JP2015219116A - Calibration method of electric charge density in space-charge distribution measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration method of electric charge density in a space-charge distribution measurement capable of highly accurately performing calibration even when a space charge is generated by application of a DC voltage when calibrating the electric charge density in the space-charge distribution measurement of the inside of an insulation material.SOLUTION: The calibration method includes the steps of: when a voltage signal measured from a measurement sample 2 to which only a pulse voltage is applied, is defined as V1, a voltage signal measured from the measurement sample to which a pulse voltage is applied with a DC voltage applied thereto, is defined as V2, and, immediately after the step-down of the DC voltage, a voltage signal measured from the measurement sample 2 to which a pulse voltage is applied with it connected to ground, is defined as V3, acquiring a voltage signal V4 calculated by V2-V3+V1; and calibrating the charge density obtained from the voltage signal V2 using the voltage signal V4.

Description

  The present invention relates to a method for calibrating charge density in space charge distribution measurement, wherein the charge density is calibrated in space charge distribution measurement.

  In general, an electric charge existing for a relatively short time or a long time may be recognized inside an insulating material to which a direct external electric field is applied. Such electric charge existing inside the insulating material is called space charge, and the electric charge that flows in the medium as an electric current within a very short time and the local electric neutrality contained in the atoms or molecules constituting the medium are maintained. The charge is different.

  The presence of the space charge distorts the electric field inside the material and creates a local high electric field portion, which affects the insulating performance of the insulating material. Therefore, it is very important for the insulation design to accurately evaluate the charge amount, position, and time change of the space charge generated in the insulating material.

  Non-Patent Document 1 describes a pulse electrostatic stress method (hereinafter referred to as PEA method) as a method for measuring a space charge distribution inside an insulating material. The principle of space charge distribution measurement by the PEA method is described as follows in Non-Patent Document 1, for example. That is, when a pulse voltage is applied to an insulating material that accumulates space charges, an electrostatic stress acts on the accumulated charges, and pressure waves are generated from the charges. In the PEA method, pressure waves that reach the surface after propagating through an insulating material are measured by converting them into voltage signals using piezoelectric elements, and space charge distribution information is obtained based on the measured voltage signals. It is.

  In actual measurement, due to the effects of pressure wave attenuation and reflection, distortion caused by the electrical characteristics of the measurement circuit, etc., the obtained voltage signal does not directly represent a charge signal. Calibration to convert to is required.

  In the calibration method described in Non-Patent Document 1, a piezoelectric element obtained by applying a low DC voltage to the insulating material so that no space charge is generated inside the insulating material and only the induced charge on the surface of the insulating material appears. Is calibrated on the basis of the theoretically derived surface charge, electric field and potential inside the material.

  Specifically, first, a voltage signal V1 of the piezoelectric element is obtained by applying only a pulse voltage in a state where a DC voltage for calibration is not applied (measurement sample is short-circuited), and then a DC voltage for calibration is obtained. Apply the pulse voltage in the applied state to obtain the voltage signal V2 of the piezoelectric element, and finally apply only the pulse voltage in the state where the DC voltage for calibration is not applied again (the measurement sample is short-circuited). Voltage signal V3 is obtained.

  Confirmation that the space charge is not generated in the measurement sample by applying the DC voltage for calibration is performed by comparing the voltage signals V1 and V3 obtained before and after applying the DC voltage, and there is no difference between them. It is done by confirming that.

Technical report of the Institute of Electrical Engineers of Japan, Technical Report of the Electrotechnical Standards “Calibration Method of Space Charge Distribution Measurement by Pulsed Electrostatic Stress Method” (JEC-TR-61004-2012)

  In the charge density calibration described in Non-Patent Document 1, it is a precondition that no space charge is generated in the insulating material when a DC voltage is applied to the insulating material for calibration. However, depending on the insulating material, even if a very low DC voltage that is the lower limit value in the measurement conditions is applied, space charge may be generated inside the material, so that accurate calibration may not be possible. .

  The object of the present invention has been made in view of the above-mentioned problems, and provides a charge density calibration method in space charge distribution measurement that can accurately calibrate the charge density in space charge distribution measurement inside an insulating material. The purpose is to do.

  In the charge density calibration method in the space charge distribution measurement according to the present invention, a voltage signal measured from a measurement sample to which only a pulse voltage is applied is V1, and the pulse voltage is applied in a state where a DC voltage is applied. When V2 is a voltage signal measured from the measurement sample and V3 is a voltage signal measured from the measurement sample to which the pulse voltage is applied with the DC voltage grounded immediately after stepping down, V2−V3 + V1 A step of obtaining a voltage signal V4 calculated by the step of calibrating a charge density obtained from the voltage signal V2 using the voltage signal V4.

  The charge density calibration method in the space charge distribution measurement according to the present invention is characterized in that the measurement sample is an electric wire or a cable.

  According to the present invention, when charge density calibration is performed in space charge distribution measurement inside an insulating material, space charge is generated inside the material even when a low DC voltage that is a lower limit value under measurement conditions is applied. Can be calibrated with high accuracy.

It is a figure which shows the outline | summary of a space charge distribution measuring apparatus. It is a figure which shows the voltage signal V1 obtained when only a pulse voltage is applied. It is a figure which shows the voltage signal V2 obtained when a pulse voltage is superimposed and applied in the state which applied the DC voltage. It is a figure which shows the voltage signal V3 obtained when a pulse voltage is applied in the state which earth | grounded DC voltage after pressure | voltage reduction. It is a figure which shows the comparison result of the voltage signal V2 and the voltage signal V4. It is a figure which shows the space charge density corresponding to the voltage signal V2 calibrated based on the voltage signal V2. It is a figure which shows the space charge density obtained by performing signal processing of the voltage signal V2 after calibrating with the voltage signal V4. It is a figure which shows the outline | summary of the space charge distribution measuring apparatus which made the measurement object the electric wire or the cable.

  A mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described with a specific example. The present embodiment relates to a charge density calibration method in space charge distribution measurement, in which charge density is calibrated in space charge distribution measurement.

1. Overall Configuration of Space Charge Distribution Measuring Device FIG. 1 is a diagram showing an overall configuration of a space charge distribution measuring device 1 that performs a calibration method to which the present invention is applied and a measurement sample to be measured.

  In the present embodiment, as a specific example of the measurement sample, a cross-linked polyethylene sheet press-molded into a sheet shape having a thickness of 3 mm and a width of 50 mm × 50 mm is used.

  The space charge distribution measuring apparatus 1 includes an upper electrode 11, a semiconductor sheet 12, a lower electrode 13, a piezoelectric element 14, a power supply circuit 15, and a measurement processing unit 16.

  In the space charge distribution measuring apparatus 1 having such a configuration, the measurement sample 2 is sandwiched in the order of the upper electrode 11, the semiconductive sheet 12, the measurement sample 2, and the lower electrode 13.

  The power supply circuit 15 is a circuit that applies a voltage between the upper electrode 11 and the lower electrode 13. Specifically, the power supply circuit 15 has a circuit configuration in which a DC power supply 151 and a pulse generator 152 are connected in parallel on a path connecting the upper electrode 11 and the lower electrode 13. With such a circuit configuration, the power supply circuit 15 applies a DC voltage to the measurement sample 2 from the DC power supply 151, and applies a pulse voltage to the measurement sample 2 from the pulse generator 152. As shown in FIG. 1, in the power supply circuit 15, it is preferable that a resistance element 153 is connected in series to a DC power supply 151, and a high-pass capacitor 154 is connected in series to a pulse generator 152.

  The measurement processing unit includes an amplifier 161, an oscilloscope 162, a calibration voltage signal calculation unit 163, a space charge density information conversion unit 164, and a calibration unit 165. In the measurement processing unit 16 having such a configuration, the voltage signal measured by the piezoelectric element 14 is amplified by the amplifier 11 and displayed by the oscilloscope 162. The calibration voltage signal calculation unit 163 calculates a calibration voltage signal to be described later using the voltage signal amplified by the amplifier 11. The space charge density information conversion unit 164 performs signal processing on the calibration voltage signal to convert it to space charge density. The calibration unit 165 calibrates the space charge density converted from the calibration voltage signal.

2. Next, a method for calibrating the charge density in the space charge distribution measurement using the space charge distribution measuring apparatus 1 will be described in detail.

(Step 1)
In a state where no DC voltage is applied, specifically, the measurement sample 2 is short-circuited, and only the pulse voltage is applied to the measurement sample to measure the voltage signal V1. As a specific example, FIG. 2 shows the voltage signal V1 measured by the oscilloscope 162 when the pulse generator 152 is driven and a pulse voltage of −250 V is applied to the measurement sample at 10 nsec.

(Step 2)
With the DC voltage applied to the measurement sample 2, a pulse voltage is applied to the measurement sample 2 to measure the voltage signal V2. As a specific example, the voltage measured by the oscilloscope 162 when the pulse generator 152 is driven and the pulse voltage of −250 V is applied to the measurement sample 2 at 10 nsec with the DC power supply 151 being driven and the DC voltage of −2 kV being applied. The signal V2 is shown in FIG.

(Step 3)
After stepping down the DC voltage applied in step 2, the DC voltage is not applied to the measurement sample 2, specifically, the measurement sample 2 is short-circuited, and only the pulse voltage is applied to the measurement sample 2 to generate the voltage signal V3. taking measurement. As a specific example, the voltage measured by the oscilloscope 162 when the pulse generator 162 is driven and a pulse voltage of −250 V is applied to the measurement sample 2 at 10 nsec in a state where the DC voltage is stepped down after the voltage signal V2 is acquired and grounded. The signal V3 is shown in FIG.

  The voltage signal V3 obtained in step 3 represents the ground characteristic of the measurement sample 2, and it is possible to know whether or not electric charges are accumulated in the measurement sample 2 by performing signal processing on the voltage signal V3. In a measurement sample such as a cross-linked polyethylene sheet in which charges are likely to accumulate, the voltage signal V3 does not coincide with the voltage signal V1 in which no charge exists in the measurement sample 2 as is apparent from the results of FIGS. It can be determined that charge has accumulated in the measurement sample 2. That is, since the voltage signal V2 cannot be calibrated as a reference waveform, the following step 4 is performed in the present embodiment.

(Step 4)
Calibration is performed using V2−V3 + V1 as a voltage signal V4 and using it as a reference waveform, that is, a calibration voltage signal.

  First, the calibration voltage signal calculation unit 163 calculates V2−V3 + V1 as a voltage signal V4, which is used as a calibration voltage signal. Here, the voltage signal V4 is a voltage signal obtained by subtracting the voltage signal V3, which is the accumulated charge, from the voltage signal V2 including information on accumulated charges, and adding the voltage signal V1 to determine the zero potential. It is. FIG. 5 shows a comparison between the voltage signal V2 and the voltage signal V4. As is apparent from FIG. 5, the voltage signal V4 is different from the voltage signal V2 and is a voltage signal in which no charge is accumulated in the measurement sample 2, and can be calibrated as a reference waveform.

  Therefore, the space charge density information conversion unit 164 performs signal processing on the calibration voltage signal V4 to convert it to space charge density. Specifically, the space charge density information conversion unit 164 performs Fourier transform on the voltage signal V4 to remove the influence of distortion in the frequency domain, and then performs inverse Fourier transform to convert the voltage signal V4 into space charge density.

  Further, the calibration unit 165 calibrates the space charge density converted from the calibration voltage signal. Specifically, the calibration unit 165 obtains an electric field distribution by integrating the space charge density converted from the calibration voltage signal, and further integrates the electric field distribution to obtain a potential distribution. Then, the calibration unit 165 calibrates the obtained electric field distribution and potential distribution by fitting them to the theoretical electric field and potential corresponding to the experimental conditions, and ends the processing related to the calibration.

(Comparative example)
As a comparative example, a description will be given of the result of calibration assuming that no charge is accumulated in the voltage signal V2. Specifically, the space charge density corresponding to the voltage signal V2 when the space charge density is obtained from the voltage signal V2 and calibrated based on the electric field distribution and potential distribution obtained by integrating the space charge density is shown in FIG. Shown in The space charge density shown in FIG. 6 is incorrect because the voltage signals V1 and V3 do not match and charges are accumulated in the measurement sample as described above.

  On the other hand, after calibration based on the voltage signal V4, the space charge density corresponding to the voltage signal V2 is shown in FIG. Comparing FIG. 6 and FIG. 7, the space charge density shown in FIG. 7 indicates that positive charges are accumulated on the cathode side.

  As apparent from FIGS. 6 and 7, in the present embodiment, by performing the processing in steps 1 to 4, the charge density calibration in the space charge distribution measurement inside the insulating material, that is, inside the measurement sample 2 is performed. In addition, even when a space charge is generated in the measurement sample 2 by applying a very low DC voltage, calibration with high accuracy is possible.

  In this embodiment, a cross-linked polyethylene sheet is used as the measurement sample 2. However, the present invention is not limited to this, and even if a material that easily generates space charge is used in the measurement sample 2, accurate calibration is possible. . In particular, polyethylene is effective because it is a material that accumulates charges quickly and is difficult to calibrate. For example, ethylene propylene rubber, silicon rubber, etc. may be used. Alternatively, a cable can be applied as a measurement sample.

3. Overall Configuration of Space Charge Distribution Measuring Device with Wire or Cable as Measurement Object As another embodiment, the overall configuration of the space charge distribution measuring device with a wire or cable as a measurement object will be described below with reference to FIG. To do.

  The space charge distribution measuring device 5 includes an upper electrode 11, a lower electrode 13, a piezoelectric element 14, a power supply circuit 15, and a measurement processing unit 16. The power supply circuit 15 includes a DC power supply 151 and a pulse generator 152. The measurement processing unit 16 includes an amplifier 161, an oscilloscope 162, a calibration voltage signal calculation unit 163, a space charge density information conversion unit 164, and a calibration unit 165. About the structure similar to the space charge distribution measuring apparatus 1 mentioned above, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  A CV cable having the following structure is used as a specific example of the electric wire or cable to be measured. That is, the cable 20 in which a conductor is coated in the order of an internal semiconductor layer, an insulator (for example, cross-linked polyethylene), an external semiconductor layer, and a metal shielding layer is used. Here, in order to be able to measure the space charge distribution of the cable 20, the conductor inside the cable 20 is connected to the DC power supply 151 of the power supply circuit 15 at one end 21 and the other end 22 of the cable 20. . For the measurement site 200 of the cable 20, the metal shielding layer and the internal semiconductor layer are peeled off from the surface of the cable 20 to expose the insulator 20b, and the lower electrode 13 is attached to the exposed insulator 20b. In addition, the upper electrode 11 is attached to the parts 250 and 250 on both ends of the measurement part 200, that is, the parts 250 and 250 covered with the metal screen 20 a, and a pulse voltage is applied from the pulse generator 152.

  As described above, by connecting the upper electrode 11 and the lower electrode 13 to the cable 20 and using the detection result from the piezoelectric element 14 connected to the lower electrode 13, the measurement processing unit 16 performs space charge distribution. Can be measured. In addition, since the cable 20 is noisy compared to the sheet-shaped measurement sample 2 described above, the voltage signal from the piezoelectric element 14 is complicated, but the measurement processing unit 16 is connected to the space charge distribution measuring device 1 described above. Similarly, the calibration unit 165 can calibrate the space charge density converted from the calibration voltage signal with high accuracy.

DESCRIPTION OF SYMBOLS 1 Space charge distribution measuring apparatus 11 Upper electrode 12 Semiconductor sheet 13 Lower electrode 14 Piezoelectric element 14
15 Power Supply Circuit 16 Measurement Processing Unit 2 Measurement Sample

Claims (2)

A voltage signal measured from a measurement sample to which only a pulse voltage is applied is V1, a voltage signal measured from the measurement sample to which the pulse voltage is applied in a state where a DC voltage is applied is V2, and the DC Obtaining a voltage signal V4 calculated by V2−V3 + V1, where V3 is a voltage signal measured from the measurement sample to which the pulse voltage is applied with the voltage grounded immediately after stepping down;
Calibrating the charge density in the space charge distribution measurement based on the voltage signal V4;
A charge density calibration method in space charge distribution measurement.   2. The charge density calibration method in space charge distribution measurement according to claim 1, wherein the measurement sample is an electric wire or a cable.

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