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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 |
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 0.035+D 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 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. |
|
Unarmoured Cables |
Aluminium Wire Armoured Cables |
||||||||||
Nom. |
Copper Wire Screen Area |
Nom. |
Approx. Overall Diameter |
Approx. Weight |
Copper Tape Screen Area |
Nom. Bedding |
Nom. Armour Wire Diameter |
Nom. |
Approx. Overall Diameter |
Approx. |
|||
Cu |
AL |
||||||||||||
Cu |
AL |
||||||||||||
mm2 |
mm |
mm2 |
mm |
mm |
kg/km |
mm2 |
mm |
mm |
mm |
mm |
kg / km |
||
25 |
2.5 |
16 |
1.5 |
20.3 |
750 |
580 |
3.4 |
1.2 |
1.6 |
1.8 |
26.3 |
1150 |
1000 |
35 |
2.5 |
16 |
1.6 |
21.3 |
870 |
650 |
3.6 |
1.2 |
1.6 |
1.8 |
27.3 |
1250 |
1050 |
50 |
2.5 |
16 |
1.6 |
22.4 |
1090 |
770 |
3.9 |
1.2 |
1.6 |
1.8 |
28.4 |
1500 |
1190 |
70 |
2.5 |
16 |
1.7 |
24.2 |
1310 |
870 |
4.3 |
1.2 |
1.6 |
1.8 |
30.0 |
1740 |
1300 |
95 |
2.5 |
16 |
1.7 |
25.8 |
1560 |
960 |
4.7 |
1.2 |
1.6 |
1.9 |
31.8 |
2030 |
1430 |
120 |
2.5 |
16 |
1.8 |
27.4 |
1830 |
1070 |
5.0 |
1.2 |
1.6 |
1.9 |
33.2 |
2310 |
1550 |
150 |
2.5 |
25 |
1.8 |
29.1 |
2130 |
1190 |
5.3 |
1.2 |
1.6 |
2.0 |
35.1 |
2660 |
1720 |
185 |
2.5 |
25 |
1.9 |
30.8 |
2490 |
1320 |
5.8 |
1.2 |
2.0 |
2.0 |
37.4 |
3120 |
1950 |
240 |
2.6 |
25 |
1.9 |
33.5 |
3040 |
1520 |
6.3 |
1.2 |
2.0 |
2.1 |
40.3 |
3740 |
2200 |
300 |
2.8 |
25 |
2.0 |
36.1 |
3650 |
1770 |
7.0 |
1.2 |
2.0 |
2.2 |
42.9 |
4400 |
2520 |
400 |
3.0 |
35 |
2.2 |
40.6 |
4680 |
2170 |
7.7 |
1.2 |
2.0 |
2.3 |
47.2 |
5490 |
2960 |
500 |
3.2 |
35 |
2.3 |
43.6 |
5670 |
2570 |
8.5 |
1.3 |
2.5 |
2.5 |
51.6 |
6760 |
3660 |
630 |
3.2 |
35 |
2.4 |
48.8 |
6980 |
2990 |
9.5 |
1.4 |
2.5 |
2.6 |
57.0 |
8200 |
4160 |
Electrical Data
Nom. |
|
Unarmoured |
Aluminium Wire Armoured Cables |
|
|||||||||||
D C |
A C |
Short Circuit Rating of |
Capaci- |
Charging Current |
Short |
Short Circuit Rating of Copper Tape Screen |
Reactance |
Inductance |
Impedance |
||||||
Trefoil |
Flat spaced |
Trefoil |
Flat |
Trefoil |
Flat Spaced |
||||||||||
Cu |
AL |
Cu |
AL |
||||||||||||
mm2 |
µΩ/m |
µΩ/m |
kA |
pF/m |
mA/m |
kA |
kA |
µΩ/m |
µΩ/m |
nH/m |
nH/m |
µΩ/ m |
µΩ/m |
||
25 |
727/1200 |
927/1538 |
3.6/2.3 |
263 |
0.32 |
2.6 |
0.4 |
136 |
194 |
400 |
590 |
936 |
1544 |
952 |
1554 |
35 |
524/868 |
668/1113 |
5.0/3.2 |
291 |
0.35 |
2.6 |
0.5 |
127 |
185 |
390 |
580 |
679 |
1121 |
695 |
1131 |
50 |
387/641 |
494/822 |
6.8/4.4 |
321 |
0.39 |
2.6 |
0.5 |
121 |
179 |
380 |
570 |
511 |
834 |
527 |
844 |
70 |
268/443 |
343/568 |
9.8/6.3 |
371 |
0.45 |
2.6 |
0.6 |
115 |
173 |
370 |
550 |
364 |
583 |
386 |
597 |
95 |
193/320 |
248/410 |
13.3/8.5 |
417 |
0.50 |
2.6 |
0.6 |
110 |
168 |
350 |
540 |
272 |
427 |
300 |
446 |
120 |
153/253 |
196/325 |
17.2/11.0 |
459 |
0.55 |
2.6 |
0.7 |
107 |
165 |
340 |
520 |
225 |
345 |
257 |
367 |
150 |
124/206 |
159/265 |
21.2/13.5 |
494 |
0.59 |
4.3 |
0.7 |
103 |
161 |
330 |
510 |
193 |
287 |
229 |
313 |
185 |
99.1/164 |
128/211 |
26.6/17.0 |
543 |
0.65 |
4.3 |
0.8 |
100 |
158 |
320 |
500 |
165 |
237 |
206 |
267 |
240 |
75.4/125 |
98/161 |
34.9/22.3 |
583 |
0.70 |
4.3 |
0.9 |
97 |
155 |
310 |
490 |
140 |
191 |
185 |
226 |
300 |
60.1/100 |
80/130 |
43.8/28.0 |
602 |
0.72 |
4.3 |
1.0 |
95 |
153 |
300 |
490 |
126 |
163 |
174 |
203 |
400 |
47.0/77.8 |
64/102 |
57.3/36.6 |
627 |
0.75 |
5.8 |
1.1 |
92 |
150 |
290 |
480 |
113 |
141 |
164 |
184 |
500 |
36.6/60.5 |
51/81 |
72.3/46.2 |
654 |
0.79 |
5.8 |
1.2 |
90 |
149 |
290 |
470 |
105 |
124 |
158 |
171 |
630 |
28.3/46.9 |
42/64 |
91.2/58.3 |
726 |
0.87 |
5.8 |
1.3 |
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