JP2010261735A - Method for testing quality of solid insulation cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for testing the quality of a long solid insulation cable which enables attainment of a test covering a full length by almost uniform inversion wave and finishing of a direct current short circuit operation at one time. <P>SOLUTION: A lead cable 6 is connected to one end part 1a of a cable 1 to be tested and a prescribed direct current voltage is impressed from a direct current voltage generating device 2 on the other end part 1c of the lead cable 6. Then, a high voltage portion of the other end part 1c and the grounding are short-circuited by a sphere gap 3 for short circuit so as to perform an operation of cutting the direct current impressed voltage and generating an inversion waveform. The prescribed direct current voltage being imposed continuously for a prescribed time, subsequently, an electric tree generated in the cutting process is subjected to development breakage and the test of the quality of the long solid insulation cable over the full length thereof is performed. Since the portion of the short-circuited end side wherein no effective inversion wave is generated is replaced by the lead cable 6, the effective inversion wave is generated in the cable to be tested, over the full length thereof. Therefore, the direct current short circuit operation is finished at one time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a quality test method for a solid insulated cable, and relates to a quality test method for guaranteeing the quality of a long solid insulated cable over its entire length.

Conventionally, a method described in Patent Document 1 has been proposed as a method for performing a quality assurance test over the entire length of a long solid insulated cable.
In the test method described in Patent Document 1, in the factory shipping test or the withstand voltage test at the time of completion in the field, first, in the first step of the cutting process, after applying the DC voltage, the charging end is short-circuited, and in the next step, The reverse end side is connected to a DC voltage generator and the same operation is performed to generate an electrical tree from the harmful defect portion. After passing through this cutting process, a predetermined DC voltage is continuously applied for a predetermined time, and the process of causing the electrical tree generated in the cutting process to progress and break down is carried out, so that the quality assurance test over the entire length of the long solid insulation cable. To do.

Japanese Patent No. 4101120

In cables with solid insulation, it is known that the accumulation of space charge in the insulator occurs when a DC voltage is applied. This causes an electric field relaxation phenomenon in the defective part, which lowers the detection capability in the defective part. It becomes a factor to make. The invention described in Patent Document 1 is an effective method for solving the problem that it is difficult to induce destruction from the defective portion by performing the cutting process.
However, in the thing of patent document 1, since the operation which short-circuits the applied DC voltage must be similarly performed from the both ends of a cable, it had the problem that the test procedure became complicated.

The reason why the DC voltage applied from both sides must be short-circuited is that the polarity reversal wave does not have a sufficient amplitude on the high-voltage short-circuit end side where the applied DC voltage is short-circuited. That is, when a short-circuit operation is performed, a polarity reversal wave with a large amplitude is generated on the side opposite to the high-voltage short-circuit end (non-short-circuit end side), whereas a polarity reversal wave generated on the high-voltage short-circuit end side has an amplitude. shallow. For this reason, in order to apply a sufficiently large polarity reversal wave to the entire length including the vicinity of both ends of the cable, it is necessary to perform a short-circuit operation on both sides.
In addition, when such handling is performed, the necessary polarity inversion wave is provided only once in the vicinity of both ends of the cable, whereas the other part is provided with two polarity inversion wave histories. Accordingly, there is a problem that the test cannot be performed under the condition of the amplitude of the polarity reversal wave having a uniform overall length.

  Therefore, the present invention provides a method for performing a quality assurance test over a full length, which is effective and cost-effective in consideration of operation at the time of polarity reversal, for a solid insulated cable, for example, a cable exceeding 2000 m. The purpose is to provide a rational and efficient test method that realizes a test based on the amplitude condition of the polarity reversal wave that is almost uniform over the entire length, and that can perform a DC short-circuit operation only once at one end. And

In the present invention, the above problem is solved as follows.
In the first step, a DC voltage generator is connected to one end of the solid insulated cable, a predetermined DC voltage is applied between the conductor and the shielding layer, and the high voltage section and the ground are short-circuited at the DC voltage application end. The operation of cutting the applied voltage to induce an electrical tree is performed at least once, and after the operation is completed, as a second step, a predetermined DC voltage is applied between the conductor of the cable and the shielding layer. In the quality test method over the entire length of the long solid insulated cable that causes the electrical tree to develop and break down when an electrical tree is generated during the cutting process, in the first step, the solid insulated cable in the first step Connect a lead voltage cable (hereinafter sometimes referred to as a “lead cable”) to a DC voltage generator and apply a DC voltage to it.
In this way, the previously prepared voltage-reducing lead cable is connected to the short-circuit end side to which the DC voltage generator is connected, and the portion where the effective polarity reversal wave on the short-circuit end side does not occur is within this power-reed lead cable portion. In this case, an effective polarity reversal wave is generated over the entire length of the solid insulated cable subjected to the test. As a result, the entire length of the solid insulated cable can be tested only by performing a short circuit operation at one end of the solid insulated cable.
There is also a method in which only a short-circuit operation is performed on one end side of the solid insulated cable without using the charging lead cable, and a fixed length portion on the short-circuit end side to which no effective polarity reversal wave is applied is discarded. This is uneconomical. Compared to such a method, the method of the present invention is economical.

  The length of the electric charging lead cable is preferably 500 m or more. This is because the portion where the effective polarity reversal wave on the short-circuit end side does not occur is generally within 200 m, and it is sufficient to use 500 m as a guide for safety.

  The difference between the characteristic impedance of the electric charging lead cable and the characteristic impedance of the solid insulated cable is preferably 10% or less of the characteristic impedance of the solid insulated cable. When the characteristic impedance differs significantly, the impedance discontinuity occurs at the connection point between the charging lead cable and the cable under test, causing unnecessary traveling wave reflection and transmission phenomenon, resulting in a voltage waveform different from the expected polarity reversal wave Occurs in the cable, causing inconvenience. Therefore, in order to minimize the influence of such reflection / transmission phenomenon, it is desirable that the difference between the characteristic impedances of the two cables is within 10%.

In the present invention, since the portion where no effective polarity reversal wave on the short-circuited end side is generated is replaced with the power-applying lead cable, the solid insulation cable that is the subject of the quality test has a polarity reversal wave that is effective over the entire length. Will occur.
For this reason, it becomes possible to perform a quality test only with DC voltage application / cutting operation from one end side, and equivalent results can be obtained without sequentially performing DC voltage cutting operation on both sides of the cable under test, The test procedure can be simplified and streamlined. Further, it becomes possible to perform a test under the amplitude condition of the polarity reversal wave having a uniform overall length.
In particular, the connection between the DC voltage generator and the test cable is 500 m or more, and the connection is made by using a charging lead cable having a characteristic impedance difference of 10% or less. An effective polarity reversal wave can be generated, and unnecessary traveling wave reflection and transmission phenomena do not occur, and the test can be performed with the expected polarity reversal wave.

It is a figure explaining the measurement point of the polarity reversal waveform generated after cutting the direct-current voltage applied to the cable. It is a conductor voltage waveform of each part of the cable under test measured by the experiment of FIG. It is a figure explaining the measuring point of a polarity reversal waveform at the time of connecting a lead cable (500m, insulation thickness 3mm, conductor size 22mm < ² >) to a to-be-tested cable. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable short circuit end by the experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable and the to-be-tested cable connection point by the experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the to-be-tested cable open end by experiment of FIG. It is a figure explaining the measurement point of a polarity reversal waveform at the time of connecting a lead cable (500m, insulation thickness 3mm, conductor size 2000mm < ² >) to a to-be-tested cable. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable short circuit end by the experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable and the to-be-tested cable connection point by the experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the to-be-tested cable open end by experiment of FIG. It is a figure explaining the measurement point of a polarity reversal waveform at the time of connecting a lead cable (500m, insulation thickness 6mm, conductor size 38mm < ² >) to a to-be-tested cable. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable short circuit end by the experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the lead cable and the to-be-tested cable connection point by experiment of FIG. It is a figure which shows the voltage waveform which generate | occur | produced in the to-be-tested cable open end by experiment of FIG. It is a figure which shows the test structure (1) for verifying the effect of this invention. It is a figure which shows the test structure (2) for verifying the effect of this invention. It is a figure which shows the polarity inversion waveform of the simulation protrusion vicinity in the test of FIG. It is a figure which shows the polarity inversion waveform of the simulation protrusion vicinity in the test of FIG.

Hereinafter, the present invention will be described based on examples.
In conducting the experiment, a solid insulated cable having a 3 mm cross-linked polyethylene as an insulator was prepared as a cable to be tested. A conductor having a size of 22 mm ² and a prototype of 3000 m was made in series. Various comparisons were made with respect to the situation of DC polarity reversal waveform generation for the purpose of detecting defects using this cable.

(1) Polarity reversal waveform generated by the prior art method The polarity reversal waveform was generated by short-circuiting the cable charging end after applying a DC voltage to the 3000 m cable by the prior art method.
The configuration of the test circuit is as shown in FIG. 1, and a DC voltage of a predetermined voltage is applied from the DC voltage generator 2 between the high voltage part 1a on one end side of the cable under test 1 and the ground, and then one end side The high voltage portion 1a and the ground were short-circuited by the short-circuiting sphere gap 3, thereby performing an operation of cutting a DC applied voltage and generating a polarity reversal waveform. The cutting wave generated by this travels as a traveling wave from the one end side 1 a to the other end 1 b side of the cable 1. This cutting wave is reflected at the open end on the other end 1b side to generate a polarity inversion wave, and this polarity inversion wave travels in the opposite direction toward the one end 1a side.

In the experiment, in order to obtain the voltage waveform of the conductor at various points along the entire length of the cable, a DC voltage sufficiently lower than the original test voltage is applied, and a DC voltage of several tens of volts that can be directly measured by the oscilloscope 4 and the probe 5 is used. The verification test was conducted.
As a result of measuring the waveform of each part with the oscilloscope 4 and the probe 5, the waveform as shown in FIG. 2 was observed in each part of the test cable 1. In FIG. 2, the horizontal axis represents time (msec), the vertical axis represents the conductor-shielding voltage, and shows the ratio to the applied voltage (the ratio (%) when the magnitude of the applied voltage is 100). The distance from the short-circuit end side (one end side 1a) of the cable is 0 m (thin line), 200 m (solid line), 500 m (thick solid line), 750 m (thin line), 1000 m (solid line), 1500 m (dotted line), 3000 m (thick line) The voltage between the conductor and the shield in the case of a solid line) is shown. As shown in the figure, the amplitude increases as the distance increases.
From this, it is confirmed that a polarity reversal wave having an effective amplitude of 80% or more of the voltage amplitude generated at the open end 1b is generated on the open end 1b side from the distance exceeding about 500 m from the short-circuited end portion 1a of the cable. Is done.

On the other hand, the region within approximately 200 m from the short-circuit end 1a side is not a polarity reversal wave having a sufficient peak value due to the influence of the short-circuit end reflection as compared with the region far from 500 m, and this portion is necessary and sufficient. It was confirmed that no polarity reversal wave was generated by a short circuit of the DC voltage. This should be considered that an appropriate voltage is not applied in a region within 200 m from the short-circuit end.
In order to ensure the reliability of the test, it is certain to consider that an effective test is not performed on a portion of about 500 m which is twice or more of the 200 m in view of safety. Therefore, the purpose can be achieved simply by removing this part after the test, but it is too uneconomical to dispose of a 500 m cable every time the test is performed.

(2) Method according to the present invention (part 1)
Therefore, assuming that the part corresponding to 500 m is prepared in advance for repeated use as a charging lead cable, a similar polarity reversal wave is generated via a 500 m lead cable of the same specification cable. The voltage waveform of was measured. The situation is shown in FIG. One end of the lead cable 6 is connected to one end 1a of the cable 1 to be tested, and a DC voltage of a predetermined voltage is applied from the DC voltage generator 2 between the high voltage portion of the other end 1c of the lead cable 6 and the ground. did. Thereafter, the high voltage portion of the other end portion 1c and the ground are short-circuited by the short-circuiting sphere gap 3 to cut the DC applied voltage and generate the polarity reversal waveform. As described above, the oscilloscope 4 and the probe 5 The waveform of each part was measured.
The cable under test 1 has a remaining length of 2500 m obtained by cutting the lead cable 6 for 500 m in order to facilitate comparison with the item (1).

4 shows a waveform generated at the short-circuited end 1c of the lead cable 6, FIG. 5 shows a waveform generated at the connection point 1a between the lead cable 6 and the cable under test 1, and FIG. 6 shows a waveform generated at the open end 1b of the cable under test 1. As described above, the horizontal axis is time (msec), the vertical axis is the conductor-shielding voltage, and the ratio to the applied voltage (the ratio (%) when the magnitude of the applied voltage is 100). ).
4 was found to be substantially the same as the waveform at the 0 m point in FIG. 2, and FIG. 6 was substantially identical to the waveform at the 3000 m point in FIG. On the other hand, FIG. 5 is almost the same as the waveform at the point of 500 m from the short-circuited end of FIG. Therefore, this method can generate a polarity reversal wave having 80% or more of the amplitude generated on the open end side over the entire length of the cable under test without performing a short circuit operation of the DC voltage from both ends of the cable under test. I found it possible.

(3) Method according to the present invention (part 2)
However, since the characteristic impedance of the power cable differs depending on the cable structure, when connecting cable cables of different sizes, discontinuity of the characteristic impedance occurs at the connection point. Therefore, a reflected wave and a transmitted wave are generated due to the impedance discontinuity, and the generated polarity reversal waveform is disturbed.
As a trial, an extremely large cable having a conductor size of 2000 mm ² with the same insulation thickness of 3 mm was used as the electric power lead cable, and the cable under test was a cable 2500 m with an insulation thickness of 3 mm and a conductor size of 22 mm ² as described in (2). I actually measured the generated waveform.
The test configuration is as shown in FIG. As shown in the figure, one end of a lead cable 6 having an insulation thickness of 3 mm and a conductor size of 22 mm ² is connected to one end 1a of the cable 1 to be tested, and as described above, a DC voltage is supplied from the DC voltage generator 2. Then, the DC applied voltage was cut to generate a polarity reversal waveform by short-circuiting with the short-circuiting sphere gap 3, and the waveform of each part was measured with the oscilloscope 4 and the probe 5 as described above.

The results of FIGS. 8, 9 and 10 are shown. 8 shows a waveform generated at the short-circuited end 1c of the lead cable 6, FIG. 9 shows a waveform generated at the connection point 1a between the lead cable 6 and the cable under test 1, and FIG. 10 shows a waveform generated at the open end 1b of the cable under test 1. As described above, the horizontal axis is time (msec), the vertical axis is the conductor-shielding voltage, and indicates the ratio to the applied voltage (ratio (%) when the magnitude of the applied voltage is 100). Yes.
As can be seen, the short-circuit waveform of the lead cable (FIG. 8), the connection point waveform of the lead cable and the cable under test (FIG. 9), and the waveform generated at the open end of the cable under test (FIG. 10) are shown in FIG. 4, FIG. 5 and FIG. 6 are significantly different in waveform and amplitude, and it can be seen that it cannot be said to be a polarity reversal waveform that fluctuates with the same voltage change width. Since the characteristic impedance of the 22 mm ² cable is 39.4 Ω and the characteristic impedance of the 2000 mm ² cable is 6.4 Ω, it can be seen that inconvenience occurs when the difference is large.

(4) Method according to the present invention (part 3)
Therefore, as a lead cable, a cable having an insulation thickness of 6 mm and a conductor size of 38 mm ² was similarly prepared, and a similar test was performed. The cable under test was a cable 2500 m having an insulation thickness of 3 mm and a conductor size of 22 mm ² as described in (2). The test configuration is as shown in FIG. As shown in the figure, one end of a lead cable 6 having an insulation thickness of 3 mm and a conductor size of 22 mm ² was connected to one end 1 a of the cable under test 1. Others are the same as FIG.
The results of FIGS. 12, 13 and 14 are shown. 12 shows a waveform generated at the short-circuited end 1c of the lead cable 6, FIG. 13 shows a waveform generated at the connection point 1a between the lead cable 6 and the cable under test 1, and FIG. 14 shows a waveform generated at the open end 1b of the cable under test 1. As described above, the horizontal axis is time (msec), the vertical axis is the conductor-shielding voltage, and indicates the ratio to the applied voltage (ratio (%) when the magnitude of the applied voltage is 100). Yes.

As can be seen, the short-circuit waveform of the lead cable (FIG. 12), the waveform of the connection point between the lead cable and the cable under test (FIG. 13), and the waveform generated at the open end of the cable under test (FIG. 14) are shown in FIG. 4 and 5 can be regarded as a polarity reversal waveform that fluctuates with a voltage change width substantially equivalent to that of FIGS. The characteristic impedance of the 3 mm thick, 22 mm ² cable is 39.4 Ω, and the characteristic impedance of the 6 mm thick 38 mm ² cable is 44.9 Ω. Thus, it has been found that when the difference in characteristic impedance is approximately 10%, the waveform disturbance can be accommodated with no practical problem. Therefore, if the characteristic impedance difference is within ± 10%, a good polarity inversion wave can be generated.

  From the above results, when applying the DC voltage in the step of cutting the DC voltage, it is preferable that the difference in the characteristic impedance is within 10% of the test cable, and that the electric charging lead cable having a length of 500 m or more is used. By connecting the cable under test, even if the DC voltage cutting operation is performed only from one terminal side, it is expected that the same effect as that obtained when the cutting operation is performed on both terminal sides is expected.

(5) Experimental verification of the present invention Therefore, in order to verify this effect in practice, the same test sample as described in the above item (4) was prepared, and the following experiment was performed. For the cable, a plurality of 2500 m CV cables having an insulation thickness of 3 mm and a conductor size of 22 mm ² were prepared.
In these, a simulated protrusion was formed by piercing a metal needle as an artificial defect 1 mm from the outer semiconductive layer side of the cable into the insulator in the immediate vicinity of one end. The specification of the lead cable in the present invention is as described in the item (4).
In addition, although the withstand voltage test of the said defect was implemented 10 samples with the same another sample previously, it was confirmed that all did not have dielectric breakdown in the voltage application of DC 140kVx24 hours.

Experiments were conducted on the cable samples provided with such protrusions in the test configuration shown in FIGS. 15 and 16. 15 and 16, 1 is a cable under test (2500 m, insulation thickness 3 mm, conductor size 22 mm ² ), 2 is a DC voltage generator, 3 is a short-circuiting ball gap, 6 is a lead cable (500 m, insulation thickness 6 mm, The conductor size is 38 mm ² ), and the simulated protrusion A is formed on the cable under test 1.
As shown in FIG. 15, an example in which the terminal 1a side on the side of the formation portion of the simulated protrusion A of the cable under test 1 is connected to the DC power source 2 and the short-circuiting ball gap 3 via the lead cable 6 is referred to as case 1. As shown in FIG. 2, the case 1 in which the terminal 1a on the side where the simulated projection A of the cable under test 1 is formed is the open end and the terminal 1b of the cable under test 1 is connected to the lead cable 6 and the DC power source 2 is referred to as case 2. The experiment was conducted.

In all experiments, DC voltage application → short circuit operation by the short-circuiting sphere gap 3 was repeated 10 times after DC voltage 140 kV was applied. As a result, neither dielectric breakdown in case 1 nor case 2 occurred in this step.
FIG. 17 shows an actual measurement voltage waveform near the creation part of the simulated projection A in case 1, and FIG. 18 shows an actual measurement voltage waveform near the creation part of the simulation projection A in case 2. The horizontal axis represents time (msec), The vertical axis represents the conductor-shield voltage (kV).
Therefore, as described in Patent Document 1, as a second step, a predetermined DC voltage was continuously applied for a predetermined time, and the electric tree generated in the cutting process was developed and destroyed. That is, when a DC voltage of 80 kV was applied to the cable under test 1 after the short-circuit operation, dielectric breakdown occurred in case 1 after about 13 minutes from the start of application and in case 2 after about 25 minutes from the start of application. It was confirmed that
Such a test was carried out under the same voltage condition (the operation of short-circuiting after applying the first step DC 140 kV 10 times and then applying a constant voltage of DC 80 kV) for each case 1 condition and case 2 condition in total 5 samples. As a result, no breakdown occurred in the first DC voltage cutting step, but it was confirmed that the breakdown occurred in the second DC voltage application step in the time shown in the table below.

As shown in FIGS. 17 and 18, the amplitude of the polarity reversal waveform generated at the short-circuited end and the open-ended side is approximately 20% different, but as can be seen from the above table, the defects due to the simulated protrusions are observed. The ability to be detected by destruction was shown to be equivalent. This is considered to be an example showing the effectiveness of the test method according to the present invention.
As described above, as a result of examining the change of the polarity reversal waveform generated at the time of cutting the DC voltage according to various embodiments, the length of the charging lead cable is set to 500 m or more, and the characteristic impedance difference between the charging lead cable and the cable under test is 10 It was clarified that the polarity inversion waveform equivalent to the embodiment described in Patent Document 1 can be sufficiently generated when the ratio is within%.
In this case, it was also confirmed that a test result equivalent to the defect detection test in Patent Document 1 can be obtained.

1 Cable to be tested 2 DC voltage generator 3 Ball gap for short circuit 4 Oscilloscope 5 Probe 6 Lead cable

Claims (1)

In the first step, a DC voltage generator is connected to one end of the solid insulated cable, a predetermined DC voltage is applied between the conductor and the shielding layer, and the high voltage section and the ground are short-circuited at the DC voltage application end. The operation of cutting the applied voltage to induce an electrical tree is performed at least once, and after the operation is completed, as a second step, a predetermined DC voltage is applied between the conductor of the cable and the shielding layer. In a quality test method for a solid insulated cable that continuously applies a predetermined time,
A quality testing method for a solid insulated cable, wherein in the first step, a voltage-applying lead cable is connected to the solid insulated cable, and a direct current voltage generator is connected thereto to apply a direct current voltage.

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