JP2006337226A - Residual charge measuring method for cv cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce noise caused by a circuit response in residual charge measurement and hereby improve the resolution of the residual charge measurement. <P>SOLUTION: A DC high voltage is applied across a conductor and a shield of a cable 3 by a DC high voltage generator 1. The cable conductor is grounded through a resistor R and is then directly grounded. An AC voltage is then applied across the cable conductor and the shield by a test transformer 2 to measure the residual charge signal. When the AC voltage is applied, the output voltage of the test transformer 2 increases with a boosting pattern output by a boosting pattern generator 2a. The boosting pattern has a waveform of which the rate of change continuously changes in an area from a zero voltage as a boost starting point of the waveform to a predetermined voltage value and an area from before a boost terminating point to a constant voltage value as a boost terminating point. Changes in the vicinity of the boost starting point and the boost terminating point are smoothed, thereby reducing noise caused by the circuit response. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 with water tree deterioration (see, for example, Patent Document 1, Patent Document 2, etc.). 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 grounding and a closed circuit between the cable conductor and the shield. 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

In the residual charge method, the charge accumulated in the water tree portion by direct voltage application is discharged using an alternating voltage.
The method for boosting the AC voltage has not been specified so far. However, in the case of a method in which the AC voltage is rapidly changed from zero voltage and linearly boosted up to a predetermined AC voltage value at a constant boosting rate, in the measurement system for residual charge measurement, the voltage rising portion and the voltage are A direct current component is generated in a region where the voltage is increased to a constant value during boosting, and this becomes a noise component.
These noise signals are caused by a circuit response when an AC voltage is applied, and a residual charge signal is superimposed on these noises.

On the other hand, since the residual charge released at a predetermined voltage is released by applying a predetermined AC voltage once, the signal obtained at the first AC voltage application is noise caused by circuit response. The signal obtained at the time of the second AC voltage application is only a noise signal resulting from the circuit response. Therefore, in principle, the AC voltage is applied twice with the same voltage pattern, and the residual voltage is subtracted from the signal at the first AC voltage application by subtracting the signal at the second AC voltage application. Only the charge signal can be acquired.
However, in reality, the noise signal generated during the first AC voltage application and the noise signal generated during the second AC voltage application are not exactly the same, and there is a residual component in these differences. Will exist and affect the resolution in residual charge measurement. Therefore, in order to improve the resolution in residual charge measurement, it is desirable to reduce the noise caused by the circuit response as much as possible.
The present invention has been made in view of the above circumstances, and an object thereof is to reduce noise caused by circuit response in residual charge measurement and to improve the resolution of residual charge measurement.

When the AC voltage is boosted linearly, both become singular points at the point where the AC voltage shifts from zero voltage to boost and when the AC voltage shifts from boost to a constant value.
It is considered that these singularities are responsible for the generation of the noise component signal of the DC component accompanying the AC voltage application. Therefore, the above-mentioned problem can be solved by changing the voltage continuously in the vicinity of both points and eliminating these singular points. That is, the noise signal can be removed by gradually boosting the AC voltage from zero voltage and gradually shifting from the boosting region to a constant value.
Based on the above, in the present invention, in the residual charge measurement, the AC voltage is continuously increased so that the rate of change gradually increases in the region from the zero voltage to the predetermined value. In the region from the predetermined voltage before the end of boosting until reaching a certain value, the rate of change is continuously increased so as to gradually decrease, and the residual charges are released.

  In the present invention, in the residual charge measurement, the boosting pattern when applying the AC voltage is boosted with a waveform that does not have a singular point instead of a linear shape. The resulting noise signal can be reduced, and the resolution of residual charge measurement 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 output of the power amplifier 2b is connected to the low voltage side of the test transformer 2, and the output of the boost pattern generator 2a is connected to the power amplifier 2b. At the time of AC voltage application, the power amplifier 2b amplifies the output of the boost pattern generator 2a and applies it to the low voltage side of the test transformer 2, and the output voltage of the test transformer 2 is output by the boost pattern generator 2a. It rises with a boost pattern.

The output of the step-up pattern generator 2a is not linear, and for example, in the region where the AC voltage changes from zero voltage to a predetermined value, it continuously rises so that the rate of change gradually increases, and the boost end In this region, the rate of change gradually increases so that the rate of change gradually decreases in the region from the previous predetermined voltage until it reaches a certain value. As the boost pattern, any waveform may be used as long as it does not have a singular point. For example, a pattern that changes in the nth power of a sine wave can be used.
The terminal (a) of the changeover switch SW is connected to the cable conductor of the CV cable 3 to be measured, the terminal (b) is connected to the voltage output terminal of the DC high voltage generator 1, and the terminal (c) is the above The AC voltage output terminal of the test transformer 2 is connected, the terminal (d) is grounded, and the terminal (e) is grounded via a resistor R.

In FIG. 1, the residual charge is measured as follows. ,
First, the terminals (a) and (b) of the changeover switch SW are connected and a DC high voltage is applied between the conductor and shield of the cable 3 from the DC high voltage generator 1.
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 residual voltage signal is measured by applying an alternating voltage rising in the above-described boosting pattern between the cable conductor and the shield by the test transformer 2.

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 4 for detecting a DC component signal.
The output of the low-pass filter 4 is input to the amplifier 5, and a residual charge signal as a measurement result is obtained from the output of the amplifier 5.
As described above, the residual charge is measured, and the insulation deterioration of the cable can be diagnosed from the temporal change of the residual charge. For example, various methods have been proposed for deterioration diagnosis based on residual charges, as described in Patent Documents 2 and 3, for example, and can be realized by using these well-known methods.

As an example of the AC voltage boosting pattern, for example, as shown in FIG. 2, the voltage may be boosted to the nth power of a sine wave instead of the linear boosting.
As the n value is increased, the change from the zero voltage at the boost start point or the change from the boosting end point to the boost end point becomes smoother, and the noise signal resulting from the circuit response becomes smaller. The value of n is selected according to the performance of the equipment used.
It should be noted that the rate of change is continuously increased in the region from the zero voltage to the predetermined voltage value at the boosting start point of the waveform and in the region from before the boosting end point to the constant voltage value that is the boosting end point. Any boosted waveform can be selected as long as the waveform changes.

Assuming the simulated residual charge signal (residual charge amount 4.5 nC) shown in FIG. 3, simulation results of detection signals in the apparatus when the simulated residual charge signal is superimposed and when not superimposed are shown in FIGS. It is shown in FIG. In the simulation, the holding time for keeping the AC voltage value constant is ignored in the cases shown in FIGS.
FIG. 4 shows a detection waveform in the case of linear boosting. 5 and 6, the final voltage to be applied is the same, and the time from the start of boosting to the completion of boosting is the same as the ¼ wave of the sine wave to the 2.4th and 3.0th powers. Shows the waveform released when the pressure is increased. The waveform indicated by the bold line at the same time indicates the change pattern of the AC voltage.
As shown in FIG. 4, when linearly boosting, a noisy signal is generated due to an extremely large circuit response compared to the residual charge signal.
By taking the difference between the waveform in which the residual charge signal is superimposed and the waveform in which the signal is not superimposed, the superimposed simulated residual charge signal can be acquired, but it cannot be distinguished unless the difference is taken. . In FIG. 4, since the vertical axis is shown with a scale of 1 × 10 ⁻³ , the waveform in which the residual charge signal is superimposed and the waveform in which the residual charge signal is not superimposed almost overlap each other.

On the other hand, when the sine wave is raised to the 2.4th power instead of the linear boost, as shown in FIG. Compared to what occurs in some cases, it is reduced to about 1/10000. That is, as shown in the figure, there is a clear difference between the waveform in which the residual charge signal is superimposed and the waveform in which the signal is not superimposed, and the simulated residual charge signal can be discriminated without taking the former difference. can do.
This situation becomes prominent when n is further increased. As an example, FIG. 6 shows a case where n = 3.0. In FIG. 6, the magnitude of the noisy signal is further reduced, and the simulated residual charge signal can be more clearly discriminated.

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 a linear pressure | voltage rise pattern and a non-linear pressure | voltage rise pattern (sin ⁿ waveform). It is a figure which shows the simulation residual charge signal superimposed in simulation. It is a figure which shows the simulation result at the time of raising an alternating voltage linearly. The AC voltage is a diagram showing a simulation result when was boosted by sin ^{n (n} = 2.3). The AC voltage is a diagram showing a simulation result when was boosted by sin ^{n (n} = 3.0).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC high voltage generator 2 Test transformer 2a Boosting pattern generator 2b Power amplifier 3 CV cable 4 Low pass filter 5 Amplifier SW changeover switch

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 boosted in a predetermined pattern is applied, and the same action as the DC voltage or the DC voltage is applied. A method for measuring a residual charge of a CV cable, in which a charge accumulated in the water tree of the CV cable is discharged and a residual charge is measured during voltage waveform application,
The AC voltage is continuously increased so that the rate of change gradually increases in a range from the zero voltage to a predetermined value, and the AC voltage is increased from the predetermined voltage before the end of boosting to a constant value. A residual charge measuring method, wherein the rate of change is continuously increased so that the rate of change gradually decreases in a region until it reaches.

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