JP2009168638A - Water tree degradation diagnostic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water tree degradation diagnostic method that measures loss current of a cable under commercial operation and improves the diagnostic accuracy by reducing the influence of external noise. <P>SOLUTION: A detection resistor 41 is connected to a sample 20 such as a CV cable in series, electricity is applied from a commercial power supply line 30, voltage reduction is caused at both ends of the detection resistor 41 by the current flowing in the detection resistor 41 by electricity application, and this voltage is amplified by an amplifier 43. Applied voltage phase information is obtained from the commercial power supply line 30 by a transformer for an instrument 50, this is differentiated by a differentiator 60 to create a signal for removing displacement current component, and the voltage obtained by level-adjusting the signal for removing displacement current component with a cancel resistor 72 is input into the amplifier 73 with a detected signal from the amplifier 43. The amplifier 73 superimposes the signal for removing displacement current component on the detected signal, removes the displacement current component in the detected signal, and outputs the loss current. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water tree deterioration diagnosis method for electrically diagnosing water tree deterioration of a sample such as a CV cable.

  A main deterioration form of a crosslinked polyethylene insulated power cable (hereinafter referred to as a CV cable), which is a typical power cable, is water tree deterioration. This water tree deterioration is an alteration in the insulator caused by the action of moisture and electric field present in the CV cable insulator, and this alteration increases with the passage of time, thereby reducing the insulation performance of the CV cable. May lead to dielectric breakdown. Degradation diagnostic techniques for diagnosing this water tree degradation are being studied.

  For example, a current transformer is connected between a transformer that generates a high voltage and a CV cable that is a sample (measurement target), and a standard capacitor is connected to the transformer side of the current transformer. Apply a high voltage AC voltage to the cable and input the current flowing through the standard capacitor and the current flowing through the cable insulation detected by the current transformer connected to the CV cable to the loss current measurement bridge. Degradation of diagnosing the degradation of the CV cable based on the third harmonic component included in the loss current by extracting only the loss current component by removing the displacement current component (capacitive current component) from the detected current A diagnostic method is known (see, for example, Patent Document 1).

  However, in the conventional loss current measuring method described in Patent Document 1, since the current transformer provided on the high voltage side applies a reactor, the capacitance of a sample such as a CV cable or other stray capacitance As a result of this combination, the detection circuit including the CV cable and the current transformer causes a resonance phenomenon, and the frequency characteristic of the detection signal is changed to cause waveform distortion. For this reason, an error occurs in the waveform analysis of the deteriorated signal. Furthermore, since the capacitance changes for each sample of the CV cable, that is, the resonance frequency changes for each sample, there is also a problem that the measurement conditions change for each sample.

As a conventional degradation diagnosis method that does not depend on the capacitance of the sample such as the CV cable or other stray capacitance, for example, a 2-channel signal transmitter is used, and the sample core wire is connected to the output end of the 2-channel signal transmitter. At the same time, a detection resistor is connected between the outer conductive part such as the shielding layer and the ground, and a current is passed through the sample. Further, a displacement current and an opposite phase signal created by the 2-channel signal transmitter are added to the sample current (synthesis). A loss current measuring apparatus that detects a loss current by processing and canceling a displacement current component from a current flowing through a sample is known (see, for example, Non-Patent Document 1).
JP 2004-354093 A 2005 IEEJ National Convention 2-S10 (17-20 pages)

  However, according to the conventional loss current measuring device described in Non-Patent Document 1, it is necessary to stop the commercial operation of the cable to be measured and connect the detector to the sample when measuring the loss current. Measurement during operation (live line) could not be performed. For this reason, when it is determined that the cable is deteriorated, it is necessary to carry out measurement again with a withstand voltage method or the like with high diagnostic accuracy, and the power outage work is required twice for the cable. In addition, it has been necessary to spend a great deal of effort to take measures against external noise that enters during the measurement of the loss current.

  Accordingly, an object of the present invention is to provide a water tree deterioration diagnosis method capable of easily measuring the loss current of a cable during commercial operation and reducing the influence of external noise to improve the diagnosis accuracy. It is in.

  In order to achieve the above object, the present invention uses a detection resistor connected in series to a measurement object and applies a voltage from a commercial power supply, and a voltage generated at both ends of the detection resistor by a current flowing through the detection resistor is used as a detection signal. , Differential voltage phase information obtained from the commercial power source is differentiated to generate a displacement current component removal signal, and a signal obtained by level-adjusting the displacement current component removal signal is superimposed on the detection signal. An object of the present invention is to provide a water tree deterioration diagnosis method characterized by removing a displacement current component and measuring a loss current and a harmonic current flowing in the measurement object.

  In order to achieve the above object, the present invention detects a voltage generated by connecting a detection resistor in series with a measurement object and applying power from a commercial power supply, and causing a current flowing through the detection resistor to be generated at both ends of the detection resistor. Displacement current component in the detection signal by superimposing a signal obtained by adjusting the level of the displacement current component removal signal generated based on the applied voltage phase information acquired from the commercial power supply (for example, differential processing) on the detection signal And measuring the loss current and the harmonic current flowing in the measurement object, and the measurement when the ratio of the loss current or the harmonic current and the capacitance of the measurement object exceeds a set value. An object of the present invention is to provide a water tree deterioration diagnosis method characterized by determining that an object is defective.

  In order to achieve the above object, the present invention detects a voltage generated by connecting a detection resistor in series with a measurement object and applying power from a commercial power supply, and causing a current flowing through the detection resistor to be generated at both ends of the detection resistor. Displacement current component in the detection signal by superimposing a signal obtained by adjusting the level of the displacement current component removal signal generated based on the applied voltage phase information acquired from the commercial power supply (for example, differential processing) on the detection signal The loss current and the harmonic current flowing through the object to be measured are measured, and the loss current or the harmonic current and the capacitance of the object to be measured are periodically measured to monitor a change with time. Another object of the present invention is to provide a water tree deterioration diagnosis method that determines the state of water tree deterioration based on the increasing tendency of the loss current or the harmonic current and the increasing tendency of the capacitance.

  According to the water tree deterioration diagnosis method of the present invention, the loss current of a cable during commercial operation can be easily measured, and the influence of external noise can be reduced to improve diagnosis accuracy.

  Before describing embodiments of the present invention, the effectiveness of cable line trend monitoring will be described. FIG. 1 shows the configuration of a loss current measurement system used for verifying the effectiveness of trend monitoring. The loss current measuring system 100 includes a two-channel signal transmitter 1 that generates two kinds of voltages v1 and v2, a power transformer 2 having a primary winding 2a connected to the two-channel signal transmitter 1, and a power transformer. The second measurement electrode 3 connected to the high potential end of the second secondary winding 2b and the second measurement electrode 3 disposed opposite to the first measurement electrode 3 with the sample 20 as a measurement object such as a CV cable interposed therebetween. The measurement electrode 4, the detection resistor (rd) 5 connected between the second measurement electrode 4 and the ground, the amplifier 6 having a pair of input terminals connected to both ends of the detection resistor 5, and the output terminal of the amplifier 6 A resistor 7 connected between the amplifier 8 and the ground, an amplifier 8 for amplifying the voltage v2 output from the two-channel signal transmitter 1, and a cancel resistor connected between the output terminal of the amplifier 8 and the output terminal of the amplifier 6. (Variable resistor) 9 and the wave at the output end of resistor 7 The and oscilloscope 10 to observe, the data recorder 11 to the terminal voltage of the resistor 7 recorded in the electronic data, and the terminal voltage of the resistor 7 is constituted by a FFT processor 12 for fast Fourier transform.

  The two-channel signal transmitter 1 is a signal source, and outputs a two-channel signal of a voltage v2 (−cos θ) for displacement current removal and a voltage v1 (sin θ) for voltage application to the voltage transformer 2. It has a configuration that outputs while synchronizing.

  The amplifier 6 is a differential amplifier that uses the voltage generated across the detection resistor 5 as an input signal, differentially amplifies the input signal to a predetermined level, and outputs it. The amplifier 6 is preferably installed as close to the sample 20 as possible together with the detection resistor 5 in order to prevent intrusion of external noise.

(Verification of the effectiveness of trend monitoring)
When measuring the loss current of the sample 20 in the loss current measurement system 100 of FIG. 1, the sample 20 is placed on the upper surface of the second measurement electrode 4 and the first measurement electrode 3 connected to the secondary winding 2b. Is placed on the upper surface of the sample 20.

  Next, the sin θ voltage v1 is applied to the primary winding 2a of the voltage transformer 2 from the 2-channel signal transmitter 1 for voltage application, and a high voltage corresponding to the winding ratio is generated in the secondary winding 2b. At the same time, a voltage v2 (−cos θ) for displacement current removal is applied to the amplifier 8.

  The high-voltage AC voltage generated in the secondary winding 2b of the electric transformer 2 is applied between the first measurement electrode 3 and the ground. With this applied voltage, a current i corresponding to the deterioration state of the sample 20 flows through the first measurement electrode 3, the sample 20, the second measurement electrode 4, and the detection resistor 5, and a voltage drop occurs in the detection resistor 5. Arise. The current i flowing through the detection resistor 5 is a combination of the displacement current flowing through the capacitance of the sample 20 and the loss current flowing through the resistance of the sample 20. Here, the loss current is a fundamental frequency current waveform in phase with the applied voltage. Therefore, in order to measure the loss current, the displacement current may be subtracted from the current i flowing through the detection resistor 5.

  Therefore, the voltage v2 for displacement current component removal is applied to the resistor 7 via the cancel resistor 9 by the two-channel signal transmitter 1, and the displacement current component of the sample 20 output from the amplifier 6 is used for displacement current component removal. Is canceled by the voltage adjusted by the cancel resistor 9.

  When the applied voltage by the applying transformer 2 is regarded as a sine wave, the displacement current flowing in the capacitance of the sample 20 is expressed by a cosine wave (simply a 90 ° advance phase of the voltage waveform = cos θ). For this reason, the level of the cancel signal Sc corresponding to the cosine wave may be changed and subtracted from the current of the detection resistor 5. At this time, the level of the cancel signal Sc applied to the resistor 7 is adjusted so that the phase of the “detection resistance current-displacement current” waveform matches the applied voltage waveform. The differential waveform obtained by this adjustment becomes a loss current waveform.

  The level of the displacement current flowing through the capacitance of the sample 20 matches the level of the cancel signal Sc. For this reason, the capacitance changes in inverse proportion to the value of the cancel resistor 9. That is, as the cancel resistance 9 increases, the cancel signal Sc decreases. In other words, the displacement current decreases as the capacitance decreases. Therefore, if the value of the cancel resistor 9 is grasped, the capacitance of the sample 20 can also be grasped.

  The waveform of the loss current generated in the resistor 7 is observed by the measurer with the oscilloscope 10, and the data is stored with the data recorder 11. Further, analysis processing necessary for trend monitoring (management) is performed by the FFT processing device 12.

(Verification of electricity test)
FIG. 2 shows the change over time in the loss current in the accelerated deterioration test with the applied frequency set at 500 Hz. FIG. 3 shows a change with time of the capacitance obtained from the value of the cancel resistance. As is apparent from FIG. 2, the loss current has increased rapidly from around the 24th day, and it can be seen that the deterioration is progressing. On the other hand, as is clear from FIG. 3, it can be seen that although the capacitance has changed abruptly until the third day of power application, the subsequent increase amount has decreased.

  FIG. 4 shows the result of recording the change with time of the loss current every 4 hours from the 35th day to the 49th day. As is clear from FIG. 4, the deterioration signal level changes daily. Also in FIG. 2, it can be seen that there is a significant change from the previous and subsequent data depending on the measurement date. From the above, it can be seen that more accurate deterioration diagnosis (deterioration determination) is possible when trend management is performed than when deterioration is determined from a single measurement result.

(Evaluation of water tree degradation)
FIG. 5 shows the state of water tree generation inside the sample corresponding to the capacitance and loss current of the sample. For example, in the case of an undegraded or lightly degraded sample, both the loss current and the capacitance are small values. On the other hand, when there is a long water tree or when there are many water trees, the loss current increases. However, it is not possible to judge whether the water tree is large or large only by the level of the loss current. Therefore, capacitance information is added.

The capacitance (C) can be obtained by the following formula (1).
The displacement current (= displacement current removal signal) is represented by [displacement current = 2π × voltage applied frequency × capacitance × voltage applied voltage]. Therefore, the capacitance (C) is
C = displacement current / (2π × applied frequency × applied voltage) (1)

  The capacitance theoretically depends on the dielectric constant and the insulation thickness when the electrode area of the sample 20 is the same. For example, if a lot of short water trees are generated, it is considered that the apparent insulation thickness is reduced, and the capacitance increases. On the other hand, when a small number of long water trees are generated, since the electrode area of the thin portion of the insulator is small, the amount of increase in capacitance is smaller than the former. Based on this idea, if the loss current is the same, it can be determined that the water tree is more dangerous as the increase in capacitance is smaller. If the capacitance is the same, it can be determined that the water tree is more dangerous as the loss current is larger.

  For example, in FIG. 5, A is a characteristic region where the sample 20 is not (lightly) deteriorated, B is a characteristic region when a long water tree is locally generated, and C is a characteristic when a small number of long water trees are generated. Area, D is a characteristic area when many short water trees are generated, E is a characteristic area when many long water trees are generated, F is a long water tree and many long water trees are localized This is the characteristic range when it occurs.

  Speaking of the relationship between the capacitance and the loss current, the A characteristic range (determination range) is a case where both the capacitance and the loss current are small, and the B characteristic range is a large loss current and a small capacitance. This is a case where the C characteristic region has a smaller loss current and a larger capacitance than the B characteristic region, and the D characteristic region has a smaller loss current and a larger capacitance than the C characteristic region. The characteristic region of E is a case where the loss current is between the characteristic region of B and the characteristic region of C and the capacitance is larger than the characteristic region of D, and the characteristic region of F has a capacitance of This is a case where the characteristic range of D is larger and the loss current is larger than the characteristic range of B.

  From the above, the case where the measurement result is in the characteristic range of E or F can be determined as “serious defect”. In such a determination, a set value (ratio of the loss current and the capacitance of the object to be measured) is set in advance for each value of loss current and capacitance, and each set value is lost. When the ratio of the measured values of current and capacitance is exceeded, it is carried out according to the classification of FIG.

  Table 1 shows the results of evaluating water tree degradation based on FIG. By recording and accumulating the relationship between the breakdown voltage or the water tree length and comparing this result with Table 1 and FIG. 5, it is possible to estimate the remaining breakdown voltage and the remaining insulation thickness.

  In FIG. 5, the loss current and the capacitance are absolute values, but the data is arranged as the amount of change (rate) from the initial value to estimate the residual breakdown voltage and the residual insulation thickness, or As shown in FIG. 6, it is also possible to determine water tree deterioration from the transition of changes in loss current and capacitance.

  FIG. 6 shows the relationship between the loss current and the capacitance in the cable. FIG. 6 shows loss current-capacitance characteristics in three samples, Samples 1, 2, and 3. It can be seen that the loss current is proportional to the capacitance of each sample. For example, the loss current of the sample 3 suddenly increases from a level exceeding the capacitance of 2.0. From this characteristic change, water tree deterioration can be determined.

  The configuration shown in FIG. 1 uses the two-channel signal transmitter 1 as a signal source, and thus cannot measure the loss current of the sample 20 in a live line state during commercial operation. Therefore, an embodiment capable of measurement in commercial operation will be described below.

[Embodiment]
(Configuration of loss current measuring device)
FIG. 7 shows the configuration of the loss current measuring apparatus according to the embodiment of the present invention. The loss current measuring apparatus 200 includes a signal detection unit 40 that is connected to the commercial power line 30 and the sample (CV cable) 20 and measures a loss current, a differentiator 60 that is connected to an instrument transformer 50, a differential And a capacitive current canceling unit 70 connected to the signal detector 60 and the signal detection unit 40 to cancel the displacement current. The output end of the signal detection unit 40 and the input end of the capacitive current cancellation unit 70 are connected by an optical fiber 90. A monitor 80 is connected to the loss current measuring apparatus 200.

  The differentiator 60 has a circuit configuration that takes in the voltage phase information of the applied voltage from an instrument transformer (PT) 50 installed on the line by the commercial power line 30 and differentiates it to generate a displacement current component cancellation signal. .

  The monitor 80 includes, for example, a display such as an LCD (liquid crystal display) that displays an observation waveform on a screen, and further, means for observing and processing a signal from the loss current measuring apparatus 200, for example, data storage means. And means for processing the loss current by FFT.

(Configuration of signal detector)
The signal detection unit 40 includes a detection resistor 41 connected in series between a high potential end H connected to the commercial power line 30 and a low potential end L connected to the core wire of the sample 20, and a parallel connection to the detection resistor 41. Switch 42, amplifier 43 having a pair of input terminals connected to high potential terminal H and low potential terminal L, E / O converter 44 connected to the output terminal of amplifier 43, amplifiers 43 and E A DC power supply unit 45 including a battery for supplying power to the electronic circuit unit of the / O converter 44.

  The detection resistor 41 is set to a resistance value at which a predetermined voltage drop is obtained by the current i flowing through the detection resistor 41 and the sample 20.

  The switch 42 prevents the detection resistor 41 from generating heat when a large load current (detection current) flows through the detection resistor 41, and prevents the detection resistor 41 from becoming a load on the line during non-measurement. The detection resistor 41 can be short-circuited automatically or manually.

  The amplifier 43 has a configuration of a differential amplifier that uses the voltage generated at both ends of the detection resistor 41 as an input signal, amplifies the input signal to a predetermined level, and outputs it as a detection signal.

  The E / O converter 44 has a circuit configuration for converting the output signal (detection signal) of the amplifier 43 from an electric signal to an optical signal and outputting the optical signal to the optical fiber 90.

(Configuration of capacitive current canceling unit)
The capacitive current canceling unit 70 is an O / E converter 71 that converts an optical signal from the E / O converter 44 into an electric signal, and a cancel resistor (variable resistor) that adjusts and outputs the output signal of the differentiator 60. 72, one input terminal connected to the output terminal of the O / E converter 71, the other input terminal connected to the output terminal of the cancel resistor 72, and the other input terminal of the amplifier 73 and the ground. And a resistor 74 connected to the. Since the capacitive current canceling unit 70 receives a signal from the signal detecting unit 40 via the optical fiber 90, the capacitive current canceling unit 70 is less susceptible to electrical noise.

(Loss current measurement method)
Next, the operation of the loss current measuring apparatus in FIG. 7 will be described. In FIG. 7, when measuring the loss current, the switch 42 is “opened” by a measurer or the like, and the AC voltage v <b> 1 is applied to the detection resistor 41 from the commercial power line 30. By applying the AC voltage v1, the current i corresponding to the deterioration state of the sample 20 passes through the commercial power supply line 30 to the detection resistor 41 to the core wire of the sample 20 to the outer conductive portion such as the shielding layer of the sample 20 to the commercial power supply line 30. Flowing through the energizing loop L, and a voltage drop occurs in the detection resistor 41. The voltage generated at both ends of the detection resistor 41 is amplified by the amplifier 43 and output as a detection signal, and then the amplified output (detection signal) is converted into an optical signal by the E / O converter 44 to the optical fiber 90. Is output.

  In the capacitive current canceling unit 70, the optical signal from the E / O converter 44 of the signal detecting unit 40 is received by the O / E converter 71 through the optical fiber 90 and converted into an electrical signal, which is detected signal. Sd is applied to the resistor 74. At the same time, the capacitive current canceling unit 70 takes in the AC voltage v <b> 2 from the differentiator 60 through the cancel resistor 72 and applies it to the resistor 74.

  The reason for differentiating the output voltage (voltage applied phase information) of the instrument transformer 50 by the differentiator 60 is that if a harmonic component, an air corona pulse or the like is superimposed on the applied voltage waveform, the displacement current component is also higher. Since a wave component and a pulse signal are included, if the applied voltage waveform is differentiated, an actual displacement current cancel signal can be obtained. Therefore, by using the output signal from the differentiator 60, these noises can be removed simultaneously with the cancellation of the displacement current.

  The AC voltage v <b> 2 output from the instrument transformer 50 is a negative cosine wave (−cos θ) for removing the displacement current component of the capacitance, and this AC voltage v <b> 2 is output adjusted by the cancel resistor 72. Thereafter, it is applied to the other input terminal of the amplifier 73. The amplifier 73 cancels the displacement current component (cos θ) by superimposing the detection signal Sd from the O / E converter 71 on the cancel signal Sc (−cos θ), and outputs only the loss current component. This loss current component signal is output to the monitor 80 and a data recorder (not shown) for display and recording. Note that the output adjustment by the cancel resistor 72 may be performed so that the peak phase of the displacement current waveform (zero cross position of the sine wave) becomes 0 while observing the output of the capacitive current cancel unit 70 with the monitor 80.

  As shown in the above equation (1), the capacitance C can be calculated by C = displacement current / (2π × voltage applied frequency × voltage applied voltage). Since the magnitude of the displacement current is the same as the cancel signal Sc when balanced, the capacitance C can be easily determined from the applied frequency, the voltage applied to the sample 20 (applied voltage), and the magnitude of the cancel signal. Can be calculated.

  In the monitor 80 and the data recorder, as shown in FIG. 2 to FIG. 4, various time-dependent changes are observed and recorded, and accumulated as loss current and capacitance data. Based on this data, FIG. Trend monitoring is executed as shown in FIG. In each measurement, after the measurement is completed, the switch 42 is “closed” so that power can be applied to the load.

(Effects of the first embodiment)
According to the first embodiment, the following effects are obtained.
(A) The detection resistor 41 is connected between the sample 20 and the commercial power supply line 30 so that the outer conductive portion of the sample 20 can be grounded, and the detection resistor 41 is connected to the sample 20 by the switch 42 when measuring the loss current. Since it can be connected to the core wire, the loss current can be frequently measured in a live line state, and trend monitoring becomes possible.
On the other hand, the conventional measurement method is difficult to measure frequently and regularly under the same conditions (such as weather conditions and temperature). The error cannot be grasped, and the deterioration diagnosis cannot be performed unless the change in the measured value clearly appears.

(B) Since the displacement current component is canceled by the signal obtained by differentiating the voltage applied phase information from the instrument transformer 50, harmonic components, air corona pulses, etc. are mixed into the commercial power supply, resulting in distortion of the voltage waveform. Even in such a case, it is possible to obtain a displacement current cancel signal in accordance with it. As a result, noise such as harmonic components and airborne corona pulses can be removed simultaneously with the cancellation of the displacement current.

(C) Since the loss current value and the capacitance value of the sample can be grasped, the state of the water tree inside the sample can be estimated as shown in FIG. it can. Thereby, basic data for estimating the remaining life of the sample 20 can be obtained.

(D) If this embodiment is used as primary screening, the state of the line can be monitored at any time in a live line state, and further, secondary screening by the withstand voltage method with high reliability can be performed only on the line with signs of deterioration. If it carries out, highly reliable deterioration diagnosis (deterioration judgment) can be performed by one stop operation.

[Other embodiments]
The present invention is not limited to the above embodiments, and various modifications can be made without departing from or changing the technical idea of the present invention.

  For example, the harmonic current may be measured in place of the loss current or together with the loss current. Thereby, it is possible to grasp the macro degradation state from the loss current (= basic frequency current having the same phase as the applied voltage), and from the harmonic current (a harmonic current component included in the total current flowing through the sample 20). The local deterioration situation can be grasped. At this time, the harmonic current on the applied voltage is canceled by the cancel signal Sc from the differentiator 60 and the cancel resistor 72 in the amplifier 73, but the harmonic component generated in the sample 20 is O along with the loss current component. The signal is output to the monitor 80 via the / E converter 71 and the amplifier 73, whereby the local deterioration state can be grasped.

  In addition, a configuration is possible in which the harmonics and pulse signals are canceled and the displacement current is not canceled. In this case, only the cancel signal Sc corresponding to the cancellation of the harmonics and pulse signals is output from the differentiator 60. That's fine. Therefore, for example, it is possible to extract a harmonic or pulse signal frequency range expected as the cancel signal Sc by a band-pass filter or the like, and use the waveform of the opposite phase as the cancel signal Sc.

  In addition, when the withstand voltage test method is combined with the loss current measurement according to the embodiment of the present invention, it is possible to determine the presence or absence of a deterioration signal under a higher electric field than the commercial operation electric field. This makes it possible to perform diagnosis with higher reliability.

It is a circuit diagram which shows the structure of the loss current measurement system used for verification of the effectiveness of trend monitoring. It is a characteristic view which shows the time-dependent change of the loss current in the accelerated deterioration test which made the applied frequency 500Hz. It is a characteristic view which shows the time-dependent change of the electrostatic capacitance calculated | required from the value of cancellation resistance. It is a characteristic view which shows the result of having recorded the time-dependent change of loss current for every predetermined time. It is explanatory drawing which showed the water tree generation | occurrence | production condition inside a sample corresponding to the sample electrostatic capacitance and loss current. It is a characteristic view which shows the relationship between the loss current and electrostatic capacitance in a cable. It is a circuit diagram which shows the structure of the loss current measuring apparatus which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2 channel signal transmitter 2 Power transformer 2a Primary winding 2b Secondary winding 3 1st measurement electrode 4 2nd measurement electrode 5 Detection resistance 6 Amplifier 7 Resistance 8 Amplifier 9 Cancel resistance 10 Oscilloscope 11 Data recorder 12 FFT Processing device 20 Sample 30 Commercial power line 40 Signal detection part 41 Detection resistor 42 Switch 43 Amplifier 44 E / O converter 45 DC power supply part 50 Transformer for instrument (PT)
60 Differentiator 70 Capacitive Current Cancellation Unit 71 O / E Converter 72 Cancellation Resistance 73 Amplifier 74 Resistance 80 Monitor 90 Optical Fiber 100 Loss Current Measurement System 200 Loss Current Measurement Device

Claims (4)

A sensing resistor is connected in series to the object to be measured and charged from a commercial power source.
The detection signal is a voltage generated at both ends of the detection resistor by the current flowing through the detection resistor.
Differentiating the applied voltage phase information acquired from the commercial power source to generate a displacement current component removal signal,
A signal obtained by level-adjusting the displacement current component removal signal is superimposed on the detection signal, the displacement current component in the detection signal is removed, and a loss current and a harmonic current flowing through the measurement object are measured. Water tree deterioration diagnosis method. A sensing resistor is connected in series to the object to be measured and charged from a commercial power source.
The detection signal is a voltage generated at both ends of the detection resistor by the current flowing through the detection resistor.
A signal obtained by level-adjusting the displacement current component removal signal generated based on the applied voltage phase information acquired from the commercial power supply is superimposed on the detection signal to remove the displacement current component in the detection signal. Measure the harmonic current flowing through the measurement object,
A water tree deterioration diagnosis method, wherein the measurement object is determined to have a defect when a ratio of the loss current or the harmonic current and the capacitance of the measurement object exceeds a set value. A sensing resistor is connected in series to the object to be measured and charged from a commercial power source.
The detection signal is a voltage generated at both ends of the detection resistor by the current flowing through the detection resistor.
A signal obtained by level-adjusting the displacement current component removal signal generated based on the applied voltage phase information acquired from the commercial power supply is superimposed on the detection signal to remove the displacement current component in the detection signal. Measure the harmonic current flowing through the measurement object,
The loss current or the harmonic current and the capacitance of the measurement object are periodically measured to monitor changes over time, and the increase tendency of the loss current or the harmonic current and the increase tendency of the capacitance are monitored. A method for diagnosing water tree deterioration, wherein the state of water tree deterioration is determined based on the method.   4. The water tree deterioration diagnosis method according to claim 2, wherein the capacitance is calculated based on the displacement current component removal signal and an applied voltage from the commercial power source. 5.

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