US1941913A - Electric cable - Google Patents

Description

Patented Jan. 2, 1934 UNITED STATES PATENT OFFICE ELECTRIC CABLE Thomas Nixon Riley, London, England, assignor to International Standard Electric Corporation, New York, N. Y.

No Drawing. Application August 29, 1930, Serial No. 478,775, and in Great Britain March 5,

3 Claims. (01. 91-70) This invention relates to the manufacture of electric cables and particularly to cables having impregnated fibrous dielectrics. i

In manufacturing cables of the impregnated 5 dielectric type difiiculties have been experienced in the cable-during itsmanufacture one or more substances, or a pre-impregnating medium, which during or after the final drying operations can be evaporated to assist in expelling the air or residual air from the dielectric. The substance or medium may be applied to the core or to a convenient part of the insulation et the cable and is-preferably such that it will not be evaporated during the initial stages of the drying of the dielectric. The medium employed should be one which is not harmful to the electric properties of the insulation and preferably one which is beneficial thereto or to the manufacture of the cable generally. The medium should also be such that it will condense to a liquid or solid form at temperatures normallyexperienced duringthe 7 working of the cable. In some instances, the

medium may be mifed with another or other substances adapted to accelerate or retard its evaporation or if it be a liquid to bring it to solid form for application.

In ca y g the invention into efiect according to one convenient mode as applied to the manufacture of high voltage cables, the copper core after stranding may be passed through a bath of, or otherwise treated or coated with a vaporizable material which is such that it does not evaporate up to temperatures of the order of 100 C. at ordinary atmospheric pressure and then the insulation applied to the 'core in the ordinary manner. Alternatively, the whole or a part of the fibrous insulation may be impregnated with the vaporizable material before or after it is applied to the cable and thereafter varnished with a suitable retaining medium which may be of a resinous nature. An example of a suitable vaporizable material is methyl naphthalene, but it is to be understood that various other substances may be employed. At the appropriate time the cable is placed in an impregnating vessel which may be a tank or the outer sheath of the cable, this container is then evacuated so that the greater part of the air is removed from the dielectric of the cable.

During the initial stages of the drying Of the dielectric the temperature and the pressure are maintained at such values that the pre-impregnating medium is not vaporized to any considerable extent. Towards the end of the drying operations or after they have been completed the temperature is raised, as for example, by passing an electric current through the core, to such an extent that the pre-impregnating medium is vaporized and gradually replaces the residual air in the body of dielectric material.

After further vacuum treatment if desired the impregnating compound may be admitted to the containing vessel inthe usual manner. If desired, acondenser may be provided and arranged in the vacuum system so that the vaporizable material which is evaporated from the cable can be recovered.

It will be appreciated from the foregoing that the invention not only provides a convenient way of expelling or assisting in the expelling of air from the cable but also provides a convenient method whereby various substances may be introduced into, or incorporated in the dielectric of the cable. This may be taken advantage of for rendering the cable more amenable to subsequent treatment or impregnation, for instance by improving the absorption properties of the dielectric, or for other purposes.

What is claimed is:

1. A method of impregnating an electric cable comprising applying a vaporizable material to the conductive core, surrounding said core with insulation, subjecting the insulated core to a drying operation under a predetermined diminished pressure and at a predetermined temperature,

raising the temperature and decreasing the pressure and then introducing an impregnating medium into said cable.

2. An electric cable in the process of manufacture having a conductive core surrounded by insulation and methyl naphthalene associated therewith.

3. A step in the process of manufacturing electric cables whichconsists in associating methyl naphthalene with the cable prior to the drying operation. I

THOMAS NIXON RILEY.