US 3717718 A
Pressurized high voltage cable with a tubular, corrugated envelope that holds a high pressure medium, and a corrugated tube receiving the envelope and provided for radially supporting the envelope. Preferably, envelope and tube each being helically corrugated with opposite sense of winding and pitch, and a pressurized medium is maintained in the space between tube and envelope, the pressure of the medium being higher than the pressure on the outside of the tube but lower than the pressure in the envelope.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Schmidtchen [451 Feb. 20, 1973 HIGH PRESSURE CABLE  Inventor: Hans-Martin Osnabruck, Germany  Assignee: Kabel-und Metallwerke Guteholinungshutte Aktlengesellschalt, Hannover, Vahrenwalden, Germany  Filed: Nov. 29, 1971  Appl. No.: 202,752
 Foreign Application Priority Data Dec. 1, 1970 Germany ..P 20 58 971.3
 US. Cl. ..l74/106 D, 138/114, 138/122, 174/27, 174/107  Int. Cl. ..H0lb 7/20  Field of Search ..174/24, 27, 28, 25 R, 25 G, 174/26 G, 15 C, DIG. 6,105 R, 106 D, 102
D, 107,103, 113 R, 16 B, 99 B; 138/112,
 References Cited UNITED STATES PATENTS 3,490,496 1/1970 Stearns ..138/1 12 2,733,288 1/1956 Webster ..l74/106 R X 2,141,912 12/1938 Hobart ..l74/27 2,866,843 12/1958 Arman ..l74/25 G FOREIGN PATENTS OR APPLICATIONS 214,265 8/1956 Australia ..l38/122 Primary Examiner-Harold Broome Assistant Examiner-A. T. Grimley Attorney-Ralf H. Siegemund [5 7] ABSTRACT Pressurized high voltage cable with a tubular, corrugated envelope that holds a high pressure medium, and a corrugated tube receiving the envelope and provided for radially supporting the envelope. Preferably, envelope and tube each being helically corrugated with opposite sense of winding and pitch, and a pressurized medium is maintained in the space between tube and envelope, the pressure of the medium being higher than the pressure on the outside of the tube but lower than the pressure in the envelope.
3 Claims, 2 Drawing Figures The present invention relates to a pressurized, high voltage cable with one or more conductors arranged in a pressurized and sealed tubular, corrugated envelope.
It is well known to envelope cables in corrugated metal tubing. Such enveloping has been provided for high power cables as well as for communication cables. The jacket or envelope'of such a cable is usually made of steel or copper; aluminum is also used occasionally. Corrugated envelopes are more flexible than conventional lead or aluminum envelopes without corrugation. It is, furthermore, known to pressurize the interior of such envelope, using oil or gas as pressure medium. For reasons of simplifying manufacturing, the corrugated envelopes are usually chosen to have circular cross-section. However, employment of eliptical tubing as pressurized jacket or envelope for cable has been suggested for reasons of improving expansion.
It was found, however, that all these corrugated envelopes may be deformed; particularly in those cases I when for reasons of improving voltage break-through,
the pressure in the envelope is to be quite high. Particularly, pressurized corrugated tubing tends to expand axially. Thus, if for reasons of improving insulation the pressure in the envelope is very high, the cable may be deformed; an already installed cable may become actually useless.
It is also known to place a strip on corrugated tubular conduits for heated or cold fluids. However, such strip will not sufficiently improve operating conditions for pressurized cables with corrugated envelopes, because the pressure acts also radially on such an envelope, and the strip will not prevent undue expansion on that account.
It is an object of the present invention to overcome the deficiencies outlined above and to suggest a new approach for solving the problems posed by the tendency of corrugated cable envelopes to expand. In accordance with the preferred embodiment of the invention, it is suggested to cover or enclose the corrugated tubular envelope with a corrugated tube that engages directly the tubular envelopes as received. It was found that now higher pressure than before can be sustained in the envelope. Conversely, for the same pressure the load per unit area on the envelope is reduced, so that the envelope can be made of thinner material. Moreover, the corrugated pressurized envelope is maintained in position by the outer tube so that even for very high pressure in the envelope there is little axial expansion.
It is a particular feature of the invention to have envelope and outer tubing provided with helical corrugation but at opposite sense of winding and pitch. Such orientation of the corrugation crests relative to each other permits axial displacement of the tubes in relation to each other, and without binding that could lead to bending of the cable.
It is another feature of the invention to pressurize the space between outer tube and envelope, the pressure having value in between the pressure external to the tube and the pressure inside of the envelope. The pressurized medium between tube and envelope acts on the outer surface of the envelope for supporting same. In case of multiple concentric tubes, the pressure is staggered in that each tube wall has to sustain only a fraction of the total pressure differential between the pressure in the innermost envelope and e.g. atmospheric pressure on the outside of the outermost tube. Thus, none of the corrugated tubing is subjected to the full 5 pressure differential that could cause its lengthening,
and each of the inner tubes is supported additionally directly by the next outer tube.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:
FIG. 1 illustrates a longitudinal section view of a portion of a pressurized jacketed cable improved in accordance with the preferred embodiment of the invention; and
FIG. 2 illustrates an isometric section view of and into a pressurized high voltage cable in accordance with the preferred embodiment of the invention.
Proceeding to the detailed description of the drawings, in FIG. 1 is illustrated an inner tube or envelope having helical corrugation. The tube 1 is filled with gas at pressure P and having insulative properties. A second tube 2 is disposed as jacket around tube 1. The second tube has likewise helical corrugation with opposite sense of winding and pitch. Accordingly, the inwardly bulging corrugation crests of tube 2 can slide on the obliquely positioned, outwardly bulging corrugation crests of tube 1. Thus, the tubes can slide relative to each other without binding, bending or bulging.
The space 3 between tubes 1 and 2 is filled with gas at a pressure P smaller than P The gas in space 3 actually supports tube 1 from the outside, so that only the pressure differential P,P. acts on the corrugation of tube 1. Tube 2 may be subjected to regular atmospheric pressure. The pressure P may be 17 atmospheres and P, may be about 8 atmospheres.
Of course, in case additional tubing is provided, radial staggering of pressure permits ultimately development of still higher internal pressure in the innermost tube 1. Most importantly, the pressure that can be maintained inside of tube 1 is much higher than permissible without the relatively high pressure that acts immediately outside of tube 1 for supporting the wall thereof.
FIG. 2 illustrates details of a gass pressure cable in accordance with another example of the present invention. There is an inner, tubular envelope 4 made from longitudinally paid strip that has been formed into a split tube, seam-welded along the edges of the resulting joint and corrugated. Three conduits 6, 7 and 8,
establish a cable 5 that is disposed in the interior of envelope 4. The tube or envelope forming process may be carried out by folding strip around the cable 5. However, the tube or envelope could be formed first and the cable is then inserted into the envelope. The invention can be practiced in either case. Nevertheless, it is pointed out that the envelope forming process around the cable is preferred.
Gas pressure is sustained in envelope 4 to increase break-through voltage of cable 5. That pressure is to be selected quite high, so that a tube supporting pressure is maintained on the outside of envelope 4. That supporting pressure, in essence, will prevent envelope 4 from flattening by operation of high internal pressure. The supporting pressure is maintained inside of a tube 9, that tube also having helical corrugation but at opposite sense of winding as the helical corrugation of envelope 4.
The outer tube 9 is clad in a plastic coating 11, or the like, to afford protection. However, a concentrically staggered arrangement of telescoped tubes may be provided for establishing stepwise increase in pressure inside of tube or envelope 4, each corrugated tube having to withstand only a fraction of the total pressure difference between atmospheric pressure and the pressure in the interior of tube 4.
The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.
1. Pressurized high voltage cable having conductors contained in a tubular envelope, the envelope holding a high pressure medium, the envelope being corrugated, the corrugations extending around the axis of the envelope and including radially outwardly bulging corrugation crests, and a tube receiving the envelope, the tube being corrugated, the corrugations of the tube extending also around the axis of the tube and including inwardly bulging corrugation crests which extend obliquely to the crests of the envelope and provided for radially supporting the envelope, whereby the inwardly bulging crests of the tube can slide on the obliquely positioned, outwardly bulging crests of the envelope.
2. Pressurized cable as in claim 1, the envelope and the tube each being helically corrugated with opposite sense of winding and pitch so that the inwardly bulging crests of the tube can slide on the obliquely positioned, outwardly bulging crests of the envelope.
3. Pressurized cable as in claim 1, there being a pressurized medium in the space between tube and envelope, the pressure being higher than the pressure on the outside of the tube but lower than the pressure in the envelope.