Cable Properties & Construction
Cable Properties
Special features which we can offer for MV cables
| Watertight construction (both radial and longitudinal). |
| Lead sheath available for options. |
| Resistant to heavy vibration. |
| Available in long delivery lengths to reduce number of joints. |
| Corrosion-free screen area. |
| Copper or aluminum conductor up to 2000mm^2. |
| Metallic sheath and radial moisture barrier made of copper wire or tape. |
| Different options for outer PE jackets (LDPE, MDPE & HDPE). |
| Different options for LSF, LSZH & FRPVC, being anti-termite or UV resistant as per BS 7835, IEC 60332 etc. |
| Strippable insulation screen. |
| Metallic screen made of multiple layers of copper tapes or a combination of copper wires and tapes to increase the earth fault current carrying capacity. |
| Increased armour conductivity by insertion of hard drawn copper wires in armour. |
Cable Construction
Caledonian medium voltage cables are manufactured using the monosil process. Caledonian provides the highly specialized plant, state-of-the-art research facilities and meticulous quality control procedures that are required for the manufacturing of PVC insulated cables for use up to 6KV and XLPE/EPR insulated cables for use at voltages up to 42 KV. The materials are all kept in cleanliness-controlled conditions throughout the production process in order to ensure the absolute homogeneity of the finished insulation materials.
Conductors
Either aluminium or copper conductors are used. Conductors up to 800mm^2 will be circular, compacted & stranded and shall comply with IEC 60228 class 2. 1000mm^2 conductor will be circular stranded type on which a layer of semi-conducting tape will be applied.
Conductor Screen
This will be an extruded layer of semi-conducting crosslinkable compound applied under simultaneous triple extrusion process over the conductor along with the insulation and the insulation screen. The triple extrusion is a single high precision operation that eliminates the possibility of any contamination between the layers which could create irregularities in the electrical field. By careful material selection and special attention to process parameters, Caledonian produces the insulation screen layers with the required degree of stripping force as stipulated by the applicable national or international standard.
Insulation
This will be an extruded layer of XLPE or EPR applied over conductor screen under triple extrusion process along with conductor screen and insulation screen. PVC may be used for 1.8/3KV and 3.6/6KV cables.
Insulation Screen
This will be a layer of semi-conducting crosslinkable compound which will be applied by triple extrusion process over the insulation.
Metallic Screen
It will consist of a layer of copper tape applied helically with overlap over insulation screen. Other combinations of metallic screens as per customer’s requirement can also be provided on request.
Laying-Up
In case of three core cables, the three cores are laid up with non-hygroscopic fillers like polypropylene(PP) fillers at interstices and a binder tape is applied with an overlap. These binder tapes can be of PVC or foamed Polyethylene.
Inner Sheath (Bedding) for Armoured Cables
Extruded layer of PVC or PE is applied over the laid up cores for armoured cables. PVC is normally of grade ST2 and PE of grade ST7 as per IEC 60502 Part 2.
Armouring
In case of armoured cables, the armour is applied helically over inner sheath. For single core cables, it is of aluminium wires and for multicore cables, the armour can be of one among the following options:
a) Galvanized steel wire.
b) Galvanized steel tape.
c) Galvanized steel strip.
Over Sheath
An extruded layer is applied over the armour in case of armoured cables and over laid up cores in case of unarmoured cables. Outer sheath material can be either PVC, PE, HDPE or MDPE. Caledonian medium voltage cables are normally supplied with red PVC over sheaths complying with BS 6622 or IEC 60502. Other colors may be provided to suit a range of installation considerations such as the effect of UV radiations and differing soil compositions. Anti-termite formulations can also be supplied in addition to graphite-coated over sheaths where on-site testing of the sheath is required.
Fire Performance on Cable Sheaths
Cables can also be supplied with special flame retardant PVC over sheaths to comply with the IEC 60332 standard. We can also supply cables with Low Smoke Halogen Free (LSZH) sheaths according to BS 7211 and BS 6724 standards or other equivalent international standards.
Cable Machinery & Equipments
The MV cable manufacturing facility at Caledonian is the most modern facility available today with the state of the art machinery & equipments. The entire MV cables manufacturing plant at Caledonian is fully air-conditioned with humidity control to ensure contamination free atmosphere. The heart of MV cable manufacturing facility is the CCV line. This line supplied by Troester, Germany and which incorporates some of the most modern features like,
- Triple extrusion head to ensure superior quality of extrusion and uniform bonding of conductor screen, XLPE insulation and the insulation screen.
- CDCC – Completely dry curing & cooling in an inert atmosphere of nitrogen.
- In line X-ray machine for checking proper concentricity as well as measuring thickness of extruded materials.
- Fully computerized auto-cure control system, which controls all driving parameters to achieve best curing of extruded materials.
- Fully automatic compound handling system in a positive pressure atmosphere ensuring a contamination free line, which is absolutely essential to achieve superior quality product.
Some of the other machines include:
- Drawing machine from Niehoff, Germany
- Cable stranding machine from Mali, Austria
- Screening machine from Ceeco, Canada
- Five drum cabling machine from Mali, Austria
- Armouring machine from Ceeco, Canada
- Extruder from Troester, Germany, etc.
With the manufacturing facilities incorporating the use of latest available technology, the MV cables offered by Caledonian provides customers with a definite advantage in terms of:
- Compete adherence to specifications,
- Superior overall performance,
- Minimum risk of insulation failures,
- Longer service life,
- Triple head extrusion.
Product Testing
Caledonian has made major investment in the testing facilities for its MV cables factory. We have equipped ourselves with the latest and most advanced cable testing facility available in the world.
Our major testing facilities include:
a) DC withstand voltage test system from Hipotronics USA.
b) Partial discharge test system from Haefely, Switzerland.
c) HV test system from Haefely, Switzerland.
d) On line conductor resistance meter from Aesa, Switzerland
Effective quality assurance procedures are essential to ensure the consistency and long term reliability and performance of all products. Caledonian always recognises the importance of quality assurance and this commitment is reflected in the company achievement of ISO 9001 certification. The design validation for our MV Cables has been done at recognized international laboratories.
With the above state of the art testing facility, we can conduct all type, routine as well as special tests mentioned in IEC 60502 Part 2, BS 6622 & other international specifications, inhouse. While 100% of the cables are tested for routine tests prior to dispatch, however upon customers’ request, other type/special tests can be carried out in house or by any third party laboratory.
The tests can be divided into different categories:
Type Tests
The type test is conducted by KEMA, Netherlands to validate a special cable design type.
Electrical type tests include the following:
- Partial discharge test (IEC 60502 clause 18.1.3)
- Bending test (IEC 60502 clause18.1.4)
- Sheath measurement (IEC 60502 clause 18.1.5)
- Heating cycle test (IEC 60502 clause 18.1.6)
- Impulse withstand test followed by a.c. voltage test (IEC 60502 18.1.7)
- High voltage test for 4 hours (IEC 60502 clause 18.1.8)
- Resistivity of semiconducting screens (IEC 60502 clause 18.1.9)
Non electrical type tests include the following:
- All non electrical type tests as required by IEC 60502
Routine Tests
Routine tests are carried out on each finished length of cable to control the overall quality of the cable. They comprise:
- Measurement of dimensions.
- Measurement of conductor resistance: the D.C. resistance of each conductor, when corrected to 20°C and 1 Km, shall not exceed the appropriate maximum value specified in IEC 60228 respectively.
- Measurement of screen resistance.
- High voltage test: an a.c. voltage of 3.5 Uo shall be applied for 5 minutes between each conductor and metallic screen. No breakdown shall occur.
- Partial discharge test: the magnitude of discharge at 1.73 Uo shall not exceed 10pC.
- Measurement of dielectric losses and capacity.
Special Tests
Special tests are carried out on 10% of the lengths for each production lot, in any case on one length. They are carried out if major changes in design are introduced.
They comprise:
- Measurement of dimensions
- Checking sheath identification
- Testing shrinkage of PE sheath
- Conductor examination
- Carrying out voltage test
- Carrying out hot set test for XLPE insulation
At Caledonian, quality assurance is an integrated part of the production process and maintained from order entry and manufacture through to testing, packaging and shipping. All quality assurance procedures are regularly audited by recognised quality organisations and all routine voltage testing is carried to more stringent levels than that required by international standards.
Specification for testing is designed in accordance to the following international standards:
- IEC 60502
- IEC 60811
- BS 5368
- DIN 56283/VDE 0273
- EDF HN 33S23
- AS&JIS
- ASTM
- etc.
We have also installed many in line devices/facilities for checking the product quality during the manufacturing process like the X-ray machine installed in the CCV line, curing optimization software, etc, to avoid any risk or failure & to ensure a long service life for our products. With these modern equipment & facilities, we ensure to maintain close manufacturing tolerances, high accuracy to customer specifications as well as effective monitoring of the entire manufacturing process to offer a world class product.
The following In-Process testing is conducted during the cable manufacturing :
Tandem Line
- Visual and physical tests
- Electrical tests
- Resistance & resistance unbalance tests
- Open & short circuit test
High Voltage Test
- Group twinner
- Visual & physical tests
- Electrical tests
- Resistance & resistance unbalance tests
- Mutual capacitance test
- Open & short circuit test
- Insulation resistance test
Sheathing
- Dimensional test
- Water penetration test
- Spark test
- Overlaps & seal bonding inspection
Armoring
- Dimensional test
- Visual inspection
Jacketing
- Dimensional test
- Overlap inspection
- Spark test
Final Testing
- Routine testing
- Resistance & resistance unbalance tests
- Mutual capacitance test
- Transmission test
- Capacitance & capacitance unbalance tests ( pair to pair and pair to ground )
- Attenuation & cross talk tests.
Cable Options
It is essential that the type of cable ordered is suitable for its intended use. Cable choice will be based on a whole range of factors including installation requirements, relevant local regulations and the electrical characteristics of appropriate cable types. The factors to be considered are:
- Nominal voltage of system.
- Highest voltage of system.
- Impulse withstand voltage.
- System frequency.
- Maximum rated current.
- For continous operation.
- For cyclic operation ( a load curve is essential )
- For overload operation, if any ( duration is essential )
- Symmetrical and asymmetrical short circuit current , both between pulses and to earth.
- Duration of fault in second.
- Required screen bonding scheme
- Both ends bonded
- Single point bonded
- Cross bonded
Ordering Information
VDE CODE: ABCDEFGH
A. Conductor
N- Standard construction in accordance to VDE standard (copper conductor)
NA- Aluminium conductor
NFA- Standard construction for twisted cable (aluminium conductor)
B. Insulation Material
Y- PVC
2X- XLPE
3G- EPR
C. Concentric Conductor Shielding Material
C- Concentric conductors of copper wires and copper tape, helically wounded
CW- Concentric conductors of copper wires in waveconal formation and and copper tape, helically wounded
CE- Concentric conductors of copper wires and copper tape over each individual conductor, helically wounded
Blank- No screen
D.Shielding Material
S- Shielding of copper wires and copper tape, helically wounded
SE- Shielding of copper wires and copper tape over each individual conductor, helically wounded
(F)- Longitudinally water proof shielding
Blank- No screen
E. Bedding Material
2Y- PE
Y- PVC
H- LSZH
K- Lead sheath
Blank- No bedding
F. Armoring Material
B- Double steel tape armouring
R- Round steel wire armouring
F- Flat steel wire armouring
Gb- Helical steel tape armouring
Blank- No armour
G. Jacket Material
2Y- PE
Y- PVC
H- LSZH
K- Lead sheath
H. Cable Types
J- Cables with green-yellow conductor are marked with protective conductor
O- Cables without green-yellow conductor are marked without protective conductor
Caledonian Order Code
MVA-BCDEFGH-IJ
A Cable Design Standard
6622- BS6622 standard
7835- BS7835 standard
502- IEC60502 standard
276- VDE0276 standard
B Conductor
A- Aluminium conductor
Blank- Copper conductor
C Insulation Material
Y- PVC
2X-XLPE
3G-EPR
D Concentric Conductor Shielding Material
C- Concentric conductors of copper wires and copper tape, helically wounded
CW- Concentric conductors of copper wires in waveconal formation and and copper tape, helically wounded
CE- Concentric conductors of copper wires and copper tape over each individual conductor, helically wounded
Blank- No screen
E Shielding Material
S- Shielding of copper wires and copper tape, helically wounded
SE- Shielding of copper wires and copper tape over each individual conductor, helically wounded
(F)- Longitudinally water proof shielding
Blank- No screen
F Bedding Material
2Y- PE
Y- PVC
H- LSZH
K- Lead sheath
Blank- No bedding
G Armoring Material
B- Double steel tape armouring
R- Round steel wire armouring
F- Flat steel wire armouring
Gb- Helical steel tape armouring
Blank- No armour
H Jacket Material
2Y- PE
Y- PVC
H- LSZH
K- Lead Sheath
I No of Cores
3C- 3 Cores
J Conductor Size
185- 185 sq mm
8A- 8AWG
