JP6626766B2 - Measurement method of nth harmonic current - Google Patents

Description

  The present invention relates to a method for measuring an nth-order harmonic current (n is a natural number of 2 or more) capable of measuring a harmonic current used for evaluating characteristics of an insulating material such as a cable and an electric device.

  The conventional method for measuring the loss current of an insulator uses a current comparison type loss current bridge that removes a fundamental current component that is 90 ° ahead of the fundamental voltage phase from the current waveform flowing through the sample insulator, and Measure the capacitance and dielectric loss tangent of the insulator. Further, a voltage applied to the sample insulator is measured by a voltage divider. The waveform analysis computer calculates a harmonic component generated by a harmonic component of the voltage included in the current based on the voltage, the capacitance, and the dielectric loss tangent. The differential amplifier obtains a loss current flowing through the sample insulator by subtracting a harmonic component calculated from the current. Instead of providing the voltage divider, the voltage may be restored from the current flowing through the standard capacitor (for example, see Patent Document 1).

  In addition, a conventional method for diagnosing deterioration of a power cable is to apply at least two types of AC voltages from a power supply to a sample and a standard capacitor, and to determine a power supply voltage phase from a current flowing through the sample by a loss current measurement bridge. ° The advanced component is removed, and the obtained loss current signal is input to the waveform analyzer. Then, a superimposed phase of the harmonic component included in the applied AC voltage and the loss current is measured with respect to the AC voltage fundamental wave component, and a superimposed phase of the harmonic component included in the applied AC voltage and the loss current is compared, and at least, The degree of change in the superimposed phase of the harmonic component contained in the loss current when two types of AC voltages are applied is measured, and the deterioration of the power cable is diagnosed from the results (for example, see Patent Document 2).

JP-A-9-325164 JP-A-11-6854

The conventional method of measuring harmonic current using a bridge circuit is to balance the bridge circuit while applying an AC voltage at the frequency of the fundamental wave component, and in that balanced state, the differential signal detected by the bridge circuit The harmonic current is measured by passing through a band-pass filter whose center frequency is the frequency of the harmonic component to be analyzed or measured, and a power supply that can ignore the effect of voltage distortion on the level of the measurement signal Required.
Although there is no problem when the insulating material is represented by a parallel equivalent circuit, it is actually an equivalent circuit in which the resistance component and the capacitance component are connected in series and parallel in a complicated manner due to water tree deterioration that occurs in the insulating material. And frequency dependence. When the characteristics of such an insulating material are measured using a bridge circuit, the balance conditions differ depending on the frequency.For example, even if the bridge circuit is balanced at the frequency of the fundamental wave component, the balance condition is not There is a problem in that the device deviates from the equilibrium state and cannot accurately measure the harmonic current, and is also affected by the harmonic voltage included in the power supply.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for measuring an nth-order harmonic current that can measure a harmonic current with high accuracy.

  In the method for measuring an n-th harmonic current according to the present invention, a power supply connected to a measurement sample and applying an AC voltage to the measurement sample, a standard capacitor having one end connected to the power supply, A parallel circuit comprising a variable capacitance and a variable resistor, a differential input resistor having one end connected to the measurement sample, and a first terminal connected to one end of the differential input resistor, A second terminal is connected to the other end of the standard capacitor, and an nth harmonic current (n is a natural number of 2 or more) flowing through the measurement sample based on a differential input between the first terminal and the second terminal. A measuring unit for measuring, the power supply, a control unit for controlling the parallel circuit and the measuring unit, using a measuring device, an n-th harmonic current measuring method for measuring the n-th harmonic current, wherein the N to be measured by the control of the control unit With an AC voltage having a frequency of a harmonic component applied from the power supply, the capacitance of the standard capacitor, the variable capacitance and the variable resistance of the parallel circuit, the capacitance of the measurement sample, and the differential A first step of adjusting the variable capacitance and the variable resistance in a bridge circuit including an input resistor to bring the bridge circuit into an equilibrium state, and controlling the control unit to adjust the variable capacitance and the variable resistance in the first step. A second step in which the measuring section measures the n-th harmonic current in a state where an AC voltage having a frequency of a fundamental wave component is applied from the power supply in a balanced state of the bridge circuit.

  In the disclosed method of measuring the nth-order harmonic current, the measurement of the harmonic current can be performed with high accuracy.

It is a schematic structure figure showing the schematic structure of the measuring device used for the nth order harmonic current measuring method concerning this embodiment. 5 is a table for explaining measurement results and effects obtained by the n-th harmonic current measurement method according to the embodiment.

(First embodiment of the present invention)
The measuring apparatus 10 according to the present embodiment includes a power supply 1 connected to a measurement sample 20 via a transformer 11 and applying an AC voltage to the measurement sample 20; a standard capacitor 2 having one end connected to the power supply 1; A parallel circuit 3 which is connected to the other end of the standard capacitor 2 and includes a variable capacitance Cv and a variable resistance Rv; a differential input resistor Rd having one end connected to the measurement sample 20; The first terminal A is connected to one end of the differential input resistor Rd through the second terminal B, the second terminal B is connected to the other end of the standard capacitor 2, and the difference between the first terminal A and the second terminal B A measuring unit 4 for measuring an nth harmonic current (n is a natural number of 2 or more) flowing through a measurement sample 20 based on a dynamic input; a power supply 1; a parallel circuit 3 (variable capacitance Cv, variable resistance Rv); And a control unit 5 for controlling the unit 4.

  The measuring apparatus 10 according to the present embodiment includes a capacitance Cs of the standard capacitor 2, a parallel circuit 3 (variable capacitance Cv, variable resistance Rv), a capacitance Cx of the measurement sample 20, and a differential input resistance Rd. Constitute a bridge circuit.

  The measurement sample 20 is an insulating material used for cables, electrical equipment, and the like. The measurement device 10 measures harmonic currents used when evaluating the characteristics of the insulation material of the measurement sample 20 and measures the insulation of the measurement sample 20. Applicable to material deterioration diagnosis.

The power supply 1 is a frequency variable power supply that includes an oscillator and an amplifier (not shown) and that can change an AC voltage and a frequency based on a control signal of the control unit 5.
The power supply 1 applies an AC voltage having a frequency of 300 Hz or less and a voltage of 20 kV or less to the measurement sample 20 via the transformer 11, for example.
The power supply 1 synchronizes the AC voltage generated by the power supply 1 with the AC voltage detected by the measurement unit 4 and outputs a synchronization signal for phase measurement in the measurement unit 4 to the measurement unit 4.

  The measurement unit 4 centers on the signal power supply frequency (the frequency fm of the fundamental wave component) or the frequency fb (= n × fm) of the nth harmonic component based on the signal power supply frequency (the frequency fm of the fundamental wave component). A bandpass filter (not shown) that can be set to a frequency is built in.

  Next, the n-th harmonic current measuring method according to the present embodiment using the measuring device 10 includes (1) a voltage adjustment step for balance adjustment, (2) a balance adjustment step for a bridge circuit, and (3) a voltage adjustment for measurement. Steps and (4) n-th harmonic current measurement step are performed in this order. In the following description, each step will be described in order.

First, (1) the voltage adjustment step for balance adjustment will be described.
The measuring unit 4 opens the contact 12 between the first terminal A and one end of the differential input resistor Rd based on the control signal of the control unit 5 to make only the second terminal B a single input.
Further, the measuring unit 4 sets the center frequency of the bandpass filter to the frequency fb (= n × fm) of the nth harmonic component to be measured based on the control signal of the control unit 5.
The control unit 5 sets the variable capacitance Cv to 0F and sets the variable resistance Rv to an arbitrary value.
Then, the power supply 1 generates an AC voltage Vb having a frequency fb (= n × fm) of an nth harmonic component to be measured based on a control signal of the control unit 5.
Further, the measuring unit 4 converts a current flowing through the standard capacitor 2 into a voltage with the variable resistor Rv and detects the voltage via the band-pass filter by a voltage dividing circuit of the capacitance Cs of the standard capacitor 2 and the variable resistor Rv. The detection result is fed back to the control unit 5.
The control unit 5 adjusts the output of the oscillator of the power supply 1 based on the detection result of the measurement unit 4 so that the detection value of the measurement unit 4 becomes a predetermined voltage value. Adjust the voltage Vb.

Next, (2) the balance adjustment step of the bridge circuit will be described.
The measuring unit 4 closes the contact 12 between the first terminal A and one end of the differential input resistor Rd based on the control signal from the control unit 5, and sets the differential input between the first terminal A and the second terminal B. And
Further, the measuring unit 4 sets the center frequency of the bandpass filter to the frequency fb (= n × fm) of the nth harmonic component to be measured based on the control signal of the control unit 5.
Then, based on the control signal from the control unit 5, the power supply 1 adjusts the AC voltage Vb of the frequency fb (= n × fm) of the nth harmonic component to be measured, which is adjusted in the above (1) voltage adjustment step for balance adjustment. Occurs.
Further, the measuring unit 4 converts a current flowing through the measurement sample into a voltage by the differential input resistance Rd by a voltage divider circuit of the capacitance Cx of the measurement sample and the differential input resistance Rd, and converts the current through the band-pass filter through the bandpass filter. The current flowing through the standard capacitor 2 is detected by the voltage dividing circuit including the capacitance Cs of the standard capacitor 2 and the parallel circuit 3 (variable capacitance Cv, variable resistance Rv). The voltage is converted by a variable resistor Rv), detected via a bandpass filter, and the detection result is fed back to the control unit 5.
Then, based on the detection result of the measurement unit 4, the control unit 5 adjusts the differential voltage of the first terminal A and the second terminal B of the measurement unit 4 such that the differential voltage is minimized (the bridge circuit is in an equilibrium state). Adjust the capacitance Cv and the variable resistance Rv.

Next, the (3) measuring voltage adjusting step will be described.
The measuring section 4 opens the contact 12 between the first terminal A and one end of the differential input resistor Rd based on the control signal of the control section 5 to make only the first terminal A a single input.
Further, the measuring unit 4 sets the center frequency of the band-pass filter to the frequency fm of the fundamental wave component based on the control signal of the control unit 5.
The control unit 5 sets the variable capacitance Cv to 0F and sets the variable resistance Rv to an arbitrary value.
Then, the power supply 1 generates an AC voltage Vm having a frequency fm of a fundamental wave component based on a control signal of the control unit 5.
Further, the measuring unit 4 converts a current flowing through the standard capacitor 2 into a voltage with the variable resistor Rv and detects the voltage via the band-pass filter by a voltage dividing circuit of the capacitance Cs of the standard capacitor 2 and the variable resistor Rv. The detection result is fed back to the control unit 5.
Then, the control unit 5 adjusts the output of the oscillator of the power supply 1 based on the detection result of the measurement unit 4 so that the detection value of the measurement unit 4 becomes a predetermined voltage value. Adjust Vm.

Lastly, the (4) n-th harmonic current measurement step will be described.
The measuring unit 4 closes the contact 12 between the first terminal A and one end of the differential input resistor Rd based on the control signal from the control unit 5, and sets the differential input between the first terminal A and the second terminal B. And
Further, the measuring unit 4 sets the center frequency of the bandpass filter to the frequency fb (= n × fm) of the nth harmonic component to be measured based on the control signal of the control unit 5.
Further, the control unit 5 sets the variable capacitance Cv and the variable resistance Rv in the balanced state of the bridge circuit adjusted in the above (2) bridge circuit balance adjustment step.
Further, the power supply 1 generates the AC voltage Vm having the frequency fm of the fundamental wave component adjusted in the above-mentioned (3) measurement voltage adjustment step based on the control signal of the control unit 5.

Then, the measuring unit 4 measures the n-th harmonic current In, the voltage Vn corresponding to the superposition phase θn of the n-th harmonic current In with respect to the voltage phase of the fundamental wave component, and the phase θvn.
Note that the relationship between the n-th harmonic current In and the voltage Vn and the superposition phase θn and the voltage phase θvn have the relationship of the following equation (1).

[Equation 1]
In = Vn / Rd
θn = θvn / n (1)

Next, measurement results and effects by the n-th harmonic current measurement method according to the present embodiment will be described with reference to FIG.
In the experiment, the capacitance Cs of the standard capacitor 2 was set to 2.00 × 10 ⁻¹⁰ F, and the capacitance Cx of the measurement sample 20 was set to 1.00 × 10 ⁻⁹ F (9.99 × F in Example 4). 10 ⁻¹⁰ F), and the order n of the nth harmonic current to be measured is set to the third order.

  In addition, in Comparative Examples 1, 2, and 3 in FIG. 2, the conventional measurement in which the frequency fb used in the balance adjustment of the bridge circuit is adjusted to the frequency fm of the fundamental wave component corresponding to the n-th harmonic current. This is an example using the method, in which the balance adjustment frequency fb and the measurement frequency fm match.

  On the other hand, in the example 1-1, the example 1-2, the example 2, and the example 3 in FIG. 2, the frequency fb used for the balance adjustment of the bridge circuit is the n-th harmonic of the frequency fm applied at the time of measurement. This is an example using the n-th harmonic current measurement method according to the present embodiment in accordance with the frequency of the wave component, and the balance adjustment frequency fb is set to be n times (here, three times) the measurement frequency fm.

First, the result of comparison between Example 1-1 and Comparative Example 1 will be described.
In Example 1-1, since the frequency fm for measuring the nth-order harmonic current was set to 15 Hz, the frequency fb for balance adjustment of the bridge circuit was set to 45 Hz, and the aforementioned (1) In the voltage adjustment step, the balance adjustment voltage Vb was adjusted to 2300 V, and in the aforementioned (3) measurement voltage adjustment step, the measurement voltage Vm was adjusted to 2300 V. As a result, in Example 1-1, the n-th harmonic current In is 1.04 × 10 ⁻⁹ A, 1.09 × 10 ⁻⁹ A, And 1.02 × 10 ⁻⁹ A.

On the other hand, in Comparative Example 1, since the frequency fm for measuring the n-th harmonic current was set to 15 Hz, the frequency fb for balance adjustment of the bridge circuit was set to 15 Hz, and the above-mentioned (1) Balance The adjustment voltage Vb is adjusted to 2300 V in the adjustment voltage adjustment step (however, the balance adjustment frequency fb is set to the measurement frequency fm), and the measurement voltage Vm is set to 2300 V in the aforementioned (3) Measurement voltage adjustment step. Was adjusted to As a result, in Comparative Example 1, the n-th harmonic current In was 4.17 × 10 ⁻⁹ A, 4.40 × 10 ⁻⁹ A, and 4.40 × 10 ⁻⁹ A in the (4) n-th harmonic current measurement step described above. It was 4.22 × 10 ⁻⁹ A.

  Therefore, in the method for measuring the n-th harmonic current according to the present embodiment (Example 1-1), the bridge circuit is balanced at the frequency of the harmonic (order) to be measured, so that the bridge circuit is compared with Comparative Example 1. It can be seen that the effect of power supply harmonics on the measurement results can be reduced.

  Moreover, Example 2 and Comparative Example 2 were compared with Example 1-1 and Comparative Example 1 in which the balance adjustment voltage Vb, the measurement voltage Vm, and the measurement frequency fm were increased twice or three times. Similarly, the results of the comparison between Example 3 and Comparative Example 3 are similar to those of Comparative Example 2 and Comparative Example 3 in the n-th harmonic current measurement method (Example 2 and Example 3) according to the present embodiment. By comparison, it can be seen that the influence of power supply harmonics on the measurement results can be reduced.

Next, the result of comparison between Example 1-2 and Comparative Example 1 will be described.
Embodiment 1-2 is an example in which the balance adjustment voltage Vb (2300 V) of Embodiment 1-1 is reduced to 1/10 (230 V), and the n-th harmonic current In is 1.01 × 10 ^-9 A, 1.08 × 10 ⁻⁹ A, and 9.36 × 10 ⁻¹⁰ A.
As is clear from this result, even when the applied voltage (balance adjustment voltage Vb) at the time of performing the balance adjustment is about 1/10 of the measurement voltage, the influence of the power supply harmonic can be reduced.

In the method for measuring the n-th harmonic current according to the present embodiment, (1) a voltage adjustment step for balance adjustment, (2) a balance adjustment step for the bridge circuit, (3) a voltage adjustment step for measurement, and (4) n The case where the processing is performed in the order of the next harmonic current measurement step has been described, but it is sufficient that at least (2) the balance adjustment step of the bridge circuit and (4) the nth harmonic current measurement step are included.
That is, (1) the voltage adjustment step for balance adjustment and (3) the voltage adjustment step for measurement are steps for adjusting the voltages (balance adjustment voltage Vb and measurement voltage Vm) applied to the measurement sample 20. The voltage applied to the measurement sample 20 may be appropriately set without performing the (1) balance adjustment voltage adjustment step and (3) the measurement voltage adjustment step.
However, detecting the voltage applied to the measurement sample 20 by the (1) voltage adjustment step for balance adjustment and (3) the voltage adjustment step for measurement depends on the applied voltage in which the degraded n-th harmonic current is applied. Therefore, it is preferable to grasp the voltage characteristics.

DESCRIPTION OF SYMBOLS 1 Power supply 2 Standard capacitor 3 Parallel circuit 4 Measuring part 5 Control part 6 Transformer 10 Measuring device 11 Transformer 12 Contact 20 Measurement sample

Claims (4)

A power supply connected to the measurement sample and applying an AC voltage to the measurement sample, a standard capacitor having one end connected to the power supply, and a parallel connection including a variable capacitance and a variable resistance connected to the other end of the standard capacitor. A circuit, a differential input resistor having one end connected to the measurement sample, a first terminal connected to one end of the differential input resistor, and a second terminal connected to the other end of the standard capacitor; A measuring unit for measuring an n-th harmonic current (n is a natural number of 2 or more) flowing through the measurement sample based on a differential input between a first terminal and a second terminal; and the power supply, the parallel circuit, and the measuring unit. And a control unit for controlling, using a measuring device including: an n-th harmonic current measuring method for measuring the n-th harmonic current,
Under the control of the control unit, the capacitance of the standard capacitor, the variable capacitance and the variable resistance of the parallel circuit, and the measurement are performed while an AC voltage having a frequency of the nth harmonic component to be measured is applied from the power supply. A first step of adjusting the variable capacitance and the variable resistance in the bridge circuit including the sample capacitance, and the differential input resistance to bring the bridge circuit into an equilibrium state;
Under the control of the control unit, in the equilibrium state of the bridge circuit adjusted in the first step, in a state where an AC voltage having a frequency of a fundamental wave component is applied from the power supply, the measurement unit controls the n-th harmonic current. A second step of measuring;
An n-th harmonic current measurement method, comprising: The method for measuring an n-th harmonic current according to claim 1,
The first step includes converting a current flowing through the measurement sample into a voltage using the differential input resistance, detecting the voltage by the measuring unit, converting a current flowing through the standard capacitor into a voltage using the parallel circuit, and performing the measurement. The control unit adjusts the variable capacitance and the variable resistance such that the differential voltage between the first terminal and the second terminal of the measurement unit is detected by the control unit. Second harmonic current measurement method. The method for measuring an n-th harmonic current according to claim 1 or 2,
Before the first step, the control unit opens a contact between a first terminal of the measurement unit and one end of the differential input resistor, sets the variable capacitance to 0, and sets the variable capacitance to zero. Setting a resistance to an arbitrary value, the measuring unit converts a current flowing through the standard capacitor into a voltage by the variable resistor, and adjusts an AC voltage having a frequency of the n-th harmonic component. A method for measuring an n-th harmonic current. The method for measuring an n-th harmonic current according to any one of claims 1 to 3,
Between the first step and the second step, the control unit opens a contact between a first terminal of the measurement unit and one end of the differential input resistor, and sets the variable capacitance to 0, the variable resistor is set to an arbitrary value, the measuring unit converts the current flowing through the standard capacitor into a voltage by the variable resistor, and adjusts the AC voltage at the frequency of the fundamental wave component. Performing an n-th order harmonic current measurement method.

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