JP2001099884A - Method for diagnosing cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for diagnosing deterioration of insulator of a high voltage cable accurately in which a CV cable of 22 kV or below can be diagnosed with high accuracy even under a noisy environment. SOLUTION: In a method for diagnosing a power cable where a micro DC current flowing through an insulator 24 is measured by means of a measuring unit 28 while applying a DC voltage and/or an AC voltage to a CV cable 21 and then deterioration of the insulator 24 is diagnosed based on the measurements, an ultrasonic wave generator 34 transmits an ultrasonic wave through the insulator 24 in order to increase the micro DC current thus enhancing detection accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for diagnosing a power cable, and more particularly to a method for diagnosing a power cable capable of accurately diagnosing the state of deterioration of an insulator.

[0002]

2. Description of the Related Art Deterioration of an insulator of a cross-linked polyethylene insulated power cable (hereinafter referred to as CV cable) is caused by a water tree phenomenon that grows from an inner semiconductive layer and an outer semiconductive layer toward the insulator, and causes a low voltage. In case of CV cable,
The water tree grows close to penetrating the insulator.

[0003] As a method of diagnosing the state of deterioration of the insulator due to the water tree, an AC or DC voltage is applied to a cable, or an AC voltage is applied under a DC bias, whereby a minute current flowing through the insulator is obtained. There is known a method of diagnosing the state of deterioration of an insulator by detecting the DC component of the insulator. In particular, in a CV cable of 6.6 kV or less, since the water tree grows so as to substantially penetrate the insulator, it is easy to catch a DC component, and this method is utilized as a suitable diagnostic method.

[0004] Further, even in a 22 kV class CV cable, the water tree grows to a state close to that of a 6.6 kVC cable even if it does not reach the penetration level. Can detect the DC component of the minute current flowing through
The deterioration state of the V cable can be diagnosed in a non-destructive state.

[0005]

However, according to the conventional power cable diagnosis method, it is difficult to diagnose insulation deterioration when a CV cable of 66 kV or more is targeted. The reason for this is that, because of the high working voltage, dielectric breakdown occurs before the water tree grows until it is suitable for diagnosis, and the level of the minute current based on the water tree before the dielectric breakdown occurs is low. It is difficult to catch.

Further, in the case of a high-voltage CV cable, three layers of an inner semiconductive layer, an insulator, and an outer semiconductive layer are usually formed by simultaneous extrusion, and foreign matter mixing into the insulator is controlled. Is strict, the behavior of the water tree is different from the case of 6.6 kV or less, which also makes it difficult to grasp the minute current.

[0007] Even in the case of a CV cable of 22 kV or less, the detected DC component is very small. Therefore, in an environment where external noise is small, it is possible to diagnose the deterioration of the insulator with high accuracy. When measurement is performed in an environment, diagnosis may be affected by noise.

Accordingly, it is an object of the present invention to provide a method for accurately diagnosing the state of deterioration of an insulator even when a high-voltage cable is used, and to provide a diagnostic method even in a noisy environment.
An object of the present invention is to provide a power cable diagnostic method capable of diagnosing the deterioration of the insulator of a CV cable of 2 kV or less with high accuracy.

[0009]

In order to achieve the above object, the present invention provides a method of diagnosing the progress of deterioration of an insulator such as cross-linked polyethylene of a power cable. A diagnostic state is set by propagating ultrasonic waves to the insulator in a state where a voltage or an AC voltage is applied, or in a state where a DC voltage is superimposed under the application of an AC voltage, and flows to the insulator in the diagnostic state. It is an object of the present invention to provide a method of diagnosing a power cable, characterized in that a state of deterioration of the insulator is diagnosed by measuring a minute DC current.

The inventors have repeated many trials and errors before establishing the above-mentioned diagnostic method. As a result, in the measurement of the DC component current flowing through the insulator in the AC charging state where the DC is biased to the power cable, when the ultrasonic wave is propagated through the insulator, the DC component current varies depending on the progress of the deterioration of the insulator. Is found to increase.

[0011] This is because when water tree is generated in the cable insulator and deterioration is progressing, a large amount of electron or ionic charge is present in the water tree, and when ultrasonic waves act on this, It is based on the phenomenon that a large amount of current flows in the tree part, and it has been confirmed that this phenomenon also occurs when DC voltage is applied to the cable and when AC voltage is applied to the cable. Have been.

In the measurement of the minute electric current, it is preferable to peel off the sheath of the power cable and use the exposed metal shielding layer as an electrode for measurement.
In this case, the measuring electrode is formed by stripping the sheath and the metal shielding layer at predetermined two places of the power cable, thereby forming a metal shielding layer left between the two stripped parts. Is practical.

[0013]

Next, an embodiment of a method for diagnosing a power cable according to the present invention will be described. FIG. 1 schematically shows an embodiment of the present invention. Reference numeral 1 denotes a CV to be diagnosed in which a conductor, an inner semiconductive layer, an outer semiconductive layer, a metal shielding layer, and a sheath are omitted. Cable 2 indicates its insulator. The insulator 2 contains an outer semiconductive layer water tree indicated by A, an inner semiconductive layer water tree indicated by B, and a bow titlery indicated by C.

The shield layer side D of the CV cable 1 is grounded, and the conductor side E is configured so that an AC voltage from the power transformer 3 and a DC voltage from the bias DC power supply 4 are applied. ing. Reference numeral 5 denotes an ultrasonic generator for applying ultrasonic waves to the insulator 2 of the CV cable 1, and reference numeral 6 denotes an ultrasonic wave propagating liquid unit for transmitting ultrasonic waves.

7 is a DC component measuring instrument incorporated in the measuring circuit, 8 is a blocking coil for measurement, 9 is a bypass capacitor for measurement, 10 is a blocking coil incorporated in a bias circuit, and 11 is a bypass capacitor for bias. , 12 indicate grounding.

In FIG. 1 having the above circuit configuration,
An AC voltage and a DC voltage are applied to the CV cable 1 from the transformer for voltage application 3 and the DC power supply 4 for bias.
A minute current generated in the insulator 2 of the cable 1 is detected by the DC component measuring device 7. In this circuit, the ultrasonic wave is transmitted from the ultrasonic generator 5 to the insulator 2, and the DC component at that time is detected by the measuring device 7 so that the effect of the ultrasonic wave propagation can be confirmed. Have been.

Table 1 shows the measurement results of the DC components based on the circuit configuration of FIG. As a CV cable to be measured,
Using three types of 22kV cables with different degrees of degradation,
AC applied voltage is 12.7 kV, DC bias voltage is 1 k
V, and the oscillation from the ultrasonic generator 6 is set to 36
kHz and 900W.

[0018]

[Table 1]

According to Table 1, CV with large water tree deterioration
In the case of the first embodiment for the cable, the DC component when the AC voltage is applied shows only one digit increase when the DC bias voltage is superimposed. Becomes significantly more pronounced, showing an order of magnitude increase. Also, in the case of the embodiment 2 in which the water tree deterioration is moderate, the DC component showing only a slight increase when the AC is applied and the DC bias is increased by one digit when the ultrasonic wave is applied.

On the other hand, on the other hand, C without deterioration of water tree
In the case of Comparative Example 1 targeting a V cable, there is no difference in the DC component between AC application, AC application / DC bias, and when ultrasonic waves are applied to these, and
Based on the above results, it is possible to accurately diagnose the progress of insulation deterioration of the CV cable. Note that a large increase effect by the ultrasonic wave means that it can be distinguished from noise.

FIG. 2 shows an application example. Reference numeral 21 denotes a CV cable, and an inner semiconductive layer 23 and an insulator 2
4. External semiconductive layer 25, metal shielding layer 26 and sheath 2
7 are formed in order. The metal shielding layer 26 and the sheath 27 are peeled off at predetermined locations F and G, thereby leaving the metal shielding layer 26 ′ in an isolated form between F and G.

Reference numeral 28 denotes a DC component measuring device connected to the metal shielding layer 26 ', and the metal shielding layer 26' is used as an electrode for measurement by this connection. Reference numeral 29 denotes a transformer for applying an AC voltage to the conductor 22, 30 denotes a bias DC power supply for applying a DC voltage, 31 denotes a blocking coil thereof, 32 denotes a bypass capacitor, and 33 denotes a ground.

Reference numeral 34 denotes an ultrasonic generator for applying ultrasonic waves to the CV cable 21, and reference numeral 35 denotes a liquid portion for transmitting ultrasonic waves. In this example, the operation is basically the same as that of FIG. 1 except that the direct current component measuring device 28 is connected to the metal shielding layer 26 ′ in connection with the conductor.

Table 2 shows that the CV cable 21 has a voltage of 22 kV.
Using a cable, an AC applied voltage of 12.7 kV, a DC bypass voltage of 1 kV, and an ultrasonic wave of 36 kHz · 9
FIG. 3 shows a measurement result of a DC component current performed based on FIG. 2 at a setting of 00 W.

[0025]

[Table 2]

According to Table 2, the case of Example 3 in which a cable having a large water tree deterioration was tested showed an order of magnitude higher when ultrasonic waves were applied than when AC was applied and AC was applied and DC was bypassed. In the case of Example 4 in which the increase of the DC component is observed and the deterioration of the water tree is moderate, a remarkable effect is similarly exhibited at different levels.

On the other hand, in the case of Comparative Example 2 in which a cable having no water tree deterioration was tested, on the other hand, the difference in the detected DC component between the time when AC was applied, the time when DC bias was applied to the cable, and the time when the ultrasonic wave acted was observed. However, based on the above results, it is possible to accurately diagnose the state of insulation deterioration of the CV cable 21 with high sensitivity.

Table 3 shows that the power supply 3 is connected to the CV cable 21 shown in FIG.
A DC voltage of 0 to 1 kV is applied.
In the method of measuring the leakage current flowing through the insulator 2 using the DC component measuring device 28,
This shows the effect when ultrasonic waves of 6 kHz and 900 W are applied. In addition, as the CV cable 21,
The 22 kV · CV cable used in each example of Table 2 was used.

[0029]

[Table 3]

According to Table 3, in Example 5 in which the water tree deterioration of the insulator was large, the detection current, which was small when only the DC voltage was applied, increased by one digit by applying ultrasonic waves. Also, in the case of Example 6 in which the water tree deterioration is moderate, the result is quadrupled.

On the other hand, Comparative Example 3 without water tree deterioration
In the case of (1), even if the ultrasonic wave is applied, the detected leakage current does not increase. Therefore, based on the above result, it is possible to easily diagnose the state of deterioration of the CV cable. In the case of a CV cable of 6.6 kV class or less, a similar effect can be obtained by applying an ultrasonic wave under the application of an AC voltage.

[0032]

As described above, according to the method for diagnosing a power cable according to the present invention, a minute DC current which is a reference for diagnosis is increased by transmitting ultrasonic waves to a power cable to be diagnosed. An accurate diagnosis can be performed by improving the S / N ratio.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a power cable diagnosis method according to the present invention.

FIG. 2 is an explanatory diagram showing an application example of the power cable diagnostic method according to the present invention.

[Explanation of symbols]

 1,21 CV cable 2,24 Insulator 3,29 Power transformer 4,30 Bypass DC power supply 5,34 Ultrasonic generator 6,35 Ultrasonic wave propagating liquid part 7,28 DC component measuring device 8 Blocking coil (For measurement) 9 bypass capacitor (for measurement) 10, 31 blocking coil (for bias) 11, 32 bypass capacitor (for bias) 12, 33 ground 22 conductor 23 internal semiconductive layer 25 external semiconductive layer 26, 26 'metal Shielding layer 27 sheath

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshimichi Murata 5-1-1, Hidaka-cho, Hitachi City, Ibaraki F-term in Power Systems Research Laboratory, Hitachi Cable, Ltd. 2G015 AA27 CA05 CA06 CA20

Claims (3)

[Claims] 1. A method of diagnosing a power cable for diagnosing the progress of deterioration of an insulator such as cross-linked polyethylene of a power cable, the method comprising: applying a DC voltage or an AC voltage to the power cable; In a state where a DC voltage is superimposed on the insulator, a diagnostic state is set by propagating ultrasonic waves to the insulator, and a minute DC current flowing through the insulator is measured in the diagnostic state to determine the deterioration state of the insulator. A method for diagnosing a power cable, comprising diagnosing the power cable. 2. The diagnosis of a power cable according to claim 1, wherein the measurement of the minute DC current uses a metal shielding layer which is exposed by stripping a sheath of the power cable as a measurement electrode. Method. 3. The measurement of the minute DC current includes forming a stripped portion by stripping a sheath and a metal shielding layer at predetermined two locations of the power cable, and forming a stripped portion between the two stripped portions. The method for diagnosing a power cable according to claim 1, wherein the remaining metal shielding layer is used as an electrode for measurement.