JP2018021812A - Device and method for measuring leakage current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leakage current measurement device which can easily and accurately detect a leakage current flowing in a measurement target electric wire without being affected by noise, for example.SOLUTION: Processing means 13 of a leakage current measurement device 1 obtains an analysis window width from a phase voltage U supplied from voltage detection means 11, converts the width into phase voltage waveform data Du, converts a voltage signal Ui supplied from current detection means 12 into current waveform data Di, Fourier-transforms the data, determines a fundamental real part Uand an imaginary part Uof the phase voltage waveform data Du and a fundamental real part Ioand an imaginary part Ioof the current waveform data Di, and calculates the following expression (1). [mathematical expression 1]SELECTED DRAWING: Figure 1

Description

  The present invention relates to a leakage current measuring method for measuring a leakage current Ior of an insulation resistance in a measured distribution line by using a single-phase two-wire distribution line consisting of a hot side L phase and a ground side N phase as a measured distribution line, and The present invention relates to a leakage current measuring apparatus to which this method is applied.

  In the distribution system, the insulation state is regularly measured to prevent leakage fire. Conventionally, when inspecting the insulation state of a power distribution system, a method of measuring the insulation resistance of a cable or facility after a power failure has been widely used.

  However, the insulation state cannot be inspected by such a method in a distribution facility where a power failure is not permitted or a factory requiring continuous operation. For this reason, a leak tester or the like that can measure the leakage current of the distribution line even in a live line state may be used. However, when the leakage current is measured by a leak tester or the like, due to the measurement principle, the measured leakage current (synthetic leakage current Io) usually exists between the voltage application portion and the ground portion of the distribution system. A large amount (invalid leakage current Ioc) due to the influence of the current flowing through the ground capacitance was included, and it was not possible to accurately measure only the leakage current (effective leakage current Ior) of the insulation resistance originally desired.

  Furthermore, load devices such as LED lighting with rectifier circuits and variable speed devices for industrial motors may be connected to recent power distribution systems. Inverter noise or the like generated from the apparatus is always superimposed on the combined leakage current Io, which also causes an error.

  Therefore, a leakage current measuring device has been proposed that uses a filter circuit (low-pass filter) to remove harmonics and inverter noise that are superimposed on the combined leakage current Io (see, for example, Patent Document 1 and Patent Document 2). ).

  Also, a leakage current measuring method that directly calculates the leakage current Ior of the insulation resistance from the combined leakage current Io by vector synthesis by the combined calculation of the fundamental wave component and the harmonic component or two types of harmonic components using Fourier transform processing. Has proposed a leakage current monitoring device that obtains a more accurate leakage current and monitors the leakage current (see, for example, Patent Document 3).

  Alternatively, the combination of the relative phase of the voltage fundamental wave component and the leakage current fundamental wave component and the leakage current fundamental wave component using Fourier transform processing, and the vector synthesis of the leakage current Ior of the insulation resistance from the combined leakage current Io A leakage current detection method to be calculated has been proposed (see, for example, Patent Document 4).

JP 2001-215247 A Japanese Patent No. 3996119 Japanese Patent No. 4167872 JP 2010-190645 A

  However, since the leakage current measuring devices described in Patent Literature 1 and Patent Literature 2 are configured to attenuate frequency components outside the cutoff frequency band, harmonics and noise components superimposed on the combined leakage current Io are not present. When the frequency is close to the power supply frequency band (fundamental frequency band), it cannot be completely removed, and thus it cannot be said that the accurate leakage current Ior of the insulation resistance can be measured.

  In addition, in the leakage current measuring devices described in Patent Document 3 and Patent Document 4, in order to calculate the leakage current Ior of the insulation resistance by vector synthesis, generally complicated calculation processing is necessary, and the calculation load is large.

  Therefore, the present invention accurately and easily determines the leakage current Ior of the insulation resistance flowing in the distribution line to be measured without being affected by harmonics from LED lighting or inverter noise generated from a variable speed device of an industrial motor. It is an object of the present invention to provide a required leakage current measuring method and leakage current measuring apparatus.

In order to solve the above-described problems, the invention according to claim 1 is directed to a single-phase two-wire distribution line including a hot side L phase and a ground side N phase as a measured distribution line, and insulation in the measured distribution line. A leakage current measuring method for measuring a leakage current Ior of a resistance, a voltage detecting step for detecting a phase voltage U between an N phase and an L phase of the distribution line to be measured, and a combined leakage current Io flowing through the distribution line to be measured A current detection step for detecting the phase voltage U, an analysis window width is obtained from the phase voltage U, and the fundamental real part U _1r and imaginary part U _{1i of} the phase voltage U and the combined leakage current Io of the phase voltage U are obtained using Fourier transform. A first calculation step for obtaining a fundamental wave real part Io _1r and an imaginary part Io _1i and a second calculation step for obtaining a leakage current Ior of the insulation resistance based on the following equation (1) are performed: To do.

Further, in the invention according to claim 2, a single-phase two-wire distribution line composed of a hot side L phase and a ground side N phase is used as a measurement distribution line, and a leakage current Ior of an insulation resistance in the measurement distribution line is measured. A leakage current measuring device that detects a phase voltage U between the N phase and the L phase of the distribution line to be measured, and a current detection unit that detects a combined leakage current Io flowing through the distribution line to be measured. The analysis window width is obtained from the phase voltage U, and the fundamental wave real part U _1r and the imaginary part U _{1i of} the phase voltage U and the fundamental wave real part Io _{1r of the} combined leakage current Io are obtained using Fourier transform. And processing means for performing a first calculation process for obtaining an imaginary part Io _1i and a second calculation process for obtaining a leakage current Ior of the insulation resistance based on the following equation (1).

  The invention according to claim 3 is the leakage current measuring device according to claim 2, wherein the processing means compares the measured leakage current Ior with a predetermined insulation state determination standard value, A discrimination process for discriminating an insulation state of the distribution line to be measured is performed.

According to the leakage current measuring method according to claim 1 and the leakage current measuring apparatus according to claim 2, harmonics caused by LED illumination, which is noise close to the power supply frequency band (fundamental frequency band), and industrial motors are possible. Even when inverter noise generated from the transmission is always superimposed on the combined leakage current Io, the analysis window width of the Fourier transform is obtained from the phase voltage U between the N phase and the L phase of the distribution line to be measured, and Fourier From the fundamental wave real part U _1r and imaginary part U _{1i of} the phase voltage U obtained by conversion, and the fundamental wave real part Io _1r and imaginary part Io _{1i of the} combined leakage current Io, a relatively simple expression (1) is obtained. The leakage current Ior of the insulation resistance can be obtained by calculation. Therefore, the leakage current Ior flowing through the ground insulation resistance can be accurately and easily obtained.

  In addition, since the leakage current measuring apparatus according to claim 3 has a function of discriminating the insulation state of the distribution line to be measured for which leakage current has been measured, the convenience of the apparatus user can be further enhanced.

It is a schematic block diagram of the state which connected the leakage current measuring apparatus to which the leakage current measuring method which concerns on this invention was applied to the distribution line to be measured. It is a vector diagram for demonstrating the measurement principle about the leakage current Ior of an insulation resistance.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration in which a leakage current measuring device 1 is connected to a distribution line of an AC power supply 2.

  The leakage current measuring apparatus 1 includes at least a voltage detection unit 11, a current detection unit 12, a processing unit 13, a storage unit 14, and a display unit 15. For example, the distribution line Ln connected to the N terminal of the AC power source 2 and an AC The distribution line Lu connected to the terminal L of the power source 2 is used as a measured distribution line, and the leakage current Ior of the insulation resistance of the measured distribution line is measured. The AC power supply 2 has an N-phase in which one of the low-voltage side single-phase windings 21 of the transformer is grounded and is connected to the N terminal, and the other of the low-voltage side single-phase windings 21 is a hot-side L Phase and connected to the L terminal.

  As an example, the AC power source 2 generates a single-phase AC voltage having a commercial frequency (phase voltage U between the N phase and the L phase) and outputs the generated phase voltage U from the terminal L. Thus, the AC power supply 2 can output the phase voltage U to the terminal L to which the distribution line Lu is connected, and supply the phase current I to the load 3 connected to the distribution line Lu. In addition, a ground capacitance C and a ground leakage resistance R exist between the distribution line Lu of the AC power supply 2 and the ground, as shown in FIG.

  The voltage detection means 11 is connected to the distribution lines Ln and Lu via a pair of voltage detection probes 16a and 16b, detects the phase voltage U via the pair of voltage detection probes 16a and 16b, and outputs it to the processing means 13 To do.

  The current detection means 12 obtains the phase current I flowing through the distribution lines Ln and Lu and the capacitance C to ground via the current transformer type current detection probe 4 attached to the distribution lines Ln and Lu in a predetermined direction. Leakage current that flows to ground via Ioc (hereinafter also referred to as “invalid leakage current”) Ioc, leakage current that flows to ground via ground resistance R (hereinafter also referred to as “effective leakage current”) Ior Io is detected, converted into a voltage signal Ui, and output to the processing means 13. The phase current I flowing in the load 3 flows in the opposite direction in each of the distribution lines Ln and Lu as shown by two types of dotted lines in FIG. 1 (each flows in the current detection probe 4 in the opposite direction). Therefore, when the current is detected by the current detection probe 4, the phase current I flowing through the distribution lines Ln and Lu is canceled, and the combined leakage current obtained by combining the reactive leakage current Ioc and the effective leakage current Ior. Only Io is detected by the current detection probe 4.

  The processing means 13 can be composed of, for example, one comparator, two anti-aliasing filters and an A / D converter, and an FPGA and CPU for calculation. That is, the processing means 13 obtains an analysis window width for 10 cycles if the phase voltage U supplied from the voltage detection means 11 is a frequency of 50 Hz, and 12 cycles if the frequency is 60 Hz, The A / D converter converts the phase voltage waveform data Du into phase voltage waveform data Du, and converts the voltage signal Ui supplied from the current detection means 12 into current waveform data Di with the other A / D converter. .

Further, the processing means 13 performs Fourier transform based on the phase voltage waveform data Du and the current waveform data Di, respectively, and the fundamental wave real part U _1r and imaginary part U _{1i of} the phase voltage waveform data Du and the current waveform data Di. A first calculation process for _{obtaining the} fundamental wave real part Io _1r and the imaginary part Io _1i is executed. Further, the processing means 13 executes a second calculation process for calculating (measuring) the leakage current Ior of the insulation resistance for the distribution line Lu based on the following formula (1).

  Next, with reference to FIG. 2, the calculation basis of the above equation (1) will be described. In order to facilitate understanding of the basis for calculating equation (1), the phase voltage U is indicated by a broken line in FIG. , And the angle when rotated counterclockwise with respect to the paper surface.

  The reactive leakage current Ioc for the distribution line Lu is advanced by 90 ° in phase with respect to the effective leakage current Ior (the same phase (0 °) as the phase voltage U). The combined leakage current Io of the leakage currents Ioc and Ior is expressed as Io = Ioc + Ior as a vector sum. Since the effective leakage current Ior exists on the same angle (0 °) as the phase voltage U as described above, the combined leakage current Io starts from 0 ° with respect to the phase voltage U as shown in FIG. It exists in the range up to 90 degrees.

  When noise or the like is not superimposed on the combined leakage current Io and is an ideal sine wave, the effective leakage current Ior is obtained as a cosine of the combined leakage current Io as can be seen from FIG. Io × cos θ (2) ”.

  Here, when the active power of the AC circuit is P, the phase voltage is U, the load current is the combined leakage current Io, and the phase angle (power factor angle) between the voltage and the load current is cos θ, the active power P is “P = U × Io × cos θ (3) ”. Then, when the active power P in the equation (3) is divided by the phase voltage U, “P ÷ U = Io × cos θ” is obtained, and when the above equation (2) is applied thereto, “Ior = P ÷ U (4)”. Therefore, only the effective leakage current Ior can be obtained from the effective power P and the phase voltage U.

Next, the fundamental wave active power P ₁ is generally calculated using the fundamental wave real part U _1r and imaginary part U _1i of the phase voltage waveform data Du, and the fundamental wave real part Io _1r and imaginary part Io _{1i of} the current waveform data Di. The effective power of a typical AC circuit is expressed by fitting it to an equation for obtaining a complex number, so that “P ₁ = | U _1r × Io _1r + U _1i × Io _1i | (5)”, and the fundamental phase voltage U ₁ is Equation (6) is obtained.

  That is, when the formulas (5) and (6) are applied to the above formula (4), the above formula (1) is obtained.

  In addition, since the above formula (1) is intended to calculate only the fundamental wave after Fourier transform, harmonics due to LED illumination, which is noise close to the power supply frequency band (fundamental frequency band), and the variable speed of industrial motors. Even if inverter noise generated from the apparatus is always superimposed on the combined leakage current Io, measurement is not affected, and there is no need to provide a separate filter circuit for removing harmonics.

  Thus, the processing means 13 can accurately detect the leakage current Ior flowing through the ground insulation resistance by performing the calculation of the equation (1).

The storage means 14 can be composed of a semiconductor memory such as a ROM or a RAM, and the above-described operation program for the processing means 13, the expression (1) for calculating the effective leakage current Ior, and the insulation state for the effective leakage current Ior. A discrimination standard value Iref (for example, 1 mA) or the like is stored in advance. The storage means 14 is used as a temporary storage area by the processing means 13, and the phase voltage waveform data Du calculated by the processing means 13, the fundamental wave real part U _1r and the imaginary part U _{1i of the} phase voltage U. The current waveform data Di, the fundamental wave real part Io _1r and the imaginary part Io _{1i of} the combined leakage current Io are stored and read out as necessary.

  The display means 15 may be constituted by a display device such as a display device (for example, LCD), or may be constituted by an analog meter, a segment type digital display, or the like. By this display means 15, the measured value of the leakage current obtained by the processing means 13 and the determination result of the insulation state are displayed visually. It should be noted that a function for outputting the measurement value and the determination result by voice synthesis may be provided separately, or an alarm device may be provided in place of the display means 15 so that an insulation abnormality alarm is generated using sound or light emission. Anyway.

  Subsequently, the operation of the leakage current measuring apparatus 1 having the above-described configuration will be described. In order to perform measurement by the leakage current measuring device 1, a pair of voltage detection probes 16a and 16b is connected to the distribution lines Ln and Lu in advance, and the current detection probe 4 is predetermined to the distribution lines Ln and Lu. It is assumed that it is installed.

  In the operating state of the leakage current measuring apparatus 1, the voltage detection means 11 detects the phase voltage U via the pair of voltage detection probes 16 a and 16 b and outputs it to the processing means 13. The current detection means 12 detects the combined leakage current Io flowing through the distribution lines Ln and Lu via the current transformer type current detection probe 4, converts it into a voltage signal Ui, and outputs it to the processing means 13.

  First, the processing means 13 receives the input of the phase voltage U and the voltage signal Ui, and if the phase voltage U is a commercial frequency of 50 Hz, the analysis window width is 10 cycles, and if the commercial frequency is 60 Hz, the analysis window width is 12 cycles. Is obtained by the comparator, and at the same time, A / D conversion processing is executed to convert the phase voltage U into the phase voltage waveform data Du and store it in the storage means 14, and the voltage signal Ui is converted into the current waveform data Di. And stored in the storage means 14.

Next, the processing means 13 executes a first calculation process. The first calculation process is based on the phase voltage waveform data Du and the current waveform data Di, respectively, and Fourier transform is performed. The fundamental real part U _1r and imaginary part U _{1i of} the phase voltage waveform data Du and the current waveform data Di are This is a process for calculating the fundamental wave real part Io _1r and the imaginary part Io _1i . U _1r , U _1i , Io _1r , Io _1i calculated by the first calculation process are also stored in the storage unit 14.

Finally, the processing means 13 executes the second calculation process. This 2nd calculation process is a process which calculates the leakage current based on the above Formula (1). In executing the second arithmetic processing, the processing means 13 firstly, the fundamental wave real part U _1r and imaginary part U _{1i of} the phase voltage waveform data Du, and the fundamental wave real part Io _1r and imaginary part Io _{1i of the} current waveform data Di. And the expression (1) is read from the storage means 14. Subsequently, the processing means 13 substitutes the fundamental wave real part U _1r and the imaginary part U _1i of the phase voltage waveform data Du and the fundamental wave real part Io _1r and the imaginary part Io _1i of the current waveform data Di into the equation (1). Thus, the effective leakage current Ior for the distribution lines Lr and Lt is calculated (measured).

  In addition, the processing means 13 shown in this embodiment shall perform the discrimination | determination process which discriminate | determines an insulation state from the value of the calculated | required leakage current. In this determination process, the processing unit 13 reads the insulation state determination standard value Iref for the effective leakage current Ior from the storage unit 14 and compares the calculated effective leakage current Ior with the insulation state determination standard value Iref to determine effective leakage. When the current Ior is equal to or greater than the standard value Iref, together with the calculated effective leakage current Ior, a determination result indicating that the effective leakage current Ior equal to or greater than the insulation state determination standard value Iref is generated (that the insulation state is defective) is displayed It is displayed on the means 15. On the other hand, when the effective leakage current Ior is less than the insulation state determination standard value Iref, together with the calculated effective leakage current Ior, a determination result indicating that the effective leakage current is less than the standard value (that the insulation state is good) is displayed. 15 is displayed.

Thus, according to the leakage current measuring apparatus 1 according to the present embodiment, the fundamental wave real part U _1r and the imaginary part U _{1i of} the phase voltage waveform data Du, and the fundamental wave real part Io _1r and the imaginary part of the current waveform data Di. Based on Io _1i and equation (1), the leakage current (effective leakage current) Ior of the insulation resistance for the distribution line Lu connected to the terminal L of the single-phase two-wire AC power supply 2 can be accurately measured. it can.

  Further, according to the leakage current measuring apparatus 1 of the present embodiment, the measured effective leakage current Ior and the insulation state determination standard value Iref defined in advance are compared by the processing means 13, and the insulation state determination which is the comparison result is determined. By displaying the result on the display unit 15, the user of the leakage current measuring device 1 can be surely and easily notified of the quality of the insulation state of the distribution line Lu.

  Further, when a breaker is separately provided in the distribution line Lu and the breaker can be cut off by a control signal from the outside, the control signal line of the breaker and the leakage current measuring device 1 are connected and insulated. When the resistance is inspected and the result of determination of the insulation state is output by the processing means 13, an operation command is output to the circuit breaker via the control signal line, so that the circuit breaker control function for quickly operating the circuit breaker is processed. If it is given to 13, it is possible to reliably prevent accidents caused by electric leakage.

  In the leakage current measuring apparatus 1 of the present embodiment, the processing unit 13 compares the measured effective leakage current Ior with the insulation state determination standard value Iref, and determines and notifies the insulation state. The function is additional. Therefore, a leakage current measuring device that only displays the measured effective leakage current Ior on the display means 15 may be used. As described above, even if the leakage current measuring device does not have an insulation state discriminating function, since the measured effective leakage current Ior is displayed on the display means 15, the effective leakage current Ior for the distribution line is measured as a leakage current measurement. The user of the apparatus can be informed, and if the user himself compares with the insulation state determination standard value Iref, the insulation state of the distribution line can be determined.

  As mentioned above, although the embodiment of the leakage current measuring device to which the leakage current measuring method according to the present invention is applied has been described with reference to the accompanying drawings, the present invention is not limited to this embodiment, and is within the scope of the claims. You may implement by diverting well-known existing equivalent technical means in the range which does not change the structure of description.

DESCRIPTION OF SYMBOLS 1 Leakage current measuring apparatus 11 Voltage detection means 12 Current detection means 13 Processing means 14 Storage means 15 Display means

Claims (3)

A leakage current measuring method for measuring a leakage current Ior of an insulation resistance in a measured distribution line, using a single-phase two-wire distribution line composed of a hot side L phase and a ground side N phase as a measured distribution line,
A voltage detection step of detecting a phase voltage U between the N phase and the L phase of the distribution line to be measured;
A current detection step of detecting a composite leakage current Io flowing through the measured distribution line;
The analysis window width is obtained from the phase voltage U, and the fundamental wave real part U _1r and imaginary part U _{1i of} the phase voltage U and the fundamental wave real part Io _1r and imaginary number of the combined leakage current Io are obtained by using Fourier transform. A first calculation step for _obtaining part Io _1i ;
A second calculation step for obtaining a leakage current Ior of the insulation resistance based on the following equation (1):
Leakage current measuring method characterized by performing.

A leakage current measuring device for measuring a leakage current Ior of an insulation resistance in a measured distribution line as a measured distribution line, a single-phase two-wire distribution line composed of a hot side L phase and a ground side N phase,
Voltage detection means for detecting a phase voltage U between the N phase and the L phase of the distribution line to be measured;
Current detection means for detecting a combined leakage current Io flowing through the measured distribution line;
The analysis window width is obtained from the phase voltage U, and the fundamental wave real part U _1r and imaginary part U _{1i of} the phase voltage U and the fundamental wave real part Io _1r and imaginary number of the combined leakage current Io are obtained by using Fourier transform. Processing means for performing a first calculation process for obtaining the part Io _1i and a second calculation process for obtaining the leakage current Ior of the insulation resistance based on the following equation (1):
A leakage current measuring apparatus comprising:

  The said processing means performs the discrimination | determination process which compares the measured leakage current Ior with the insulation state discrimination | determination standard value prescribed | regulated previously, and discriminate | determines the insulation state about the said to-be-measured distribution line. 2. The leakage current measuring device according to 2.

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