JP2015078905A - Calibration sample for space charge measurement and calibration method using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration sample having small size and a favorable handling property.SOLUTION: A calibration sample comprises a cylindrical insulation part 11 consisting of insulation material, and electrodes 12 and 13 provided at an inner periphery and an outer periphery of the cylindrical insulation part 11 respectively.

Description

  The present invention relates to a calibration sample for measuring space charge for measuring the amount and distribution of space charge accumulated in a material in a power cable by applying a voltage, and a calibration method using the same.

  In DC cables using polymer insulation materials such as cross-linked polyethylene as the insulator, the space charge that appears in the insulator due to the application of DC voltage greatly affects the insulation characteristics. It is important to evaluate accurately. A pulse electrostatic stress method is generally used for measuring space charge in an insulating material.

  In the pulse electrostatic measurement method, a sample to be measured for space charge is sandwiched between electrodes, and a pulse voltage is applied while applying a DC voltage (bias voltage) from one of the electrodes. At this time, a pressure wave of vibration generated from the sample is applied. Is detected by a piezoelectric element. Then, the amount of electric charge is obtained from the magnitude of the detected pressure wave, and the position where the electric charge has existed is obtained from the elapsed time from when the pulse is applied until the pressure wave is detected. Thus, the charge density distribution in the thickness direction of the sample can be obtained.

In a measurement apparatus that performs measurement by the pulse electrostatic measurement method described above, it is necessary to perform calibration before performing measurement. This calibration operation is performed as follows using a thin plate-shaped calibration sample made of a material (for example, a ceramic sintered body) that hardly generates space charges.
(1) Apply pulse voltage without applying DC voltage. (2) Apply pulse voltage with DC voltage applied. (3) Apply pulse voltage again without applying DC voltage. The above is performed in order.
Then, the waveform based on the pressure wave obtained in the above (1) and (3) is compared, and it is confirmed in (2) that no charge has accumulated in the calibration sample.
Further, based on the measurement waveform of the pressure wave obtained in the above (2), calibration of the axis in the thickness direction of the sample and calibration of the charge distribution are performed (for example, see Patent Document 1 and Non-Patent Document 1).

JP 09-311122 A

JEC-TR Electrical Society Technical Report Technical Report Calibration Method for Space Charge Distribution Measurement by Pulse Electrostatic Stress Method JEC-TR-61004-2012 "5. Calibration Procedure" published by the Institute of Electrical Engineers, December 25, 2012

By the way, when measuring the charge density distribution of a thick sample such as an insulating layer of a high-voltage power cable, it is necessary to apply a high-voltage DC voltage to the sample. That is, it is necessary to increase the voltage of the DC voltage generator of the measuring device.
When such a calibration of the measuring apparatus is performed using a conventional thin plate-shaped calibration sample, it is necessary to increase the creepage distance so that the front and back electrodes do not short-circuit through the surface of the calibration sample. That is, it is necessary to prepare a calibration sample having a large area and to increase the distance from the front and back electrodes to the outer peripheral edge of the sample.
However, since it is difficult to handle a sample having a large area in the two-dimensional direction as described above, there is a problem that it takes time for calibration work.

  An object of the present invention is to provide a calibration sample for space charge measurement that is easy to handle and a calibration method using the same.

  The invention according to the calibration sample of the present application that solves the above-described problems includes a cylindrical insulating portion made of an insulating material, and electrodes provided on the inner periphery and the outer periphery thereof, respectively.

  In this calibration sample, since the electrodes are provided inside and outside the cylindrical insulating portion, both electrodes do not short-circuit in the circumferential direction of the insulating portion. Therefore, it is not necessary to consider the creepage distance in the circumferential direction. Therefore, it is only necessary to consider the creepage distance only in the axial direction of the calibration sample. In other words, the calibration sample can be adapted to a high DC voltage simply by extending the insulating part in the one-dimensional direction, and the calibration sample having a small size and good handleability can be provided by suppressing expansion in the two-dimensional direction. Is possible.

  As for the external shape of the insulating part of the calibration sample, it is desirable that the cross section in the direction intersecting the axial direction is circular.

In the calibration sample, it is preferable that the conductor electrode is provided at a position eccentric from the center of the insulating portion.
By configuring the calibration sample in this way, calibration can be performed by changing the thickness of the insulating portion by changing the position where the pressure wave is detected along the circumferential direction of the outer periphery of the insulating portion. That is, it becomes possible to easily adjust the thickness of the insulating portion during calibration.

In the calibration sample, it is preferable that the insulating portion has a shape whose thickness varies depending on the position in the axial direction.
By configuring the calibration sample in this manner, calibration can be performed by changing the thickness of the insulating portion by changing the position where the pressure wave is detected along the axial direction of the insulating portion. That is, it becomes possible to easily adjust the thickness of the insulating portion during calibration.

In the calibration sample, it is preferable that the insulating portion is formed of a resin material.
By comprising in this way, it becomes easy to shape | mold arbitrarily about the shape and dimension of an insulation part.

In the calibration sample, it is preferable that the insulating portion is formed of a polymethyl methacrylate resin.
With this configuration, it is possible to provide a calibration sample that can suppress the generation of space charge and perform more appropriate calibration.

  The present invention according to a calibration method for solving the above-described problems is a space charge measurement method using the calibration sample, wherein a DC voltage is applied to one of the electrodes and a pulse voltage is applied to the other electrode. Before and after detecting the output waveform of the piezoelectric element in the state, only the pulse voltage is applied to the other electrode to detect the output waveform of the piezoelectric element, and the pulses performed before and after these are detected. By comparing the output waveform of the piezoelectric element in a state where only the voltage is applied, it is determined that there is no charge remaining on the calibration sample when both the DC voltage and the pulse voltage are applied. To do.

  By the calibration method, space charge measurement can be performed more appropriately.

According to the present invention, it is possible to provide a calibration sample that is small and has good handleability.
Moreover, according to the present invention, it is possible to provide a calibration method suitable for space charge measurement.

It is a perspective view of the calibration sample for space charge measurement. It is a block diagram of a space charge measuring device. 3A and 3C are diagrams showing reference signal waveforms, and FIG. 3B is a diagram showing calibration signal waveforms. It is a perspective view of the other example of a calibration sample. It is a perspective view of other example of a calibration sample.

[Outline of Embodiment of the Invention]
Hereinafter, a calibration sample for space charge measurement (hereinafter simply referred to as “calibration sample”) and a space charge measurement device will be described with reference to the drawings as embodiments of the present invention.
The space charge measuring device is based on the premise that a cylindrical insulating layer formed on the outer periphery of the conductor portion of the power cable is a target (measurement sample) for space charge measurement. Next, a description will be given of the space charge measuring device and a calibration sample suitable for the calibration work performed before the space charge measurement.

[Calibration sample]
As shown in FIG. 1, the calibration sample 10 includes a cylindrical insulating portion 11 made of an insulating material, a conductor electrode 12 provided on the inner periphery of the insulating portion 11, to which a DC voltage is applied, and the conductor electrode 12. And shielding electrodes 13 and 13 to which a pulse voltage is applied.

The insulating part 11 is made of an insulating resin, for example, PMMA (polymethyl methacrylate resin, commonly called acrylic resin). When a DC voltage is applied to the polymethyl methacrylate resin in a range not satisfying a predetermined limit value, almost no space charge is generated and the space charge characteristics are stable.
The insulating portion 11 has a through hole having a circular cross section at the center thereof. And it is desirable that the inner diameter and outer diameter of the insulating portion 11 be equal to or close to the inner diameter and outer diameter of the insulating layer of the power cable to be subjected to space charge measurement.
Here, when an example is given about the dimension of the insulation part 11, the outer diameter is 10-30 [mm], the full length is 1 [m], and thickness is 3-5 [mm]. However, it is not limited to these numerical values, and can be appropriately changed according to the dimensions of each part of the power cable that is the target of space charge measurement.

The conductor electrode 12 is a rod-like body having a circular cross section somewhat longer than the insulating portion 11, and both end portions thereof protrude from the insulating portion 11.
The conductor electrode 12 and the insulating portion 11 may be formed separately, and the conductor electrode 12 may be inserted into the through hole of the insulating portion 11, or the insulating portion 11 is formed on the outer periphery after the conductor electrode 12 is formed. You may do it.
The gap between the outer peripheral surface of the conductor electrode 12 and the inner peripheral surface of the insulating portion 11 is preferably small, and more preferably in close contact with each other.

In addition, although the conductor electrode 12 protrudes from the insulating part 11, the connection with the DC power supply 20 mentioned later becomes easy, but the protrusion of the conductor electrode 12 is not essential.
For example, it is possible to connect the DC power supply 20 to the end face of the conductor electrode 12 by making the lengths of the conductor electrode 12 and the insulating portion 11 equal.

The shielding electrodes 13, 13 cover the outer peripheral surface of the insulating part 11 with an intermediate part in the center line direction of the insulating part 11 interposed therebetween. These shielding electrodes 13 and 13 are formed with the same width. The shield electrodes 13 and 13 may be formed on the outer peripheral surface of the insulating portion 11 by a metal film forming technique or may be formed by winding a metal foil.
Further, each of the shielding electrodes 13 and 13 has a sufficient creeping distance from the end portion of the insulating portion 11 in order to maintain the insulation state with the conductor electrode 12.
A non-shielding portion 14 exists between the shield electrodes 13 and 13, and the pressure wave of vibration generated from the sample is detected in the non-shielding portion 14.
The conductor electrode 12 and the shielding electrodes 13 and 13 are both made of a good conductor, for example, aluminum (including an aluminum alloy), gold, brass, or the like.

[Space charge measuring device]
As shown in FIG. 2, the space charge measuring apparatus 100 includes a DC power source 20 that applies a DC voltage as a bias voltage to a calibration sample or a measurement sample, and a pulse that applies a pulse voltage to the calibration sample or the measurement sample. A generator 30 and a piezoelectric element 40 as a detector for detecting a pressure wave generated when the calibration sample or the measurement sample vibrates are provided.
Furthermore, the space charge measuring apparatus 100 performs an amplifier (not shown) that amplifies the detection signal of the piezoelectric element 40, an oscilloscope 60 that displays the waveform of the amplified detection signal, and predetermined signal processing on the detection signal. And a personal computer (hereinafter referred to as “PC”) 70 as a signal processing unit.
FIG. 2 shows a state where the calibration sample 10 is installed.

The DC power supply 20 is connected to one end of the conductor electrode 12 protruding from the insulating portion 11 and applies a predetermined DC voltage to the conductor electrode 12.
The direct-current voltage applied from the direct-current power supply 20 may be either positive or negative, and the value of the applied voltage is appropriately determined according to the material of the insulating portion 11 and the thickness in the radial direction. The DC power supply 20 applies, for example, a DC voltage of 50 to 3000 [kV] to the conductor electrode 12.

The pulse generator 30 applies a pulse voltage of the same polarity and the same potential to the two shielding electrodes 13 and 13 simultaneously.
The pulse voltage applied from the pulse generator 30 may be either positive or negative, and the value of the pulse voltage is appropriately determined according to the thickness of the insulating portion 11 in the radial direction and the detection resolution of the piezoelectric element 40. The value of the pulse voltage is appropriately determined according to the material of the insulating portion 11 and the thickness in the radial direction. For example, the pulse generator 30 applies a DC voltage of 1 [kV] to the shielding electrodes 13 and 13.

The calibration sample 10 is fixedly supported by bolting the fixing block 42 while being placed on the upper surface of the detection table 41 in the non-shielding portion 14. The detection table 41 and the fixed block 42 are both conductors, and the calibration sample 10 is fixed in a state where only the non-shielding part 14 is in contact with the shield electrodes 13 and 13.
The piezoelectric element 40 is provided on the lower surface side of the detection table 41. Liquid silicon is applied to the detection table 41 so that the pressure wave of vibration is transmitted from the non-shielding part 14 to the piezoelectric element 40 satisfactorily. The piezoelectric element 40 outputs a voltage signal corresponding to the pressure wave transmitted from the non-shielding portion 14, is amplified by the amplifier 50, and is input to the oscilloscope 60.

The oscilloscope 60 converts the amplified detection signal from the piezoelectric element 40 into a time-series waveform and displays it on a monitor.
The PC 70 is connected to the piezoelectric element 40 via the oscilloscope 60. And PC70 inputs the control command which starts pulse transmission with respect to the pulse generator 30, and records the elapsed time from pulse transmission and the output strength of the detection signal of the piezoelectric element 40. FIG. And the data of the time-sequential change of the pressure detected with the piezoelectric element 40 are produced | generated.
Then, predetermined signal processing is performed on the generated data, the apparatus is calibrated, and parameters useful for space charge measurement are acquired.

[Calibration method using calibration sample]
A calibration method using the space charge measuring apparatus 100 will be described.
The calibration sample 10 is fixed to the detection table 41, the conductor electrode 12 is connected to the DC power source 20, and the shield electrodes 13 and 13 are connected to the pulse generator 30.

Then, a pulse signal that is periodically repeated is applied to the calibration sample 10 without applying a DC voltage, and a detection signal of the piezoelectric element 40 is recorded. At this time, the PC 70 calculates the addition average of the detection signals of the piezoelectric elements 40 based on the individual pulse voltages. The detection signal waveform obtained at this time is referred to as a reference signal waveform.
FIG. 3A shows an example of a reference signal waveform. Note that each signal waveform shown in FIG. 3 is subjected to predetermined signal processing.

Next, a pulse voltage is applied to the calibration sample 10 in a state where a DC voltage in a range where no space charge is generated is applied to the insulating portion 11 of the calibration sample 10. The PC 70 calculates the average of the detection signals of the piezoelectric elements 40 based on the periodically repeated pulse voltage. The detection signal waveform obtained at this time is called a calibration signal waveform.
FIG. 3B shows an example of a calibration signal waveform. Induced charges are generated at the interface between the conductor electrode 12 and the insulating part 11 and the interface between the shielding electrode 13 and the insulating part 11, respectively, and a pressure wave peak is generated.
In the case of a normal calibration signal waveform, there is a portion where the signal level is 0 between the two peaks. If there is no portion where the signal level is 0, noise from the pulse generator 30 and insufficient resolution to detect the position where the pressure wave is generated can be considered. Recalibration is required.

Again, a pulse voltage that is periodically repeated without applying a DC voltage is applied to the calibration sample 10, and the addition average of detection signals of the piezoelectric elements 40 based on the individual pulse voltages is calculated by the PC 70. FIG. 3C shows an example of a reference signal waveform obtained at this time.
Then, the PC 70 compares the reference signal waveform obtained at this time with the first reference signal waveform.

  In the above comparison, when the two reference signal waveforms are within the range that can be regarded as the same or the same and there is no increase or decrease, the insulation of the calibration sample 10 is performed when the DC voltage is applied to obtain the calibration signal waveform. This means that no space charge was generated in the portion, and the calibration signal waveform obtained at this time is used as an appropriate waveform for calibration.

In the above comparison, if the two reference signal waveforms are not within the same range, or if there is an increase / decrease, there may be space charge generation, noise generation, a space charge measuring device failure, etc. .
In this case, the measurement of the calibration sample 10 is performed again after taking measures against noise around the calibration sample 10 and checking the defective portion of the space charge measuring device. If the reference signal waveform still increases or decreases, the measurement of the calibration sample 10 is performed again by exchanging the insulating portion 11 of the calibration sample 10 or reducing the DC voltage with respect to the conductor electrode 12.

When an appropriate calibration signal waveform is obtained, deconvolution processing is performed on the calibration signal waveform as signal processing, and an impulse response used for the deconvolution processing is stored.
Further, the time axis of the calibration signal waveform is converted into a position axis in the thickness direction of the insulating portion. Then, the calibration signal waveform is integrated at the position, and the detection signal axis is calibrated to the electric field axis. At this time, the PC 70 obtains an appropriate coefficient K and stores it in the calibration.
The electric field distribution waveform thus obtained is differentiated by position to obtain a charge distribution waveform.

[Space charge measurement]
When space charge measurement is performed on a measurement sample such as a power cable, the measurement sample is installed in the space charge measurement device 100 in the same manner as the calibration sample 10.
Then, with the DC voltage applied, the pulse voltage is applied to the measurement sample, and the addition average of the detection signals of the piezoelectric elements 40 based on the periodically repeated pulse voltage is calculated by the PC 70.
Further, deconvolution processing is performed on the detection signal waveform in the same manner as in the case of the calibration sample. At this time, the impulse response used in the deconvolution process of the calibration sample is used.
Then, the time axis of the detection signal waveform after the deconvolution processing is converted to the position axis in the thickness direction of the insulating portion, the detection signal waveform is integrated with the position, and the detection signal axis is used using the coefficient K used in the calibration sample. Is calibrated to the electric field axis.
And the electric field distribution waveform obtained by this is differentiated by the position, and the charge distribution waveform in the measurement sample is acquired.
Thereby, the distribution of space charge can be acquired in the thickness direction of the insulating layer of the power cable.

[Technical effects of the embodiment]
As described above, the calibration sample 10 has the insulating portion 11 in the cylindrical shape, and the conductor electrode 12 is provided inside thereof, and the shielding electrodes 13 and 13 are provided on the outer periphery thereof. Therefore, both electrodes are short-circuited in the circumferential direction. There is no. Although it is necessary to adjust the creeping distance between the conductor electrode and the shield electrode in the axial direction, it is only necessary to adjust the length of the insulating portion 11 for this purpose. Therefore, when a DC high voltage is applied to the conductor electrode 12, it is only necessary to extend the calibration sample only in the one-dimensional direction (axial direction). A calibration sample can be provided.

  Further, two shielding electrodes 13 and 13 are provided on the outer periphery of the insulating portion 11, and the piezoelectric element 40 detects the vibration pressure wave at the non-shielding portion 14 between them, so that the pressure wave due to the application of the pulse voltage is amplified. Therefore, better detection can be performed.

Further, the calibration sample 10 has a cylindrical shape of the insulating portion 11 and a conductor electrode 12 provided at the center, and therefore can have a structure approximate to a power cable. A more suitable parameter can be obtained by measuring the space charge of the cable.
Furthermore, by making the thickness of the insulating portion 11 of the calibration sample 10 equal or approximate to the thickness of the insulating layer of the power cable, it is possible to obtain a more appropriate parameter.

  Further, in the calibration method using the calibration sample 10, since the reference signal waveforms of two times by applying only the pulse voltage are compared, an appropriate calibration signal waveform can be obtained, and an impulse response and coefficient suitable for space charge measurement. A parameter consisting of K can be acquired, and more appropriate space charge measurement can be performed.

[Other examples of calibration samples]
The calibration sample 10 is provided with the concentric columnar conductor electrode 12 inside the cylindrical insulating portion 11, but the arrangement and shape thereof can be changed as appropriate.
For example, as shown in the calibration sample 10A of FIG. 4, the cylindrical conductor electrode 12 may be arranged at a position eccentric from the center with respect to the cylindrical insulating portion 11.
In this case, the same effect as changing the thickness of the insulating part 11 can be obtained depending on which position in the outer peripheral direction of the insulating part 11 the pressure wave is detected by the piezoelectric element 40. For this reason, it becomes easy to adjust by adjusting the thickness of the insulating part 11.

Further, as shown in a calibration sample 10B in FIG. 5, a truncated cone-shaped conductor electrode 12 may be disposed concentrically at the center of the cylindrical insulating portion 11.
In this case, it is possible to obtain the same effect as changing the thickness of the insulating portion 11 depending on which position along the axial direction of the insulating portion 11 the piezoelectric element 40 is disposed and pressure waves are detected. it can. For this reason, calibration can be easily performed by adjusting the thickness of the insulating portion 11.
In addition, even when the outer diameter of the conductor electrode 12 is constant and the insulating portion 11 has a truncated cone shape, the insulating portion 11 depends on which position along the axial direction of the insulating portion 11 the piezoelectric element 40 is disposed. The effect of changing the thickness of can be obtained.

  Further, the conductor electrode 12 may be shorter than the insulating portion 11. In this case, a voltage can be applied by soldering an insulated wire to the end portion of the conductor electrode 11 inserted into the through hole of the insulating portion 11.

10, 10A, 10B Calibration sample 11 Insulating part 12 Conductor electrode 13 Shielding electrode 14 Non-shielding part 20 DC power supply 30 Pulse generator 40 Piezoelectric element 60 Oscilloscope 70 PC
100 Space charge measuring device

Claims (6)

  A calibration sample for space charge measurement, comprising: a cylindrical insulating portion made of an insulating material; and electrodes respectively provided on an inner periphery and an outer periphery thereof.   The calibration sample for space charge measurement according to claim 1, wherein the inner peripheral electrode is provided at a position eccentric from a center of the insulating portion.   The calibration sample for space charge measurement according to claim 1, wherein the insulating portion has a shape whose thickness varies depending on an axial position thereof.   The space charge measurement calibration sample according to any one of claims 1 to 3, wherein the insulating part is formed of a resin material.   The space charge measurement calibration sample according to claim 4, wherein the insulating portion is formed of a polymethyl methacrylate resin. A space charge measurement method using the calibration sample according to any one of claims 1 to 5,
Before and after detecting the output waveform of the piezoelectric element with a DC voltage applied to one of the electrodes and a pulse voltage applied to the other electrode, only the pulse voltage is applied to the other electrode. Apply to detect the output waveform of the piezoelectric element,
By comparing the output waveform of the piezoelectric element with only the pulse voltage applied before and after these, no residual charge was generated on the calibration sample when both the DC voltage and the pulse voltage were applied. A calibration method using a calibration sample for space charge measurement, characterized in that

Images