JPH0368614B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an insulated junction box for power cables, which comprises an electrical connection part, that is, an edge cut part of an external shielding layer, installed in the middle of the junction box in the longitudinal direction. It is about improvement.

[Prior art] Until now, this type of insulated junction box for power cables was
It was constructed as shown in FIGS. 1 to 4. That is, in FIGS. 1 to 3, reference numeral 1 indicates that the cable sheath 2, cable shielding layer 3, and cable insulator 4 of the power cables 5 to be connected are sequentially stripped off and the exposed cable conductors 6 are electrically connected to each other. a connecting sleeve that connects mechanically and mechanically;
Reference numeral 7 denotes a connecting portion reinforcing insulator provided on the periphery of the cable conductor connecting portion between the two cable insulators 4, 4, which serves to electrically insulate and reinforce the portion. 8 is the connection part reinforcing insulator 7
The connecting portion is an external shielding layer provided on the circumference of the cable, and both ends thereof are electrically connected to each cable shielding layer 3, and an electrically insulating portion, that is, a border portion 9 is installed approximately in the center thereof. It consists of To explain this edge cutting part 9 in more detail, as shown in FIG. An insulator is provided on the top so that the end of the right shielding layer 8 wraps a certain length with the end of the left shielding layer 8, and furthermore, an insulator is provided so as to cover the circumference of the lapped portion of these left and right shielding layers 8, 8. 10. Reference numeral 11 denotes a metal protection tube installed around the end portions of both cable sheaths 2, 2 and around the left and right shielding layers 8, 8, and 12 refers to an electrical protection tube provided approximately in the center of this protection tube 11. This is the insulating part, that is, the edge cutting part. To explain this edge cut part 12 a little more, it consists of an insulating tube 13 interposed between the end flanges 110 of each protection tube 11, a mounting bolt 14 that presses and fixes the flange 110 to the side surface of the insulating tube 13, and an insulating tube. a packing 15 interposed between the flange 110 and the mounting bolt 14;
It consists of 6. Reference numeral 17 denotes a seal portion for sealing the cable sheath side end of each protection tube 11.

[Problems to be Solved by the Invention] By the way, these left and right connecting portion external shielding layers 8, 8
The purpose of cutting the edges of the protection tubes 11 and 11 is to enable the adoption of cross bonding, which is done in order to reduce the potential induced in the sheath 2 of the power cable during normal use. If a lightning surge or switching surge enters the conductor 6 of the power cable due to 9 must withstand this surge abnormal voltage.

However, with the recent increase in the voltage of power cables, the surge-like abnormal voltage that occurs has also increased, and troubles such as dielectric breakdown at the edge cut portion 9 have begun to occur. If dielectric breakdown occurs in this part, the insulating junction box no longer functions, and the junction box must be dismantled and reassembled, which requires a great deal of cost and time.

On the other hand, since the aforementioned abnormal surge voltage is also applied to the edge cut portion 12 of the protective tube 11, the insulating tube 1
If the dielectric strength of the surface of the insulating tube 13 is lower than that of the edge cut portion 9, it is possible to cause flash flashing on the surface of the insulating tube 13 before the edge cut portion 9 causes dielectric breakdown. This will prevent dielectric breakdown from occurring. However, since the surface flash voltage of the insulating tube 13 is usually higher than the dielectric breakdown voltage of the edge cut portion 9, measures are taken to lower the surface flash voltage. Figure 3 is an example of this,
Here, a plate-shaped metal electrode 18 is provided on the surface of the insulating cylinder 13.
is installed. However, if a flash occurs on the surface of the insulating tube 13, the flash will leave a flash trace on the surface, and eventually the insulating tube 13 will have to be reassembled at some point. Recently, as shown in FIG. 4, a structure in which a discharge gap 19 is provided inside the insulating cylinder 13 and metal electrodes 20 installed on both sides of the gap are used to generate an air discharge has been partially considered.
However, in this case, it is difficult to manufacture because a discharge gap is created inside the casting resin, and it is difficult to adjust the distance between the electrodes.

[Means for Solving the Problems] The present invention has been made for the purpose of providing an insulated connection box for power cables that can solve the problems of the prior art described above. The electrically insulating part, that is, the edge cut part, is made of an insulating cylinder having a recess on its outer surface, and extends through the walls on both sides of the recess of the insulating cylinder, and extends through the ends of the insulating cylinder on the side of the recess. The movable electrode includes at least a pair of movable electrodes that face each other at a predetermined distance and are electrically connected to the protective tube.

Incidentally, the connection portion protection tube is most commonly made of metal, but is of course not limited to this. In addition, for example, a hard resin cylinder having an arbitrary conductive layer provided on its inner and outer surfaces may be used.

Further, as the insulating cylinder, for example, a cylinder made of hard synthetic resin such as epoxy resin or phenolic resin is preferable.

Furthermore, the recess can be considered in two ways: a case where the recess is provided over the entire circumference of the outer surface of the insulating tube, and a case where the recess is provided in a part of the outer surface.

[Example] Next, one embodiment of the present invention will be described.

The feature of the present invention is that, in the conventional insulated junction box for power cables described above, the structure of the electrically insulating part, that is, the edge cut part, interposed in the middle of the connection protection tube is improved, so it will not be described here. Only the structure of the edge cut portion after the improvement will be explained. For other parts, please refer to FIG. 1.

FIG. 5 shows the structure of the edge cutting portion after improvement in this embodiment. As shown in the figure, a recess 131 is provided on the outer periphery of the central part of the insulating tube 130 made of epoxy resin, and the left and right mounting bolts 14
0 is inserted from the end flange 110 of each protection cylinder 11 on the protection cylinder side, and further penetrates the insulating cylinders 130', 130' on both sides of the recess 131, with its tip protruding into the recess 131. However, if high voltage is applied in this state, the mounting bolt 140
It is possible to cause a conflict between them. 150
Reference numeral 160 indicates a packing, and 160 indicates an embedded metal fitting that is placed inside the insulating cylinder 130 and is screwed into the mounting bolt 140.

Since the spacing between the mounting bolts 140 can be arbitrarily selected, it is possible to set the flash voltage in this part lower than the dielectric breakdown voltage of the internal edge cutting part 9, and the flash fault here can be avoided. Since it is a medium flash fault, damage caused by flash fault can be prevented by insulating tube 130.
Never give on the surface.

6 and 7 respectively show other embodiments of the present invention, and FIG. 6 shows the mounting bolt 140.
Attach a new electrode metal body 141 to the tip of the
The tip of this metal body 141 is exposed in the recess 131 so that the left and right sides face each other. In FIG. They are exposed inside the recess 131, and substantially the same effect can be expected in either case.

Although the case of the power cable intermediate connection section has been described above, the present invention can also be used in the power cable terminal connection section.

[effect] The following effects can be expected from the present invention.

Since flash faults caused by abnormal surge voltage intrusion become air flash faults, there are no discharge marks left on the surface of the insulating tube, which was a concern in the past, and we can provide an insulated junction box with excellent long-term stability. .

To manufacture an insulating tube, a stable insulating tube can be provided using conventional technology without requiring a special casting mold.

Since the distance between the flash-flash electrodes of the insulating tube can be set arbitrarily visually, it is possible to set the flash-flash voltage according to the dielectric breakdown strength of the internal edge cut portion, and therefore the insulation of the inner edge cut portion can be set as desired. Destruction can be prevented and damage caused when surge abnormal voltage enters can be minimized.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional insulated junction box for power cables, Figs. 2 and 3 are explanatory diagrams of its internal and external edge cutting parts, Fig. 4 is an explanatory diagram of other external edge cutting parts, and Fig. 5 7 to 7 are explanatory views of essential parts of embodiments of the insulated junction box for power cables of the present invention. 1; Connection sleeve, 2; Cable sheath, 3;
cable shielding layer, 4; cable insulator, 5; power cable, 6; cable conductor, 7; connection part reinforcing insulator, 8; connection part external shielding layer, 9; edge cutting part,
10; Insulator, 11; Metal protective tube, 12; Edge cut portion, 13; Insulating tube, 14; Mounting bolt, 1
5; Packing, 16; Embedded metal fitting, 17; Seal portion, 18; Metal electrode, 19; Discharge gap, 20;
Metal electrode, 110; end flange, 130, 13
0'; Epoxy resin insulating cylinder, 131; Recessed part,
140; Mounting bolt, 141, 142; Metal body for electrode, 150; Packing, 160; Embedded metal fitting.

Claims (1)

[Scope of Claims] 1. A connecting portion protection tube with an electrically insulating portion interposed in the middle of its longitudinal direction is installed on the circumference of the connecting portion reinforcing insulator, in which the electrically insulating portion is An insulating tube having a concave portion on its outer surface, and an insulating tube that penetrates through the walls on both sides of the concave portion, and the ends of the concave side face each other at a predetermined distance. and at least a pair of movable electrodes each electrically connected to the protective tube. 2. The insulated connection box for power cables according to claim 1, in which a metal tube is used as the connection portion protection tube. 3. The insulated connection box for power cables according to claim 1, in which a metal bolt is used for the movable electrode.