JP2011027449A - Leakage current measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a leakage current of two distribution wires for taking-out and forming a single phase from three phases. <P>SOLUTION: A leakage current measuring device 1 which measures the leakage current (composite effective leakage current) Ior flowing through insulation resistances, concerning two distribution wires Lu and Lv in a three-phase three-wire system distribution line formed in Y connection includes: a voltage detection unit 2 for detecting the phase-to-phase voltage Vvu between the two distribution wires Lu and Lv; a current-voltage conversion unit 3 for detecting the composite current (composite leakage current) Io of the currents flowing through the two distribution wires Lu and Lv; and a processing unit 4 for calculating the difference θ in phase between the phase-to-phase voltage Vvu and the composite leakage current Io, and the value (Io) of the composite leakage current Io, and measuring the leakage current Ior on the basis of Ior=¾2×Io×sinθ¾. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a leakage current measuring device used for insulation inspection of a three-phase three-wire distribution line.

  As this type of leakage current measuring apparatus, a leakage current measuring apparatus (leakage current measuring apparatus) disclosed in Patent Document 1 below is known. In this leakage current measuring device, the voltage measuring means sequentially inputs and measures the line voltage or ground voltage of each phase of the power supply of the star distribution system, and the zero phase current measuring means is connected to the distribution line and this distribution line from the power supply. Star-shaped (Y-type) distribution measured by voltage measuring means from the zero-phase current measured by the zero-phase current measuring means by the signal processing means by measuring the zero-phase current flowing through the electrical equipment as the load equipment. An effective component that is a component in the same phase as the line voltage or ground voltage input to the system power supply and an effective component and an invalid component with a phase difference of 90 degrees are calculated for each input voltage sequentially, and the calculation means outputs a signal The effective component and invalid component for each voltage of the zero-phase current calculated by the processing means, the value of the zero-phase current and the voltage input by the voltage measuring means or the set voltage value to the ground of the distribution line and electrical equipment It calculates a leakage current flowing through the edge resistance.

  In this case, in the star distribution power supply, when a voltage is applied to the grounded capacitance in a balanced state, the current flowing through the grounded capacitance of each phase has the same magnitude and a phase difference of 120 degrees, resulting in a three-phase The current value of the current flowing through the ground capacitance obtained by summing the minutes is zero. On the other hand, if a leakage current that flows through the ground insulation resistance occurs as a result of insulation deterioration, the combined value of this current and the current flowing through the ground capacitance is measured as a zero-phase current that is the sum of the leakage currents. Since the combined value of the current flowing through the capacitance is 0, the leakage current flowing through the ground insulation resistance is calculated by the above calculation. Therefore, in this leakage current measuring device, the leakage current flowing through the ground insulation resistance of the star-type distribution system distribution line and the electrical equipment connected thereto can be detected safely in a state with little error while being energized. .

JP 2009-145122 A (page 5, FIG. 2)

  By the way, the currently proposed leakage current measuring device for a three-phase three-wire distribution line only measures a zero-phase current, which is the sum of currents for three phases, like the leakage current measuring device described above. Since there is no leakage current measuring device that can measure the leakage current of two distribution lines that are configured by taking out a single phase from three phases, such a single-phase distribution line There has been a problem to be solved that the leakage current cannot be measured.

  The present invention has been made in view of such problems, and it is a main object of the present invention to provide a leakage current measuring apparatus capable of measuring leakage current of two distribution lines configured by taking out a single phase from three phases. And

In order to achieve the above object, the leakage current measuring apparatus according to claim 1 is configured to measure a leakage current Ior of an insulation resistance of any two distribution lines in a three-phase three-wire distribution line constituted by Y connection. A measuring device for detecting a phase voltage between the two distribution lines; a current detection unit for detecting a combined current of currents flowing through the two distribution lines; and the interphase voltage and the combined current And a processing unit for calculating the leakage current Ior based on the following formula (1).
Ior = | 2 × Io × sin θ | (1)

  The leakage current measuring device according to claim 2 is the leakage current measuring device according to claim 1, wherein the processing unit compares the measured leakage current Ior with a predetermined standard value, Determine the insulation state for one distribution line.

  Further, the leakage current measuring apparatus according to claim 3 is the leakage current measuring apparatus according to claim 1 or 2, wherein the processing unit compares the phase difference θ with a predetermined angle range that is defined in advance. An error is displayed on the display when the angle is out of the range.

  According to the leakage current measuring apparatus of the first aspect, the interphase voltage between any two distribution lines and the combined current (phase current of the two distribution lines) in a three-phase three-wire distribution line constituted by Y connection. Since this is canceled out, the combined reactive leakage current and the combined effective leakage current become a combined leakage current (the combined leakage current) and Io, the combined current Io and the above equation (1) based on this It is possible to accurately measure the leakage current (synthetic effective leakage current) Ior of the insulation resistance for the two distribution lines.

  According to the leakage current measuring apparatus of claim 2, the processing unit compares the measured combined effective leakage current Ior and a predetermined standard value to determine the insulation state between the two distribution lines. By displaying the result of this determination on the display unit or the like, the operator of the leakage current measuring device can reliably and easily recognize the quality of the insulation state of the two distribution lines.

  Further, according to the leakage current measuring device of claim 3, when the phase difference θ is outside the prescribed angle range defined in advance, the processing unit displays an error on the display unit. The two distribution lines are misconnected to terminals other than the three-phase terminals to be originally connected in the low-voltage side three-phase winding, or each of these current detection probes for measuring, for example, the combined current of the two distribution lines It is possible to reliably and easily recognize that the mounting direction to the distribution line may be wrong.

1 is a configuration diagram showing a configuration of a leakage current measuring device 1. FIG. It is a vector diagram for demonstrating the measurement principle about the leakage current (synthetic effective leakage current) Ior of an insulation resistance (when only Ioru exists). It is a vector diagram for demonstrating the measurement principle about the leakage current (synthesis effective leakage current) Ior of an insulation resistance (when only Iorv exists).

  Hereinafter, the best mode of a leakage current measuring apparatus will be described with reference to the accompanying drawings.

  First, the configuration of the leakage current measuring apparatus 1 will be described with reference to the drawings.

  1 includes a voltage detection unit 2, a current detection unit 3, a processing unit 4, a storage unit 5, and an output unit 6. For example, a low-voltage side three-phase winding 11 of a transformer has a Y shape. Insulation resistance leakage current (hereinafter also referred to as “composite effective leakage current”) Ior for two distribution lines Lu and Lv connected to the three-phase terminals U and V of the AC power supply 12 connected to Has been. In this case, as an example, the AC power supply 12 generates a three-phase AC voltage of commercial frequency (phase voltages Vu, Vv, Vw whose phases are shifted by 120 ° with respect to the neutral point N) and the generated phase voltage. Vu, Vv, and Vw are output from the three-phase terminals U, V, and W. With this configuration, the AC power supply 12 outputs an interphase voltage Vvu between the three-phase terminals U and V to which the distribution lines Lu and Lv are connected, and a phase is applied to the load 14 connected between the distribution lines Lu and Lv. A current Ivu is supplied. In this example, as an example, a grounding capacitor 13 is connected to each of the three-phase terminals U, V, W of the AC power supply 12. A ground capacitance Cu and a ground leakage resistance Ru exist between the distribution line Lu and the ground, and a ground capacitance Cv and a ground leakage resistance Rv exist between the distribution line Lv and the ground. Yes.

  As shown in FIG. 1, the voltage detection unit 2 is connected to the distribution lines Lu and Lv via a pair of voltage detection probes 21 and 21. Further, the voltage detection unit 2 detects the interphase voltage Vvu via the pair of voltage detection probes 21, 21 and outputs it to the processing unit 4. The current detection unit 3 obtains the phase current Ivu flowing through the distribution lines Lu and Lv and the ground capacitance Cu through the current transformer type current detection probe 22 attached to the distribution lines Lu and Lv in a predetermined direction. Leakage current (hereinafter also referred to as “invalid leakage current”) Iocu via the ground, leakage current flowing to ground via the ground leakage resistance Ru (hereinafter also referred to as “effective leakage current”) Ioru, ground electrostatic A leakage current flowing to the ground via the capacitance Cv (hereinafter also referred to as “invalid leakage current”) Iocv and a leakage current flowing to the ground via the ground leakage resistance Rv (hereinafter also referred to as “effective leakage current”) Iorv The combined leakage current Io is detected and converted into a voltage signal Vi and output to the processing unit 4. In this case, the phase current Ivu flowing in the load 14 flows in the opposite direction (flows in the current detection probe 22 in the opposite direction) to the distribution line Lu and the distribution line Lv, as shown in FIG. For this reason, when the current is detected by the current detection probe 22, the phase current Ivu flowing through the two distribution lines Lu and Lv is canceled out, so that the current detected by the current detection probe 22 is the above two invalid leakage currents Iocu and Iocv. And two effective leakage currents Ioru and Iorv are combined leakage current Io.

For example, the processing unit 4 includes two A / D converters and a CPU (both not shown). With this configuration, the processing unit 4 converts the interphase voltage Vvu output from the voltage detection unit 2 into the interphase voltage waveform data Dv by one A / D converter, and also outputs the voltage signal Vi output from the current detection unit 3. Is converted into current waveform data Di by the other A / D converter, and A / D conversion processing to be stored in the storage unit 5 is executed. Further, the processing unit 4 calculates a combined leakage current Io based on the current waveform data Di, and calculates the interphase voltage Vvu and the combined leakage current Io based on the interphase voltage waveform data Dv and the current waveform data Di. And a phase difference calculation process for calculating a phase difference θ between them. In addition, the processing unit 4 calculates (measures) a leakage current that calculates (measures) a combined effective leakage current Ior of the insulation resistance (the combined current of the effective leakage currents Ioru and Iorv) on the distribution lines Lu and Lv based on the following formula (1). Execute the calculation process.
Ior = | 2 × Io × sin θ | (1)
| X | indicates the absolute value of the numerical value x.

  Hereinafter, the calculation basis of the above formula (1) will be described with reference to FIGS.

  In the configuration in which the AC voltage is supplied from the AC power source 12 in which the low-voltage side three-phase winding 11 is connected to the Y shape via the distribution line, when the insulation failure occurs, it is connected to the three-phase terminals U, V, and W. It is known that the insulation state of one of the distribution lines is significantly deteriorated, and the other two distribution lines are mostly healthy. Therefore, as shown in FIG. 1, insulation failure is also caused in the two distribution lines Lu and Lv connected to the three-phase terminals U and V of the AC power source 12 in which the low-voltage side three-phase winding 11 is connected in a Y shape. When it occurs, it is considered that the insulation state of one of the distribution lines is significantly deteriorated, and the other distribution line is healthy. That is, it is considered that the effective leakage current that occurs when insulation failure occurs in the two distribution lines Lu and Lv (when the insulation state deteriorates) is only one of the effective leakage currents Ioru and Iorv. . Further, it is considered that the ground capacitances Cu and Cv of the distribution lines Lu and Lv exist in a balanced state regardless of whether or not insulation failure occurs. In other words, the reactive leakage currents Iocu and Iocv are considered to have the same current value.

  First, the case where only the effective leakage current Ioru has occurred and an insulation failure has occurred (when an insulation failure has occurred in the distribution line Lu) will be described with reference to FIG. The effective leakage current Iorv that has not occurred is indicated by a broken line. The phase voltages Vu, Vv, Vw and the interphase voltage Vvu are also shown by broken lines in order to facilitate understanding of the invention. In the following, the angle of each vector is expressed as an angle when rotated counterclockwise with the interphase voltage Vvu as a reference (0 °).

  As shown in FIG. 2, the reactive leakage current Iocu for the distribution line Lu is 90 ° ahead of the effective leakage current Ioru (the same phase (330 °) as the phase voltage Vu), and the distribution line Lv. The reactive leakage current Iocv is advanced by 90 ° with respect to the effective leakage current Iorv (the same phase (210 °) as the phase voltage Vv). Further, as described above, the current values of both reactive leakage currents Iocu and Iocv are the same. Therefore, the combined reactive leakage current Ioc of both reactive leakage currents Iocu and Iocv is in phase (0 °) with the interphase voltage Vvu. In this case, the combined leakage current Io of the leakage currents Iocu, Ioru, Iocv, and Iorv is zero, and the combined reactive leakage current of the reactive leakage currents Iocu and Iocv is Ioc. Is expressed as Io = Ioc + Ioru. Since the effective leakage current Ioru exists on the same angle (330 °) as the phase voltage Vu as described above, the combined leakage current Io starts from 330 ° with reference to the interphase voltage Vvu as shown in FIG. It will be in the range of 30 ° up to 360 °.

  Here, the length of the perpendicular line a drawn from the tip of the combined leakage current Io onto the virtual straight line L1 having the same phase as the interphase voltage Vvu is | Io × sin θ |. Moreover, the length of the perpendicular line b dropped on the virtual straight line L1 from the tip of the effective leakage current Ioru is the same length as the perpendicular line a. The angle formed by the effective leakage current Ioru and the virtual straight line L1 is 30 °. Therefore, the length (current value) of the effective leakage current Ioru is represented by | 2 × b | = | 2 × Io × sin θ |. Further, since the effective leakage current Iorv for the distribution line Lv is zero, the effective leakage current Ioru becomes the combined effective leakage current Ior of the insulation resistance for the distribution lines Lu and Lv. Therefore, the above formula (1) is established.

  Next, the case where only the effective leakage current Iorv occurs and an insulation failure occurs (when the insulation failure occurs in the distribution line Lv) will be described with reference to FIG. The phase voltages Vu, Vv, Vw and the interphase voltage Vvu are indicated by broken lines.

  As shown in FIG. 3, the combined reactive leakage current Ioc of the reactive leakage currents Iocu and Iocv exists in the same state as in FIG. 2 (the same phase as the interphase voltage Vvu). Therefore, the combined leakage current Io obtained by combining the combined invalid leakage current Ioc and the effective leakage current Iorv (the same phase (210 °) as the phase voltage Vv) is based on the interphase voltage Vvu as shown in FIG. It exists in the range of 150 degrees from 210 degrees to 360 degrees. Here, the length of the perpendicular line a drawn from the tip of the combined leakage current Io onto the virtual straight line L1 having the same phase as the interphase voltage Vvu is | Io × sin θ |. Further, the length of the perpendicular line c dropped from the tip of the effective leakage current Iorv onto the virtual straight line L1 is the same length as the perpendicular line a. The angle formed by the effective leakage current Iorv and the virtual straight line L1 is 30 °. Therefore, the length (current value) of the effective leakage current Iorv is also | 2 × c | = | 2 × Io × sin θ |. In addition, since the effective leakage current Ioru is zero, the effective leakage current Iorv becomes the combined effective leakage current Ior of the insulation resistance for the distribution lines Lu and Lv. Therefore, the above formula (1) is established.

  The storage unit 5 includes a semiconductor memory such as a ROM and a RAM. Further, the storage unit 5 stores in advance an operation program for the processing unit 4, the above formula (1) for calculating the combined effective leakage current Ior, and a standard value Iref (for example, 1 mA) for the combined effective leakage current Ior. Has been. In addition, the storage unit 5 is used as a work memory by the processing unit 4 and stores interphase voltage waveform data Dv and current waveform data Di. For example, the output unit 6 includes a display device such as a display device (for example, an LCD) and is configured as a display unit. With this configuration, the output unit 6 displays the result of the leakage current calculation process performed by the processing unit 4 (the combined effective leakage current Ior) and the determination result of the insulation state.

  Subsequently, the operation of the leakage current measuring apparatus 1 will be described. It is assumed that a pair of voltage detection probes 21 and 21 are connected to the distribution lines Lu and Lv in advance, and the current detection probe 22 is attached to the distribution lines Lu and Lv in a predetermined direction.

  In the operating state of the leakage current measuring apparatus 1, the voltage detection unit 2 detects the interphase voltage Vvu via the pair of voltage detection probes 21, 21 and outputs it to the processing unit 4. The current detection unit 3 detects the combined leakage current Io flowing through the distribution lines Lu and Lv via the current transformer type current detection probe 22, converts it into a voltage signal Vi, and outputs it to the processing unit 4.

  The processing unit 4 first performs an A / D conversion process for a predetermined period or more of the commercial frequency while inputting the interphase voltage Vvu and the voltage signal Vi to convert the interphase voltage Vvu into interphase voltage waveform data Dv. The voltage signal Vi is converted into current waveform data Di and stored in the storage unit 5 while being stored in the storage unit 5. Next, the processing unit 4 executes a current calculation process, and based on the current waveform data Di stored in the storage unit 5, the current value of the combined leakage current Io (hereinafter also referred to as “current value Io”). Calculate and store in the storage unit 5. Subsequently, the processing unit 4 executes a phase difference calculation process, and based on the interphase voltage waveform data Dv and the current waveform data Di stored in the storage unit 5, between the interphase voltage Vvu and the combined leakage current Io. Is calculated and stored in the storage unit 5.

  Finally, the processing unit 4 executes a leakage current calculation process. In this leakage current calculation process, the processing unit 4 first reads out the current value Io, the phase difference θ and the above equation (1) of the combined leakage current Io from the storage unit 5, and calculates the current value Io and the phase difference θ by the equation ( Substituting into 1), the combined effective leakage current Ior for the distribution lines Lu and Lv is calculated (measured). Next, the processing unit 4 reads the standard value Iref for the composite effective leakage current Ior from the storage unit 5 and compares the calculated composite effective leakage current Ior with the standard value Iref so that the composite effective leakage current Ior is the standard value. When the value is equal to or greater than Iref, the output unit 6 displays a determination result indicating that the combined effective leakage current Ior greater than the standard value Iref is generated together with the calculated combined effective leakage current Ior (that the insulation state is defective). On the other hand, the processing unit 4 compares the calculated combined effective leakage current Ior with the standard value Iref. When the combined effective leakage current Ior is less than the standard value Iref, the processing unit 4 combines the calculated combined effective leakage current Ior and the combined effective leakage current Ior. Is displayed on the output unit 6 to indicate that is less than the standard value (that the insulation state is good).

  As described above, according to the leakage current measuring apparatus 1, the Y-shaped wire is connected based on the phase difference θ between the interphase voltage Vvu and the combined leakage current Io, the combined leakage current Io, and the above equation (1). It is possible to accurately measure the leakage current (synthetic effective leakage current) Ior of the insulation resistance of the two distribution lines Lu and Lv connected to the three-phase terminals U and V of the AC power supply 12.

  Further, according to the leakage current measuring apparatus 1, the processing unit 4 compares the measured combined effective leakage current Ior with the standard value Iref defined in advance, and displays the comparison result on the output unit 6, The operator of the leakage current measuring apparatus 1 can reliably and easily recognize the quality of the insulation state of the distribution lines Lu and Lv.

  In addition, although demonstrated by giving the example which measures the synthetic | combination effective leakage current Ior of the insulation resistance about the two distribution lines Lu and Lv connected to the three-phase terminals U and V of the AC power supply 12, although not shown, the AC Even in the configuration in which the two distribution lines Lv and Lw are connected to the three-phase terminals V and W of the power supply 12 and the configuration in which the two distribution lines Lw and Lu are connected to the three-phase terminals W and U of the AC power supply 12, The phase difference θ between the interphase voltage Vwv (or Vuw) and the combined leakage current Io is measured in the same manner as measuring the combined effective leakage current Ior for the distribution lines Lu and Lv using the measuring device 1. Based on the combined leakage current Io and the above equation (1), the leakage current (synthetic effective leakage current) Ior of the insulation resistance for the distribution lines Lv, Lw and the distribution lines Lw, Lu can be measured with high accuracy. Further, it is possible to determine the insulation state by comparing the measured combined effective leakage current Ior and the standard value Iref. In addition, the processing unit 4 compares the measured combined effective leakage current Ior with the standard value Iref to determine the insulation state. However, the processing unit 4 compares the measured combined effective leakage current Ior with the standard value Iref. It is also possible to employ a configuration in which the combined effective leakage current Ior is output to the output unit 6 without doing so. Even in this configuration, since the measured combined effective leakage current Ior is output (displayed in this example) by the output unit 6, the operator of the leakage current measuring apparatus 1 determines the combined effective leakage current Ior for the two distribution lines. It is possible to know, and by comparing with the standard value Iref yourself, it is possible to determine the insulation state of the two distribution lines.

  Further, as described above, the distribution lines Lu and Lv are connected to the three-phase terminals U and V of the low-voltage side three-phase winding 11 of the transformer in the AC power supply 12, and the current detection probe 22 is connected to the distribution lines Lu and Lv. Is mounted in a predetermined orientation, the combined leakage current Io is within a range of 30 ° from 330 ° to 360 ° with reference to the interphase voltage Vvu shown in FIG. 2, and the interphase voltage shown in FIG. It always exists within the range of 150 ° from 210 ° to 360 ° with respect to Vvu, that is, within the range of 150 ° from 210 ° to 360 ° with reference to the interphase voltage Vvu. Therefore, this angle range is stored in the storage unit 5 in advance as the specified angle range θref, and the processing unit 4 specifies the phase difference θ between the interphase voltage Vvu calculated by the phase difference calculation process and the combined leakage current Io. Compared with the angle range θref, when the phase difference θ is outside the specified angle range θref, the distribution lines Lu and Lv are erroneously connected to terminals other than the three-phase terminals U and V of the low-voltage side three-phase winding 11. It is also possible to adopt a configuration in which the output unit 6 displays a display (error display) indicating that there is a possibility that the current detection probe 22 is attached to the distribution lines Lu and Lv. In addition, the two distribution lines Lv and Lw connected to the three-phase terminals V and W of the low-voltage side three-phase winding 11 and the two distribution lines Lw and Lu connected to the three-phase terminals W and U are also distributed. The electric wires Lv and Lw are based on the interphase voltage Vwv, and the distribution wires Lw and Lv are based on the interphase voltage Vuw, so that in both cases, the specified angle range θref is the same as in the case of the distribution wires Lu and Lv described above. An angle range of 150 ° from 210 ° to 360 ° can be set. For this reason, the two distribution lines Lv, Lw and the two distribution lines Lw, Lu are also three-phase of the low-voltage side three-phase winding 11 of these two distribution lines in the same manner as the distribution lines Lu, Lv. The possibility of erroneous connection to the terminals U, V, and W and the possibility of erroneous attachment of the current detection probe 22 to these two distribution lines can be determined.

  Further, although the AC power supply 12 having the configuration in which the grounding capacitor 13 is connected to each of the three-phase terminals U, V, and W has been described as an example, the AC power supply having the configuration in which the neutral point N is grounded is also leaked. The current measuring device 1 is used to measure the combined effective leakage current Ior for the two distribution lines, to determine the insulation state of the two distribution lines based on the measured combined effective leakage current Ior, Determine the possibility of incorrect connection of three distribution lines to the three-phase terminals U, V, W of the low-voltage side three-phase winding 11 and the possibility of incorrect mounting of the current detection probe 22 to these two distribution lines. Of course, it can be done.

DESCRIPTION OF SYMBOLS 1 Leakage current measuring apparatus 2 Voltage detection part 3 Current detection part 4 Processing part Ior Leakage current Iref Standard value Lu, Lv Distribution line Vvu Interphase voltage

Claims (3)

A leakage current measuring device for measuring a leakage current Ior of an insulation resistance for any two distribution lines in a three-phase three-wire distribution line constituted by Y connection,
A voltage detector for detecting an interphase voltage between the two distribution lines;
A current detection unit for detecting a combined current of currents flowing through the two distribution lines;
A leakage unit that calculates a phase difference θ between the interphase voltage and the combined current and a current value Io of the combined current and measures the leakage current Ior based on the following equation (1). Current measuring device.
Ior = | 2 × Io × sin θ | (1)   The leakage current measuring device according to claim 1, wherein the processing unit compares the measured leakage current Ior with a standard value defined in advance to determine an insulation state of the two distribution lines.   The leakage current measuring device according to claim 1, wherein the processing unit displays an error on the display unit when the phase difference θ is out of the reference angle range as compared with a predetermined angle range defined in advance.

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