FI58408C - ISOLERAD HOEGSPAENNINGSKABEL - Google Patents

Description

S "~" 71 Γ «1 ANNOUNCEMENT _. . _.

W (11) UTTAOONIMOSSKIlIFT 5 8408 i C (45) Patent granted on 12 January 1981

Patent meddelat * (51) Kv.rk.-Wci.3 H 01 B 9/00 SUOMI — FINLAND <W> Patunttlhakumus - Patuntmeknlng 782531 (22) Hukumltptlvt - An * eknlri | * d »| 18.08.78 (23) AikupiM — GHtifh * t * d * f 18.08.78 (41) Become Stuck - Blhrtt offumllg 19.02.80

Patent and Registry Administrators .... ...._______. „, _ *. ___ (44) Nlhttvikslpunoo Ja lciniL | ullulsim pvm. - latent- ocn registerstyrelsan AraMcan utlagrf och utUkrIftun publlcund 30.09.80 (32) (33) (31) Byyrfutty ucuolkuus —Buglrd priorKet (71) Oy Nokia Ab, Pursimiehenkatu 29 ~ 31, Mailbox U19, 00101 Helsinki 10, Finland-Finland ( FI) (72) Jouko Ilari Liuke, Helsinki, Heikki Antero Vesola, Vantaa, Finland-Finland (Fl) (7 * 0 Oy Kolster Ab (5 * 0 Insulated high voltage cable - Isolerad högspänningskabel The present invention relates to an insulated high voltage cable comprising an insulating layer and an electrical conductor within it, comprising an inner part braided of electrically conductive metal wires and a metal sheath surrounding it.

A high-voltage cable is already known, in which the conductor is normally made entirely twisted from separate wires. The disadvantage is the lack of surface tightness and also the unevenness of the surface, which e.g. causes a harmful corona effect in high voltage cables.

A conductor structure is also known (DE application publication 2 162 210), in which the uppermost layer is a metal tube, the purpose of which is e.g. protect the conductor from corrosion.

On the other hand, from materials that are much more resistant to corrosion than aluminum, it is difficult or impossible to produce a pipe that meets the same requirements by methods suitable for aluminum. For example, a weld seam is never as smooth in surface as a seamless pipe, and the tightness of the seam is not certain.

2 58408

A disadvantage in tubular and especially closed conductors is generally known to be that the inductive resistance at alternating current is slightly higher than in a conventionally wound conductor, especially in a large cross-section conductor. However, the relative importance of the disadvantage can be reduced by keeping the pipe wall strength reasonable. In addition, the tube has structurally better conductivity than the surface layer of the stranded conductor. The reliability of the manufacturing method increases the economic potential to increase the cross-section of the conductor sufficiently for the required alternating current.

Thus, it has hitherto been thought that a tubular metal sheath should not be used as the outermost layer of a stranded conductor, since the AC resistance of such a conductor is somewhat higher than that of a conventional sheath conductor of the same surface area under eddy currents.

However, it has now surprisingly been found that this effect is quite negligible compared to the advantages which can be achieved with a certain type of sheath structure.

The invention is based on the idea that the conductor of an insulated high-voltage cable has a tubular outer layer made of aluminum, which is airtight and smooth. Inside the tube is a conductor known per se, mainly a stranded and sealed conductor made of aluminum or copper wires. The pipe and the inner part have a small clearance in the manufacturing dimensions.

More specifically, the high-voltage cable according to the invention is mainly characterized in that the metal sheath is made of aluminum by extrusion so that its outer surface is seamless and smooth throughout, its cross-section is 5-50% of the total cross-section of the electrical conductor and six.

It should be noted, however, that in defining the scope of protection, this patent specification and the accompanying drawing must be taken into account in their entirety, as required by the Patents Act.

The advantages of the invention are to achieve almost all the advantages of a solid conductor, but to maintain a substantially better flexibility. The tightness of the conductor surface is an advantage when coating the conductor as a cable with plastic or a similar material: in a high-voltage cable with a conductor shield and insulation. When coating a normal stranded wire, you may see plastic or similar material penetrating between the wires, which often results in damage to the cable when the wire is loaded. Another advantage of reliable tightness is the potential damage to the cable: when water reaches the intact conductor, it is sufficient to repair the damage circuit. The same is true if the surface pipe of the conductor breaks: water gets inside the conductor but cannot get out elsewhere to damage the insulation. Even then, adequate remedial action is taken at the point of damage. On the other hand, the smoothness of the conductor surface 58408 has the advantage that the jchdin shield coming on top of it in a high voltage cable can be thinner than with a relatively uneven stranded conductor. When bending a conductor, the pipe is also made to follow the bending easily, since the manufacturing method, usually extrusion known per se, requires soft aluminum. In addition, the clearance between the tube and the inner part allows the parts to slide relative to each other. At the same time, the tube eliminates the risk that adjacent wires in the surface layer of the stranded conductor, when sliding during bending, would damage the plastic on top of the cable.

The invention will now be considered in more detail with the aid of exemplary embodiments according to the accompanying drawing.

Figure 1 shows a cross-sectional view of a cable with a circular cross-section of a cable according to the invention.

Figure 2 shows a cross-sectional view of a cross-sectional electrical conductor of a cable according to the invention.

The inner part 1 of the conductor is stranded in a manner known per se and can be unsealed or sealed (Fig. 1) in order to save space. An aluminum tubular jacket part 2 is extruded on the stranded part in a manner known per se, so that a small gap is left between it and the inner part 1 or that it presses at most lightly against the inner part 1. Instead of extrusion, any other method known per se can be used, by means of which the tubular jacket part is made tight and the outer surface smooth, e.g. various pipe welding methods in which aluminum strip is used as a starting material.

In principle, the tubular jacket part 2 should be as thin as possible, but not so thin as to wrinkle. On the other hand, the tubular sheath part 2 forms an essential part, e.g. 20-50%, of the total cross-sectional area of the conductor.

An example is a 110 kV cable with a total aluminum conductor cross-section of 1400 nm. The wire diameter is 44 rnn. The average thickness of the sheath part is about 3 nm (lower limit 2.75 nm). The aluminum sheath is surrounded by a semiconducting layer with a thickness of about 1 nm. The thickness of the insulation layer surrounding this layer is about 15 nm. The insulating layer is further surrounded by a 0.5 to 2.0 nm thick glare shield, a 3 nm thick contact shield or similar metal layer, and an outer 3.5 nm thick plastic sheath. These layers surrounding the aluminum sheath are not indicated in Figure 1 by reference numeral 3.

The clearance of the jacket part 2 and the inner part 1 is of the order of 0.1 nm, which corresponds to a loose sliding tightness.

Since the outer surface of the jacket part 2 is smooth, there is no harmful Corona L effect on this surface.

It is clear that the idea according to the invention is also applicable to conductors with a non-circular cross-section, e.g. the sector conductors according to Fig. 2.