JP5541463B2 - CV cable deterioration diagnosis method - Google Patents

Description

  The present invention relates to a method for diagnosing insulation deterioration of a CV cable subjected to water tree degradation, and relates to a method for diagnosing deterioration that can non-destructively diagnose the remaining performance of a cable insulator.

When moisture enters the insulator of the power cable in the usage environment, a water tree is generated in the insulator due to the action of moisture and voltage. The length of the water tree grows with time.
Since the inside of the water tree is filled with water having a low resistance, the generation and extension of the water tree results in acting as a conductive foreign substance in the insulator, resulting in enhancement of the electric field. When the electric field reaches the dielectric breakdown strength, dielectric breakdown (all-path breakdown) of the insulator occurs, resulting in a dielectric breakdown accident.
In order to prevent such an insulation breakdown accident, whether or not a water tree has occurred in the power cable insulation, or the longer the water tree, the higher the degree of insulation performance degradation. It is important to maintain a diagnostic method to determine how long the water tree is.
In the case of a power cable of a voltage class of less than 11 kV, since the electric field strength used is low and the water tree itself has a certain degree of insulation performance, the bridge water tree through which the water tree penetrates the insulator If this occurs, it does not immediately lead to dielectric breakdown. For this reason, the presence or absence of a water tree is determined by applying a DC voltage between the conductor and the outer periphery of the insulating layer and measuring the leakage current generated through the low-resistance water tree that penetrates the insulator. Has been conventionally used because of its simplicity.

On the other hand, in an extra high voltage cable of 11 kV or higher, unlike a power cable of a voltage class of less than 11 kV, since the electric field strength used is high, dielectric breakdown occurs before the generated water tree penetrates the insulator. Most cases. In this case, since the water tree does not penetrate through the insulator, in terms of an equivalent circuit, the low resistance water tree and the healthy insulator are connected in series. Even if the leakage current is measured, a large current does not flow and it is difficult to detect the water tree.
Based on the above background, many diagnostic methods have been developed and examined so far. Among the cables belonging to the special high voltage cables with a voltage class of 11 kV or higher, the remaining in 22/33 kV class or 66/77 kV class cables. The charge method and the loss current method are actually applied as maintenance diagnostic techniques.

  In the residual charge method, a DC voltage or this alternative waveform is applied as a pre-process (pre-charging), and then an AC voltage is applied in a step-like manner (measuring power) in the post-process. In this method, a charge signal is detected, and the maximum AC voltage at which a residual charge signal is detected at this time is used as an indicator for deterioration diagnosis (see, for example, Patent Document 1). In the residual charge method, the present inventor has proposed a method using an AC cutoff waveform as an alternative to the DC voltage in the previous process in order to shorten the measurement time (see, for example, Patent Document 3). Furthermore, in the residual charge method, the emission voltage (electric field strength) is obtained by separating the residual charge signal waveform obtained by applying a predetermined high-voltage AC voltage once instead of stepwise applying the post-process voltage. Has also been proposed (see Non-Patent Document 1, for example).

  On the other hand, the loss current method detects a loss current which is a resistive component having the same phase as the applied voltage phase from the current flowing through the insulator when the AC voltage is applied to the CV cable, This is a method of analyzing this and diagnosing deterioration (see, for example, Patent Document 2 and Patent Document 4). That is, when the water tree is present in the insulator, the loss current waveform includes harmonics, and the waveform is distorted from a sinusoidal shape. This is believed to be due to nonlinearity in the voltage-current characteristics of the water tree section. The loss current method is a method of extracting a third harmonic component from the distorted waveform and diagnosing deterioration based on the magnitude and phase difference of the current.

Japanese Patent No. 3629409 Japanese Patent No. 3910867 Japanese Patent No. 4383393 Japanese Patent No. 4092645

Hiroyuki Ima, Hideo Tanaka, Toyoji Tsukamoto, Hideaki Sato, “Evaluation Method of Residual Charge Signal by Waveform Separation”, Proc. 2-5 to 2-6,

As described above, the residual charge method and the loss current method are conventionally known as methods for diagnosing deterioration of a CV cable. However, the residual charge method and the loss current method differ in the equipment and equipment used for measurement.
That is, in the residual charge method, for example, as shown in FIG. 2 of Patent Document 1 and FIG. 1 of Patent Document 3, a device for direct current charging or a device for cutting off after applying an alternating voltage is necessary. On the other hand, in the loss current method, as shown in FIG. 1 of Patent Document 2 and FIG. 1 of Patent Document 4, a device and a loss for applying an AC voltage with a relatively low third harmonic content are shown. A device such as a current measurement bridge is required, and a device suitable for each diagnostic method is required.
If the equipment used in one method can be used to diagnose deterioration using the other method, the residual charge method and loss can be obtained using one type of equipment without preparing the equipment used in each method. Deterioration diagnosis by the current method can be performed and convenience is improved, but at present, it is necessary to prepare a device corresponding to each.

By the way, as a technology for maintenance diagnosis in power devices such as transformers and electric motors, diagnosis is performed by a plurality of methods regardless of only one deterioration diagnosis method or abnormality diagnosis method, and the results are comprehensively used. There is a way to make a diagnosis. Thereby, it is possible to improve the accuracy of the final diagnosis result by complementing each diagnosis method.
However, in the power cable deterioration diagnosis, as described above, since the equipment used for each method is different, a comprehensive diagnosis is not made by applying a plurality of methods. For this reason, the accuracy of the diagnostic result depends on the accuracy of the method used.
In addition, we perform degradation diagnosis on the actual line by the residual charge method, and then conduct a breakdown voltage test, which is a destructive test, to compare the evaluation result at the laboratory level with the evaluation result on the actual line and verify its effectiveness Although there are cases, this is only for the purpose of verifying the accuracy of the residual charge method, and it is practically impossible to make a similar evaluation for all the lines that have been subjected to the degradation diagnosis measurement. (Needless to say, it is not preferable to perform a test involving destruction on a real line.)

In other words, in general, the accuracy of the deterioration diagnosis result can be determined by conducting a destructive test on the sample that has been subjected to the deterioration diagnosis and verifying it at the preliminary examination stage in a laboratory or the like. Although it is possible to carry out the measurement in the power cable line, the accuracy of the diagnostic measurement result cannot be clarified by performing a destructive test.
Therefore, it is conceivable to improve the accuracy of the deterioration diagnosis result by performing diagnosis using two methods of the residual charge method and the loss current method, comprehensively judging the results, and performing the deterioration diagnosis. .
However, at present, the equipment used in the residual charge method and the loss current method are different as described above, so if one line is diagnosed by two or more methods, one diagnosis is completed. After that, it is necessary to withdraw the equipment for diagnosis and re-install the equipment for the next diagnosis. It takes a lot of time, and the power outage time for diagnosis on the line cannot be long. This is difficult to realize.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide a deterioration diagnosis method capable of performing deterioration diagnosis by a loss current method using equipment used for the residual charge method. Is to provide.
The second object of the present invention is to improve the accuracy of the deterioration diagnosis result by using the loss current method and the residual charge method in combination.

In view of the above background, paying attention to the residual charge method and the loss current method that have already been applied to the actual line, a method for deriving an indicator of deterioration diagnosis used in the other diagnostic method from the signal obtained by one diagnostic method It was investigated. As a result, the present inventor has completed the invention of the present application for deriving a deterioration diagnosis index used in the loss current method based on the method used in the residual charge method. In other words, only the equipment used for the residual charge method is used to perform the measurement.
In the residual charge method, conventionally, a DC voltage is applied as a pre-process before the measurement is performed, charges are accumulated in the water tree section, and then a AC voltage for measurement is applied as a post-process to generate a residual charge. Measurement was being carried out. However, when a direct current voltage is applied to an actual line, the power cable has a large capacitance, and thus there is a problem that it takes a long time to step up and down the voltage. In order to shorten this time and shorten the measurement time, as described above, the present inventor previously proposed a method using an AC cutoff waveform as an alternative to a DC voltage in the previous process (the above-mentioned patent). Reference 3).
The residual charge method using the AC cutoff waveform as the applied voltage in the previous process is realized by a technique for cutting off the AC voltage near zero phase. Using this technique, the residual voltage can be measured by interrupting the AC voltage at an arbitrary phase and applying a predetermined AC voltage in the subsequent process.
The present invention is a further development of this technology. The present inventor found that the residual charge amount detected when the AC voltage is cut off at an arbitrary phase (θ _a ) in the previous step is the charge amount (Q ₀₎ accumulated during the half wavelength before the cut off phase. from), a charge amount obtained by subtracting the amount corresponding to the movement under the reverse polarity voltage division electrodeposition of until blocked phase (theta _a), the amount of charge is detected to change the phase (theta _a) to block Was found to change, and the present invention was conceived.

These movements of the charge amount reflect the movement of the charges inside the water tree under AC voltage application. Therefore, the current waveform can be acquired by measuring the residual charge amount in each cutoff phase and differentiating it with time. This current waveform is nothing but the current flowing due to the water tree, and by analyzing the frequency of this current waveform, the magnitude of the third harmonic component used in the loss current method described in Patent Document 2 and The phase difference with respect to the phase of the applied AC voltage can be derived.
Further, by evaluating the magnitude (I ₃ ) and phase (θ ₃ ) of the third-order harmonic component current thus derived by the loss current method described in Patent Document 2, the degree of deterioration Can be diagnosed.

By the way, when performing a deterioration diagnosis, it is desirable to make a comprehensive judgment using a plurality of deterioration diagnosis methods in order to derive an appropriate diagnosis result, and a plurality of diagnosis methods are provided within a limited work time. It is desirable to do.
Therefore, it is desirable to perform the deterioration diagnosis by the residual charge method before or after performing the deterioration diagnosis by the loss current method in the above procedure.
As the residual charge method, if the residual charge method based on the step charging method used in Patent Document 1 is performed, it is possible to derive the emission voltage (electric field strength) used as a parameter of the degradation index in the method.
Alternatively, as in the residual charge method shown in Non-Patent Document 1, the emission voltage (electric field strength) is also obtained by separating the residual charge signal waveform obtained by applying a predetermined alternating voltage once. Can guide you.
Thus, the degree of deterioration of the target cable can be evaluated by the loss current method, and can be evaluated by the residual charge measurement method.

Based on the above, the present invention solves the above problems as follows.
(1) Deterioration diagnosis method for CV cable, which is a pre-process for imposing an AC cutoff waveform that interrupts AC voltage at an arbitrary phase on the CV cable, and the charge accumulated in the water tree section of the CV cable in this previous process And measuring the residual charge by changing the phase for cutting off the AC voltage applied in the previous step and measuring the residual charge amount for each cutoff phase. After the residual charge amount is differentiated and converted into a current signal, a harmonic component contained in the current signal is obtained by frequency analysis of the current signal, and diagnosis is performed.
(2) In the above (1), the harmonic component used for the deterioration diagnosis is a third harmonic component.
(3) In the above (2), the deterioration diagnosis after acquiring the harmonic component is performed using the magnitude of the third harmonic component and the phase difference with respect to the voltage phase.
(4) Before or after the deterioration diagnosis of (1) is performed, residual charge measurement is performed, a component with respect to the voltage of the residual charge signal is obtained, deterioration diagnosis is performed by the residual charge method, and deterioration diagnosis of (1) is performed. Combine the results to derive a comprehensive diagnosis result.

In the present invention, the following effects can be obtained.
(1) According to the deterioration diagnosis method of the present invention, since the deterioration diagnosis by the loss current method can be performed by the apparatus that performs the residual charge method, the diagnosis apparatus can be shared, and there is no need to prepare a diagnosis apparatus for each method. .
(2) If one diagnostic device is attached to the CV cable, deterioration diagnosis by the residual charge method and deterioration diagnosis by the loss current method can be performed, so obtaining diagnosis results corresponding to the two methods is acceptable for actual diagnosis. It is possible to obtain a diagnosis result with high accuracy as compared with the conventional maintenance diagnosis method that relies on the diagnosis result obtained by one conventional deterioration diagnosis method.

It is a figure which shows the structural example of the electrical charging and measurement apparatus of the Example of this invention. It is a figure which shows the example (1) of the interruption | blocking waveform of an alternating voltage. It is a figure which shows the example (2) of the interruption | blocking waveform of an alternating voltage. It is a figure which shows the time change of the residual charge amount at the time of changing the interruption | blocking phase of an alternating voltage. It is a figure which shows the electric charge amount in each interruption | blocking phase. Is a diagram illustrating a method of performing the deterioration determination of the magnitude of the third harmonic component current (I ₃₎ and the phase (theta _3). It is a figure explaining the reason why a current signal equivalent to a loss current signal can be obtained from a residual charge signal obtained by an AC cutoff method. It is a figure which shows the residual charge signal obtained by the alternating current interruption method, a loss current signal, and a 3rd harmonic component. It is a figure which shows the example (1) of a measurement pattern in the case of performing the deterioration diagnosis by a loss current measuring method and a step electric power generation method using the residual charge signal obtained by the alternating current interruption method. It is a figure which shows the example (2) of a measurement pattern in the case of performing the deterioration diagnosis by a loss current measuring method and a step electric power generation method using the residual charge signal obtained by the alternating current interruption method. It is a figure which shows the example (3) of a measurement pattern in the case of performing the deterioration diagnosis by the loss current measuring method and the step electric power application method (waveform separation) using the residual charge signal obtained by the alternating current interruption method. It is a figure which shows the example of data stored in the database used when performing a waveform separation method. It is a figure explaining waveform separation. It is a figure which shows the example (4) of a measurement pattern in the case of performing the deterioration diagnosis by the loss electric current measurement method and the step voltage application method (waveform separation) using the residual charge signal obtained by the alternating current interruption method. It is a figure which shows the phase characteristic of the residual charge amount acquired by changing the interruption | blocking phase of an alternating voltage according to the procedure of this invention.

<Example 1>
FIG. 1 is a diagram showing an example of the configuration of a power application and measurement apparatus according to an embodiment of the present invention.
As shown in the figure, the power application apparatus includes a test transformer 1 and a boost pattern generator 2 for applying an alternating voltage. A measurement target cable 3 is connected to the test transformer 1.
The primary side of the test transformer 1 is connected to the output of the boost pattern generator 2, and when the AC voltage is applied, the output voltage of the test transformer 1 rises in a pattern corresponding to the output of the boost pattern generator 2. . Moreover, the AC voltage applied to the measurement target cable 3 can be cut off at an arbitrary phase by giving a cut-off signal to the booster pattern generator 2.
The deterioration diagnosis method of this embodiment includes a pre-process, a post-process, an analysis process, and a diagnosis process.
In the pre-process, an AC voltage is applied between the cable conductor and the shield of the measurement target cable 3 from the test transformer 1 (pre-charging) and cut off at a predetermined phase (hereinafter, referred to as “cut-off phase”). ) Charges are accumulated in the water tree by this pre-process.
In the post-process, the charge accumulated in the water tree is released by the measurement voltage application, and the amount of the remaining charge is determined by measuring the released charge.
As a method of releasing, the voltage is stepped up and measured by adding the charges released at each stage, and all the releasable with the accumulated charges can be released. There is a method of measuring residual charges by applying a sufficiently high alternating voltage (hereinafter referred to as “predetermined alternating voltage”) once.
The operations of the pre-process and the post-process are repeated while changing the cutoff phase of the AC voltage applied in the pre-process.
Examples of the cutoff waveform are shown in FIGS. The vertical axis in the figure is the normalized applied voltage, the horizontal axis is the phase, and FIGS. 2 and 3 show the cases where they are cut off at the phases A and B, respectively.
Hereinafter, such a method of applying an AC voltage and blocking at a predetermined phase to acquire the residual charge amount is also referred to as an “AC blocking method”.

As described above, the AC voltage (pre-charge) is interrupted at an arbitrary phase, and then the predetermined AC voltage is applied (measurement charge) to measure the residual charge amount. When the results of the plurality of times are summarized, the residual charge amount waveform (residual charge signal) shown in FIG. 4 is obtained. In the figure, the vertical axis indicates the normalized AC voltage and the residual charge amount, and the horizontal axis indicates the cutoff phase. The solid line shows the pre-applied AC voltage, and the dotted line plots the residual charge amount obtained when the AC voltage shown in the figure is blocked at each phase (residual charge signal).
Here, as will be described later, the residual charge amount detected when a predetermined alternating voltage is applied (measurement application) after the pre-appliance is cut off at _a certain phase (θ _a ) is shown in FIG. As shown in Fig. 2, in the phase (θ _a ), the charge of the amount of charge (Q ₀ ) accumulated during the previous half wavelength moves under the voltage application of the reverse polarity up to the phase (θ _a ) This is the reduced charge amount Qa. Further, in the phase (θ _b ), the amount of charge Qb subtracted from the Q ₀ is the amount of charge that has been moved under voltage application of reverse polarity up to the phase (θ _b ). The same applies to other phases.
These movements of charge reflect the movement of charges inside the water tree under AC voltage charge, and all of them were acquired under AC voltage charge. This is considered to be a phenomenon that always occurs during this period.

Here, since the residual charge signal shown in FIG. 4 and FIG. 5 is a change in the amount of charge, a current waveform can be obtained by differentiating it over time, and this current waveform is caused by the water tree. By analyzing the frequency of this signal, the magnitude of the third harmonic component used in the loss current method described in Patent Document 2 and the phase difference with respect to the applied voltage phase can be derived. it can.
Actually, it is impossible to measure the residual charge by continuously interrupting the AC voltage at an arbitrary phase. Therefore, the residual charge is measured at discrete cutoff phases, and the value between the phases is 2 What is necessary is just to perform the linear interpolation between points, and approximate the whole by a suitable curve. In this way, the residual charge amount waveform is derived, and a current signal corresponding to this is obtained by differentiating the charge amount waveform, and is a diagnostic parameter used in the loss current method disclosed in Patent Document 2. The magnitude (I ₃ ) and phase (θ ₃ ) of a certain third harmonic component current are derived.

FIG. 6 is a diagram for explaining the determination method described in Patent Document 2. FIG. 6 shows an example of determination lines and measurement data when the line length is 100 m or less.
In the determination method described in Patent Document 2, the magnitude and phase of a harmonic current generated by water trees having different lengths are obtained in advance, and based on this, as shown in FIG. The decision line curve S is drawn on an orthogonal plane with the phase and the vertical axis representing the magnitude of the harmonic component.
Then, the magnitude of the third harmonic component and the phase with respect to the applied voltage phase obtained as described above are plotted on FIG. 6, and the plot position of the measurement result is on the left side of this locus (white A blank plot) is judged as good, and if it is on the right side (black plot), it is diagnosed as defective.

Next, as described above, from the residual charge signal obtained by the AC cutoff method, the reason why the magnitude of the third harmonic component used in the loss current method and the phase difference with respect to the applied voltage phase can be derived. explain.
7 and 8 are diagrams for explaining the reason why a current signal equivalent to a loss current signal can be obtained from the residual charge signal obtained by the AC interruption method. 7A shows the AC voltage and the cutoff phase, FIG. 7B shows an outline of the state of charge accumulation in the water tree, FIG. 7C shows the residual charge signal (residual charge amount), and FIG. An AC voltage waveform (A in the figure), a residual charge signal (B in the figure), a differential waveform (current waveform) in the residual charge signal (in the figure C), and a third harmonic component (D in the figure) are shown.

As shown in FIG. 7 (a), after AC voltage A is applied (pre-applied), when AC voltage A is cut off at the θ ₀ timing whose phase is near ₀ , as shown in FIG. 7 (b). The maximum amount of charge is stored in the water tree. Then, when a predetermined alternating voltage is applied (measurement application) and the residual charge amount is measured, a signal S ₀ is obtained as shown in FIG. 5C, and the integrated charge amount is −Q. Become.
Next, in the case of blocking at the timing of θ ₁ in FIG. 7A, some charges (a pair of charges in the figure) are eased as shown in FIG. Accumulation of charge is performed. When the residual charge is measured thereafter, a signal S ₁ is obtained as shown in FIG. 5C, and the charge amount of the integral value is −Q + Q ₁ .
Next, when shut off at the timing of θ ₂ , as shown in FIG. 5B, for example, three pairs of charges are relaxed, and at the same time, charge accumulation in the reverse direction is performed.
When the residual charge is measured after this, a signal of S ₂ is obtained as shown in FIG. 5C, and the charge amount of the integrated value becomes −Q + Q ₂ .
Further, when the interruption is performed at the timing of θ ₃ , as shown in FIG. 5B, for example, all charges are relaxed and at the same time, charge accumulation in the reverse direction is performed.
Performed to perform the residual charge measured after this, signals S ₃ is obtained as shown in FIG. (C), the charge amount of the integrated value becomes + Q.

The residual charge signal obtained in the above manner in each cutoff phase is plotted on the chart showing the AC voltage waveform with the horizontal axis as the cutoff phase and the vertical axis as the residual charge amount. A residual charge signal waveform Q (t) shown in curve 8 of FIG. 8 is obtained.
Further, when the residual charge signal waveform Q (t) is differentiated with respect to time (phase), a current signal I (t) shown by a curve C in FIG. 8 can be obtained. This current signal is a current that flows due to the water tree. By analyzing the frequency of this signal, the magnitude of the third harmonic component [I ₃ ] used in the loss current method, shown by curve D in FIG. And the phase difference [θ ₃ ] with respect to the applied voltage phase can be derived.

That is, in the present embodiment, a current signal substantially equivalent to the loss current signal is obtained from the residual charge signal obtained by the AC interruption method according to the following principle.
(1) The decrease in the amount of charge is caused by the movement of charges, as shown in FIG. The presence of charge transfer means that current flows.
(2) This charge transfer also occurs even when an alternating voltage is normally applied. The amount of charge detected when the interruption timing is changed is the same as detecting the movement of charges when an alternating voltage is applied.
(3) The loss current measured by the loss current method is a current signal detected when an AC voltage is applied to the CV cable. This loss current signal reflects the movement of charge inside the water tree. The third harmonic component in the loss current signal has a particularly high correlation with the water tree.
(4) On the other hand, the waveform of the residual charge amount (residual charge signal) measured as shown in FIG. 7C by changing the timing of interruption is a time change of the charge amount. The current component that flows due to the water tree can be derived. Therefore, it can be said that the current signal obtained by differentiating the residual charge signal waveform measured by changing the timing of the interruption is substantially equivalent to the loss current signal.

  According to the above-described degradation diagnosis method, the degradation diagnosis based on the loss current method can be performed with the residual charge method apparatus shown in FIG. There is an advantage that diagnosis can be performed.

In the diagnosis by the loss current method, there are concerns about the influence of harmonic components contained in the power supply voltage, so various countermeasures have been devised (for example, see Patent Document 4). According to the degradation diagnosis method, the diagnostic parameters (I ₃ and θ ₃ ) used for the degradation diagnosis by the loss current method are derived on the basis of the residual charge method whose measurement target is a low frequency component. There is also a feature that a diagnostic parameter can be obtained without special consideration regarding the influence of the harmonic component contained in.

<Example 2>
By the way, when performing the deterioration diagnosis, it is desirable to make a comprehensive determination using a plurality of deterioration diagnosis methods as described above in order to derive an appropriate diagnosis result.
Therefore, in this embodiment, a deterioration diagnosis method for evaluating the residual charge method by the step charging method used in Patent Document 1 before or after performing the deterioration diagnosis by the above-described loss current method will be described. .

FIG. 9 is a diagram showing an example (1) of a measurement pattern. Degradation diagnosis by the loss current measurement method from the residual charge signal obtained by the AC interruption method described above, and the step voltage application method described in Patent Document 1 above. It is a figure explaining the case where deterioration diagnosis by is performed together. FIG. 9 (a) shows the measurement of the residual charge by the measurement pattern P1, and FIG. 9 (b) shows the procedure when the degradation diagnosis is performed by the loss current method described in FIG. 6 using the measured residual charge amount. FIG. 6C shows a measurement pattern B of deterioration diagnosis by the step charging method, which is a kind of the residual charge method, and residual electric signals detected at the respective applied voltages.
When performing the deterioration diagnosis due to the loss current from the residual charge signal obtained by the AC cutting method, as shown in FIG. 6 (a), before Division photoelectrically performed by alternating voltage shutoff phase theta ₀ of the AC voltage as the previous step blocked (before Division electrostatic voltage (1):. in the figure is shown by a circled number hereinafter), then voltage application to AC voltage for measurement to take out the residual charges for blocking the phase theta ₀ as a later step (Measured voltage charging (1)). Thereby, the residual charge amount with respect to the cutoff phase θ ₀ is obtained. Note that the voltage applied to the measurement voltage is a high voltage at which everything that can be released by the charge accumulated in the water tree is released.
Then, in the same manner as described above, the AC voltage is pre-charged to cut off the AC voltage at the cutoff phase θ ₁ (the pre-voltage voltage (2), and then the AC voltage to extract the residual charge for the cutoff phase θ ₁ (Measurement voltage charging (2)) This gives the residual charge for the cutoff phase θ _1. Similarly, taking out the residual charge signal for each cutoff phase while changing the cutoff phase, Repeat until θ _m until the residual charge amount for each blocking phase is obtained.
Then, as described above, a waveform corresponding to the current value is acquired from the amount of change in the phase of the charge amount, and as shown in FIG. 5B, the third harmonic component is acquired by analyzing the waveform corresponding to the current. The magnitude (I ₃ ) and phase (θ ₃ ) of the third harmonic component current obtained in this way are plotted on the graph shown in FIG. 6, and depending on which side of the judgment curve is located. Deterioration diagnosis (by loss current method) is performed.

Also, before or after the deterioration diagnosis, the residual charge method is evaluated by the step voltage method shown in FIG.
That is, after applying AC voltage as the pre-charging (pre-charging voltage A), the AC voltage of the pre-charging is cut off at the cutoff phase θ ₀ (= 0 °), and then the AC voltage is stepped up in steps. While applying the voltage (measurement voltage V1 to V5), the residual charge signal at the voltages V1 to V5 is detected for each measurement voltage V1 to V5, and the maximum alternating current at which the residual charge signal is detected at this time The voltage is used as an index for deterioration diagnosis by the residual charge method. In the case of FIG. 3C, the maximum AC voltage at which the residual charge signal is detected is V3, and the breakdown value of the CV cable is estimated from this voltage V3.
In this way, diagnostic indexes for both the loss current method and the residual charge method can be obtained, and a highly accurate diagnostic result can be obtained by comprehensively judging the diagnostic results corresponding to the two deterioration diagnoses. Can do.

  FIG. 10 is a diagram showing an example (2) of another measurement pattern. FIG. 10 (a) shows the measurement of the residual charge by the measurement pattern P2, and FIG. 10 (b) uses the residual charge amount. 6 shows a procedure in the case of performing the deterioration diagnosis by the loss current method described in FIG. The residual electric signal at the time is shown.

The measurement pattern P2 shown in FIG. 6A is an example in which the pre-charging of the previous process and the charging of the AC voltage for measurement in the post-process are used together. In this example, as shown in FIG. 6A, the AC voltage is pre-applied to cut off the AC voltage at the cut-off phase θ ₀ (pre-charge voltage (1)), and then the cut-off phase θ _0. At the same time that the residual charge is taken out, “measurement voltage application (1) and pre-application voltage (2)” is newly applied.
This voltage application is cut off at the cut-off phase θ ₁ . As a result, a residual charge for the previous cutoff phase θ ₀ is obtained, and pre-charging for the next residual charge measurement is performed.
Next, the residual charge for the cutoff phase θ ₁ is taken out, and at the same time, “measurement voltage application (2) and pre-application voltage (3)” for newly storing the charge is applied. This voltage application is cut off at the cut-off phase θ ₂ . As a result, a residual charge for the previous cutoff phase θ ₁ is obtained, and a pre-charging for the next residual charge measurement is performed. Similarly, the residual charge signal for each cutoff phase is extracted while changing the cutoff phase, and as described above, the residual charge amount for each cutoff phase is obtained.
Then, as described above, a waveform corresponding to the current value is acquired from the amount of change in the phase of the charge amount, and as shown in FIG. 5B, the third harmonic component is acquired by analyzing the waveform corresponding to the current.
Further, as shown in FIG. 10C, the residual charge method is evaluated by the step charging method as in FIG. 9C, and the maximum AC voltage at which the residual charge signal is detected at this time is evaluated for deterioration. As an indicator of

FIG. 11 is a diagram showing another example (3) of measurement patterns. FIG. 11A shows a measurement pattern P1 in the case of performing a deterioration diagnosis by a loss current method from a residual charge signal obtained by an AC interruption method. (Same as FIG. 9A), FIG. 9B shows a procedure in the case where the residual charge amount is obtained and the deterioration diagnosis is performed by the loss current method described in FIG. The feature of FIG. 11 is that the residual charge method by the waveform separation method described in Non-Patent Document 1 is performed as shown in FIG.
The deterioration diagnosis by the loss current method is the same as in FIG. That is. As shown in FIG. 11A, the residual charge signal for each cutoff phase is extracted while changing the cutoff phase, and this is repeated until the cutoff phase θ _m is reached to obtain the residual charge amount for each cutoff phase, as described above. Then, a current value equivalent waveform is obtained from the amount of phase change of the charge amount, and as shown in FIG. 11B, the third harmonic component is obtained by analyzing the current equivalent waveform, and deterioration diagnosis is performed.
Further, when the residual charge method is evaluated by waveform separation as shown in FIG. 11C, the pre-charge AC voltage is cut off at the cut-off phase θ ₀ (= 0 °), and then the measurement charge is applied. An AC voltage is applied as electricity, and a residual charge signal is detected. At this time, a sufficiently high AC voltage is applied once so that all the charges that can be released by the charges accumulated in the water tree can be released. In this example, an AC voltage of voltage V4 is applied. Thereafter, the residual charge signal thus obtained is subjected to waveform separation by the waveform separation method, and the maximum AC voltage at which the residual charge signal is detected is obtained and used as an indicator for deterioration diagnosis.

Hereinafter, the waveform separation method will be described.
In order to separate the waveforms, first, an AC voltage for measurement is applied while stepping up from a low voltage to a high voltage (step application; for example, the AC voltages V1, V2, V3, and V4 are charged). A database storing the residual charge signal obtained by this is prepared in advance.
When diagnosing deterioration of a CV cable, an AC voltage equal to or higher than the highest voltage at which a residual charge signal is obtained is applied once to obtain a residual charge signal. From this actually measured residual charge signal, the waveform of the residual charge signal for each AC applied voltage stored in the database is separated. That is, of the residual charge signals stored in the database, the residual charge signal obtained by the lowest voltage measurement voltage is removed from the actually measured residual charge signal to obtain a residual residual charge signal. Next, the residual charge signal obtained by the next low-voltage measurement voltage application is removed from the residual residual charge signal to obtain a residual residual charge signal. By repeating this, the deterioration diagnosis is performed from the voltage applied to the measurement when the remaining residual charge signal disappears. Thereby, a residual charge signal equivalent to the case where an AC voltage is applied in an arbitrary step can be obtained, and the water tree deterioration of the CV cable can be diagnosed with high accuracy in a short measurement time.
That is, a residual charge signal is obtained by a one-time charging method, and the obtained residual charge signal is waveform-separated using data in a database storing a residual charge signal obtained by an arbitrary number of steps prepared in advance. This waveform separation can be performed automatically using, for example, computer software.

A specific example is shown in FIG.
FIG. 5A shows a residual charge signal (waveform A) obtained by a single voltage application method and an AC voltage application pattern (waveform E1) applied at that time (measurement application). In this example, when the AC voltage E1 is applied, the residual charge signal of waveform A rises. The AC voltage E1 reaches the voltage V3 after S seconds, and the residual charge signal lasts for t1 seconds from the time when the AC voltage E1 reaches the voltage V3.
FIG. 5B shows data stored in the database.
That is, FIG. 6B shows a residual charge signal (waveform B) obtained when the AC voltage V1 (waveform E2) is applied and a residual charge signal obtained when the AC voltage V2 (waveform E3) is applied. A residual charge signal (waveform D) obtained when a charge signal (waveform C) and an AC voltage V3 (waveform E4) are applied is shown.

As shown in FIG. 6B, the waveform B of the residual charge signal is obtained when the AC voltage E2 rises when the waveform AC voltage E2 is applied, and at the same time the residual charge signal rises (time point a1), the AC voltage After the AC voltage E2 reaches the voltage V1 S1 seconds after E2 rises, the residual charge signal lasts for t1 seconds, and the residual charge signal becomes zero at time point b1.
In the waveform C, when the alternating voltage E3 is applied and reaches the same voltage V1 as the alternating voltage E2, the residual charge signal rises (time point a2), and the alternating current is S2 (= 2S1) seconds after the alternating voltage E3 rises. After the voltage E3 reaches V2 (= 2V1), the residual charge signal lasts for t1 seconds, and the residual charge signal becomes zero at time b2.
In waveform D, when the AC voltage E4 is applied and reaches the same voltage V2 as the AC voltage E3, the residual charge signal rises (time point a3), and the AC voltage is S3 (= 3S1) seconds after the AC voltage E4 rises. After the voltage E4 reaches V3 (= 3V1), the residual charge signal lasts for t1 seconds, and the residual charge signal becomes 0 at time point b3.

Based on the data shown in FIG. 12B stored in the database, the residual charge signal obtained when a predetermined maximum AC applied voltage is applied once is separated into waveforms as shown in FIG.
It is assumed that a residual charge signal shown in waveform A as shown in FIG. First, as shown in FIG. 12B, the waveform of the residual charge signal obtained when the AC voltage V1 is applied is separated.
A residual charge signal waveform B obtained when the AC voltage V1 shown in FIG. 12B is applied is extracted from the database. Next, as shown in FIG. 13B, the waveforms A and N are aligned in the vertical axis direction so that the rising points of the waveform A and the waveform B overlap with each other. Double (At this time, the distance between the start point a1 and the end point b1 of the waveform B is not changed) and corrected to the waveform.
Let this waveform multiplied by n be B ′. This waveform B ′ is a residual charge signal component obtained when the voltage V1 included in the waveform A is applied.
Next, by subtracting the waveform B ′ from the waveform A, the residual charge signal component of the voltage V1 included in the waveform A is removed, and the residual charge signal component of the waveform A1, which is the remaining residual charge signal component, is obtained.

Next, a residual charge signal waveform C obtained when the AC voltage V2 is applied is extracted from the database. Next, as shown in FIG. 12C, the waveform A is aligned in the vertical axis direction so that the start points of the waveform A1 and the waveform C, which are the remaining residual charge signal components, are aligned with the region Br of the waveform A1. m times. The waveform multiplied by m is defined as C ′. This waveform C ′ corresponds to the residual charge signal component obtained when the voltage V2 included in the waveform A1 is applied.
Next, by subtracting the waveform C ′ from the waveform A1, the residual charge signal component of the voltage V2 included in the waveform A1 is removed, and the residual charge signal component of the waveform A2, which is the remaining residual charge signal component, is obtained.
Thereafter, the residual charge signal component similar to the residual charge signal obtained by the step voltage application method can be obtained by removing the residual charge signal component by the same procedure and dividing the residual charge signal by the required number. As described above, the maximum AC voltage at which the residual charge signal is detected is used as an indicator for deterioration diagnosis.

FIG. 14 is a diagram showing an example (4) of another measurement pattern. FIG. 14 (a) shows the measurement of residual charge by the measurement pattern P2, and FIG. FIG. 6C shows a procedure for performing deterioration diagnosis by the loss current measuring method described in FIG. 6, and FIG. 6C shows a case in which the residual charge method is evaluated by the waveform separation method described in Non-Patent Document 1. Yes.
The measurement pattern shown in FIG. 9A is an example in which the pre-charging shown in FIG. 10 and the charging of the AC voltage for measurement are used in combination. In this example, as shown in FIG. 6 (a), cut off an alternating voltage shutoff phase theta ₀ performed before Division electric AC voltage, then a measurement in order to extract the residual charge for the shutoff phase theta ₀ The AC voltage is charged. As a result, a residual charge with respect to the cutoff phase θ ₀ is obtained.
Then, an AC voltage for the measurement as before Division conductive blocks the AC voltage shutoff phase theta _1, then voltage application to AC voltage to retrieve the residual charge for the shutoff phase theta _1. As a result, a residual charge for the cutoff phase θ ₁ is obtained. Similarly, the residual charge signal for each cutoff phase is extracted while changing the cutoff phase, and as described above, the residual charge amount for each cutoff phase is obtained.
Then, as described above, a waveform corresponding to the current value is acquired from the amount of change in the phase of the charge amount, and as shown in FIG. 5B, the third harmonic component is acquired by analyzing the waveform corresponding to the current.

Further, when the residual charge method is evaluated by waveform separation, as shown in FIG. 5C, after applying the highest AC voltage V3 as the pre-charging, the cutoff phase θ ₀ (= 0 °) Then, the AC voltage of the pre-charging is cut off, and then the AC voltage is applied to detect the residual charge signal. The residual charge signal thus obtained is waveform-separated by the above-described waveform separation method, and the maximum AC voltage at which the residual charge signal is detected is deteriorated as described in FIGS. 9C and 10C. Use as an index of diagnosis.

The results of evaluation according to the method of the present invention are shown below.
FIG. 15 shows the phase characteristics of the residual charge amount obtained by changing the AC voltage cutoff phase according to the procedure of the present invention in an extra-high voltage removal cable that has passed 20 years or more.
The approximate curve shown with a broken line is applied to the data, a differential waveform of the waveform is obtained, and the magnitude (I ₃ ) of the third harmonic component, which is a deterioration diagnosis parameter of the loss current method, is imposed by frequency analysis. The phase difference (θ ₃ ) with respect to the electric voltage phase was determined.
The derived results are shown in Table 1. Moreover, the said parameter acquired by the loss current method with respect to the same sample was shown in the same table as a comparative example.

It is confirmed that the deterioration diagnosis parameter in the loss current derived from the residual charge method according to the present invention is consistent with the deterioration diagnosis parameter derived from the loss current method.
From the numerical values shown in Table 1, it is determined that the test sample exhibits a level of deterioration that requires caution determination, that is, remediation is recommended in the deterioration determination result in the loss current method shown in Patent Document 2. .
On the other hand, according to the degradation determination method in the residual charge method disclosed in Patent Document 1, since the residual charge signal is detected up to a predetermined applied maximum AC voltage, the insulation performance is such that renovation is recommended. It can be determined that the deterioration has been reduced to the same level, and it can be confirmed that the deterioration determination results of both are the same.

1 Test Transformer 2 Boost Pattern Generator 3 Measurement Cable 4 Low-pass Filter 5 Amplifier

Claims (4)

This is a method for diagnosing degradation of CV cables, in which a charge is accumulated in the water tree section of the CV cable in the previous process of imposing an AC cutoff waveform that blocks AC voltage at an arbitrary phase on the CV cable. And a post process for measuring the residual charge,
Change the phase at which the AC voltage to be applied in the previous step is interrupted, measure the residual charge amount for each interrupt phase, and determine the relationship between the interrupt phase and the residual charge amount,
The residual charge amount is differentiated and converted into a current signal, and then a harmonic component included in the current signal is acquired and analyzed by frequency analysis of the current signal. Method. The method for diagnosing deterioration of a CV cable according to claim 1, wherein the harmonic component used for deterioration diagnosis is a third harmonic component. The deterioration diagnosis method for a CV cable according to claim 2, wherein the deterioration diagnosis after acquiring the harmonic component is performed using a magnitude of the third harmonic component and a phase difference with respect to a voltage phase thereof. . Before or after the execution of the deterioration diagnosis according to claim 1, the residual charge is measured, the component with respect to the voltage of the residual charge signal is acquired, the deterioration diagnosis by the residual charge method is performed, and the deterioration diagnosis result according to claim 1 is combined, A method for diagnosing deterioration of a CV cable, characterized in that a deterioration diagnosis result is derived comprehensively.

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