Oman Cables Technical Handbook

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Table of Contents Sr. No.

Details

Page

1

Product Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

2

Criteria for selection of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

3

Conductor details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

4

Electric Field in MV cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

5

General characteristics of Insulating Materials . . . . . . . . . . . . . . . . . . . . . . . . .15

6

General characteristics of Sheathing Materials . . . . . . . . . . . . . . . . . . . . . . . .16

7

Continuous Current Ratings and rating factors . . . . . . . . . . . . . . . . . . . . . . . .20

8

Short Circuit Current ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

9

Cables Storage and Installation Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

10

Testing of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

11

Insulation Resistance Test and significance . . . . . . . . . . . . . . . . . . . . . . . . . . .50

12

Voltage drop – utility and values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

13

Earthing and Bonding methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

14

PVC vs XLPE cables – Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

15

Overhead Conductor – Characteristics and Applications . . . . . . . . . . . . . . . . .61

16

Frequently Asked Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

17

Conversion Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

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OCI Product Range Oman Cables offers a wide range of cables for demands made upon electrical, mechanical and thermal qualities. The products listed below are the most popular ones. However, OCI can meet a customer’s special requirements. 1)

Electric Wires: a)

Building wires from 1.5 mm2 to 630 mm2

b)

Single core PVC and LSF insulated wires 450/750 Volts to BS 6004, BS 7211, IEC 60227

c)

Multicore 300/500 Volts Circular, PVC Insulated, PVC Sheathed Wires to BS 6004, IEC 60227

2)

d)

2 Core, 3 Core Flat Wires with and without earth continuity conductor to BS 6004

e)

PVC Insulated Flexible Cords to IEC 60227

f)

300/500 Volts Flexible Cables BS 6500, IEC 60227

0.6/1 kv, XLPE and PVC insulated, PVC and LSF Sheathed Cables to IEC 605021, BS 6346, BS 7889, BS 5467, BS 6724 and specific customer requirements with: a)

Copper and Stranded Aluminium Conductors

b)

Single core and multicore cables

c)

Unarmoured cables

d)

Aluminium wire armoured single core cables

e)

Galvanized Steel Wire and Galvanized Steel Tape armoured multicore cables.

f)

Control cables with and without armour, with and without screen (copper tape/copper wire).

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Medium Voltage XLPE insulated cables to IEC 60502-2, BS 6622, BS 7835, BS 7870 and specific customer requirements up to and including 46 kV: Copper and Aluminium Conductors: a)

Single core cables 25 mm2 to 1000 mm2

b)

Three core cables 25 mm2 to 500 mm2

c)

Single core and Three core un-armoured cables with copper tape/copper wire screen.

d)

Aluminium wire armoured single core cables.

e)

Galvanized Steel Wire and Galvanized Steel Tape armoured multicore cables.

We can offer cables with Optional Features such as: Watertight Conductors Bonded or Strippable Insulation Screen Copper Wire/Copper Tape Screen Cables with longitudinal water barriers at screen and armour level. Cables with Radial water barrier (PE Laminated Aluminium Tape). Cables with LLDPE, MDPE, HDPE, FRRT, FRLS Outer Sheath. 4)

Overhead Conductors to IEC, BS, ASTM, DIN, VDE, AS Standards a)

Bare and PVC/XLPE Insulated Hard Drawn Copper Conductors

b)

Bare and PVC/XLPE insulated all Aluminium conductors (AAC, AAC/PVC, AAC/XLPE).

c)

All Aluminium Alloy conductors (AAAC)

d)

Aluminium Conductors Steel Reinforced (ACSR)

e)

Aluminium Conductors Aluminium Clad Steel Reinforced (ACSR/AW).

f)

Aluminium Conductors Aluminium Alloy Reinforced (ACAR).

g)

Aluminium Alloy Conductor Steel Reinforced (AACSR).

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h)

Galvanized Steel and Alumoweld Earth Wires.

i)

Aerial Bundle Cables (Duplex, Triplex, Quadruplex).

Special Cables a)

Watertight Cables

b)

Fire Retardant Cables to IEC 60332-3-24, IEC 60332-3-23, IEC 60332-3-22.

c)

Cables with LLDPE, MDPE, HDPE, FRRT, FRLS Outer Sheath.

d)

Cable with Oil Resistant and/or Termite Resistant and/or FRRT and/or FRLS Outer Sheath.

e) 6)

Instrumentation Cables.

PVC Compounds for Insulation and Sheathing of Electric Cables. To name a few: Type A,T11, T13, Type 6, Type 9, Type ST2, FR, FRLS, FRRT, ATR etc.

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Criteria for selection of Power Cables Cable Type and Size should be selected keeping in the view the following: 1) Application 2) Working Voltage, Earthed or Unearthed System 3) Load Current, Duty Cycle, Frequency 4) Installation methods and conditions 5) Short time duty and system protection 6) Acceptable Voltage drop 7) Economics

How do these factors influence the choice of cables? 1)

Application of the cable determines the basic factors for choice of cable type. a)

Conductor material – Copper is the virtually unchallenged material as a conductor. Aluminium, can also be used as Conductor material as it is very economical.

b)

Insulating Material – good insulating material should have low thermal resistivity and low dielectric losses. Please refer to the chart for major characteristics of different materials.

c)

Power cables are usually with armour to carry earth fault current and to give mechanical protection against damage during installation and service. For higher fault rating and higher tensile strength steel wires are used in multicore cables. Single core in AC circuits, use non magnetic material. Stainless steel is difficult to justify on cost grounds and Aluminium is the normal choice.

d)

External covering/sheaths are used over the armour. Polyethylene or PVC is material most often used. Please refer to the chart for properties of sheathing material.

2)

System voltage determines Voltage class of cables.

3)

Current rating and intermittent load is the decisive factor for fixing conductor size. Factors such as Ground & Air temperature, thermal resistivity of soil, depth of laying, number of cables in circuit etc. affect specified current ratings.

4)

Chemical substances in the environment might need special requirements on outer covering. Cables are vulnerable to termite and rodent attacks.

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The short circuit current and its duration determines the size of conductor and thermal requirement of insulation.

6)

Voltage drop is also major factor in deciding the conductor size of the cable. Voltage drop of the cable for a given route length should not exceed the statutory requirements.

7)

The design of the cable for a particular application must be optimised taking into account all the above factors. In case expert guidance is desired, please contact OCI.

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Class of Conductors: Class 1:

Solid Conductor - used in cables for fixed installations.

Class 2:

Started Conductor - used in cables for fixed installations.

Class 5:

Flexible conductor - used in flexible cables and cords.

Class 6:

Flexible Conductor - used in flexible cables and cords. Conductors are more flexible than Class 5 when more flexibility is required

Table – Class 1 solid conductors for single core and multicore cables 1 Nominal cross sectional area m2

2

3

4

Maximum resistance of conductor at 20˚C Circular, annealed copper Aluminium and aluminium conductors alloy conductors, circular Plain Metal-Coated or shaped /km /km /km

Ω

Ω

Ω

0.5

36.0

36.7

–

0.75

24.5

24.8

–

1.0

18.1

18.2

–

1.5

12.1

12.2

–

2.5

7.41

7.56

–

4

4.61

4.70

–

6

3.08

3.11

–

10

1.83

1.84

3.08(a

16

1.15

1.16

1.91(a

25

(b

0.727

–

1.20(a

35

0.524(b

–

0.868(a

50

(b

0.387

–

0.641

70

0.268(b

–

0.443

95

0.193(b

–

0.320(d

120

0.153(b

–

0.253(d

150

(b

–

0.206(d

(b

–

0.164(d

0.124

185

0.101

240

0.0775(b

–

0.125(d

300

(b

–

0.100(d

0.0620

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Table – Class 1 solid conductors for single core and multicore cables 1 Nominal cross sectional area m2

2

3

4

Maximum resistance of conductor at 20˚C Circular, annealed copper Aluminium and aluminium conductors alloy conductors, circular Plain Metal-Coated or shape /km /km /km

Ω

Ω

Ω

400

0.0465(b

–

0.0778

500

–

–

0.0605

630

–

–

0.0469

800

–

–

0.0367

1000

–

–

0.0291

1200

–

–

0.0247

a)

Aluminium conductors 10 mm2 to 35 mm2 circular only.

b)

Solid copper conductors having nominal cross-sectional areas of 25mm2 and above are used for particular types of cable e.g., mineral insulated, and not for general purpose.

c)

For solid aluminium alloy conductors having the same nominal cross-sectional area as an aluminium conductor, the resistance value should be multiplied by 1.162 unless otherwise agreed between manufacturer and purchaser.

d)

For single core cables, four sectoral shaped conductors may be assembled into a single circular conductor. The maximum resistance to the assembled conductor should be 25% of that of the individual component conductors.

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Class 2 stranded conductors for single-core and multi-core cables 1 Nominal crosssection al area

mm2 0.5 0.75 1.0 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300 400 500 630 800 1000 1200 1400 a 1600 1800 a 2000 2500

2 3 4 5 Minimum number of wires in the conductor Circular Circular Compacted Shaped Cu

Al

Cu

7 7 7 7 7 7 7 7 7 7 7 19 19 19 37 37 37 37 61 61 61 91 91 91

– – – – – – – 7 7 7 7 19 19 19 37 37 37 37 61 61 61 91 91 91

– – – 6 6 6 6 6 6 6 6 6 12 15 18 18 30 34 34 53 53 53 53 53 b) b) b) b) b) b)

Al

Cu

Al

6

7

6 6 6 6 6 12 15 15 15 30 30 30 53 53 53 53 53

6 6 6 12 15 15 15 30 30 30 53 53 53 – – –

9

10

Maximum resistance of conductor at 20˚C Aluminium or aluminium alloy conductors Metal-coated Plain wires wires

Annealed copper conductor Plain wires

Ω/km

– – – – – – – – – 6 6 6 12 15 18 18 30 34 34 53 53 53 – – –

8

36.0 24.5 18.1 12.1 7.41 4.61 3.08 1.83 1.15 0.727 0.524 0.387 0.268 0.193 0.153 0.124 0.0991 0.0754 0.0601 0.0470 0.0366 0.0283 0.0221 0.0176 0.0151 0.0129 0.0113 0.0101 0.0090 0.0072

Ω/km

Ω/km

36.7 24.8 18.2 12.2 7.56 4.70 3.11 1.84 1.16 0.734 0.529 0.391 0.270 0.195 0.154 0.126 0.100 0.0762 0.0607 0.0475 0.0369 0.0286 0.0224 0.0177 0.0151 0.0129 0.0113 0.0101 0.0090 0.0072

– – – – – – – 3.08 1.91 1.20 0.868 0.641 0.443 0.320 0.253 0.206 0.164 0.125 0.100 0.0778 0.0605 0.0469 0.0367 0.0291 0.0247 0.0212 0.0186 0.0165 0.0149 0.0127

a)

These sizes are non-preferred. Other non-preferred sizes are recognized for some specialized applications but are not within the scope of this standard

b)

The minimum number of wires for these sizes is not specified. These sizes may be constructed from 4, 5 or 6 equal segments (Milliken)

c)

For stranded aluminium alloy conductors having the same nominal cross-sectional area as an aluminium conductor the resistance value should be agreed between the manufacturer and the purchaser.

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Class 5 flexible copper conductors for single core and multi-core cables 1

2

3

Nominal crosssectional area

Maximum diameter of wires in conductor (mm) Class 5

Class 6

0.5

0.21

0.75 1.0

4

Maximum resistance of conductor at 20˚C Plain wires Metal-coated wires /km /km

Ω

Ω

0.16

39.0

40.1

0.21

0.16

26.0

26.7

0.21

0.16

19.5

20.0

mm2

1.5

0.26

0.16

13.3

13.7

2.5

0.26

0.16

7.98

8.21

4

0.31

0.16

4.95

5.09

6

0.31

0.21

3.30

3.39

10

0.41

0.21

1.91

1.95

16

0.41

0.21

1.21

1.24

25

0.41

0.21

0.780

0.795

35

0.41

0.21

0.554

0.565

50

0.41

0.31

0.386

0.393

70

0.51

0.31

0.272

0.277

95

0.51

0.31

0.206

0.210

120

0.51

0.31

0.161

0.164

150

0.51

0.31

0.129

0.132

185

0.51

0.41

0.106

0.108

240

0.51

0.41

0.0801

0.0817

300

0.51

0.41

0.0641

0.0654

400

0.51

0.0486

0.0495

500

0.61

0.0384

0.0391

630

0.61

0.0287

0.0292

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Electric Field in Medium Voltage XLPE Cables As shown in the figure below, the electric field is the highest at conductor surface, reducing towards the outer surface of the insulation.

Field distribution within a high voltage XLPE cable Purpose of Semiconducting screens for such cables – Conductor Screening:1. To provide uniform stress over the relatively rough stranded conductor surface. 2. To provide close bonding between the conductor and adjacent insulation so as to exclude any interspersed voids that may constitute sources of partial discharge. Insulation Screening 1. With the outer shield grounded, the electric field of the conductor attains radial symmetry and is confined to Insulation for safety consideration. 2. To distribute electrical stress uniformly along the periphery of the cable 3. Intimate contact between Insulation and semiconducting layer prevents partial discharge. 4. To prevent surface discharges and reduce electrical interferences Please see the difference between shape of Electric field of shielded (screened) cable and unshielded cable

Non-Shielded

Shielded

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Outer Covering materials selection chart Mechanical Abrasion Resistance Tensile Strength Elongation Compression Resistance Flexibility Environmental Flame Moisture Fresh or salt water Petroleum oils Motor oil Fuel oil Crude oil Creosote Paraffinic Hydrocarbons Gasoline Kerosene Alcohols Isopropyl Wood Grain Mineral Acids Sulfuric Acid Nitric Acid Hydrochloric Acid Fixed Alkalis Sodium hydroxide (lye) Potassium hydroxide (potash) Calcium hydroxide (lime) Ketones Acetone Methyl ethyl ketone (MEK) Esters Ethyl Acetate Most lacquer thinners Halogenated Hydrocarbons Chloroform Carbon Tetrachloride Methyl Chloride

PVC

Polyethylene

Good Excellent Good Good Good

Excellent Excellent Excellent Excellent Fair

–

–

Good – Good – – Good – Poor – Good – – – Fair – – – Excellent – – – Good – – Poor – – Poor – – – Poor

Poor – Exceptional – Excellent (Slight swelling above 60˚C) Good – Excellent (Slight swelling at higher temperatures) – – Good – – – Excellent – – – Excellent – – Good – – Good – – – Poor

Yes 23-30% 26 14˚F (-10˚C) Fair 80˚C

No 17-18% 0 -40˚F (-40˚C) Fair 80˚C

General Leaves protective residue after combustion Oxygen Index (ASTM D-2863) Halogen content – % Wt. Minimum installation temperature Dimensional stability under heat Maximum operating temperature 14 OCI/PBTB/Rev-001/010909

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Insulation Material Characteristics Sl. No. 1 2

3

4 5 6 7 8

9 10

11

12 13 14

15

Description Tensile Strength and Elongation at break Min. tensile strength Min. elongation at break Accelerated ageing for specified period at specified temp. followed by Tensile Strength and Elongation at break No. of days ageing Ageing temperature Max. variation of tensile strength from unaged specimen Max. variation of elongation from unaged specimen Hot Set Test: – Temperature – Time under load – Mechanical stress Max. elongation under load Max. permanent elongation after cooling Low temperature bend test: Temperature at which specimen shall not crack Low temperature elongation test: Test temperature Minimum Elongation Low temperature impact test: Temperature at which specimen shall not crack Pressure test at high temperature: Test temperature Maximum indentation Loss of Mass (only for T11 insulation as per BS) Ageing: Number of days Ageing Temperature Maximum loss of mass Resistance to cracking (Heat shock test) Temperature at which the specimen shall not crack Water absorption – electrical method Temperature at which specimen shall not crack Duration Maximum variation of mass Maximum permissible shrinkage: – Temperature – Duration Maximum permissible shrinkage Insulation Resistance const (Ki) at max. rated temp. Volume Resistivity at maximum rated temperature Ozone Resistance test Temperature at which specimen shall not crack Duration Ozone Concentration Acidic (corrosive) gases evolved Level of HCl pH (minimum) Conductivity (maximum)

Unit

PVC (Type A)

XLPE (0.6/1 kV)

LSF (0.45/.75 kV)

N/mm2 %

12.5 150

12.5 200

10 125

Days ˚C N/mm2 % % %

7 100±2 12.5 ±25 150 ±25

7 135±3 – ±25 – ±25

7 135±3 – ±30 – ±30

˚C Minutes N/cm2 % %

N/A N/A N/A N/A N/A

200±3 15 20 175 15

200±3 15 20 100 25

˚C

-15±2

N/A

-15±2

˚C %

-15±2 20

N/A N/A

-15±2 30

˚C

N/A

N/A

-15±2

˚C %

80±2 50

N/A N/A

110±2 50

Days ˚C mg/cm2

7 80±2 2.0

N/A N/A N/A

N/A N/A N/A

˚C

150±2

N/A

N/A

˚C Hours mg/cm2

70±2 240 –

85±2 336 (14 days) 1.0

N/A N/A N/A

˚C Hours % M.Ohm.Km Ohm.cm

N/A 130±3 N/A 1 N/A 4 0.037 (70˚C) 3.67 (90˚C) 1010(70˚C) 1012(90˚C)

N/A N/A N/A 0.002 (90˚C) 1011(20˚C)

˚C Hours ppm

N/A N/A N/A

N/A N/A N/A

25±2 24 250 to 300

%

N/A N/A N/A

N/A N/A N/A