JP4336328B2 - CV cable residual charge measurement method - Google Patents

Description

  The present invention relates to a residual charge measurement method for diagnosing the insulation performance of a CV cable having a water tree deteriorated.

A residual charge measurement method is known as a method for diagnosing insulation deterioration of a CV cable that has deteriorated water trees (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and the like). The residual charge measuring method measures the charge accumulated in the water tree of the CV cable by imposing a DC voltage, and diagnoses the residual performance of the cable insulator in a non-destructive manner. It is attracting attention as.
In the residual charge measurement, a predetermined DC voltage is applied to the cable, and after being grounded, an AC voltage is applied. When the water tree is present in the cable insulator, charges are accumulated in the water tree portion by applying a DC voltage.
This type of charge is not easily released even when grounded and the cable conductor / shield is closed circuit. However, these charges are easily released by applying an alternating voltage thereafter. These emitted charges are detected as a direct current component by using a low-pass filter.
JP-A-5-307060 JP-A-8-62280 JP 2003-329723 A

As described above, in the residual charge method, the DC component current is detected, but in the actual line, noise is superimposed on the measurement target line due to induction of the side line, etc., and a DC component is generated in the measurement circuit system. There is a case.
Since the frequency component of the residual charge signal and the frequency component of the noise component are almost the same, it becomes a big problem when the residual charge is measured on the actual line.
To eliminate this, use a phase that is not the measurement target phase as an antenna phase, detect noise superimposed on this phase, subtract it from the measurement signal from the measurement target line, and superimpose it on the measurement target line A method for removing the noise component is considered (see, for example, Patent Document 3).

In principle, the superimposed noise can be removed by the same method, but in reality, the characteristics of the signal detection / transmission system from the measurement target phase and the signal detection / transmission system from the antenna phase are exactly the same. It is difficult to make it a characteristic. For this reason, the superimposed noise component cannot be completely removed and remains. Such residual noise becomes a problem particularly when a small residual charge signal is detected.
The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce noise superimposed on a residual charge signal and improve the resolution of the residual charge signal to be measured.

In the present invention, in order to solve the above-described problem, another phase on which noise is superimposed to the same extent as the measurement target phase that is the target of residual charge measurement is defined as the antenna phase, and prior to the residual charge measurement, the measurement target phase and the above-described phase are measured. A noise signal superimposed on each antenna phase is detected.
Then, a correction value is obtained using both of the detected noise signals, and at the time of residual charge measurement, either the signal detected from the measurement target phase or the signal detected from the antenna phase is corrected. After correcting based on the value, a difference between signals detected from the measurement target phase and the antenna phase is obtained to obtain a residual charge signal in which the influence of noise is reduced.

  In the present invention, when measuring the residual charge, individual noise waveforms of the measurement target phase and the antenna phase are separately obtained, and correction processing is performed on the other waveform with reference to one waveform, and remains in the differential waveform. Since noise is reduced, noise superimposed on the residual charge signal can be reduced, and the resolution of the measured residual charge signal can be improved.

FIG. 1 shows the configuration of a residual charge measuring apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the power application device is composed of a DC high voltage generator 1 for accumulating electric charges in a water tree, a test transformer 2 for applying an AC voltage during measurement, and a changeover switch SW. . The DC high voltage generator 1 outputs a DC voltage or a voltage having an alternative waveform corresponding to the DC voltage.
The terminal (a) of the changeover switch SW is connected to the measurement target phase 3a of the CV cable 3 to be measured, the terminal (b) is connected to the voltage output terminal of the high voltage generator 1, and the terminal (c) is The test transformer 2 is connected to the AC voltage output terminal, the terminal (d) is grounded, and the terminal (e) is grounded via a resistor R.

A measurement signal is taken out from the low voltage side of the test transformer 2, and this measurement signal is input to a low-pass filter 4a for detecting a DC component signal.
Further, the phase outside the measurement target that is considered to have the same level of noise as the measurement target phase 3a is defined as the antenna phase 3b, and when the correction value of the noise component is obtained as described below, A measurement signal that is a noise component is extracted, and this measurement signal is input to a low-pass filter 4b for detecting a DC component signal.
The outputs of the low-pass filters 4a and 4b are input to measuring instruments 5a and 5b for amplifying and detecting weak signals, respectively. The outputs of the measuring instruments 5a and 5b are given to a personal computer (PC) 6 for storing and processing data.

In FIG. 1, prior to the residual charge measurement, noise signals are individually detected from the measurement target phase and the antenna phase by the measurement system shown in FIG.
The residual charge signal is usually detected while an AC voltage is applied, and the width of the appearance of the waveform is about 10 seconds as shown in FIG. 2, and a similar frequency that remains in such a time domain. It may be difficult to distinguish a noise component having a residual charge signal. Alternatively, it is desirable to remove the signal that is originally desired because it may be buried in noise. Therefore, a correction value is obtained by executing a waveform operation that minimizes the noise component. Here, the correction value means a constant multiplied by a signal from the antenna phase.

The correction value is obtained as follows.
The changeover switch SW is connected to the terminal (c), the noise signal of the measurement target phase 3a is taken out from the low voltage side of the test transformer 2, is input to the measuring instrument 5a through the low-pass filter 4a, and is measured by the measuring instrument 5a. A noise signal of the target phase 3a is obtained. Further, a noise signal is extracted from the antenna phase 3b, and is input to the measuring device 5b through the low-pass filter 4b, and the noise signal of the antenna phase 3b is obtained by the measuring device 5b. The personal computer 6 calculates the correction value based on the noise signal obtained from the measurement target phase 3a and the noise signal obtained from the antenna phase 3b.
This correction value can be obtained by, for example, obtaining a ratio of the noise signal obtained from the measurement target phase 3a and the noise signal obtained from the antenna phase 3b and averaging the ratio.

After the above operation, a residual charge measurement is performed.
First, the terminals (a) and (b) of the changeover switch SW are connected, and a DC high voltage is applied from the DC high voltage generator 1 between the conductor and the shield of the measurement target phase 3a.
Next, after the terminal (a) is connected to the terminal (e) and the voltage application is completed, the cable conductor is grounded to the ground via the resistor R, and then the terminal (a) is connected to the terminal (d) and directly grounded. To do.
Thereafter, the terminal (a) is connected to the terminal (c), and the test transformer 2 applies a predetermined AC voltage between the cable conductor and the shield of the measurement target phase 3a.

The measurement signal of the measurement target phase 3a is taken out from the low-voltage side of the test transformer 2, and is input to the measuring instrument 5a via the low-pass filter 4a. A residual charge signal including the signal).
On the other hand, the noise signal extracted from the antenna phase 3b is input to the measuring device 5b through the low-pass filter 4a, and the measurement signal (noise signal) of the antenna phase 3b is obtained from the output of the measuring device 5b.
The personal computer 6 multiplies the signal obtained from the antenna phase by the correction value and then subtracts the waveform from the signal obtained from the measurement target phase 3a to obtain a residual charge signal with reduced noise components.

In the above description, the signal obtained from the antenna phase is corrected with the correction value. However, the signal of the measurement target phase may be corrected with the correction value. In that case, it is necessary to correct the absolute value in the finally obtained waveform.
The processing in the personal computer 6 can be implemented in hardware by using a constant multiplier or the like as a device in advance, but since it is considered that there is a difference between the two in the signal transmission system, the signal transmission system is the same. It is more preferable to capture a signal and apply it as a software.
As described above, the residual charge can be measured, and the cable insulation can be diagnosed from the temporal change of the residual charge. For example, various methods have been proposed for deterioration diagnosis by the residual charge method as described in Patent Documents 2 and 3, and can be realized by using these well-known methods. .

FIG. 3 shows each noise signal detected when noise signals are individually measured from the measurement target phase 3a and the antenna phase 3b prior to the residual charge measurement. In the figure, the horizontal axis represents time (seconds), the vertical axis represents output (V), the solid line represents the phase to be measured, and the dotted line represents the noise signal detected from the antenna phase.
As shown in the figure, the waveform shapes of both are roughly the same, but it is understood that they are not the same waveform.
FIG. 4 shows a simple differential waveform of the waveforms detected from the measurement target phase 3a and the antenna phase 3b, and a differential waveform after the correction value is obtained and corrected by the correction value as described above. . In the figure, the horizontal axis represents time (seconds), the vertical axis represents output (V), the solid line represents the differential waveform before correction, and the dotted line represents the differential waveform after correction.
As shown in the figure, the remaining noise components are reduced by performing the correction processing according to the present invention.

It is a figure which shows the structural example of the residual charge measuring apparatus of the Example of this invention. It is a figure which shows an example of a residual charge measurement signal. It is a figure which shows the example of the noise component waveform of a measurement object phase and an antenna phase. It is a figure which shows the difference waveform of the noise component of a measurement object phase and an antenna phase, and the difference waveform after correction | amendment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC high voltage generator 2 Test transformer SW changeover switch 3 CV cable 3a Phase to be measured 3b Antenna phase 4a, 4b Low-pass filter 5a, 5b Measuring instrument 6 Personal computer

Claims (1)

After applying a DC voltage or a voltage waveform having the same action as the DC voltage to the CV cable, an AC voltage is applied, and at the time of applying the DC voltage or a voltage waveform having the same action as the DC voltage. A method for measuring a residual charge of a CV cable, wherein the charge accumulated in the water tree of the CV cable is discharged and the residual charge is measured.
The antenna phase is the other phase in which noise is superimposed to the same extent as the phase to be measured for residual charge measurement.
Prior to the residual charge measurement, the noise signal superimposed on each of the measurement target phase and the antenna phase is detected, and a correction value is obtained using both of the detected noise signals. After correcting either the signal detected from the target phase or the signal detected from the antenna phase with the correction value, the difference between the signal detected from the measurement target phase and the antenna phase is obtained, and the noise A method for measuring a residual charge of a CV cable, wherein a residual charge signal with reduced influence is obtained.

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