JP5620324B2 - Insulation deterioration diagnosis method and insulation deterioration diagnosis device for power cable - Google Patents

Description

  The present invention relates to an insulation deterioration diagnosis method and an insulation deterioration diagnosis device for a power cable, and more particularly to a technique for diagnosing insulation deterioration of a power cable due to a water tree by a residual charge method.

Water tree degradation is one of the major insulation deterioration phenomena that determine the withstand voltage life characteristics of rubber / plastic insulation cables (hereinafter, power cables) such as crosslinked polyethylene insulated vinyl sheath cables (hereinafter, CV cables). Water tree degradation is a collection of minute water voids in the electric field concentration area such as foreign matter and voids in the insulator and protrusions of the semiconductive layer when the power cable is used over a long period of time in the presence of water. Is formed into a dendritic shape, and this is a phenomenon that progresses in the direction of the electric field.
As the water tree grows, it degrades the insulation performance of the power cable and eventually causes dielectric breakdown accidents during operation. For this reason, in the insulation deterioration diagnosis of power cables, it is an important issue to detect water tree deterioration nondestructively and with high reliability.
As an effective method for nondestructively detecting this water tree degradation, a residual charge method has been proposed in which a charge is left in the insulation of a power cable by DC charging or AC charging, and this residual charge is detected as a deterioration signal. (For example, Patent Documents 1 to 3).

FIG. 1 is a diagram schematically showing the principle of the residual charge method. In FIG. 1, the structure of the power cable is simplified, a part is shown in a fan shape, and the illustration of the internal semiconductive layer, the external semiconductive layer, and the vinyl sheath is omitted.
In the residual charge method, as shown in FIG. 1A, a DC voltage is first applied to an insulator of a power cable. When a water tree is generated in the insulator, a space charge is accumulated at the interface between the water tree generation part (hereinafter, water tree deteriorated part) and the healthy part, and at the same time, a charge appears in the conductor and the shielding layer.
Next, as shown in FIG. 1B, the conductor and the shielding layer are short-circuited and grounded. When the conductor and the shielding layer are short-circuited and grounded, the charges on the conductor and the shielding layer immediately disappear. On the other hand, the charges accumulated in the insulator (particularly the water tree deteriorated part) do not disappear immediately but remain for a long time. The greater the progress of water tree degradation, the greater the amount of charge remaining in the insulator.
And as shown in FIG.1 (c), an alternating voltage is applied to the insulator of a power cable, and the direct current component which appears in a detection circuit at this time is detected by a detector. When an AC voltage is applied to the insulator in which the charge remains, the movement and disappearance of the restrained charge is promoted, so that the residual charge due to water tree deterioration can be detected in a short time. Since the detected DC component (residual charge) changes according to the progress of water tree deterioration, the insulation deterioration diagnosis of the power cable can be performed based on this.

  When the insulation deterioration diagnosis of the power cable is performed by the residual charge method, as shown in FIG. 1, charges can be accumulated in the insulator by direct current application. However, in recent years, the number of cable lines connected to reduction devices such as gas-insulated switchgear (C-GIS) has increased, and the number of cases where it is difficult to perform DC charging has increased. Yes. For example, in C-GIS, there are reports of concern about the effects of DC charging, such as damage to an insulator caused by a metal foreign object charged by DC charging being attached to a spacer and serving as a starting point for discharge.

  In order to solve such a problem, in Patent Documents 2 and 3, when applying the residual charge method, charges are accumulated in the insulator of the power cable by AC charging without using DC charging. Patent Document 2 discloses a technique in which AC charging is interrupted in the vicinity of the zero cross, and electric charges are accumulated in the water tree degradation portion by a half-wave voltage (hereinafter, final half-wave voltage) immediately before the interruption. Patent Document 3 discloses a technique for accumulating electric charges in a water tree degradation portion by applying half-wave rectification of an AC voltage.

Japanese Patent No. 3184712 (Japanese Patent Laid-Open No. 8-62280) Japanese Patent No. 4383393 (Japanese Patent Laid-Open No. 2007-40861) JP 2007-271542 A

However, in the technique described in Patent Document 2, overshoot may occur when AC power is interrupted near the zero cross (see FIG. 2 of Patent Document 2). When this overshoot occurs, the residual charge accumulated at the final half-wave voltage is released, so that the detection sensitivity may decrease depending on the magnitude of the overshoot. In addition, since the magnitude of the overshoot varies depending on the capacitance of the power cable to be measured, in order to suppress overshoot, it is necessary to apply power with a voltage waveform corresponding to the measurement target. Waveform control technology is required.
Further, the technique described in Patent Document 3 requires a rectifier for half-wave rectifying the AC voltage. In addition, the power cable is a capacitive load, and if it is applied using the voltage waveform that has been half-wave rectified by the rectifier as it is, the power cable is smoothed, so a low load device must be provided and adjusted. This complicates the configuration of the insulation deterioration diagnostic apparatus.

  The present invention has been made in order to solve the above-described problems, and is capable of detecting a residual charge in an insulator of a power cable with high sensitivity and capable of realizing a highly reproducible insulation deterioration diagnosis and insulation method and insulation for the power cable. An object is to provide a deterioration diagnosis apparatus.

The method for diagnosing deterioration of a power cable according to the present invention applies an AC voltage to an insulator of the power cable, and terminates the AC voltage application at the zero cross point, so that the last half wave just before the zero cross point is applied. A first step of storing electric charge in the insulator with a voltage;
A residual charge accumulated in the insulator is discharged by applying an AC voltage to the insulator, and a DC component appearing in the detection circuit at this time is detected as a deterioration signal indicating deterioration of the insulator. An insulation deterioration diagnosis method having two steps,
When applying the final half-wave voltage in the first step, the frequency of the final half-wave voltage is reduced from a predetermined frequency to 0 Hz.

The insulation deterioration diagnosis device according to the present invention applies an AC voltage to an insulator of a power cable, and terminates the AC power application at the zero cross point, so that the final half-wave voltage immediately before the zero cross point is used. A first step of accumulating charge in the insulator;
A residual charge accumulated in the insulator is discharged by applying an AC voltage to the insulator, and a DC component appearing in the detection circuit at this time is detected as a deterioration signal indicating deterioration of the insulator. An insulation deterioration diagnosis apparatus used for an insulation deterioration diagnosis method having two steps,
A signal generator for generating an arbitrary voltage waveform when applying an AC voltage in the first step and the second step;
A power amplifier that amplifies and outputs the AC voltage input from the signal generator;
A transformer for amplifying the AC voltage input from the power amplifier to charge a power cable;
A detector for measuring a residual charge of a power cable released by applying an AC voltage in the second step,
The signal generator generates a voltage waveform in which the frequency of the final half-wave voltage drops from a predetermined frequency to 0 Hz when the final half-wave voltage is applied in the first step.

  Here, “terminate AC power application” means substantially by setting the frequency of the AC voltage to 0 Hz, or setting the AC voltage value (setting value for defining the AC voltage, for example, the peak voltage value) to 0V. Is to end AC charging. Further, the “final half-wave voltage” is a voltage from the zero crossing point at which the AC charging ends to the previous zero crossing point, and the polarity of the voltage may be positive or negative.

  According to the present invention, by reducing the frequency of the final half-wave voltage to 0 Hz, an overshoot that is likely to occur immediately after the AC power application is cut off near the zero crossing is effectively suppressed, and the final half-wave voltage causes the insulation to enter the insulator. Charge is accumulated. Accordingly, the discharge of electric charges due to overshoot is suppressed, and the residual charge detection sensitivity is improved, so that it is possible to diagnose insulation deterioration with high reproducibility. Further, since no special device such as a half-wave rectifier or a low load device is required to realize the present invention, there is no possibility that the device configuration of the insulation deterioration diagnosis device is complicated.

It is a figure which shows the principle of a residual charge method typically. It is a figure which shows schematic structure of the insulation deterioration diagnostic apparatus used for the insulation deterioration diagnosis of an electric power cable. It is a figure which shows the voltage waveform of the alternating current charging performed for electric charge accumulation | storage in 1st Embodiment. It is a figure shown about the measurement of the residual charge by the electric charge direct reading short time raising / lowering method. It is a figure which shows the voltage waveform of the alternating current charging performed for electric charge accumulation | storage in 2nd Embodiment. It is a figure which shows the voltage waveform of the alternating current charging performed for electric charge accumulation | storage in the modification of 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 2 is a diagram illustrating an example of an insulation deterioration diagnosis apparatus used for insulation deterioration diagnosis of a power cable. The insulation deterioration diagnosis apparatus 1 shown in FIG. 2 diagnoses deterioration of an insulator by a residual charge method using a power cable 20 such as a CV cable as a measurement target. In general, the power cable 20 is centered on a conductor made of copper, aluminum or the like, and an inner semiconductive layer, an insulator (crosslinked polyethylene in the case of a CV cable), an outer semiconductive layer, a metal shielding layer, and a vinyl sheath are arranged in a concentric order. It has a formed structure.

  As shown in FIG. 2, the insulation deterioration diagnosis apparatus 1 includes a signal generator 11, a power amplifier 12, a transformer 13, and a detector 14. The conductor of the power cable 20 to be measured is connected to the secondary side of the transformer 13 via the switch 15, and the metal shielding layer is grounded via the detector 14.

  The signal generator 11 is a so-called function generator capable of generating an arbitrary voltage waveform. The AC generator for accumulating electric charge in the insulator of the power cable 20 and the residual electric charge are released by discharging the accumulated electric charge. A predetermined AC voltage is output at the time of AC power application for detecting. The signal generator 11 can continuously change the AC voltage value or frequency in a predetermined period. In the signal generator 11, for example, by setting an AC voltage value, a frequency, and a time, AC power can be applied to the power cable 20 to be measured with a desired voltage waveform. The AC voltage output from the signal generator 11 is input to the power amplifier 12.

  The power amplifier 12 amplifies and outputs the input AC voltage. The AC voltage output from the power amplifier 12 is input to the primary side of the transformer 13. For example, the power amplifier 12 amplifies an alternating voltage of about several volts up to about 200V.

  The transformer 13 boosts the AC voltage input to the primary side and outputs it from the secondary side. The insulator of the power cable 20 is charged by the AC voltage output from the secondary side of the transformer 13. For example, the transformer 13 boosts an AC voltage of about 200 V to about 20 kV.

  One end of the detector 14 is connected to the metal shielding layer of the power cable 20 and the other end is grounded. The detector 14 detects a direct current component when the electric charge accumulated in the insulator of the power cable 20 is released. An insulation deterioration diagnosis of the power cable 20 is performed based on the DC component.

  In addition, if the insulation degradation diagnostic apparatus 1 is a structure which can be applied with an arbitrary voltage waveform with respect to the insulator of the power cable 20, another structure will not be restrict | limited in particular. For example, one end of the detector 14 may be connected to the signal generator 11 and the other end may be grounded (see FIG. 1 of Patent Document 3).

When performing insulation deterioration diagnosis of the power cable 20 using the insulation deterioration diagnosis device 1 shown in FIG. 2, first, an AC voltage is applied to the insulator of the power cable 20, and this AC charging is terminated at the zero cross point. As a result, charges are accumulated in the insulator (first step). When the AC power application is terminated at the zero crossing point, charges are accumulated in the insulator at the final half-wave voltage immediately before the termination.
Then, by applying an AC voltage to the insulator of the power cable 20, the residual charge accumulated in the insulator is released, and the DC component appearing in the detection circuit at this time is used as a deterioration signal indicating the deterioration of the insulator. Detect (second step). Based on this deterioration signal, the degree of deterioration of the insulator (the progress of water tree deterioration) is diagnosed.

In the first embodiment, in the first step, an AC voltage having a voltage waveform shown in FIG. 3 is applied to the insulator of the power cable 20. That is, until the timing t ₀ , the AC voltage value is constant (V = V ₀ ) and the frequency is constant (f = f ₀ , for example, commercial frequency 50 Hz) is applied to the insulator of the power cable 20. To charge. For example, when the power cable 20 to be measured is a 6.6 kV class CV cable, the peak voltage value of the AC voltage output from the secondary side of the transformer 13 is 5.4 kV (effective value: 3.8 kV). Thus, the AC voltage value of the signal generator 11 is set.

Then, during the period from timing t _{0 to} t ₂ , that is, during AC power application at the final half-wave voltage, the frequency f of the AC voltage is gradually decreased from the frequency f ₀ until timing t ₀ to ₀ Hz. Thereby, the period of the last half-wave voltage becomes longer than the period of the alternating voltage before the last half-wave voltage. Further, by gradually decreasing the frequency f of the AC voltage from the frequency f ₀ to 0 Hz between the timings t ₀ and t ₂ , a waveform of the final half-wave voltage that is continuously and smoothly attenuated is formed. Is charged to the insulator. In FIG. 3, the frequency f becomes 0 Hz at the timing t ₂ , and the AC charging is finished.
Note that the initial value of the frequency of the final half-wave voltage may be a value other than f ₀ . However, in order to suppress the concern about the occurrence of noise due to the frequency change, it is desirable that the initial value of the frequency of the final half-wave voltage is matched with the frequency f ₀ until immediately before.

The voltage waveform shown in FIG. 3 is easily generated by setting the time, frequency, and AC voltage value as shown in Table 1 in the signal generator 11, for example. At this time, (decay time of the AC voltage) final half-wave voltage voltage application time by setting t ₀ ~t ₂ properly, it is possible to effectively suppress the occurrence of overshoot. In an experiment conducted by the present inventors, the frequency f of the AC voltage is reduced to 0 Hz so that the charging time t _{0 to} t ₂ of the final half-wave voltage is about one cycle of the AC voltage before the final half-wave voltage. By reducing it, the occurrence of overshoot could be prevented.

In order to appropriately set the last half-wave voltage application time t _{0 to} t ₂ , the waveform state of the AC voltage applied to the insulator of the power cable 20 (particularly the waveform state of the last half-wave voltage). ) Is previously confirmed with an oscilloscope, and a setting for obtaining a desired voltage waveform (voltage waveform in which overshoot does not occur) may be acquired.

As described above, in the first embodiment, in the first step, the frequency f of the final half wave is gradually decreased from a predetermined frequency (for example, the frequency f ₀ before the final half wave voltage) to 0 Hz (variable). Frequency control).
This effectively suppresses overshoot that is likely to occur immediately after AC charging is terminated at the zero cross point, and charges are accumulated in the insulator by the final half-wave voltage. Accordingly, the discharge of electric charges due to overshoot is suppressed, and the residual charge detection sensitivity is improved, so that it is possible to diagnose insulation deterioration with high reproducibility. Moreover, since it is not necessary to provide the insulation degradation diagnostic apparatus 1 with a special device such as a half-wave rectifier or a low load device, there is no possibility that the device configuration becomes complicated.

If the control is such that the waveform of the final half-wave voltage is a waveform that continuously attenuates until the end of power application (timing t ₂ in FIG. 3), a control pattern for gradually decreasing the frequency f. There are no particular restrictions on the rate of decrease in frequency f. Specifically, if the control pattern is set so that the waveform of the final half-wave voltage can be differentiated at a point where the frequency f is 0 Hz and has a smooth curve shape with a differential coefficient of “0”. Good.
If the waveform of the final half-wave voltage is a non-differentiable waveform (discontinuous waveform) that blocks AC charging near the zero cross, overshoot is likely to occur, but the smooth curve as described above If it is a shape, generation | occurrence | production of an overshoot can be prevented effectively.

  By the way, in the measurement of the residual charge in the second step, the DC component (increase in residual charge) that appears in the detection circuit when the AC voltage is applied is detected by the detector 14. In addition to residual charges (true residual charges) caused by water tree degradation, residual charge components (error components) not caused by water tree degradation are included. Therefore, it is desirable to apply the method (charge direct reading short time raising / lowering method) disclosed in Japanese Patent Application Laid-Open No. 11-148959 in measuring the residual charge in the second step. The same applies to a second embodiment described later and modifications thereof.

That is, in the second step, as shown in FIG. 4, the instantaneous value is obtained in a time shorter than the response time of the alternating voltage that rises and falls in a short time, specifically, the residual charge (error component) not caused by water tree degradation. An AC voltage that rises from 0V to a predetermined peak value and immediately drops to 0V without holding the voltage is repeatedly applied to the insulator of the power cable 20 three times, and is detected during each AC power application. Measure the increase in residual charge. The increase in residual charge due to the first AC charging is ΔQ ₁ , the increase in residual charge due to the second AC charging is ΔQ ₂ , and the increase in residual charge due to the third AC charging is ΔQ ₃ . when, Q ₀ = ΔQ ₁ -ΔQ ₂ used as × determination amount of insulation degradation of Q ₀ which is calculated by (ΔQ ₂ / ΔQ ₃₎ (degradation signals).

Residual charges resulting from water tree degradation have a characteristic of quick response to AC voltage (complete in a few seconds), and are therefore included only in the increase ΔQ ₁ in the residual charge during the first AC application. . On the other hand, the increments ΔQ ₂ and ΔQ ₃ of the residual charge during the second and third AC charging can be regarded as error components.
Therefore, the true residual charge is selectively extracted by correcting the increase ΔQ ₁ of the _first residual charge with the increase ΔQ ₂ and ΔQ ₃ (only the error component) of the _second and _third residual charges. Is done. In other words, the above-described method can detect a true deterioration signal that does not include an error component, thereby realizing a highly reliable insulation deterioration diagnosis.

[Second Embodiment]
In the first embodiment, the AC voltage during charge accumulation is attenuated by controlling only the frequency of the final half-wave voltage. However, in the second embodiment, the frequency of the final half-wave voltage and the AC voltage are attenuated. By controlling both values, the AC voltage during charge accumulation is attenuated.

Specifically, in the second embodiment, an AC voltage having a voltage waveform shown in FIG. 5 is applied to the insulator of the power cable 20 in the first step. That is, until the timing t ₀ , the AC voltage value is constant (V = V ₀ ) and the frequency is constant (f = f ₀ , for example, commercial frequency 50 Hz) is applied to the insulator of the power cable 20. To charge. For example, when the power cable 20 to be measured is a 6.6 kV class CV cable, the peak voltage value of the AC voltage output from the secondary side of the transformer 13 is 5.4 kV (effective value: 3.8 kV). Thus, the AC voltage value of the signal generator 11 is set. Such AC charging is the same as in the first embodiment.

Then, during the period of timing t _{0 to} t ₂ , that is, during AC power application at the final half-wave voltage, the frequency f of the AC voltage is gradually decreased from the frequency f ₀ until the timing t ₀ to ₀ Hz, and the AC voltage value V gradually decreases from the AC voltage V ₀ which to timing t ₀ to 0V to. As a result, it is possible to control the waveform of the final half-wave voltage more finely than the first embodiment, such as the inclination of the waveform, and an AC voltage that is more continuously and smoothly attenuated is imposed on the insulator of the power cable 20. Electricity. In FIG. 5, the frequency f becomes 0 Hz and the AC voltage value V becomes 0 V at the timing t ₂ , and the AC voltage application is finished.

Note that the initial value of the frequency of the final half-wave voltage may be a value other than f ₀ . However, in order to suppress the concern about the occurrence of noise due to the frequency change, it is desirable that the initial value of the frequency of the final half-wave voltage is made to coincide with the frequency f ₀ until immediately before. Also, the initial value of the AC voltage value of the final half-wave voltage may be a value other than V ₀ .

The voltage waveform shown in FIG. 5 is easily generated by setting the time, frequency, and AC voltage value as shown in Table 2 in the signal generator 11, for example. At this time, (decay time of the AC voltage) final half-wave voltage voltage application time by setting t ₀ ~t ₂ properly, it is possible to effectively suppress the occurrence of overshoot. In an experiment conducted by the present inventors, the frequency f of the AC voltage is reduced to 0 Hz so that the charging time t _{0 to} t ₂ of the final half-wave voltage is about one cycle of the AC voltage before the final half-wave. In addition, the occurrence of overshoot could be prevented by reducing the AC voltage value V to 0V.

[Modification of Second Embodiment]
In the second embodiment, the initial value of the AC voltage V of the final half-wave voltage and an AC voltage value V ₀ which is to timing t _0, for gradually reducing from V ₀ to 0V, the final half of the time t ₁ The peak value (absolute value) V _{p of the} wave voltage is smaller than the initial AC voltage value V ₀ (see FIG. 5). That is, there is a possibility that the amount of accumulated charges may be reduced as compared with the first embodiment.
Therefore, when increasing the amount of charge to be accumulated and improving the detection sensitivity of the residual charge, the AC voltage value and frequency of the final half-wave voltage are controlled as in this modification.

In this modification, an AC voltage having a voltage waveform shown in FIG. 6 is applied to the insulator of the power cable 20. That is, as the peak value V _p of the last half-wave voltage at the timing t ₁ coincides with V _0, the initial value of the AC voltage V of the final half-wave voltage, than the AC voltage V ₀ which to timing t ₀ Set to high value V ₁ . Then, the AC voltage value V of the final half-wave voltage is gradually decreased from V ₁ to 0V.

The voltage waveform shown in FIG. 6 is easily generated by setting the time, frequency, and AC voltage value as shown in Table 3 in the signal generator 11, for example. At this time, (decay time of the AC voltage) final half-wave voltage voltage application time by setting t ₀ ~t ₂ properly, it is possible to effectively suppress the occurrence of overshoot. In an experiment conducted by the present inventors, the frequency f of the AC voltage is reduced to 0 Hz so that the charging time t _{0 to} t ₂ of the final half-wave voltage is about one cycle of the AC voltage before the final half-wave. In addition, the occurrence of overshoot could be prevented by reducing the AC voltage value V to 0V.

Thus, in the modification, the initial value of the AC voltage value of the final half-wave voltage is set higher than the AC voltage value V ₀ before the final half-wave voltage. As a result, even if the AC voltage value of the final half-wave voltage is gradually reduced, the amount of charge accumulated in the insulator of the power cable 20 is ensured, so that it is possible to prevent the residual charge detection sensitivity from being lowered.
In the modification, the initial value of the AC voltage value of the final half-wave voltage is set so that the peak value V _p of the final half-wave voltage matches V ₀ , but the initial value of the AC voltage value is It can be set as appropriate as long as sufficient detection sensitivity of the residual charge is obtained.

As described above, in the second embodiment and its modifications, in the first step, the frequency f of the final half-wave voltage is gradually reduced from a predetermined frequency (for example, the frequency f ₀ before the final half-wave voltage) to 0 Hz. At the same time, the AC voltage value V of the final half-wave voltage is gradually decreased from a predetermined voltage value to 0 V (variable voltage variable frequency control). This makes it possible to perform insulation deterioration diagnosis with high reproducibility, as in the first embodiment.

If the control is such that the waveform of the final half-wave voltage is a waveform that smoothly and smoothly attenuates until the end of power application (timing t ₂ in FIGS. 5 and 6), the frequency f and the AC voltage value V are gradually increased. There are no particular restrictions on the control pattern (such as the rate of decrease in the frequency f and the rate of decrease in the AC voltage value V). Specifically, control is performed so that the waveform of the final half-wave voltage has a smooth curve shape that is differentiable at a point where the frequency f is 0 Hz and the AC voltage value V is 0 V, and the differential coefficient is “0”. It suffices if a pattern is set.
If the waveform of the final half-wave voltage is a non-differentiable waveform (discontinuous waveform) that blocks AC charging near the zero cross, overshoot is likely to occur, but the smooth curve as described above If it is a shape, generation | occurrence | production of an overshoot can be prevented effectively.

  In the insulation deterioration diagnosis method according to the first embodiment, the second embodiment, and the modification thereof, the detected residual charge is approximately 70 as compared with the case where the charge is accumulated in the insulator by DC charging. The value was around%. In other words, these insulation deterioration diagnosis methods are inferior in detection sensitivity compared with the case where charges are accumulated by direct current charging, but sufficient values are obtained as detection sensitivity, so that the charge accumulation due to direct current charging cannot be used. It is extremely useful on the track.

As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.
For example, in the above-described embodiment, charges are accumulated in the insulator by AC application of the negative final half-wave voltage, but charges are accumulated in the insulator by AC application of the positive final half-wave voltage. You may do it. Further, for example, the device configuration of the insulation deterioration diagnosis device 1 can be changed as appropriate within a range in which the present invention can be realized.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Insulation deterioration diagnostic apparatus 11 Signal generator 12 Power amplifier 13 Transformer 14 Detector 15 Switch 20 Power cable

Claims (4)

A first step of applying an AC voltage to the insulator of the power cable and ending the AC application at the zero cross point to accumulate electric charge in the insulator at the final half-wave voltage immediately before the zero cross point. When,
A residual charge accumulated in the insulator is discharged by applying an AC voltage to the insulator, and a DC component appearing in the detection circuit at this time is detected as a deterioration signal indicating deterioration of the insulator. An insulation deterioration diagnosis method having two steps,
An insulation deterioration diagnosis method for a power cable, wherein the frequency of the final half-wave voltage is reduced from a predetermined frequency to 0 Hz when the final half-wave voltage is applied in the first step.   When applying the final half-wave voltage, the frequency of the final half-wave voltage is decreased from a predetermined frequency to 0 Hz, and the alternating voltage value of the final half-wave voltage is decreased from a predetermined voltage value to 0 V. The insulation deterioration diagnosis method for a power cable according to claim 1.   3. The insulation deterioration diagnosis method for a power cable according to claim 2, wherein the predetermined voltage value is set higher than an AC voltage value before the final half-wave voltage. A first step of applying an AC voltage to the insulator of the power cable and ending the AC application at the zero cross point to accumulate electric charge in the insulator at the final half-wave voltage immediately before the zero cross point. When,
A residual charge accumulated in the insulator is discharged by applying an AC voltage to the insulator, and a DC component appearing in the detection circuit at this time is detected as a deterioration signal indicating deterioration of the insulator. An insulation deterioration diagnosis apparatus used for an insulation deterioration diagnosis method having two steps,
A signal generator for generating an arbitrary voltage waveform when applying an AC voltage in the first step and the second step;
A power amplifier that amplifies and outputs the AC voltage input from the signal generator;
A transformer for amplifying the AC voltage input from the power amplifier to charge a power cable;
A detector for measuring a residual charge of a power cable released by applying an AC voltage in the second step,
Insulation deterioration diagnosis, wherein the signal generator generates a voltage waveform in which the frequency of the final half-wave voltage decreases from a predetermined frequency to 0 Hz when the final half-wave voltage is applied in the first step. apparatus.

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