MV and LV cables

 

7.3.2 Medium Voltage Cables

Medium Voltage cables will have the following characteristics:

• • Operation voltage: 15 kV rms
• • System maximum voltage for equipment 17.5 kV rms
• • Insulation voltage: 8.7/15 kV
• • Conductor: Aluminium (Class 2 as per IEC 60228)
• • Sections: See Appendix 2
• • Cable type: Single-core
• • Insulation: XLPE (90 ºC)
• • Screen: Copper wire with tape (200 A during 0.5 sec-

 

ond)*. To be earthed at both ends.

• • Over-sheath: PVC (90 ºC, red colour, non-fading)

 

*200 A earthing transformers are foreseen in 15 kV system design

 

7.3.3 Low Voltage Power Cables

Low Voltage cables will have the following characteristics:

• • Insulation voltage: 0.6/1 kV
• • Conductor: Copper (Solid round or stranded class 2)
• • Sections: See Appendix 2
• • Cable type: Single-core (120 mm2 or above) or multicore
• • Insulation: XLPE (Low smoke, Low emission of halogen,

 

non-hygroscopic inner covering)

• • Screen: Required except for single core cables

 

(Cooper tape or copper braid / Earthed at both ends)

• • Oversheath: Low smoke, Low emission of halogen,

 

UV resistant Flame retardant Cat C, 90 ºC operation.

 

7.3.4 Control, Measuring and Signalling Cables

Control measuring and signalling cables must have the following characteristics

• • Insulation voltage: 0.6/1 kV

 

• • Conductor: Stranded copper (Class 2 or 5)
• • Sections: See Appendix 2
• • Cable type: Multi-core
• • Insulation: XLPE (Low smoke, Low emission of halogen, non-hy-groscopic inner covering)
• • Screen: Required except for single core cables. (Copper tape or copper braid / Earthed at both ends)
• • Oversheath: Low smoke, Low emission of halogen, UV resistant

(90 ºC)

 

8 MV Cable Manufacturing Requirements

8.1 Conductors

Conductors shall be made of aluminium class 2 as per IEC 60228.

The conductors shall be unbroken for each complete drum length of cable. Drums with spliced con-ductors will be unacceptable.

8.2 Conductor Screen

The semi-conductive extruded cross-linked material shall provide a smooth cylindrical equipotential to which the insulation can be intimately bonded. The material shall be compatible in all respects with its conductor and insulation materials.

8.3 Cable Insulation

Minimum insulation requirements shall be:

• • Medium Voltage cables, high grade, low loss, extruded XLPE rated 90 ºC.

 

The insulation shall be based on a design voltage stress which has been proven to be completely satisfactory in service. As maximum freedom from the possibility of failure is essential, highly stressed insulation which has not been fully proven in service shall not be used even if it has satis-factorily passed the type test.

The average thickness of insulation shall be in accordance to IEC 60502-2. Minimum insulation thickness at any point shall not be less than the nominal values specified in IEC 60502. The thickness of any separator or screen on the conductor or over the insulation shall not be included in the thick-ness of the insulation.

For 26/45 kV cable, the indications of IEC 60840 must be fulfilled.

8.4 Insulation Screen

Semi-conductive compound of extruded layer firmly bonded to the XLPE insulation. The conductor screen, the insulation and the insulation screen are to be extruded in a single process to keep the interface smooth.

For 26/45 kV cable, the indications of IEC 60840 must be fulfilled.

8.5 Metallic Screen

Metallic screen will be made of aluminium tapes and must fulfil IEC 60502 requirements.

The metallic screen must be able to stand 200 A during 0.5 second and 10 mm2 cross-section as a minimum.

For 26/45 kV cable, the indications of IEC 60840 must be fulfilled.

8.6 Outer Sheath

The over-sheath shall be tough PVC and must satisfy a 90 ºC operation. Cable sheath shall be flame-retardant complying with lEC 60332-3 Cat C.

The over-sheath shall be permanently identified to clearly show the following:

• • Manufacturer's name.
• • Rated circuit voltage.
• • Conductor size.
• • Number of conductors.
• • Insulation material (not trade name).
• • Outer jacket material (not trade name).
• • Year of manufacture.
• • Sequential footage marks in metres.

 

For 26/45 kV cable, the indications of IEC 60840 must be fulfilled.

8.7 Cables colour and conductors identification

For MV cables, the colour of the outer cover shall be red.

 

9 LV Power Cable Manufacturing Requirements

9.1 Conductors

Conductors shall be solid round or stranded (IEC 60228 Class 1 or class 2), made of annealed high conductivity copper with a 99.95% minimum purity for all power cables.

The conductors shall be unbroken for each complete drum length of cable. Drums with spliced con-ductors will be unacceptable.

9.2 Cable Insulation

Minimum insulation requirements shall be:

• • Low Voltage 400 V single-core power cables insulation 0.6/1 kV, high grade, low loss, extruded XLPE rated 90 ºC (short-circuit 250 ºC)

 

The insulation shall be based on a design volta ge stress which has been proven to be completely satisfactory in service. As maximum freedom from the possibility of failure is essential, highly stressed insulation which has not been fully proven in service shall not be used even if it has satis-factorily passed the type test.

The average thickness of insulation shall be in accordance to IEC 60502. Minimum insulation thick-ness at any point shall not be less than the nominal values specified in IEC 60502. The thickness of any separator or screen on the conductor or over the insulation shall not be included in the thickness of the insulation.

 

9.3 Filler and Binder (multiconductor cables)

Flame retardant and moisture resistant non-hygroscopic fillers shall be used in the interstices of the multi-conductor cable to give the completed cable a circular·cross-sectional shape.

A suitable inner jacket shall be extruded over the completed circular multi-conductor cable to keep the fillers in place.

The material used for inner coverings and fillers shall be suitable for the operating temperature of the cable and compatible with the insulating material.

9.4 Metallic Screen

Metallic screen is foreseen for LV power cables except for single core cables (because of EMC).

Metallic screen of these cables will be of cooper tape or copper braid to be connected to earth at both ends.

 

9.5 Outer Sheath

Cable sheath shall be flame-retardant complying with lEC 60332-3 Cat C, low smoke and low emis-sion of halogen as per IEC standard. The over-sheath must be black coloured, except the LV cable for internal lighting whose over-sheath will be white-coloured. (To be indicated in BOQ).

The over-sheath shall be permanently identified to clearly show the following:

• • Manufacturer's name.
• • Rated circuit voltage.
• • Conductor size.
• • Number of conductors.
• • Insulation material (not trade name).
• • Outer jacket material (not trade name).
• • Year of manufacture.
• • Sequential footage marks in meters.

 

10 LV Control Cable Manufacturing Requirements

As general rule, control and instrumentation wiring procedure shall be as follows:

• • For standard analogue signals, pairs or triads shall be used. For standard digital signals and groups of digital signals, multiconductors shall be used. For electric control signals (110 Vdc 2.5 mm2 cross-section will be considered, for digital signals and analogue signals at 48 Vdc 1.5 mm2 cross-section will be considered)
• • Copper conductors shall be used.
• • For standard analogue signals, 0.6 kV insulation shall be considered. For standard digital signals, 0.6 / 1 kV insulation shall be considered.
• • Low smoke and low emission of halogen flame retardant.
• • For analogue signals, every two cores shall be laid-up to form a pair.
• • All cables shall have a metallic screen to reduce electrostatic and electromagnetic influ-ences at a minimum. The coupling resistance (effect of the screen) shall not exceed 250 Ohm/km at 30 MHz (common characteristic values for the screening effect).

 

The control cables shall have a common screen (Copper tape or copper braid).

Cables must generally have appropriate electrical protection against inductive/resistive influences and lightning.

For measuring and control cables above 60 V the cable jacket shall be oil-resistant and flame-re-tardant.

The individual cores of the twisted pair control cables shall be identified by numbers.

All cable ends will be marked with a clear cable number.

At least 10% spares wires shall be considered for signals and control cables.

 

2 Standards

Calculations will be done according to the following applicable standards

• • IEC 60183 “Guide to the selection of high-voltage cables”
• • IEC 60228 “Conductors of insulated cables”
• • IEC 60287 “Electric cables – Calculation of the current rating”
• • IEC 60364-5-52 “Selection and erection of electrical equipment – Wiring systems”
• • IEC 60502-1 “Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um = 1.2 kV) up to 30 kV (Um = 36 kV) Part 1: Cables for rated voltages of 1 kV (Um = 1.2 kV) up to 30 kV (Um = 36 kV)”
• • IEC 60502-2 “Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um = 1.2 kV) up to 30 kV (Um = 36 kV)”
• • IEC 60909 “Short circuit current in three-phase A.C. systems”
• • IEEE 399 “IEEE Recommended Practice for Industrial and Comercial Power Systems Anal-ysis”