Medium Voltage Cables
Medium Voltage Cables to BS 6622 Medium Voltage Cables to IEC 60502 Medium Voltage Cables to VDE 0276

Medium Voltage Cables to BS 6622

Single Core Cables to BS 6622

Application

The single core cables are designed for distribution of electrical power with nominal voltage Uo/U ranging from 3.8/6.6KV to 19/33KV and frequency 50Hz. They are suitable for installation mostly in power supply stations, indoors and in cable ducts, outdoors, underground and in water as well as for installation on cable trays for industries, switchboards and power stations.

Standards

BS 6622
BS 7835 (LSZH)

Construction

Conductor

Plain annealed copper or aluminium complying with IEC 60228/BS 6360. Copper conductors shall be stranded (class 2) and aluminium conductors shall be either solid or stranded (class 2).

Conductor Screen

Extruded layer of semi-conducting cross-linkable compound is applied over the conductor and shall cover the surface completely. The minimum thickness is 0.3mm and the maximum resistivity shall not exceed 500 Ohm-m at 90°C.

Insulation

Insulation is of cross-linked polyethylene compound XLPE (GP8) conforming to BS 7655-1.3 or EPR (GP7), conforming to BS 7655-1.2.

Table 1. Insulation Thickness

Nom. Cross
Section Area
Insulation Thickness at Nominal Voltage
3.8/6.6KV (Um=7.2KV) 6.35/11KV (Um=12KV) 8.7/15KV(Um=17.5KV) 12.7/22KV(Um=24KV) 19/33KV(Um=36KV)
mm² mm mm mm mm mm
70 – 185 2.5 3.4 4.5 5.5 8.0
240 2.6 3.4 4.5 5.5 8.0
300 2.8 3.4 4.5 5.5 8.0
400 3.0 3.4 4.5 5.5 8.0
Above 500 3.2 3.4 4.5 5.5 8.0

Insulaton Screen

Extruded layer of semi-conducting cross-linkable compound is applied over the insulation. The extruded semi-conducting layer shall consist of bonded or cold strippable semi-conducting compound capable of removal for jointing or terminating. As an option, a semi- conducting tape may be applied over the extruded semi-conducting layer as a bedding for the metallic layer. The minimum thickness is 0.3 mm and the maximum resistivity is 500 Ohm-m at 90°C. The screen is tightly fitted to the insulation to exclude all air voids and can be easily hand stripped on site.

Metallic Layer

The metallic layer shall consist of either copper tapes or a concentric layer of copper wires or a combination of tapes and wires. The metallic layer provides an earth fault current path, capable of withstanding fault current to earth of 1000A for one second at maximum temperature 160°C. Copper wires are applied over the conducting water blocking layer with a minimum diameter of 0.5mm. And over the copper wires, copper tape with minimum thickness of 0.1mm can be applied helically with overlap. Total cross section of copper wire screen layer is shown in table 2.

Table 2. Minimum Total Cross Section of Copper Wire Screen & DC Resistance of the screen

Nominal Cross-Section of Cables Minimum Cross-Section of Copper Wire Screen DC Resistance of the Copper Wire Screen at 20°C
mm² mm² Ω
up to 120 16 1.06
150-300 25 0.72
400-630 35 0.51

Separation Sheath (for armoured cable)

The separation sheath comprises a layer of extruded PVC, PE or LSZH. The nominal thickness is calculated by 0.02Du + 0.6mm where Du is the fictitious diameter under the sheath in mm. The nominal separation sheath thickness shall not be less than 1.2mm.

Armour (for armoured cable)

The armour consists of round aluminium wire with diameter specified as in Table 3.

Table 3. Armour Wire Diameter

Fictitious Diameter Under the Armour Armour Wire Diameter
mm mm
>  <   
  25 1.6
25 35 2.0
35 60 2.5
60 - 3.15

 

Over Sheath

Overall sheath comprises a layer of extruded either PVC type 9 conforming to BS 7665-4.2 or MDPE type TS2 conforming to BS 7655-10.1. LSZH can be offered as an option. The oversheath is normally black in colour. When a DC voltage test is to be performed on the oversheath, a semi-conducting layer such as graphite coating shall be applied over the surface of the extruded oversheath. The nominal oversheath thickness is calculated by 0.035D+1.0 where D is the diameter immediately under the oversheath in mm. For cables with the oversheath not applied over the armour, the nominal oversheath thickness shall not be less than 1.4mm. And for cables with oversheath applied over the armour, the nominal oversheath thickness shall not be less than 1.8mm.

Physical Properties

Operating Temperature: up to 90°C

Temperature Range: -5°C ( PVC sheath ); -20°C ( PE sheath )

Short Circuit Temperature: 250°C (short circuit duration up to 5 seconds)

Bending Radius: 15 x OD

Table 4. Nominal /Operating /Test Voltages

Rated Voltage Uo/U Operating Voltage (Um) Testing Voltage (rms)
3.8/6.6KV 7.2KV 15KV
6.35/11KV 12KV 25.5KV
8.7/15KV 17.5KV 35KV
12.7/22KV 24KV 51KV
19/33KV 36KV 76KV

Single Core 3.8/6.6KV (Um=7.2KV) Dimensional Data

Nom.
Cross-
Section
Area
  Aluminium Wire Armoured Cables
Nom.
Insulation Thickness
Copper Tape Screen Area Nom. Bedding
Thickness
Nom. Armour Wire Diameter Nom.
Sheath Thickness
Approx. Overall Diameter Approx.
Weight
Cu AL
mm2 mm mm2 mm mm mm mm kg / km
50 2.5 3.9 1.2 1.6 1.8 28.4 1500 1190
70 2.5 4.3 1.2 1.6 1.8 30.0 1740 1300
95 2.5 4.7 1.2 1.6 1.9 31.8 2030 1430
120 2.5 5.0 1.2 1.6 1.9 33.2 2310 1550
150 2.5 5.3 1.2 1.6 2.0 35.1 2660 1720
185 2.5 5.8 1.2 2.0 2.0 37.4 3120 1950
240 2.6 6.3 1.2 2.0 2.1 40.3 3740 2200
300 2.8 7.0 1.2 2.0 2.2 42.9 4400 2520
400 3.0 7.7 1.2 2.0 2.3 47.2 5490 2960
500 3.2 8.5 1.3 2.5 2.5 51.6 6760 3660
630 3.2 9.5 1.4 2.5 2.6 57.0 8200 4160

Electrical Data

Nom.
Cross-
Section
Area
  Short Circuit
Rating of
Armour
1 sec
 
D C
Resis
tance
CU / AL
A C
Resis
tance
CU / AL
Short Circuit Rating of
Conductor
CU / AL
1 sec
Capaci-
tance
Char
ging Current
Reactance Inductance Impedance
Trefoil Flat  
spaced
Tre
foil
Flat
Spaced
Trefoil Flat Spaced
Cu AL Cu AL
mm2 µΩ/m µΩ/m kA pF/m mA/m kA µΩ/m µΩ/m nH/m nH/m µΩ/ m µΩ/m
50 387/641 494/822 6.8/4.4 321 0.39 6.4 121 179 380 570 511 834 527 844
70 268/443 343/568 9.8/6.3 371 0.45 6.6 115 173 370 550 364 583 386 597
95 193/320 248/410 13.3/8.5 417 0.50 6.8 110 168 350 540 272 427 300 446
120 153/253 196/325 17.2/11.0 459 0.55 7.3 107 165 340 520 225 345 257 367
150 124/206 159/265 21.2/13.5 494 0.59 7.6 103 161 330 510 193 287 229 313
185 99.1/164 128/211 26.6/17.0 543 0.65 10.4 100 158 320 500 165 237 206 267
240 75.4/125 98/161 34.9/22.3 583 0.70 11.2 97 155 310 490 140 191 185 226
300 60.1/100 80/130 43.8/28.0 602 0.72 12.2 95 153 300 490 126 163 174 203
400 47.0/77.8 64/102 57.3/36.6 627 0.75 13.6 92 150 290 480 113 141 164 184
500 36.6/60.5 51/81 72.3/46.2 654 0.79 19.1 90 149 290 470 105 124 158 171
630 28.3/46.9 42/64 91.2/58.3 726 0.87 21.2 87 145 280 460 97 110 151 160

Single Core 6.35/11KV (Um=12KV)
Single Core 8.7/15KV (Um=17.5kV)
Single Core 12.7/22KV (Um=24kV)
Single Core 19/33KV (Um=36kV)
Current Rating for 3.8/6.6KV (Um=7.2KV), 6.35/11KV (Um=12KV) & 8.7/15KV (Um=17.5KV)
Current Rating for 12.7/22KV (Um=24KV)
Current Rating for 19/33KV (Um=36KV)

Current Rating Conditions:

Ground Temperature:20°C
Ambient Temperature (air):
30°C
Depth of Soil: 0.8m
Thermal Resistance of Soil: 1.5K•m/W