JP2000046884A - Method for correcting charge density in space charge measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease a correction error to a change density in a space charge measurement for a dielectric object having two different permittivities. SOLUTION: A high voltage pulse Vp(t) of a narrow pulse width is applied to both ends of a measurement sample 50 which is a dielectric object having two different permittivities #11, #12 via electrodes 4, 5. A detection voltage signal V(0), V(D) corresponding to a pressure wave generated at an interface between the measurement sample 50 and the electrode 4, 5 is operated by a preliminarily determined operation element of a deconvolution process, thereby correcting a space change density of the measurement sample. At this time, a proportional constant (k) of the preliminarily measured two permittivities of the measurement sample is obtained, and multiplied by the low permittivity #12 which is the preliminarily determined operation element of the deconvolution process, thereby obtaining an operation element of the deconvolution process. Since the thus-obtained operation element is applied, the space charge density of a part of the dielectric object having the low permittivity can be corrected with a small error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calibrating charge density in measuring space charge of dielectrics having different dielectric constants.

[0002]

2. Description of the Related Art Conventionally, in a nondestructive space charge measurement method such as a PEA method (pulse electrostatic stress method), since an elastic wave is used, a sound velocity, an acoustic impedance, a dielectric constant, etc. of a measurement sample are used. It is necessary to calibrate in consideration of.
For example, in the case of the PEA method, a pulse voltage is applied to a measurement sample to cause a pulse electrostatic force to act on a charge in a dielectric of the measurement sample to generate a pressure wave in the dielectric. Then, the time change of the pressure wave is detected by the piezoelectric element, and the detected voltage signal is sent to the arithmetic unit by the digital oscilloscope at a predetermined sampling rate. After calculating and averaging a predetermined number of times, the arithmetic unit performs deconvolution processing to calibrate the space charge density.

More specifically, as shown in FIG. 2, mainly a DC generator 12, a pulse voltage generator 13, electrodes 14, 15,
A parallel plate measurement sample 60 is sandwiched between the electrodes 14 and 15 of the space charge measurement device 10 including the piezoelectric element 16, the signal detection unit 17, and the calculation unit 18, and the pulse voltage generator 13 applies a pulse to the measurement sample 60. A high-voltage pulse V _P (t) having a small width is applied. As a result, a pulse-like Maxwell stress f (x, t) acts on the interface between both electrodes. The Maxwell stress f (x, t) is a stress resulting from a difference between the dielectric constant of the measurement sample 60 and the dielectric constant of the electrodes 14 and 15, and the piezoelectric element 1
6. The detected voltage signal VS (t) detected at 6 and the space charge density ρ
The relationship with (x) can be derived.

Hereinafter, the relationship between the detection voltage signal VS (t) and the space charge density ρ (x) will be described. For simplicity, it is assumed that the measurement sample 60 and the electrodes 14 and 15 are sufficiently large, and the size per unit area is derived. First, assuming that the Maxwell stress acting on the interface between the ground electrode 14 and the measurement sample 60 is f (0, t),

[0005]

(Equation 2)

[0006] Here, E is the interface electric field strength, e _P is the interface voltage pulse electric field, and ε is the dielectric constant of the dielectric of the measurement sample 60. Further, in _{e P (t) = V P} (t) / d, V P is the applied pulse voltage, d is the sample thickness. At this time, a pressure wave p ₁ generated at the interface between the ground electrode 14 and the measurement sample 60 (FIG. 2C)
Is, E (0) so >> becomes only the second term of e _P If equation 11,

[0007]

(Equation 3)

[0008] Here, C is a constant determined by the acoustic properties of the measurement sample 60, ε ₀ is the vacuum dielectric constant, and ε _r is the relative dielectric constant of the measurement sample 60. Therefore, the magnitude and the polarity of the obtained pressure wave p ₁ depend on the ground electrode 14 and the measurement sample 6.
It is proportional to the electric field strength E (0) at the interface of 0. Similarly, the pressure wave p ₃ (FIG. 2C) generated at the interface between the electrode 15 and the measurement sample 60 is proportional to the electric field strength E (d) at the interface between the electrode 15 and the measurement sample 60. Incidentally, it will arrive at the piezoelectric element 16 with a delay time pressure wave p ₃ propagating inside the measurement sample 60.

Since these pressure waves p ₁ and p ₃ can be detected by the piezoelectric element 16 as detection voltage signals VS ₁ and vs ₃ (FIG. 2D), the electric field strength at the interface between both electrodes can be known. Next, a sheet-like charge on the sample 60 inside of the position x _P sigma
When ₂ Maxwell stress acting on (FIG. 2 (b)) and f (x _P, t),

[0010]

(Equation 4)

## EQU1 ## This is the Maxwell stress f
This is because (x _P , t) is Coulomb force. Therefore, the pressure wave p ₂ generated at the position x _P inside the measurement sample 60 is

[0012]

(Equation 5)

Then, the detection voltage signal VS ₂
(FIG. 2D). When the space charge is not in the form of a sheet, it can be handled as such a superposition of the sheet-like charges. Since the charge distribution inside the measurement sample 60 generally satisfies the expression 14, the detection voltage signal VS ₁ Detection voltage signal VS ₂ , VS ₃
Represents the position, and the magnitude represents the charge density.

Here, the ground electrode 14 and the measurement sample 60
Detection voltage signal VS ₁ proportional to the electric field strength E (0) at the interface of
The detection voltage signal VS ₂ which is proportional to the sheet-like charge σ ₂ inside the measurement sample 60 is compared. Since the measurement sample 60 sandwiched between the electrodes 14 and 15 of the space charge measurement device 10 is a parallel plate dielectric, the electric field strength E (0) at the interface between the ground electrode 14 and the measurement sample 60, the induced charge σ _{1 at} this interface, and Has the following relationship:

[0015]

(Equation 6)

Therefore, Equation 12 can be rewritten as follows.

[0017]

(Equation 7)

This equation is exactly the same as the pressure wave p ₂ generated by the sheet-like charge σ ₂ inside the measurement sample 60.

[0019]

(Equation 8)

Therefore, it can be understood that all the equations including the interface charges σ ₁ and σ _{3 of the} measurement sample 60 can be handled by a common equation.
Next, the relationship between the surface charge density σ (x) at the interface of the measurement sample 60 and the space charge density ρ (x) will be derived. As shown in Equation 17,
When the surface charge density σ (x) and the space charge density ρ (x) of the interface of the measurement sample 60 are represented by the same formula, a contradiction occurs in which units are different. This phenomenon is a common phenomenon not only in the PEA method but also in the PWA method (pressure wave method), but is solved as follows.

In these measuring methods, the detected voltage signal is measured by a digital oscilloscope, and becomes a data string discretized at that time. Each data is measured according to the sampling interval of the digital oscilloscope.
0 indicates the charge amount of each layer divided in the thickness direction. For example, if the sound velocity in the measurement sample 60 is 2000 m / s and the sampling interval is 1 GHz / s, one sample is 2
It corresponds to a thickness of μm. Therefore, when the electric charge of each layer is in the form of a sheet like the accumulated electric charge at the interface, it becomes equal to the volume electric charge uniformly distributed over a thickness of 2 μm.

As described above, when all the charges are considered as a collection of sheet-like charges having a thickness of 2 μm, Equation 17 can be converted into the following equation of space charge distribution.

[0023]

(Equation 9)

From the relationship between the detected voltage signal VS (t) and the space charge density ρ (x), an equation for the deconvolution processing in the arithmetic section 18 is derived. The detection voltage signal VS (t) actually measured by the PEA method is a voltage waveform obtained by detecting the pressure wave p (t) generated by the electrostatic force with the piezoelectric element 16. Therefore, the sound speed of the measurement sample 60 is set to Vsamp
Then, since the position x in the measurement sample 60 can be converted into time t from the relationship of x = V _samp × t, if the space charge distribution is a function of time ρ (t), the space charge distribution becomes

[0025]

(Equation 10)

The deconvolution is as follows. Here, VS ₁ (f) is the result of Fourier transform of VS ₁ , VS (f) is VS (t), and R (f) is ρ (t). R1 (f) is obtained by converting the interface charge σ ₁ of the measurement sample 60 into a space charge density,
This is the result of Fourier transform. Therefore, the interface charge σ
_If the magnitude of ₁ and the detection voltage signal VS1 obtained by measuring the magnitude of ₁ are obtained, the charge density can be calibrated.

Since there is generally no measurement material whose interface charge density is known, Equation 19 cannot be applied as it is.
By applying V _dc , the charge amount σ ₁ at the interface can be set to an arbitrary value. Therefore, assuming that the thickness of the measurement sample 60 is d, the charge amount σ ₁ is

[0028]

[Equation 11]

## EQU1 ## Further, since the detection voltage signal is discretized as described above, when the charge amount σ ₁ is converted into the volume charge density, the sampling interval is set to τ.

[0030]

(Equation 12)

## EQU1 ## Here, ρ (0) is the space charge density at the position x = 0, and the height ρ in the discrete Fourier transform
Equal to the impulse of (0). Therefore, R1 (f) obtained by Fourier-transforming this becomes a constant ρ (0) independent of frequency.
Therefore, Expression 19 of the deconvolution processing is

[0032]

(Equation 13)

## EQU1 ## Therefore, if seeking detection voltage signal VS ₁ obtained when applying a DC voltage V _dc as the reference waveform, the Fourier space charge distribution from the detection voltage signal VS of the measurement sample having an unknown space charge (t) The transformation R (f) is determined. Then, this is subjected to an inverse Fourier transform to obtain a space charge density ρ (x).

[0034]

However, in such a conventional charge density calibration method in space charge measurement, since the calibration is performed on the assumption that the dielectric constant of the dielectric is uniform, the power cable connection portion and the power When applied to dielectrics with different dielectric constants, such as two-layer dielectrics for equipment and water-tree degraded parts and healthy parts in insulating materials such as power cables and power equipment, one sample has a different dielectric constant. Therefore, there was a problem that the calibration error became large.

The present invention has been made to solve the above-mentioned conventional problems, and includes a water cable in a double-layer dielectric such as a power cable connection portion and a power device, and an insulating material such as a power cable and a power device. An object of the present invention is to provide a charge density calibration method in space charge measurement that can reduce a calibration error even when applied to dielectrics having different dielectric constants such as a deteriorated part and a healthy part.

[0036]

The charge density calibration method in space charge measurement of the present invention that achieves the above object is as follows.
By applying a high-voltage pulse having a narrow pulse width to both ends of a dielectric having two different dielectric constants via electrodes, a detection voltage signal corresponding to a pressure wave generated at an interface between the dielectric and the electrode is determined in advance. In the charge density calibration method in the space charge measurement in which the space charge density of the dielectric is calibrated by performing arithmetic processing by an arithmetic element of the deconvolution processing, the space of the dielectric part having the lower dielectric constant of the two dielectric constants is calculated. When the charge density is calibrated by a predetermined operation element of the deconvolution processing, a proportional constant of two previously measured dielectric constants of the dielectric is obtained, and the proportional constant is determined by the predetermined deconvolution processing. The operation element of the deconvolution process multiplied by the low dielectric constant as the operation element is applied.

According to the charge density calibration method in the space charge measurement, a space charge density corresponding to the dielectric constant of each part can be obtained, so that a highly accurate space charge measurement with a small calibration error can be performed. Further, in the charge density calibration method in the space charge measurement of the present invention, when the space charge measurement is the PEA method, a predetermined operation element of the deconvolution processing is:

[0038]

[Equation 14]

(Where R (f) is the Fourier-transformed value of the space charge distribution ρ (t), ρ (0) is the space charge density at position x = 0, and VS (f) is the detected voltage signal V (t) Is the value obtained by Fourier transform of V
S ₁ (f) is a value obtained by Fourier-transforming the detection voltage signal V (0), V _dc is a DC voltage applied to the dielectric, V _{sa mp} is the sound velocity of the dielectric, τ
Is the sampling interval. In addition, kε _{2 =} ε ₁ , ε ₂ is a dielectric constant of a dielectric part having a low dielectric constant, ε ₁ is a dielectric constant of a dielectric part having a high dielectric constant, and k is a proportional constant. Also, ε ₂ = ε ₀ ε _r , ε ₀ is the vacuum permittivity, and ε _r is the relative permittivity of a portion of the dielectric material having a low permittivity. )
It is. Thus, by multiplying ε ₀ ε _r by the proportional constant of the two dielectric constants, it is possible to calibrate the space charge density of the portion of the dielectric having a low dielectric constant with a small error.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a charge density calibration method in space charge measurement according to the present invention will be described with reference to the drawings. Note that the measurement sample is a two-layer dielectric having different dielectric constants. The measurement apparatus to which the charge density calibration method in the space charge measurement of the present invention is applied, for example, as shown in FIG. 1, has the same basic configuration as the conventional measurement apparatus based on the PEA method (pulse electrostatic stress method). A DC generator 2, a pulse voltage generator 3, electrodes 4 and 5, a piezoelectric element 6, a signal detector 7, and a calculator 8 are provided.

The DC generator 2 has the + side connected to one end of the protection resistor R, the − side connected to the ground, and the other end of the protection resistor R connected to the electrode 5. The connection point between the other end of the protection resistor R and the electrode 5 is connected to one end of the pulse voltage generator 3 via the capacitor C, and the other end of the pulse voltage generator 3 is connected to the ground electrode 4. This pulse voltage generator 3
The connection point between the other end and the ground electrode 4 is connected to the ground. The ground electrode 4 is a measurement sample 50 made of a two-layer dielectric.
Layer 50 having a high dielectric constant ε ₁ (FIG. 1 (a))
a, the electrode 5 has a low dielectric constant ε of the measurement sample 50.
₂ (FIG. 1 (a)) is surface bonded to the end face of the other layer 50b.

Therefore, the DC generator 2
To apply the DC voltage _Vdc , the charge amount σ (0) at the interface between the ground electrode 4 and one of the layers 50a (FIG. 1)
(C)) and the charge amount σ (D) (FIG. 1 (c)) at the interface between the electrode 5 and the other layer 50b can be set to arbitrary values. Further, the pulse voltage generator 3 can apply a high-voltage pulse V _P (t) having a narrow pulse width to the measurement sample 50 in which the interface charges σ (0) and σ (D) have been generated. Pulse-like Maxwell stress f (0) (FIG. 1 (d)) is applied to the interface between one layer 50a and the electrode 5 and the other layer 50b.
Maxwell stress f (D) at the interface of
(D)) will work respectively.

The piezoelectric element 6 is fixed to one end 4a of the ground electrode 4. The other end 4b of the ground electrode 4 is
0 is the detection unit. Such a piezoelectric element 6 is connected to a signal detecting section 7 provided with a digital oscilloscope, and the signal detecting section 7 is connected to an arithmetic section 8. Signal detector 7
Is for sending the detected voltage signal V (t) detected by the piezoelectric element 6 to the arithmetic unit 8 at a predetermined sampling rate by a digital oscilloscope. The arithmetic unit 8 performs addition and averaging of the detection voltage signal V (t) sent from the signal detection unit 7 a predetermined number of times, and then performs deconvolution processing to calibrate the space charge density.

The operation element of the deconvolution processing in the operation unit 8 is an element capable of calculating the space charge density in the measurement sample 50 having different dielectric constants ε ₁ and ε ₂ with a small calibration error. The operation element of the first deconvolution process for calibrating the space charge density of one layer 50a having a high dielectric constant ε ₁ of 50 is as follows:

[0045]

(Equation 15)

Then, the operation element of the conventional predetermined deconvolution processing is applied. Here, R (f) is a value obtained by Fourier-transforming the space charge distribution ρ (t), and ρ (0) is a position x = 0.
, VS (f) is a value obtained by Fourier-transforming the detected voltage signal V (t), VS ₁ (f) is a value obtained by _performing a Fourier transform on the detected voltage signal V (0), and V _samp is the fourth value of the measurement sample 50. One layer 50a
Τ is a sampling interval. Also, ε ₁ = ε ₀
ε _r , ε ₀ is the vacuum dielectric constant, and ε _r is the relative dielectric constant of the first layer 50 a of the measurement sample 50.

On the other hand, the operation element of the second deconvolution processing for calibrating the space charge density of the other layer 50b having the low dielectric constant ε ₂ of the measurement sample 50 is as follows:

[0048]

(Equation 16)

Then, the proportional constant k of the _two previously measured dielectric constants ε ₁ and ε ₂ of the dielectric 50 is determined, and the high dielectric constant ε ₁ of the operation element of the first deconvolution processing is calculated.
Is replaced by a low dielectric constant ε ₂ , and the obtained constant of proportionality k is multiplied by a low dielectric constant ε ₂ which is an operation element of the first deconvolution processing. Here, ε ₂ = ε ₀ ε _r , ε _r is the relative dielectric constant of the second layer 50b of the measurement sample 50, and V _samp is the sound velocity of the second layer 50b of the measurement sample 50.

Therefore, if the detection voltage signal V (0) obtained when the DC voltage _Vdc is applied is determined as a reference waveform, the detection voltage signal V (t) of the measurement sample 50 having an unknown space charge can be obtained. , The Fourier transform R (f) of the space charge distribution is obtained. Then, this is subjected to an inverse Fourier transform to obtain a space charge density ρ (x). Here, the space charge density of the other layer 50b having a low dielectric constant epsilon ₂ of the measurement sample 50, when the calibration operation elements of the second deconvolution processing, multiplied by a proportional constant k to the lower dielectric constant epsilon ₂ Explain why you must do so. For simplicity,
The measurement sample 50 and the electrodes 4 and 5 are assumed to be sufficiently large to guide the space charge density.

When a high-voltage pulse V _P (t) having a narrow pulse width is applied to the two-layer dielectric measurement sample 50 having different dielectric constants ε ₁ and ε ₂ by the pulse voltage generator 3, the pulse is applied to the interface between both electrodes. Maxwell stresses f (0) and f (D) (FIG. 1 (d)) work. The Maxwell stresses f (0) and f (D) are stresses caused by the difference between the dielectric constant of each dielectric of the measurement sample 50 and the electrodes 4 and 5.

If the voltage pulse electric field at the interface between the ground electrode 4 and the measurement sample 50 is e _P (0), and the voltage pulse electric field at the interface between the electrode 5 and the measurement sample 50 is e _P (D),

[0053]

[Equation 17]

[0054]

(Equation 18)

Is as follows. However, x ₁ is the thickness of the first layer 50a of the sample 50, x ₂ is the thickness of the second layer 50b of the measurement sample 50, D is the total thickness of the measurement sample 50. From these equations,

[0056]

[Equation 19]

[0057]

(Equation 20)

When the first layer 50a and the second layer 50b of the measurement sample 50 have the same dielectric constant (ε ₁ = ε ₂ ),

[0059]

(Equation 21)

When the dielectric constants of the first layer 50a and the second layer 50b of the measurement sample 50 are different, (ε ₁ = kε
₂ ),

[0061]

(Equation 22)

Is obtained. Accordingly, as shown in FIG. 1 (b), a first layer 50a of the high measurement sample 50 is the dielectric constant epsilon ₁
It can be seen that the interface voltage pulse electric field E _p (0) is k times lower than the interface voltage pulse electric field E _p (D) of the second layer 50b of the measurement sample 50 having a low dielectric constant ε ₂ . Thereby, for example, as shown in FIG. 1C, the surface charge densities σ (0), σ (D)
Are the same,

[0063]

(Equation 23)

[0064]

(Equation 24)

Thus, the Maxwell stress f (0) acting on the interface voltage pulse electric field e _p (0) and the interface voltage pulse electric field e _p (0)
There will be a k-fold difference from the Maxwell stress f (D) acting on _p (D). Thus, when calibrating the true surface charge densities σ (0) and σ (D) from the measured detection voltage signals v (0) and v (D), the calibration takes into account the difference of k times the dielectric constant. Then, accurate space charge densities ρ (0) and ρ (D) can be obtained (FIGS. 1E and 1F).

In the space charge measuring device 1 provided with the operation unit 8 having such a deconvolution process as an operation element,
Two-layer dielectrics 50a, 50 having different dielectric constants ε ₁ , ε ₂
A method for measuring the space charge of the measurement sample 50 composed of b will be described. First, the piezoelectric element 6 of the space charge measuring device 1
Is fixed to the ground electrode 4 having the high dielectric constant ε of the measurement sample 50.
The first layer 50a having _1, keep each interview is dressed electrode 5 to the second layer 50b having a low dielectric constant epsilon ₂ of the measurement sample 50. In this state, the measurement sample 5 is
When a DC voltage _Vdc is applied to 0, an arbitrary value of surface charge σ (0), σ (D) is applied to the interface between the ground electrode 4 and one layer 50a and the interface between the electrode 5 and the other layer 50b, respectively. Is induced. The surface charge σ (0), σ the measurement sample 50 (D) is derived, when a pulse voltage generator 3 applies a narrow pulse voltage V _P of the width of the high voltage, the piezoelectric element 6 is the ground electrode 4
And a detection voltage signal V (0) corresponding to a pressure wave generated in one layer 50a of the measurement sample 50, the electrode 5 and the measurement sample 5
And a detection voltage signal V (D) corresponding to the pressure wave generated in the other layer 50b.

The detection voltage signal V (0) and the detection voltage signal
V (D) is sent to the calculation unit 8 by the digital oscilloscope of the signal detection unit 7 at a predetermined sampling rate.
The calculation unit 8 includes a detection voltage signal V (0) and a detection voltage signal V (D).
Is added and averaged a predetermined number of times, and then the arithmetic elements of the first deconvolution processing are:

[0068]

(Equation 25)

An operation element of the second deconvolution processing,

[0070]

(Equation 26)

Thus, one layer 50 of the measurement sample 50 is
a and the space charge density of the other layer 50b are respectively calibrated. Thereby, each layer 50a, 50b of the measurement sample 50 is
Since the space charge density according to the dielectric constants ε ₁ and ε ₂ can be obtained, space charge measurement with a small calibration error and high accuracy can be performed.

In the embodiment of the present invention, the charge density calibration method is applied to the PEA method. However, the present invention is not limited to this, and may be applied to the PWP method (pressure wave method). In the embodiment of the present invention, a two-layer dielectric is measured. However, the present invention is not limited to this. Any dielectric having two different dielectric constants can accurately measure the space charge density. Can be measured. For example, in the case of a water tree deteriorated part and a sound part in one insulating material, the water tree deteriorated part is measured by a method of measuring the permittivity of the water tree deteriorated part (Japanese Patent Application No. 10-57257) filed by the present applicant. By measuring the dielectric constant of the above, it is possible to perform more accurate charge density calibration in space charge measurement.

Specifically, a water tree deterioration measuring device (see FIG.
(Not shown) are connected to the water tree deterioration part of the insulating material and
And sound parts. And arithmetic processing unit
At different frequencies ω₁, Ω_TwoSet the insulation with AC generator
Different frequencies ω applied to the sample ₁, Ω_TwoVoltage Ve at^JK(However
And K = θ. ) And current Ie^JQ(However, Q = θ + φ
And ) And measure each frequency ω₁, Ω_TwoComplex in per
Operate the impedance Z and calculate the complex impedance Z
From each frequency ω₁, Ω_TwoCapacitance C1, C2 and
And the conductances G1 and G2 are predetermined arithmetic elements,

[0074]

[Equation 27]

[0075]

[Equation 28]

[0076]

(Equation 29)

[0077]

[Equation 30]

By substituting the values into the arithmetic processing, the dielectric constant ε _W of the water tree deteriorated portion of the insulating material can be accurately measured. Note that C _P is the capacitance of the healthy part, C _W is the capacitance of the water tree deteriorated part, l _W is the water tree length of the water tree deteriorated part, ε ₀ is the vacuum permittivity, ε _P is the relative permittivity of the insulating material, S
Is the area where water trees are generated. With this, accurate dielectric constants of the water tree deteriorated portion and sound portion of the insulating material can be used as calculation data of the charge density calibration method in the space charge measurement of the present invention, so that more accurate charge density calibration is performed. be able to.

[0079]

As described above, according to the charge density calibration method for space charge measurement of the present invention, calibration is performed by deconvolution processing according to each dielectric constant of a dielectric having two different dielectric constants. Therefore, power cable connection, double-layer dielectrics for power equipment, etc., water tree deterioration parts and sound parts in insulating materials for power cables, power equipment, etc.
Even when applied to an inhomogeneous dielectric, the calibration error can be reduced. Thereby, highly accurate space charge measurement with a small calibration error can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a charge density calibration method in space charge measurement according to the present invention, wherein (a) is a circuit diagram showing a space charge measuring device, and (b) shows an electric field distribution by applying a pulse voltage. FIG. 3C is a diagram showing a surface charge density, FIG. 4D is a diagram showing a force acting on an interface between an electrode and a measurement sample, FIG. 5E is a diagram showing a voltage waveform detected by a piezoelectric element, and FIG. The figure which shows a density.

FIG. 2 is a diagram showing a charge density calibration method in a conventional space charge measurement, in which (a) is a circuit diagram showing a space charge measurement device,
(B) is a diagram showing surface charge density and space charge density,
(C) is a diagram showing a pressure wave, and (d) is a diagram showing a voltage waveform detected by a piezoelectric element.

[Explanation of symbols]

4 ..... ground electrode 5 ----- electrode epsilon ₁ ..... high dielectric constant epsilon ₂ ----- low dielectric constant V _P ----- narrow pulse width high voltage pulse V (t), V (0), V (D) ..... Detection voltage signal

Claims (2)

[Claims] 1. Detection according to a pressure wave generated at an interface between the dielectric and the electrode by applying a high-voltage pulse having a narrow pulse width to both ends of a dielectric having two different dielectric constants via electrodes. A charge density calibration method in space charge measurement for calibrating a space charge density of the dielectric by performing arithmetic processing on a voltage signal by a predetermined operation element of deconvolution processing, wherein a low dielectric constant of the two dielectric constants is used. When calibrating the space charge density of the part of the dielectric having the predetermined deconvolution processing operation element,
An arithmetic element for deconvolution processing in which a proportional constant of the two previously measured dielectric constants of the dielectric is obtained, and the proportional constant is multiplied by the low dielectric constant to be an arithmetic element for the predetermined deconvolution processing A charge density calibration method in space charge measurement, characterized in that: 2. The arithmetic element of the predetermined deconvolution processing when the space charge measurement is the PEA method is as follows: (However, R (f) is a value obtained by performing a Fourier transform on the space charge distribution ρ (t), ρ (0) is a space charge density at the position x = 0, and VS (f) is a Fourier transform of the detected voltage signal V (t). VS ₁ (f) is a value obtained by Fourier transforming the detection voltage signal V (0), V _dc is a DC voltage applied to the dielectric, V _samp is the sound speed of the dielectric, and τ is a sampling interval. Also, kε _{2 =} ε ₁ , ε ₂ is the dielectric constant of the dielectric part having the low dielectric constant, ε ₁ is the dielectric constant of the dielectric part having the high dielectric constant, and k is the proportional constant. , Ε ₂ = ε ₀ ε _r , ε ₀ is the vacuum dielectric constant, and ε _r is the relative dielectric constant of the portion of the dielectric material having the low dielectric constant.) Charge density calibration method for space charge measurement.