JP3190158B2 - Method for detecting insulator defects or impurities - Google Patents

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 a resin insulator such as cross-linked polyethylene used for insulating power cables and the like, and more particularly, to a non-destructive inspection with high accuracy. It relates to a method that can be detected.

[0002]

2. Description of the Related Art As is well known, a power cable has a structure in which an outer periphery of a conductor is sequentially coated 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 similar transparent or translucent resin insulator, in the manufacturing process, metal particles, or foreign substances such as scorch particles are mixed, There are problems such as formation of defective portions such as minute voids and protrusions, and incorporation of ionic impurities composed of undecomposed products of additives. If such foreign matters, defects, or impurities exist inside the insulator, the insulation performance of the power cable may be reduced due to the presence of such foreign matters, defects, or impurities, 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. A method was implemented to guarantee the quality of the insulator.

[0004]

However, in the above-mentioned method, since the observer's own ability greatly influences the quality control accuracy, the observation accuracy varies depending on the skill of the observer, and the observer's skill is also increased. Reduction of observation accuracy due to fatigue is a problem. In addition, in recent years, as power cables have been increased in size, increased in pressure, and improved in quality, there has been a tendency that even if the size of foreign matter contained in the insulator is extremely small, a problem arises. However, there is a problem in terms of limitations.

[0005] As a method for inspecting impurities in a resin insulator, a method is used in which a part of the insulator is shredded or sliced, a sample is taken out, and analyzed using infrared spectroscopy or ion chromatography. However, since all of these methods are destructive inspections that destroy the test object, for example, only samples are taken out from both ends of the power cable and inspected, and inspection over the entire length of the power cable is substantially performed. There is a problem that can not be executed. In these analysis methods, the inspection sensitivity is limited in the order of ppm, 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 distribution of space charges accumulated in the cable insulator is a very important judgment factor in diagnosing deterioration of the cable and the like. I have. For this reason,
Various methods have been proposed for measuring space charge distribution in cable insulation. As a method for measuring the space charge inside the insulator, a heat stimulation current method, a Maxwell stress method, a heat pulse method and the like are known, but with these methods, the space charge distribution cannot be directly obtained. Also,
As a method for obtaining the space charge distribution, the electron beam method is known, but this method is a destructive inspection, and once measured, the accumulated charge is lost, and it is not possible to determine the change with time of the charge distribution. . Therefore, these methods are not suitable for measuring the space charge distribution of the cable insulator.

As another method for quantitatively measuring the space charge distribution in an insulator, a pulse electrostatic stress method is known. In this method, a high-voltage pulse is applied 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 distortion in the sample, and the strain causes the insulator sample to move from the insulator sample. This is a method of detecting the generated elastic wave using 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 accumulation position. For this reason,
From these signal levels and arrival times, the charge distribution inside the insulator can be quantitatively measured.

However, in the above-described measurement method using the pulsed electrostatic stress method, when a sheet-like insulator sample is measured, components other than the charge distribution of the insulator sample itself are included in the obtained charge distribution. It has been found to be mixed. This is considered to be caused by reflection of the elastic wave 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-like insulator sample is measured by the measurement method by the pulse electrostatic stress method, the elastic wave propagating in the cable insulator is radial because the cable insulator is cylindrical. Therefore, the input timing of the elastic wave differs depending on the position on the plane incidence 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 waveform of the actual elastic wave.
For this reason, in order to accurately detect the space charge distribution of the cable insulator, it is necessary to grasp in advance the effects caused by these timing shifts and reflection components, and to remove these influences after the detection. However, there is a problem that the analysis takes time.

In view of the above, the present inventors have improved the measuring device in order to measure only the pure charge distribution obtained from the sample itself in both the sheet-like insulator sample and the cable-like insulator sample. 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, on the contrary, the space charge component distribution may have defects or defects existing inside the insulator sample itself. The inventors have found that the present invention is extremely effective in detecting foreign substances or ionic impurities, and have reached the present invention.

[0010] The present invention has been made in view of the above circumstances, can be inspected in a non-destructive state without destroying the insulator to be measured, and up to the number of electrons regardless of the skill of the worker It is an object of the present invention to provide a method for detecting a defect or an impurity in an insulator that can be precisely quantified.

[0011]

According to a first aspect of the present invention, a semiconductor device is provided with a semiconductive layer on both sides of an insulator sample so as to sandwich the insulator sample. Connecting a pair of electrodes to the insulator sample, applying a high voltage pulse to the insulator by the electrodes to generate an elastic wave, and adjusting the elastic impedance between the electrode and the insulator sample by the semiconductive layer. The acoustic wave obtained is measured by an acoustic sensor, and the space charge distribution accumulated in the insulator is measured based on the output signal of the acoustic sensor. It detects defects or impurities in the body.

According to a second aspect of the present invention, there is provided an insulator sample according to the first aspect, wherein a hollow cable insulator that covers an inner conductor and an inner semiconductive layer is used as the insulator sample. A high voltage pulse is applied between the connected electrode and an electrode provided via an external semiconductive layer provided outside the cable insulator, and the space charge distribution of the cable insulator is measured. A defect or impurity in the insulator is detected from the waveform of the distribution.

According to a third aspect of the present invention, in order to solve the above-mentioned problems, the space charge distribution according to the first or second aspect is provided as:
Positive charge accumulation is seen on the negative side of the insulator sample,
When negative charge accumulation is seen on the positive side, the presence of ionic impurities is estimated, and when the charge distribution has an irregular shape as the space charge distribution, the presence of defects and foreign substances is estimated. .

[0014]

[Function] The original space charge distribution of an insulator sample can be obtained by detecting only the elastic waves originally generated by the insulator sample by removing factors such as reflection and absorption of the elastic wave propagating in the insulator sample. From the analysis of the charge distribution,
It is possible to estimate the presence of defects such as ionic impurities and microvoids and foreign substances such as fibrous impurities contained in the insulator sample. For example, when positive charge accumulation is found on the minus side of the insulator sample and negative charge accumulation is seen on the plus side, the presence of ionic impurities inside the insulator sample can be estimated. If the charge distribution shows a distorted waveform regardless of whether it is on the plus side or the minus side, it can be assumed that a substance that reflects or diffracts elastic waves exists inside the insulator sample. It can be estimated that defects such as microvoids and fibrous impurities exist inside the body.

On the other hand, 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, the surface of the insulator sample reflects an acoustic wave. Since there is no space charge distribution, the original space charge distribution of the insulator sample containing no unnecessary charge distribution component detected by the reflection of the elastic wave can be obtained. Further, a cable insulator can be used as the insulator sample, and a defect, a foreign substance, or an ionic impurity 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. FIG. 1 to FIG. 3 are diagrams showing the configuration of a space charge distribution measuring device for a cable insulator used in 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 supply 8 is connected to one end of the inner conductor 2 of the sample cable 1 via a resistor 6 and a switch 7 in series. Can be applied selectively. Further, a high-voltage pulse generator 11 is connected to the other end of the internal conductor 2 via a switch 9 and a coupling capacitor 10, so that a high-voltage pulse can be selectively applied to the internal conductor 2 by this configuration. Has become.

On the other hand, a plate-like support base 12 is provided below the sample cable 2, and a plate-like upper electrode 13 is provided directly above the sample cable 2, and the support base 12 and the upper electrode 13 are connected to each other. At each of the four corners, the support 12 is fastened via a support 14 and the support 12 is grounded. An acoustic sensor 15 is provided on the support base 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 includes a brass shield container 20 having an open upper surface, and an input electrode 21 attached to an upper portion thereof.
The piezoelectric element 22, the absorber 23, the extraction electrode 24, and the insulator 25 are sequentially stacked so as to be stacked below the input electrode 21 in the inside of the element 0. 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 at the upper end of the input electrode 21 so as to be in close contact with the lower surface of the sample cable 1, and this receiving portion 21a is shown in FIG. As shown in the figure, the lower part of the receiving part 21a is formed with flanges 21b, 21b, and the opening of the shield container 20 is closed by these flanges 21b, 21b.

The piezoelectric element 22 is formed by forming a conductive film such as aluminum on both upper and lower surfaces of a film made of polyvinylidene fluoride (PVDF), and is provided in close contact with the bottom surface of the input electrode 21. Note that the piezoelectric element 22 has a capacity of 11 in ordinary space charge measurement.
Although it is formed to a thickness of about 0 μm, in the present invention, it is necessary to measure a small amount of impurities, impurities having low 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 whose acoustic impedance is substantially equal to that of the piezoelectric element 22. When the piezoelectric element 22 is formed of polyvinylidene fluoride as described above, for example, polymethyl methacrylate (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 that the absorber 23 can be in close contact with the lower surface of the input electrode 21 via the film-like piezoelectric element 22. A projection 23b is formed at the lower part. The extraction electrode 24 is formed to have a concave cross-section so that the projection 23b of the absorber 23 can be inserted, and a plate-shaped insulator 25 is provided on the bottom surface thereof. 12.

The electrode on the lower surface side of the piezoelectric element 22 and the extraction electrode 24 are electrically connected at both ends via a conductor 27 such as a 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 an extraction portion 28 formed in the container 20.
Is connected to the lead wire 29 drawn out of the
A detection signal is taken out from the lead wire 29. The lead wire 29 is connected to a computer 33 via a broadband 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. For example, the input resistance of the amplifier is only 1 MΩ, and all the others are matched to 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 a defect or an impurity 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 internal conductor 21, electric charges are accumulated in the internal 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 charge induced at the interface between the two semiconductive layers 3 and 5, and distortion occurs inside the cable insulator 4, whereby the elastic waves 35 are radially generated.

The high voltage pulse to be loaded is:
In ordinary space charge measurement, the time is set to about 50 to 90 nsec. However, in the present invention, it is necessary to measure a small amount of impurities, impurities with low mobility, and small defects, and it is necessary to measure with high sensitivity. Therefore, since a defect or an impurity for which only a small signal can be obtained is measured, it is necessary to increase the externally applied voltage, and it is necessary 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. With this configuration, 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 in the plus region and the minus region and become 0, which is undetectable. Can be detected separately.

As shown in FIG. 4, the elastic wave 35 includes a negative pulse 35a immediately after the application of the high-voltage pulse and a positive pulse 35b that arrives slightly later than the negative pulse 35a.
The former negative 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 pulse 35b is an elastic wave generated by plasma charges distributed on the inner peripheral side of the cable insulator. It is a wave, and the arrival time difference between the two indicates the location of the charge. This elastic wave 35 reaches the piezoelectric element 22 through the same acoustic impedance at the same distance in the input electrode 21 as shown in FIG.

The elastic wave 35 input to the piezoelectric element 22 is
Here, it is converted into an electric signal, and the electrode on the lower surface and the tin foil 2
It is extracted to the outside as a detection signal via 7, an extraction electrode 24 and a lead wire 29. Further, the piezoelectric element 22 and the absorber 2
The elastic wave 35 that has reached the interface with 3 is input to the absorber 23 that has been acoustically matched without being reflected, and is attenuated by this absorber 23. In this acoustic sensor 15,
Since the elastic wave 35 is absorbed by the absorber 23 without being reflected, the detected detection signal is hardly affected by the reflected wave,
As shown in FIG. 4, a pulse-like signal that faithfully reflects the influence of the input elastic wave 35 is obtained.

On the other hand, as shown in FIG.
The detection signal includes some electrical noise, but the signal 36 due to the elastic wave is a pulse-like signal, and the electrical noise 37 has an oscillating waveform. It can be clearly distinguished. The output signal of the acoustic sensor 15 is amplified by the broadband amplifier 31 and input to the signal processing circuit 32. The signal processing circuit 32 performs an averaging process in which detection signals are repeatedly superimposed, for example, using a high-voltage pulse as a trigger, thereby obtaining a detection signal from which random noise has been removed. 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-described structure, the piezoelectric element 22 is formed of a polyvinylidene fluoride film, and each interface between the input electrode 21, the piezoelectric element 22, and the absorber 23 is coaxially curved with the sample cable 1. And an absorber 23 acoustically matched to the piezoelectric element 21 is disposed on the lower surface of the piezoelectric element 21, so that the elastic wave propagated from the sample cable 1 can be observed without being affected by the reflected wave.
For this reason, it is possible to accurately measure the space charge distribution of the cable insulator using the pulse electrostatic method. Therefore, using this measuring device, it is possible to evaluate the insulator and investigate the removed cable, for example, to find the cause of the occurrence of the water tree.

When the above-described apparatus is used, the measurement can be performed with the switch 7 open for the sample cable 1 having a charging history, or with the switch 7 closed and a DC voltage applied. good. Also, according to this method,
Since the sample cable 1 can be tested in a non-destructive manner, it can be applied not only to the measurement of the change over time in the space charge distribution during the charge deterioration test, but also to a live line deterioration diagnosis technique.

Here, for example, it is assumed that when the space charge distribution is measured by the above-described method using the insulator sample of cross-linked polyethylene by the above-described method, a charge distribution as shown in FIG. 7 is obtained. If such a positive parabolic charge distribution appears on the minus side and a negative parabolic charge distribution appears on the plus side, the insulator sample contains ionic impurities due to the decomposition residue of the cross-linking agent. It can be estimated that the sample is an insulator sample. Next, when the same measurement as described above was performed using an insulator sample having the same composition as above and a charge distribution having a distorted waveform as shown in FIG. 8 was obtained,
Microvoids or fibrous materials exist inside the insulator sample, which can be presumed to be due to elastic wave reflection phenomena due to these materials, and microvoids or fibrous defects exist 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 matter or defects is measured, the parabolic or irregular waveform is not detected at all. From the above, by analyzing the obtained space charge distribution waveform, the ionic impurities of the insulator sample,
Defects such as microvoids and fibrous foreign substances can be detected. Moreover, when measuring the space charge distribution, if the piezoelectric element is thinned and the pulse width of the high-voltage pulse is shortened, the measurement accuracy can be improved, so that the number of electrons with a much higher sensitivity than the ppm order can be accommodated. Measurements are also possible.

FIG. 5 shows an example of an apparatus for measuring the space charge distribution of a flat insulator sample 40. In the device of this example, the same configuration as the device of the previous embodiment includes:
The same reference numerals are given and the description of those parts is omitted. In this apparatus, the semiconductive layer 4 is formed on the upper surface of the insulator sample 40.
1 is provided on each lower surface with a semiconductive layer 42, and an insulator sample 4
In this configuration, an upper electrode 43 is provided below the lower electrode 44, and a lower electrode 44 is provided below the lower electrode 44. A piezoelectric element 45 and an elastic wave absorber 46 are stacked below the lower electrode 44. A conductive film is formed on each of the upper and lower surfaces of the piezoelectric element 45.
The upper conductive film 5 is grounded, and the lower electrode is connected to the broadband amplifier 31, the signal processing circuit 32, and the computer 33 as in the device of the previous embodiment. The semiconductive layer 41,
Reference numeral 42 denotes a material in which particles such as carbon are dispersed in a resin material such as polyethylene, and the thickness thereof is preferably 0.5 mm or less, more preferably 0.2 to 0.5.
mm is preferable. If the semiconductive layers 41 and 42 are formed thicker than 0.5 mm, the elastic waves propagating inside the insulator sample 40 are attenuated by the semiconductive layers 41 and 42 and reach 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 insulator by using the space charge distribution measuring device configured as described above and detecting a defect or an impurity thereof will be described. First, with the lower electrode 44 grounded, the switch 7
Is connected to the DC voltage power supply 8 side, and when a high voltage of, for example, 20 kV is applied to the upper electrode 43, charges are accumulated in the insulator sample 40. In this state, the switch 9 is closed and the high-current generating circuit outputs -1 k
When a high voltage pulse of V, 10 nsec is applied to the upper electrode 43, static electricity is generated in the induced charges induced at the interface between the two semiconductive layers 41, 42 of the insulator sample 40, and distortion occurs inside the insulator sample 40. This generates an elastic wave. By detecting this elastic wave in the same manner as in the above-described embodiment and performing arithmetic processing by the computer 33,
The space charge distribution of the insulator sample 40 can be calculated.

In the apparatus of this embodiment, a space charge distribution can be obtained by bringing the upper electrode 43 and the lower electrode 44 into direct contact with the insulator sample 40. Is undesirably detected. This reflected wave makes the thickness of the piezoelectric element 45 110 μm.
During observation at a normal level where 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
This is a level that can be easily corrected and removed by the computer 33. However, in the present invention, it is necessary to measure a small amount of impurities, impurities having low mobility, and small defects, and it is necessary to measure with high sensitivity. Therefore, when the reflected wave is generated, a measurement error may be caused. 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
The generation of the reflected wave can be prevented by matching the elastic impedance between the insulator 44 and the insulator sample 40. Thus, even when measurement with high resolution is performed, space charge distribution can be measured with high accuracy without being affected by reflected waves.

When the space charge distribution of the insulator sample is measured using the apparatus shown in FIG. 5, a space charge distribution similar to that of the above-described example can be obtained. It can detect defects such as ionic impurities and microvoids in the body sample, or the presence of fibrous impurities.

As described above, the thickness of the piezoelectric element was changed from 110 μm to 28 μm, and the pulse width was set to 50 ns.
ec to 10 nsec and the resolution is 200μ
m to about 50 μm. Here, FIG.
(A) As shown in FIG.
When the positive and negative charges are accumulated at a distance of, the output on the plus side and the minus side overlap with each other when the resolution is 200 μm and become 0, but the resolution is 50 μm.
Then, a space charge distribution can be obtained as a waveform as shown in FIG.

(Experimental Example 1) Space charge distribution of an insulator sample (80 mm long, 80 mm wide, 3 mm thick) made of cross-linked polyethylene using dicumyl peroxide (DCP) as a cross-linking agent was measured using the apparatus shown in FIG. 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 both upper and lower surfaces of the insulator sample by press fusion, and the electrodes were brought into contact via the semiconductive layer. The piezoelectric element was made of polyvinylidene fluoride having a thickness of 28 μm, 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 is seen on the minus side of the insulator sample, and minus charge accumulation is seen on the plus 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 above by the same means as above. From the results shown in FIG. 8, the obtained charge accumulation distribution curve shows a distorted waveform, which seems to be a waveform resulting from reflection or diffraction of an elastic wave inside the insulator sample. Therefore, it is presumed that the insulator sample has microcracks or fibrous defects that reflect or diffract elastic waves. In the insulator samples shown in FIGS. 7 and 8, if there is no foreign matter, defect, or ionic residue, the charge density distribution curve does not appear and the value of the charge density 0 is maintained.

[0037]

As described above, according to the method of the present invention, it is possible to detect only the elastic waves originally generated by the insulator sample by removing factors such as reflection and absorption of the elastic waves propagating in 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 defects such as ionic impurities and microvoids and fibrous impurities contained in the insulator sample 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 an ionic impurity inside the insulator sample can be estimated. If the charge distribution shows a distorted waveform regardless of whether it is on the positive or negative side, it can be estimated that a substance that reflects or diffracts elastic waves exists inside the insulator sample. It can be estimated that defects such as microvoids and fibrous impurities exist inside the insulator.

Further, when a semiconductive layer is interposed between the insulator sample and the electrode, unlike the case where the electrode is directly contacted with the insulator sample, reflection of elastic waves occurs on the surface portion of the insulator sample. Therefore, the original space charge distribution of the insulator sample containing no unnecessary components due to reflection can be obtained. Further, a cable insulator can be used as the insulator sample. In this case, a defect, a foreign substance, or an ionic impurity in the hollow insulator sample can be detected by estimating from a space charge distribution waveform.

[Brief description of the 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.

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

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

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

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

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

FIG. 7 is an explanatory view 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 a measurement result obtained by testing an insulator sample including a defect and a foreign substance.

[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,

Continued on the front page (72) Inventor Mitsutaka Yata 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd. (72) Inventor Satoshi Takahashi 1-5-1, Kiba, Koto-ku Tokyo References JP-A-4-52566 (JP, A) JP-A-4-140670 (JP, A) JP-A-5-196773 (JP, A) JP-A-6-66877 (JP, A) 6-74999 (JP, A) JP-A-5-180896 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 31/12 G01N 29/16

Claims (3)

(57) [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 are connected to the insulator sample via the semiconductive layer, and a high voltage pulse is applied by the electrodes. Applying to an insulator to generate an elastic wave, adjusting the elastic impedance between the electrode and the insulator sample by the semiconductive layer to prevent a reflected wave, and measuring the obtained elastic wave with an acoustic sensor, A space charge distribution accumulated in the insulator is measured based on an output signal of the acoustic sensor, and a defect or an impurity in the insulator characterized by detecting a defect or an impurity in the insulator from a waveform of the space charge distribution. How to detect 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 are used. A high voltage pulse is applied between the electrodes provided through the layer to measure a space charge distribution of the cable insulator, and a defect or impurity in the insulator is detected from a waveform of the space charge distribution. The method for detecting defects or impurities in an insulator according to claim 1. 3. As a space charge distribution, when a positive charge accumulation is seen on the minus side of the insulator sample and a negative charge accumulation is seen on the plus side, the presence of ionic impurities is estimated, and the space charge is estimated. 3. The method for detecting a defect or an impurity in an insulator according to claim 1, wherein the presence of a defect or a foreign substance is estimated when an irregularly shaped charge distribution is found as the distribution.