Direct current oil-filled self contained cable

Details Direct current oil-filled self contained cable Direct current oil-filled self contained cable

1994-02-25

1996-01-02

Nimmo, Morris H.

Electricity: conductors and insulators

Conduits, cables or conductors

Insulated

174 25R, 174120SC, H01B 702, H01B 906

Patent

active

054810701

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a direct current (hereinafter abbreviated to DC) oil-filled self contained (hereinafter abbreviated to OF) cable used as a long power cable, particularly a long distance submarine power cable, for large electric power transmission.


PRIOR ART

Heretofore, oil immersed solid power cables, or mass-impregnated non-draining (MIND) cables and OF cables have been adaptable as DC cables. In the case of DC OF cables, kraft paper with high impermeability and which is excellent in breakdown strength is often used, because such dielectric characteristics as permittivity or dielectric tangent are, unlike alternating current (hereinafter abbreviated to AC) cables, not significant to DC cables. They are otherwise not much different from AC cables in basic structure.
DC Cables must have (1) sufficient DC withstanding characteristics, (2) sufficient withstanding characteristics against such abnormal voltages as lightening surges etc. and (3) sufficient withstanding characteristics against polarity reversal and, moreover, must satisfy the required carrying capacity.
DC stress distribution in insulation is determined by the .rho.-characteristic of the insulation. This .rho.-characteristic in turn varies with temperature and stress. It undergoes a complex change, as the temperature distribution in the insulation changes.
As far as the conventional DC cables in use with the kraft paper insulation are concerned, the DC stress distribution determined by the aforementioned .rho. characteristic is not the prominent factor of their design, but these cables have rather been designed on the basis of impulse design as with AC cables, and more particularly on the basis of the electric stress which will develop when an impulse with opposite polarity superposed onto DC is applied on the conductor.
For discussions on DC cables for large electric power transmission, not only is impulse strength required, as in AC cables, but DC withstand-voltage strength is required as well. In this case, evaluating the necessary thickness of the insulation would generally result in a large thickness, detracting from ensuring the required transmission capacity. As a countermeasure, the conductor resistance may be reduced by increasing the conductor size, to cut down its current loss, thereby ensuring the transmission capacity. But this approach would involve productivity reduction, cable size increase, cost rise and other various problems.


DISCLOSURE OF THE INVENTION

Against this background, the present invention provides a DC OF cable in which the above described problems have been solved, Its first characteristic feature lies in that its main insulation is composed of a composite insulation tape (hereinafter abbreviated to PPLP) formed by laminating a low dielectric loss plastic film and kraft paper, that .rho.-grading is applied by combining therewith another or other PPLP(s) differing in plastic film ratio, as required, and that 1-10 sheets or layers of kraft paper are wound on the aforementioned PPLP main insulation to arrange its layer(s) on the inside and/or outside thereof.
Its second characteristic feature is that its main insulation is composed of PPLP, that .rho.-grading is applied by combining therewith another or other PPLP(s) differing in plastic film ratio, as required, and that 3-5 sheets or layers of carbon paper are wound on the aforementioned PPLP main insulation to arrange its layer(s) on the inside and/or outside thereof.
Further, its third characteristic feature lies in that its main insulation is composed of PPLP, that .rho.-grading is applied by combining therewith another or other PPLP(S) differing in plastic film ratio, as required, that 3-5 sheets or layers of carbon paper are wound at least just onto the conductor, and that 1-10 sheets or layers of kraft paper are wound on the PPLP insulation to arrange its layer(s) on the inside and/or outside thereof.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an insulation configuration of a DC OF cable embod

REFERENCES:
patent: 3749812 (1973-07-01), Reynolds et al.
patent: 4329536 (1982-05-01), Sato et al.
patent: 4602121 (1988-07-01), Priaroggia
patent: 4859804 (1989-08-01), Hata et al.
patent: 4994632 (1991-02-01), Bosisio et al.

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