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

Three Core Cables to BS 6622

Application

The three core cables are designed for distribution of electrical power with nominal voltage Uo/U ranging from 3.6/6.6KV 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

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 Nom. 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.

Inner Covering & Fillers:

For cables with a collective metallic layer or cables with a metallic layer over each individual cores with additional collective metallic layers, semi-conducting inner covering and fillers shall be applied over the laid up cores. The inner covering is made of non hygroscopic material, except if the cable is to be made longitudinally watertight. The inner covering shall be extruded or lapped.
The approximate thickness of extruded inner coverings is given in Table 2:

Table 2. Approximate Thickness Of Extruded Inner Coverings

Ficititous Diameter Over Laid Up Cores Approx. Thickress of Extruded Inner Covering
mm mm
>  <   
- 25 1.0
25 35 1.2
35 45 1.4
45 60 1.6
60 80 1.8
80 - 2.0

*The approximate thickness of lapped inner coverings shall be 0.6mm.

Metallic Layer:

The metallic layer shall be applied over each core or applied as a collective screen. The metallic screen 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 is shown in table 3.

Table 3. Minimum Total Cross Section Of Copper Wire Screen & DC Resistance Of The Screen

Nominal Cross-Section
Area of Cable
Minimum Cross-Section
of Copper Wire Screen Area
DC Resistance of the Copper Wire Screen
mm² mm² mm
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 galvanized steel wire applied over the inner covering with diameter specified as in Table 4.

Table 4. Armour Wire Diameter

Fictitiious 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 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: 12 x OD

Table 5. 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

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

Nom.
Cross-
Section
Area
  Steel Wire Armoured Cables
Nom.
Insulation Thickness
Copper Tape Screen Area Nom.
Bedding
Thick
ness
Nom. Armour Wire Diam
eter
Nom.
Sheath Thick
ness
Approx. Overall Diameter Approx.
Weight
CU AL
mm2 mm mm2 mm mm mm mm kg / km
50 2.5 3.8 1.3 2.5 2.5 51.5 5640 4690
70 2.5 4.3 1.3 2.5 2.6 55.0 6570 5240
95 2.5 4.7 1.4 2.5 2.7 58.9 7760 5890
120 2.5 5.0 1.5 2.5 2.8 62.1 8810 6510
150 2.5 5.3 1.5 2.5 2.9 65.8 10110 7310
185 2.5 5.8 1.6 2.5 3.0 69.5 11520 7960
240 2.6 6.3 1.7 2.5 3.2 75.9 13920 9140
300 2.8 7.0 1.8 3.15 3.5 83.1 17400 11620
400 3.0 7.7 2.0 3.15 3.7 93.0 21900 13980

Electrical Data

Nom.
Cross-
Section
Area
        Current Ratings
D C Resistance
CU / AL
A C Resistance
CU / AL
Short Circuit Rating of
Conductor
CU / AL
1 sec
Capaci-
tance
Charging Current Short Circuit Rating of Copper Wire Screen
Per Core
1 sec
Short
Circuit
Rating of
Armour Per
Core
1 sec
Reac-tance Induc-
tance
Ground Duct Air
CU AL CU AL CU AL
mm2 µΩ/m µΩ/m kA pF/m mA/m kA kA µΩ/m nH/m A A A
50 387/641 494/822 6.8/4.4 332 0.40 2.6 9.4 102 330 210 160 180 135 220 170
70 268/443 343/568 9.8/6.3 383 0.46 2.6 9.9 97 310 255 195 215 165 270 210
95 193/320 248/410 13.3/8.5 432 0.52 2.6 10.8 92 290 300 230 255 200 330 250
120 153/253 196/325 17.2/11.0 474 0.57 2.6 11.4 89 280 340 265 290 225 375 295
150 124/206 159/265 21.2/13.5 511 0.61 4.3 12.3 87 280 380 295 330 255 430 330
185 99.1/164 128/211 26.6/17.0 562 0.67 4.3 13.1 86 270 430 335 370 290 490 385
240 75.4/125 98/161 34.9/22.3 602 0.72 4.3 14.2 83 260 490 380 425 335 570 450
300 60.1/100 80/130 43.8/28.0 622 0.75 4.3 19.0 82 260 540 435 470 375 650 510
400 47.0/77.8 64/102 57.3/36.6 648 0.78 5.8 21.4 80 250 590 480 520 420 700 570

Three Core 6.35/11KV (Um=12KV)
Three Core 8.7/15KV (Um=17.5KV)
Three Core 12.7/22KV (Um=24KV)
Three Core 19/33KV (Um=36KV)