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 0.035+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. Cross- Section Area		Unarmoured  Cables					Aluminium Wire Armoured Cables
	Nom. Insulation Thickness	Copper Wire Screen Area	Nom. Sheath Thickness	Approx. Overall Diameter	Approx. Weight		Copper Tape Screen Area	Nom. Bedding Thickness	Nom. Armour Wire Diameter	Nom. Sheath Thickness	Approx. Overall Diameter	Approx. Weight
												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. Cross- Section Area						Unarmoured Cables	Aluminium Wire Armoured Cables
	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 1 sec	Short Circuit Rating of Copper Tape Screen 1 sec	Reactance		Inductance		Impedance
								Trefoil	Flat     spaced	Trefoil	Flat Spaced	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