JP3832339B2 - Power cable life estimation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for estimating the life of a power cable, and more particularly, to a method for estimating the life of a power cable that does not cause dielectric breakdown of a severely deteriorated cable and can reliably perform life estimation.
[0002]
[Prior art]
It is known that power cables (hereinafter referred to as CV cables) having crosslinked polyethylene as an insulator cause insulation deterioration due to the generation of bow-tie water trees due to long-term use in a humid atmosphere. As a diagnostic method for detecting the degree, a withstand voltage test and a degradation signal detection test are known.
[0003]
The former method performs a dielectric breakdown test by applying to a cable a commercial frequency voltage set to a predetermined peak value higher than the operating voltage, or a DC voltage or ultra-low frequency voltage with an alternative voltage waveform. The test results are highly reliable and meaningful in terms of preventing a severely deteriorated cable line from causing a breakdown accident during operation.
[0004]
On the other hand, the latter method detects a signal caused by deterioration caused by voltage application from a cable and determines the degree of deterioration based on the magnitude of the detected deterioration signal, and is characterized by a nondestructive test. Yes.
[0005]
[Problems to be solved by the invention]
However, according to the conventional cable life estimation method based on these deterioration diagnoses, in the case of life estimation that depends on the withstand voltage test, it is assumed that the target cable is If it is severely deteriorated with a remaining life of 2 years, it has the problem of causing dielectric breakdown of the cable that can be used for 2 years. On the other hand, if the life is estimated depending on the deterioration signal detection test, it is generated. When the water tree length is small compared to the thickness of the insulator, there is a problem that it is difficult to estimate the life due to the weak degradation signal.
[0006]
Accordingly, an object of the present invention is to provide a method for estimating the life of a power cable that does not cause dielectric breakdown of a severely deteriorated cable and can reliably perform life estimation.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention diagnoses the degree of deterioration of a power cable and estimates the remaining life of the power cable from the diagnosis result.
A combination of a withstand voltage test for applying a predetermined level of voltage to the power cable to check for dielectric breakdown and a degradation signal detection test for detecting a degradation signal when a voltage is applied to the power cable. Before the execution of the voltage test, the deterioration signal detection test with a voltage lower than the predetermined level voltage is performed,
When a clear detection signal due to deterioration is confirmed in the deterioration signal detection test performed, the life of the power cable is estimated based on the confirmed detection signal,
Provided is a method for estimating the life of a power cable, wherein when a clear detection signal due to deterioration is not confirmed in the deterioration signal detection test, the life of the power cable is estimated by performing the withstand voltage test. is there.
[0008]
As a voltage waveform applied to the withstand voltage test, a commercial frequency voltage, an AC voltage having a frequency close to the commercial frequency, or an ultra-low frequency voltage is preferable. Therefore, it is preferable to apply the loss current method in which the loss current is measured in a state where an alternating voltage is applied and the degree of deterioration is determined based on the magnitude of the loss current.
[0009]
In the present invention, the voltage applied to the withstand voltage test is preferably a commercial frequency voltage, an AC voltage having a frequency close to the commercial frequency, or an ultra-low frequency voltage. In view of the meaning, application of the loss current method is preferable.
[0010]
The combination of these voltages and methods makes it possible to increase the voltage to the withstand voltage test level in the form of taking over the applied voltage for the deterioration signal detection test, so that the performance of the work becomes efficient. Note that it is preferable to step up the voltage for the withstand voltage test step by step in order to avoid dielectric breakdown when the test cable is severely deteriorated.
[0011]
In addition, as a specific detection circuit for the loss current method, the detection circuit shown in IEEJ Technical Report 668 “Special High Voltage CV Cable Insulation Degradation State and Trend of Insulation Diagnosis Technology” is preferable, and withstand voltage test Examples of other deterioration signal detection tests that can be used in combination with the DC component method or the DC bias method.
By using the present invention, it is possible to check the soundness of the intermediate connection part or the terminal connection part of the cable line or the damage of the cable by partial discharge.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a power cable life estimation method according to the present invention will be described.
First, a withstand voltage test, which is one test used in the present invention, will be described.
Fig. 1 shows the relationship between breakdown voltage and water tree, which is the basis of the establishment, and the length of the bow-tie water tree at a commercial frequency voltage (50 Hz) using a 66 kVCV cable used for a long time on a real line as a test sample. It shows the relationship with the dielectric breakdown value.
[0013]
According to this figure, it is shown that the breakdown voltage of a CV cable subjected to water tree degradation is related to the length of the water tree, and the breakdown voltage decreases as the water tree becomes longer. In addition, when the length of the bow-tie water tree of this cable used for 23 years was investigated, the maximum length was 3030 μm, and therefore the growth rate was confirmed to be about 200 μm / year at the fastest. .
[0014]
Based on the above results, for example, assuming that a voltage for a withstand voltage test to be performed to determine the remaining life of 5 years is set to 50 kV, and this is applied to the curve of FIG. The length of the water tree that causes dielectric breakdown at a voltage of 50 kV is 3300 μm.
[0015]
On the other hand, assuming that the operation of the CV cable having a water tree having a length of 3300 μm is continued under a voltage of 40 kV and the water tree continues to grow until breakdown, the water tree length at the time of breakdown is as shown in FIG. According to this, it is 4300 μm.
[0016]
Therefore, what can be said from the above is that if the cable has a water tree length of less than 3300 μm and can withstand a test voltage of 50 kV, the water tree can be used for 5 years at an operating voltage of 40 kV based on the growth rate of the water tree. The tree length will never be 4300 μm, so it can be said that this cable cannot break down within 5 years.
[0017]
The above is the background to the establishment of the withstand voltage test, and the test is performed based on the prediction of the water tree length based on the data and the setting of the applied voltage corresponding to this prediction. Lifetime is guaranteed.
[0018]
FIG. 2 shows a degradation signal detection test which is the other test. (A) is an example of a measured waveform of an applied voltage and a detection signal (degraded signal), and (b) is a loss applied to this measurement. The detection circuit in the current method (disclosed circuit in the aforementioned IEEJ technical report) is shown.
The waveform of the detection signal (a) is for a CV cable that has undergone severe water tree degradation, and the degradation state clearly appears. Therefore, when the waveform reaches this level, the degree of deterioration can be easily recognized.
[0019]
In this embodiment, a deterioration signal detection test using a voltage lower than the withstand voltage test is first performed among the above two tests. In this test, if a clear detection signal due to deterioration is confirmed as shown in FIG. 2A, the test ends at that point, and the applied voltage is released and the cable life is estimated based on the magnitude of the detection signal. Is done.
[0020]
On the other hand, in the degradation signal detection test, if a clear detection signal suitable for life estimation is not confirmed, a withstand voltage test with a predetermined voltage is continued, and the remaining life is guaranteed based on the results. Is done. At this time, since it has already been confirmed that the test cable is not severely deteriorated by the execution of the deterioration signal detection test, the probability of dielectric breakdown due to the execution of the withstand voltage test is greatly reduced.
[0021]
According to the life estimation method performed as described above, since the deterioration signal detection test is performed before the withstand voltage test, the severely deteriorated cable is captured at the stage of the deterioration signal detection test which is a nondestructive test. Therefore, it is possible to prevent dielectric breakdown of severely deteriorated cables due to withstand voltage tests that had been scattered in the past, and it is difficult to estimate the life based on weak detection signals when relying only on the deterioration signal detection test. This can be effectively eliminated.
According to this method, since the cable life is estimated based on either a clear deterioration signal detection in the deterioration signal detection test and a withstand voltage test, it is possible to perform highly reliable life estimation. Become.
[0022]
【The invention's effect】
As described above, according to the power cable life estimation method according to the present invention, the withstand voltage test and the deterioration signal detection test are used in combination, and the deterioration signal detection with a lower voltage than the withstand voltage test is performed before the withstand voltage test. When a test is performed and a clear detection signal due to deterioration is confirmed in this test, the life is estimated based on the confirmed detection signal, while a clear detection signal due to deterioration is not confirmed in the deterioration signal detection test. Since the withstand voltage test is performed with a predetermined voltage, it is possible to prevent dielectric breakdown of a severely deteriorated cable due to a withstand voltage test as in the prior art.
[0023]
In addition, life estimation is performed based on either a degradation signal detection test when a clear detection signal indicating degradation is confirmed, or a withstand voltage test that has certain characteristics in the test results, so the lifetime is highly accurate. An estimation result can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a relationship between a dielectric breakdown voltage and a water tree length in a withstand voltage test of a CV cable.
FIGS. 2A and 2B are explanatory diagrams of a deterioration signal detection test of a CV cable, in which FIG. 2A is an example of a measured waveform of an applied voltage and a detection signal in a loss current, and FIG. 2B is a loss current applied to the waveform measurement of FIG. The detection circuit of the method is shown.

Claims (4)

In the power cable life estimation method of diagnosing the degree of deterioration of the power cable and estimating the remaining life of the power cable from the diagnosis result,
A combination of a withstand voltage test for confirming the presence or absence of dielectric breakdown by applying a predetermined level of voltage to the power cable and a degradation signal detection test for detecting a degradation signal when a voltage is applied to the power cable. Before the execution of the voltage test, the deterioration signal detection test with a voltage lower than the predetermined level voltage is performed,
When a clear detection signal due to deterioration is confirmed in the deterioration signal detection test performed, the life of the power cable is estimated based on the confirmed detection signal,
A deterioration diagnosis method for a power cable, wherein when a clear detection signal due to deterioration is not confirmed in the deterioration signal detection test, a life of the power cable is estimated by performing the withstand voltage test. The step of the withstand voltage test is performed by using a commercial frequency voltage, an AC voltage having a frequency close to the commercial frequency, or a very low frequency voltage as the voltage of the predetermined level. The method for estimating the life of a power cable according to item 1. The step of the degradation signal detection test is performed based on a loss current method in order to match the commercial frequency voltage in the withstand voltage test, an AC voltage having a frequency close to the commercial frequency, or an ultra-low frequency voltage. The method for estimating the life of a power cable according to claim 2. 4. The life estimation of a power cable according to claim 3, wherein the step of the withstand voltage test is performed under a step-up to the voltage of the predetermined level that has succeeded the applied voltage in the deterioration signal detection test. Method.

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