JP2978718B2 - Normal connection of power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a normal connection portion of a power cable for connecting a pair of power cables, and more particularly to a normal connection portion of a power cable capable of easily detecting a partial discharge.

[0002]

2. Description of the Related Art Conventionally, as a partial discharge detecting device for detecting a partial discharge (PD) generated in an electric power cable, for example, a device using a tuned detection method and a method using an AE (acoustic emission) sensor are known. Proposed.

A tuned detection device using a tuned detection method is
A coupling capacitor and a detection impedance are connected in series between the inner conductor at the end of the power cable and the metal shielding layer, and a potential difference generated between both ends of the detection impedance is extracted by a tuning amplifier having a tuning frequency of several hundred kHz. It is like that.

[0004] However, this tuned detection device has a problem in that it is necessary to extract a signal from the inner conductor of the power cable, so that detection under a live line is difficult, and a dedicated coupling capacitor is also required. . In addition, since the tuning frequency of this device is several hundred kHz, it is easily affected by ambient noise, and although good detection accuracy can be obtained in experiments in a shielded room, it is difficult to apply it to a cable after installation. There are drawbacks.

On the other hand, a detection device using an AE sensor is
The AE sensor detects an elastic wave propagating inside the insulator due to partial discharge. This device is not affected by electrical noise, but is strong because ultrasonic waves have straightness. There is a problem that it has directivity and the detection sensitivity is extremely reduced depending on the detection position.

[0006] As a partial discharge detection method which solves these drawbacks, a metal shield layer is insulated at a connection portion of a power cable, and a potential difference generated between the two metal shield layers sandwiching the insulating portion when a partial discharge occurs is determined by using the two metal shield layers. A detection method of detecting by a detection impedance connected between the shield layers has also been proposed ("Partial discharge test result of 275 kV CV cable line in Minamiikegami line"; Katsuta et al., EIM-90-20, IEICE Insulation Materials Research Group Material EIM-90-20). .

[0007] However, this method is limited in its application only to the connection portion where the metal shielding layer is insulated, and lacks safety in the event of a short circuit accident because the metal shielding layer is not grounded. There is. In addition, there is a disadvantage that the apparatus becomes large and measurement requires skill.

Therefore, the present inventors have detected a wideband signal (hereinafter, referred to as a partial discharge signal) generated by partial discharge and propagated through the inner conductor and the metal shielding layer of the power cable in the longitudinal direction of the cable by a resonance circuit. Proposed a resonant type partial discharge detector (Japanese Patent Application No. 2-310197). In this resonance type partial discharge detection device, the resonance circuit is configured by an electrode disposed on the outer peripheral surface of the sheath of the power cable and forming a metal shielding layer and a coupling capacitor of the power cable, and a coil connected to the electrode. , A partial discharge sensor.

[0009]

However, when the above-described resonance type partial discharge detection device is applied to a normal connection portion of a power cable, there are the following problems. That is, at the normal connection portion of the power cable, the metal shield layer of the power cable is electrically connected by an external shield layer such as a copper tape, and a partial discharge signal is generated outside the external shield layer due to the external shield layer. Do not leak to Therefore, conventionally, as shown in FIG. 2, when a plurality of power cables 11 are connected by a normal connection portion 12 and an insulation connection portion 13, a partial discharge sensor is installed at or near the insulation connection portion 13, It is necessary for the insulated connection 13 to detect a partial discharge signal generated in the normal connection 12 and propagated in the longitudinal direction of the cable 11. Further, when the power cables of all the lines are connected at the normal connection portion such as the connection portion of the triplex power cable, it is necessary to detect the partial discharge signal at the terminal portion 14 of the power cable 11 as shown in FIG. There is. However, in the methods shown in FIGS. 2 and 3, since the partial discharge signal generated at the normal connection is detected at a position distant from the normal connection, the partial discharge signal is attenuated and the measurement sensitivity is reduced. There is a point. In addition, since a partial discharge signal passing through a plurality of connection portions is detected, there is a disadvantage that it is difficult to evaluate a position (connection portion) where the partial discharge has occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a normal connection portion of a power cable capable of easily detecting a signal due to partial discharge when partial discharge occurs. And

[0011]

SUMMARY OF THE INVENTION An ordinary connection portion of a power cable according to the present invention includes a reinforcing insulating layer formed around an inner conductor connecting portion of a pair of power cables, and a reinforcing insulating layer formed around the reinforcing insulating layer. A power cable having an outer shield layer electrically connecting the metal shield layers of the pair of power cables, and a cylindrical connection box surrounding the inner conductor connection portion, the reinforcing insulating layer and the outer shield layer. In the connection portion, the external shielding layer is provided with an opening through which a signal generated by partial discharge can leak, the connection box includes an insulating cylinder,
A pair of metal cylinders arranged on both sides of the insulating cylinder;
And a conductive material for electrically connecting the pair of metal cylinders.

[0012]

According to the present invention, the outer shielding layer formed around the reinforcing insulating layer is provided with an opening through which a signal generated by partial discharge can leak, and the connection box is formed of an insulating cylinder and the insulating cylinder. Is constituted by a pair of metal cylinders arranged on both sides. Therefore, the partial discharge signal generated by the partial discharge and propagated in the longitudinal direction of the cable leaks through the opening of the outer shielding layer, and further leaks out of the junction box through the insulating cylinder of the junction box. Thus, if the partial discharge sensor is arranged outside the connection box, a partial discharge signal can be detected. In this case, since the pair of metal cylinders of the connection box are electrically connected by the conductive material, the electric potential of the power cable becomes equal on both sides of the connection box.

[0013]

Next, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a normal connection portion of a power cable according to an embodiment of the present invention. The inner conductors of the two power cables 1 are electrically connected to each other, and a reinforcing insulating layer 2 is formed around the inner conductor connection. A conductive outer shielding layer 3 is formed around the reinforcing insulating layer 2, and the outer shielding layer 3 electrically connects the metal shielding layers of each power cable. The outer shielding layer 3 is provided with a slit (opening) 4 extending spirally from one power cable 1 side to the other power cable 1 side. In this slit 4 part, the reinforcing insulating layer 2 is provided. It is exposed. The inner conductor connection portion, the reinforcing insulating layer 2 and the outer shielding layer 3 provided around the connection portion are housed in a cylindrical connection box 10. The connection box 10 includes a pair of metal cylinders 5a and 5b,
a, 5b. The metal cylinders 5a and 5b are electrically connected by bond wires 7.

For example, when a partial discharge is generated at a position indicated by a symbol A in FIG. 1, a high-frequency signal (partial discharge signal) is generated by the partial discharge, and the partial discharge signal causes the internal conductor and the metal shielding layer of the cable to pass through. Propagation in the longitudinal direction of the cable. In this case, in the present embodiment, since the slit 4 is provided in the outer shielding layer 3, a part of the partial discharge signal leaks to the outside of the outer shielding layer 3 through the slit 4, and further, the insulating cylinder 6 leaks out of the connection box 10. Therefore, the partial discharge can be detected by installing the partial discharge sensor outside the connection box 10.

As a partial discharge sensor, for example, a junction box 1
It is possible to use a sensor including an antenna for receiving the partial discharge signal leaked from zero and a resonance circuit connected to the antenna. However, the type of the sensor is not particularly limited as long as the partial discharge signal leaking from the connection box 10 can be detected.

In this embodiment, the partial discharge signal leaks out of the connection box 10 through the slit 4 provided in the outer shielding layer 3 and the insulating tube 6 provided in the connection box 10 as described above. Also, a partial discharge can be detected at the ordinary connection. In addition, since the partial discharge generated in the normal connection portion can be detected in the vicinity of the generation point,
Good sensitivity can be obtained. Furthermore, for example, by installing partial discharge sensors at all cable connections,
There is an effect that the position where the partial discharge has occurred can be easily evaluated.

[0017]

As described above, according to the present invention, since an opening is provided in the outer shielding layer and a part of the connection box is formed of an insulating tube, the connection is usually generated at the connection part. The partial discharge can be detected by a partial discharge sensor arranged outside the junction box. In addition, for example, by installing partial discharge sensors at all cable connection portions, there is an effect that the position where partial discharge has occurred can be easily evaluated.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a normal connection portion of a power cable according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example of a conventional method for measuring partial discharge of a power cable and its problems.

FIG. 3 is a schematic diagram showing another example of a conventional method for measuring partial discharge of a power cable and its problems.

[Explanation of symbols]

 1, 11; Power cable 2: Reinforced insulating layer 3: Outer shielding layer 4: Slit 5a, 5b; Metal cylinder 6; Insulating cylinder 7; Bond wire 10; Connection box 12; Normal connection 13; Insulated connection

Continuation of the front page (56) References JP-A-3-175380 (JP, A) JP-A-2-154171 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01R 31 / 12-31/20 H02G 15/08

Claims (1)

(57) [Claims] 1. A reinforcing insulating layer formed around an inner conductor connecting portion of a pair of power cables, and a metal shielding layer of the pair of power cables formed around the reinforcing insulating layer is electrically connected. In a normal connection portion of a power cable having an outer shielding layer to be connected and a cylindrical connection box surrounding the inner conductor connecting portion, the reinforcing insulating layer and the outer shielding layer, the outer shielding layer has a signal generated by partial discharge. The connection box electrically connects the insulating cylinder, a pair of metal cylinders disposed on both sides of the insulating cylinder, and the pair of metal cylinders. A normal connection portion of a power cable, comprising a conductive material.