JP3524345B2 - Withstand voltage test method for rubber and plastic insulated power cables - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a withstand voltage test method for rubber and plastic insulated electric cables (including lines) deteriorated by water trees, and in particular, it is possible to determine the presence or absence of ground trees caused by breakage. The present invention relates to a withstand voltage test method for rubber / plastic insulated power cables.

[0002]

2. Description of the Related Art Detection of so-called non-bridging water trees in which the water tree does not penetrate through an insulator is very important in the deterioration diagnosis of rubber and plastic insulated power cables (hereinafter simply referred to as "cables") that have deteriorated water trees. It is a problem. Therefore, according to Japanese Patent Application No. 8-58736, we have determined the conditions for charging such as AC (commercial frequency alternating current, hereinafter referred to as AC) voltage, which has a very low frequency, ultra-low frequency voltage, and damped oscillatory wave voltage. We propose a method to detect harmful water trees based on the presence or absence of breakage and to judge the remaining life of the cable.

On the other hand, in a cable in which the water tree has deteriorated, a water tree having a certain length is often distributed over the entire length of the cable, but the distribution also has various forms.
Therefore, when the breakdown occurs during the withstand voltage test as described above including the DC withstand voltage test, the soundness that does not cause the damage (the soundness here does not mean that the water tree does not occur). , Which means that it can still be used for operation), there is a possibility that an electrical tree called a grounding tree will be generated from the water tree of the cable part, which is considered to be possible. Here, the ground tree refers to a water tree or other defects caused by the effect of accumulated charge or the generation of an oscillating overvoltage due to the ground fault of the cable or forced grounding when a voltage is applied. An electrical tree that arises from an electric field concentration portion such as a portion.

Further, it is conceivable that an electric tree is generated from the water tree even when the destruction is not accompanied as described above. If the generated electrical tree does not lead to breakdown, the result is that the withstand voltage test has been cleared, and the electrical tree will be put into operation despite the loss of soundness. The occurrence of such an electrical tree has a high risk of causing the tree to develop and be destroyed even at the subsequent AC operating voltage, and hinders the healthy operation of the cable line. Therefore, it is important to judge the presence or absence of harmful electrical trees such as the ground tree and the electrical tree generated during the withstanding voltage test.

[0005]

However, there is no method for determining the presence or absence of a ground tree in a deteriorated cable due to breakdown during a withstand voltage test, and whether the remaining portion of the cable can be used for operation. The decision was very difficult. In addition, there is a possibility that the presence or absence of the electric tree generated during charging can be judged by the partial discharge measurement by an appropriate method, but in the withstand voltage test of a deteriorated cable, there are very few cases where the partial discharge is measured. . Therefore, in order to completely avoid the above-mentioned danger, the cable subjected to the withstand voltage test must be replaced over the entire length.
However, exchanging the entire length of the cable is not an economically effective means, and confirms the soundness of the part where no damage has occurred,
It is preferable to put it into operation again. The present invention has been made in view of the above circumstances, and its object is to:
It is an object of the present invention to provide a withstand voltage test method capable of easily discriminating the presence or absence of an electrical tree caused by destruction.

[0006]

[Means for Solving the Problems] First, a case where a cable is broken during a withstand voltage test of a cable line will be described.
It For example, assume that a withstand voltage test is performed on the cable line shown in FIG. In FIG. 1, 1 is an air terminal, 2 is a joint, and 3 is a cable portion. In the figure, it is assumed that the cable portion is broken during the withstand voltage test by applying the test voltage to the cable. If the cable breaks during the withstand voltage test as described above, the span where the breakage occurred is cut off and a new sound cable 3'is formed as shown in Fig. 2 depending on the position of the breaking point and the laying form of the cable. Insert. After arranging the cable lines after destruction in this way, an ultra low frequency voltage lower than the voltage used in the above withstanding voltage test is applied to these cables.

Since the effect on the water tree existing in the cable differs depending on the test voltage waveform, when the voltage waveforms of the test voltage used in the first withstand voltage test and the second withstand voltage test are different, The voltage applied in the second withstand voltage test is not necessarily lower than the voltage applied in the first time as described above (the voltage applied in the first withstand voltage test and the voltage applied in the second withstand voltage test). The relationship with will be described later).

The above-mentioned second withstand voltage test can also be performed with AC. However, since the extremely low frequency voltage has an excellent ability to re-extend the electric tree, the test voltage used in the first withstand voltage test after the cable is broken. By applying an ultra-low frequency voltage lower than (the test voltage value converted to an ultra-low frequency voltage as described later), the water tree is not affected and only the electrical tree is extended, leading to destruction. It will be possible. Therefore, if the test causes a breakdown, it means that the electrical tree was present, and if the breakdown does not occur, it can be considered that the electrical tree has not occurred. The ultra low frequency voltage is 0.01 Hz
It is desirable to use one having a frequency of about 1 Hz, and
With an ultra-low frequency voltage having a frequency of 01 Hz or less, it becomes the same as applying a DC voltage, and it becomes impossible to extend only the electrical tree. Also, when AC is used as the test voltage, the test equipment becomes larger than when using an ultra low frequency voltage,
The upper limit of the frequency is about 200 Hz because of the practical limit of configuring the device.

In the above description, the broken portion is replaced with another cable after the cable is broken. However, as shown in FIG. 3, a simple aerial terminal 4 is provided and a second withstand voltage test is performed. Good. On the other hand, if the cable line is not destroyed during the first withstanding voltage test, the test voltage is once dropped and then the above-mentioned ultra-low frequency voltage (or AC voltage) is applied as the second withstanding voltage test. It is possible to judge whether or not there is an electric tree generated from a harmful water tree in the cable line by turning on the electric power and examining the presence or absence of destruction. Partial discharge occurs when the electric tree expands. Therefore, by simultaneously performing partial discharge measurement during these tests, it is possible to determine whether or not re-extension of the electrical tree has occurred. Further, by this, it is possible to avoid the risk of ending the withstanding voltage test while generating the electrical tree, and therefore it can be said that the presence or absence of the electrical tree can be determined with higher sensitivity.

Next, the relationship between the voltage applied in the first withstanding voltage test and the voltage applied in the second withstanding voltage test will be described. As described above, the test voltage waveform has different effects on the water tree existing in the cable, and if the waveform of the test voltage applied to the degraded water tree cable is different, a certain length of the water tree existing in the cable is present. The voltage that destroys will have different values. For example, the water tree is destroyed at a lower voltage when an AC voltage is applied than when an ultralow frequency voltage is applied. Therefore, when the test voltage of the same waveform is applied in the first and second withstand voltage tests, the value of the voltage applied in the second withstand voltage test is lower than the value of the voltage applied in the first time. However, for example, when the AC voltage is applied in the first withstanding voltage test and the ultra low frequency voltage is applied in the second withstanding voltage test, the ultra low frequency voltage applied in the second withstanding voltage test is , It is not always lower than the AC voltage applied in the first withstanding voltage test.

That is, since the voltage that destroys a certain length of water tree existing in the cable has different values for ultra-low frequency, AC, DC, and damped oscillatory wave voltage, it has an arbitrary length. A voltage that can destroy the water tree is obtained for various waveforms, and the length of the water tree is deleted from the waveform to obtain a very low frequency voltage that destroys the water tree of a certain length.
The relationship between C, DC, and the damped oscillatory wave voltage can be obtained. Therefore, the AC voltage, the DC voltage, and the damped oscillatory wave voltage can be converted into the ultra low frequency voltage that destroys the water tree of the same length, and similarly, the ultra low frequency voltage, the DC voltage, and the damped oscillatory wave voltage. To destroy a water tree of the same length
It can be converted into C voltage. Here, an ultra low frequency voltage, an AC voltage, and a DC that destroy the water tree of the same length as described above.
The voltage and the value of the damped oscillatory wave voltage are referred to as the voltage that gives the same destruction effect to the cable in which the water tree has deteriorated.

FIG. 4 shows an AC voltage, DC, which gives a destruction effect equivalent to an ultra low frequency voltage to a cable in which water tree has deteriorated.
FIG. 3 is a diagram showing a voltage and a damped oscillatory wave voltage, in which the horizontal axis shows voltage values of various waveforms, and the vertical axis shows a destructive effect equivalent to a destructive effect given to a cable deteriorated by water tree. It shows the value of possible ultra-low frequency voltage, 1
3 to 3 respectively show the relationship between the damping vibration wave voltage, the AC voltage, the DC voltage and the ultra low frequency voltage. In the figure, for example, the value of the ultra-low frequency voltage is 73.2 kV, which gives the same destruction effect as the AC voltage of 30 kV, and when AC 30 kV is applied to the first withstanding voltage test, the second The withstand voltage test voltage will impose a very low frequency voltage lower than 73.2 kV.

FIG. 5 shows a DC voltage, DC, which gives a destruction effect equivalent to an AC voltage to a tree-degraded cable.
FIG. 4 is a diagram showing the relationship between voltage and damped oscillatory wave voltage, where the horizontal axis shows the voltage value of various waveforms and the vertical axis can give a destructive effect equivalent to the destructive effect given to the cable by the voltages of the various waveforms. The values of the AC voltage are shown, and 1 to 3 respectively show the relationship between the damping vibration wave voltage, the ultra low frequency voltage, the DC voltage and the AC voltage. In the figure, for example, 100
The value of the AC voltage that can give the same destruction effect as the DC voltage of kV is 27.7 kV, and when DC100 kV is applied to the first withstand voltage test, the second withstand voltage test voltage is 27. An AC voltage lower than 7 kV will be applied.

The present invention has been made by paying attention to the above points, and solves the above problems as follows. (1) Water tree An electrical tree generated by the above withstand voltage test after performing a withstand voltage test with a voltage of an arbitrary waveform in order to determine the presence or absence of harmful water trees present in deteriorated rubber or plastic insulated cables or cable lines. In order to determine the presence or absence of the above, in a withstand voltage test method, a second withstand voltage test is performed using an alternating voltage of 0.01 Hz to 200 Hz, and the presence or absence of an electrical tree is determined by the presence or absence of cable breakage due to the withstand voltage test. , Have a water tree in advance
A water cable of any length can be
Conduct a withstand voltage test with the destructible voltage as the test voltage,
Find the range of water tree length generated by the electrical tree,
The electric tree generated from the tree can be re-stretched and destroyed
The AC voltage of 0.01 Hz to 200 Hz is obtained, and the first
The voltage value of the arbitrary waveform used in the withstand voltage test for the first time gives a destruction effect equivalent to the destruction effect of the test voltage of the arbitrary waveform on the cable in which the water tree has deteriorated.
The above water tree is converted to an AC voltage value of 200 Hz and set to a voltage lower than the converted AC voltage value .
0.01H that can re-extend and destroy the electric tree generated from
A second withstand voltage test is performed using an alternating voltage of z to 200 Hz. (2) Partial discharge measurement is performed during the withstand voltage test of (1) above, and re-extension of the electrical tree by the second withstand voltage test is determined based on the presence or absence of partial discharge.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The method for determining the voltage used for the first withstanding voltage test is described in the above-mentioned Japanese Patent Application No. 8-58736. There are various selections of the test voltage value depending on the purpose, etc., but here, when using various waveform voltages that can destroy a water tree of any length as the test voltage, by performing the withstand voltage test. The range of the length of the water tree generated by the electrical tree was determined, and the voltage at which this electrical tree could be destroyed in the second withstand voltage test was determined. Then, a second withstand voltage test is performed using the voltage obtained as described above,
It was decided to confirm the occurrence of harmful electrical trees.
In the following examples, the case where an ultra-low frequency voltage of 0.1 Hz and an AC voltage are used as the voltage used for the second withstanding voltage test is shown. As you can see, 0.01Hz to 200H
An alternating voltage of z can be used.

In order to perform the withstand voltage test as described above, the length of the water tree, the voltage at which the water tree can be destroyed, the voltage generated by the water tree to the electric tree, and the electric tree generated from the water tree are determined. It is necessary to find the voltage that can be destroyed. Therefore, the above characteristics were investigated using a 33 kVCV cable. The insulation thickness of the cable is 8
mm. First, a sample cable having a water tree was created. Immerse the cable in 70 ° C warm water and
A high frequency voltage of kHz was applied to generate and extend a water tree.

Cables were taken out at various cumulative charging times, some of them were disassembled and investigated to measure the maximum water tree length, and the remaining cable samples were subjected to the following tests. (1) A destructive test was performed using an ultra low frequency voltage of 0.1 Hz, and the relationship between the water tree length and the ultra low frequency destructive voltage shown in FIG. 6 was obtained. (2) The relationship between the voltage generated by the electric trio and the water tree length was investigated by simulating the destruction by directly grounding during the application of the ultra low frequency voltage. Thereby, the relationship between the electrical tree generation voltage and the water tree length shown in FIG. 7 was obtained. (3) By using the accelerated deterioration cable in which the electrical tree generated voltage obtained in (2) is applied and grounded to generate the electrical tree from the water tree, the tree re-extension voltage of the ultra-low frequency voltage is applied. investigated. As a result, the voltage at which the electric tree generated from the water tree shown in FIG.

Here, according to the ultra-low voltage value to be applied,
It takes different time to extend the electric tree and reach the destruction. The curve 1 in FIG. 8 shows the case where destruction was reached after 10 minutes of the test time, and the curve 2 shows the curve where destruction was reached after the test time of 60 minutes. FIG. 9 is a summary of the above three test results for the ultra low frequency voltage. From FIG. 9, for example, the ultra-low frequency voltage required when screening a water tree having a length of 6 mm indicated by 1 is 71.5 kV. For example, when a margin of 1.1 is given to this, the withstand voltage test voltage is 78.
It becomes 6 kV. At this time, the electric tree caused by the destruction is generated in the water tree length shown by 2 or more.

The voltage which can destroy the electric tree generated from the water tree of this length is obtained at the point indicated by 3 in FIG. 9 and is 50.7 kV. If a margin of 1.1 is given to this, if breakdown occurs in the first withstand voltage test, 2
A test voltage of 55.8 kV is required for the fourth withstand voltage test. That is, after the withstanding voltage test of the ultra-low frequency voltage of 78.7 kV, regardless of the presence or absence of the breakdown, by applying the ultra-low frequency voltage of 55.8 kV and confirming the presence or absence of the destruction, the electric power generated in the cable line is confirmed. Since it is possible to determine whether or not a tree is generated, the withstand voltage test of the cable line becomes more reliable. If the time of the second withstand voltage test is set to 1 hour, the test voltage can be reduced. From FIG. 9, the test voltage for the second time is a value of 10 minutes.
It can be reduced from 0.7 kV with reference to 34.4 kV which is a 60-minute value. If a margin of 1.1 is given to this, the second withstand voltage test voltage becomes 37.8 kV.

FIG. 10 shows the relationship between the first test voltage of the ultra low frequency and the second test voltage obtained by the above method.
The curve 1 shows the case where the second withstand voltage test time is 10 minutes, and the curve 2 shows the case where the test time is 60 minutes. From the figure, the second test voltage differs depending on the withstand voltage test time. That is, the lower the withstand voltage test voltage of the second time, the longer the test time is required. Excessive test conditions are not suitable for practical use, so the withstand voltage test time is 60
If the number of minutes is set, the second withstand voltage test voltage is a voltage within the range indicated by the diagonal lines from the relationship between the initial ultra-low frequency test voltage and the ratio of the first and second test voltages shown in FIG. 11. In this case, the minimum value of the second withstand voltage test needs to be suppressed to about 40% of the initial test voltage. Further, it is appropriate that the maximum value of the second withstand voltage test is suppressed to about 85% in consideration of the variation in the breakdown voltage of the initial test voltage. It is known that the initial low frequency breakdown voltage does not change in the test time of 10 minutes to 60 minutes.

From the above, it can be said that it is desirable to determine the second test voltage with 40 to 85% of the initial ultra-low frequency test voltage as a guide. In addition, for example, by performing partial discharge measurement during the second withstand voltage test, partial discharge caused by re-extension of the electrical tree is observed, and the accuracy of determining whether or not the electrical tree is generated is improved. Above, 33
An example of applying a very low frequency voltage to the kVCV cable (insulation thickness 8 mm) for the first withstanding voltage test was shown, but even when various waveforms were used, as described above, the voltage value was changed to the very low frequency voltage or If converted into AC voltage, the ultra low frequency voltage and AC voltage to be applied in the second withstanding voltage test can be determined.

Although the test voltage changes when the cable insulation thickness changes, even in this case, a voltage lower than the infra-low frequency voltage that gives the same destruction effect as the voltage used in the first withstand voltage test is applied to the second withstand voltage. It has been separately confirmed that the electrical tree generated in the cable can be discriminated and removed by using it as a test. According to the following examples, the first withstand voltage test is performed on cables having various voltage waveforms and different insulation thicknesses, and then the second withstand voltage test is performed using the present invention to confirm the presence or absence of electrical tree generation. Indicates that it was possible.

[0023]

Example 1 A 100 m warm water accelerated deterioration cable having a maximum water tree length of about 6 mm was prepared. This cable has a damped vibration wave of 65kV / 1 time and an ultra low frequency voltage of 60kV
When a withstand voltage test was performed for 60 minutes, it was broken 3 minutes and 10 seconds after the application of the ultra low frequency voltage. Divided into two cables by removing the breaking point after disruption, newly the <br/> provided, respectively it terminal breaking point side and ready to be re-voltage application. The damping vibration wave of 65 kV corresponds to an ultra-low frequency of 62.2 kV from FIG. When an extremely low frequency voltage of 50 kV within the shaded area in FIG. 11 was applied to these two cables, the first cable withstood 60 minutes, but the second cable broke after 5 minutes and 20 seconds.

As a result, no electric tree was generated in the first cable, and the second cable was damaged by a damped vibration wave of 65 kV / 1 time and an ultralow frequency voltage of 60 kV / 60 minutes during a withstand voltage test. , Suggests that an electrical tree was occurring. Upon disassembling and investigating the first cable over the entire length, a water tree was present, but no electrical tree was found.

[0025]

Example 2 A water tree-deteriorated cable similar to the cable shown in Example 1 was prepared for 100 m. When an extremely low frequency voltage of 75 kV was applied to this cable while performing partial discharge measurement, it was destroyed at the same time as the partial discharge occurred after 5 minutes and 30 seconds. After breaking, the breaking point was removed, the cable was divided into two, and new terminals were provided on the breaking point side. These two
To the cable of the book, the ultra low frequency voltage 5 read from Fig. 11
When 0 kV was applied while measuring partial discharge, the first one withstood 60 minutes without partial discharge, but the second one caused partial discharge immediately after application, resulting in discharge charge amount and generation. The frequency increased and finally it was destroyed after 35 minutes and 20 seconds.

Furthermore, the breaking point of the broken second cable was removed and the cable was cut into two, and one of them was charged again while measuring a partial discharge at an ultra low frequency voltage of 50 kV. Partial discharge occurred. Before the cable was broken, the test was terminated after the electricity was applied for 10 minutes, and the cable was disassembled to find one location where an electrical tree was found in the water tree. From this, even if the harmful electric tree was not destroyed, the presence of the harmful electric tree was found by measuring the partial discharge during the withstand voltage test, and the withstand voltage test was performed with the electric tree left. You can avoid the risk of ending. Therefore, the partial discharge measurement during the withstand voltage test is a procedure for more highly sensitively determining the presence or absence of the electrical tree.

[0027]

Example 3 A water tree-deteriorated cable similar to that shown in Example 1 was prepared for 100 m. DC1 on this cable
When a withstand voltage test of 00 kV / 10 minutes was performed, a test time of 10 minutes was endured. The ultra low frequency voltage having the same destruction effect as DC 100 kV is 68.4 kV from FIG. Therefore, a withstand voltage test of ultra-low frequency of 55 kV / 60 minutes was performed on this cable, and a test time of 60 minutes was endured. After disassembling and investigating this cable over the entire length,
We could not find the part where the electrical tree was generated from the water tree.

[0028]

[Example 4] CV cable of 77 kV (insulation thickness 13 m
In m), a water tree was generated by a high frequency accelerated deterioration test. While performing partial discharge measurement on this cable,
When a withstand voltage test of 70 kV / 10 minutes was performed, it was 3 minutes 2
Partial discharge occurred after 0 seconds. At this point, the test was interrupted and the voltage dropped. This partial discharge is considered to be due to the electric tree generated from the water tree. This AC 70kV
The ultra-low frequency voltage that has the same destruction effect as
It is 72 kV. Therefore, as the second withstand voltage test,
Ultra low frequency 12 which is 0.7 times the voltage of the above ultra low frequency
0 kV was used. As a result, it was destroyed after 8 minutes and 50 seconds.

[0029]

Example 5 A water tree-degraded cable similar to that of Example 4 was subjected to a withstand voltage test at an ultralow frequency of 160 kV / 60 minutes, and as a result, breakdown occurred after 13 minutes. Remove the destroyed part, 2
The cable divided into the books was subjected to a withstand voltage test of 120 kV / 60 minutes at an ultra-low frequency as a second withstand voltage test, and it withstood the test for 60 minutes. The AC voltage that has the same destruction effect as the ultra-low frequency of 160 kV is 6
This corresponds to 4.8 kV. Therefore, when the other cable was subjected to a withstand voltage test of AC 45 kV / 60 minutes as a second withstand voltage test, it withstood the test for 60 minutes.
Upon disassembling and investigating these two cables, no part of the electrical tree was generated from the water tree.

[0030]

Example 6 A water tree-deteriorated cable similar to that shown in Example 1 was prepared for 100 m. DC1 on this cable
When a withstand voltage test of 00 kV / 10 minutes was performed, it was 4 minutes 1
Failure occurred after 0 seconds. The broken part of this cable was removed, a new joint was provided, and a sound cable was inserted. The AC voltage having the same destruction effect as DC 100 kV corresponds to AC 27.7 kV as shown in FIG. Therefore, as a second withstand voltage test for a cable in which a new healthy cable is inserted, AC20kV /
A withstand voltage test of 60 minutes was performed. As a result, after 5 minutes and 30 seconds, it was destroyed in a portion other than the newly inserted sound portion. Upon disassembling and investigating this cable over the entire length, there was no part where an electrical tree was generated in the newly inserted healthy cable, but there were 3 points where an electrical tree was generated in the parts other than the healthy cable. It turns out that there is.

As described above, from the results of Examples 1 to 6, the voltage used in the first withstand voltage test was converted into an ultra-low frequency voltage or an AC voltage having a destruction effect equivalent to the voltage, and the converted voltage was used. 2 using low infrasound voltage or AC voltage
By conducting the second withstand voltage test, it was confirmed that the presence or absence of harmful electrical trees caused by the first withstand voltage test can be determined from the presence or absence of cable breakage in the second withstand voltage test.

[0032]

As described above, by using the withstand voltage test method of the present invention, it is possible to determine whether or not a harmful electric tree is generated due to the withstand voltage test. For this reason, the reliability of the unbroken cable part is secured,
It becomes possible to make a decision to use it again.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a line form of a cable for performing a withstand voltage test.

FIG. 2 is a diagram showing a state in which a breaking point is removed and a sound cable is newly inserted.

FIG. 3 is a diagram showing a state in which a breaking point is removed and a new terminal is provided.

FIG. 4 is a diagram showing a relationship between a water tree breakdown voltage and an ultra-low frequency breakdown voltage of various waveforms.

FIG. 5 is a diagram showing the relationship between water tree breakdown voltage and AC breakdown voltage of various waveforms.

FIG. 6 is a diagram showing a relationship between a water tree length and an ultralow frequency breakdown voltage.

FIG. 7 is a diagram showing a relationship between a water tree length and an electric tree generation voltage.

FIG. 8 illustrates a very low frequency voltage capable of re-extending an electrical tree.

FIG. 9 is a diagram showing a relationship between a withstand voltage test voltage and an extremely low frequency voltage capable of re-extending an electric tree.

FIG. 10 is a diagram showing a relationship between a withstand voltage test voltage at an initial ultra-low frequency and an ultra-low frequency test voltage in a second withstand voltage test.

FIG. 11 is a diagram showing a ratio of an initial ultra low frequency test voltage and a second ultra low frequency test voltage.

[Explanation of symbols]

1 aerial terminal 2 joint 3 cables 3'healthy cable 4 Aerial terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Sakakibara Hiroyuki Sakaki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Hidero Tanaka 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Industry Co., Ltd. (56) Reference JP-A-2-105070 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 31/12-31/20

Claims (2)

(57) [Claims] 1. A withstand voltage test with an arbitrary waveform voltage is performed to determine the presence or absence of a harmful water tree present in a rubber or plastic insulated cable or cable line that has deteriorated in a water tree. In order to determine the presence or absence of an electrical tree, a second withstand voltage test is performed using an alternating voltage of 0.01 Hz to 200 Hz, and a withstand voltage test is performed to determine the presence or absence of an electrical tree based on the presence or absence of cable breakage due to the withstand voltage test. Method using a sample cable with a water tree in advance
The test voltage is the voltage that can destroy a water tree of
Conduct a voltage test to determine the water tree length generated by the electrical tree.
Find the range and re-stretch the electrical tree that originated from this water tree.
AC voltage of 0.01Hz to 200Hz that can be spread and destroyed
Then, the voltage value of the arbitrary waveform used in the first withstand voltage test is applied to give a destruction effect equivalent to the destruction effect of the test voltage of the arbitrary waveform on the water tree-degraded cable.
Converted to an AC voltage value of 01 Hz to 200 Hz, the second withstand voltage test was generated from the water tree set to a voltage lower than the converted AC voltage value .
0.01Hz ~ 20 that can re-stretch and destroy the electric tree
Rubber characterized by being performed using an AC voltage of 0 Hz
Withstand voltage test method for plastic insulated power cables. 2. A rubber / plastic insulation characterized by performing partial discharge measurement during the withstand voltage test according to claim 1 and determining the re-extension of the electrical tree by the second withstand voltage test from the presence or absence of partial discharge occurrence. Withstand voltage test method for power cables.