JPH06258380A - Detecting method for defect or impurity of insulator - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is capable of performing an inspection in a non-destructive state without destroying an insulator to be measured, and capable of performing a precise quantitative determination up to the electronic number level regardless of the skill level of an operator. It is an object to provide a method of detecting possible insulator defects or impurities. According to the present invention, semiconducting layers 3 and 5 are provided on both sides of an insulator sample 40 so as to sandwich the insulator sample 40, and a pair of electrodes are connected to the insulator sample 40 via the semiconducting layers 3 and 5. Connected to the electrode, a high-voltage pulse is applied to the insulator sample to generate an elastic wave, and the semiconductive layer adjusts the elastic impedance between the electrode and the insulator sample to prevent a reflected wave. The obtained acoustic wave is measured by an acoustic sensor, the space charge distribution accumulated in the insulator is measured based on the output signal of the acoustic sensor, and defects or impurities in the insulator are determined from the waveform of the space charge distribution. It is something to detect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting defects or impurities contained in an insulator made of a resin such as cross-linked polyethylene used for insulation of power cables, etc. It relates to a method capable of detection.

[0002]

2. Description of the Related Art As is well known, a power cable has a structure in which an outer circumference of a conductor is sequentially covered with an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a shielding layer, a sheath and the like. Crosslinked polyethylene used for the insulating layer of this power cable, or a transparent or semitransparent resin insulator similar to this, in the manufacturing process, foreign particles such as metal particles or scorch particles are mixed, There are problems such as generation of fine voids and protrusions such as protrusions, and mixing of ionic impurities made of undecomposed additives. If such foreign matters, defects, or impurities are present inside the insulator, the insulation performance of the power cable may be deteriorated due to these, and the reliability of the power cable may be impaired.

For this reason, conventionally, when quality control of the insulator is performed, a part of the manufactured insulator is cut out thinly and observed with a microscope. From the number and size of foreign matter, a portion other than the cut-out portion is cut off. A method of assuring the quality of the insulation has been implemented.

[0004]

However, in the above method, since the ability of the observer himself has a great influence on the accuracy of quality control, the observation accuracy varies depending on the skill of the observer, and The deterioration of observation accuracy due to fatigue is a problem. In addition, in recent years, with the increase in size, pressure and quality of power cables, even if the size of foreign matter contained in the insulator is extremely small, it tends to be a problem. There is a problem that causes a limit in terms of.

As a method for inspecting impurities in a resin insulator, a part of the insulator is shredded or sliced to take out a sample, and the sample is analyzed by infrared spectroscopy or ion chromatography. However, since all of these methods are destructive tests that destroy the inspection body, for example, only samples are taken from both ends of the power cable for inspection, and inspection over the entire length of the power cable is substantially There is a problem that cannot be executed. Further, in these analysis methods, the inspection sensitivity is limited to the ppm order, but in some cases, higher accuracy may be required.

On the other hand, when a CV cable or the like is used for DC power transmission, it is known that the space charge distribution accumulated in the cable insulator is an extremely important judgment material for diagnosing the deterioration of the cable and the like. There is. For this reason,
Various methods have been proposed for measuring the space charge distribution in cable insulation. The thermally stimulated current method, the Maxwell stress method, the thermal pulse method, and the like are known as methods for measuring the space charge inside the insulator, but the space charge distribution cannot be directly obtained by these methods. Also,
The electron beam method is known as a method for obtaining the space charge distribution, but this method is a destructive inspection, and once it is measured, the accumulated charge is lost, and it is not possible to obtain the change over time in the charge distribution. . Therefore, these methods are not suitable for measuring the space charge distribution of cable insulation.

Incidentally, the pulse electrostatic stress method is known as another method for quantitatively measuring the space charge distribution in the insulator. This method applies a high-voltage pulse to an insulator sample in which space charges are accumulated, thereby causing an electrostatic force to act on the charge in the insulator to cause strain in the sample, and this strain causes the insulator sample to This is a method of detecting the generated elastic wave by a piezoelectric element. The output signal level of this piezoelectric element depends on the amount of space charge inside the insulator, and
The time difference from the application of the high voltage pulse to the detection of the elastic wave depends on the distance from the charge storage position. For this reason,
From these signal levels and arrival times, the charge distribution inside the insulator can be quantitatively measured.

However, according to the above-mentioned conventional measuring method by the pulse electrostatic stress method, when a sheet-shaped insulator sample is measured, components other than the charge distribution of the insulator sample itself are included in the obtained charge distribution. It is known to be mixed. This is considered to be caused by reflection of elastic waves inside the insulator sample, or mismatch of acoustic impedance between the electrode that charges the insulator sample and the insulator sample. On the other hand, when the space charge distribution of the cable-shaped insulator sample is measured by the measurement method using the pulse electrostatic stress method, since the cable insulator is cylindrical, elastic waves propagating in the cable insulator are radial. As a result, the input timing of the elastic wave varies depending on the position on the plane incident surface of the piezoelectric element, and the input elastic wave is reflected on the surface of the piezoelectric element. Therefore, the detection signal does not faithfully reflect the actual waveform of the elastic wave.
Therefore, in order to accurately detect the space charge distribution of the cable insulator, it is necessary to grasp the influences caused by these timing shifts and reflection components in advance and remove these influences after the detection. However, there was a problem that analysis was time-consuming.

Therefore, the inventors of the present invention have improved the measuring device in order to measure only the pure charge distribution obtained from the sample itself in any of these sheet-like insulator samples and cable-like insulator samples. The above problems are gradually being solved. However, it becomes possible to measure a pure space charge component obtained from the sample itself, and while analyzing the measurement result, conversely, the distribution of the space charge component causes defects such as defects and defects existing inside the insulator sample itself. They have found that they are extremely effective in detecting foreign substances or ionic impurities, and have reached the present invention.

The present invention has been made in view of the above circumstances, and it is possible to perform an inspection in a non-destructive state without destroying an insulator to be measured, and to the electronic number level regardless of the skill level of an operator. It is an object of the present invention to provide a method for detecting defects or impurities in an insulator, which enables accurate quantification.

[0011]

In order to solve the above problems, a semiconductive layer is provided on both sides of an insulator sample so as to sandwich the insulator sample, and the semiconductive layer is interposed between the semiconductive layers. Connect a pair of electrodes to the insulator sample, apply a high-voltage pulse to the insulator by the electrode to generate an elastic wave, and adjust the elastic impedance between the electrode and the insulator sample by the semiconductive layer. To prevent reflected waves, measure the obtained elastic wave with an acoustic sensor, measure the space charge distribution accumulated in the insulator based on the output signal of this acoustic sensor, and insulate from the waveform of this space charge distribution. It detects defects or impurities in the body.

In order to solve the above-mentioned problems, the invention according to claim 2 uses, as the insulator sample according to claim 1, a hollow cable insulator covering an inner conductor and an inner semiconductive layer, and the inner conductor is used as the inner conductor. A high voltage pulse is applied between the connected electrode and an electrode provided via an external semiconductive layer provided outside the cable insulator to measure the space charge distribution of the cable insulator. This is to detect defects or impurities in the insulator from the waveform of distribution.

In order to solve the above-mentioned problems, the invention according to claim 3 provides a space charge distribution according to claim 1 or 2.
Positive charge accumulation is seen on the negative side of the insulator sample,
When negative charge accumulation is observed on the positive side, the existence of ionic impurities is estimated, and when the space charge distribution has an irregularly shaped charge distribution, the existence of defects or foreign particles is estimated. .

[0014]

The original space charge distribution of the insulator sample can be obtained by removing the factors such as reflection and absorption of the elastic wave propagating in the insulator sample and detecting only the elastic wave originally generated by the insulator sample. Yes, from the analysis of its charge distribution,
It is possible to estimate the existence of defects such as ionic impurities and microvoids contained in the insulator sample, and the presence of foreign matter such as fibrous impurities. For example, when positive charge accumulation is observed on the negative side of the insulator sample and negative charge accumulation is observed on the positive side, the presence of ionic impurities can be estimated inside the insulator sample. If the charge distribution shows a distorted waveform regardless of whether the charge distribution is on the positive side or the negative side, it can be presumed that there is a substance that reflects or diffracts elastic waves inside the insulator sample. It can be inferred that defects such as microvoids and fibrous impurities exist inside the body.

On the other hand, when the semiconductive layer is interposed between the insulator sample and the electrode, unlike the case where the electrode is brought into direct contact with the insulator sample, the elastic wave is reflected on the surface portion of the insulator sample. Since there is no unnecessary charge distribution component detected by reflection of elastic waves, the original space charge distribution of the insulator sample can be obtained. Furthermore, a cable insulator can be used as the insulator sample, and defects, foreign matters or ionic impurities in the hollow insulator sample can be detected from the waveform of the space charge distribution obtained in this case.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are views showing the configuration of a space charge distribution measuring device for a cable insulator used when carrying out the method of the present invention. The sample cable 1 to be measured is
In this example, as shown in FIG. 2, the inner conductor 2, the inner semiconductive layer 3, the cable insulator (insulator sample) 4, and the outer semiconductive layer 5 are coaxially arranged in order from the center. As shown in FIG. 1, a DC voltage power source 8 is connected to one end of the inner conductor 2 of the sample cable 1 through a resistor 6 and a switch 7 in series. With this configuration, a DC voltage or a ground potential is applied to the inner conductor 2. Can be selectively applied to. Further, a high voltage pulse generator 11 is connected to the other end of the inner conductor 2 via a switch 9 and a coupling capacitor 10 so that a high voltage pulse can be selectively applied to the inner conductor 2 by this configuration. Has become.

On the other hand, a plate-shaped support base 12 is provided below the sample cable 2, and a plate-shaped upper electrode 13 is provided directly above the sample cable 2, and the support base 12 and the upper electrode 13 are provided respectively. At the four corners, the support base 12 is fastened via the columns 14, and the support base 12 is grounded. An acoustic sensor 15 is installed on the support 12, and the sample cable 1 is held between the upper surface of the acoustic sensor 15 and the lower surface of the upper electrode 13.

As shown in FIG. 2, the acoustic sensor 15 is provided with a brass shield container 20 having an open upper surface and an input electrode 21 attached to the upper portion thereof.
The piezoelectric element 22, the absorber 23, the extraction electrode 24, and the insulator 25 are sequentially laminated inside the 0 so as to be laminated below the input electrode 21. At the upper end of the input electrode 21, a receiving portion 21a having a concave curved surface having the same radius of curvature as the outer diameter of the sample cable 1 is formed so as to be in close contact with the lower surface of the sample cable 1. This receiving portion 21a is shown in FIG. As shown in FIG. 5, the flange 21b is formed at the lower part of the receiving portion 21a, and the opening of the shield container 20 is closed by the flanges 21b and 21b.

The piezoelectric element 22 comprises a film made of polyvinylidene fluoride (PVDF) and conductive films such as aluminum formed on both upper and lower surfaces thereof, and is provided in close contact with the bottom surface of the input electrode 21. It should be noted that the piezoelectric element 22 has a value of 11
Although it is formed to have a thickness of about 0 μm, in the present invention, it is necessary to measure a trace amount of impurities, impurities with small mobility, and small defects, and it is necessary to measure with high sensitivity. For example, about 28 μm) is preferable. The absorber 23 is formed of a resin having substantially the same acoustic impedance as that of the piezoelectric element 22, and when the piezoelectric element 22 is formed of polyvinylidene fluoride as described above, for example, polymethylmethacrylate (PMMA) is used.
And the like. A concave curved surface having the same radius of curvature as the sample cable 1 is formed on the upper surface of the absorber 23 so as to be in close contact with the lower surface of the input electrode 21 via the film-shaped piezoelectric element 22. A convex portion 23b is formed on the lower portion. The extraction electrode 24 is formed to have a concave cross-section so that the convex portion 23b of the absorber 23 can be inserted, and a plate-shaped insulator 25 is provided on the bottom surface side of the extraction electrode 24. It is installed on 12.

The electrodes on the lower surface side of the piezoelectric element 22 and the extraction electrode 24 are electrically connected, for example, at both ends via a conductor 27 such as tin foil sandwiched between these electrodes and the absorber 23. It is connected to the. Further, the extraction electrode 24 is connected to the container 20 via the extraction part 28 formed in the container 20.
Is connected to the lead wire 29 that is drawn out of the
A detection signal is taken out from this lead wire 29. The lead wire 29 is connected to a computer 33 via a wide band amplifier 31 and a signal processing circuit 32 for performing an averaging process as shown in FIG. 1, so that the computer 33 calculates a space charge distribution. Has become. Note that these detection systems are connected by a double shielded coaxial cable, and for example, the input resistance of the amplifier is only 1 MΩ, and the others are matched with 50Ω.

Next, a method of measuring the space charge distribution of the cable insulator 1 by using the space charge distribution measuring device configured as described above and detecting the defects and impurities thereof will be described. First, with the input electrode 21 and the shield container 20 grounded, the switch 7 is connected to the DC voltage power supply 8 side,
When a high voltage of, for example, 20 kV is applied to the inner conductor 21, charges are accumulated in the inner conductor 2. In this state, when the switch 9 is closed and a high voltage pulse of, for example, −1 kV and 10 nsec as shown in FIG. 4 is applied to the inner conductor 2 from the high voltage generation circuit, as shown in FIG.
Static electricity is generated in the induced charges respectively induced at the interfaces between the semiconductive layers 3 and 5, and strain is generated inside the cable insulator 4, whereby elastic waves 35 are radially generated.

The high voltage pulse to be loaded is
In the usual space charge measurement, it is set to about 50 to 90 nsec, but in the present invention, it is necessary to measure a trace amount of impurities, impurities with small mobility, and small defects, and it is necessary to perform measurement with high sensitivity. Therefore, since defects and impurities that can obtain only a small signal are measured, it is necessary to increase the voltage applied from the outside and to obtain an accurate value by increasing the resolution. Therefore, as described above, if the thickness of the piezoelectric element 22 is changed from about 90 μm to about 28 μm and the pulse width is changed from about 50 nsec to about 10 nsec, the resolution of about 200 μm can be increased to about 50 μm. By doing so, when the thickness of the piezoelectric element 22 is set to 90 μm and the pulse width is set to 50 nsec, both pulses overlap with each other in the plus region and the minus region and become undetectable. Can be detected separately.

As shown in FIG. 4, the elastic wave 35 is composed of a negative polarity pulse 35a immediately after the application of the high voltage pulse and a positive polarity pulse 35b arriving slightly later than the negative pulse 35a.
The former negative polarity pulse 35a is an elastic wave generated by positive charges distributed on the outer peripheral side of the cable insulator 4, and the latter positive polarity pulse 35b is elastic wave generated by plasma charges distributed on the inner peripheral side of the cable insulator. It is a wave, and the difference in arrival time between the two indicates the existence position of the electric charge. As shown in FIG. 3, the elastic wave 35 reaches the piezoelectric element 22 through the same acoustic impedance and the same distance in the input electrode 21.

The elastic wave 35 input to the piezoelectric element 22 is
Here, it is converted into an electric signal, and the electrodes on the bottom surface and the tin foil 2
It is taken out to the outside as a detection signal through 7 and the take-out electrode 24 and the lead wire 29. In addition, the piezoelectric element 22 and the absorber 2
The elastic wave 35 reaching the interface with 3 is input to the absorber 23 that is acoustically matched without being reflected, and is attenuated by the absorber 23. In this acoustic sensor 15,
Since the elastic wave 35 is not reflected and is absorbed by the absorber 23, the detection signal to be detected has almost no influence of the reflected wave,
As shown in FIG. 4, the pulse-shaped signal faithfully reflects the influence of the input elastic wave 35.

On the other hand, as shown in FIG.
Although the detection signal of 1 contains some electric noise, the signal 36 due to the elastic wave is a pulse-shaped signal, and the electric noise 37 is an oscillating waveform. Can be clearly distinguished. The output signal of the acoustic sensor 15 is amplified by the wide band amplifier 31 and input to the signal processing circuit 32. In the signal processing circuit 32, for example, a detection signal from which random noise is removed is obtained by performing an averaging process in which detection signals are repeatedly overlapped with a high voltage pulse as a trigger. This signal is input to the computer 33 as detection data. The computer 33 calculates the space charge distribution of the sample cable 1 by converting the input data into a charge amount.

As described above, according to the apparatus having the above structure, the piezoelectric element 22 is formed of polyvinylidene fluoride film, and the boundary surfaces of the input electrode 21, the piezoelectric element 22 and the absorber 23 are coaxial with the sample cable 1. In addition to disposing the absorber 23 on the lower surface of the piezoelectric element 21, the absorber 23 acoustically matched with the piezoelectric element 21 is arranged, so that the elastic wave propagated from the sample cable 1 can be observed without being affected by the reflected wave.
Therefore, it is possible to accurately measure the space charge distribution of the cable insulator using the pulse electrostatic method. Therefore, this measuring device can be used to evaluate the insulator such as the search for the cause of the water tree and to investigate the removed cable.

In the case of using the above apparatus, the sample cable 1 having a charge history may be measured with the switch 7 in the open state or with the switch 7 closed and the DC voltage applied. good. Also, according to this method,
Since the sample cable 1 can be tested nondestructively, it can be applied not only to the measurement of the temporal change of the space charge distribution during the charge deterioration test, but also to the hot wire deterioration diagnosis technology.

Here, for example, when the space charge distribution is measured by the above-mentioned method using the above-mentioned apparatus using an insulator sample of crosslinked polyethylene, it is assumed that the charge distribution as shown in FIG. 7 is obtained. When such a positive parabolic charge distribution appears on the negative side and a negative parabolic charge distribution appears on the positive side, the inside of the insulator sample contains ionic impurities resulting from the decomposition residue of the crosslinking agent. It can be presumed to be an insulator sample. Next, when an insulator sample having the same composition as the above is used to perform the same measurement as the above and a charge distribution having an irregular waveform as shown in FIG. 8 is obtained,
It can be presumed that microvoids or fibrous substances exist inside the insulator sample, and it can be presumed to be due to the reflection phenomenon of elastic waves by these substances.There are microvoids and fibrous defects in the insulator sample. It can be estimated that

On the other hand, when the space charge distribution of an insulator sample containing no ionic impurities, foreign matters, or defects is measured, the parabolic or distorted waveform is not detected at all. From the above, by analyzing the obtained space charge distribution waveform, ionic impurities of the insulator sample,
Defects such as micro voids and fibrous foreign substances can be detected. In addition, when measuring the space charge distribution, the measurement accuracy can be improved by thinning the piezoelectric element and shortening the pulse width of the high-voltage pulse, so it is possible to support the number of electrons with much higher sensitivity than the ppm order. It is also possible to measure.

FIG. 5 shows an example of an apparatus for measuring the space charge distribution of the flat plate-shaped insulator sample 40. In the device of this example, the same configuration as the device of the previous embodiment,
The same reference numerals are given and the description of those portions is omitted. In this device, the semiconductive layer 4 is formed on the upper surface of the insulator sample 40.
1 is provided with a semiconductive layer 42 on the lower surface, and
0 is provided with an upper electrode 43 and a lower electrode 44 below, and a piezoelectric element 45 and an elastic wave absorber 46 are laminated below the lower electrode 44. Conductive films are formed on the upper and lower surfaces of the piezoelectric element 45, respectively.
The conductive film on the upper part of 5 is grounded, and the lower electrode is connected to the wide band amplifier 31, the signal processing circuit 32 and the computer 33 as in the device of the previous embodiment. The semiconductive layer 41,
42 is a resin material such as polyethylene in which particles of carbon or the like are dispersed, and the thickness thereof is preferably 0.5 mm or less, more preferably 0.2 to 0.5.
About mm is preferable. If the semiconductive layers 41 and 42 are formed to have a thickness of more than 0.5 mm, the acoustic wave propagating inside the insulator sample 40 is attenuated at the semiconductive layers 41 and 42 and reaches the piezoelectric element 45. The generated elastic wave may be different from the original one.

Next, a method of measuring the space charge distribution of the flat plate-like insulator by using the space charge distribution measuring device configured as described above and detecting the defects and impurities thereof will be described. First, with the lower electrode 44 grounded, the switch 7
Is connected to the DC voltage power source 8 side and a high voltage of 20 kV, for example, is applied to the upper electrode 43, electric charges are accumulated in the insulator sample 40. In this state, the switch 9 is closed, and the high-current generating circuit outputs -1k as in the above-described embodiment.
When a high voltage pulse of V and 10 nsec is applied to the upper electrode 43, static electricity is generated in the induced charges induced at the interfaces between the semiconductive layers 41 and 42 of the insulator sample 40, and the inside of the insulator sample 40 is distorted. Occurs, which causes an elastic wave to be generated. By detecting this elastic wave in the same manner as in the above-described embodiment and performing arithmetic processing on the computer 33,
The space charge distribution of the insulator sample 40 can be calculated.

In the apparatus of this embodiment, the space charge distribution can be obtained by directly contacting the upper electrode 43 and the lower electrode 44 with the insulator sample 40. In that case, the reflected wave with respect to the distribution curve is obtained. Is detected, which is not preferable. This reflected wave causes the thickness of the piezoelectric element 45 to be 110 μm.
At the time of normal level observation in which the pulse width of the high voltage pulse is set to about 50 nsec, the obtained space charge distribution curve is small and can be ignored, or
It is a level that can be easily corrected and removed in the computer 33. However, in the present invention, it is necessary to measure a small amount of impurities, impurities with small mobility, and small defects, and it is necessary to measure with high sensitivity. Therefore, if the reflected wave is generated, a measurement error may occur due to this. Therefore, as described above, the semiconductive layer 41 is provided between the insulator sample 40 and the upper electrode 43, and the lower electrode 44 and the insulator sample 40 are provided.
By providing the semiconductive layer 42 between the electrode 43 and
It is possible to prevent the generation of the reflected wave by matching the elastic impedances of 44 and the insulator sample 40. As a result, even when high-resolution measurement is performed, the space charge distribution can be measured with high accuracy without being affected by the reflected wave.

When the space charge distribution of the insulator sample is measured using the apparatus shown in FIG. 5, the same space charge distribution as in the case of the above-described example is obtained, so that the obtained space charge distribution provides insulation. It is possible to detect ionic impurities in a body sample, defects such as microvoids, or the presence of fibrous impurities.

By the way, as described above, the thickness of the piezoelectric element is changed from 110 μm to 28 μm, and the pulse width is 50 ns.
Change from ec to 10 nsec and change the resolution to 200μ
It can be increased from m to about 50 μm. Here, FIG.
100 μm inside the insulator sample 40 as shown in FIG.
When positive and negative charges are accumulated at a distance of, the output on the plus side and the minus side will overlap and become 0 when the resolution is 200 μm, but the resolution is 50 μm.
Then, the space charge distribution can be obtained as a waveform as shown in FIG.

Experimental Example 1 Space charge distribution of an insulator sample (length 80 mm, width 80 mm, thickness 3 mm) made of cross-linked polyethylene using dicumyl peroxide (DCP) as a cross-linking agent. Figure 7 shows the measurement results.
Shown in. At the time of this measurement, a semiconductive layer made of an ethylene copolymer having a thickness of 3 mm was adhered to the upper and lower surfaces of the insulator sample by press fusion, and the electrodes were contacted via the semiconductive layer. The piezoelectric element was made of polyvinylidene fluoride having a thickness of 28 μm, and the applied high voltage pulse was −1 kV and the pulse width was 10 nsec. From the results shown in FIG. 7, in this insulator sample, positive charge accumulation was observed on the negative side of the insulator sample, and negative charge accumulation was observed on the positive side of the insulator sample. That is, it is presumed to have ionic impurities.

Next, FIG. 8 shows the result of measurement of another insulator sample having the same composition as described above by the same means as described above. From the results shown in FIG. 8, the obtained charge accumulation distribution curve shows a distorted waveform, which is considered to be a waveform resulting from the reflection or diffraction of elastic waves inside the insulator sample. Therefore, it is presumed that this insulator sample has microcracks or fibrous defects that reflect or diffract elastic waves. In the insulator samples shown in FIGS. 7 and 8, if no foreign matter, defect or ionic residue is present, the charge density distribution curve does not appear and the charge density of 0 is maintained.

[0037]

As described above, according to the method of the present invention, it is possible to eliminate the factors such as reflection and absorption of the elastic wave propagating in the insulator sample and detect only the elastic wave originally generated by the insulator sample. By calculating the original space charge distribution of the insulator sample, it is possible to estimate the presence of foreign substances such as ionic impurities and microvoids contained in the insulator sample and fibrous impurities from the analysis of the charge distribution. it can. For example, if positive charge accumulation is seen on the negative electrode side of the insulator sample and negative charge accumulation is seen on the positive electrode side,
The presence of ionic impurities can be estimated inside the insulator sample. If the charge distribution shows a distorted waveform regardless of whether it is on the positive electrode side or the negative electrode side, it can be presumed that there is a substance that reflects or diffracts elastic waves inside the insulator sample. It can be presumed that defects such as microvoids and fibrous impurities exist inside the insulator.

Also, when a semiconductive layer is interposed between the insulator sample and the electrode, unlike the case where the electrode is brought into direct contact with the insulator sample, reflection of an elastic wave occurs on the surface portion of the insulator sample. Since it does not exist, the original space charge distribution of the insulator sample that does not include unnecessary components due to reflection can be obtained. Furthermore, a cable insulator can be used as the insulator sample, and in this case also, defects, foreign matter or ionic impurities in the hollow insulator sample can be estimated and detected from the waveform of the space charge distribution.

[Brief description of drawings]

FIG. 1 is a side view showing an example of a space charge distribution measuring device used for carrying out the method of the present invention.

2 is a cross-sectional view of the device shown in FIG. 1 taken along the line AA.

FIG. 3 is an explanatory diagram showing generated elastic waves.

FIG. 4 is an explanatory diagram showing an input high voltage pulse, an elastic wave generated and a detection signal.

FIG. 5 is a configuration diagram showing another example of the space charge distribution measuring device used when carrying out the method of the present invention.

FIG. 6 is an explanatory diagram showing a charge distribution generated in an insulator sample and a waveform obtained in that case.

FIG. 7 is an explanatory diagram showing an example of measurement results obtained by testing an insulator sample containing ionic impurities.

FIG. 8 is an explanatory diagram showing an example of measurement results obtained by testing an insulator sample containing defects and foreign matters.

[Explanation of symbols]

 1 sample cable, 2 inner conductor, 3 inner semiconductive layer, 4 cable insulator, 5 outer semiconductive layer, 8 DC voltage power supply, 11 high voltage pulse generator, 13 upper electrode, 22 piezoelectric element, 33 computer, 40 insulation Body sample, 41 semiconductive layer, 42 semiconductive layer, 43 upper electrode, 44 lower electrode, 45 piezoelectric element,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsutaka Yata 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Stock Company (72) Inventor Takashi Takahashi 1-5-1 Kiba, Koto-ku, Tokyo Stock Association Inside Fujikura

Claims (3)

[Claims] 1. A semiconductive layer is provided on both sides of an insulator sample so as to sandwich the insulator sample, a pair of electrodes is connected to the insulator sample through the semiconductive layer, and a high voltage pulse is applied by the electrodes. Applying to an insulator to generate an elastic wave, preventing the reflected wave by adjusting the elastic impedance between the electrode and the insulator sample by the semiconductive layer, the resulting elastic wave is measured by an acoustic sensor, The space charge distribution accumulated in the insulator is measured based on the output signal of the acoustic sensor, and the defect or impurity in the insulator is detected from the waveform of the space charge distribution. Method of detecting impurities. 2. A hollow cable insulator covering an inner conductor and an inner semiconductive layer is used as an insulator sample, and an electrode connected to the inner conductor and an outer semiconductive member provided outside the cable insulator. A high voltage pulse is applied between the electrode and a layer to measure the space charge distribution of the cable insulator, and defects or impurities in the insulator are detected from the waveform of this space charge distribution. The method for detecting defects or impurities in an insulator according to claim 1. 3. As a space charge distribution, when positive charge accumulation is observed on the negative side of the insulator sample and negative charge accumulation is observed on the positive side, the presence of ionic impurities is estimated to determine the space charge. The method for detecting defects or impurities in an insulator according to claim 1 or 2, wherein the presence of defects or foreign matter is estimated when a distorted charge distribution is observed.