JP4690932B2 - Insulation degradation diagnosis method for power cables - Google Patents

Description

  The present invention relates to an insulation deterioration diagnosis method for power cables, and more particularly to an insulation deterioration diagnosis method for diagnosing insulation deterioration of power cables caused by water trees.

  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 polyethyleninsulated polyvinyl-chloride sheathed cable) cables) There is deterioration.

  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, the 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.

  Therefore, the residual charge method has been developed as an effective method for detecting water tree deterioration of power cables such as CV cables. The procedure of the residual charge method will be described with reference to FIG. First, as shown in FIG. 17 (a), a DC voltage is applied to the cable insulator, and then the electrodes of the insulator are short-circuited and grounded as shown in FIG. 17 (b). As shown in c), an AC voltage or the like is applied to the insulator, and the 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 an insulator by applying a DC voltage or the like to a power cable, and then grounded to remove the DC applied voltage, and then the electric charges bound in the insulator (in the water tree) Is discharged by applying an AC voltage or the like, and a DC current accompanying the movement of the charge or the charge is detected by a detector as a deterioration signal.

  Also, in actual cable lines, insulation performance such as locations other than highly harmful water trees, such as the interface between different connection materials such as rubber and epoxy, and minute water voids that do not reach the water tree, etc. Charges are also accumulated by direct current voltage application at places where there is no influence, and this is a factor that decreases the accuracy of insulation deterioration diagnosis.

  As a method for solving this problem, based on the knowledge that “the residual charge signal generated from the harmful water tree has a much faster response to the AC charge than the residual charge signal from other components”, FIG. Has been proposed (see, for example, Patent Document 1).

In this AC charging method, an AC voltage is boosted to a predetermined voltage, and then the voltage is immediately reduced without holding the voltage, and charges generated from a harmful water tree using the charges ΔQ _{1 to} ΔQ ₃ appearing at that time. In this method, Q ₀ is calculated by the approximate expression Q ₀ = ΔQ ₁ −ΔQ ₂ × (ΔQ ₂ / ΔQ ₃ ). By using this AC power application method, the correlation between the deterioration signal due to the water tree and the insulation performance (AC breakdown voltage) is improved, and the accuracy of insulation deterioration diagnosis is improved.
Japanese Patent No. 3663286

However, the charge Q ₀ calculated from the AC power application method based on the above-described conventional knowledge indicates a deterioration state of the entire cable line, and is detected as a relatively large value as the cable becomes longer. For this reason, in actual degradation determination, Q ₀ / value Q ₀ / divided by Q ₀ by the effective length L of the cable (the remaining length excluding locations where degradation is unlikely to occur such as new spans and cavernous spans). Degradation determination is performed using L.

  That is, since the deterioration signal that averages the degree of deterioration in the entire cable line is determined, as shown in FIG. 19, when the entire cable line is in a uniform deterioration state and in a non-uniform deterioration state Thus, there is a problem that the values used for the deterioration diagnosis are the same, and the distinction between the uniform deterioration state and the local deterioration state becomes ambiguous.

  Further, when calculating the effective length L, it is necessary to prepare in advance a line information card or the like that records the cable laying age and laying state, and there is a problem that the procedure before the test is complicated.

  Accordingly, an object of the present invention is to provide a method for diagnosing deterioration of a power cable that is not easily affected by non-uniformity in the length of the measurement target cable and the degree of deterioration in the longitudinal direction.

In the method for diagnosing deterioration of power cable insulation according to the present invention, the power cable is grounded after applying a DC voltage from a DC power source, and after the grounding, the AC voltage is applied to the power cable from the AC power source, and the power cable remains. in insulation degradation diagnosis method of the power cable to measure charge, upon voltage application of the AC voltage, lifting divide the AC voltage in a short time, and the predetermined distance while the peak value of the buck-boost of voltage application was Noboru Ue stepwise In the AC charging process repeatedly applying power , and measuring the residual charge detected for each repeated charging at the predetermined interval in each AC charging process , among the residual charge values detected for each AC power application , And a residual charge measuring step using an AC voltage applied when the maximum residual charge is detected as a deterioration determination value.

  According to this method, if the deterioration state is uniform over the entire power cable line, it is possible to perform the deterioration determination ignoring the length element, that is, the deterioration determination without consideration, and the longitudinal direction of the power cable. Even when there is a variation in the deterioration state, it is possible to make a deterioration determination that is not much different from a cable in a uniform deterioration state, and it is possible to perform a more easily understood deterioration diagnosis.

The power cable insulation deterioration diagnosis method of the present invention is the power cable insulation deterioration diagnosis method configured as described above , wherein in the AC power application step , the total time of the step-up / step-down of the AC voltage applied in each step is constant. Take the method of

The power cable insulation deterioration diagnosis method of the present invention is the power cable insulation deterioration diagnosis method configured as described above , wherein in the AC power application step, the peak value of the AC voltage is increased and decreased in a rectangular shape. Take the method of using electricity . Also, the insulation deterioration diagnosis method for power cables of the present invention is the insulation deterioration diagnosis method for power cables having the above-described configuration , wherein the AC power application step performs each AC power application a plurality of times continuously at the same peak value, The residual charge measuring step employs a method of calculating a residual charge value for each AC charging, using a charge that appears each time a plurality of AC voltages are applied in the AC charging step.

  According to these methods, if the deterioration state is uniform over the entire power cable line, it is possible to determine the deterioration without considering the length element, and there is variation in the deterioration state in the longitudinal direction of the power cable. Even in this case, it is possible to make a deterioration determination that is not significantly different from a cable in a uniform deterioration state, and it is possible to perform a deterioration diagnosis that is easier to understand.

The power cable insulation deterioration diagnosis method of the present invention is the power cable insulation deterioration diagnosis method configured as described above , wherein, in the AC power application step , the step-up / step-down of the AC voltage at the same peak value is continuously performed in each step. In the residual charge measurement step, the increase in residual charge that appears every time the peak value is applied continuously in each step is measured, and the first AC voltage is measured. ΔQ _a is the increase in residual charge due to the second voltage application, ΔQ _b is the increase in residual charge due to the second AC voltage application, and ΔQ _{c is} the increase in residual charge due to the third AC voltage application. and then calculates the charge by subtracting the _{ΔQ b × (ΔQ b / ΔQ} c) from _{ΔQ a Q 0 = ΔQ a -ΔQ} b × (ΔQ b / ΔQ c), wherein each alternating the charge _{Q 0} which is the calculated Those who use the residual charge at the time of charging The take.

According to this method, by using the charges ΔQ _a , ΔQ _b , ΔQ _c that appear due to the AC voltage applied at each step as the residual charge value at the time of AC charging at each step, The charge Q ₀ generated from the above is calculated by ΔQ _a −ΔQ _b × (ΔQ _b / ΔQ _c ) to obtain a residual charge value for each step.

  The residual charge value calculated for each step in this way is obtained by removing the error charge composed of charges other than the water tree, and the residual charge value becomes the maximum among the residual charge values from which these error charges are removed. By using the AC voltage as the deterioration determination value, a highly reliable insulation deterioration diagnosis can be performed.

  Therefore, even if the applied voltage to the power cable to be measured becomes high and there is a possibility that error charges other than the water tree increase, according to the present method, the measured residual charge value is Highly reliable insulation deterioration diagnosis can be performed without including error charges other than the increasing water tree.

  According to the present invention, if the deterioration state is uniform over the entire power cable line, it is possible to determine the deterioration without considering the length element, and there is a variation in the deterioration state in the longitudinal direction of the power cable. However, it is possible to make a deterioration determination that is not much different from a cable in a uniform deterioration state, and it is possible to perform a deterioration diagnosis that is easier to understand.

  Hereinafter, an embodiment to which an insulation deterioration diagnosis method for power cables according to the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of the insulation deterioration diagnosis apparatus according to the first embodiment. In FIG. 1, an insulation deterioration diagnosis apparatus 100 includes a DC power supply 1, a ground resistor 2, an AC power supply 3, a changeover switch 4, a short-circuit switch 5, a detection capacitor 6, an AC voltage control device 7, Voltage detecting device 8. 20 in the figure is a measurement target cable.

  The DC power source 1 has a positive electrode side grounded and a negative electrode side connected to the contact 4a of the changeover switch 4 and outputs a DC voltage Vdc. In this case, the DC voltage Vdc of the DC power supply 1 is negative, but there is no problem even if it is positive. The grounding resistor 2 has one end grounded and the other end connected to the contact 4 b of the changeover switch 4. The AC power supply 3 has a low voltage part (not shown) connected to the detection capacitor 6 and a high voltage part (not shown) connected to the contact 4c of the changeover switch 4 to output an AC voltage Vac.

  The change-over switch 4 includes three contact points 4a to 4c and a movable piece 4d, and the downstream side of the movable piece 4d is connected to the end portion 23 of the measurement target cable 20. The changeover switch 4 connects the movable piece 4d to the contact 4a when applying the DC voltage Vdc to the measurement target cable 20, and connects the movable piece 4d to the contact 4b when grounding the measurement target cable 20. When the AC voltage Vac is applied to the cable 20, the movable piece 4d is connected to the contact 4c. Therefore, the changeover switch 4 can apply the DC voltage Vdc, the ground, and the AC voltage Vac to the terminal portion 23 of the measurement target cable 20 by switching the movable piece 4d.

  The short-circuit switch 5 has one end grounded and the other end connected to a connection portion between the low-voltage portion of the AC power supply 3 and the detection capacitor 6. The short-circuit switch 5 short-circuits the detection capacitor 6 by closing the contact.

  When the AC voltage control device (AC voltage control unit) 7 performs AC voltage application from the AC power supply 3 to the measurement target cable 20, the step-up / down time and peak value of the AC voltage output from the AC power supply 3, and Control the charging interval. Specifically, the AC voltage control device 7 repeatedly applies AC voltage to the measurement target cable 20 at predetermined intervals while stepping up and down the AC voltage in a short time and increasing the peak value stepwise. Control to power.

  Further, the AC voltage control device 7 can continuously apply AC power a plurality of times at the same peak value, and outputs AC from the AC power supply 3 when performing the AC power application for a plurality of times. Controls the voltage step-up / down time and voltage application interval. Note that each AC power application of the AC voltage control performed by the AC voltage control device 7 using the AC power supply 3 and continuously performed at the same peak value is referred to as the same peak value power application for convenience.

  The DC voltage detection device 8 detects a DC voltage generated in the detection capacitor 6 when AC power is applied to the measurement target cable 20. In this way, the DC voltage detection device 8 can measure the residual charge value when AC voltage is applied to the measurement target cable 20 using the detected DC voltage.

  In addition, the DC voltage detection device 8 is configured such that when AC power is continuously applied a plurality of times at the same voltage value (same peak value) (at the time of the same peak value power application), a plurality of times of each AC power application ( Using the charge appearing in the same peak value charging), the residual charge value at the time of alternating current charging for each step constituted by the same peak value charging is calculated.

  For example, when the AC voltage is boosted or lowered by the AC voltage controller 7 in a short time and repeatedly applied at predetermined intervals while increasing the peak value in steps, the AC voltage is applied at the same voltage three times for each step. Shall be. In this case, the DC voltage detection device 8 uses the electric charge appearing for each of a plurality of AC voltage charges (same peak value charges) in each step, and thus the residual charge for each step, that is, for each peak value of a different AC voltage. Calculate the value.

Specifically, the DC voltage detection device 8 measures the increment of the residual charge due to the AC voltage application of the same voltage (the same peak value), that is, the AC voltage application of each step. To do. Here, regarding the increase in the residual charge measured in each step, the increase in the residual charge due to the first AC voltage application is ΔQ _a, and the increase in the residual charge due to the second AC voltage application is ΔQ a. and _b, and increase of residual charge by the third round of the AC voltage division electrostatic and Delta] Q _c.

Increment Delta] Q _a of the residual charge, Delta] Q _b, using Delta] Q _c, the DC voltage detector 8, the charge minus _{ΔQ b × (ΔQ b / ΔQ} c) from _{ΔQ a Q 0 = ΔQ a -ΔQ} b X (ΔQ _b / ΔQ _c ) is calculated as a residual charge value at each step.

  The insulation deterioration diagnosis device 100 uses the calculated residual charge value via the DC voltage detection device 8, and performs a deterioration diagnosis using the AC voltage that maximizes the calculated residual charge value as the deterioration determination value.

  The measurement target cable 20 is a CV cable, and includes a conductor 21, an insulator 22 that covers the periphery of the conductor 21, and a metal shielding layer 24 that covers the periphery of the insulator 22. Further, a lead wire from the changeover switch 4 is connected to the end portion 23 of the measurement target cable 20. The metal shielding layer 24 is grounded.

  Next, the measurement procedure of the measurement target cable 20 in the insulation deterioration diagnosis apparatus 100 of FIG. 1 will be described.

  First, the short-circuit switch 5 is brought into a short-circuit state, the movable piece 4d of the changeover switch 4 is connected to the contact 4a, and the DC voltage Vdc of the DC power source 1 is applied to the terminal portion 23 of the measurement target cable 20. Next, the short-circuit state of the short-circuit switch 5 is maintained, the movable piece 4d of the change-over switch 4 is switched from the contact 4a to the contact 4b, the terminal portion 23 of the measurement target cable 20 is grounded, and the applied DC applied voltage is removed. .

  Next, the short-circuit switch 5 is opened, the movable piece 4d of the changeover switch 4 is switched from the contact 4b to the contact 4c, and the AC voltage Vac of the AC power supply 3 is applied to the terminal portion 23 of the measurement target cable 20. At this time, the electric charge discharged from the insulator 22 of the measurement target cable 20 is detected by the DC voltage detection device 8 as the DC voltage Vs between the terminals of the detection capacitor 6, thereby entering the insulator 22 of the measurement target cable 20. The restrained residual charge Q is measured.

  The insulation deterioration diagnosis apparatus 100 according to the present embodiment is characterized in an AC charging method. The AC charging method will be described with reference to FIGS.

  FIG. 2 is a diagram showing a change in the residual charge Q detected by each AC charging by repeatedly increasing and decreasing the AC voltage Vac in a short time and repeatedly applying power at regular intervals while increasing the peak value stepwise. is there.

In FIG. 2, first, the AC voltage control device 7 boosts the AC voltage to V _{1 and} then steps down immediately without holding the voltage. Thereafter, the same step-up / step-down operation is repeated at regular intervals while increasing the peak values V ₂ , V ₃ ,..., V ₁₀ in steps. The residual charge detected by the detection capacitor 6 due to this AC charging is defined as Q (Q ₁ , Q ₂ , Q ₃ ,..., Q ₁₀ ). At this time, as shown in FIG. 3, the voltage value at which the residual charge Q is the largest is used as the deterioration determination value. In the example of FIG. 3, since the residual charge Q ₄ of the peak value detected in the case of the V ₄ of the AC voltage having the greatest value, using the AC voltage V ₄ as the deterioration determination value.

  With reference to FIGS. 4 to 7, it will be described that the use of this AC charging method makes it possible to detect residual charges that have a quick response to AC charging.

4 and FIG. 5, the AC voltage V ₁ , V ₂ , V ₃ ,..., V ₁₀ is applied to the power cable that is greatly deteriorated by the above AC power application method, and the residual charge Q is detected. Shows the case. 6 and FIG. 7, the AC voltage V ₁ , V ₂ , V ₃ ,..., V ₁₀ is applied to the power cable with small deterioration by the above-described AC charging method, and the residual charge Q is detected. Shows the case.

In the example shown in FIGS. 4 and 5, when an AC voltage is applied to a power cable that is highly deteriorated by the above-described AC power application method, the residual charge Q ₃ appears most greatly when the AC voltage V ₃ is used. Yes. Further, in the example shown in FIGS. 6 and 7, when an AC voltage is applied to the power cable with small deterioration by the above AC voltage applying method, the residual charge Q ₆ is the largest when the AC voltage is V _6. Appears.

  Based on these results, when AC voltage is applied to two types of power cables with different degrees of deterioration by the above AC power application method, the maximum residual charge is reduced with a relatively low AC voltage when the degree of deterioration is large. In contrast, when the degree of deterioration is small, the maximum value of the residual charge appears at a relatively high voltage.

  In other words, it can be said that “the power cable having a higher degree of deterioration has a faster response to the AC voltage”. In other words, the response of the residual charge to the AC voltage appears actively at a relatively low voltage.

  Next, it will be described with reference to FIGS. 8 to 12 that the influence of the length of the power cable and the variation in deterioration in the longitudinal direction on the deterioration diagnosis is reduced by adopting the AC power application method.

  FIG. 8 shows a measurement example of the residual charge Q when the deterioration state is uniform over the entire cable line. In the figure, (a) shows a power cable having a length a in which the deterioration state is uniform, (b) shows the measurement result of the residual charge by the AC power application method, and (c) shows a uniform deterioration state. A power cable having a certain length 4a is shown, and (d) shows a measurement result of residual charge by the AC power application method.

In this case, if the uniform degradation state throughout the cable line, although the change value of the residual charge Q on the length, the voltage V ₃ to the maximum value of the residual charge Q appears is unchanged. For this reason, if the deterioration state is the same, deterioration determination can be performed ignoring the length element, and deterioration diagnosis that is easier to understand can be performed.

  9 to 11 show measurement examples of the residual charge Q when the deterioration state is not uniform over the entire cable line.

  In FIG. 9, (a) shows a power cable having a length a that is greatly deteriorated over the entire cable line, and (b) shows a measurement result of residual charge by the AC power application method. In FIG. 10, (a) shows a power cable having a length a whose deterioration state is small over the entire cable line, and (b) shows a measurement result of residual charge by the AC power application method.

FIG. 9 shows the same measurement results as those in FIGS. 8A and 8B. On the other hand, FIG. 9A shows the maximum value of the residual charge Q of the cable of the same length with a small deterioration state shown in FIG. It is manifested in a relatively high AC voltage V ₈ as shown in (b). FIG. 11A shows an example of a cable in which a region having a large deterioration state and a region having a small deterioration state are mixed in the length a shown in FIGS. The measurement result of the residual charge by the AC power application method for this cable is shown in FIG.

In this case, even when variations are present in a degraded state in the longitudinal direction of the cable, the maximum value of the residual charge Q is manifested as a residual charge Q ₃ when voltage application voltage V _3, accumulated in the largest part is deteriorated state It can be seen that information on the residual charge Q is not lost. For this reason, even when there is variation in the deterioration state in the longitudinal direction of the cable, it is possible to make a deterioration determination that is not significantly different from a cable in a uniform deterioration state, and it is possible to perform a more easily understandable deterioration diagnosis.

  As described above, in the insulation deterioration diagnosis device 100 according to the present embodiment, when an AC voltage is applied to the cable 20 to be measured, the AC voltage Vac is stepped up and down in a short time, and the peak value is stepwise. The voltage is repeatedly applied while being raised, and the AC voltage V at which the maximum residual charge Q appears among the residual charges Q detected by each AC charging is used as the deterioration determination value. For this reason, if the deterioration state is uniform over the entire power cable line, it is possible to determine the deterioration without considering the length element, and even if there is a variation in the deterioration state in the longitudinal direction of the power cable, it is uniform. Deterioration determination that is not much different from a deteriorated cable can be performed, and a more easily understood deterioration diagnosis can be performed.

  Therefore, by applying the AC power application method of the present embodiment to the conventional insulation deterioration diagnosis device, the insulation deterioration of the power cable which is not easily affected by the non-uniformity of the length of the measurement target cable and the deterioration degree in the longitudinal direction. A diagnostic method can be provided.

  In the insulation degradation diagnosis apparatus 100 of the above embodiment, as an AC power application method, the case where AC voltage is stepped up and down in a short time and repeatedly applied at regular intervals while increasing the peak value stepwise is shown. However, it is not limited to this power generation pattern. Hereinafter, other AC power application patterns will be described with reference to FIGS.

  FIG. 12 shows an example in which the step-up / step-down speed of the AC voltage in each step is constant. FIG. 13 shows an example in which the AC voltage is stepped up and down to make the total power application time t in each step constant. FIG. 14 shows an example in which the peak value of the AC voltage is marked and the total power application time t of each step is made constant. Also with these AC charging methods, the AC voltage V at which the maximum residual charge Q appears among the residual charges Q detected by each AC charging can be used as the deterioration determination value.

  In the above-described AC voltage applying method in insulation degradation diagnostic apparatus 100 of the present embodiment, residual charge Q measured by applying AC voltage V having a different peak value, that is, by applying AC voltage for each step. May be detected in any manner without departing from the above configuration.

For example, for the residual charge Q, in each step of AC voltage application with different peak values, the operation of raising and lowering the AC voltage from zero to a specified value (V ₁ , V ₂ ,..., V ₁₀ ) is continuously performed a plurality of times. Further, it may be calculated using the residual charge that appears by performing AC power application a plurality of times in succession.

  That is, after applying a DC voltage from a DC power supply to the power cable, it is grounded, and after the grounding, the AC voltage is stepped up and down from the AC power supply to the power cable in a short time, and repeated at predetermined intervals while increasing the peak value in steps. In the AC power application process for applying power, the step-up / step-down of the AC voltage at the same peak value is repeated three times continuously for each step.

In the residual charge measuring process performed after this AC charging process, in each step, the increment of the residual charge due to the continuous peak value charging is measured, and the first AC voltage is applied. ΔQ _a is the increase in residual charge due to AC, ΔQ _b is the increase in residual charge due to the second AC voltage application, ΔQ _c is the increase in residual charge due to the third AC voltage application, and ΔQ charges minus _{ΔQ b × (ΔQ b / ΔQ} c) from _{a Q 0} = calculates the _{ΔQ a -ΔQ b × (ΔQ b} / ΔQ c). The calculated charge Q ₀ is set as the residual charge value at each AC application, and the AC voltage at which the residual charge value at each AC application with different peak values is maximized is set as the deterioration determination value.

  With reference to FIG. 15 and FIG. 16, the AC power application method in the insulation degradation diagnosis apparatus 100 of the present embodiment will be described in detail as another example of the AC power application method.

  FIG. 15 is a diagram illustrating a relationship between an AC voltage and a residual charge according to another example of the AC power application method according to the present embodiment. Note that FIG. 15 shows a case where the AC voltage Vac is stepped up and down in a short time in FIG. 2 and is repeatedly applied at regular intervals while increasing the peak value in a stepwise manner. It is the figure which showed the change of the residual charge Q detected by applying electricity (here 3 times).

In FIG. 15, first, the AC voltage control device 7 boosts the AC voltage to V _{1 and} then steps down immediately without holding the voltage. This is repeated several times, here three times. As described above, the AC voltage V ₁₁ , V ₁₂ , and V _{13 that} are repeatedly performed at the same voltage V ₁ a plurality of times (here, three times) constitute a one-step AC voltage V ₁ . Note that the time for the pressure increase / decrease includes a time shorter than the relaxation time of the residual charge that is unrelated to deterioration.

Thereafter, the same step-up / step-down operation and repeated operation are performed step by step while increasing the peak values V ₂ , V ₃ ,..., V ₁₀ in steps, that is, a plurality of times at each peak value. Here, the step-up / step-down of the AC voltage (peak value charging) is repeated three times. Specifically, voltage application _V 31 of the plurality of times of alternating voltage at a plurality of times of alternating voltage voltage application _{V 21, V 22, V 23} , the peak value _{V 3} at peak value _{V 2, V 32, V 33} , ... A plurality of times of AC voltage application V ₁₀₁ , V ₁₀₂ , V ₁₀₃ at the peak value V ₁₀ are performed. In this manner, the voltage application (peak value voltage application) at the same voltage value three times is repeated at regular intervals, and the voltage is increased stepwise for each step. This constant interval may be the same as the interval between steps.

  In each peak value charging, the AC voltage is reduced from zero to a predetermined value, which is equal to or longer than the relaxation time of the residual charge generated from the deteriorated portion and shorter than the relaxation time of the residual charge unrelated to the deterioration ( After boosting in about 5 seconds, the voltage is lowered to zero without holding the voltage. In addition, the fall time from the step-up of the AC voltage to 0 is about 5 to 15 seconds.

In this way, by performing AC charging at each step by repeating AC charging of the same peak value a plurality of times, the residual charges detected by the detection capacitor 6 are changed to ΔQ ₁₁ , ΔQ ₁₂ , ΔQ ₁₃ ,. ·, ΔQ ₁₀₃ .

For example, in FIG. 15, in the first one-step AC voltage application (peak value V ₁ ), the residual charge detected by the detection capacitor 6 by the in-step AC voltage (V ₁₁ , V ₁₂ , V ₁₃ ) performed a plurality of times. Is (ΔQ ₁₁ , ΔQ ₁₂ , ΔQ ₁₃ ). Further, in the second step AC voltage application (peak value V ₂ ), the residual charge detected by the detection capacitor 6 by the in-step AC voltage (V ₂₁ , V ₂₂ , V ₂₃ ) performed a plurality of times is (ΔQ ₂₁ , ΔQ ₂₂ , ΔQ ₂₃ ).

Similarly, in each step AC charging (peak values V ₃ , V ₄ , V ₅ ,..., V ₁₀ ) in which the peak values increase in order, the AC voltages in the respective steps are V ₃₁ , V ₃₂ , V ₃₃ , V ₄₁ , V ₄₂ , V ₄₃ , V ₅₁ , V ₅₂ , V ₅₃ ,..., V ₁₀₁ , V ₁₀₂ , V ₁₀₃ . The residual charges detected by the detection capacitor 6 by the AC voltage within these steps are ΔQ ₃₁ , ΔQ ₃₂ , ΔQ ₃₃ , ΔQ ₄₁ , ΔQ ₄₂ , ΔQ ₄₃ , ΔQ ₅₁ , ΔQ ₅₂ , ΔQ ₅₃ ,. ₁₀₁ , ΔQ ₁₀₂ , and ΔQ ₁₀₃ .

  Using the residual charge detected in the detection capacitor 6 in this way (the increase ΔQ of the residual charge Q due to the measured peak value application), the DC voltage detection device 8 performs each AC application with the same voltage. The residual charge Q is calculated with the error charge removed.

For example, DC voltage detection is performed using residual charges (ΔQ ₁₁ , ΔQ ₁₂ , ΔQ ₁₃ ) detected by the detection capacitor 6 when AC voltage is applied a plurality of times (here, three times) with the same voltage V _1. The device 8 calculates a charge Q ₁ = ΔQ ₁₁ −ΔQ ₁₂ × (ΔQ ₁₂ / ΔQ ₁₃ ) obtained by subtracting ΔQ ₁₂ × (ΔQ ₁₂ / ΔQ ₁₃ ) from the residual charge Q ₁ at V ₁ from ΔQ _11. . Similarly, residual charge value _{Q 2} in the case of _{V 2} is calculated by _{ΔQ 21 -ΔQ 22 × (ΔQ 22} / ΔQ 23), residual charge _{Q 3} when the _{V 3} is ΔQ ₃₁ -ΔQ ₃₂ × (ΔQ ₃₂ / ΔQ ₃₃ ). Further, the residual charge Q _{4 at} V ₄ is calculated by ΔQ ₄₁ −ΔQ ₄₂ × (ΔQ ₄₂ / ΔQ ₄₃ ). Residual charge _{Q 5} when the V ₅ is calculated by _{ΔQ 51 -ΔQ 52 × (ΔQ 52} / ΔQ 53), ..., residual charge _{Q 10} is _{ΔQ 101 -ΔQ 102 × (ΔQ 102} / ΔQ when the _{V 10 103} ).

As is well known, the equation for determining this charge (Q ₀ = ΔQ _a −ΔQ _b × (ΔQ _b / ΔQ _c ) is a highly harmful water tree (long water tree or water tree with high internal conductivity). Residual charges originating from are much faster than the remaining charges originating from other factors (small water tree, connection interface, etc.), and the response is completed within a few seconds. That is, the charge response due to deterioration is fast, the charge due to the error factor is slow, and only the residual charge component (deterioration signal) that has a quick response is to be extracted. By using the method using this equation, only the charge having a quick response to the AC charging can be extracted, and the reliability of the diagnosis is greatly improved.

  In this way, the DC voltage detection device 8 uses the residual charge for each step of applying the AC voltage at the step of applying the AC voltage at the measured same voltage value (same peak value), and the AC voltage is applied for each step. The residual charge value Q is calculated. An example of the calculated residual charge value Q is shown in FIG.

  FIG. 16 is a diagram showing a change in the residual charge value during AC power application in each step shown in FIG. 15 according to the present embodiment.

As shown in FIG. 16, the voltage value at which the residual charge Q is the largest is used as the deterioration determination value. In the example of FIG. 16, similarly to FIG. 3, since the residual charge Q ₄ of the peak value detected in the case of the V ₄ of the AC voltage having the greatest value, using the AC voltage V ₄ as the deterioration determination value .

  As described above, according to another example of the AC voltage application method using the insulation deterioration diagnosis apparatus 100 of the present embodiment, the voltage is AC-charged and the voltage peak value is increased in a stepped manner. Apply electricity repeatedly at intervals. In addition, a plurality of AC charges are repeated for each step, and the residual charge value of the step itself is calculated using the residual charges in the AC charge for each step.

Specifically, the DC voltage detection device 8 uses the detection capacitor 6 to perform the _first AC charging at each AC charging step in which AC voltage is applied at the same voltage value (same peak value, for example, V ₁ ). The increase ΔQ (for example, ΔQ ₁₁ ) of the residual charge before and after is measured.

After measuring the increase ΔQ of the residual charge before and after the first AC charging, the second AC charging (for example, V ₁₂ ) is performed in the same manner as the first, and the second AC is applied. An increase in residual charge (for example, ΔQ ₁₂ ) before and after the application of voltage is measured.

Next, the third AC charging (for example, V ₁₃ ) is performed in the same manner as the first time, and the increase in residual charge (for example, ΔQ ₁₃ ) before and after the third AC charging is measured.

After completion of these measurements, the insulation deterioration diagnosis device 100 provides the residual charge Q ₁ with a short relaxation time obtained as Q ₁ = ΔQ ₁₁ −ΔQ ₁₂ × (ΔQ ₁₂ / ΔQ ₁₃ ) via the DC voltage detection device 8. The residual charge value of the step itself is used for deterioration diagnosis.

  As a result, as the AC voltage applied to the power cable increases, the residual charge value calculated for each AC charging step may increase even if the error charge as a charge from other than the water tree may increase. Since the error charge is removed, the residual charge value is highly reliable.

  That is, in the residual charge value calculated for each step, the influence of the error charge is remarkably reduced. Therefore, even if the deterioration state is uniform over the entire power cable line, the deterioration determination can be realized in a highly reliable state without considering the length element. In addition, even when there is a variation in the deterioration state in the longitudinal direction of the power cable, it is possible to make a highly reliable deterioration determination that is not much different from a uniformly deteriorated cable. be able to.

  The insulation degradation diagnosis method for power cables according to the present invention realizes insulation degradation diagnosis for power cables that are not easily affected by non-uniformity in the length and longitudinal extent of the cable to be measured. It is useful when applied to deterioration diagnosis.

The block diagram which shows the structure of the insulation degradation diagnostic apparatus which concerns on one embodiment of this invention The figure which shows the relationship between the alternating voltage by the alternating current powering method which concerns on this Embodiment, and a residual charge The figure which shows the change of the residual charge value at the time of the alternating current application of each step of FIG. 2 which concerns on this Embodiment The figure which shows the relationship between an alternating voltage and a residual charge at the time of applying the alternating current power generation method which concerns on this Embodiment to the power cable with a large deterioration The figure which shows the change of the residual charge value at the time of the alternating current application of each step of FIG. 4 which concerns on this Embodiment The figure which shows the relationship between an alternating voltage and a residual charge at the time of applying the alternating current power generation method which concerns on this Embodiment to a power cable with little deterioration. The figure which shows the change of the residual charge value at the time of the alternating current application of each step of FIG. 6 which concerns on this Embodiment (A) is a diagram showing an example of a power cable having a length a and a uniformly deteriorated state according to the present embodiment, and (b) is a residual charge value when stepped AC charging is performed on the power cable of (a). (C) is a diagram showing an example of a power cable having a length of 4a and a uniformly deteriorated state, and (d) is a residual charge value when stepped AC power is applied to the power cable of (c). Diagram showing changes in (A) which concerns on this Embodiment is a figure which shows the example of a power cable with a large deterioration state with length a, (b) is a residual charge value at the time of performing step-like alternating current power application to the power cable of (a) Diagram showing changes in (A) which concerns on this Embodiment is a figure which shows the example of a power cable with a small deterioration state with length a, (b) is a residual charge value at the time of performing step-like alternating current power application to the power cable of (a) Diagram showing changes in (A) which concerns on this Embodiment is a figure which shows the example of a power cable with the variation in deterioration of a length direction, (b) is a residual charge at the time of performing step-like alternating current power application to the power cable of (a) Diagram showing changes in value The figure which shows the example which made constant the step-up / step-down speed of the alternating voltage of each step which concerns on this Embodiment. The figure which shows the example which makes the total electric charging time constant in each step of the alternating voltage concerning this Embodiment The figure which shows the example which makes the total electric charging time constant in each step by stamping the peak value of the alternating voltage which concerns on this Embodiment The figure which shows the relationship between the alternating voltage by the alternating current powering method which concerns on this Embodiment, and a residual charge The figure which shows the change of the residual charge value at the time of the AC power application in each step shown in FIG. 15 which concerns on this Embodiment. As a procedure of the conventional residual charge method, (a) is a diagram showing an applied state of a DC voltage, (b) is a diagram showing a grounded state, and (c) is a diagram showing an applied state of an AC voltage. A figure showing the conventional AC charging method The figure which shows the example of the uniform degradation state and the non-uniform degradation state in the conventional cable track

Explanation of symbols

1 DC power supply 2 Ground resistance 3 AC power supply 4 Changeover switch 4
4a to 4c Contact point 4d Movable section 5 Short-circuit switch 6 Capacitor for detection 7 AC voltage control device 8 DC voltage detection device 20 Cable to be measured 21 Conductor 22 Insulator 23 Termination portion 24 Metal shielding layer 100 Insulation deterioration diagnosis device

Claims (5)

In a method for diagnosing deterioration of a power cable in which a DC voltage is applied to a power cable from a DC power supply and then grounded, and after the grounding, an AC voltage is applied to the power cable from an AC power supply and a residual charge of the power cable is measured. ,
Upon voltage application of the AC voltage, lifting divide the AC voltage in a short time and, while the peak value of the buck-boost of voltage application was Noboru Ue stepwise, and Exchange Section collector step of repeatedly Division conductive at predetermined intervals,
In the AC charging process, the residual charge detected for each repeated charging at the predetermined interval is measured, and when the maximum residual charge is detected among the residual charge values detected for each AC charging , the charging is performed. A residual charge measurement step using the AC voltage as a deterioration judgment value,
A method for diagnosing deterioration of an insulation of a power cable, comprising: 2. The method for diagnosing degradation of power cable insulation according to claim 1, wherein, in the AC power application step, the total time of the step-up / step-down of the AC voltage applied in each step is made constant. 3. The method for diagnosing degradation of power cable insulation according to claim 2 , wherein, in the AC power application step, the peak value of the AC voltage is stepped up and stepped down in a rectangular shape . In the AC power application process, each AC power application is continuously performed a plurality of times at the same peak value,
  The residual charge measurement step calculates a residual charge value for each AC charging by using a charge that appears each time a plurality of AC voltages are applied in the AC charging step.
  The insulation deterioration diagnosis method for a power cable according to claim 1. In the AC power application process, the step-up / step-down of the AC voltage at the same peak value in each step is continuously repeated three times,
In the residual charge measurement step, an increase in the residual charge that appears for each successive application of the peak value in each step is measured, and an increase in the residual charge due to the first AC voltage application. ΔQ _a , the increase in residual charge due to the second AC voltage application as ΔQ _b , the increase in residual charge due to the third AC voltage application as ΔQ _c, and ΔQ _a to ΔQ _b × and (ΔQ _b / ΔQ _c) to calculate the charge _{Q 0} = ΔQ _{a -ΔQ b} × minus the (ΔQ _b / ΔQ _c), the residual charge value of the charge _{Q 0} which is the calculated time of each exchange Section electrostatic To
The insulation deterioration diagnosis method for a power cable according to claim 1.

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