JPH07280877A - Method for detecting defect at joint of rubber-plastic insulated power cable - Google Patents

Abstract

PURPOSE:To provide a method for detecting a defect, among others, a delamination between layers at a joint of a power cable with high sensitivity. CONSTITUTION:Conductors 1, 1 of two rubber-plastic insulated power cables A1, A2 are interconnected and an inner semiconductive layer 2', a reinforcing insulator layer 3', and an outer semiconductive layer 4' are formed on the outer periphery of the connected conductors thus jointing the power cables. In order to detect a defect at such joint B, the joint B is heated at 50 deg.C or above for a predetermined time and a partial discharge at the joint B is measured while applying a voltage to the conductors 1, 1. An X-ray image at the joint B may be picked up after the thermal processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defect in a connection portion of a rubber / plastic insulated power cable, and more particularly, it is possible to easily and surely detect even a minute defect existing in the connection portion. Regarding the method of detecting.

[0002]

2. Description of the Related Art A rubber / plastic insulated power cable (hereinafter referred to as a power cable) A, which has been widely used for high voltage power transmission, is usually constructed on the basis of a sectional structure as shown in FIG. That is, a cable core is formed by forming the inner semiconductive layer 2, the insulator layer 3, and the outer semiconductive layer 4 on the outer circumference of the conductor 1 in this order, and further, the outer circumference of the outer semiconductive layer 4 is covered with a metal shielding layer. 5 and the outer periphery of the metal shielding layer 5 is covered with a sheath layer 6 to form a protective layer.

The above-mentioned inner semi-conductive layer 2, insulator layer 3, and outer semi-conductive layer 4 are extruded and coated with a resin composition based on an olefin resin containing a cross-linking agent and then the whole. It is formed by crosslinking the base resin by pressurizing and heating. If necessary, after forming the outer semiconductive layer 4, a semiconductive cloth tape may be further wound around the outer periphery of the outer semiconductive layer 4 and then covered with the metal shielding layer 5, or the outer periphery of the metal shielding layer 5 may be covered. It is also practiced to wind the holding tape around and fix the metal shielding layer.

The interconnection of the power cable A having such a cross-sectional structure is usually performed as follows. Figure 3
Will be explained. First, the connection terminals of the _two power cables A ₁ and A ₂ to be connected are processed to form the conductor 1, the inner semiconductive layer 2, the insulator layer 3, the outer semiconductive layer 4, and the metal shielding layer 5. The outer peripheral surface of each is exposed. And
The conductors 1, 1 are connected and fixed by abutting the end faces of the conductors 1, ₁ of the power cables A ₁ , A ₂ against each other and crimping the outside of the abutted portion with a sleeve 7.

Then, an inner semiconductive layer 2'is formed outside the connecting portion of the conductor so as to cover the exposed outer peripheral surfaces of the inner semiconductive layers 2 and 2 of the power cables A ₁ and A ₂ , respectively. On the outside of the inner semiconductive layer 2 ′, a reinforcing insulating layer 3 ′ is formed so as to cover the exposed outer peripheral surfaces of the insulating layers 3 and 3 of the power cables A ₁ and A ₂ , and the reinforcing layer 3 ′ is further reinforced. Insulator layer 3 '
An outer semiconductive layer 4 ′ is sequentially formed on the outer side of the power cables A ₁ and A ₂ so as to cover the exposed outer peripheral surfaces of the outer semiconductive layers 4 and 4.

Then, on the outside of the outer semiconductive layer 4 ',
The metal shield layer 5 ′ is formed so as to cover the exposed outer peripheral surfaces of the metal shield layers 5 and 5 of the power cables A ₁ and A ₂ , and the connection portion B shown in FIG. 3 is formed. The reinforcing insulator layer 3'in the connection portion B is formed by the tape molding method or the extrusion molding method, respectively.
The former tape molding method is a method of winding an insulating tape having a predetermined characteristic and pressurizing and heating the wound layer to form each layer, and the latter extrusion molding method is a method of connecting at the time of forming the reinforcing insulator layer. A method of arranging a predetermined mold outside the part, injecting an electrically insulating resin composition into the mold, and pressurizing and heating the resin composition to crosslink to form a target layer Is.

The inner semiconductive layer and the outer semiconductive layer are usually formed by using a semiconductive heat-shrinkable tube or winding a semiconductive tape. However, the following problems are likely to occur at the time of forming the connecting portion B described above.
For example, foreign matter such as fibers or metals may be mixed in from the outside or a void may be generated due to some reason at the time of forming each layer, particularly the reinforcing insulating layer 3 ′. In addition, adhesion failure may occur between the layers of the connecting portion B or between the layers and the outer peripheral surfaces of the corresponding layers of the power cables A ₁ and A ₂ . In particular, when the reinforcing insulator layer is formed by the tape molding method, adhesion failure may occur even between the winding layers of the tape. Furthermore, an internal semiconductive layer in the connection portion B,
Small protrusions may occur on the surfaces of the outer semiconductive layers 2'and 4 '.

If the above-mentioned defects occur in the connecting portion B, the dielectric breakdown of the connecting portion B progresses at the starting point of these defects when the line is operated after the connection. Therefore, at the time of forming the connecting portion B, the work of forming each layer is carefully and thoroughly standardized so as not to cause the above defects. At the same time, a detection operation for checking the presence or absence of a defect is performed on the connection portion B after the connection is completed.

Conventionally, as a method of detecting the above-mentioned defects,
For example, a method of deciding the presence / absence of a defect is adopted by irradiating the connection portion B with X-rays at room temperature to take a photograph. In this defect detection operation by X-ray irradiation, as shown in FIG. 4, the cooling high voltage power cable 23 is connected to the X-ray source 19 from the high voltage generator 20 via the controller 21 and the cooler 22. In front of the X-ray source 19, the power cable connecting portion B with the metal shielding layer removed is arranged, and the X-ray photographing film 25 having the scatter removal filter 24 attached to the rear surface thereof is arranged. This is performed by irradiating the connecting portion B with the X-rays 26 generated by the X-ray source 19. The X-rays 26 that have passed through the connecting portion B expose the X-ray film 25, and if there is a defect in the connecting portion B,
Those defects are photographed. In this defect detection operation, an equalizer 27 is usually provided between the X-ray source 19 and the connecting portion B in order to equivalently equalize the transmission length of the X-rays passing through the connecting portion B. ing.

[0010]

However, in the above-described conventional inspection method using X-rays, it depends on the type of defect, the position where the defect exists, the size of the connecting portion B, and the like. If the defect is a mixed foreign matter, the size thereof is 100 μm or more, and if the defect is a void, only the size 200 to 300 μm can be detected. It is difficult to detect defects such as poor adhesion between layers.

From the above, in the case of defect detection by X-ray irradiation, for example, the magnification at the time of X-ray imaging is increased, and the number of imaging portions of the connection portion B is increased to make an effort to increase the probability of defect detection. Moreover, measures such as devising the X-ray imaging method such as changing the shape of the equalizer are taken. However, even if such measures are taken,
It was difficult to reliably detect defects such as poor adhesion between layers.

Further, when detecting a defect in the connection portion, partial discharge or tan δ is measured over the entire length of the completed line, but in the case of this method as well, a defect in the connection portion is detected in terms of sensitivity. It is difficult to detect selectively. By the way, at the time of actual operation of the line, the connecting portion B is usually subjected to a heat cycle having a maximum temperature of about 80 to 90 ° C. due to heat generation of the conductor.

When the connection portion is subjected to the heat cycle as described above, if the above-mentioned defects such as peeling and voids are present in the connection portion, these defects have a greater adverse effect on the dielectric breakdown characteristics of the connection portion. Exert. INDUSTRIAL APPLICABILITY The present invention solves the above-mentioned problems in the conventional defect detection method in the connection portion of the power cable, can detect even a minute defect, and can also detect a defect due to defective adhesion between layers. An object of the present invention is to provide a method for detecting a defect in a connection portion of a power cable that can be performed.

[0014]

In order to achieve the above-mentioned object, in the present invention, the conductors of two rubber / plastic insulated power cables are connected to each other, and the inner half is connected to the outer periphery of the connecting conductor. When detecting defects in the connection part where the conductive layer, the reinforced insulator layer, and the external semiconductive layer are formed,
A rubber characterized by performing a partial discharge measurement at the connection part while heating the connection part at a temperature of 50 ° C. or higher for a predetermined time at least once and then applying a voltage to the conductor.
A method for detecting a defect in a connection portion of a plastic insulated power cable (hereinafter, referred to as a first detection method) is provided.

Further, in the present invention, as in the first detection method, after heating the connection portion to a temperature of 50 ° C. or higher for a predetermined time, the connection portion is irradiated with X-rays and photographed. Provided is a method of detecting a defect in a connection portion of a characteristic rubber / plastic insulated power cable (hereinafter, referred to as a second detection method). First, the first defect detection method of the present invention is performed based on the fact that when an insulating layer causes a dielectric breakdown, a partial discharge occurs in the insulating layer as a precursory phenomenon. That is, a known partial discharge test is performed on the connection part of the power cable, the partial discharge is observed under a predetermined measurement sensitivity, and if the occurrence of the partial discharge is recognized, the connection part of the measurement target is defective. Is determined to exist.

The first defect detection method and an example of the detection system for carrying out the method will be described below in detail with reference to the drawings. As shown in FIG. 1, the connection portion B of the power cable is
After the outer circumferences of the connected conductors 1 and 1 are pressure-bonded with the sleeve 7 in the same manner as in the conventional case, the inner semiconductive layer 2 ′ and the reinforcing insulator layer 3 ′ made of a cross-linked body of a predetermined resin composition are attached to the outer circumferences. , The outer semiconductive layer 4 ′ is sequentially formed, and the metal shielding layer 5 ′ is arranged outside the outer semiconductive layer 4 ′.

The outer semiconductive layers 4 and 4 of the power cables A ₁ and A ₂ are thickened by cutting the outer peripheral surface located in the vicinity of the connecting portion B into a ring with a desired width, for example, the entire circumference. The thin portions 4a, 4a having a thickness of about 1/4 to 1/3 of the thickness of the outer semiconductive layers 4, 4 are formed. This thin portion 4a, 4a
Are formed to have an electrical resistance value of several kΩ to several tens of kΩ.

The power cable A₁, A₂Metal shield
The metal shielding layer 5 ′ of the layer 5 and the connecting portion B is the thin portion 4 described above.
a, 4a, separated at the location corresponding to the power cable
A₁, A ₂Metal shielding layer 5 and connecting portion B metal shielding layer 5 '
The electrical continuity between and is cut off. Thin part mentioned above
Formation of 4a, 4a and separation between metal shielding layers 5, 5 '
Due to this, at the time of defect detection described later, the portion at the connection portion B
The detection sensitivity of the discharge is the power cable A₁, A₂Shadow from the side
It becomes difficult to receive the sound.

The outside of the entire connecting portion B is covered with a protective case C made of, for example, copper so as to be shielded from the outside. The protective case C includes fixed tubes 8 and 9 fixed to the sheath layers 6 and 6 of the power cables A ₁ and A ₂ , respectively.
And a slide tube 10 located between these fixed tubes 8 and 9.
It is configured with.

One ends 8a and 9a of the fixed tubes 8 and 9, respectively.
Is externally fitted and fixed to the sheath layers 6 and 6 of the power cables A ₁ and A ₂ , and these fixing points have an airtight structure by using a seal member 11, and the other ends 8b of the fixed tubes 8 and 9 are fixed. , 9b are arranged to face each other. The other end 8b of the fixture 8 has a flange shape,
The outer peripheral surface of the other end 9b of the fixture 9 has a sliding surface structure.

One end 10a of the slide tube 10 arranged between the fixed tubes 8 and 9 has a flange shape, and the other end 8b of the fixed tube 8 is fastened to the flange by a bolt-nut to be airtight. A structure can be formed, and the inner peripheral surface 10b of the slide tube 10 has a fixed tube 9
Has a sliding surface structure that meshes with the sliding surface structure on the outer peripheral surface of the other end 9b.

Therefore, the inner peripheral surface 10 of the slide tube 10 is
After b is engaged with the sliding surface structure at the other end of the fixed tube 9,
The slide tube 10 is slid to the fixed tube 8 side at the other end, one end 10a of the slide tube 10 is brought into contact with the other end 8b of the fixed tube 8, and both flanges are fastened with bolts and nuts. C is assembled. A hole 8c is formed in the fixed tube 8, and a cable 12 for detecting partial discharge is hermetically inserted into the hole 8c via an insulating member.

One end 12a of the cable 12 is brought into contact with the metal shielding layer 5'of the connecting portion B, and the other end 12b is grounded via the detection impedance 14 to be used for the partial discharge measuring apparatus 1.
Connected to 5. Further, during the heat treatment, the slide tube 10 of the protective case C is moved to the left as shown by the phantom line in the figure to expose the connection portion B, and the heat-sensitive portion 13a of the cable 13 such as a thermocouple is made of metal. The temperature of the connection B is measured by contacting the shielding layer 5 ′. Then, the other end of the cable 13 shown by a virtual line is connected to the temperature measuring device 16.

Further, fixed tube 8, fixed tube 9, slide tube 1
0 is provided with projecting pieces 8e, 9c, 10c, respectively, which are all grounded. The fixed tubes 8 and 9 are electrically connected to the metal shielding layers 5 and 5 located in the vicinity through the wires 28 and 28, respectively. The detection of the defect in the connection portion B is performed as follows.

First, the slide tube 10 is slid toward the power cable A ₂ side as shown by the phantom line in the figure to connect the connecting portion B.
Expose the outer periphery of. Then, one end 12 of the cable 12
a and the heat-sensitive portion 13a of the cable 13 are brought into contact with and fixed to the metal shielding layer 5'at the connection portion B. Cable 12
The position of the one end 12a is not particularly limited as long as it is a position that reflects the temperature of the connection portion B. The position of the heat-sensitive portion 13a is usually suitable on the central surface of the connection portion B.

The connecting portion B is once heated to a temperature of 50 ° C. or higher. As the heating means in that case, for example, as shown by the phantom line in FIG. 1, the heater 17 arranged so as to cover the outer periphery of the metal shielding layer 5 ′ can be cited. In addition, an induction heating device may be provided outside the connection portion B for heating, or furthermore, the conductor may be energized for resistance heating.

In any of the above methods, the temperature of the connecting portion B is measured by the heat-sensitive portion 13a of the cable 13,
The signal is confirmed by the temperature measuring device 16 connected to the lead wire 18. At this time, the temperature of the connecting portion B is 50
If the temperature is lower than ° C, minute defects cannot be detected. Therefore, it is necessary to heat the connecting portion B to a high temperature of 50 ° C. or higher. However, when the temperature of the connecting portion B is excessively increased, the resin composition of each layer constituting the connecting portion B is It causes heat deterioration and heat distortion in the cable. Therefore, it is preferable to heat the connection portion B so that the temperature is approximately 80 ° C. or higher and 120 ° C. or lower.

It is sufficient to perform the heat treatment of the connecting portion B once, but no problem occurs even if it is performed twice or more. The heating time may be at least 30 minutes, usually about 1 to 8 hours. After the heat treatment, the conductors 1 and _{1 of} the power cables A ₁ and A ₂ are connected to an AC power source to apply a voltage to the conductors. Then, the partial discharge charge amount at that time is measured.
The electric field is not particularly limited, but in practice, it is preferably formed by applying an AC voltage having a frequency of 50 Hz or 60 Hz.

Since the connecting portion B is cut off from the power cables A ₁ and A _{2 by} the thin portions 4a and 4a of the power cables A ₁ and A ₂ , a signal input from the tip 12a of the cable 12 to the partial discharge measuring device 15 is obtained. Is a signal in which the partial discharge and noise in the power cables A ₁ and A ₂ are blocked, and is a signal indicating the magnitude of the partial discharge in the connection portion B.

Therefore, if the detection sensitivity in the partial discharge measuring device 15 is set to a sensitivity equivalent to noise and the defect detection work is performed in that state, and the partial discharge charge amount exceeding the sensitivity is measured, the It can be determined that the connection B has a defect. The connection part in which such a signal is detected is determined to be defective, the connection part is disassembled, and an operation for reconstructing the connection part without defect is performed.

Next, the second defect detection method will be described. First, after forming the connecting portion B, the heater 17 is arranged directly on the outer periphery of the connecting portion B, for example, as in the case of FIG. 1, and the connecting portion B is heated to 50 ° C. or higher. After the heating process is completed, the heater is removed from the connection part B, the outermost metal shielding layer 5'is peeled off, and the connection part B is irradiated with X-rays as shown in FIG. The reason why the metal shielding layer 5 ′ is peeled off when a defect is detected is to allow X-rays to pass through to the connection part B.

The X-rays pass through the connecting portion B to expose the X-ray photographing film, and if there is a defect in the connecting portion B, it is photographed on the film. At this time, the connection part B is once 50
Since it is heated to ℃, do not heat it as before.
Unlike the case of detecting defects due to line irradiation, for example, when there is delamination or a minute defect, the defect is surely photographed. When detecting defects after heat treatment, partial discharge and X-ray imaging may be performed together.

[0033]

【Example】

Examples 1 to 6 and Comparative Examples 1 to 4 A 154 kV power cable having a conductor cross-sectional area of 800 mm ² was connected. At this time, the reinforcing insulator layer in the connection portion was formed by the tape molding method. This connecting portion is called a connecting portion (1).

Also, the conductor cross-sectional area of 2000 mm ² is 275 k.
The V power cable was connected. At this time, the reinforcing insulating layer in the connecting portion was formed by extrusion molding. This connecting portion is called a connecting portion (2). At the time of forming each connecting portion, a vertical 10-mm length is provided at the interface between the insulating layer of the power cable and the reinforcing insulating layer.
mm, a width of 10 mm, and a connection part thinly coated with silicone grease (this is called a test connection part) and a connection part not coated with the silicone grease (this is called a healthy connection part) were formed.

When the test connection portion of the connection portion (1) was not heated and each connection portion was disassembled without applying electric power to the conductor, and the location where the silicone grease was applied was observed,
At the interface between the insulation layer of the power cable and the reinforced insulation layer,
Peeling with a width of 20 mm and a width of 15 mm was observed. The outer circumference of each of these connecting portions was once heated at the indicated temperature for the indicated time by the method shown in Table 1.

One day and night after the end of the heat treatment, the conductors 1 and 1 are energized, the detection sensitivity of the partial discharge measuring device 15 is set to the indicated value, and an AC voltage of 50 Hz is applied to the connection portion. The occurrence of partial discharge was investigated. The voltage applied to the conductor when a partial discharge was generated in excess of the detection sensitivity at each connection was examined, and the results are shown in Table 1.

Further, each of the above-mentioned connecting portions was subjected to X-ray photography by the measuring system shown in FIG. Imaging conditions are as follows: X-ray source: M160 (manufactured by Rigaku Corporation), focus: 0.4 mm,
Voltage: 40 kV, voltage: 40 kV, current: 5 mA, shooting time: 9 minutes, film: Fuji 1X ・ 100 (manufactured by Fuji Film Co., Ltd.).

The obtained photographing results are shown in Table 1.

[0039]

[Table 1]

As is clear from Table 1, in the case of a sound connection part of the connection part (1), the detection voltage is 12 p and the applied voltage is 12 pC.
Partial discharge does not occur even at 00 kV (Comparative Example 4). However, in the case of the test connection portion of the connection portion (1), the occurrence of partial discharge was observed at 230 kV even under the same conditions (Example 1). Further, in the case of the test connection portion of the connection portion (1), if the heat treatment is not performed, the partial discharge does not occur even if the detection sensitivity is 0.5 pC and the applied voltage is 1200 kV (Comparative Example 1). However, when the heat treatment at 50 ° C. or higher is performed, partial discharge occurs and the existence of peeling defects can be confirmed even at an applied voltage of 205 to 230 kV, as is clear in Examples 1 to 4. . However, in the case of the test connection portion of the connection portion (1), the partial discharge does not occur even at 1200 kV in the heat treatment at 40 ° C. (Comparative Example 3).

Further, in the case of the sound connection portion of the connection portion (2),
Even if the detection sensitivity is 0.5 pC and the applied voltage is 1200 kV, no partial discharge is observed (Comparative Example 2). However, in the case of the connection under test, even if the detection sensitivity is 1 pC, the applied voltage 310
Partial discharges can be detected at kV or 250 kV (Examples 5 and 6). Further, as is clear from the results of the X-ray imaging of Example 1 and Comparative Example 1, even in the case of the same connection part (1), delamination that could not be imaged without heat treatment was performed by heat treatment. You can shoot by doing. That is, a defect that cannot be detected by the conventional X-ray photography can be detected by the method of the present invention.

From the above, it can be seen that the present invention is effective as a method for detecting a defect in a connection portion.

[0043]

As is apparent from the above description, according to the method of the present invention, once the connection portion of the power cable is heated to a temperature of 50 ° C. or higher, the partial discharge generated voltage due to the defect existing in the connection portion is generated. Can be significantly reduced, and defects can be radiographed. That is, according to the method of the present invention, even a defect that cannot be detected at room temperature can be detected.

Therefore, when a power cable is connected to form a completed line, defects in the connection can be detected with high sensitivity and easily, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a state of a connecting portion of a power cable when a defect detecting method of the present invention is carried out.

FIG. 2 is a sectional view showing an example of a sectional structure of a power cable.

FIG. 3 is a partial cross-sectional view showing a connection portion of a power cable.

FIG. 4 is a schematic view showing a system for radiographing a connection portion of a power cable.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 conductor 2 inner semiconductive layer 2'inner semiconductive layer of connection part 3 insulator layer 3'insulator layer of connection part 4 outer semiconductive layer 4a thin part of outer semiconductive layer 4 4'external semiconductive part of connection part Layer 5 Metal shielding layer 5'Metal shielding layer at connecting portion 6 Sheath layer 6'Sheath layer at connecting portion 7 Sleeve 8 Fixed tube 8a One end of fixed tube 8 8b Other end (flange shape) of fixed tube 8c Hole 8d Grounding Projecting piece 9 fixed tube 9a one end of fixed tube 9 9b other end of fixed tube 9 (sliding surface structure) 9c earth projecting piece 10 slide tube 10a slide tube 10 one end (flange shape) 10b slide tube 10 Inner peripheral surface (sliding surface structure) 10c Grounding protrusion 11 Sealing member 12 Partial discharge detection cable 12a One end of cable 12 12b The other end of cable 12 13 Cable for extracting temperature signal at connection part 13a Heat-sensitive part of cable 13 14 Detection impedance 15 Partial discharge measuring device 16 Temperature measuring device 17 Heater 18 Lead wire 19 X-ray source 20 High voltage generator 21 Controller 22 Cooler 23 Cooling high voltage power cable 24 Scattering removal filter 25 X-ray film 26 X-ray 27 Equalizer 28-line

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hajime Noda 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. A defect of a connecting portion in which conductors of two rubber / plastic insulated power cables are connected to each other, and an inner semiconductive layer, a reinforcing insulating layer, and an outer semiconductive layer are formed on the outer periphery of the connecting conductor. When detecting the above, after heating the connection portion to a temperature of 50 ° C. or higher for a predetermined time at least once,
A method for detecting a defect in a connection portion of a rubber / plastic insulated power cable, characterized by performing partial discharge measurement in the connection portion while applying voltage to the conductor. 2. A defect of a connecting portion in which conductors of two rubber / plastic insulated power cables are connected to each other, and an inner semiconductive layer, a reinforcing insulating layer, and an outer semiconductive layer are formed on the outer periphery of the connecting conductor. When detecting the above, after heating the connection portion to a temperature of 50 ° C. or higher for a predetermined time at least once,
A method for detecting a defect in a connection portion of a rubber / plastic insulated power cable, wherein the connection portion is irradiated with X-rays and a photograph is taken. 3. The method for detecting defects in a connection portion of a rubber / plastic insulated power cable according to claim 1, wherein a heater is wound around the outer periphery of the connection portion to heat the connection portion.