60 to 180 deg. in relation to the reference point a corresponding to the magnitude of the R-phase Igr and Igc.

Also, in cases where only the T-phase Igr occurs in the electric lines A, for example, a synthetic vector derived from the T-phase Igr and Igc, that is, the leakage current I0flowing through the electric lines A, can be represented as shown inFIG. 5E. It should be noted that the aforementioned equation (5) can be derived to calculate the T-phase Igr as shown inFIG. 5E. Also, it should be noted that the phase contrast θ of the leakage current I0varies 120 to 180 deg. in relation to the reference point a corresponding to the magnitude of the T-phase Igr and Igc.

The operations of the leakage current interrupter1according to the present invention to detect the leakage current Igr flowing through the electric lines A under testing and break the latter on the basis of the detected leakage current Igr will be explained below with reference to the flow diagram shown inFIG. 6. It should be noted that the leakage current interrupter1is intended to be housed in an existing earth leakage breaker but it may be installed outside the existing earth leakage breaker if it cannot be housed therein.

In step ST1, the user switches a rotary switch (not shown) of the leakage current interrupter1corresponding to the type of the electric lines A under testing (single-phase two-wire system, single-phase three-wire system or three-phase three-wire system). It should be noted that in step ST1, the electric lines A are broken.

In step ST2, the user operates the setting unit31to set an arbitrary value.

In step ST3, the user turns on the leakage current interrupter1.

Thereafter, in the leakage current interrupter1, the leakage current calculator27calculates the leakage current Igr through the electric lines A under testing, and the judging unit29judges whether the leakage current Igr has reached the arbitrary value. When the judging unit29in the leakage current interrupter1determines that the leakage current Igr has reached the arbitrary value, the circuit breaker30will break the electric lines A.

FIG. 7shows a first result of the actual leakage current measurement of the electric lines A in the leakage current interrupter1according to the present invention. The result shown inFIG. 7is the result of a measurement made at a power board of a rooftop power incoming and distribution box (high-voltage incoming panel) (power frequency: 50 Hz; mains voltage: 200 V; type of low-voltage lines under testing: three-phase three-wire, 150 kVA; room temperature: 41° C.; humidity: 43%).

In the experiment, a resistor of 20 kΩ was connected as a dummy insulation resistance to the R phase at a time point between 6 min and 9 min (3 min) from the start of measurement, a resistor of 20 kΩ was connected as a dummy insulation resistance to the T phase at a time point between 9 min and 11 min (2 min) from the start of measurement, the resistors were disconnected at a time point between 11 min and 12 min (1 min) from the start of measurement, a resistor of 10 kΩ was connected as a dummy insulation resistance to the R phase at a time point between 12 min and 13 min (1 min) from the start of measurement, a resistor of 10 kΩ was connected as a dummy insulation resistance to the T phase at a time point between 13 min and 15 min (2 min) from start of measurement, and the resistors were disconnected in 15 min from the start of measurement.

For example, in cases where a resistor of 20 kΩ is connected as a dummy insulation resistance to the R phase, a current having the following theoretical value for the dummy insulation resistance will additionally flow through the electric lines A under testing:
Igr=V/R=200/(20×103)=10 mA

In the leakage current interrupter1, a leakage current Igr of 12.3 mA was detected when the resistor of 20 kΩ was connected as a dummy insulation resistance to the R phase at a time point of 6 min from the start of measurement as shown inFIG. 7. Since the leakage currents Igr before a lapse of 6 min from the start of measurement, at a time point between 11 min and 12 min after the start of measurement and 15 min from the start of measurement are 2 mA in cases where the resistors are each not connected as a dummy insulation resistance, subtraction of 2 mA from the leakage current Igr after the resistor of 20 kΩ is connected to the R phase will result in 10.3 mA, which means that the leakage current interrupter1according to the present invention could measure a change of 10.3 mA. This value is generally the same as the theoretical value (10 mA).

Also, in cases where a resistor of 20 kΩ is connected as a dummy insulation resistance to the R phase, a synthetic resistance derived from the dummy insulation resistance and resistance before connection of the resistor of 20 kΩ (Gr≈105.46 kΩ (mean value of resistance Gr between a time point before lapse of 6 min from the start of measurement)) will be given as shown below. In the leakage current interrupter1, the resistance Gr measured at a time point of 6 min from the start of measurement is 17.2 kΩ which is generally the same as the aforementioned theoretical value (16.3 kΩ) as shown inFIG. 7.
Gr=(20×103×105.46×103)/(20×103+105.46×103)≈16.3 kΩ

Also in cases where a resistor of 20 kΩ is connected as a dummy insulation resistance to the T phase, the current for the dummy insulation resistance is theoretically increased by 10 mA as above. In the leakage current interrupter1, the leakage current Igr detected at a time point between 9 min and 11 min from the start of measurement is nearly 12.4 mA and subtraction of 2 mA from the measured value results in 10.4 mA which is nearly the same as the theoretical value (10 mA), as shown inFIG. 7.

Also, the synthetic resistance Gr when the resistor of 20 kΩ is connected as a dummy insulation resistance to the T phase is theoretically 16.3 kΩ as above and the measured synthetic resistance is 17.4 kΩ, which means that the measured resistance is almost the same as the theoretical value.

Also, in the leakage current interrupter1, both the theoretical values of the leakage current Igr and Gr when the resistor of 10 kΩ was connected as a dummy insulation resistance to the R or T phase are also almost the same as their respective measured values as shown inFIG. 7.

Further, in the leakage current interrupter1, when the resistors as the dummy insulation resistance were disconnected at time point between 11 min and 12 min from the start of measurement and at a time point 15 min after the start of measurement, the leakage current Igr, I0and Gr were again the same as those measured before connection of the resistors as the dummy insulation resistance (at a time point between 1 min and 5 min from the start of measurement).

FIG. 8shows a second result of the actual leakage current measurement of the electric lines A in the leakage current interrupter1according to the present invention. The result shown inFIG. 8is the result of a measurement made at a power board of a power incoming and distribution box (high-voltage incoming panel) (power frequency: 50 Hz; mains voltage: 200 V; type of low-voltage lines under testing: three-phase three-wire, 150 kVA).

In the experiment, a capacitor of 0.22 μF was connected as a dummy capacitance to each of the R and T phases at a time point between 1 min and 4 min (3 min) from the start of measurement, a resistor of 20 kΩ was connected as a dummy insulation resistance to the T phase at a time point between 3 min and 4 min (1 min) from the start of measurement, and the capacitor and resistor were disconnected at a time point of 4 min from the start of measurement. That is, at the time point between 3 and 4 min from the start of measurement, the capacitor was connected to each of the R and T phases and the resistor was connected to the T phase.

When the capacitor of 0.22 μF was connected as a dummy capacitance to each of the R and T phases, the capacitive reactance X was as follows:
X=½πfC=1/(2π×50×(0.22×10−6+0.22×10−6)≈7.23×103

Therefore, a current I having the following value will additionally flow through the electric lines:
I=V/X=200/7.23×103≈27.6 mA

Also, in cases where a resistor of 20 kΩ is connected as an insulation resistance to the T phase, a current having the following theoretical value for the dummy insulation resistance will additionally flow through the electric lines A under testing:
Igr=V/R=200/(20×103)=10 mA

In the leakage current interrupter1, a leakage current Igr of 7.8 mA was detected and I0of 100.8 mA was detected when the capacitor of 0.22 μF was connected as a dummy capacitance to each of the R and T phases at a time point of 1 min from the start of measurement as shown inFIG. 8. It should be noted that I0is a synthetic current derived from the leakage current Igr arising from an insulation resistance and leakage current Igc arising from a capacitance.

Since the leakage current Igr, when no capacitor as a dummy capacitance is connected, is 7.6 mA (leakage current Igr measured at a time point before elapse of 1 min from the start of measurement) as shown inFIG. 8, so it will vary little when a capacitor is connected as a dummy capacitance to each of the R and T phases.

On the other hand, the synthetic current I0, when no capacitor as a dummy capacitance is connected, is 75.9 mA (I0at a time point before elapse of 1 min from the start of measurement). Subtraction of I0(75.9 mA) before the capacitor as a dummy capacitance is connected from I0(100.8 mA) after the capacitor is connected will result in 24.9 mA which is the additional leakage current Igc. The additional leakage current Igc is nearly equal to the theoretical value (27.6 mA).

Also, in the leakage current interrupter1, the leakage current Igr of 21.0 mA was detected and I0of 107.0 mA was detected when a capacitor was connected as a dummy capacitance to each of the R and T phases and a resistor was connected as dummy insulation resistance to the T phase at a time point between 3 min and 4 min from the start of measurement as shown inFIG. 8.

Subtraction of the leakage current Igr (8 mA (at a time point of 3 min from the start of measurement)) before the resistor as a dummy insulation resistance is connected to the T phase from the leakage current Igr (21 mA) after the resistor is connected will result in 13 mA which is almost equal to the theoretical value (10 mA).

Operations of the comparator18and calculator19when the resistor of 10 kΩ is connected as a dummy insulation resistance to the R phase will be explained below with reference toFIGS. 9 to 11.

The comparator18is supplied with the converted voltage V1from the LPG12and voltage V2from the LPF16as shown inFIG. 9. The phase contrast between the converted voltage V1and voltage V2is 120 deg. The comparator18converts the converted voltage V1supplied from the LPF12into a square-wave signal and supplies the square-wave signal to the calculator19as shown inFIG. 10A. Also, the comparator18converts the voltage V2supplied from the LPF16into a square-wave signal and supplies the square-wave signal to the calculator19as shown inFIG. 10B.

The calculator19makes an EXOR calculation on the basis of the square-wave signal resulting from the conversion of the converted voltage V1and square-wave signal resulting from the conversion of the voltage V2as shown inFIG. 11. The calculator19determines a phase pulse width of less than ¼ of one cycle on the basis of a signal resulting from the EXOR calculation, and supplies the determined phase pulse width to the phase angle calculator22.

The leakage current interrupter1constructed as above according to the present invention detects a leakage current I flowing through the electric lines A under testing, converts the detected leakage current I into a voltage and removes a harmonic component from the converted voltage, detects a voltage V2from a voltage line included in the electric lines A and removes a harmonic component from the detected voltage V2, accurately determines a phase angle θ of the leakage current I flowing through the electric lines A on the basis of the converted voltage V1having the harmonic component removed and the voltage V2having the harmonic component removed, calculates only a leakage current Igr arising from an earth insulation resistance from the accurate phase angle θ and root-mean-square value I0of the converted voltage V1having the harmonic component removed, monitors the calculated leakage current Igr, and breaks the electric lines A when the leakage current Igr has exceeded an arbitrary value. Therefore, since the leakage current interrupter1according to the present invention can positively detect only a leakage current Igr arising from an earth insulation resistance in units of mA even if a leakage current Igc arising from the earth capacitance is increased due to an increased length of the electric lines A under testing or due to an inverter or the like which provides a harmonic distortion power, it can monitor the leakage current Igr and break the electric lines A under testing only when the leakage current Igr has exceeded the arbitrary value. Therefore, the leakage current interrupter1according to the present invention will not break the electric lines A like the conventional earth leakage breaker even if the leakage current Igr is increased due to any element (increased leakage current Igc) other than the leakage current Igr.

Also, the leakage current interrupter1according to the present invention can detect a leakage current Igr without momentary interruption of the power supply to electric lines, mechanical facility and the like, and can locate a current leakage or short circuit before the latter leads to a catastrophe such as a short circuit-caused fire or the like.

Also, since the leakage current interrupter1according to the present invention determines a reference point from a voltage developed on transmission lines without using any existing reference point as in the frequency infusion method, it can accurately measure a leakage current Igr flowing through the electric lines A under testing.

In the foregoing, the present invention has been described in detail concerning certain preferred embodiments thereof as examples with reference to the accompanying drawings. However, it should be understood by those ordinarily skilled in the art that the present invention is not limited to the embodiments but can be modified in various manners, constructed alternatively or embodied in various other forms without departing from the scope and spirit thereof as set forth and defined in the appended claims.

INDUSTRIAL APPLICABILITY

As described in the foregoing, in the leak current breaker and method according to the present invention, a leakage current flowing through electric lines under testing is detected, the detected leakage current is converted into a voltage and a harmonic component is removed from the converted voltage, a voltage developed on a voltage line included in the electric lines is detected and a harmonic component is removed from the detected voltage, a phase angle of the leakage current flowing through the electric lines is accurately determined based on the converted voltage having the harmonic component removed and the voltage having the harmonic component removed, a leakage current alone, arising from an earth insulation resistance, is calculated from the accurate phase angle and root-mean-square value of the converted voltage having the harmonic component removed, the calculated leakage current Igr is monitored, and the electric line is broken when the leakage current has exceeded an arbitrary value. Therefore, in the leak current breaker and method according to the present invention, it is possible to accurately calculate a power frequency (50 or 60 Hz in cases of a commercial power supply) in the electric lines from the voltage having the harmonic component removed and accurately detect a phase contrast between the signal waveform of the input leakage current having the harmonic component removed and that of the voltage having the harmonic component removed on the basis of the calculated power frequency. Thus the phase angle of the leakage current can accurately be calculated. Also, a leakage current arising from only an earth insulation resistance is calculated from the accurate phase angle and root-mean-square value of the leakage current having the harmonic component removed, and the electric lines under testing are broken in cases where the calculated leakage current has exceeded an arbitrary value. Thus, even if the earth capacitance is increased due to an increased length of the electric lines under testing or due to a harmonic distortion current caused by an inverter, it is possible to detect a leakage current alone, arising from only the earth insulation resistance and which will possibly cause a catastrophe such as a short circuit-caused fire or the like and break the electric lines under testing on the basis of the detected leakage current.

Also, with the leak current breaker and method according to the present invention, it is possible to measure a leakage current Igr simply and safely without having to momentarily turn off electric lines and mechanical facility for detection of the leakage current.