JP2017026491A - Deterioration diagnosis method of of cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the deterioration diagnosis method of an OF cable capable of performing deterioration diagnosis simply and more certainly.SOLUTION: The deterioration diagnosis method of an OF cable includes: a first process in which an AC voltage is applied to an OF cable; a second process in which a DC voltage is applied to the OF cable subjected to the AC voltage and the cable is grounded; and a third process in which after the grounding, an AC voltage is applied to the OF cable to make it discharge residual electric charges, the residual electric charges are measured as the residual electric charges after application of the DC voltage, and deterioration of the OF cable is diagnosed based on the measured residual electric charges after application of the DC voltage.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a deterioration diagnosis method for an OF cable (oil-filled cable).

  Conventionally, in an OF cable line as a power cable, if flammable gas such as acetylene gas is contained in insulating oil due to internal discharge or the like, the insulation performance is lowered and the risk of dielectric breakdown accident is increased. For this reason, in an OF cable line configured by connecting OF cables at the joint, the insulating oil in the OF cable line is collected from the joint part or the terminal part periodically or when necessary, and is included in the insulating oil. The deterioration diagnosis of the OF cable line is performed based on the amount of combustible gas generated (see, for example, Patent Document 1).

  In addition, in a CV cable (Cross-linked polyethylene insulated polyvinyl-chloride sheathed cable) line as a power cable, when AC voltage is applied for a long time under wet conditions, It is known that trees are generated, and that water trees are a factor in reducing insulation performance. For insulation measurement technology for diagnosing water tree degradation, many methods have been proposed in the past, and residual charge measurement is known because of its high correlation with the degree of water tree degradation and breakdown voltage (for example, Patent Document 2).

  In this residual charge measurement, first, a DC power is applied to the sample cable, then grounded to remove the DC applied voltage, and then an AC voltage is applied. Only the DC charge component (residual charge) is detected from the current flowing through the cable insulation. The residual charge amount is calculated by integrating the generated current signal as a deterioration signal.

JP-A-5-252632 Japanese Patent Laid-Open No. 11-148959

  By the way, in the deterioration diagnosis of the conventional OF cable line, the insulation oil collected through the oil collection connector of the joint part connecting the OF cable is analyzed. For this reason, even if the combustible gas is generated in the OF cable line, the combustible gas cannot be detected from the collected insulating oil unless the combustible gas diffuses to the vicinity of the oil collecting connector. That is, although internal discharge in the vicinity of the oil collecting connector at the joint can be confirmed, but internal discharge has occurred away from the joint where the oil has been collected, flammable gas cannot be detected in the collected insulating oil and normal There is a risk of misdiagnosis.

  Therefore, in order to perform a more accurate deterioration diagnosis, it is necessary to collect oil from all the joint portions, which takes time and is not necessarily detectable.

  Here, as the method for diagnosing the deterioration of the CV cable as a power cable different from the OF cable, the above-described residual charge measurement is also considered. In the first place, the residual charge measurement is used to diagnose deterioration of the water tree generated in the CV cable. To do. Therefore, it was difficult to apply to an OF cable having a structure in which a water tree provided with an insulator immersed in insulating oil is not generated, and there was no idea to apply.

  This invention is made | formed in view of this point, and it aims at providing the degradation diagnostic method of OF cable which can perform a degradation diagnosis simply and more reliably.

  One aspect of the deterioration diagnosis method for an OF cable according to the present invention includes a first step of applying an AC voltage to the OF cable, and applying a DC voltage to the OF cable to which the AC voltage is applied. A second step of grounding, and applying an AC voltage to the OF cable after the grounding, releasing the residual charge and measuring the residual charge after the DC voltage application, and measuring the DC voltage after the measurement And a third step of diagnosing the deterioration of the OF cable based on the residual charge.

  According to the present invention, the deterioration diagnosis of the OF cable can be performed easily and more reliably.

The figure which shows an example of the measurement circuit for implementing this invention The figure which uses for description of the degradation diagnosis method of OF cable which concerns on one embodiment of this invention The figure which shows the relationship between the residual electric charge discharged | emitted in the alternating voltage application before applying a direct voltage with respect to OF cable, an applied time, and an applied voltage The figure which shows the relationship of the residual electric charge discharge | released in the alternating voltage application after applying a direct voltage with respect to OF cable, an applied time, and an applied voltage The figure which shows the relationship of the residual electric charge discharge | released in the alternating voltage application after applying a direct voltage with respect to OF cable, an applied time, and an applied voltage The figure which shows the X1 part in FIG.

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

  In the present embodiment, the OF cable to be subjected to deterioration diagnosis is an OF cable in which a predetermined length of OF cable is connected in series in the ground to provide an intermediate connection portion, and end connection portions to which devices and the like are connected at both ends. Includes cable tracks. The OF cable has, in order from the center, an oil passage, a cable conductor, a cable insulation layer, a metal sheath, an anticorrosion layer, and the like formed by winding oil-impregnated paper.

  FIG. 1 is a diagram illustrating an example of a measurement circuit for carrying out the present invention, and is a diagram illustrating a configuration of a deterioration diagnosis apparatus as a measurement circuit. In FIG. 1, a degradation diagnosis apparatus 100 includes a DC power supply 11, a grounding resistor 12, an AC power supply 13, a changeover switch 14, a short-circuit switch 15, a detection capacitor 16, a power application control unit 17, a DC voltage. And a detection unit 18. In addition, the OF cable 1 which is a measurement target of the deterioration diagnosis apparatus 100 uses a test cable having the same configuration as the OF cable configured by using oil-impregnated paper wound around a cable conductor as a cable insulating layer.

  The DC power supply 11 has a negative electrode side (high voltage side) connected to the contact 14a of the changeover switch 14 and outputs a DC voltage Vdc. In this case, the DC voltage Vdc of the DC power supply 11 is negative, but there is no problem even if it is positive. One end of the ground resistor 12 is grounded, and the other end is connected to the contact 14 b of the changeover switch 14. The AC power supply 13 has a low voltage part (not shown) grounded, and a high voltage part (not shown) connected to the contact 14 c of the changeover switch 14 to output an AC voltage Vac.

  The changeover switch 14 includes three contact points 14a to 14c and a movable piece 14d. The downstream side of the movable piece 14d is connected to one end portion (one end portion of the cable conductor) 1a of the OF cable 1 as a measurement target cable. Yes. The changeover switch 14 connects the movable segment 14d to the contact 14a when applying the DC voltage Vdc to the OF cable 1, and connects the movable segment 14d to the contact 14b when grounding the OF cable 1. When the AC voltage Vac is applied to the OF cable 1, the movable piece 14d is connected to the contact 14c. Therefore, the changeover switch 14 can charge the DC voltage Vdc, ground, and apply the AC voltage Vac to the one end 1a of the OF cable 1 by switching the movable piece 14d. Note that the switching operation of the changeover switch 14 may be controlled by the power application control unit 17. In that case, the power application control unit 17 can control the DC power supply 11 to freely apply a DC voltage to the OF cable 1.

  One end of the short-circuit switch 15 is grounded, and the other end is connected to a connection portion between the shielding layer (metal sheath) 1 b of the OF cable 1 and the detection capacitor 16. The short-circuit switch 15 short-circuits the detection capacitor 16 by closing the contact.

  One end of the detection capacitor 16 is connected to the shielding layer (metal sheath) 1b of the OF cable 1, and the other end is grounded.

  When the AC power is applied from the AC power supply 13 to the OF cable 1, the power application control unit 17 controls the step-up / down time and peak value of the AC voltage output from the AC power supply 13 and the power application interval. The DC voltage detector (DC voltmeter) 18 detects a DC voltage generated in the detection capacitor 16 when AC power is applied to the OF cable 1. That is, the charge discharged from the OF cable 1 during AC power application is detected by the detection capacitor 16 (capacitance Cd), and the DC voltage detection unit 18 measures the voltage Vs appearing at both ends thereof.

  FIG. 2 is a diagram for explaining an OF cable deterioration diagnosis method according to an embodiment of the present invention. FIG. 2 shows the order of the types of voltages applied to the OF cables.

  In the present embodiment, for example, the deterioration diagnosis of the OF cable 1 that is the measurement target cable is performed by using the deterioration diagnosis apparatus 100 of FIG.

  First, an AC voltage is applied to the OF cable 1 in a short time (first step), and then a DC voltage is applied and grounded (second step). An AC voltage is applied again after the grounding, and the deterioration diagnosis of the OF cable is performed based on the residual charge measured when the AC voltage is applied (third step). In FIG. 2, the AC voltage is applied by applying a short-time AC voltage that is boosted from zero to a predetermined value in a short time and then immediately dropped to zero without holding the voltage. The power transmission time and the interval for performing a plurality of times are arbitrary. FIG. 2 shows a case where AC voltage application in the first step, that is, AC voltage application before DC voltage application is repeated three times at a predetermined interval (for example, 2 minutes). Further, the DC voltage application time and the grounding time are arbitrary times (for example, DC application time 7 minutes, grounding time 10 minutes). Note that the magnitude of the AC voltage (effective value) and the magnitude of the DC voltage are substantially the same (for example, 6 kVrms).

  In performing the deterioration diagnosis using such residual charges, there are two measurement procedures.

  Below, two measurement procedures are demonstrated using the degradation diagnostic apparatus 100. FIG.

<Measurement procedure 1>
A measurement procedure 1 of the OF cable 1 in the deterioration diagnosis apparatus 100 of FIG. 1 will be described.

First, the short-circuit switch 15 is opened, the movable piece 14d of the changeover switch 14 is connected to the contact 14c (the state shown in FIG. 1), and the AC voltage Vac of the AC power supply 13 is applied to one end 1a of the OF cable 1. . At this time, the electric charge discharged from the insulator (not shown) of the OF cable 1 is detected by the DC voltage detection unit 18 as the DC voltage Vs between the terminals of the detection capacitor 16, so that the OF cable 1 (specifically, The residual charge amount Q ₁ confined in the insulator of the OF cable is measured (measurement process). Here, AC voltage application (for example, Vac = 6 kVrms) is repeated a predetermined number of times (for example, 2 minutes) in a short time. An example of the residual charge thus measured is shown in FIG. FIG. 3 shows the relationship between the residual charge (nC), the applied time (minutes), and the applied voltage (kV) released in the AC voltage application before applying the DC voltage to the OF cable 1. The residual charge (nC) is the residual charge detected by the DC voltage detection unit 18, the graph G 1 indicates the applied voltage (kV) when the AC voltage is applied, and the graph G 2 is detected by the DC voltage detection unit 18. The amount of residual charge to be generated is shown. Here, the residual charge amount immediately after voltage application of third and Q _1.

  Next, the short-circuit switch 15 is brought into a short-circuit state, the movable piece 14 d of the changeover switch 14 is switched from the contact point 14 c to the contact point 14 a, and the DC voltage Vdc of the DC power supply 11 is applied to the one end 1 a of the OF cable 1. For example, the DC voltage Vdc is applied for 7 minutes.

  Next, while maintaining the short-circuit state of the short-circuit switch 15, the movable piece 14d of the changeover switch 14 is switched from the contact 14a to the contact 14b, and the one end 1a of the OF cable 1 is grounded for a predetermined time (for example, 10 minutes).

Next, the shorting switch 15 is opened, the movable piece 14d of the changeover switch 14 is switched from the contact point 14b to the contact point 14c, and the AC voltage Vac of the AC power source 13 is again applied to the one end 1a of the OF cable 1. At this time, the electric charge discharged from the insulator of the OF cable 1 is detected by the DC voltage detection unit 18 as the DC voltage Vs between the terminals of the detection capacitor 16. Accordingly, OF (specifically OF cable insulation) Cable 1 to measure the residual charge amount Q ₂ to which is constrained within. Here, alternating voltage application (for example, Vac = 6 kVrms) in a short time is repeated a predetermined number of times (3 times) at a predetermined interval (for example, 2 minutes). An example of the residual charge measured in this way is shown in FIG. FIG. 4 shows the relationship between the residual charge (nC), the applied time (minutes), and the applied voltage (kV) released in the AC voltage application after applying a DC voltage to the OF cable 1. The residual charge (nC) is the residual charge detected by the DC voltage detection unit 18, the graph G3 indicates the voltage (kV) at the time of AC charging, and the graph G4 is detected by the DC voltage detection unit 18. The residual charge amount is shown. Here, the residual charge amount immediately after voltage application of third and Q _2.

In the measurement procedure 1, the residual charge released from the OF cable 1 at the time of AC voltage application before and after DC voltage application is measured, and deterioration diagnosis is performed based on the difference between the measured residual charge amounts Q ₁ and Q ₂ .
Here, a plurality of samples assuming a test cable having a deteriorated OF sheet containing 100 ppm of copper as the OF cable 1 to be measured was created in consideration of individual differences. Among the prepared samples, an undegraded sample 1 that does not perform power application (for example, Vac = 6 kVrms) that simulates the actual use state of the OF cable, and before deterioration diagnosis assuming continuous power application in the actual use electric field. Samples 2 and 3 were charged (for example, 75 days). Table 1 shows the results of diagnosing deterioration of these samples 1 to 3 by measurement procedure 1.

As can be seen by comparing these samples 1 to 3, the difference between the residual charge amounts Q ₁ and Q ₂ (Q ₁ − Q ₂ ) is large (twice or more). As a result, the residual charge that is measured before and after the DC voltage application and at the time of the AC application due to the deterioration portion formed in the OF cable becoming larger due to the continuous application of the normal electric field. The difference is considered to increase.
As a result, a difference diagnosis (Q ₁ -Q ₂ ) between the residual charge amounts Q ₁ and Q ₂ is calculated, and the deterioration diagnosis that considers that the deterioration of the OF cable, specifically, the deterioration of the insulating layer, is larger as the difference is larger. Can be done. Thereby, the deterioration diagnosis of the entire OF cable can be performed more easily and more reliably than the method of performing the deterioration diagnosis by collecting oil.

<Measurement procedure 2>
The measurement procedure 2 is performed by the behavior of the residual charge released from the insulator of the OF cable 1 when the AC voltage is applied after grounding, that is, by the DC voltage detector 18. The deterioration diagnosis of the OF cable 1 is performed based on the behavior of the residual charge to be measured.

  Specifically, in the measurement procedure 1 of the OF cable 1 in the degradation diagnosis apparatus 100 of FIG. 1, when the AC voltage is applied for the first time, the residual charge is calculated using the DC voltage detection unit 18 when the AC voltage is applied. Without measurement, the residual charge is detected only when the AC voltage is applied after the DC voltage is applied. Here, in order to clearly show the behavior of the residual charge detected when the AC voltage is applied after the DC voltage is applied, the OF cable to be measured is more charged than the OF cable used in FIGS. The residual charge measured by the measurement procedure 2 using a test cable having a long time is shown.

  In measurement procedure 2, as in measurement procedure 1, first, short-circuit switch 15 is opened, movable piece 14d of changeover switch 14 is connected to contact 14c (the state shown in FIG. 1), and AC voltage Vac of AC power supply 13 is connected. Is applied to one end 1 a of the OF cable 1. Here, AC voltage application (for example, Vac = 6 kVrms) is repeated a predetermined number of times (for example, 2 minutes) in a short time. Next, the short-circuit switch 15 is brought into a short-circuit state, the movable piece 14 d of the changeover switch 14 is switched from the contact point 14 c to the contact point 14 a, and the DC voltage Vdc of the DC power supply 11 is applied to the one end 1 a of the OF cable 1. For example, the DC voltage Vdc is applied for 7 minutes.

  Next, after maintaining the short circuit state of the short circuit switch 15, the movable piece 14d of the changeover switch 14 is switched from the contact point 14a to the contact point 14b, and the one end 1a of the OF cable 1 is grounded for a predetermined time (for example, 10 minutes), Remove the applied DC voltage.

  Next, the shorting switch 15 is opened, the movable piece 14d of the changeover switch 14 is switched from the contact point 14b to the contact point 14c, and the AC voltage Vac of the AC power source 13 is again applied to the one end 1a of the OF cable 1. At this time, the electric charge discharged from the insulator of the OF cable 1 is detected by the DC voltage detection unit 18 as the DC voltage Vs between the terminals of the detection capacitor 16. Thereby, the residual electric charge restrained in the insulator of the OF cable 1 is measured. Here, alternating voltage application (for example, Vac = 6 kVrms) in a short time is repeated a predetermined number of times (3 times) at a predetermined interval (for example, 2 minutes). An example of the residual charge measured in this way is shown in FIG.

  FIG. 5 shows the relationship between the residual charge (nC), the applied time (minutes), and the applied voltage (kV) released in the AC voltage application after applying a DC voltage to the OF cable 1.

Specifically, FIG. 5 shows a residual charge (nC) discharged in the AC charging after the DC voltage is applied to the OF cable 1 having a longer charging time than the OF cable shown in FIG. The relationship between electric time (minutes) and applied voltage (kV) is shown. Here, it is assumed that the OF cable 1 shown in FIG. 5 is applied for a time that is about 3.3 times longer than the OF cable shown in FIG. 4 (247 days in actual use).
Further, the residual charge (nC) shown in FIG. 5 is the residual charge detected by the DC voltage detector 18, the graph G5 shows the voltage (kV) at the time of AC charging, and the graph G6 shows the DC voltage detector. 18 shows a residual charge detection amount (residual charge amount) detected. FIG. 6 is a diagram illustrating a portion X1 in FIG.

  In the measurement procedure 2, the behavior (residual charge change ΔQ) of the residual charge (nC) released at the time of AC voltage application after applying a DC voltage to the OF cable 1 is measured.

  The behavior of the residual charge (nC) at this time is usually accompanied by a change with time that becomes a downward slope, whereas the residual charge (DC component to be detected) is suppressed and detected. The residual charge remaining decreases (see the X1 portion in FIG. 5). This behavior also appears in FIG. 4 used in the description of the measurement procedure 1 although the change amount is small as shown by the X portion. Further, as shown by the X1 portion in FIG. 5, the residual charges (nC) measured at the time of AC power application several times (three times in FIG. 5) show the same behavior. Similarly, in the X portion of FIG. 4, the residual charges (nC) measured at the time of AC power application several times (three times in FIG. 4) show the same behavior.

  In addition, when comparing the X portion of FIG. 4 and the X1 portion of FIG. 5, the longer time (FIG. 5) in which the OF cable 1 to be measured is continuously charged with the used electric field applied the DC voltage. The behavior (residual charge change ΔQ) of the residual charge (nC) released later during AC charging becomes large (see the X1 portion in FIG. 5). That is, the change in the residual charge at the time of AC voltage application after the AC voltage application, the DC voltage application, and the grounding are sequentially applied to the OF cable 1 is the AC current before the measurement of the OF cable 1 to be measured. The longer the charging period, the more prominent.

  In the measurement procedure 2, an AC voltage is applied to the OF cable 1, and then a DC voltage is applied and grounded. Then, the AC voltage is applied again and discharged from the OF cable insulator (not shown). Then, the DC component detected by the DC voltage detector 18 is measured and its behavior is diagnosed. That is, as shown by a graph G6 in FIG. 6, it is a change that decreases after the residual charge change ΔQ rises. If the change is large, it is determined that there is a discharge portion in the OF cable 1 and there is a deteriorated portion. can do. Therefore, according to the measurement procedure 2 described above, the deterioration diagnosis of the entire OF cable can be performed more easily and more reliably than the method of performing the deterioration diagnosis by collecting oil.

  As described above, in the present embodiment, the measurement procedure 1 is used to evaluate the amount of accumulated charge due to the presence / absence of direct current charging, thereby diagnosing the presence / absence of a degraded portion due to internal discharge in the OF cable and the size of the degraded portion. can do.

  Further, using measurement procedure 2, the presence or absence of a deteriorated portion due to internal discharge in the OF cable and the size of the deteriorated portion are diagnosed from the behavior of the residual charge (change in residual charge ΔQ) during AC charging after DC charging. be able to.

  Furthermore, by using these measurement procedure 1 and measurement procedure 2 together, it becomes easier to grasp the behavior of deterioration, and for the OF cable line, not only the vicinity of the attached parts such as the joint, but also the deterioration of the entire OF cable line is evaluated. Easy to do.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
The embodiment of the present invention has been described above. The above description is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited to this. That is, the description of the configuration of the apparatus and the shape of each part is an example, and it is obvious that various modifications and additions to these examples are possible within the scope of the present invention.

  The OF cable deterioration diagnosis method according to the present invention has an effect of more easily and more reliably performing OF cable deterioration diagnosis, and can be easily applied to an OF cable line laid in the ground. Deterioration diagnosis can be performed accurately.

DESCRIPTION OF SYMBOLS 1 OF cable 1a One end part 1b Shielding layer 11 DC power supply 12 Ground resistance 13 AC power supply 14 Change-over switch 14a, 14b, 14c Contact 14d Movable piece 15 Short-circuit switch 16 Detection capacitor 17 Electric power supply control part 18 DC voltage detection part 100 Deterioration diagnosis apparatus

Claims (4)

A first step of applying an alternating voltage to the OF cable;
A second step of applying a DC voltage to the OF cable to which an AC voltage is applied, and grounding the OF cable;
After the grounding, an AC voltage is applied to the OF cable to release a residual charge, which is measured as a residual charge after the DC voltage is applied. Based on the measured residual charge after the DC voltage is applied, the OF A third step of diagnosing cable degradation;
Having
OF cable deterioration diagnosis method. The first step includes a measurement step of measuring the residual charge before the DC voltage is applied by discharging the residual charge accumulated in the insulator of the OF cable.
In the third step, based on the difference between the residual charge before the DC voltage application measured in the first step and the residual charge after the DC application measured in the third step, the insulator To diagnose deterioration,
The OF cable deterioration diagnosis method according to claim 1. In the third step, the deterioration of the insulation of the OF cable is diagnosed by the amount of change in the residual charge after the DC voltage application measured at the time of AC voltage application.
The OF cable deterioration diagnosis method according to claim 1. The first step includes a measurement step of measuring the residual charge before the DC voltage is applied by discharging the residual charge accumulated in the insulator of the OF cable.
In the third step, the difference between the residual charge before the DC voltage application measured in the first step and the residual charge after the DC application measured in the third step, and the AC in the third step Diagnosing the deterioration of the insulator based on the amount of change in residual charge after the DC voltage application measured at the time of voltage application,
The OF cable deterioration diagnosis method according to claim 1.

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