JP2009069065A - Device for measuring effective leakage current - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for measuring an effective leakage current capable of detecting incorrect connection, in effective leakage current measurement for a three-phase three-line power distribution system. <P>SOLUTION: The device 10 for measuring the effective leakage current includes a leakage current input section 12 and an A/D conversion circuit 2b for detecting a combined leakage current flowing between the three-phase three-line power distribution system and a grounded point, a voltage input section 11 and an A/D conversion circuit 2a for detecting a line-to-line voltage of the power distribution system, and a calculation section 3 for calculating an effective leakage current via a resistance to earth of the power distribution system, by using the combined leakage current and the phase angle between the line-to-line voltage and the combined leakage current. The device includes a determination section 7 for determining incorrect connection of the device 10 to the power distribution system by detecting that, when a certain line-to-line voltage is captured into the device 10 as an acquired voltage, the phase angle between the acquired voltage and the combined leakage current is not within a predetermined angle range corresponding to the acquired voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an effective leakage current measuring device used for, for example, power supply line insulation inspection, and more particularly to an effective leakage current measuring device capable of detecting an erroneous connection of a measuring device in a three-phase three-wire distribution system. It is.

A power supply line monitor that analyzes and evaluates the quality of a power distribution system by measuring the fundamental wave effective value, fundamental wave phase angle, leakage current, harmonics, and the like of the power distribution system is described in Patent Document 1, for example.
FIG. 5 is a block diagram when the power supply line monitor described in Patent Document 1 is used as the effective leakage current measuring instrument 10A for a three-phase three-wire distribution system.

In FIG. 5, a, b, and c are three-phase three-wire electric circuits, R _a and R _c are ground resistances of the electric circuits a and c, C _a and C _c are ground capacitances of the electric circuits a and c, and 11 is The line voltage between the two electric circuits (for example, the line voltage V _ab between the electric circuit a and the ground electric circuit b by the B type grounding) is input as a reference voltage (also referred to as an acquired voltage) at the time of measuring effective leakage current. Rutotomoni, voltage input unit for adjusting the level of the input voltage value, ZCT synthetic leakage current is connected to a ground path b (effective leakage current, the vector sum of the invalid leakage current) zero-phase detecting an I _g current transformer , 12 is a leakage current input unit that receives the combined leakage current _{Ig and} adjusts the level thereof, 2a and 2b are A / D conversion circuits, 3 is a calculation unit (CPU) that calculates an effective leakage current, etc. Input data and calculation results of the calculation unit 3 collected via the A / D conversion circuits 2a and 2b Reference numeral 5 is a reference waveform data memory storing sin wave and cos wave reference waveform data, and 6 is an output section for displaying the result of calculation by the calculation section 3 or transmitting it to the outside.
Here, the reference waveform data has the same period as the input voltage waveform to the voltage input unit 11, and is data created in advance on the table with the same resolution as the A / D conversion circuits 2a and 2b.

Next, FIG. 6 is a vector diagram showing the principle for _{obtaining the} effective leakage current I _gr with the configuration of FIG. The effective leakage current I _gr is a vector sum of the leakage currents I _gra and I _grc flowing in the ground resistances R _a and R _c in FIG. 5 respectively, but it is rare that an insulation failure of the electric paths a and c occurs at the same time. Therefore, ground resistance _R a, the effective leakage current _{I gr} by _{R c} are ground resistance _R a, the leakage current due to either of _{R c,} that _is, I gr _{= I gra} or _I gr _{= I grc} and thinking, Good. Note that I _gra is in phase with V _ab and I _grc is in phase with V _cb .
A method for measuring the effective leakage current I _gr according to the prior art will be briefly described below with reference to FIG.

Now, assuming that the acquired voltage is V _ab , the arithmetic unit 3 in FIG. 5 firstly, the voltage V _{ab for} a predetermined wave number fetched from the voltage input unit 11 and sin wave data and cos wave in the reference waveform data memory 5. The product-sum operation is performed using the data, and the first integrated value and the second integrated value of the voltage V _ab are obtained. Similarly, the arithmetic unit 3 performs product-sum calculation using the sin wave data and combining leakage current I _g of predetermined wave number of captured from the leak current input 12, and a cos wave data, the synthetic leakage current I _g A first integrated value and a second integrated value are obtained.
Here, since the calculation method of each integrated value is not the gist of the present invention, the description thereof is omitted.

Next, a first integrated value of these voltages V _ab and synthetic leakage current I _g, by using the second integrated value, as shown in FIG. 6, the phase angle of the voltage V _ab and synthetic leakage current I _g to the reference waveform θ ₁ and θ ₂ are obtained, respectively. Then, the first integrated value of the combined leakage current I _g, the second integrated value and by using the phase angle theta _2, determine the fundamental component I _g of synthetic leakage current I _{g (1).}
When not only the effective leakage current I _gr but also the insulation resistance is obtained, in addition to the above, the voltage V _ab is calculated using the first integrated value, the second integrated value, and the phase angle θ ₁ of the voltage V _ab. The fundamental wave component V _ab (1) is obtained.

Further, the phase difference between the theta ₁ and theta _2, i.e. obtains the phase angle theta synthetic leakage current _{I g} for the voltage _{V ab.}
If the leakage currents I _gca and I _gcc due to the ground capacitances C _a and C _c are equal, the reactive leakage current I _gc, which is a vector composite value thereof, is in phase with V _ca as shown in FIG. The effective leakage current I _gr due to the ground resistances R _a and R _c is I _gr = I _gra or I _gr = I _grc as described above.

Therefore, in FIG. 6, considering that the phase difference of I _gra , I _grc , and I _gc is 60 °, the effective leakage current I _gr can be obtained by Equation 1.
[Formula 1]
I _gr = I _g (1) cos θ + I _g (1) sin θ / tan 60 °
= (2 / √3) × I _g (1) × sin (θ + 60 °)
The calculation unit 3 in FIG. 5 obtains the effective leakage current I _gr by the calculation of the above formula 1, displays the measured value together with the combined leakage current _Ig and the phase angle θ on the output unit 6, and outputs it as necessary. The data is transmitted from the unit 6 to the outside.

JP 2006-234402 A (Claims 7 and 9, paragraphs [0070] to [0078], FIG. 5 and the like)

As described above, according to the prior art, it can be obtained from the a phase angle θ the effective leakage current I _gr synthetic leakage current I _g of the fundamental wave component I _{g (1).}
However, paths a, b, the wrong connection of the voltage input section 11 with respect to c, even going calculated phase angle θ of the composite leakage current I _g for the voltage V _ab, other line voltage (e.g., V _cb ) it will seek the phase angle of the composite leakage current I _g for, as a result, the the value of the actual value of the effective leakage current I _gr computed by equation 1 has a problem that greatly different.
Here, except for the case where the electric circuits a and b to be connected are mistaken for the electric circuits c and b (that is, V _ab and V _cb are mistaken), the electric circuits a and b are connected in reverse to the erroneous connection. In this case, the polarity is wrong ( _Vab and _Vba are wrong).
Moreover, the case where the direction of the zero phase current transformer ZCT is wrong is also included.

In the single-phase three-wire and three-phase four-wire distribution systems, there is no particular problem even if the connection is incorrect as described above. However, the effective leakage current I _gr differs greatly depending on the connection. In this distribution system, it has been desired that an erroneous connection can be determined with high accuracy prior to the calculation of the effective leakage current I _gr .

  On the other hand, in the three-phase power measuring apparatus, conventional techniques that enable detection of erroneous connection of the apparatus include, for example, Japanese Patent Laid-Open No. 2000-338147 “Power Measuring Device” and Japanese Patent Laid-Open No. 2001-124806 “Three-Phase Power Measuring Device and A “three-phase watt-hour meter and its connection state determination method” and the like are known, but no function capable of determining an erroneous connection in advance as a function of an effective leakage current measuring device has been provided yet.

  Therefore, the problem to be solved by the present invention is to provide an effective leakage current measuring device capable of easily and accurately detecting misconnection when measuring effective leakage current for a three-phase three-wire distribution system. is there.

In order to solve the above-mentioned problem, the invention according to claim 1 detects a combined leakage current flowing between a three-phase three-wire distribution system and a grounding point,
Means for detecting the line voltage of the distribution system;
A phase angle between the line voltage and the combined leakage current, and a means for calculating an effective leakage current through a ground resistance of a distribution system using the combined leakage current;
In the effective leakage current measuring instrument with
When a certain line voltage is input to the measuring instrument as an acquired voltage, it is detected that the phase angle between the acquired voltage and the combined leakage current does not exist within a predetermined angle range corresponding to the acquired voltage And determining means for determining an erroneous connection of the measuring device to the power distribution system.

  The predetermined angle range has a width of 120 ° as described in claim 2 or a width of 60 ° as described in claim 3 in order to further improve the accuracy of determination of erroneous connection. It is desirable.

  Further, according to a fourth aspect of the present invention, the determination operation by the determination means may be performed with a determination of erroneous connection for each acquired voltage and combined leakage current using at least two line voltages as the acquired voltages.

According to the first, second, or fourth aspect of the invention, when the phase angle of the combined leakage current does not exist within a predetermined angle range determined according to the acquired voltage, the measuring device (voltage input) Or the combined leakage current detection means) can be determined to be misconnected. Since the determination logic in this case is relatively simple, the determination logic can be easily realized by making a slight change to the software of the existing effective leakage current measuring instrument, and there is no risk of increasing the cost.
Moreover, according to the invention which concerns on Claim 3, it becomes possible to determine an erroneous connection with still higher precision.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an effective leakage current measuring instrument 10 according to the embodiment, and the same components as those in FIG. 5 are given the same numbers.

In FIG. 1, a, b, and c are three-phase three-wire electric circuits, R _a and R _c are ground resistances of the electric circuits a and c, and C _a and C _c are ground electrostatics of the electric circuits a and c. capacity, 11 line voltage between the two paths is input as acquired voltage, the voltage input section for performing the level adjustment, ZCT detects the leakage current I _g is connected to a ground path b of B type grounding zero A phase current transformer, 12 is a leakage current input unit for adjusting the level of leakage current _Ig , and the like, and 2a and 2b are A / D conversion circuits connected to the input units 11 and 12, respectively.
Further, the arithmetic unit 3 composed of a CPU or the like receives the data stored in the memory 4 (output data of the A / D conversion circuits 2a and 2b), the reference waveform data in the reference waveform data memory 5 and the like, as in the prior art. To calculate the effective leakage current I _gr .

In this embodiment, the determination part 7 is provided in the output side of the said calculating part 3, This determination part 7 is provided with the function to detect the misconnection of the voltage input part 11 with respect to the electric circuit a, b, c. .
This erroneous connection detection function is as follows.

For example, in order to obtain voltage and V _ab, acquiring voltage preliminarily set to enable leakage current measurement device 10 as deemed proper connection in the case of V _ab. When the voltage input unit 11 is properly connected to the electrical path a, b (normal connection), the phase angle θ between the voltage V _ab and the leakage current I _g is detected by the arithmetic unit 3, shown in FIG. 2 Thus, it is in the range of 0 ° to 120 ° with the phase angle of the acquired voltage V _ab as a reference (= 0 °). The reason for this will be described below.

That is, when only the electric circuit a is deteriorated in insulation, if the reactive leakage current I _gc is ignored, I _g = I _gra (= I _gr ), that is, I _g is in phase with V _ab and θ = 0 ° Become. Further, when only the electric circuit c is deteriorated in insulation, if the reactive leakage current I _gc is ignored, I _g = I _grc (= I _gr ), that is, I _g is in phase with V _cb and θ = 60 ° Become. Here, even considering invalid leakage current I _gc, I _g is always present with a phase angle θ of more than 0 °.
On the other hand, in an ideal state where there is no insulation deterioration in the electric paths a and b, I _g = I _gc and only the reactive leakage current I _gc is obtained, and I _g is in phase with V _ca , so θ = 120 °. .

Therefore, when the voltage input unit 11 is correctly connected to the electric paths a and b and the acquired voltage at the voltage input unit 11 is V _ab , the range where θ exists is 0 ° to 120 ° as described above. . Similarly, the range where θ exists when the acquired voltage is V _bc is 120 ° to 240 ° when the phase angle of V _ab is set as a reference (= 0 °), and when the acquired voltage is V _ca 240 ° to 360 ° (0 °), 300 ° to 60 ° when the acquisition voltage is V _cb , 60 ° to 180 ° when the acquisition voltage is V _ac , 180 ° to 300 when the acquisition voltage is V _ba °.

Therefore, when the determination unit 7 detects that the phase angle θ does not exist in the range of 0 ° to 120 ° according to the acquired voltage, for example, V _ab , the electric paths a and b to which the voltage input unit 11 should originally be connected. Is not connected, or the direction in which the zero-phase current transformer ZCT is connected is wrong, and the voltage input unit 11 or the zero-phase current transformer ZCT (which cannot be specified either) is connected incorrectly. judge. If it is determined that there is an incorrect connection, a signal is sent from the determination unit 7 to the output unit 8 and an alarm is output by voice or a display (such as "Please check because the connection is incorrect"). Just let me know.

Here, FIG. 3 is a schematic diagram showing the range in which θ exists during normal connection for each acquired voltage with the phase angle of the acquired voltage as a reference (0 °). For example, when the acquired voltage is V _ab 0 ° to 120 ° where the phase angle of _ab is 0 °, and 240 ° to 360 ° (0 °) where the phase angle of V _ca is 0 ° when the acquired voltage is V _ca , θ in each normal connection It means that it is in the existence range. FIG. 4 is a table showing FIG.
As shown in FIG. 3, it can be seen that the effective leakage current I _gr becomes dominant when θ decreases in the clockwise direction, and the reactive leakage current I _gc becomes dominant when θ increases in the counterclockwise direction.

As described above, according to this embodiment, it is possible to determine the erroneous connection state of the measuring device by paying attention to the phase angle θ.
Here, in the above embodiment, as described in claim 2, a misconnection is determined based on whether or not the phase angle θ between the acquired voltage and the combined leakage current is within a range having a width of 120 °. is doing.
However, even if the connection is normal, the phase angle θ may exceed 120 ° due to the unbalance of the capacitances C _a and C _{c to} the ground, so it should be determined that the connection is normal. The angle range may be set with a width wider than 120 °.

Further, in an ideal state where there is no insulation deterioration in path, so disable leakage current I _gc of the leakage current I _g is dominant, the phase angle theta, the maximum value of the range that can be present according to the acquired voltage For example, when the acquired voltage is V _ab , θ is close to 120 °.
Accordingly, the determination angle range in the determination unit 7 is further narrowed, for example, a range of 60 ° to 120 ° with reference to the phase angle of the acquired voltage, and a case where θ is a value outside this range is determined as an erroneous connection. In addition, it is possible to improve the determination accuracy of erroneous connection in a state where there is no insulation deterioration.
That is, as described in claim 3, it is also effective to determine a misconnection by setting the width of the determination angle range to 60 °.

In this way, the angle range during normal connection when the acquired voltage is V _ab is 60 ° to 120 °, the range when V _bc is 180 ° to 240 °, and the range when V _ca is 300 ° to 360 ° (0 °), the range when V _cb is 0 ° to 60 °, the range when V _ac is 120 ° to 180 °, the range when V _ba is 240 ° to 300 °, 6 acquisitions With respect to the voltage, the angle ranges at the time of normal connection do not overlap, and it is possible to set a state in which 0 ° to 360 ° is divided into six equal parts. Thereby, it is possible to further improve the determination accuracy for determining the erroneous connection when θ does not exist within the corresponding range for each acquired voltage.

As shown in FIGS. 3 and 4, even if θ exists within a predetermined angle range corresponding to the acquired voltage, it cannot be determined that the connection is normal. For example, when the acquired voltage is V _ab and θ is in the range of 0 ° to 120 °, according to FIGS. 3 and 4, this range exists when the acquired voltage is V _cb or V _ac. There is a case of normal connection (connected to electric circuits a and b) and a case of incorrect connection (incorrect connection to electric circuits c and b, or incorrect connection to electric circuits a and c). Will get.
That is, even if θ is in the range of 0 ° to 120 °, the possibility that the voltage input unit 11 is erroneously connected to the electric circuits c and b or the electric circuits a and c cannot be denied.

Therefore, in order to improve the detection accuracy of erroneous connection, the above-described determination operation may be performed for two acquired voltages, for example, V _ab and V _cb . That is, as the first determination operation, it is determined whether or not θ is within a range of 0 ° to 120 ° with respect to the acquired voltage V _ab . It is determined whether or not θ is within a range of 300 ° to 60 ° with respect to the acquired voltage V _cb .

As a result of the second determination operation, if θ is in the range of 300 ° to 60 ° with respect to the acquired voltage V _cb , as a result, θ is in the range of 0 ° to 60 °. Therefore, there is no possibility that the acquired voltage was _Vac during the first determination operation (possibility of erroneous connection to the electric paths a and c).
When θ is not in the range of 300 ° to 60 ° with respect to the acquired voltage V _{cb as} a result of the second determination operation, θ is in the range of 60 ° to 120 °. . Therefore, there is no possibility that the acquired voltage was V _cb during the first determination operation (possibility of erroneous connection to the electric circuits c and b).

  As described above, even when the angle range for determining the erroneous connection is a predetermined angle range based on the phase angle of the acquired voltage, the determination of the erroneous connection is performed by repeatedly performing the determination operation on a plurality of acquired voltages. Accuracy can be increased.

Next, as an embodiment of the invention according to claim 4, whether it is an erroneous connection of the voltage input unit 11 or an erroneous connection of the zero-phase current transformer ZCT as a combined leakage current detection means (incorrect connection direction). A method of specifying will be described.
If the acquired voltages are V _ab and V _cb, it is determined whether or not V _cb is within a range of 60 ° ± 10 ° with respect to the acquired voltage V _ab . It is determined that the connection of the input unit 11 is normal. When V _cb does not exist within the range of 60 ° ± 10 °, it is determined that the connection of the voltage input unit 11 at that time is an incorrect connection.
If the connection is determined to be normal, or present in the range phase angle θ is 0 ° to 120 ° between one (e.g. V _ab) Synthesis leakage current I _g of the two acquired voltage If it does not exist, it is found that the zero-phase current transformer ZCT is an erroneous connection.

It is a block diagram which shows embodiment of this invention. It is a vector diagram which shows the principle which detects a misconnection by embodiment of this invention. In embodiment of this invention, it is the schematic diagram which showed the range which (theta) exists at the time of normal connection for every acquisition voltage. FIG. 4 is a diagram showing FIG. 3 as a list. It is a block diagram which shows a prior art. It is a vector diagram which shows the principle which calculates | requires effective leakage current by a prior art.

Explanation of symbols

10: Effective leakage current measuring instrument 11: Voltage input unit 12: Leakage current input unit 2a, 2b: A / D conversion circuit 3: Calculation unit 4: Memory 5: Reference waveform data memory 7: Determination unit 8: Output unit ZCT: Zero phase current transformer

Claims (4)

Means for detecting a combined leakage current flowing between a three-phase three-wire distribution system and a ground point;
Means for detecting a line voltage of the distribution system;
A phase angle between the line voltage and the combined leakage current, and a means for calculating an effective leakage current through a ground resistance of the distribution system using the combined leakage current;
In the effective leakage current measuring instrument with
When a certain line voltage is input to the measuring instrument as an acquired voltage, it is detected that the phase angle between the acquired voltage and the combined leakage current does not exist within a predetermined angle range corresponding to the acquired voltage And an effective leakage current measuring device comprising a determining means for determining an erroneous connection of the measuring device to the power distribution system. The effective leakage current measuring instrument according to claim 1,
An effective leakage current measuring instrument characterized in that the predetermined angle range has a width of 120 °. The effective leakage current measuring instrument according to claim 1,
An effective leakage current measuring instrument characterized in that the predetermined angle range has a width of 60 °. In the effective leakage current measuring device according to any one of claims 1 to 3,
The effective leakage current measuring device, wherein the determination means executes an operation of determining an erroneous connection for each acquired voltage and the combined leakage current, using at least two line voltages as the acquired voltage.

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