Three Core 3.8/6.6KV Steel Wire Armoured Cable 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.

CONSTRUCTION :

Three Core 3.8/6.6KV Steel Wire Armoured Cable 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
Nom. Cross Section Area	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
>	<
35	45	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 over sheath is normally black in colour. When a DC voltage test is to be performed on the over sheath, a semi-conducting layer such as graphite coating shall be applied over the surface of the extruded over sheath. The nominal over sheath thickness is calculated by 0.035+D where D is the diameter immediately under the over sheath in mm. For cables with the over sheath not applied over the armour, the nominal over sheath thickness shall not be less than 1.4mm. And for cables with over sheath applied over the armour, the nominal over sheath thickness shall not be less than 1.8mm.

PHYSICAL PROPERTIES :

Operating Temperature: up to 90°C
Temperature Range: -5°C ( PVC or LSZH sheath ); -20°C ( PE sheath )
Short Circuit Temperature: 250°C (short circuit duration up to 5 seconds)
Bending Radius: 15 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

DIMENSIONAL DATA :

Three Core 3.8/6.6KV (Um=7.2KV) Medium Voltage Steel Wire Armoured Cable

Nom. Cross- Section Area		Unarmoured Cables					Steel 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
	Nom. Insulation Thickness	Copper Wire Screen Area	Nom. Sheath Thickness	Approx. Overall Diameter	CU	AL	Copper Tape Screen Area	Nom. Bedding Thickness	Nom. Armour Wire Diameter	Nom. Sheath Thickness	Approx. Overall Diameter	CU	AL
mm²	mm	mm²	mm	mm	kg/km		mm²	mm	mm	mm	mm	kg/km
25	2.5	16	2.1	37.7	2205	1740	3.4	1.2	2.0	2.2	44.5	3890	3465
35	2.5	16	2.3	41.2	2690	2010	3.6	1.2	2.5	2.3	46.8	4420	3730
50	2.5	16	2.5	44.9	3340	2350	3.8	1.3	2.5	2.5	51.5	5640	4690
70	2.5	16	2.6	48.0	4050	2730	4.3	1.3	2.5	2.6	55.0	6570	5240
95	2.5	16	2.7	51.7	5000	3180	4.7	1.4	2.5	2.7	58.9	7760	5890
120	2.5	16	2.8	54.7	5890	3590	5.0	1.5	2.5	2.8	62.1	8810	6510
150	2.5	25	2.9	58.4	6960	4160	5.3	1.5	2.5	2.9	65.8	10110	7310
185	2.5	25	3.0	61.9	8160	4650	5.8	1.6	2.5	3.0	69.5	11520	7960
240	2.6	25	3.2	68.1	10210	5530	6.3	1.7	2.5	3.2	75.9	13920	9140
300	2.8	25	3.5	73.6	12380	6670	7.0	1.8	3.15	3.5	83.1	17400	11620
400	3.0	35	3.7	83.8	16190	8430	7.7	2.0	3.15	3.7	93.0	21900	13980

ELECTRICAL DATA :

Nom. Cross- Section Area						Unarmoured Cables	Steel Wire Armoured Cables			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 Copper Tape Screen Per Core 1 sec	Reac- tance	Induc- tance	Ground		Duct		Air
	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 Copper Tape Screen Per Core 1 sec	Reac- tance	Induc- tance	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
25	727/1200	927/1538	3.6/2.3	272	0.33	2.6	0.4	113	370	140	115	125	95	145	115
35	524/868	668/1113	5.0/3.2	301	0.36	2.6	0.5	108	350	170	135	150	115	175	140
50	387/641	494/822	6.8/4.4	332	0.40	2.6	0.5	102	330	210	160	180	135	220	170
70	268/443	343/568	9.8/6.3	383	0.46	2.6	0.6	97	310	255	195	215	165	270	210
95	193/320	248/410	13.3/8.5	432	0.52	2.6	0.6	92	290	300	230	255	200	330	250
120	153/253	196/325	17.2/11.0	474	0.57	2.6	0.7	89	280	340	265	290	225	375	295
150	124/206	159/265	21.2/13.5	511	0.61	4.3	0.7	87	280	380	295	330	255	430	330
185	99.1/164	128/211	26.6/17.0	562	0.67	4.3	0.8	86	270	430	335	370	290	490	385
240	75.4/125	98/161	34.9/22.3	602	0.72	4.3	0.9	83	260	490	380	425	335	570	450
300	60.1/100	80/130	43.8/28.0	622	0.75	4.3	1.0	82	260	540	435	470	375	650	510
400	47.0/77.8	64/102	57.3/36.6	648	0.78	5.8	1.1	80	250	590	480	520	420	700	570