Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
2002-11-27
2004-09-07
Dinkins, Anthony (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C174S08400S, C174S085000, C174S087000, C174S093000, C174S07000A, C174S068100, C174S135000
Reexamination Certificate
active
06787703
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a connection structure and a connection member for electrical connection of power cables.
2. Description of Relevant Art
The power cable is constituted with: a cable conductor (hereafter sometimes simply called “conductor”) configured as a bundle of core wires for transmission of required electric power; a cable insulator (hereafter sometimes simply called “insulator”) configured for insulation about the conductor and made of, for example, a plastic material such as bridged polyethylene; a cable screen (hereafter sometimes simply called “screen”) configured for electric screening about the insulator, and a cable outer cover (hereafter sometimes simply called “outer cover” or “cover”) configured for coverage and protection about the screen.
It therefore is necessary for electrical connection of power cables to employ a connection structure that has, as portions thereof, respective connection elements adaptive for power transmission, insulation, electric screening, and coverage and protection, and is provided with related considerations, in particular, for ensured prevention of breakdown due to insulation breakage at a connection portion for insulation.
In this respect, for power cables transmitting medium-voltage or high-voltage power, having great potential differences between a connection portion for power transmission and a connection portion for electric screening, there is needed a severe check for possible insulation breakage due to local concentration of electric field or stress.
This is specifically discussed below.
FIG. 9
illustrates a conventional connection structure CN
100
employed for electrical connection between a pair of medium- or high-voltage power transmitting and plastic-insulated power cables PC
1
and PC
2
, showing a longitudinal section at one side about an axis C.
The connection structure CN
100
includes: a power transmitting connection portion (hereafter sometimes called “power transmitting portion” or “transmission portion”)
120
configured for electrical connection between stripped conductors
2
and
2
(more specifically, conductor ends, like intra) of power cables PC
1
and PC
2
at the left and right; a screening connection portion (hereafter sometimes called “screening portion”)
130
configured for electrical connection between stripped screens
6
and
6
of power cables PC
1
and PC
2
; an insulating connection portion (hereafter sometimes called “insulating portion”)
140
filled between the transmission portion
120
and the screening portion
130
and configured to conformingly fit on stripped plastic insulators
5
and
5
of power cables PC
1
and PC
2
; and a covering and protecting connection portion (hereafter sometimes called “covering portion)
150
configured, as a two-piece separable protection case in the figure, to water-lightly fit on outer covers
7
and
7
of power cables PC
1
and PC
2
, covering outer periphery of the: screening portion
130
.
Like later-described corresponding embodiments of the invention, the covering portion may be configured, not simply as a two-piece separable protection case, but also as a structure in which a thermally shrinkable tube made of polyethylene or equivalent is fit water-tight on the screening portion, or as a structure in which the screening portion is covered by a glass-fiber reinforced epoxy resin tube, with a compound filled water-tight in between.
The transmission portion
120
is configured with a tubular conductor
8
fit on ends of the cable conductors
2
and
2
, a layer
9
of conductive rubber tape wound-fit on the tubular conductor
8
and remaining stripped parts of the cable conductors
2
and
2
, and a buried relatively thick inner electrode
121
fit conforming on the wound layer
9
of rubber tape and ends of the cable insulators
5
and
5
.
The internal electrode
121
is molded by filling a semi-conductive rubber material in a dedicated die therefor, as a substantially tubular member having at both ends thereof axially protruding outer peripheral parts
121
a
and
121
b.
The screening portion
130
is configured as a tubular outer electrode
131
with tapered end faces
131
a
and
131
b
at both ends, which is molded by filling a semi-conductive rubber material in a dedicated die therefor.
The insulating portion
140
is configured as a tubular insulating member
141
with tapered end faces
141
a
and
141
b
at both ends, which is made, by filling a polyethylene propylene base rubber material in a dedicated die with preset molds of inner and outer electrodes
121
and
131
, as an integral pre-molded connection member PM
100
.
Like later-described corresponding embodiments of the invention, the insulating portion may be prefabricated, before filling a semi-conductive rubber material to form the outer electrode
As a desideratum, there has been needed a power cable connection structure of connection member allowing reduction of cost in such manufacture.
The connection structure CN
100
of
FIG. 9
, employed for medium- or high-voltage power transmission, has great potential differences developed between the inner electrode
121
and the outer electrode
131
, and needs severe prevention against breakdown of insulation member
141
due to electric stress concentration. It therefore has structures shown in FIG.
10
A and FIG.
10
B.
FIG.
10
A and
FIG. 10B
are details of part-A and part-B of
FIG. 9
, respectively.
In the connection structure CN
100
, for prevention of insulation breakdown, each end of inner electrode
121
(
FIG. 10A
simply shows the right end
121
b
.) has an edge thereof rounded by a relatively large radius R as shown in
FIG. 10A
, to be 10 mm or more thick at the end, resulting in a radius difference exceeding 30 mm between the inside diameter of inner electrode
121
and the outside diameter of outer electrode
131
in
FIG. 9
, i.e., the thickness of pre-molded connection member PM
100
, of which reduction also has been a desideratum.
Further, in the connection structure CN
100
, as shown in
FIG. 10B
, the outer electrode
131
is formed as an electric field controlling stress cone large of radius to simply conform to the cable screen
6
, resulting in a relatively large dimension in thickness as well as in length thereof, leading to a long size of connection.
SUMMARY OF THE INVENTION
The present inventors made eager investigations in view of the foregoing points, to find that a rubber electrode layer constituted as a sheet-shaped semi-conductive rubber layer covered (i.e. coated or laminated) at a prescribed region thereof with a rubber layer high of permittivity (i.e. dielectric constant) can be used as a screening electrode in a power-transmitting portion and/or an electric screening portion to control the concentration of electric stress in insulator within a vicinity of the covered region, to a significant degree.
In addition the high-permittivity rubber layer can achieve the control of electric stress concentration at a successfully effective level in practice, providing that it has a high specific permittivity (&egr;
h
) equal to or greater than a specific permittivity (&egr;
c
) of cable insulator times five. For example, for a typical &egr;
c
=2.3, the high-permittivity &egr;
h
may well be 15 to practically achieve a definite reduction in thickness of pre-molded connection member. It is noted that this condition (&egr;
h
=15) is met in any of later-described embodiments of the invention.
The content of find is illustrated for particular cases in FIG.
11
A and
FIG. 11B
, where like elements of
FIG. 10
are designated by like reference characters to omit redundancy.
FIG. 11A
illustrates a connection structure in which a rubber electrode layer RE constituted as a sheet-shaped semi-conductive rubber layer SC covered at an outer periphery thereof with a high-permittivity rubber layer HP is interposed between a rubber tape wound layer
9
of a power transmitting portion and a rubber layer EPR of an insulating portion, and exte
Niinobe Hiroshi
Watanabe Kazuo
Dinkins Anthony
Fujikura Ltd.
Lee Jinhee
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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