JP2011242206A - Insulation deterioration diagnosis method and insulation deterioration diagnosis device of power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation deterioration diagnosis method and an insulation deterioration diagnosis device which are capable of diagnosing a state of a part where insulation deterioration of a power cable due to a water tree is worst, without depending on a length of the power cable.SOLUTION: The insulation deterioration diagnosis method comprises: a measurement step of measuring an impressed voltage of an AC voltage as a second impressed voltage and an amount of residual charge emitted by voltage impression, in parallel; an increment measurement step of measuring an increment of residual charge due to boost of the AC voltage on the basis of residual charge at the time of the start of AC voltage impression; a rise time measurement step of measuring a rise time when the increment of residual charge reaches a prescribed value; an AC voltage value measurement step of measuring an AC voltage value of the AC voltage being impressed at the rise time; a rise electric field calculation step of calculating an AC electric field at the time when the increment of residual charge reaches the prescribed value, as a rise electric field on the basis of the measured AC voltage value; and a diagnosis step of diagnosing a state of a part where insulation deterioration of the power cable is worst, on the basis of the calculated rise electric field.

Description

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

  As one of the major insulation deterioration phenomena that determine the withstand voltage life characteristics of rubber and plastic power cables such as cross-linked polyethylene insulated power cables (hereinafter referred to as CV (Cross-linked polyethylene insulated polyvinyl-chloride sheathed cable) cables) There is tree degradation.

  This water tree degradation is caused by the concentration of electric fields such as voids, foreign matter, and protrusions in the insulator when an AC voltage is applied to rubber / plastic power cables over a long period of time in an environment where water exists. This is a phenomenon that occurs when a minute water void group is formed in the portion and this progresses in the electric field direction.

  As the water tree grows, this water tree lowers the breakdown voltage and eventually causes a breakdown of the power cable during operation. For this reason, in the insulation deterioration diagnosis of power cables such as CV cables, it is an important issue to detect water tree deterioration with high reliability.

  Thus, as an effective technique for detecting water tree deterioration of power cables such as CV cables, for example, a residual charge method as shown in Patent Document 1 has been developed. The procedure of the residual charge method will be described with reference to FIG. In the residual charge method, first, a DC voltage is applied to a cable insulator as shown in FIG. 1 (a), and then the electrodes of the insulator are short-circuited and grounded as shown in FIG. 1 (b). Then, as shown in FIG. 1C, an AC voltage or the like is applied to the insulator, and a DC component appearing at this time is detected as a deterioration signal due to the water tree.

  In the residual charge method, space charges are accumulated in the insulator by applying a direct current voltage or the like to the power cable. Next, the conductor and shielding charge (not shown) due to the DC applied voltage are removed by short-circuiting and grounding between the electrodes of the insulator. During this time, the space charge of the deteriorated portion, that is, the charge restrained in the insulator (space charge in the water tree, etc.) partially remains without disappearing. After that, due to the application of AC voltage, the charge (space charge in the water tree, etc.) constrained in the insulator is quickly released and released, and the charge or DC current accompanying the transfer of charge is a degradation signal. As detected by the detector.

  Such a conventional residual charge method is evaluated using the total charge amount detected from the entire power cable.

  For this reason, in the conventional method, the evaluation by the residual charge method is detected as the same amount of charge when the minute deterioration exists uniformly in the longitudinal direction of the power cable and when the large deterioration exists locally. There is a possibility, and it cannot be judged strictly.

  The purpose of residual charge measurement is to detect harmful water trees that directly lead to dielectric breakdown. For this reason, it is necessary to remove a signal generated from a portion irrelevant to deterioration, for example, a heterogeneous insulator interface of a connection portion or a minute water tree that does not directly cause dielectric breakdown as an error component.

  In Patent Document 2 and Patent Document 3, the time characteristic of the residual charge that appears during AC charging after DC charging grounding, specifically, the signal generated from a harmful water tree has a fast response to AC charging. A focused insulation deterioration diagnosis method is described.

  The insulation deterioration diagnosis method described in Patent Document 2 is based on the magnitude of the residual charge that appears while boosting AC charging from zero to a predetermined value, and the amount of change in the residual charge while holding a predetermined voltage after boosting. The deterioration state of the power cable is diagnosed by comparing with.

  In the insulation deterioration diagnosis method described in Patent Document 3, as shown in FIG. 10A described later, an operation of measuring an increase in residual charge due to AC charging is repeated three times, and the first AC charging is performed. This is a diagnostic method in which the charge obtained by subtracting the increase in residual charge from the second and third AC charges from the increase in residual charge is used as the deterioration determination amount.

  Further, in Patent Document 4, as an electric charging method for accumulating electric charges in the water tree portion of the power cable, electric charges are accumulated by a half-wave waveform of AC voltage instead of DC voltage, and AC voltage is applied to charge. A method for releasing and measuring the residual charge is disclosed.

Japanese Patent Publication No. 5-28350 JP-A-8-62280 Japanese Patent Laid-Open No. 11-148959 JP 2007-40861 A

  According to the insulation degradation diagnosis method described in Patent Document 2 and Patent Document 3, signals generated from locations unrelated to degradation, for example, heterogeneous insulator interfaces of connection parts, or minute water trees that do not directly connect to dielectric breakdown are errors. It was possible to diagnose the degree of deterioration by removing a component as a component and extracting a deteriorated portion having a quick response to AC charging.

  However, in the measurement methods described in Patent Document 2 and Patent Document 3, the water tree degradation that is quick in response to all the AC charges existing in the measurement cable is added to the extracted residual charge that is quick in response to the AC charge. Part will be included.

  For example, in Patent Document 3, an AC voltage is boosted from zero to a predetermined value in a short time and then immediately lowered to zero to measure the residual charge increase ΔQ due to AC short-term charging. Residual charges having a quick response to electricity are exhausted during the first AC charging, and only the residual charges unrelated to deterioration are present in the increase in the residual charges obtained by the second AC charging (Patent Document 3). Paragraphs 0026-0028).

  If the cable length to be measured is a short cable of about 10 m, it can be regarded as a substantially uniform deterioration state over the entire length of the cable. However, as the cable length becomes longer, the existence probability of local deteriorated portions having different degrees of deterioration increases. The actually installed cable is on the order of several tens of meters to several kilometers, and it is estimated that there are a plurality of local degradation sites in the measured residual charges.

  On the other hand, the dielectric breakdown of the power cable is determined not by the number of deteriorated portions but by the single water tree deteriorated portion where the most deterioration of the power cable has progressed. In the measurement methods described in Patent Document 2 and Patent Document 3, for example, when there is one portion in the cable where water tree degradation has progressed remarkably until just before dielectric breakdown, insulation breakdown does not occur immediately but is moderate. There is a possibility that the residual charge amount is detected as the same value when there are a plurality of insulation deterioration portions. This tendency becomes higher as the cable length becomes longer and the probability of the presence of a locally deteriorated portion increases.

  In other words, even if a portion unrelated to deterioration is removed as an error component, the method of extracting and evaluating the total amount of residual charges due to water tree deterioration remains the same, and the degree of individual water tree deterioration in the entire cable length is the same. Even so, when the cable length to be measured is long, the amount of charge changes depending on the number of water tree degradation portions, and is affected by the number of water tree degradation portions.

  Moreover, when the total charge amount is divided by the length of the cable and evaluated as the degree of deterioration per unit length, if there is one part in the cable where water tree deterioration has progressed significantly until just before dielectric breakdown, the length of the cable When dividing by the average and averaging, especially in a line having a long cable length, it is evaluated as a small numerical value per unit, and there is a possibility of overlooking a seriously deteriorated portion. Therefore, there is a need for an insulation degradation judgment method that diagnoses only the most degraded single water tree degradation part in the cable without affecting the length of the cable, specifically the number of water tree degradation parts in the entire cable length. ing.

  In addition, even if it implements by the method described in patent document 4 which accumulates an electric charge by the half wave waveform of an alternating voltage instead of direct current voltage, applies an alternating voltage, discharges an electric charge, and measures a residual charge, The problem that the detected residual charge amount affects the length of the cable, specifically, the number of water tree degradation portions in the entire length of the cable cannot be solved.

  An object of the present invention is to provide an insulation deterioration diagnosis method and an insulation deterioration diagnosis apparatus capable of diagnosing the state of the place where the insulation deterioration of the power cable due to the water tree is most advanced without depending on the length of the power cable. That is.

  In the method for diagnosing deterioration of a power cable according to the present invention, a first power is applied to the power cable, electric charges are accumulated in the water tree section, and then an AC voltage is applied to the power cable as a second power. In the method for diagnosing deterioration of a power cable that detects charges accumulated in the water tree portion, the applied voltage of the AC voltage as the second applied voltage and the amount of residual charges released by the applied voltage are set in parallel. Measurement step, an increase amount measurement step for measuring the increase amount of the residual charge due to the boosting of the AC voltage, and the increase amount of the residual charge become a predetermined value. A rising time measuring step for measuring the rising time, an AC voltage value measuring step for measuring an AC voltage value during power application at the rising time, and an increase amount of the residual charge is determined based on the AC voltage value. Exchange when the value of Having a field, the rising field calculating step of calculating a rising electric field, on the basis of the rising field calculated, the diagnostic step of diagnosing the condition of maximum insulation deterioration of a power cable, a.

  The insulation deterioration diagnosis device of the present invention includes a first power applying means for applying an electric power to a power cable that is an object of insulation deterioration diagnosis, a second electric applying means for applying an AC voltage to the power cable, and the first AC voltage boosting based on the measurement of AC voltage as the second charging, a measuring means for measuring the amount of residual charge released by this charging in parallel, and the residual charge at the start of AC charging An increase amount measuring means for measuring the increase amount of the residual charge due to, a rise time measuring means for measuring the rise time when the increase amount of the residual charge becomes a predetermined value, and an alternating voltage during the charging at the rise time AC voltage value measuring means for measuring a value, and, based on the AC voltage value, a rising electric field calculating means for calculating an AC electric field when the amount of increase in the residual charge becomes a predetermined value as a rising electric field, Based on the calculated rising electric field Employs a configuration comprising a diagnostic means for diagnosing the condition of maximum insulation deterioration of a power cable, a.

  ADVANTAGE OF THE INVENTION According to this invention, the state of the location where the insulation degradation of the power cable by a water tree most advanced can be diagnosed, without being dependent on the length of a power cable. In addition, it is possible to reliably diagnose a single maximum deteriorated part in the cable without being affected by the response variation of the residual charge due to variations in the AC voltage application and without depending on the length of the measurement cable. Can do.

It is a figure which shows the procedure of the conventional residual charge method, (a) is a figure which shows the applied state of DC voltage, (b) is a figure which shows a ground state, (c) is a figure which shows the applied state of AC voltage The figure which shows the residual charge-time characteristic under the alternating current electric power as a 2nd electric power in the state which applied the 1st electric power to the electric power cable of the principle explanation, and accumulated the electric charge in the water tree part. Fig. 2 is a schematic diagram of the results of Fig. 2 according to the degree of water tree degradation. Schematic diagram of the case where the water tree deterioration degree is mixed in the explanation of the principle of severe, medium, and mild Diagram showing an example of actual measurement data explaining the principle Figure showing the correlation between the rising electric field and the AC breakdown electric field after calculating the rising electric field using the measurement method of the present invention in the power cable removed from the principle explanation, and then conducting a destructive test of the power cable. The figure which shows the structure of the insulation degradation diagnostic apparatus which concerns on one embodiment of this invention. The figure which shows the other structure of the insulation degradation diagnostic apparatus which concerns on this Embodiment. The figure which shows the other structure of the insulation degradation diagnostic apparatus which concerns on this Embodiment. The figure which compares and shows the measurement pattern of the residual charge measuring method by this Embodiment, and the conventional residual charge measuring method Diagram for explaining the determination of a combination of the total charge amount Q ₀ of the residual charge and the rising field of the residual charge in the insulation degradation diagnosis method of the power cable according to this embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Principle explanation)
First, the length of the water tree and the residual charge response in the insulation cable degradation diagnosis method of the present invention will be described.

<Water tree length and residual charge response>
FIG. 2 is a diagram showing a residual charge-time characteristic under AC charging as a second charging in a state in which the first charging is performed on the power cable and electric charges are accumulated in the water tree portion. FIG. 2A shows the residual charge due to the sample having a long water tree degradation of about 1000 μm. FIG. 2 (b) shows the residual charges due to the sample in which bow-tie water trees of about 100 μm frequently occur but long water trees are hardly present. Comparing FIG. 2 (a) and FIG. 2 (b), it can be confirmed that the longer the water tree length, the faster the response behavior to AC charging.

  FIG. 3 is a diagram schematically showing the result of FIG. 2 according to the degree of water tree degradation.

As shown in FIG. 3 (a), a large length of the water trees of the power cable insulation unit, that is, in the case of severe degradation, faster response of the residual charge for Affairs Division conductive, the rise time t ₁ is shorter . On the contrary, as shown in FIG. 3C, when the length of the water tree of the power cable insulator is small, that is, when it is slightly deteriorated, the response of the residual charge to the AC charging is slow, and the rise time t ₃ Becomes longer.

  Since this rise time depends on the degree of local deterioration of the power cable, it is not affected by the length of the power cable. The time during which AC power is boosted to a predetermined voltage is about several seconds, but the response of the residual charge of detrimental water tree degradation to AC power is exhausted during AC power boost.

  For this reason, the rise time is always the time during the boosting of the AC voltage. This rise time is defined by measuring the amount of increase in residual charge based on the amount of residual charge at the start of AC charging. For example, when the increase reaches 1 nC, a predetermined increase from the start of AC charging The time when the amount is reached.

  FIG. 4 is a diagram schematically illustrating a case where the degree of water tree deterioration is mixed in severe, medium, and mild.

  As shown in FIG. 4, in the cable line actually laid, there are many cases where there are a plurality of severely deteriorated portions, moderately, and slightly deteriorated portions, and in this case, the response of each residual charge It becomes a composite value.

  FIG. 5 is a diagram schematically showing an example of actual measurement data.

  As shown in FIG. 5, the rise time is determined in the section where the degree of deterioration is the greatest in the entire length of the power cable, and therefore, it becomes possible to determine the largest single deterioration part in the longitudinal direction of the power cable.

  By the way, when this residual charge response time is applied to deterioration diagnosis, the response of the residual charge changes due to variations in the AC voltage applied even in the same cable. Since the response of the residual charge of the harmful water tree degradation to AC charging is exhausted within a few seconds after the start of charging, this AC charging variation cannot be ignored. In addition, since deterioration diagnosis is measured with local laying cables, even if the voltage value and gradient are unified, it cannot be said that they are generally the same due to variations in power distribution and the connection status to the cables, but simply measured locally. It is dangerous to diagnose the deterioration state uniformly from the same criterion for the response time of the residual charge to AC charging.

  The present invention pays attention to the relationship between the response time of the residual charge to AC charging, specifically, the time when the increase amount of the residual charge reaches a predetermined value (threshold) and the AC electric field value during charging.

The power cable insulation deterioration diagnosis method of the present invention sequentially executes the following (1) to (6).
(1) The AC voltage as the second voltage is measured in parallel with the applied voltage of the AC voltage and the residual charge released by the applied voltage. Here, “measured in parallel” is to measure the amount of residual charge released by applying an AC voltage while measuring the amount of residual charge during the application of AC voltage. That means. Further, the rising voltage of the AC voltage and the residual charge are calculated using time (for example, time) as common data. Calculation of the rising voltage and the residual charge using time as common data is referred to as “synchronizing”.
(2) Using the residual charge at the start of AC charging as a reference, the amount of increase in the residual charge due to boosting of the AC voltage is measured.
(3) The rise time when the amount of increase in the residual charge reaches a predetermined value is measured.
(4) Measure the alternating voltage value during the charging at the rise time.
(5) Based on the AC voltage value, an AC electric field when the amount of increase in residual charge reaches a predetermined value is calculated as a rising electric field.
(6) Diagnose the state of the maximum insulation deterioration portion of the power cable based on the calculated rising electric field.

  In this way, by diagnosing the rising electric field of the residual charge with respect to AC charging, it is independent of the length of the power cable and the variation of AC charging, and the single water tree deterioration part where the most insulation deterioration has progressed Can be diagnosed. Note that the first voltage application may be any of a DC voltage, an impulse voltage, and an AC voltage, and the method of applying the charge in the water tree portion of the power cable is not particularly limited.

  FIG. 6 shows a power cable removed product (length: several tens to several hundreds of meters), after calculating a rising electric field by the measurement method of the present invention, conducting a destructive test of the electric power cable, FIG. 6A is a correlation diagram between the rising electric field and the AC breakdown electric field, and FIG. 6B is a diagram illustrating the rising electric field in FIG. 6A.

  As shown to Fig.6 (a), it shows that withstand voltage is so large that the numerical value of an alternating current breakdown electric field is large, and a cable will be in a healthy state. As shown in FIG. 6 (b), the rising electric field is a state in which a first voltage is applied to the power cable and electric charges are accumulated in the water tree portion, and an AC voltage is applied to the power cable as a second voltage. It is the electric field value of AC charging during the rise time when the response of the residual charge is detected by applying power.

  As shown in FIG. 6A, there is a positive correlation between the rising electric field and the AC breakdown electric field regardless of the length of the measurement cable. That is, when only a slight deterioration exists in the entire power cable, the response of the individual residual charges to the AC charging is slow, and the rise time that becomes a predetermined increase amount becomes long. In the meantime, since the AC charging is boosted, the rising electric field when the residual charge rises increases.

  On the other hand, if the entire power cable is severely deteriorated even at one location, it responds faster than the residual charge of other deteriorated parts with respect to AC charging, the rise time for the predetermined increase amount is shortened, and the rise electric field is also small. Become. Therefore, by determining the rising electric field that is a criterion for deterioration from the required withstand voltage, diagnosis of the installed power cable becomes possible, and appropriate measures such as replacement of the power cable can be performed.

<Configuration of insulation deterioration diagnosis device>
[When the first charge is DC voltage]
FIG. 7 is a diagram showing the configuration of the insulation deterioration diagnosis apparatus according to the embodiment of the present invention, and is a block diagram of a measurement circuit when the first voltage application is a DC voltage.

  As shown in FIG. 7, the insulation deterioration diagnosis apparatus 100 includes a DC power supply 101, a ground resistor 102, an AC power supply 103, a residual charge detector 104, a changeover switch 105, a measurement unit 110, and a deterioration diagnosis unit 120. And a power generation control unit 130. The insulation deterioration diagnosis device 100 performs insulation deterioration diagnosis of the power cable 20 that is a measurement target.

  A power cable 20 (hereinafter also referred to as a “measurement cable”) 20 that is a measurement target is a CV cable, a conductor (not shown), an insulator (not shown) and an insulator covering the periphery of the conductor. It is comprised from the metal shielding layer 21 which covers the circumference | surroundings. In addition, a lead wire from the changeover switch 105 is connected to the end portion 22 of the measurement target cable 20. The metal shielding layer 21 is grounded. Hereinafter, for convenience, the terminal portion 22 of the measurement target cable 20 is referred to as a power application end portion 22 as an end portion to which power is applied, and an end portion of the measurement target cable 20 that is separated from the power application end portion 22 is referred to as a far end portion 23. Called.

  The DC power source 101 is a DC voltage generator, and corresponds to a first power applying means that applies power to the power cable 20 that is a subject of insulation deterioration diagnosis. The DC power supply 101 has a positive electrode side grounded and a negative electrode side connected to the contact 105a of the changeover switch 105, and outputs a DC voltage Vdc. In this case, the DC voltage Vdc of the DC power supply 101 is negative, but there is no problem even if it is positive.

  One end of the ground resistor 102 is grounded, and the other end is connected to the contact 105 b of the changeover switch 105.

  The AC power supply 103 is an AC voltage generator, and corresponds to a second power applying unit that applies an AC voltage to the power cable 20. The AC power supply 103 has a low voltage section (not shown) connected to the residual charge detector 104 and a high voltage section (not shown) connected to the contact 105c of the changeover switch 105, and outputs an AC voltage Vac.

  When the AC charge is applied to the measurement target cable 20, the residual charge detector 104 detects the charge remaining in the measurement target cable 20 and outputs a detection signal indicating the charge to the measurement unit 110.

  Specifically, the residual charge detector 104 detects a DC voltage or an impact voltage generated in a detection capacitor (not shown). Note that one end of the detection capacitor is connected to the low-voltage portion of the AC power supply 103, and the other end is grounded. In addition, the other end of the short-circuit switch whose one end is grounded is connected to the connection between the detection capacitor and the low voltage portion of the AC power supply 103. This short-circuit switch short-circuits the detection capacitor by closing the contact.

  In this way, the residual charge detector 104 measures the residual charge value when AC power is applied to the measurement target cable 20 using the detected DC voltage or impact voltage, and sends it to the measurement unit 110 as a detection signal. Output.

  The changeover switch 105 includes three contact points 105 a to 105 c and a movable piece 105 d that is switched by the power application control unit 130. The downstream side of the movable segment 105 d is connected to the power application end 22 of the measurement target cable 20.

  The changeover switch 105 connects the movable piece 105d to the contact 105a when applying the DC voltage Vdc to the measurement target cable 20, and connects the movable piece 105d to the contact 105b when grounding the measurement target cable 20. The changeover switch 105 connects the movable piece 105d to the contact 105c when the AC voltage Vac is applied to the measurement target cable 20.

  The measurement part 110 measures the applied voltage of the alternating voltage as the second applied voltage and the amount of residual charge released by the applied voltage in parallel. The measurement unit 110 measures the amount of increase in the residual charge due to the boosting of the AC voltage with reference to the residual charge at the start of AC voltage application. Further, the measurement unit 110 measures the rise time when the increase amount of the residual charge becomes a predetermined value. Furthermore, the measurement part 110 measures the alternating voltage value during the charging in the rise time.

  Based on the AC voltage value measured by the measuring unit 110, the deterioration diagnosis unit 120 calculates an AC electric field when the amount of increase in the residual charge reaches a predetermined value as a rising electric field, and calculates the calculated rising electric field. Based on this, the state of the maximum insulation deterioration portion of the power cable 20 is diagnosed. In particular, the degradation diagnosis unit 120 diagnoses a single maximum degradation unit in the power cable 20. Note that the calculation of the rising electric field may be performed in the measurement unit 110.

  The voltage application control unit 130 can freely change the voltage value of the DC voltage applied to the measurement target cable 20 by controlling the changeover switch 105 and the DC power supply 101 as the first voltage application. In addition, the power application control unit 130 controls the changeover switch 105 and the AC power supply 103 as the second power application, and applies an AC voltage from the AC power supply 103 to the measurement target cable 20.

  Next, the measurement operation of the measurement target cable 20 in the insulation deterioration diagnosis device 100 of FIG. 7 will be described. Power application to the measurement target cable 20 in each measurement pattern is performed by the power application control unit 130 via the DC power supply 101 and the AC power supply 103.

The insulation deterioration diagnosis device 100 performs a first voltage application on the power cable 20, accumulates charges in a water tree unit (not shown), and then applies an AC voltage to the power cable 20 as a second voltage application. Then, an insulation deterioration diagnosis method for the power cable 20 for detecting the electric charge accumulated in the water tree portion is executed.
(1) In the insulation degradation diagnostic apparatus 100 connected to the charging end 22 of the measurement target cable 20, when the first charging is a DC voltage, first, the movable piece 105d of the changeover switch 105 is connected to the contact 105a. . That is, the DC power source 101 is connected to the measurement target cable 20, and a DC voltage is applied to the power application end portion 22 of the measurement target cable 20 as the first voltage application.
(2) Next, the movable piece 105d of the changeover switch 105 is connected to the contact 105b. That is, the contact of the changeover switch 105 is connected to the grounding resistor 102, the conductor of the power cable 20 and the metal shielding layer 21 are short-circuited, and the conductor of the power cable 20 is grounded.
(3) Next, the movable piece 105d of the changeover switch 105 is connected to the contact 105c. That is, the contact of the changeover switch 105 is connected to the AC power source 103, and an AC voltage is applied to the power cable 20 as the second power application. At this time, the charge remaining in the power cable 20 is detected using the residual charge detector 104. The charge detected at this time is the charge remaining in the water tree degradation part.
(4) The measurement unit 110 measures in parallel the charge detected by the residual charge detector 104 and the alternating voltage being applied using a voltmeter in synchronization. This corresponds to the <measurement step> in which the applied voltage of the alternating voltage as the second applied voltage and the amount of residual charge released by the applied voltage are measured in parallel.
(5) The deterioration diagnosis unit 120 measures the rising time when the detected increase in the residual charge reaches a predetermined value, calculates the rising AC electric field from the applied AC voltage value at the time, and calculates the AC Judgment of deterioration from electric field. Using the residual charge at the start of AC charging as a reference, measure the amount of increase in residual charge due to AC voltage boost <Increase measurement process>, and measure the rise time when the amount of increase in residual charge reaches a specified value Based on the <Rise Time Measurement Process>, the AC voltage value during charging at the rise time <AC Voltage Value Measurement Process>, and the amount of increase in the residual charge reached a predetermined value based on the AC voltage value This corresponds to a <rising electric field calculation step> for calculating the alternating electric field at the time as a rising electric field, and a <diagnosis step> for diagnosing the state of the maximum insulation deterioration portion of the power cable based on the calculated rising electric field.

[When the first charge is impulse voltage]
FIG. 8 is a diagram showing another configuration of the insulation deterioration diagnosis apparatus according to the embodiment of the present invention, and is a block diagram of a measurement circuit when the first voltage application is an impulse voltage. The same components as those in FIG. 7 are denoted by the same reference numerals, and description of overlapping portions is omitted.

  As shown in FIG. 8, the insulation deterioration diagnosis apparatus 100A includes an impulse voltage generator 101A instead of the DC power supply 101 of FIG.

  The impulse voltage generator 101 </ b> A applies an impulse voltage to the measurement target cable 20. In the impulse voltage generator 101A, the frequency component and the peak voltage value of the impulse voltage applied to the measurement target cable 20 are variably controlled by the power application control unit 130.

  The impulse voltage generator 101A is configured by series-parallel of interactors, and the frequency switching in the impulse voltage generator 101A can be realized by appropriately switching a plurality of provided interactors. The impulse voltage generation device 101A may be configured by a MOS (Metal Oxide Semiconductor) transistor circuit instead of the interactor.

  The impulse voltage generator 101 </ b> A is connected to one end portion of the measurement target cable 20 (referred to as a power application end portion 22) via the changeover switch 105 and applies an impulse voltage to the measurement target cable 20 from the power application end portion 22 side. To do.

  The voltage application control unit 130 controls the changeover switch 105 and the impulse voltage generation device 101A as the first voltage application, and the impulse voltage generation device 101A applies a predetermined frequency component or impulse of a peak voltage value to the measurement target cable 20. Apply voltage. In addition, the power application control unit 130 controls the changeover switch 105 and the AC power supply 103 as the second power application, and applies an AC voltage from the AC power supply 103 to the measurement target cable 20.

Next, the measurement operation of the measurement target cable 20 in the insulation deterioration diagnosis device 100A of FIG. 8 will be described. Power application to the measurement target cable 20 in each measurement pattern is performed by the power application control unit 130 via the impulse voltage generator 101 </ b> A and the AC power supply 103.
(1) In the insulation deterioration diagnosis device 100 connected to the charging end 22 of the measurement target cable 20, when the first charging is an impulse voltage, first, the movable piece 105d of the changeover switch 105 is connected to the contact 105a. . That is, the impulse voltage is connected to the measurement target cable 20, and the impulse voltage is applied to the power application end portion 22 of the measurement target cable 20 as the first voltage application.
(2) Next, the movable piece 105d of the changeover switch 105 is connected to the contact 105b. That is, the contact of the changeover switch 105 is connected to the grounding resistor 102, the conductor of the power cable 20 and the metal shielding layer 21 are short-circuited, and the conductor of the power cable 20 is grounded.
(3) Next, the movable piece 105d of the changeover switch 105 is connected to the contact 105c. That is, the contact of the changeover switch 105 is connected to the AC power source 103, and an AC voltage is applied to the power cable 20 as the second power application. At this time, the charge remaining in the power cable 20 is detected using the residual charge detector 104. The charge detected at this time is the charge remaining in the water tree degradation part.
(4) The measurement unit 110 measures in parallel the charge detected by the residual charge detector 104 and the alternating voltage being applied using a voltmeter in synchronization.
(5) The deterioration diagnosis unit 120 measures the rising time when the detected increase in the residual charge reaches a predetermined value, calculates the rising AC electric field from the applied AC voltage value at the time, and calculates the AC Judgment is made based on the electric field.

[When the first charge is AC voltage]
FIG. 9 is a diagram showing another configuration of the insulation deterioration diagnosis apparatus according to the embodiment of the present invention, and is a block diagram of a measurement circuit when the first voltage application is an AC voltage. The same components as those in FIG. 7 are denoted by the same reference numerals, and description of overlapping portions is omitted.

  As shown in FIG. 9, in the insulation deterioration diagnosis device 100 </ b> B, the first voltage is AC voltage, and the AC power source 103 is also used to generate AC voltage of the first voltage.

  The power application control unit 130 controls the changeover switch 105 and the AC power source 103 to apply the first voltage AC voltage and the second voltage AC voltage to the measurement target cable 20 from the AC power source 103.

Next, the measurement operation of the measurement target cable 20 in the insulation deterioration diagnosis device 100B of FIG. 9 will be described. The power application to the measurement target cable 20 in each measurement pattern is performed by the power application control unit 130 via the AC power supply 103.
(1) In the insulation degradation diagnostic apparatus 100 connected to the charging end 22 of the measurement target cable 20, when the first charging is an AC voltage, first, the movable piece 105d of the changeover switch 105 is connected to the contact 105c. . That is, an AC voltage is connected to the measurement target cable 20, and an AC voltage is applied to the power application end portion 22 of the measurement target cable 20 as the first voltage application.
(2) Next, the movable piece 105d of the changeover switch 105 and the contact 105c are disconnected, and the first power application to the power cable 20 is interrupted.
(3) Next, the movable piece 105d of the changeover switch 105 is connected to the contact 105c. That is, the contact point of the changeover switch 105 is connected to the AC power source 103, and an AC voltage having a polarity opposite to that of the first voltage at the time of interruption is applied from the AC power source 103 to the power cable 20 as a second voltage. At this time, the charge remaining in the power cable 20 is detected using the residual charge detector 104. The charge detected at this time is the charge remaining in the water tree degradation part.
(4) The measurement unit 110 measures in parallel the charge detected by the residual charge detector 104 and the alternating voltage being applied using a voltmeter in synchronization. This corresponds to the <measurement step> in which the applied voltage of the alternating voltage as the second applied voltage and the amount of residual charge released by the applied voltage are measured in parallel.
(5) The deterioration diagnosis unit 120 measures the rising time when the detected increase in the residual charge reaches a predetermined value, calculates the rising AC electric field from the applied AC voltage value at the time, and calculates the AC Judgment of deterioration from electric field. Using the residual charge at the start of AC charging as a reference, measure the amount of increase in residual charge due to AC voltage boost <Increase measurement process>, and measure the rise time when the amount of increase in residual charge reaches a specified value Based on the <Rise Time Measurement Process>, the AC voltage value during charging at the rise time <AC Voltage Value Measurement Process>, and the amount of increase in the residual charge reached a predetermined value based on the AC voltage value Corresponding to <Rising electric field calculation process> that calculates the AC electric field at the time as a rising electric field and <Diagnostic process> that diagnoses the state of the maximum insulation degradation part of the power cable based on the calculated rising electric field .
(6) After the measurement is completed, the movable piece 105d of the changeover switch 105 is connected to the contact 105b and grounded.

  FIG. 10 is a diagram comparing measurement patterns of the residual charge measurement method according to the present embodiment and the conventional (Patent Document 3) residual charge measurement method. In FIG. 10, after charge is accumulated in the water tree portion of the CV cable by the first voltage application, the residual charge is measured by the second voltage application.

  As shown in FIG. 10A, in the conventional method, the amount of change in charge ΔQ1 to ΔQ3 in each charge is used for calculating the deterioration signal. It was necessary.

  On the other hand, in the residual charge measuring method according to the present embodiment, as shown in FIG. 10B, the evaluation of the degree of deterioration can obtain the rise time and rise electric field of the residual charge response in one electric charge. The measurement is completed in 3 to 5 minutes, and the time can be shortened.

  Here, the charge due to the deterioration of the interface between the different insulators in the connection and the minute water tree that does not lead to dielectric breakdown slows the response to AC charging and does not overlap the rise time region of the deterioration diagnosis. There is no influence on the residual charge measurement method according to the embodiment.

  The residual charge measurement method according to the present embodiment can also be applied to existing residual charge measurement data. That is, even in existing data, by evaluating the rising electric field at the rising time of the residual charge from AC charging, it is possible to diagnose the largest single insulation degradation portion in the cable.

Furthermore, residual charge measuring method according to the present embodiment, it is possible to determine that combines rising electric field of the residual charge the total charge amount Q ₀ of the residual charge.

Figure 11 is a diagram for explaining the determination of a combination of the total charge amount Q ₀ of the residual charge and the rising field of the residual charge.

For example, if the rising electric field is small, it indicates that there is locally water tree degradation portion of the severe, a careful even with a small total amount of charge Q ₀ of the residual charge. In addition, even if the rising electric field is large and there is no locally severely deteriorated portion, if the total charge amount Q ₀ of the residual charge is large, it indicates that the water tree deteriorated portion exists over the entire length of the power cable. Therefore, be careful. In this way, in the determination that combines the total charge amount Q ₀ of the residual charge and the rising electric field of the residual charge response, whether the water tree degradation exists uniformly in the longitudinal direction of the power cable or locally exists, In either case, deterioration diagnosis can be performed more appropriately.

  As described above in detail, in the present embodiment, after the first power is applied to the power cable 20 and electric charges are accumulated in the water tree portion, an AC voltage is applied to the power cable 20 as the second power. In the insulation degradation diagnosis method for the power cable 20 that detects the charge accumulated in the water tree portion, the applied voltage of the AC voltage as the second applied voltage, and the amount of residual charge released by the applied voltage A measurement process for measuring the parallel charge, an increase measurement process for measuring the increase in the residual charge by boosting the AC voltage, based on the residual charge at the start of AC charging, and the increase in the residual charge is a predetermined value. Based on the measured AC voltage value, the amount of increase in the residual charge is determined based on the measured AC voltage value and the rise time measuring process that measures the rise time. Interchange when it reaches a predetermined value The field has a rise field calculating step for calculating a rising electric field, based on the calculated rising electric field, a diagnostic step of diagnosing the condition of maximum insulation deterioration of a power cable, a.

  According to this insulation deterioration diagnosis method, it is not affected by the response variation of the residual charge due to the variation in the AC voltage application, etc. A deteriorated part can be diagnosed. It is possible to diagnose the state of the single maximum insulation deterioration portion in the cable, which cannot be determined only by removing the noise component from the relationship between the residual charge response time and the residual charge amount in the conventional example. In particular, since it does not depend on the length of the power cable, it is possible to diagnose the state where the insulation degradation of the power cable due to the water tree has progressed most. Further, since this insulation deterioration diagnosis method is based on the AC electric field value, it is not necessary to consider the change in the residual charge response time due to the variation in AC voltage application.

  In this way, by diagnosing the rising electric field of the residual charge with respect to AC charging, it is independent of the length of the power cable and the variation of AC charging, and the single water tree deterioration part where the most insulation deterioration has progressed Can be diagnosed. Note that the first voltage application may be any of a DC voltage, an impulse voltage, and an AC voltage, and the method of applying the charge in the water tree portion of the power cable is not particularly limited.

  In the present embodiment, AC charging and residual charge are actually measured in parallel. In this case, the time during which alternating current is applied is calculated at the stage of calculation processing after all measurements are completed, and the behavior of electric charge is calculated. It is also possible to perform measurement by performing an operation such as applying a trigger at the application start stage of the AC voltage.

  The insulation deterioration diagnosis method by the insulation deterioration diagnosis apparatus according to the present invention is not limited to the above embodiments, and can be implemented with various modifications.

  In each of the above embodiments, the first power application, the grounding, and the second power application of the AC voltage are performed from the power application end 22 side. It is also possible to charge from 23.

  In the above embodiment, the names of the power cable insulation deterioration diagnosis method and the insulation deterioration diagnosis device are used. However, this is for convenience of explanation, the device is a water tree deterioration diagnosis device, and the method is a cable deterioration diagnosis method. Etc.

  Furthermore, the type, number, connection method, and the like of each part constituting the insulation deterioration diagnosis device, for example, the power transmission control part, are not limited to the above-described embodiment.

  The power cable insulation deterioration diagnosis method described above is also realized by a program for causing this insulation deterioration diagnosis method to function. This program is stored in a computer-readable recording medium.

  INDUSTRIAL APPLICABILITY The insulation degradation diagnosis method and insulation degradation diagnosis apparatus for a power cable according to the present invention have an effect capable of diagnosing insulation degradation of a power cable caused by a water tree, and do not depend on the length of the power cable. This is useful as an insulation deterioration diagnosis method for diagnosing the state of the place where the insulation deterioration of the power cable has most advanced.

DESCRIPTION OF SYMBOLS 20 Electric power cable 100,100A, 100B Insulation degradation diagnostic apparatus 101 DC power supply 101A Impulse voltage generator 102 Ground resistance 103 AC power supply 104 Residual charge detector 105 Changeover switch 110 Measuring part 120 Degradation diagnostic part 130 Electric power distribution control part

Claims (4)

After the first power is applied to the power cable and the electric charge is accumulated in the water tree part, as the second electric charge, an AC voltage is applied to the electric power cable and the electric charge accumulated in the water tree part is detected. In the insulation deterioration diagnosis method for power cables,
A measurement step of measuring in parallel the applied voltage of the alternating voltage as the second applied voltage and the amount of residual charge released by the applied voltage;
With reference to the residual charge at the start of AC charging, an increase amount measuring step for measuring the increase amount of the residual charge by boosting the AC voltage,
A rise time measuring step of measuring a rise time when the amount of increase in the residual charge becomes a predetermined value;
An AC voltage value measuring step of measuring an AC voltage value during charging at the rise time;
Based on the AC voltage value, a rising electric field calculation step of calculating an AC electric field when the amount of increase in the residual charge becomes a predetermined value as a rising electric field;
Based on the calculated rising electric field, a diagnostic step of diagnosing the state of the maximum insulation deterioration portion of the power cable;
A method for diagnosing deterioration of insulation of power cables having power.   The insulation degradation diagnosis method for a power cable according to claim 1, wherein the first voltage application is applied by any one of a DC voltage, an impulse voltage, and an AC voltage.   The method for diagnosing deterioration of power cable insulation according to claim 1, wherein in the diagnosis step, a single maximum deterioration portion in the power cable is diagnosed. A first power application means for applying an electric power to the power cable to be subjected to insulation deterioration diagnosis;
Second power applying means for applying an AC voltage to the power cable;
Measuring means for measuring in parallel the applied voltage of the alternating voltage as the second applied voltage and the amount of residual charge released by the applied voltage;
With reference to the residual charge at the start of AC charging, an increase amount measuring means for measuring the increase amount of the residual charge by boosting the AC voltage,
Rise time measuring means for measuring the rise time when the increase amount of the residual charge has reached a predetermined value;
AC voltage value measuring means for measuring the AC voltage value during charging at the rise time;
Based on the AC voltage value, a rising electric field calculating means for calculating an AC electric field when the amount of increase in the residual charge reaches a predetermined value as a rising electric field;
Diagnostic means for diagnosing the state of the maximum insulation deterioration part of the power cable based on the calculated rising electric field;
An insulation deterioration diagnosis device comprising:

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