JPS6038804B2 - power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power cable that reduces metal sheath loss and achieves low cost power cable loss.

As one measure to reduce the metal sheath loss of conventional power cables, there is a plan to reduce eddy current loss by increasing the sheath resistance, but this has little effect unless the resistance is increased considerably.

When stainless steel is used as the sheath instead of the currently used amyl sheath, its specific resistance is about 250 times that of aluminum, so the effect of reducing eddy current loss is significant. However, if a stainless steel sheath is used, it is necessary to reduce the thickness of the stainless steel sheath in order to suppress eddy current loss and prevent loss of flexibility, resulting in insufficient ground fault capacity. Therefore, if parallel conductors are provided and connected to the metal sheath to compensate for the lack of ground capacity, circulating current will occur between the parallel conductors and the metal sheath, increasing circuit loss.
Furthermore, even if a parallel conductor using a high-resistance metal sheath is not provided, if the grounding type is a so-called solid bond in which the metal sheath is directly grounded, the sheath resistance is large, resulting in a dramatic increase in circuit loss. There is also the idea of adding a bare conductor vertically over a high-resistance metal source to compensate for ground fault capacitance, but this reduces the apparent sheath resistance and circuit loss, but it also causes eddy current loss to occur in the bare conductor. , it does not result in loss reduction. Another method of placing a parallel conductor in the middle of the three phases of the cable has been attempted, but since it is located in the center of the three phases, eddy currents are canceled out, but arc heat and impact caused by arc transfer to the parallel conductor However, all cables had the disadvantage of being subject to significant damage. This invention eliminates the drawbacks such as insufficient metal sheath ground fault capacity, increased circuit loss, and increased eddy current loss when increasing sheath resistance as a measure to reduce metal sheath loss. In the structure, between the outermost layer of the cable core and the metal sheath,
This power cable is characterized in that at least one coated conductor is spirally wound in the longitudinal direction of the cable.

This invention will be explained in more detail below with reference to the drawings.

FIG. 1A is a cross-sectional view of a power OF cable embodying the present invention, and FIG. 1B is a diagram showing the upper half in a notched state and the lower half in a vertical cross-sectional state.

In the figure, cable conductor layer 1, insulator layer 2, external semiconductor conductor layer 3
IZ
A coated conductor 4 is wound spirally on the cable core at a predetermined pitch in the longitudinal direction. When the coated conductor is spirally wound, it is often wound directly on the cable core as shown in FIGS. 1A and 1B or along the inner surface of the metal sheath 5 due to manufacturing reasons. The latter case is shown in FIGS. 2A and B'. In many cases, the metal sheath is corrugated to give it flexibility, so in such cases where the spiral pitch and the corrugated pitch are different, the coated conductor 4 is The metal sheath 5 is placed on the corrugated ridges on the inner surface. This coated conductor 4 consists of a conductor 8 and a covering material 9,
The covering material 9 completely covers the periphery of the conductor 8 and is insulated.

The conductor 8 may have any shape, such as a single conductor as shown in FIG. 3A or a group of multiple conductors as shown in FIG. 3B. The arranged coated conductor 4 is grounded before each connection in the cable line, so that the constantly generated current and the ground fault current flow to the ground.

If the eddy current were to be generated constantly, the problem with the induced eddy current would be the induction from the pond phase.
When an eddy current is generated, instantaneous polarization occurs in the same direction in the coated conductor on the side opposite to the pond phase side (the positive and negative reversals are repeated at the same time as alternating current), so the coated conductor 4 is connected to the cable. Simply attaching them vertically will not result in an improvement since eddy currents forming reciprocating paths will flow inside.

In the metal cable of this invention, the coated conductor 4 is spirally wound around the outside of the cable core, so that when viewed in the longitudinal direction, they cancel each other out, and although a voltage 4 is generated at each portion, no current is generated.

Therefore, in the power cable of the present invention, circuit loss is reduced due to the apparent resistance reduction of the metal sheath, and eddy current loss is not increased. Furthermore, in the event of an accident, if a ground fault occurs, the covered conductor 4 is closer to the cable conductor layer 1 than the metal sheath 5, so in most cases the ground fault will occur directly to the covered conductor.

For this reason, the coated insulating material of the coated conductor 4 is always coated with the coated conductor 4.
It is desirable that the sheathing insulation is such that the sheathing 9 will not break down due to the voltage applied to it, and will easily fall to the ground in the event of an accident. Even if a ground fault occurs directly to the metal sheath 5 without a ground fault to the covered conductor 4, if a high-resistance material such as stainless steel is used for the metal sheath 5, the local potential of the metal sheath 5 will instantly rise, and the metal The covering material 9 of the covered conductor 4 that is in contact with the sheath 5 is destroyed, and a ground fault current immediately flows through the covered conductor 4, which has a low resistance. Therefore, the structure is such that arc transfer that could damage the cable does not occur. When the covered conductor 4 arranged in the cable is grounded at both ends of the cable, in order not to impair the leakage current canceling effect of each covered conductor, for example, in the case of at least two or more covered conductors or a group of covered conductors, Covered conductor is A
, B, C, and D, and if you connect A and B together and then C and D together at one end of the ground, even if you touch the ground at the end of the pond, A and B and C and D are all the same, etc. ground all at once.

Furthermore, if one end of the covered conductor 4 is grounded, the following effects can be obtained.

That is, when both ends are grounded, a circulating current flows through the ground due to the current induced in the sheath, but when one end is grounded, there is no return path to the ground, and no increase in circuit loss occurs. Fault current flows from the fault point to the covered conductor and into the ground point. In this invention, the cross-sectional area of the covered conductor placed outside the cable core is determined by the ground fault current capacity.

If all the ground fault current flows through the coated conductor, for example, 8
In a 7-way V x 2,000-ground ○F cable, if the cross-sectional area of the aluminum sheath here is 536 squares, the cross-sectional area of the copper of the covered conductor is 3.
30 boils is enough. Therefore, if the number of coated conductors is IZ, it is sufficient to use a rectangular copper wire with a thickness of 27.5 mm and 2.2 ribs on the 12.5 side. As the covering insulating material, it is preferable to use a thin-walled material that can easily receive ground fault current and has a dielectric strength that does not break down under constant voltage.

Examples of things that are easy to manufacture in this sense are:
Phosphorous coating of resin such as formal resin or polyimide resin is preferable. As mentioned above, the power cable according to the present invention compensates for the lack of ground fault capacity by providing a covered conductor to reduce metal sheath loss, and by arranging the covered conductor in a spiral shape between the cable core and the metal, This mainly contributes to lower loss in ultra-high voltage OF cables by canceling out eddy currents that may occur in the covered conductor, and allowing ground fault current to flow instantly through the covered conductor without causing a large arc in the event of an accident. be.

[Brief explanation of the drawing]

1 and 2 show an example of the OF cable according to the present invention, with FIG. 1A being a cross-sectional view thereof, and FIG. 1B being an upper half cutaway view and a lower half vertical cross-sectional view thereof. FIG. 2A is a cross-sectional view of another example, and FIG. 2B is an upper half cutaway view and a lower half vertical cross-sectional view of another example. FIGS. 3A and 3B are cross-sectional views showing an example of a covered conductor group.
1...Cable conductor layer, 2...Insulator layer,
3...External semiconductor conductor layer, 4...Coated conductor,
5...metal sheath, 6...corrosion protection layer, 7...insulating oil layer, 8...conductor, 9...covering insulating material. Blinds Figure l (A) Figure l Old 1 Figure 2 (A) Figure 2 (B) Figure 3 [A] Figure 3 (B)

Claims (1)

[Claims] 1. In a power cable having a metal sheath outside the cable core, at least one coated conductor is spirally wound in the longitudinal direction of the cable between the outermost layer of the cable core and the metal sheath. A power cable characterized in that it is arranged with 2. The power cable according to claim 1, wherein two or more of the arranged covered conductors are grounded.The same covered conductor or a group of covered conductors are grounded at both ends. . 3. The power cable according to claim 1, wherein only one end of the arranged covered conductor is grounded, and the other end is left open.