JPS596106Y2 - insulation junction box - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the sheath protection of a high voltage power cable, and more particularly to a power cable line in which a discharge gap portion is eliminated in a sheath protection device.

In general, in three-phase power transmission and distribution lines using single-core power cables, in order to prevent circulating current from flowing through the cable sheaths, the cable sheaths are connected with an insulating junction box 1, as shown in Figure 1, and the cable sheaths are A bonding wire 2 is used to cross-bond between the two, and the cross-bond points are connected to the discharge gap 3.3', 3'' and the nonlinear resistor 4.4', 4'' through a cable sheath protection device. .

In this case, if a current i due to switching surge or other abnormal voltage enters the A-phase cable conductor, a corresponding current i' will be induced in the cable sheath, but the cable sheath is insulated in the junction box. Since they are connected, this current will flow through the discharge gap 3', the nonlinear resistor 4', the ground, the nonlinear resistor 4'', and the discharge gap 3'' as shown by the dotted line.

Therefore, the discharge gap must be large enough to allow current i' to flow.

On the other hand, in the discharge gap, as shown in FIG.
There is a characteristic that the discharge voltage tends to be high for a voltage with a steep rising waveform.

For this reason, even though a protective device is installed on the insulated connection, its limited voltage (14
In many cases, a voltage of more than KV) appears at the insulating connection, and as a result, the protective device does not function to its full potential.

For this purpose, as shown in FIG. 3, there is provided a protective case 6 that houses the nonlinear resistor 5, a terminal 7 located at the upper part of the case, and electrically connected to the upper end of the nonlinear resistor 5.
An electrode 8 is located at the lower part of the protective case 6 and is electrically connected to the ground lead wire, and the upper end is electrically connected to the lower end of the nonlinear resistor 5, and the lower end is connected to and separated from the electrode 8. A sheath protection device has been proposed that includes a spring 10 that is electrically connected to an electrode plate 9 that is freely pressed.

Although the sheath protection device with such a structure is reasonably effective in preventing the generation of overvoltage due to the discharge delay in the gap described above, Since it is attached to the wall of the manhole, the length of the lead wire is long (approximately 3 to 1
(approximately 0 m), the resulting voltage drop is large, so when a surge enters the insulated junction box, a voltage two to three times the rating of the sheath protection device is generated.

However, in a structure in which the sheath protection device is attached to the wall of a manhole, it is impossible to shorten the lead wire.

Further, since the spring 10 is present in the protective case 6, such a sheath protection device inevitably becomes large in size and heavy in weight.

The present invention has been made based on the above-mentioned circumstances, and provides an insulated junction box in which a sheath protection device is directly attached between the metal sheaths of both connecting cables.

This invention is based on the following findings obtained from theoretical studies and actual measurements.

That is, it has been found that a sufficient surge suppression effect can be obtained by simply connecting the electrodes at each end to the respective sheaths of the insulated junction box without grounding the electrode at one end of the sheath protection device.

In the present invention, a non-linear resistance element known as a gapless arrester is used to miniaturize the sheath protection device, and its electrode terminals are connected to each sheath of the insulating junction box to achieve the above object.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

As shown in FIG. 4, each surface of the disc-shaped nonlinear resistance element 11 has a disc-shaped electrode 14.15 with one terminal 12.13 protruding in the radial direction. These structures are mounted so as to extend along one diameter of the resistor element 11, and are molded with a waterproof layer 16 made of resin, rubber, etc., with the portion near the end of each terminal exposed. ing.

Note that this waterproof layer is curved so as to become part of a cylindrical surface having an axis parallel to the element diameter.

The sheath protection device 17 having the above structure is attached to the insulating junction box 18 as shown in FIG.

That is, the electrode terminals 12 and 13 of the sheath protection device 17 are connected and attached to the sheath terminals 20 protruding from each sheath anticorrosion layer 19 of the insulating connection box 18 via the lead wires 21.

As mentioned above, the sheath protection device of the present invention
Since the lead wire 21 can be directly attached to the sheath of the insulating junction box, the length of the lead wire 21 can be reduced to a minimum (approximately 50 cm), thereby suppressing abnormal voltage generated in the sheath of the insulated junction box when a surge enters.

Note that the present invention is not limited to the above embodiments.

For example, the shape of the nonlinear resistance element may be any shape other than a disk shape.

Furthermore, the waterproof layer does not necessarily need to be curved.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram to explain the installation state of a sheath protection device for a conventional cross-bond insulation connection, Figure 2 is an explanatory diagram showing the Vt characteristics of a discharge gap, and Figure 3 is a diagram of a conventional sheath protection device. An explanatory diagram of the device, FIGS. 4A, B, and C are a cutaway plan view and a cutaway front view of the sheath protection device used in the present invention,
A cutaway side view and FIG. 5 are front views of one embodiment of the present invention. 11...Nonlinear resistance element, 14.15...
...Electrode, 12, 13... Electrode terminal, 16...
...Waterproof layer, 19...Anti-corrosion layer, 20...
...Sheath terminal.

Claims (1)

[Scope of utility model registration request] It has an insulating tube that insulates between the sheaths, and on both sides of this insulating tube,
The insulated junction box sheath is provided with an insulated junction box sheath that conducts with the metal sheath of both connecting cables, and each of the insulated junction box sheaths is provided with sheath terminals that protrude from a corrosion-resistant layer coated on its outer periphery, and these sheath terminals have , an insulating connection is made by connecting each of the electrode terminals of a sheath protection device by covering only the electrode terminals with a waterproof layer molded with a non-linear resistance element that suppresses abnormal voltage occurring between both ends of the insulating cylinder; box.