Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
2001-12-19
2003-09-23
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C174S093000, C174S073100
Reexamination Certificate
active
06624357
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tubular cable adapter for use as transition in jointing and/or terminating medium voltage impregnated paper insulated cable, comprising an impregnating compound barrier sleeve, a semi-conductive layer partially covering said impregnating compound barrier sleeve, and a support member for maintaining said impregnating compound barrier sleeve and said semi-conductive layer in a radial expanded state, said support member being removable from said impregnating compound barrier sleeve.
When a medium voltage cable, and more particularly a impregnated paper insulated cable, e.g. a 3-phase paper insulated “Mineral Insulated Non Draining” type cable with common lead sheath, needs to be connected, terminated or jointed, by means of accessories normally used for polymeric insulated “dry” cables, it is current practice to apply a barrier layer over the impregnated paper insulating layers. This barrier layer seals the impregnating compound inside the paper layers, protects the paper-insulated cable and provides the same interface as for a dry cable on which the accessories can then be built.
In the present state of the art, a known solution is based on the use of a cold shrinkable tubular cable adapter as for instance disclosed by the European Patent Application EP-A1-0 780 949 entitled “Universal cable adapter, cable joint using the adapter and method of making same” of the “Minnesota Mining and Manufacturing Company” (3M™), first filed EP-95203627 on 23.12.1995.
FIG. 1
represents a longitudinal view of a tubular cable adapter
100
of this prior art. The cold shrinkable tubular cable adapter comprises:
an impregnating compound barrier tubular member
10
, made from an elastic material and covering an insulating conformable material
11
such as a mastic,
a semi-conductive layer
20
, made from a semi conductive material such as a liquid silicone with conductive fillers added, covering partially and at one end the barrier member
10
,
and a support member
30
maintaining the barrier member
10
in a radial expanded state, the support member
30
being removable by pulling on the free end
300
of a helical strip.
Paper insulated cables for medium voltage applications of 10 kV to 30 kV most often are of 3-core design, i.e. 3 paper-insulated cores are housed inside a common metallic shield, e.g. a lead sheath. Each of these insulated cores can have an electrical screening layer, generally made of metalized paper (so called individually screened core) or not (belted core).
FIG. 2
shows a schematic example of the adapter
100
installed over one of the prepared belted cores
40
,
41
,
42
of a triphase paper cable
110
. On the right side of
figure 2
, just beyond the break out
101
, the cable
110
contains a common lead sheath
14
mainly covered by a trifurcating glove
16
. Only the prepared core
40
is entirely represented on figure
2
. The prepared core
40
consists of an impregnated paper insulation
12
, partially covered by a metalized paper screening layer
13
previously applied in such core. The prepared core
40
is extending from the break-out
101
towards the adapter
100
to be installed. Before the installation of three adapters as adapters
100
over each core
40
,
41
,
42
, it is necessary to install on each respective core
40
,
41
,
42
a metallic tubular braid
150
,
151
,
152
, which needs to be supported by an individual support member (not shown). Furthermore, a short protective tube (not visible) supported by another additional support member (not shown) is installed over such braids
150
,
151
,
152
. All support members are then removed and other steps, not detailed here, performed.
Each braid
150
,
151
,
152
is then folded back over the trifurcating glove
16
covering the protective tubes.
Thus, before adapters
100
can be installed on each core
40
,
41
,
42
different elements need to be installed, of which two are shrinkable and have their own support member.
SUMMARY OF THE INVENTION
The adapter
100
is installed so that the semi-conductive layer
20
is located above the screening layer
13
and its extremity is in contact with the tubular metallic braid
150
.
Indeed, such adapters are used as a transition and provide a cable interface similar to the one of a dry cable. To complete the junction or the cable termination after the installation of adapter
100
, a conventional joint device normally used between polymeric insulated “dry” cables covers such adapters.
This prior art solution is not satisfactory since there are various complex steps for achieving the required structure before completing the junction or the cable termination. This complexity and the high number of steps run the risk of causing mistakes and time loss.
An object of the present invention is to provide a tubular cable adapter modified to substantially reduce the cost and the installation time for a cable termination or a cable connection on an impregnated paper insulated cable.
To this end, the present invention provides a tubular cable adapter for use as transition in jointing and/or terminating a medium voltage impregnated paper insulated cable, comprising an impregnating compound barrier sleeve, a semi-conductive layer partially covering said impregnating compound barrier sleeve, and a support member for maintaining said impregnating compound barrier sleeve and said semi-conducive layer in a radial expanded state, said support member being removable from said impregnating compound barrier sleeve,
characterized in that said tubular cable adapter further comprises a conductive member in contact with said semi-conductive layer and covering at least partially said impregnating compound barrier sleeve and said semi-conductive layer.
This single tubular cable adapter may be used to seal and shield the whole length of a prepared paper cable without metallic sheath and other outer sheaths in order to provide the same interface as for a dry cable A portion of the impregnating compound barrier sleeve not covered by the semi-conductive layer serves as the interface with the known accessories such as a classical joint.
The conductive member of the invention enables to make electric contacts and thus serves as fault current carrier and ensures the link between the different screens of the assembly. Moreover, it is a security element for protecting people during any accidental damaging of the core below it.
After the removal of the support member, the impregnating compound barrier sleeve extends from the break out of the paper cable to the conductor connection and is mainly located over the paper insulation layer of a paper cable. If present, a screening layer applied on the impregnated paper insulation is previously removed over a necessary distance in a conventional manner.
Unlike the prior art, no additional elements with their own support members need to be installed on the prepared cable before the adapter installation. The invention thus allows an easier and faster installation because of the less number of parts and less possibility of mistakes. It is also less expensive as the prior art solution.
Another characterizing embodiment of the present invention is that the conductive member can extend at one end beyond the impregnating barrier sleeve and can cover entirely the semi-conductive layer.
Thus, at such end, the conductive member can be brought into electrical contact with the lead sheath of the paper insulated cable.
Advantageously, the conductive member and the impregnating compound barrier sleeve can both be exposed, that is non recovered, at one same end of the support member.
In this way, at such end, the creation of an interface similar to that of a dry cable for a cable termination or a junction can be facilitated since the conductive member can be brought directly in electrical contact with a conductive member of an accessory and the impregnating compound barrier sleeve directly protects such accessory against the impregnating compound of the cable.
In a preferred embodiment of the inventi
Nexans
Nguyen Chau N.
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