The present invention relates to a low tension XLPE underground cable used for power transmission and delivery. More particularly, the present invention relates to XLPE cable with ultra violet retardant properties thus reducing the ultra violet aging property and providing a longer life to the cable.

BACKGROUND OF THE INVENTION:

Cross-Linked Polyethylene (XLPE) insulated cables have been proven as a better alternative to polyvinyl chloride (PVC) insulated cables. XLPE cables have excellent dielectric properties and better thermal strength thus making them a viable option for medium and high voltage transmission. XLPE cables have various advantages to its counterparts like low cost (nearly 25% to its counterparts), easier installation process, no fire-risk during installation, and longevity.

Most common breakdown of cables occur due to: a) penetration of UV rays, b) electrical stress, and c) mechanical/thermal stress. Most common and neglected cause of breakdown is penetration of UV rays. XLPE insulated cables are exposed to embrittlement when exposed to Ultraviolet rays from sun. XLPE insulated cables develop cracks with continuous exposure to UV rays thus making the cable of no utility as cracks expose to moisture ingression, failure at exposed sections, and safety issues with people managing these cables. This is called ultra violet aging problem. This ultra-violet aging problem adds to frequent replacement of cable, untimely faults and power breakdown, procurement of additional UV retardant kits and paints. This adds to a significant increase in maintenance cost of these cables.

Carbon Black compound has been used in the past in the outer jacket of the cable to prevent perforation of UV Rays to the XLPE coating and thus preventing development of cracks as described in ‘An infrared radiation reflecting cable’ (Publication No: WO 2010058385 A1, Application No: PCT/IB2009/056013, Inventor: Graeme Alexander). Although, outer jacket of the cable has to be partially removed while installation and thus while the cable is in use, UV rays are still exposed to XLPE coating thus causing ultra violet aging problem.
Moreover, coloring of cables is required for core identification purposes as a standard regulation in various countries including but not limiting to United States, European States, and India. The red, blue, and yellow color pigmentation of cables gives more exposure to UV rays.

An improvised XLPE cable with smarter color identification of cables is the need of the hour which is not prone to ultraviolet aging problem thus increasing its life and utility and at around the same or reduced cost of current alternatives.

OBJECT OF THE INVENTION:

It is thus the basic object of the present invention to provide UV retardant property to the XLPE cable with use of black pigmented additive and provide extruded color lines on the XLPE cable for core identification purposes which is also a regulatory requirement in various countries.

SUMMARY OF THE INVENTION:
A cable comprising: at least one inner conductor cable; at least one insulation cover co-axially covering the at least one inner conductor cable; and an armor enclosing all of the at least one conductor cables and at least one hollow insulation cover; wherein the at least one insulation cover is made of cross-linked polyethylene (XLPE) with black color pigment. Black color pigment added to the XLPE material provides UV Retardant properties to the cable thus avoiding cracking of cables and provide cables with a longer life. XLPE layers are also marked with extruded colour lines for core identification purposes as it is also a regulatory requirement in various countries. The present invention is a same cost alternative to existing products but comes with additional UV retardant properties thereby increasing life of cable and drastically reducing maintenance costs thus adding customer delight.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:

Figure 1(a) shows an XLPE insulated cable exposed to sunlight UV Rays.

Figure 1(b) shows an XLPE insulated cable developing cracks when exposed to sunlight UV Rays.

Figure 2 shows an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES:

A power cable 100 is shown in Figure 1(a) exposed to UV Rays generated from sun 200. The power cable comprises of a sheath or jacket 110 covering conductor cables 130. Conductor cables 130 are covered with XLPE (cross-linked polyethylene) insulation layers 120. Sheath or Jacket 110 is usually made of PVC material which is exposed to UV rays, thus allowing XLPE insulation layers 120 being exposed to UV rays. XLPE material when exposed to UV rays on a continual basis starts developing cracks 140 as illustrated in Figure 1(b). When these cracks develop, cable is exposed to moisture thus allowing a chance of short circuiting. Cracks also lead to untimely power outages. Due to generation of these cracks, customers have to schedule maintenance, bear loss of power outages and more often than not, procure and install UV retardant kits on to these power cables thus adding a huge cost of maintenance.

The present invention holds UV retardant properties within same manufacturing cost as the non-UV retardant property XLPE Cable, thus providing customer delight.

One embodiment 300 of the present invention is illustrated in Figure 2. A sheath 310 covers three conductor cables 330. These conductor cables 330 are insulated with a layer of XLPE layers 320. These XLPE layers 320 are made of XLPE material with black colour pigments. These black colour pigments do not allow UV rays to pass through the cables and thereby prevent generation of cracks.

In many countries, colouring of cables with pre-defined colours for identification of cables is a regulatory requirement. When cables are coloured with a coloured layer, the coloured layer is also exposed to UV rays, thus defeating the purpose of UV retardant property of cable. Therefore, in the present invention, a colour line 340 is extruded on the XLPE layers with black pigments 320.

The present invention with black pigment additive in XLPE layer and extruded colour line for identification of core meets the regulatory requirement in India - IS: 7098.

The black colour pigment added to the XLPE layer provides UV retardant properties based on the Beer-Lambert Law wherein the absorption coefficient of material is tested on UV rays transmission through the XLPE black pigmented layer.

CLAIMS:1. A cable comprising:
at least one inner conductor cable;
at least one insulation cover co-axially covering the at least one inner conductor cable; and
an armor enclosing all of the at least one conductor cables and at least one hollow insulation cover;
wherein the at least one insulation cover is made of cross-linked polyethylene (XLPE) with black color pigment.
2. The cable as claimed in claim 1, wherein the cable is manufactured using conventional extrusion process with wet curing.
3. The cable as claimed in claim 1, wherein the cable comprises three inner conductor cables, three XLPE with black color pigment insulation covers co-axially covering the three inner conductor cables correspondingly, and an armor enclosing all of the three conductor cables and three insulation covers.
4. The cable as claimed in claim 3, wherein the three XLPE insulation covers are marked with an extruded line of color for identification purposes.
5. The cable as claimed in claim 4, wherein the colors used for marking are red, yellow, and blue.
6. The cable as claimed in claim 1, wherein the cable is designed with specifications to meet Indian Standard IS: 7098.