Three Core 12.7/22KV Medium Voltage 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 12.7/22KV Medium Voltage 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 12.7/22KV (Um=24KV) 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
					CU	AL						CU	AL
mm²	mm	mm²	mm	mm	kg/km		mm²	mm	mm	mm	mm	kg/km
35	5.5	16	2.7	51	3750	2880	5.2	1.5	2.5	2.8	62.3	6870	6140
50	5.5	16	2.8	54	4240	3250	5.4	1.5	2.5	2.9	65.6	7710	6810
70	5.5	16	2.9	58	5050	3650	5.9	1.6	2.5	3.0	69.0	8710	7370
95	5.5	16	3.0	62	6010	4110	6.2	1.7	2.5	3.2	73.1	10000	8130
120	5.5	16	3.1	65	6990	4660	6.6	1.7	3.15	3.3	77.7	12040	9730
150	5.5	25	3.2	68	8130	5330	6.9	1.8	3.15	3.4	81.7	13550	10750
185	5.5	25	3.3	72	9410	5870	7.4	1.9	3.15	3.6	85.5	15150	11610
240	5.5	25	3.5	79	11490	6880	7.8	2.0	3.15	3.7	91.3	17710	12840
300	5.5	25	3.7	84	13710	7890	8.2	2.0	3.15	3.9	96.0	20170	14360
400	5.5	35	3.9	91	17230	9440	9.0	2.2	3.15	4.1	104.8	24520	16480

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
35	524/868	668/1113	5.0/3.2	168	0.67	2.6	0.7	129	410	170	135	155	120	180	145
50	387/641	494/822	6.8/4.4	183	0.73	2.6	0.8	122	390	210	160	185	140	225	175
70	268/443	343/568	9.8/6.3	207	0.83	2.6	0.8	115	370	255	195	225	170	275	215
95	193/320	248/410	13.3/8.5	229	0.92	2.6	0.9	110	350	295	230	260	205	330	260
120	153/253	196/325	17.2/11.0	249	1.00	2.6	0.9	106	340	335	260	300	235	380	300
150	124/206	159/265	21.2/13.5	266	1.06	4.3	1.0	103	330	375	290	335	265	430	335
185	99.1/164	128/211	26.6/17.0	289	1.16	4.3	1.0	100	320	420	330	380	300	490	390
240	75.4/125	98/161	34.9/22.3	318	1.27	4.3	1.1	95	300	480	380	430	345	570	460
300	60.1/100	80/130	43.8/28.0	348	1.39	4.3	1.2	93	300	530	425	480	385	650	520
400	47.0/77.8	64/102	57.3/36.6	383	1.53	5.8	1.3	87	280	590	480	520	420	700	570