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| Cable Specification |
General Information about Technical Specification Need to Required for Reference Standard of HV & EHV Power Cable
This specification describes the requirement for design manufacture testing delivery installation and commissioning of double circuit of 132 kV single core copper conductor XLPE power cable and associated accessories. Quantity / Route length shall be as per bill of requirement.
For the above route cables shall be laid buried in ground. There shall be three single core cables as above for each circuit.
Contractor shall be responsible for complete turnkey job which will involve final route survey (after award of contract) design manufacturing testing and delivery of cable and associated accessories to site testing of cables at site digging of cable trenches laying of cables in trenches back filling of trenches, installation / creation of joints and termination testing of feeder after installation and commissioning.
The cables and accessories shall comply with the current issues of IEC standards and documents detailed in this specification and other standards as appropriate.
IEC 60228 Conductor for insulated cable
IEC 60229 Tests cable over sheaths
IEC 60230 Impulse tests on cables and their accessories
IEC 60270 Partial discharge measurements
IEC 60287 Calculation of continuous current carrying capacity.
IEC 60502 Power cables with extruded insulation and their accessories
IEC 60840 Test for power cables with extruded insulation for rated voltage above 30 kV up to 150 kV
IEEE 48 Test procedures and requirements for high-voltage cable
IEEE 404 Joints for use with solid dielectric cables rated voltage 5kV -138kV
All 132 kV cable circuits shall be installed by direct burial at an average depth of 1.0 M. Cable ends shall be terminated with porcelain termination at both ends.
The terminations shall be suitable for out door installation in heavily polluted atmosphere and shall be razed completely weather proof through the cable sealing ends.
Cable joints shall be suitable for under ground dried installation with uncontrolled backfill and Chances of flooding by water. Cable joints shall have adequate mechanical protection features.
Cables Operating Conditions
The cable and accessories shall be suitable for use under the following conditions
a) Nominal system voltage 132 kV
b) Highest system voltage 145 kV
c) System frequency 50 Hz
d) System Earthing Solidly Earthed
e) Impulse level 650 kV
f) Maximum earth fault current 31.5 kA
g) Maximum duration of fault current 3 Second
h) Maximum continuous conductor temperature 90º C
i) Maximum conductor temperature under short circuit 250° C
j) Average ambient air temperature 40° C
k) Maximum ground temperature (Trench) 30° C
l) Soil Thermal receptivity (ground level) 120° C com/watt
The current rating of the cable in trenches shall be determined by the calculation method given in IEC 60287.
Cable Installation Condition
The contractor shall make all the cable laying arrangement on his own including compensation for road cutting and accord of right of way, if any.
However the employer shall assist for getting clearance/permission from Govt. Authorities / Municipal Authorities for digging of trenches / cutting of roads or any such work as may be required for installation of cables and accessories.
The power cables shall be laid in trefoil formation. The depth of burial shall be approximately 1.0 meter.
The sheath / screen bonding system shall provide a continuous current path through the cable sheath/screen and shall be bonded and earthed as applicable.
Technical Requirements of 132 kV XLPE Cable
The cable shall be manufactured either by the vertical continuous vulcanization (VCV) or MDCV extrusion and dry curing process censuring circularity and consentaneity of the extruded layers around the conductor. The details of process of curing to be adopted shall be mentioned during the offer.
The manufacturing process shall be cosigned to eliminate irregularities like protrusions voids and contamination etc. to ensure the long term reliability of the cable.
Raw materials used for manufacture of cable shall be of highest quality and it shall meet material standards mentioned in IEC 60840. The materials shall be clean and packed in moisture and dust proof packing. Material received by manufacturer should be checked / tested to confirm that it meets material specification.
Loading of the extruder in the manufacturing plant shall be performed entirely closed and dust proof environment. Contamination shall be avoided by use of a fully enclosed material handing system. The use of special means like pressurized air etc for transport of granules shall as far as practicable be avoided.
All three layers (conductor screen, XLPE insulation and insulation screen) shall be extruded in one simultaneous triple extrusion process though common triple cross head. The endures and triple cross head shall be designed to prevent stagnation of materials to eliminate hot spots and ensure smoothness of the conductor screen and core screen surfaces.
The cross linking curing and cooling shall be carried out in one operation and shall be a dry curing process under high pressure to eliminate the formation of voids in the insulation and contaminants in the dielectric.
Process conditions such as curing and cooling temperatures production speed etc. shall be closely monitored during manufacture to ensure a good degree of cross linking through the whole insulation.
Type Test Reports for Cable
The tender shall submit type test report for the tests conducted on similar type of XLPE cables and accessories of same / higher voltage grade. Type test report either from the manufactures Accredited own laboratory or from the independent testing laboratory is acceptable.
The tender should separately quote charges for the type test for cables and accessories as optional price. The purchaser may ask the contractor to carry out the type tests if he desires.
Cable Construction
The cable shall have stranded compacted round copper conductor taped with semi conducting tapes conductor screening with extruded semi conducting thermosetting compound layer with completely dry cured XLPE insulation, adequate insulation screening including extruded semi conducting thermosetting compound layer, taped with semi conducting water swell able tape, extruded corrugated Aluminum sheathed and overall extruded termite repellent black PE sheathed with outer conducting layer obtained by simultaneous extrusion with PE sheath.
Conductor of Cable
The conductor shall be stranded compacted round copper conductor complying the requirement of flexibility clause 12-2 of IEC 60228.
The wires shall be made of high conductivity copper and shall be stranded mid compacted. The copper / aluminum used for the conductor shall be of highest purity.
The nominal area of conductor shall be 500 sq. mm for both the circuits.
The minimum number of wires in conductor and max dc resistance of conductor shall be as per table II of IEC 602283
Conductor Screen
The conductor screen shall consist of an extruded layer of thermosetting semi conducting compound and shall be continuous and cover the whole surface of the conductor. The screen shall be firmly bonded to XLPE insulation.
The minimum thickness of conductor screen shall be 1.0 mm (approx.)
A non-gyroscopic semi conducing tape may be applied to the conductor under extruded layer.
The outer surface of the conductor screen shall be circular and free from irregularities.
Insulation of Conductor of Cable
The insulation shall be cross linked polyethylene (XLPE). The insulation material shall comply with the requirement of Table - iv of IEC 60840.
The insulation shall be applied by extrusion and vulcanization to form a compact homogeneous body free from micro voids and contaminants.
The nominal thickness shall be decided by the manufacturer which shall not result the voltage stress at conductor screen surface more than 6.5 kV/mm at normal operating voltage
Insulation Screen of Cable
The insulation screen shall consist of an extruded layer of thermosetting semi conducting compound and shall be continuous and cover the whole surface area of insulation. It shall be firmly bonded to the insulation.
The minimum thickness of insulation screen shall be 0.8mm.
Longitudinal Water Barrier of Cable
The under sheath water barrier shall consist of a semi conducting moisture swelling layer covering the whole surface area of the insulation screen.
The barrier shall restrict longitudinal water penetration under the metallic sheath. The minimum thickness of water swell able tape shall be 0.3mm
Metal Sheath of Cable
The metallic sheath shall be of extruded Corrugated Aluminum as per relevant IEC 60840.
The metallic sheath shall be extruded using a continuous screw press and shall be free from all extrusion defects.
The nominal thickness of corrugated Aluminum sheath shall be as per the recommendation of IEC 60840 and shall be so designed to carry the specified earth fault current of 31.5 kA for 3 Seconds.
Outer sheath of Cable
The outer sheath shall consist of an extruded layer of black medium density polyethylene with an outer conductive layer.
The nominal thickness of outer sheath shall not be less than the value calculated as per the recommendation of IEC 60502
The outer sheath shall be of sufficient hardness to discourage termite attacks. The properties of outer sheath material shall be as per IEC 60840.
Marking on outer sheath of Cable
The following particulars shall be marked on cable outer sheath at suitable regular intervals.
a) Manufacture's name and / or trade name
b) Voltage grade viz 76/132 kV
c) Cable size (No. cf core x conductor cross section)
d) Year of manufacture
e) Purchaser's name i.e. DPDC.
The spacing between one set of marking and line beginning of the next on the legend shall not exceed 150mm.
Sealing and Drumming of Cable
Immediately after the works and tests both ends of every length of cable shall be sealed by means of heat shrinkable end caps.
Cables shall be wound on metallic drums. All the drums shall be arranged to take a round spindle and is lagged with strong closely fitting wooden battens so as to prevent damage to the cable.
Each drum shall bear an identification number permanently stenciled or branded on the outside of the flange. Particulars of the cable i.e. voltage grade conductor size length gross weight net weight, direction of rolling and name of manufacturer and year of manufacture etc. shall be clearly marked on one flange of the drum.
Standard drum length shall be 500 meters. A tolerance of +3% will be permissible on standard drum length
However exact drum length shall be advised to successful bidder after award of contract. Exact drum length shall be decided by joint route survey with purchaser's engineer and contractors engineer after award of contract.
Joints of Cable
The dielectric design of the joint shall be optimized. The electric stress distribution along the interface between the insulator and the cable shall take into account the dimensions of the joint and the cable and the dielectric permittivity of the insulation. The material of insulator shall have good thermo mechanical behavior.
The materials used in the assembly of the joint shall be compatible with the martial of the insulator and the cable insulation.
The conductor shall be connected by means of an approved arrangement. The tensile strength of the connector shall meet the requirements of the copper conductor.
The joints shall be of remolded construction. This design shall comprise a one price factory tested synthetic rubber joint with all stress management element provided during the molded process in the factory.
Outdoor Termination
The terminations shall be porcelain compost type of insulators suitable for outdoor installation in heavily polluted atmosphere. It should resistant to UV exposure. The termination stress control shall be by means of electrometric stress cone.
The stress cone design shall inhibit possible mechanical stress and deformation of the cable insulator surface during operation and be also capable of accommodating minor radial and longitudinal movement without detriment of the dielectric stresses in the insulation shield.
Supply and installation including foundations of structures for supporting of 132 kV cable Termination shall be included in the scope of the bidder.
High Voltage Test Set of Cable
The Hight Voltage Test Set shall test medium and high voltage Bus bars, Switchgears and Cable with AC and both positive and negative DC polarity. The test voltages should be stepless and adjustable. The kV meter and mA meter should work in multiple ranges. Proper safety control unit shall be incorporated in the machine.
Tests for cables and accessories
All type routine and acceptance (special) tests as per IEC 60840
The bidder must furnish the type tests report / certificates from an independent testing laboratory / manufacturer own accredited laboratory, for type tests conducted on cable of same of higher voltage grade, not older than five years on the date of bidding.
The cost towards type tests shall be separately indicated in the offer for evaluation. The bidders specifically state whether cost towards type tests is indicated in the bid or it shall be free of cost.
The supplier shall give clear three weeks notice in advance to the purchaser to arrange for inspection witness of tests.
The manufacture of 132 kV cable must have at least ISO 9001 certified quality assurance system of the laboratory. Documentary evidence shall have to be submitted with the offer.
Routine Tests
The following routine tests shall be carried out on each manufactured length
a) Partial discharge test
b) Voltage test
c) DC voltage test on outer sheath
d) Conductor resistance test
Special (Acceptance) Tests
The following tests shall be made on samples which for the tests in items (b) and (g), may be the complete drum length of cable taken to represent batches.
a) Conductor examination
b) Measurement of electrical resistance of conductor
c) Measurement of thickness of insulation and non-metallic sheath
d) Measurement of thickness of metallic sheath
e) Measurement of overall cable diameter
f) Hot set test for XLPE insulation
g) Measurement of capacitanc
Frequency of Tests
The above special (acceptance) tests shall be made on one length from each manufacturing series of the same type and size of cable but shall be limited to not more than 10% of the number of lengths in any contract rounded upper unity.
Type Tests
The following type tests shall be made on cables covered in scope of contract, by contractor before the dispatch of cable from manufacturer's works if the cables are already tested it will be at the sole discretion of the purchaser whether to waive the type test or ask for repetition of all or some specific tests. Contractor may quote type test charge for individual test in his bid for evaluation purpose.
The following tests shall be included in the type tests Electrical Tests
a) Bending test following by partial discharge test
b) Tan δ measurement
c) Heating cycle voltage test followed by partial discharge measurement.
d) Impulse withstand test followed by a power frequency voltage test.
Test on cable components
a) Check for cable construction
b) Resistivity of semi conducting layers
c) Test for determining the mechanical properties of insulation before and after ageing
d) Test for determining the mechanical properties of non-metallic sheath before and after ageing.
e) Ageing tests on pieces of complete cable to check compatibility of materials.
f)Pressure test at high temperature on sheath
g) Hot set test on XLPE insulation
h) Carbon black content of PE sheath
i) Shrinkage test on XLPE insulation
j)Longitudinal water penetration test for water tightness between core and metallic sheath
Tests at site after installation
Pre commissioning tests on site which shall be performed by the successful bidder shall include the following
a)DC voltage test on outer sheath at 10 kV (DC) for one minute between metallic sheath screen and external conducting surface.
b)On completion of cable laying and jointing work the complete installation shall be checked with a DC voltage of 3 U applied for 15 minutes.
c)AC test voltage for 24 Hrs with the normal phase to earth voltage of the system (U), this is alternative to DC voltage test as per (b) above.
Tests for Accessories
Copy of routine / sample tests performed on cable access ones by the manufacture at his works shall be submitted to the purchaser along with supplies.
Type test if not already conducted or if the type tests conducted earlier than five years from the date of supply complete type tests on all cable accessories shall be performed before dispatch and test report shall be submitted along with ht supply.
DESPATCH
No cable dispatch shall be made without approval to the test certificate from the purchaser. All dispatches shall be made to the consignees intimated by the purchaser.
Cable Lengths
The correct total quantity the number of drums the length of cable on each drum shall be ascertained by the contractor from the purchaser at the time of manufacture. This is in view of any change in the already finalized route plan profile which may arise due to any unforeseen circumstances between the period of placing the order and commencement of manufacturer.
