JP2000292476A - Power cable deterioration diagnosis method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To significantly reduce the total cost required for deterioration diagnosis while maintaining signal detection sensitivity at a practical level. SOLUTION: A first voltage V1 having a frequency f1 and a second voltage V2 having a frequency f2 (where V is
1 ≧ V2) is superimposed, and a loss current component obtained by removing a capacitive component of the frequency component f1 included in the current flowing through the insulator of the power cable 4 is measured.
Then, the current component and the frequency components contained therein are examined, and the deterioration diagnosis of the power cable 4 is performed based on the components of the frequencies f1 and f2 and the frequency components other than the third harmonic component. In the above measurement, as the applied voltage at the time of measurement,
First and second instantaneous peak values of the total voltage are lower than 10 kV and the average stress of the insulator by applying the first voltage component is higher than 0.1 kV / mm in effective value. Is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing deterioration of a power cable having deteriorated water tree.

[0002]

2. Description of the Related Art Conventionally, various non-live-line diagnostic techniques performed by applying an AC voltage have been proposed. However, any of the conventionally proposed technologies measure at a ground voltage at which the cable to be diagnosed is used. In these conventional techniques, it is customary to apply a voltage using a test transformer for applying an AC voltage.

[0003]

The ground voltage is, for example, 3
Since it is 19.1 kV in the case of the 3 kV line and 38.1 kV in the case of the 66 kV line, a large-capacity transformer is required to apply such a voltage to the cable laid on the actual line. Such a transformer has a problem in that the equipment weight becomes very large because the applied line has a large capacitance, though the generated voltage is not so high. For example, 20 k capable of applying 19.1 kV to a line whose capacitance is 2.5 μF.
When designing a V transformer, the total weight exceeds 5t.

[0004] Generally, power cable lines are often constructed underground in an overcrowded urban area, so it is extremely difficult to bring such large-sized equipment for testing. Also, when cables are used for these underground transmission lines, the terminal connection of the cables should be a gas insulated switch (GI).
A structure directly connected to S) is often used. This is housed in a case where the high-pressure portion is insulated with sulfur hexafluoride (SF6) gas, which has excellent insulation properties. For this reason, there is usually no high-voltage exposed area in the substation room installed under the building, etc., and equipment can be installed without considering the insulation separation distance, and the substation itself can be made smaller. It is possible.

However, on the contrary, it is a fact that the voltage is prevented from being applied from outside for the purpose of diagnosing the deterioration of the cable line. If voltage is to be applied to the end connection of the cable because there is no high voltage exposed part, GIS
Once the internal SF6 gas is recovered, a voltage applying adapter for testing is attached, SF6 gas is filled again, and measurement is performed.
After the test is completed, an extremely complicated procedure of collecting the gas again, removing the voltage application adapter, and restoring the GIS is required. This is costly as well as time-consuming. Generally, a cost of about one million yen is required to perform the degradation diagnosis once, but the gas processing of the GIS requires substantially the same amount. In other words, an incidental cost equal to the cost required for the original measurement is generated, resulting in a situation in which economic efficiency is extremely low.

In order to solve the above problems, the voltage applied to the cable at the time of measurement may be reduced. Thus, the capacity of the transformer can be reduced, and the size of the transformer can be reduced. However, since the degradation signal obtained by lowering the measurement voltage becomes smaller, there is a problem that the signal detection sensitivity is deteriorated. As described above, in the prior art, the test transformer becomes large, it is inconvenient to use it in a city, and it takes enormous cost to operate it.
The problem is that the cost of gas treatment required for applying a voltage to the GIS line is high. If the size of the equipment is reduced by lowering the measurement voltage, the detection sensitivity of the deteriorated signal is deteriorated, and the practicality is lost.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and an object of the present invention is to eliminate the above-mentioned problems while maintaining signal detection sensitivity at a practical level, and to perform deterioration diagnosis. To significantly reduce the total cost of

[0008]

In order to reduce the total cost required for the test, it is still essential to greatly reduce the measurement voltage and to reduce the size and weight of the equipment. Then, it is necessary to realize a method of applying a voltage without gas processing in the GIS terminal line. As a result of various studies for this purpose, a terminal called a ground terminal used for so-called megger measurement, etc., was attached to the outside of the GIS gas case from the conductor lead-out rod at the end of the cable. It was found that it was possible to use it as a voltage application part to the cable conductor only by operating the switch without performing the above operation.

[0009] The insulation performance of this part is approximately 10 DC voltage.
The investigation revealed that the voltage was kV or less. Therefore, it is understood that when a voltage is applied using this ground terminal, a voltage lower than this can be applied. This voltage value is 1 which is the ground operation voltage of the 22 kV cable.
Since it is lower than 2.7 kV, not all diagnostic methods can be applied to effectively perform the deterioration diagnosis at such a voltage. Low measurement voltage means that
This leads to lower detection sensitivity of the deteriorated signal, which is a phenomenon that occurs when the noise level becomes relatively higher than the deteriorated signal.

[0010] The noises which are problematic in the deterioration diagnosis method using the AC voltage include DC noise, noise having the same frequency component as the applied voltage, and odd harmonic noise of the frequency of the applied voltage, particularly third harmonic noise. In most degradation diagnosis methods, the degradation signal usually appears in the direct current, the same frequency band as the applied voltage, and the odd harmonic band of the applied voltage.Therefore, when the measurement voltage is reduced, the degradation signal is buried in noise. In many cases, an effective diagnosis cannot be made. However, the first voltage V having the frequency f1 is applied to the deteriorated power cable.
1 and a second voltage V2 having a frequency f2 (where V1 ≧ V
2) is superimposed, and the loss current component obtained by removing the capacitive component of the frequency component f1 included in the current flowing through the insulator of the power cable is measured. And other frequency components other than the third harmonic component thereof, for example, f2 + 2 × f1 or |
It became clear that a frequency component of f2-2 × f1 | appeared.

Therefore, if the frequencies f1 and f2 are selected so that both of these frequency components do not become the third harmonic of the input signal, and these can be taken out as a degraded signal, the influence of the third harmonic noise of the power supply can be obtained. Deterioration diagnosis can be performed with good sensitivity and high accuracy without receiving the noise. For example, a first voltage having a frequency f as an AC voltage component as an applied voltage to the cable and a second voltage having a frequency 2f as an AC voltage component having a voltage value lower than the first voltage are superimposed and applied, Observing a loss current obtained by removing a capacitive current component having a frequency f, which is a component that is 90 ° ahead of the AC voltage and pressure component of the first voltage, from the total charging current flowing from the cable, a frequency of 4f is obtained as a deterioration signal. A signal with components is obtained.

According to this method, since the frequency component of 4f becomes an even-order harmonic with respect to any of the two frequency components applied to the cable, a deteriorated signal can be generated in a region where the noise level is originally low. It became clear that the required detection sensitivity could be secured even if the signal level became low. However, even in this case, the voltage may not be reduced as much as possible, and a minimum level is required. As a result of various experiments, it has been clarified that the minimum effective measurement can be performed by applying an electric field having an effective value of 0.1 kV / mm or more, depending on the line condition.

With the above arrangement, the measuring voltage can be reduced, the equipment scale of the test transformer can be reduced, the handling thereof can be facilitated, and the operating cost can be reduced. Further, since the measurement voltage can be reduced, it is possible to apply a voltage from the GIS ground terminal, and it is possible to omit the gas treatment in the GIS part and reduce the cost required for this. At the same time, by adopting the above-described method as the deterioration diagnosis measurement, it is possible to prevent a decrease in sensitivity due to a decrease in the measurement voltage, and to obtain a deterioration diagnosis method capable of obtaining a certain level of accuracy at low cost.

Further, when the timing when the second harmonic voltage is superimposed on the fundamental wave, that is, when the superimposed phase is changed, the fourth harmonic current also changes accordingly, and the change of the magnitude of the current component changes. By measuring the magnitude, the degree of deterioration of the cable can be diagnosed. Further, as a result of examining the relationship between the degree of deterioration of the cable and the generated fourth harmonic current, the superimposed phase of the second voltage V2 with respect to the first voltage V1 and the generated Since the relationship of the superposed phase of the fourth harmonic component to the first voltage changes according to the degree of deterioration of the power cable, the degree of deterioration can be diagnosed using this relation. Therefore, even if these relationships are used, the operating voltage can be reduced by lowering the measured voltage as in the above case.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When the cable insulator deteriorates, nonlinearity appears in the voltage-current characteristics. When the characteristics are expressed by the Taylor expansion approximation, the voltage and the current are proportional to the normal Ohm's law. In addition, it has been experimentally confirmed that a current component proportional to the cube of the voltage is generated. The nonlinear system capable of expressing the characteristics as described above includes the frequency f1
When an input signal having two frequencies of f1 and f2 is given, f1 and f2 are generated as frequency components as described above.
(Input frequency) In addition to 3 × f1, 3 × f2 (the third harmonic of the input frequency), f2 + 2 × f1, | f2-2 × f1
|, F1 + 2 * f2 and | f1-2 * f2 | are output by theoretical calculations.

Here, when the voltage value of the frequency f1 is V1 and the voltage value of the frequency f2 is V2, and the relationship of V2 ≦ V1 holds, except for the input frequency and their third harmonics, f2 + 2 × f1 and It has been found that two frequency components | f2-2 × f1 | are output largely. Therefore, if the frequencies f1 and f2 are selected so that both of these frequency components do not become the third harmonic of the input signal, and if these can be extracted as a deteriorated signal, accurate and accurate without being affected by power supply harmonics This makes it possible to diagnose deterioration. For example, if f1 = 50 Hz and f2 = 70 Hz, the two frequency components are 30 Hz and 170 Hz, and 50 × 3 = 1 which is the third harmonic of the frequencies f1 and f2.
It can be seen that neither 50 Hz nor 70 × 3 = 210 Hz.

In order to observe such a frequency component, it is necessary to remove the capacitive component contained in the current flowing through the cable insulator, as in the usual measurement of the loss current. For this purpose, for example, the following operation is performed. (1) A first voltage V having a frequency f1 is applied to the power cable.
1 is applied, the loss current component obtained by removing the capacitance component of the frequency f1 included in the current flowing through the insulator of the power cable is measured, and the current waveform and the frequency component included therein are examined. Next, while maintaining the first voltage the same, the second voltage V2 having the frequency f2
(Where V1 ≧ V2) is further superimposed and applied, and the loss current component is measured.

(2) Loss current obtained by removing the capacitance component of frequency f1 contained in the current flowing through the insulator of the power cable when the first voltage V1 having frequency f1 is applied to the power cable. After measuring the component, the operation for removing the capacitive component is left as it is, and then the first voltage V1 having the frequency f1 is changed to the same voltage as the first voltage V1 having the frequency f1. A loss current component is measured when a voltage waveform obtained by combining a second voltage V2 having a frequency f2 (where V1 ≧ V2) is applied. Specifically, first, a voltage V1 is applied to perform a bridge operation for measuring a loss current, and the voltage V1 is once turned off while the balance state is fixed. Thereafter, a waveform in which the voltage V1 and the voltage V2 are combined in advance is directly applied to the cable, and the output of the bridge is observed. By measuring the loss current and observing the frequency component by the method as described above,
Deterioration of the cable can be detected without being affected by harmonics included in the main power supply, and accurate deterioration diagnosis can be performed even if a power supply having a high power supply harmonic content is used.

As for the method of selecting the frequencies f1 and f2, as described above, f2 + 2 × f1 or | f2-2 × f
As long as 1 | does not correspond to any of the third harmonic components of f1 and f2, the effect is theoretically exerted by any combination of f1 and f2. However, considering the actual measurement at the cable laying site, if the relationship between the magnitudes of the applied voltages is V1 ≧ V2, f2 is changed to f2.
It is the most rational combination of f1 and f2 that is twice or 1 / n (n is an integer of 3 or more), and f1 is the commercial frequency.

This is for the following reason. First, f
If both 1 and f2 are other than the commercial frequency, two devices (frequency conversion power supply devices) for generating the respective frequencies are required. However, the first voltage V1 having the frequency f1 is prepared as the commercial frequency. Only one frequency conversion power supply device is required, and the capacity of the frequency conversion power supply device may be smaller than f2 when the commercial frequency is used. Second, by setting f2 to a frequency synchronized with f1, an averaging process can be performed at the time of obtaining a loss current waveform, so that more accurate measurement can be performed. For these two reasons, it is preferable that f1 be a commercial frequency and f2 be an integral multiple or an integral fraction of f1. When the cable is a capacitive load and the applied voltage is the same, considering that the capacity of the power supply device to be prepared increases in proportion to the frequency, the upper limit of f2 is 2 of f1 (commercial frequency).
Double is the practical limit.

If a frequency three times as high as f1 is used as f2, the frequency of the degraded signal generated by the principle of the present invention (f22 × f1 = 5 × f1, | f2-2 × f1 | = f
Since 1) corresponds to the applied voltage itself and the fifth harmonic component thereof, the result is contrary to the object of the present invention in that the degraded signal is shifted to a frequency component not affected by noise. Further, when a frequency four times as high as f1 is used as f2, the same effect can be obtained as in the case where a frequency twice as high as f1 is used. However, when the same voltage is applied, the capacity of the power supply device is reduced. It is twice as large and has no practical advantage.

Further, the frequency component f2 + 2 × f1 or | f2-2 × f1 | generated due to the deterioration under the superimposed voltage of the voltages V1 and V2 is f1, f2 and their third harmonic components and third harmonic components. If a frequency that does not correspond to the fifth harmonic component having a large influence that appears as a noise component next to the wave component is selected, the result is as shown in Table 1. In Table 1, the portion surrounded by the dotted line is the same as the third or fifth harmonic of the applied voltage whose deterioration signal is.

[0023]

[Table 1]

As is clear from Table 1, at frequencies where f2 is an integral part of f1, except for the case where the frequency is f / 2, the degraded signal is not affected by the harmonic components of the applied voltage. It can be seen that this occurs. From the above, it can be understood that setting the frequency f2 to twice or 1 / n (where n is an integer of 3 or more) of f1 and setting f1 to the commercial frequency is the most effective combination in practical use. By the way, the fourth harmonic current is generated by superimposing and applying the second harmonic voltage to the fundamental wave voltage, and changes the timing when the second harmonic voltage is superimposed on the fundamental wave, that is, changes the superimposed phase. Then, the fourth harmonic current also changes accordingly.

For example, when the value of the fourth harmonic current is measured when θv2 is changed from −90 ° to 90 ° and superimposed on a sample in which the insulator is deteriorated, the fourth harmonic current is examined. Changes so as to oscillate for two cycles with a constant amplitude as shown in FIG. 3 at −90 ° ≦ θv2 ≦ 90 °. The manner in which the fourth harmonic changes with respect to θv2 depends on the degree of deterioration of the cable.
The harmonic current has a large variation in value due to a change in θv2, and the variation is relatively small when deterioration has not progressed much. Therefore, the degree of deterioration of the cable can be diagnosed by examining the change characteristic of the fourth harmonic current with respect to θv2.

Further, when the relationship between the degree of deterioration of the cable and the generated fourth harmonic current was examined, the second voltage V
2 with respect to the first voltage V1 and the fourth
It has been found that the relationship of the superimposed phase of the harmonic component to the first voltage changes according to the degree of deterioration of the power cable.
That is, the fourth harmonic current is the fundamental voltage V1 of the frequency f.
And a voltage V2 having a frequency 2f that is twice as high as that applied to the cable, the voltages of the two types of frequencies interact with each other under the non-linearity of the water tree. Corresponding to the superimposed state of V1 and the superimposed phase V2, that is, the superimposed phase difference between them (this is represented by θv2), the superposed phase of the fourth harmonic component generated in the loss current (the phase difference with respect to the fundamental wave voltage at θ4). Of course) also changes.

Therefore, the superimposed phase difference θv2 and the superimposed phase θ
The relationship between the superimposed phase difference θv2 of the fundamental wave voltage V1 and the superimposed voltage V2 and the superimposed phase θ4 of the fourth harmonic component in the loss current are shown in FIG. It turned out that it changes as shown in FIG. According to this, the superimposed voltage generator side previously sets the superimposed phase difference θv2 and measures the superimposed phase θ4 of the fourth harmonic component in the loss current of the cable, and as the degree of deterioration of the cable progresses, The superimposed phase θ4 moves from the minus side to the plus side, and the degree of deterioration of the cable can be diagnosed.

Further, the relationship between the superimposed phase difference θv2 of the voltage and the superimposed phase θ4 of the fourth harmonic component in the loss current is approximated by a straight line determined according to the degree of deterioration of a constant slope as shown in FIG. By utilizing the fact that the superimposed voltage difference generator side does not set the superimposed phase difference θv2 in advance, the superimposed phase of the fourth harmonic component measured under a certain voltage superimposed state and the second superimposed phase at that time The degree of deterioration of the power cable can also be diagnosed from the superimposed phase of the voltage, which makes the diagnosis easier. Therefore, the second voltage V1 with respect to the first voltage V1
The deterioration diagnosis can be performed by utilizing the relationship between the superimposed phase difference θv2 of 2 and the superimposed phase θ4 of the fourth harmonic component in the loss current.

According to the above-described deterioration diagnosis method, it is possible to accurately and accurately perform the deterioration diagnosis without being affected by the third harmonic noise of the power supply. Is reduced, the equipment scale of the test transformer is reduced, and this handling can be facilitated. Hereinafter, a specific embodiment of the present invention using the above-described deterioration diagnosis technique will be described. In the following description, a case will be described in which the deterioration diagnosis is performed based on the magnitude of the fourth harmonic current, but the change characteristic of the fourth harmonic current with respect to θv2,
Alternatively, the same applies to the case where deterioration diagnosis is performed using the relationship between the superimposed phase difference θv2 of the second voltage V2 with respect to the first voltage V1 and the superimposed phase θ4 of the fourth harmonic component in the loss current.

(1) Test Samples The following two types of cables were used as test samples in the experiment. - aging was used used water tree degradation cable flooded 25 years in an environment dismantled by, using 22kVCVT3 × 150mm ² insulation thickness 6 mm. Manufactured by a wet crosslinking method, the inner conductor is extruded and the outer conductor is a so-called ET type of tape. When the AC breakdown voltage was investigated in the investigation after the removal, it was about 40 to 70 kV. Since the capability at the time of manufacture of this class is expected to be 150 kV or more, the insulation performance is reduced to less than 1/2 of that time. ing. A water tree survey was conducted by sampling.
0 μm, and it was found that the outer water tree extended to about 3000 to 4000 μm. As compare for new not cable deteriorated cable, using 22kVCVT3 × 150mm ² in new insulation thickness 6 mm. The breakdown voltage is 350 kV or more, which is sufficient for a cable of the present production level.

(2) Experiment 1 Using the above cable, the measurement result of the degradation signal when the applied voltage was lowered was measured, and the case where only the commercial frequency AC voltage was applied and the third harmonic in the loss current was measured. And a case where the AC voltage twice as high as that of the commercial frequency was applied and the fourth harmonic of the commercial frequency in the loss current was measured. In this experiment, the measurement voltage was considerably lower than the operation voltage of 12.7 kV, and the measurement was performed in the following three cases. [1] A case where 3 kV is applied only to a 50 Hz commercial frequency AC voltage and the third harmonic in the loss current is measured. [2] A case where the fourth harmonic (200 Hz) of the loss current is measured by applying a 50 Hz commercial frequency AC voltage of 2 kV and a voltage of 100 Hz having a frequency twice as high as 0.6 kV. [3] A case where the fourth harmonic (200 Hz) in the loss current is measured by applying a 50 Hz commercial frequency AC voltage of 1 kV and a voltage of 100 Hz having a frequency twice as high as 0.3 kV.

In the experiment, the length of the cable was set to 50 m, and
A measurement was made. In the case of [1], voltage was applied to the cable by using a test transformer in the circuit shown in FIG. That is, as shown in the figure, a standard capacitor 5 is connected in parallel with the power cable 4, a voltage is applied from the power source 1 (frequency f1) via the test transformer 10, and flows through the insulator of the power cable 4. The current and the current flowing through the standard capacitor 5 were input to the loss current measurement bridge 3, and a component having a phase advanced by 90 ° with respect to the first voltage V1 was removed from the current flowing through the insulator to extract a loss current. Then, the output of the loss current measurement bridge 3 is led to the oscilloscope 6,
The waveform was analyzed by the computer 7.

In the case of [2] and [3], a test transformer was used in the circuit shown in FIG. That is, as shown in the figure, a standard capacitor 5 is connected in parallel with a power cable 4, and a power source 1 (frequency 50 Hz) and a power source 2 (frequency 1
00 Hz) through the test transformers 10 and 11, the current flowing through the insulator of the power cable 4 and the current flowing through the standard capacitor 5 are input to the loss current measuring bridge 3, and From the flowing current, the first voltage V
A component having a phase advanced by 90 ° with respect to 1 was removed to extract a loss current. Then, the output of the loss current measurement bridge 3 was led to the oscilloscope 6, and the waveform was analyzed by the computer 7.

In [1], a power source was used in which attention was paid to a certain extent to suppress the influence of harmonics, particularly the third harmonic, to a certain extent. As a result, the content of the third harmonic in the applied voltage was about 0. .4%. On the other hand, [2],
In [3], a method of matching zero crossings such that Asin (ωt) + Bsin (2ωt) of a voltage of 50 Hz when superimposing 100 Hz is adopted, and special consideration is given to harmonics generated in the applied voltage. The experiment was performed without doing it. As treatment of the experimental data, Table 2 shows the result of organizing the magnitude of the measured current.

[0035]

[Table 2]

As is clear from this, in the case of [1], the measurement result shows the same value for both the aged cable and the new cable, and it is not possible to determine whether the deterioration has progressed. On the other hand, in the cases of [2] and [3], a clear difference is seen in the magnitude of the deterioration signal measured for both the aged cable and the new cable.
In [1], it is impossible to distinguish whether or not deterioration has progressed, even though consideration is made so that harmonics do not enter the applied voltage at the time of measurement. On the other hand, in [2] and [3], similar measures for harmonics are taken. There is a remarkable difference between the two, such that the presence or absence of the progress of deterioration can be determined without performing the above. Thus, by applying a voltage having a single frequency, the applied voltage third
When performing deterioration diagnosis using harmonics, effective deterioration diagnosis cannot be performed if the measurement voltage is lowered. On the other hand, a fundamental wave voltage having a certain frequency and a voltage having a frequency twice that of the fundamental wave voltage are superimposed and applied. The effectiveness of the method of performing the deterioration diagnosis using the fourth harmonic of the wave voltage has basically been confirmed.

(3) Experiment 2 Next, the extent of the lower limit electric field at which effective deterioration diagnosis can be performed by the method of the present invention was investigated. In the experiment, a 100 Hz voltage corresponding to 30% of the voltage was superimposed and applied to the aged cable and the new cable while changing the 50 Hz voltage, and the fourth harmonic current observed at that time was measured. Table 3 shows the results.

[0038]

[Table 3]

As can be seen, the fourth harmonic current observed in the new cable does not change significantly even when the applied voltage is changed. This means that the measured current is almost noise. On the other hand, the fourth
It can be seen that the harmonic current gradually decreases as the applied voltage decreases. Thus, a voltage having a frequency twice that of the fundamental frequency is superimposed and applied to the fourth fundamental frequency.
In the method of performing deterioration diagnosis by measuring harmonic current,
It can be seen that the effectiveness of the deterioration diagnosis is impaired by unnecessarily lowering the measurement voltage. Then, the lower limit which may be reduced was examined.

One criterion here is whether or not the current value obtained as the deteriorated signal is twice or more the noise level. Although this is a so-called S / N ratio, if it is at a level exceeding 2, it is possible to discriminate noise from signals. Looking at the data in Table 1 from this viewpoint, it can be seen that if the basic voltage at the time of measurement exceeds 0.6 kV, it is satisfied. Since the test sample this time has an insulation thickness of 6 mm, the average stress of the cable is 0.1 kV / mm. Therefore, if at least this level of stress is applied, S
It has been found that the measurement can be performed with a sufficiently large / N ratio.

(4) Examination On the other hand, to measure the deteriorated signal largely, it is sufficient to increase the applied voltage.
The test transformer used for on-site measurement needs to be small. The size and weight of the transformer are determined by the applied voltage and the capacitance of the applied cable line. Investigation of the capacitance of the cable line for which the degradation diagnosis is to be performed reveals that it is approximately 3μ.
It was found that 90% or more of the track could be covered by setting the upper limit to about F. Therefore, the maximum capacitance is 3 μF,
Assuming that the basic voltage frequency is 50 Hz and the frequency of the voltage to be superimposed is 100 Hz, the maximum voltage value is 30% of the basic voltage.
%, The weight of the test transformer at various maximum generated voltages was estimated. This includes equipment as a power application system including all auxiliary devices such as a voltage regulator, a compensating reactor, and a control panel. Table 4 shows the results.

[0042]

[Table 4]

From the viewpoint of the mobility of the deterioration diagnosis, it is necessary to satisfy the condition that the test equipment can be generally brought to the site. In this sense, you can drive with a normal driver's license.
It is desirable that the vehicle can be loaded on a t-car. From this viewpoint, it can be seen that the upper limit is the case where the maximum output voltage is 10 kV. If the output voltage is smaller than this, the test device can be brought to the site without a license that is not necessarily general-purpose such as a large vehicle driving license.

(5) Conclusion As a result of the above experiments and examinations, if the measurement satisfying the following conditions is performed, it is possible to determine the deterioration state with sufficient measurement sensitivity, and it is necessary to consider the on-site measurement and to operate It has been found that the measurement can be performed with a test device having flexibility and general versatility. [1] As a measurement method, a voltage having a frequency f as a first AC voltage component as an applied voltage and a frequency 2 as a second AC voltage component having a voltage value lower than the first voltage component are used.
A voltage having a frequency f is superimposed and applied, and a capacitive current component having a frequency f which is a 90 ° lead component with respect to the first AC voltage component is removed from a current component having a frequency f in a total charging current flowing from the cable. A method of diagnosing the degree of deterioration by focusing on the fourth harmonic component in the loss current obtained by the above method is employed. [2] The applied stress of the first AC component voltage at the time of measurement is at least 0.1 kV / mm or more. [3] The maximum value of the first AC component voltage at the time of measurement is 10 kV
Must be:

[0045]

As described above, according to the present invention,
Maintaining the necessary and sufficient signal detection sensitivity and making it possible to perform deterioration diagnosis using portable test equipment for general purposes,
Deterioration diagnosis with good maneuverability and excellent on-site operability can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a measurement circuit (1) used in an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a measurement circuit (2) used in an embodiment of the present invention.

FIG. 3 is a diagram showing how a fourth harmonic current changes with respect to a second harmonic voltage superimposed phase.

FIG. 4 is a diagram illustrating a relationship between a superimposed phase θv2 of a fundamental wave voltage and a superimposed voltage and a superimposed phase θ4 of a fourth harmonic current in a loss current measured under the superimposed voltage.

[Explanation of symbols]

 1, 2 power supply 3 loss current measurement bridge 4 power cable 5 standard capacitor 6 oscilloscope 7 computer 10, 11 test transformer

Claims (7)

[Claims] 1. A first power cable having a frequency f1.
When the voltage V1 and the second voltage V2 having the frequency f2 are superimposed and applied, the capacitive component of the frequency component f1 included in the current flowing through the insulator of the power cable is removed. The current component and the frequency component contained therein are examined, and the deterioration diagnosis is performed based on the frequency components other than the frequency f1 and f2 components and the third harmonic component contained therein. A power cable deterioration diagnosis method, wherein as an applied voltage at the time of measurement, the instantaneous peak value of all voltages is lower than 10 kV, and the average stress of the insulator caused by applying the first voltage component is reduced. , Effective value 0.1k
A method for diagnosing deterioration of a power cable, comprising using a superimposed waveform of first and second voltage components having a value higher than V / mm. 2. A power cable having a first frequency f1.
When the voltage V1 and the second voltage V2 having the frequency f2 are superimposed and applied, the capacitive component of the frequency component f1 included in the current flowing through the insulator of the power cable is removed. The loss current component obtained by performing the above is measured, and of the frequency components included in the loss current, f2 + 2
Xf1 or | f2-2 × f1 | is a method of diagnosing deterioration of a power cable which performs diagnosis by focusing on the frequency component, wherein the instantaneous peak value of all voltages is lower than 10 kV as an applied voltage at the time of measurement. In addition, the average stress of the insulator caused by applying the first voltage component is 0.1 k in effective value.
A method for diagnosing deterioration of a power cable, comprising using a superimposed waveform of first and second voltage components having a value higher than V / mm. 3. The frequencies f1 and f of the two types of AC voltages
3. The method for diagnosing deterioration of a power cable according to claim 1, wherein a combination having a frequency f2 twice as large as f1 is used as a combination of the two. 4. The frequencies f1 and f of the two types of AC voltages
3. The method for diagnosing deterioration of a power cable according to claim 1 or 2, wherein a combination in which f2 is 1 / n times f1 (n is an integer of 3 or more) is used as a combination of the two. 5. The method for diagnosing deterioration of a power cable according to claim 1, wherein the first voltage V1 having a frequency f1 is applied to the power cable. The loss current component obtained by removing the capacitance component of the frequency f1 included in the current flowing therein is measured, and the current waveform and the frequency component included therein are examined. Then, the first voltage is made the same. The loss current component when the second voltage V2 having the frequency f2 (where V1 ≧ V2) is further superimposed and applied is measured while maintaining the current waveform, and the current waveform and the frequency component included therein are examined. A deterioration diagnosis method for a power cable, characterized in that the deterioration diagnosis is performed based on the components of the frequencies f1 and f2 in the loss current of both of them and the frequency components other than the third harmonic component thereof. 6. The method of diagnosing deterioration of a power cable according to claim 1, wherein the power cable is insulated when a first voltage V1 having a frequency f1 is applied to the power cable. The loss current component obtained by removing the capacitive component of the frequency f1 included in the current flowing through the body is measured. Then, the operation of removing the capacitive component is left as it is and the frequency f1 is maintained. Loss current component when a voltage waveform obtained by combining the first voltage having the frequency f1 and the second voltage V2 having the frequency f2 (where V1 ≧ V2) is applied instead of the first voltage V1. Is measured, the current waveform and the frequency components contained therein are examined, and deterioration diagnosis is performed based on the frequency components f1 and f2 and the frequency components other than their third harmonic components in the loss current of both. And a power cable deterioration diagnosis method. 7. A method for diagnosing deterioration of a power cable according to claim 1, 2, 3, 4, 5, or 6, wherein the first voltage V1 is a commercial frequency voltage. Deterioration diagnosis method.