JP2001135162A - Power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power cable most suited for application to e.g. plasma explosion, where a large current is repeatedly supplied to flow in a short time, avoiding inconveniences due to repulsion between a conductor and a return conductor. SOLUTION: The power cable comprises a plurality of high-voltage cables 30 each having a conductor 41, an insulating layer 42 and a shielding layer 43, and a plurality of grounded return conductors 31. The high-voltage cables 30 and the return conductors 31 are formed in one unit. If the high-voltage cables as forward passages and the return conductors are independently formed, no electromagnetic force works between the conductor and the shielding layer in each of the high-voltage cables, and no gap is formed between the insulating layer and the shielding layer, therefore hardy causing destruction of the high- voltage cables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable most suitable for applications in which a large current is repeatedly applied in a short time, such as for plasma blasting.

[0002]

2. Description of the Related Art A plasma blasting method is known as one of the rock blasting methods (JP-A-4-222794). this is,
As shown in FIG. 4, a hole 21 is formed in a rock 20 to be blasted, a highly viscous electrolytic solution 22 is filled in the hole, and a coaxial electrode 23 for blasting is immersed in the electrolytic solution. Next, the electrode
23 emits at least 100 million watts of electrical energy per 1 millionth of a second. As a result, the electrolyte 22 between the coaxial electrodes causes dielectric breakdown to generate plasma, and is exploded by a shock wave S accompanying the pressure of the plasma. To supply electric energy, a capacitor bank 25 connected to a power supply source 24 is used. The capacitor bank 25 is connected to the switch 26 and the trigger device
27 is activated by a remote trigger 28 to activate the switch 26 to supply power through the coaxial power cable 29.

[0003] An example of such a coaxial power cable 29 is shown in FIG. This power cable is
1, comprising an inner semiconductive layer 2, an insulator 3, an outer semiconductive layer 4, a return conductor 5, an anticorrosion layer 6, and a reinforcing layer 7. The conductor 1 is connected to one of the coaxial electrodes, and the return conductor 5 is connected to the other of the coaxial electrodes. A large-capacity pulse current flows through the conductor 1 of the power cable in a short time, and a return current in the opposite direction to the conductor 1 flows through the return conductor 5. Therefore, both conductors
In some cases, a repulsive force acts between 1 and 5 to cause the return conductor 5 to slightly move in the outer peripheral direction to cause a shift. The reinforcing layer 7 is for suppressing displacement or swelling of the return conductor 5.

[0004]

However, the above power cable has the following problems. When the current increases, it becomes difficult to reinforce the return conductor 5 to hold it. Increasing the thickness of the reinforcing layer 7 is an example of securing the force for holding down the return conductor 5, but this involves a problem that the outer diameter of the cable becomes large and it becomes difficult to bend.

[0005] The movement of the return conductor 5 creates a gap between the external semiconductive layer 4 and the return conductor 5, and if discharge occurs repeatedly in this gap, dielectric breakdown may occur.

There is a limit to the tightening by the reinforcing layer 7. In some cases, the movement of the return conductor 5 cannot be suppressed only by the tightening by the reinforcing layer 7, and in that case, the return conductor 5 formed of a copper wire may be deformed.

[0007] It is difficult to make a connector that fits the above cable. Since the shield layer is used as a return conductor to bear the current, the return conductor becomes thick depending on the degree of the current, and it becomes difficult to form a connector that allows a large current for both the conductor and the return conductor.

The current concentrates on the outer periphery of the conductor due to the skin effect, and the conductor cross section cannot be used effectively. At 10 kHz, current flows only about 1 mm from the surface of the conductor. In the case of a conductor having a large diameter, even if the cable is twisted, the effect of equalizing the impedance due to the twisting cannot be expected unless the innermost element wire does not come out to the outermost layer.

Accordingly, it is a primary object of the present invention to provide a power cable which can eliminate the inconvenience caused by repulsion between a conductor and a return conductor.

[0010]

According to the present invention, the above object is achieved by forming the high voltage side cable and the return path conductor, which are the forward path, independently, and configuring each of the high voltage side cable and the return path conductor with a plurality of lines. .

That is, the power cable of the present invention comprises a conductor,
A plurality of high-side cables comprising an insulating layer and a shielding layer;
A plurality of return conductors which are grounded are provided, and the high voltage side cable and the return conductor are configured as an integral cable.

If the high-voltage side cable and the return path conductor, which are the forward path, are formed independently of each other, no electromagnetic force acts between the conductor and the shielding layer in the high-voltage side cable. Since there is no gap in the high-voltage side cable, breakage of the high-voltage side cable hardly occurs.

Further, by using a plurality of high-voltage side cables and return conductors, one conductor can be reduced in size. If a connector is formed for each individual conductor, a small connector can be used. In particular, since the return current does not flow through the shield layer of the high-voltage side cable, the processing of the shield layer is simple.

Further, since one conductor in each of the high-voltage side cable and the return conductor can be reduced, the effect of uniformizing the impedance by the wire insulation is increased. Therefore,
It is desirable that at least one of the conductor of the high-voltage side cable and the return conductor is formed of a stranded wire insulated from wires. In addition,
The integration of the high voltage side cable and the return conductor can be easily realized by twisting both.

[0015]

Embodiments of the present invention will be described below. FIG. 1 is a schematic sectional view of a power cable for pulse power according to the present invention, which is optimal for supplying power for plasma blasting. This power cable is composed of six high voltage side cables 30 and seven return path conductors 31. The seven return path conductors 31 are twisted together, and the six high voltage side cables 30 are twisted around the outer periphery to be integrally formed. Have been.

The high voltage side cable is used as a flow path for a forward current from a pulse power source. The cable 30 includes a conductor 41, an insulating layer 42 (including an inner semiconductive layer and an outer semiconductive layer), a shielding layer 43, and a sheath 44 in this order from the center.
It is preferable that the conductor 41 of the high-voltage side cable is constituted by a strand wire insulated from the strand.

On the other hand, the return conductor 31 is used as a return current flow path. Since the return conductor 31 does not need to withstand high pressure, a cable with thin insulation may be used. For example, a stranded wire subjected to formal wire insulation is conceivable.

Since the high-voltage side cable 30 and the return conductor 31 are twisted, the cable state can be maintained without any measures against bulging due to electromagnetic repulsion. However, the twist of the high voltage side cable 30 and the return conductor 31 may be restricted by further coating the outside of the high voltage side cable.

With this configuration, the high voltage side cable 30
Electromagnetic force does not work between the conductor 41 and the shielding layer 43 in,
Since there is no gap between the insulating layer and the shielding layer,
High voltage side cable is less likely to break. In addition, since one conductor in each of the high-voltage side cable 30 and the return conductor 31 can be reduced, the effect of uniformizing the impedance by strand insulation increases.

Preferably, the connector of the power cable is configured as shown in FIG. The connector 50 is connected to each of the high-voltage side cables 30 that are to be forwarded. On the other hand, seven return conductors 31 are collectively connected to one connector 51. Of course, a connector may be connected to each of the return conductors 31. In this way, the connector may be formed for each high-voltage side cable by separating the return path conductor 31 from the outward path and dividing the outward path into a plurality of high-voltage side cables 30.
Further, since it is not necessary to supply a return current to the shielding layer 43 of the high voltage side cable, the processing of the shielding layer 43 is simple and the connector may have a simple configuration. Further, since the return conductor itself does not need to withstand high pressure, the connector connected to the return conductor 31 also has a simple structure.

Incidentally, the pulse power cable of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

[0022]

As described above, according to the power cable of the present invention, no electromagnetic force acts on the shielding layer of the high-voltage side cable, so that no gap is formed between the power cable and the insulating layer and the electric cable is stable in electric field. Further, since the conductor of the high voltage side cable is divided into a plurality of conductors, the connector can be small.

Further, if the conductors and return conductors of the high-voltage side cable divided into a plurality of wires are insulated by wires, the conductors can be further divided into smaller portions, and the burden current of each wire can be made uniform. Impedance can be reduced, and Joule loss in the cable can be reduced.

Therefore, it is most suitable for use as a power supply cable in a plasma blast method or the like.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a power cable of the present invention.

FIG. 2 is a layout view of a connector connected to the cable of FIG. 1;

FIG. 3 is a cross-sectional view of a conventional power cable.

FIG. 4 is an explanatory view of a plasma blast method.

[Explanation of symbols]

1 conductor 2 inner semiconductive layer 3 insulator 4 outer semiconductive layer 5 return conductor 6 anticorrosion layer 7 reinforcing layer 8 electrode layer 9 holding layer 10 core 20 rock 21 hole 22 electrolyte 23 coaxial electrode 24 power supply 25 capacitor bank 26 Switch 27 Trigger device 28 Remote trigger 29 Coaxial power cable 30 High voltage side cable 31 Return conductor 41 Conductor 42 Insulation layer 43 Shielding layer 44
Sheath 50 Connector 51 Connector

Claims (2)

[Claims] 1. A high voltage side cable comprising a conductor, an insulating layer and a shielding layer, and a plurality of grounded return conductors, wherein the high voltage side cable and the return conductor are formed as an integral cable. A power cable, characterized in that: 2. The power cable according to claim 1, wherein at least one of the conductor of the high-voltage side cable and the return conductor is formed of a strand wire insulated from a wire.