JP2009115754A - Device and method for measuring leakage current in electric equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for measuring the leakage current Igr value flowing through a ground insulation resistor of electric equipment and its circuit that are driven by a switching power supply such as an inverter. <P>SOLUTION: A signal processing section 14 for signal-processes the ground voltages VU, VV and VW of the switching power supply 2 sequentially input by a change-over switch 10 and the leakage current 10 detected from a power supply cable 4 by a zero-phase current transformer 8, and measures the phase difference between one of the ground voltages VU, VV and VW and the leakage current 10, and signal-processes it. The leakage current Igr flowing via a ground leakage resistor 7 is calculated based on the effective value of the leakage current 10 obtained in the signal processing section 14, the effective values of the ground voltages VU, VV and VW, and the phase difference between one of the ground voltages VU, VV and VW and the leakage current 10. The leakage current Igr calculated by the arithmetic section 15 is displayed on a display section 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a leakage current measuring apparatus and method for measuring leakage current in an electric device that measures a leakage current flowing from a voltage application portion to a ground portion of an electric device having an electric motor driven by a switching power source such as an inverter.

  The use of electricity is convenient, but if it is not properly managed and used, it also has very dangerous aspects, and there are many possibilities of causing serious accidents such as electric fires and electric shocks. For example, one of the causes of the serious accident is an insulation failure of an electric circuit or an electric device. As a method of examining the insulation state of the electric circuit and the electric device, a method of measuring the electric circuit and electric device to be measured with a power failure and measuring with an insulation resistance meter has been a conventional standard.

  As in recent years, there are drawbacks such as restrictions on application to distribution lines where continuous power failure is not permitted, continuous operation factories, and the like. In other words, in the current social situation, computers are used in various areas of society, and a system that operates continuously for 24 hours has been constructed by the spread of intelligent buildings and factory automation (FA). In order to investigate, it is in a situation where it cannot temporarily be brought into a power failure state.

  Especially when measuring leakage current in electrical equipment that has an electric motor driven by a switching power supply such as an inverter, measure only the electric motor to protect the switching power supply composed of electronic circuits from high voltage during insulation resistance measurement. Therefore, it takes a lot of time and effort for the power outage procedure, opening the connection, and reconnecting. As a result, the line stop time is limited in a continuous operation factory or the like, and there is a problem that application of the insulation resistance meter is limited.

  Therefore, at present, leakage current measurement that can be measured without turning off electricity from the method of insulation resistance meter with power outage due to the demand for society uninterrupted due to such advanced informationization, insulation failure management of electric circuits and electrical equipment. A method is being used. And various preventive measures during energization in which the leakage current is measured by an earth leakage breaker, an earth leakage fire alarm, or the like and the insulation state is managed have been proposed.

  As disclosed in Japanese Patent Laid-Open No. 3-179271 (Patent Document 1), Japanese Patent Application Laid-Open No. 2002-125313 (Patent Document 2), etc. In general, a method of detecting a leakage current from a charged part of an electric circuit and an electric device to a grounded part, that is, a zero-phase current I0, which is detected by a zero-phase current transformer, is performed. The leakage current I0 is composed of the vector sum of the leakage current Igr that flows through the insulation resistance between the charging part and the grounding part of the electric circuit and electrical equipment, and the leakage current Igc that flows through the ground capacitance that normally exists in this insulating part. Yes.

  In an electric device having an electric motor driven by a switching power source such as an inverter, the operating frequency (hereinafter referred to as a basic frequency) and voltage of the electric motor constantly change, and the ground voltage itself directly related to the leakage current also changes. . Further, the current Igr at the time of measuring the ground insulation resistance of the motor is often several mA or less, and measurement itself is extremely difficult under the above-described conditions.

The distribution method measuring method for grounding one of the 200V three-phase three wires, which is another method, measures the phase difference between the zero-phase current Io and the line voltage, and from this value, the value of the leakage current Igr is measured. Is calculated. Although it is possible to measure the distribution system on the commercial frequency power supply side from the switching power supply, it is difficult to measure the motor driven on the switching power supply side where the frequency changes and the ground voltage also changes. The method of measuring the leakage current Igr by adding a special circuit is also the same, which causes a failure of the switching power supply and adversely affects the operation of the motor that performs precise control.
JP-A-3-179271 JP 2002-125313 A

  The present invention detects the leakage current Igr flowing through the insulation resistance of the electric motor of the electric device in the energized state, particularly the leakage current Igr flowing through the ground insulation resistance of the electric device having the electric motor driven by the switching power supply in the operating state. It is an object of the present invention to provide a leakage current measuring device and a measuring method thereof in an electrical device that can be used.

  In order to solve the above-described problem, the leakage current measuring apparatus in the electric apparatus according to the present invention is configured such that the voltage measuring unit sequentially inputs and measures the ground voltage of each phase of the switching power supply, and the zero-phase current measuring unit receives the electric motor or the The phase of the switching power supply measured by the voltage measuring means from the zero phase current I0 measured by the signal processing means by the zero-phase current measuring means is measured. The effective component, which is a component in the same phase direction as the ground voltage, is calculated for each phase sequentially input, and the calculation means calculates the effective component and voltage measurement means for each phase of the zero-phase current I0 calculated by the signal processing means. The leakage current Igr flowing through the ground insulation resistance of the electric device is calculated from the ground voltage value of each phase of the switching power supply input.

  In order to solve the above problems, the leakage current measurement method for an electrical apparatus according to the present invention sequentially inputs and measures the ground voltage of each phase of the switching power supply in the voltage measurement process, and the motor and the electric Measure the zero-phase current I0, which is the ground leakage current that flows through the equipment and wiring, and from the zero-phase current I0 measured in the zero-phase current measurement process in the signal processing process, The effective component, which is the component in the same phase direction as the ground voltage, is calculated for each phase sequentially input, and the effective component for each phase of the zero-phase current I0 calculated in the signal processing step in the calculation step and input in the voltage measurement step The leakage current Igr flowing through the ground insulation resistance of the electric device is calculated from the ground voltage value of each phase of the switching power supply.

  The three-phase voltage generated when the switching power supply drives the electrical equipment is the central potential of the +/- potential of the DC voltage portion generated as a result of rectifying the commercial frequency voltage received from outside in the switching power supply device. A three-phase voltage (hereinafter, this three-phase voltage is called a drive voltage) having the same magnitude with a phase difference of 120 degrees is generated with respect to the zero potential. The ground voltage at the zero potential point (hereinafter referred to as ground zero potential voltage) has different voltage values and frequency components depending on the grounding method of the external commercial frequency power supply. For example, one of three phases In the ground system, the ground potential voltage is a so-called phase voltage obtained by dividing the line voltage of an external commercial frequency power source by √3, and the frequency is the commercial frequency and this harmonic. The frequency of the drive voltage is in the range of 0 to 30 Hz at low speed and is generally in the range of 30 to 60 Hz during operation. The voltage is 60 Hz, the rated voltage of the motor, and less than 60 Hz is almost proportional to the frequency. Become. Therefore, the ground voltage of the switching power supply output terminal is a combination of both voltages, and the frequency is a superposition of the waveform of the average of both frequencies and a half frequency difference. For example, when the commercial frequency is 60 Hz and the driving frequency is 30 Hz, waveforms of 45 Hz and 15 Hz are superimposed, and when the driving frequency is 50 Hz, the frequencies of 55 Hz and 5 Hz are superimposed. The combined voltage value fluctuates in a long cycle, and the maximum value is the sum of the maximum values of both voltage values. Further, the voltage / current waveform of the switching power supply includes a combination of square waves obtained by cutting a DC voltage, and thus includes many harmonic components having a high frequency.

  As described above, the ground voltage of the switching power source is a set of power sources having different three-phase driving voltages and single-phase ground potential voltages. It explains by the method of matching. In the electric device according to the present invention, a ground capacitance exists between a portion to which a voltage is applied and a grounded metal portion covering the portion or the ground. Since this ground capacitance shows almost the same capacitance value for each of the three phases of the driving voltage, when a driving voltage having a frequency f and a phase voltage value E is applied to the ground capacitance C, The current flowing through the ground capacitance is the same, the phase difference is 120 degrees, and the total current value for the three phases is zero. For a single-phase ground zero potential voltage having a frequency f0 and a voltage value E0, the current flowing through the ground capacitance of each phase is in the same direction and is a total value. If a leakage current Igr flowing through the ground insulation resistance r is generated as a result of the insulation deterioration, a combined value of this current and the sum of the currents flowing through the above-mentioned ground capacitance is measured as the leakage current I0.

  When the leakage current Igr flows through the ground leakage resistance r to the phase where the ground voltage of the switching power supply is input for measurement, if the leakage current due to the driving voltage of the phase voltage value E is I0d, the three-phase as described above The total current flowing through the ground capacitance C is 0, and only the current flowing through the ground leakage resistance r, so the leakage current I0d is expressed by the following equation (1).

I0d = E / r (1)
Next, let I00 be the leakage current due to the voltage of the ground potential 0 with the voltage value E0, and let j be the component symbol that is 90 degrees ahead of the voltage E0 by the vector symbol method, the current flowing through the capacitor C is the applied voltage E0. Since it is further 90 degrees and is the sum of the three phases, the leakage current I00 is expressed by the following equation (2).

I00 = E0 / r + j · 2πf0 × 3CE0 (2)
At the time of the maximum ground voltage, when the driving voltage of the phase voltage value E and the peak value of the ground potential voltage of the voltage value E0 overlap, that is, when the vector directions coincide, the total value of both voltages becomes E + E0. Assuming that the leakage current at this time is I0, the equation (1) and equation (2) are added according to the principle of superposition, and the leakage current I0 becomes as shown in the following equation (3).

I0 = I0d + I00 = (E + E0) / r + j · 2πf0 × 3CE0 (3)
In the above equation (3), since the portion (E + E0) / r is the leakage current Igr flowing through the ground leakage resistance r, the leakage current Igr at the time of the ground voltage (E + E0) is expressed by the following equation (4). The

Igr = (E + E0) / r (4)
Therefore, in order to obtain the leakage current Igr, the ground voltage of a phase of the switching power supply is input as a voltage for measurement, and the component of the leakage current I0 in the same phase direction as the input voltage, that is, the value of the real part is obtained. As shown in the equations (3) and (4), this value is the value of the leakage current Igr when the input phase ground voltage (E + E0).

  This Igr portion is a real number portion where j is not attached in Equation (3), and is composed only of Equation (4) not related to frequency, which is convenient for measurement when the frequency changes like a switching power supply. .

  In actual measurement, the input ground voltage fluctuates in a relatively long cycle of several seconds to several tens of seconds. Therefore, the Igr value is measured several times in the time zone when this voltage is maximum, and the maximum value is measured for the input phase. Adopted as the value of Igr. Further, from the above equation (3), when the phase difference between the leakage current I0 and the input voltage (E + E0) is represented by a vector, the angle formed by the leakage current I0 and the input voltage (E + E0), that is, the phase angle is 0 to 90 degrees. If the phase with unexpected noise or ground leakage resistance r is different from the phase where the ground voltage is input for measurement, the phase angle may be out of this range. It is also a measurement condition that the angle is within a range of 90 degrees.

  As described above, when the ground voltage input phase coincides with the phase where the ground leakage resistance r exists, the relationship as described above is established. Therefore, the ground voltage input phase is switched and sequentially measured, and the maximum value of Igr in the phase is measured. Is the Igr value at the time of input voltage (E + E0). When the ground leakage resistance r exists in a plurality of phases, the total value of the Igr values of the plurality of phases is set as the Igr value at the input voltage (E + E0). Next, since the input voltage (E + E0) at the time of measurement may not reach the rated ground voltage V0 of the electric device depending on the operating conditions, the value of Igr measured at this time is used as the rated ground voltage V0 of the electric device. And the measured ground voltage.

  Further, since the waveform of the input voltage (E + E0) varies depending on the frequency and this affects the measured value of Igr, the measured value of Igr is corrected using a coefficient related to the frequency.

  According to the present invention, since the value of the leakage current Igr can be measured even when the electric device driven by the switch power supply is in an operating state, the degree of insulation deterioration can be constantly monitored and It is possible to prevent a fault from occurring. Moreover, the reliability of the whole equipment can be remarkably improved. Furthermore, even in the periodic inspection work required by law, it is possible to save power and time for power disconnection, release the connection, and then perform reconnection, etc., and further reduce the cost.

  Hereinafter, embodiments of a leakage current measuring device and a measuring method in an electrical apparatus to which the present invention is applied will be described with reference to the drawings.

  First, the configuration when the present invention is applied to the measurement of the leakage current Igr of an electric device having an electric motor driven by a switching power supply will be described with reference to FIG.

  In FIG. 1, a power distribution three-phase power source 1, which is a commercial frequency, has one of the distribution lines or a neutral point of a power transformer grounded and connected to supply power to a switching power source 2 such as a servo motor. Yes. The frequency at the time of electric equipment operation from the three output terminals U, V, W of the switching power supply 2 changes in the range of 0 to 30 Hz from the start to the low speed, and changes in the range of 30 Hz to 60 Hz in the steady operation. However, a drive voltage that changes in a range from about 40% of the rated voltage of the electric device to the rated voltage is supplied to the electric device 5 via the feeder cable 4. The ground voltage of terminals U, V, and W changes from the rated voltage of the motor to about 85% when one line of the distribution line of the commercial frequency power supply is grounded, and the change in frequency during steady operation is around the commercial frequency. Since it is 10-20 Hz, the same measurement as a commercial frequency is possible.

  In the electric motor 5, a ground capacitance 6 exists between a winding portion to which a voltage is applied and a frame portion including an iron core. There is also a ground leakage resistance 7.

  In the schematic system diagram shown in FIG. 1, the leakage current measuring device inputs a three-phase power supply voltage from the output terminal 3 of the switching power supply 2 through the measurement cable 11 to the measuring instrument 17 and zeros from the power supply cable 4. The zero-phase current I0 is input to the measuring device 17 via the phase current transformer 8, and the leakage current Igr of the motor is measured.

  The measuring instrument 17 performs signal processing on the ground voltages VU, VV, VW of the switching power supply 2 sequentially input by the switching switch 10 and the leakage current I0 detected by the zero-phase current transformer 8 from the power supply cable 4. A signal processing unit 14 that measures and processes a phase difference between any one of the ground voltages VU, VV, and VW and the leakage current I0, an effective value of the measured current I0 obtained by signal processing from the signal processing unit 14, and the ground Based on the phase difference between the effective value of the voltages VU, VV, VW and any one of the ground voltages VU, VV, VW and the leakage current I0, the leakage current Igr flowing through the ground leakage resistance r is calculated.

  The leakage current measuring device further includes a display unit 16 that displays the leakage current Igr calculated by the calculation unit 15.

  That is, in the diagram shown in FIG. 1, in the measuring instrument 17 of the leakage current measuring device, the ground voltage VU, VV, VW of the switching power supply 2 is sequentially input to the signal processing unit 14 by the switching switch 10. Further, the leakage current I 0 detected by the zero-phase current transformer 8 is also input to the signal processing unit 14. The signal processing unit 14 also performs signal processing for measuring the phase difference between the ground voltages VU, VV, VW and the leakage current I0. The calculation unit 15 calculates the effective value of the measurement current I0 obtained by the signal processing from the signal processing unit 14, the effective value of the ground voltages VU, VV, VW, the ground voltage VU, VV, VW and the leakage current I0. Based on the phase difference, the leakage current Igr flowing through the ground leakage resistance r described above is calculated. The display unit 16 displays the leakage current Igr calculated by the calculation unit 15.

  FIG. 2 is an equivalent system of the schematic system diagram and the leakage current measuring apparatus shown in FIG. That is, FIG. 2 is equivalent to a circuit in which the voltage source 19 including the distribution power source 1 and the switching power source 2 is combined with the driving voltage of EU, EV, and EW and the ground potential 0 of E0 as shown in FIG. is there. The zero phase current I 0 is detected by the zero phase current transformer 8 and supplied to the measuring instrument 17.

  The three-phase drive voltages EU, EV, EW and the ground 0 potential voltage E0 are superimposed on each other to become the ground output voltage. However, this voltage value is not constant, and due to the characteristics of the switching power supply, each phase has a relatively long cycle. Fluctuates. This phenomenon also makes measurement with the conventional measurement method difficult, but in the present invention, the Igr value is measured a plurality of times in the time zone in which the ground voltage is maximum, and the maximum value is the input voltage (E + E0). The value of Further, from the above-described equation of I0, the phase difference between the leakage current I0 and the input voltage (E + E0), the angle between the leakage current I0 and the input voltage (E + E0) in the vector, that is, the phase angle is 0 degree to 90 degrees. Although it is in the range, if the phase where the unexpected noise or ground leakage resistance r exists is different from the input phase, it may be out of this range, so the phase angle may be in the range of 0 to 90 degrees. The measurement conditions. Assuming that the phase angle is θ, the phase angle θ is in the range shown in the following equation (5).

90 degrees>θ> 0 degrees (5)
This measurement is performed in the same way while sequentially inputting the ground voltage of each phase, and the maximum value that meets the conditions or the total value of the measured values of the phases that meet the conditions among the input phases is the measured value at that time. And

  The wiring 4 and the electrical device 5 have a ground capacitance 6 in each of the three phases, and a leakage current Igc flows therethrough. The value of the ground capacitance 6 of each phase is substantially equal, and the total of the leakage current Igc of each phase due to the drive voltage generated by the switching power supply 2 is 0, but the value of the single-phase voltage value E0 depends on the ground potential 0 voltage. Current is superimposed.

  The zero-phase current transformer 8 surrounds the power feeding cable 4 and outputs the leakage current of the electric device 5 to the measuring instrument 17 as the value of the zero-phase current I0. If the insulation between the electrical equipment and the grounding portion deteriorates, as described above, the leakage current Igr flows through the ground leakage resistance 7, so that this current also leaks through the ground capacitance 6 due to the ground potential 0 voltage. To zero-phase current I0.

  In this manner, the voltage value of the ground voltage of each phase of the switching power supply 2 is a gradual fluctuation due to the combined voltage of the drive voltage E and the ground 0 potential voltage E0 having different frequencies and magnitudes. Since the peak value of both voltages substantially coincides at the time when this combined voltage shows the maximum value, measurement is performed a plurality of times during this time period. The value of the leakage current Igr at this time is expressed by the above-described equation (4).

  In the time zone in which the drive voltage E and the peak value of the ground zero potential voltage E0 substantially coincide with each other, the ground voltages VU, VV, VW of the respective phases of the switching power supply 2 are successively increased to a maximum value (E + E0) with a certain time difference. Become.

  The expressions (3) and (4) shown above are expressions when the ground voltage is (E + E0) and the ground leakage resistance 7 exists in the phase where the ground voltage indicates (E + E0). is necessary. Accordingly, the ground voltages VU, VV, and VW are sequentially input by the switching switch 10 to perform measurement, and when the ground leakage resistance 7 exists, the measured Igr value is measured by inputting the ground voltage of another phase. Since it becomes larger than the value, the value of the maximum Igr at that time is set as the value of Igr when the ground voltage is (E + E0). Further, when the ground leakage resistance 7 exists in a plurality of phases, the sum of the values of Igr measured for each phase is set as the value of Igr.

  The relationship between the leakage current I0 and the input voltages VU, VV, VW and their maximum values (E + E0) is represented by the vector diagram of FIG. 3. The phase angle of the leakage current I0 with respect to the input ground voltage is θ. From the equations (3) and (4), Igr when the input ground voltage shows the maximum value (E + E0) is an in-phase component with the input voltage (E + E0) of I0 at this time, and from the following equation (6) Desired.

Igr = I0 × cos θ (6)
Then, the Igr value affected by the frequency of the input ground voltage is corrected by the frequency, and when the input ground voltage (E + E0) does not reach the rated ground voltage V0 of the electrical device, Igr is It is corrected by equation (7).

Correction Igr = Igr × V0 / (E + E0) (7)
Next, details of the signal processing unit 14 in FIG. 1 will be described with reference to FIG. FIG. 4 is a diagram illustrating a specific configuration of the signal processing unit 14. The signal processing unit 14 includes an I0 detector 20 that detects a zero-phase current I0, an amplifier 21, a filter 22, an effective value converter 23, a phase difference measuring device 24, a voltage detector 31, an amplifier 32, A filter 33 and an effective value converter 34 are provided.

  The I0 detector 20 takes in the zero-phase current that is the sum of the leakage currents of the electric motor 5 from the power supply cable 4, that is, the leakage current I0 through the zero-phase current transformer 8. The amplifier 21 amplifies the leakage current I0 detected by the I0 detector 20 to an appropriate amount. The filter 22 attenuates the frequency exceeding the frequency of the drive voltage of the leakage current I0 amplified by the amplifier 21. The effective value converter 23 performs both-wave rectification on the alternating current waveform of the leakage current I 0 filtered by the filter 22, converts it to an analog value proportional to the effective value, and inputs the analog value to the calculation unit 15.

  The phase difference measuring device 24 measures a phase angle θ between the leakage current I0 and the input voltage V among the ground voltages VU, VV, VW of each phase of the switching power supply 2. In the vicinity of the time point when the voltage V shows the maximum value (E + E0), both waveforms processed by the filter 22 and the filter 33 approximate the waveform of FIG. 6, and the leakage current I0 is shown in the vector diagram of FIG. Is ahead of the voltage V. A fixed pulse waveform with the same peak value is output as IZ and VZ in FIG. 6 from the time when both waveforms have zero magnitude, that is, so-called zero crossing after passing the so-called horizontal axis. The difference between the two pulses is represented by phase difference pulses VZ to IZ, and the area S1 shown in FIG. 6 is proportional to the phase difference θ, that is, the phase angle θ. Along with the area S2 of the half wave pulse of I0, it is input to the 14 arithmetic unit, and the arithmetic processing shown in the following equation (8) is performed.

θ = 180S1 / S2 (8)
Further, the frequency can be known from the time difference between the rising and falling times of the quantitative pulse waveform VZ, and the measured Igr value is corrected based on this value.

  The voltage detector 31 divides and captures the W-phase ground voltage of the output terminal 3 of the switching power supply 2. The amplifier 32 amplifies the W-phase ground voltage detected by the voltage detector 31 to an appropriate amount. The filter 33 attenuates the frequency exceeding the drive voltage maximum frequency of the ground voltage of the W phase amplified by the amplifier 32. The effective value converter 34 rectifies the W-phase ground voltage filtered by the filter 33, converts it into an analog value proportional to the effective value, and inputs the analog value to the arithmetic unit 15.

  In the calculation unit 15, the values of the pulse areas S 1 and S 2 output from the phase difference measuring device 24 are obtained from the phase angle θ and the effective value converters 23 and 34 obtained according to the above equation (8) for calculating the phase angle. From the output current I0 and sequentially output ground voltage values VU, VV, VW, the maximum value (E + E0), the value of Igr is calculated according to the above-mentioned formulas (6) and (7), and the measured ground voltage The value is corrected according to the frequency.

  In addition, the calculation unit 15 instructs the switching switch 10 to select a suitable input phase while confirming that θ satisfies the conditional expression (5) described above, and the value or total of Igr at this time is selected. The value of Igr is set to the value of Igr when the ground voltage is (E + E0), and it is determined that the input phase showing the maximum value of Igr is the phase in which the leakage current Igr is most increased.

  Furthermore, the time zone in which the changing input voltage shows the maximum value is judged, and a plurality of measurements are commanded in the time zone, and the maximum Igr value is temporarily selected among the measured values, and then the input phase is switched. The same measurement is performed, the maximum Igr value of the temporarily selected values or the total value of the measured Igr values is corrected by the above equation (7), and the corrected Igr value is output to the display unit 16. It is displayed as the value of Igr.

  As described above, according to the leakage current measuring apparatus configured as shown in FIG. 1, the leakage current Igr flowing through the insulation resistance of the electric motor included in the electric device in the energized state, in particular, the electric motor having the electric motor driven by the switching power source. The leakage current Igr flowing through the ground insulation resistance of the device can be detected in the operating state, and the phase in which the leakage current Igr is increasing can be determined.

  Further, as shown in FIG. 5, the leakage current measuring apparatus according to the present invention is provided with a circuit breaker 9 (CBU, CBV, CWB) in the power distribution cable 4, and the circuit breaker 9 (CBU) is calculated according to the calculation result of the calculation unit 15. , CBV, CBW). The calculating part 15 interrupts | blocks all the lines using the circuit breaker 9, when the value of the leakage current Igr obtained by the calculation exceeds a predetermined value. For this reason, an electric device having an electric motor driven by a switching power supply can quickly shut off all the lines when the leakage current that has flowed through the ground insulation resistance becomes larger than a predetermined value. Accidents due to leakage current can be prevented.

  Furthermore, as shown in FIG. 5, the leakage current measuring apparatus according to the present invention further includes an alarm 18 that issues an alarm when the value of the leakage current Igr calculated by the calculation unit 15 exceeds a predetermined value. It may be. As a result, the electric device having the electric motor driven by the switching power supply promptly notifies the alarm device 18 that there is an abnormality when the leakage current that has flowed through the ground insulation resistance becomes larger than a predetermined value. It is possible to prevent accidents due to excessive leakage current.

  In the leakage current measuring apparatus according to the present invention, only one of the breaker 9 and the alarm device 18 may be provided depending on the environment and conditions used.

  The leakage current measuring apparatus described with reference to FIGS. 1 and 5 executes the leakage current measuring method of the present invention. That is, the switching switch 10 inputs each relative ground voltage of the switching power supply 2 and performs a voltage measurement step. The zero-phase current transformer 8 performs a zero-phase current measurement step for measuring a ground leakage current flowing out from the switching power supply 2. The signal processing unit 14 of the measuring instrument 17 compares the phase of the leakage voltage I0 measured by the zero-phase current transformer 8 with the measurement voltage input by the switching switch 10 in the measurement voltage measurement step. And the area of the half-cycle pulse S2 of the leakage current I0 is calculated. The calculation unit 15 calculates the phase angle θ from the phase difference pulse S1 calculated by the signal processing unit 14 performing the signal processing step and the half-cycle pulse S2 of the leakage current I0, and sequentially calculates the phase angle θ and the leakage current I0. A calculation step of calculating a leakage current Igr flowing through the ground insulation resistance r from the input ground voltage is performed.

  In distribution systems and electrical equipment, insulation measurement is required from the viewpoint of preventing electrical disasters. Previously, measurements were taken after a power failure, but in recent years power failures have been limited. In particular, many electric motors driven by switching power supplies such as inverters are used in robots, automatic machines, and other mechanical equipment. Leads to. The present invention makes it possible to measure these devices, which could not be performed before, without causing a power failure, and also enables preventive maintenance by continuous monitoring. The number of practical use of these switching power supply driving devices has been increasing year by year, and the requirement for ensuring the reliability of these facilities has been improved, so that they can be used in these fields.

It is a block diagram of a schematic system and a leakage current measuring device showing a configuration when the present invention is applied to measurement of a leakage current Igr of an electric motor driven by a switching power supply. It is the schematic system diagram of FIG. 1, and the equivalent circuit of a leakage current measuring apparatus. It is a vector diagram showing the relationship between zero phase current I0, input voltages VU, VV, VW, phase angle θ, and leakage current Igr. It is a block diagram which shows the signal processing part which comprises the leakage current measuring apparatus which concerns on this invention. It is a block diagram which shows the leakage current measuring apparatus which concerns on this invention provided with the structure which controls a circuit breaker and an alarm device. It is a figure showing the phase relationship of the waveform of V and the leakage current I0 in case the input voltage V is the maximum value time zone.

Explanation of symbols

  1 Power Distribution Power Supply, 2 Switching Power Supply, 3 Output Terminals, 4 Feeding Cable, 5 Electrical Equipment, 6 Ground Capacitance, 7 Ground Leakage Resistance, 8 Zero Phase Current Transformer, 9 Circuit Breaker, 10 Switching Switch, 11 Measurement Cable , 14 Signal processing unit, 15 Calculation unit, 16 Display unit, 17 Measuring instrument, 18 Alarm

Claims (11)

A ground voltage measuring means for measuring a ground voltage of each of the three phases of the switching power source that drives the electric device;
Zero-phase current measuring means for measuring a zero-phase current that is a ground leakage current flowing through an electric device including an electric wire and / or an electric motor fed from the switching power supply;
Signal processing means for calculating a phase difference between the ground voltage of each phase measured by the ground voltage measuring means and the zero phase current measured by the zero phase current measuring means;
From the phase difference calculated by the signal processing means, the ground voltage measured by the ground voltage measuring means, the zero phase current measured by the zero phase current measuring means, and the rated ground voltage of the electric device. An apparatus for measuring leakage current in an electrical apparatus, comprising: an arithmetic means for calculating a leakage current flowing in a ground insulation resistance of the electrical apparatus. The calculation means uses the values of the ground voltage (E + E0), the zero phase current I0, the phase difference θ, and the rated ground voltage V0 of the electric device, and is derived from the ground insulation resistance from the following equation (1). The leakage current measuring apparatus according to claim 1, wherein the leakage current Igr is calculated.
Igr = I0 × cos θ × V0 / (E + E0) (1)   The ground voltage, the zero-phase current measurement, and the measurement for calculating the phase difference are performed for each phase in a time zone in which the ground voltage value or the leakage current value due to the ground insulation resistance is maximum. The leakage current measuring device according to claim 1, wherein the leakage current measuring device is performed once.   The ground voltage, the zero-phase current measurement, and the measurement for calculating the phase difference are performed for each phase in a time zone in which the ground voltage value or the leakage current value due to the ground insulation resistance is maximum. And the leakage current caused by the ground insulation resistance is calculated on the condition that the absolute value of the phase difference calculation value is in the range of 0 to 90 degrees or 0 to ¼ cycle. Item 2. The leakage current measuring device according to Item 1.   5. The leakage current according to claim 4, wherein the leakage current caused by the ground insulation resistance is calculated for each phase, and the total value obtained is calculated as the value of the leakage current caused by the ground insulation resistance. measuring device.   6. The leakage current measuring device according to claim 3, wherein a calculation is performed to correct a leakage current value caused by the ground insulation resistance by a coefficient related to a frequency value of the ground voltage. .   7. The leakage current measuring device according to claim 1, further comprising alarm means for issuing an alarm when the value of the leakage current calculated by the calculation means exceeds a predetermined value. .   The leakage current measurement according to any one of claims 1 to 7, further comprising a blocking means for cutting off the electric circuit when the value of the leakage current calculated by the calculation means exceeds a predetermined value. apparatus.   2. The leakage current measuring apparatus according to claim 1, wherein the signal processing means calculates the phase difference and converts the ground voltage value and the zero-phase current value of each phase of the switching power supply into an effective value. . A ground voltage measurement process for measuring a ground voltage of each of the three phases of the switching power source that drives the electric device;
A zero-phase current measurement step of measuring a zero-phase current that is a ground leakage current flowing through an electric device including an electric wire and / or an electric motor fed from the switching power supply;
A signal processing step for calculating a phase difference between the ground voltage of each phase measured by the ground voltage measurement step and the zero phase current measured by the zero phase current measurement step;
From the phase difference calculated by the signal processing step, the ground voltage measured by the ground voltage measurement step, the zero phase current measured by the zero phase current measurement step, and the rated ground voltage of the electrical device. And a calculation step of calculating a leakage current flowing through the ground insulation resistance of the electric device.   The measurement of the ground voltage, the zero-phase current, and the calculation of the phase difference are performed a plurality of times for each phase in a time zone in which the leakage voltage value due to the ground voltage value or the ground insulation resistance is maximum. The leakage current measuring method according to claim 10.