NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING, MUMBAI
CABLE CONSTRUCTION & MANUFACTURING PROCESS
UNDER THE GUIDANCE OF
Dr. KVSS NARAYANA RAO
Submitted By
PRASENJIT
HOJAI
SARVESH HIREMATH
ROLL NO-66
ROLL NO-88
Cable Construction & Manufacturing Process
fig-power cable parts
Power Cable
mainly subdivided into parts-
1. Conductor
2.
Insulation
3. Metallic
Sheath
4. Bedding
5. Armouring
6.
Outersheath
Conductor
Copper or Aluminium used for the Conductors obtained
in the form of rods. The 8.0 mm Copper or 9.5mm aluminium rods. After testing,
rods are drawn into wires of required sizes. These wires are formed into final
Conductor in the stranding machines under strict Quality Assurance
Program.
Insulation
Cross linked polyethylene compound or PVC is insulated
over Conductor by Extrusion process. XLPE insulated cores are cured
by steam curing in vulcanizing chamber to provide thorough cross-linking.
The raw materials & thickness of Insulation are
maintained under strict Quality Control and conform to B.S. 5467 / IEC 60502
Part-1 or B.S. 6346 / IEC 60502 Part-1 Standards for XLPE & PVC cables respectively.
Laying Up
The insulated cores are laid up with a right hand, or
alternating left & right hand, direction of lay in the sequence of the core
numbers or colours. Where ever necessary non-hygroscopic PP / PVC Fillers &
binder tape are used to form a compact and reasonably circular cable.
Bedding
All armoured cables have extruded PVC bedding. The PVC
used for bedding is compatible with the temperature of Insulation
material.
Armour
When armouring is required, the armour consists of
single layer of Galvanised steel wire. The armour is applied helical, with a
left hand direction. We also provide other armours such as steel strip, tape or
tinned copper. Single core cables are armoured with Aluminium or copper wires.
OuterSheath
The standard cables are manufactured with Extruded
black PVC Type-9 of B.S. 7655 or ST-2 of IEC 60502. Outer sheath is embossed or
printed with the information required by the related standards. Special FR,
FRLS compounds are used for outer sheathing of cables, to suit customer’s
specification requirements.
Cable
Manufacture
An extruded cable production line is
a highly sophisticated manufacturing process that must be run with great care
to assure that the end product will perform reliably in service for many years.
It consists of many sub processes that must work in concert with each other. If
any part of the line fails to unction properly, it can create problems that
will lead to poorly made cable and will potentially generate many metres of
scrap cable. The process begins when pellets of insulating and semiconducting
compounds are melted within the extruder. The melt is pressurised and this
conveys material to the crosshead where the respective cable layers are
formed. Between the end of the screw and the start of the crosshead.it is
possible to place meshes or screens, which act as filters. The purpose of these
screens was, in the earliest days of cable extrusion, to remove particles, or
contaminants that might be present within the melt. While still used today, the
clean characteristics of today’s materials minimize the need for this type of
filter. In fact, if these screens are too tight, they themselves can generate
contaminants in the form of scorch or precross linking.
Nevertheless, appropriately sized
(100 to 200-micron hole size) filters are helpful to stabilize the melt and
protect the cable from large foreign particles that most often enter from the
materials handling system.
The most current technology uses a
method called a true triple extrusion process where the conductor shield,
insulation and insulation shield are coextruded simultaneously. The cables
produced in this way have been shown to have better longevity (Figure 3) [7].
After the structure of the core is formed the cable is crosslinked to impart
the high temperature performance. When a CV tube is used fine control of the
temperature and residence time (linespeed) is required to ensure that the core
is crosslinked to the correct level.
Jackets
In most MV, HV and EHV cable
applications, the metal sheath/neutral is itself protected by a polymeric
oversheath or jacket. Due to the critical performance needed from the
oversheath, there are a number of properties that are required, such as good
abrasion resistance, good processability, reasonable moisture resistance
properties, and good stress cracking resistance. Experience has shown that the
material with the best composite performance is a PE-based oversheath, though
PVC, Chlorosulfonated Polyethylene and Nylon have been used as jacket
materials.
Tests on XLPE cables retrieved after
10 years of operation show that the mean breakdown strength falls by almost 50%
(from 20 to 11 kV/mm – HDPE & PVC, respectively) when PVC is used as a
jacket material. Many utilities now specify robust PE based jackets as a
result. The hardness of PE is also an advantage when protection is required
from termite damage.
Jackets extend cable life by
retarding the ingress of water and soluble ions from the ground, minimizing
cable installation damage and mitigating neutral corrosion. Ninety three
percent of investor-owned utilities in the USA specify a protective jacket. The
semiconductive jacket or oversheath is recommended for high lightning incident
areas or joint-use trenches where telecommunications cables co-exist with power
cables.
Inspection
and Test Plan for Power Cable
The inspection and test plan for
power cable article provides you information about power cable test and power
cable inspection in manufacturing shop.
- Witnessing voltage and
insulation resistance tests or alternative spark tests.
- For 33Kv cable, witness
dielectric power factor voltage test.
- Dimensional checking on sample
off-cut i.e. construction consistency, insulation thickness, external
sheath screen, armours and mans of main components.
- Visual checking in respect of
cable formation, core and external sheath colors, marking legibility.
- Testing on material sample i.e.
conductor coating, insulation external jacket for elongation, heat strocle
blending and characteristics of armour, metal and sheath components
including zinc coating.
Third
Party Inspection for Power Cable Configuration
Third
party inspector checks the power cable configuration in accordance to drawing
and datasheets. Following items is taken in account:
- Cable type
- Number of conductors
- Conductor size
- Conductor color coding
- Insulation type and size
- Fillers
- Water stoppers
- Armour
- Shield
- Outer diameter
- Other specified
elements/dimensions
- Cable identification
References:-
-
Electrical Power Cable
Engineering by Bruce S. Bernstein and William A. Thu
- L.V. Power and
Control Cables by Oman Cables Industry
- TR-101670 “Underground Transmission Systems Reference Book: 1992 Edition,” Electric Power Research Institute
- http://ieeexplore.ieee.org/Xplore/home.jsp