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Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT

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Bs53l t: Part 2: Specification for AC circuit-breakers of rated (... wItage above 1 kW — Rating: 1976

BS5424: Specification for controlgear for voltages up to and

.161 ncluding 1000 V AC and 1200 V DC: 1977

FiS147: Section 2.3: Specification for thermal electrical relays: 198-1

	lEE skinIng Regulations: currently 15th Edition 1981; 16th
	Edirion to be i s sued
I	c.; DCD Standard 197: Cable supporting steelwork: April 1979

:111 BS3692: Specification for 1S0 metric precision hexagon bolts,

..,:rews and r,u(s. NIetric units: 1967

'21] CDCD Standard 216: Cable cleating arrangements

Burki A. N. and Sabine A. M.; Connecting solid-conductor aluminium cables in terminal boxes: The Engineer: December

1963

Solars P. M. A.: Wire wrapped joints — a review: Electrocomponent science and technology: Volume 1, pp 17-25: 1974

References

1241 BS476: Part 8: Fire tests on building materials and structures

—test methods and criteria for the fire resistance of elements of building construction: 1972

[25]BS476: Part 4: Fire tests on building materials and structures

—non-combustibility test for materials: 1970 (1984)

1261 BS476: Part 7: Fire tests on building materials and structures

— surface spread of flame tests for materials

(271 Alderton J. R., Anderson P. C., and Cakebread R. J.: Calculation and measurement of the earth impedance of an eh.. substation: Proc IEE, Vol 125, No. 12: December 1978

[281 IEEE Standard 80: IEEE guide for safety in substation grounding: 1986

[29]Tagg G. F.: 'Earth resistances': George Newries, London: 1964

[30]Wenner Dr. F.: Scientific Paper 258: Bureau of Standards: 1915

[31]Engineering Recommendation S34: A guide for assessing the rise of earth potential at substation sites: May 1986

607

Cabling	Chapter 6

Appendix A

Values of resistance and reactance for single-core elastomeric-insulated cables (90°C maximum conductor temperature)

		Conductor		Armour

	DC	AC	Equivalent	DC
Cable type	resistance	resistance	star reactance	resistance
	at	at	at	at
	20 ° C, pfl/m	90° C, ;.I.S1/m	50 Hz, pf/trn	20° C, 4/rn

It kV Cables
Single-core	100	129	158	200
300 mm 2
Single-core	60.5	79	142	170
500 mm 2
3.3 kV Cables
Single-core	77.8	100.5	150	110
400 mm 2
415 V Cables
Single-core	77.8	100.5	150	110
400 mm 2

Note: Equivalent star reactance values are for a single cable per phase laid in flat formation

608

Appendix B

Values of resistance and reactance for multicore PVC-insulated cables (70°C maximum conductor temperature)

				Conductor		Armour

			DC	AC	Equivalent	DC
Cable type			resistance	resistance	star reactance	resistance
			at	at	at	at
			20° C, itillm	70° C, ,itil/m	50 Hz, Aft/m	20° C, 1.11/m

3.3 kV Cables
3-core 150		mm 2	206	248	80.0	240
3-core 240		mm 2	125	151	76.5	150
415 V Cables
2-core	2.5 mm 2		7410	8866	100.0	9100
3-core	2.5 mm 2		7410	8866	100.0	8800
4-core	2,5 mm 2		7410	8866	100.0	7900
2-core	4	mm 2	4610	5516	98.5	7500
3-core	4	mm 2	4610	5516	98.5	7000
4-core	4	mm2	4610	5516	98.5	4600
2-core	6	mm 2	3080	3685	93.5	6800
3-core	6	mm 2	3080	3685	93.5	4600
4-core	6	mm 2	3080	3685	93.5	4100
2-core	16	mm 2	1910	2295	86.0	1 40
3-core	16	mm 2	1910	2295	86.0	130
4-core	16	mm 2	1910	2295	86.0	1200
2-core	35	mm 2	868	1043	82.0	1400
3-core	35	mm2	868	1043	82.0	1100
4-core	35	mm 2	868	1043	82.0	960
2-core	70	mm2	443	532	79.0	570
3-core	70	mm 2	443	532	79.0	480
4-core	70	mm 2	443	532	79.0	420
3-core 120		mm 2	253	304	77.0	280
4-core 120		mm2	253	304	77.0	240
3-core 185		mm 2	164	197	77.0	230
4-core 185		mm2	164	197	77.0	150
3-core 300		mm 2	1 00	120	76.0	mo
4-core 300		mm 2	100	120	76.0	120

The constant mass temperature coefficient at 20 ° C per kelvin are:

Copper	=	0.00393
Aluminium	=	0.00403
Galvanised	=	0.0045
steel wire

Note: Cables up to and including 6 mm 2 have copper conductors and steel wire armour.

Cables 60 mm 2 and larger have aluminium conductors and armour.

609

Cabling

Appendix C

Current ratings for elastomeric-insulated cables

The current ratings are based on a maximum conductor temperature of 90° C with ambient temperature of 25 ° C, with single-point bonding and no core transposition.

		Current rating, A
Cable type
Cable type	Direct in		In single-	In air
	Direct in		In single-
	the ground		way ducts
	the ground		way ducts

11 kV Cables
Single-core 300 mm 2	500		480	675
Single-core 500 mm 2	645		610	900
3.3 kV Cables
Single-core 400 mm 2	575		550	785
415 V Cables
Single-core 400 mm 2	575		550	785

Note: All cables have stranded aluminium conductors

TIP

Chapter 6

610

Appendix ID

Appendix D

Current ratings for PVC-insulated cables

The current ratings are based on a maximum conductor temperature of 70 ° C and an ambient temperature of 25 ° C.

				Current rating, A
Cable type
Cable type			Direct in		In single-	In air
			Direct in		In single-
			the ground		way ducts
			the ground		way ducts

3.3 kV Cables
3-core 150		mm 2	257		217	265
3-core 240		mm 2	338		285	361
415 V Cables
2-core	2.5 mm 2		41		34	33
3-core	2.5 mm 2		35		29	28
4-core	2.5 mm 2		35		29	28
2-core	4	mm 2	55		45	44
3-core	4	mm 2	47		38	38
4-core	4	mm 2	47		38	38
2-core	6	mm2	69		57	56
3-core	6	mm 2	59		46	48
4-core	6	mm2	59		48	48
2-core	16	mm2	91		75	77
3-core	16	mm 2	77		62	65
4-core	16	mm 2	77		62	65
2-core	35	mm2	142		115	120
3-core	35	mm 2	120		97	104
4-core	35	mm 2	120		97	104
2-core	70	mm 2	209		170	185
3-core	70	mm 2	176		144	161
4-core	70	mm 2	176		144	161
3-core 120		mm 2	243		199	232
4-core 120		mm2	243		199	232
3-core 185		mm 2	309		254	306
4-core 185		mm 2	309		254	305
3-core KO		mm 2	407		338	421
4-core 300		mm 2	407		338	421

Notes: 3.3 kV cables have solid aluminium conductors.

415 V cables with nominal conductor areas of 2.5 mm 2 , 4 mm 2 and 6 mm 2 have stranded-copper conductors.

All other 415V cables have solid aluminium conductors.

611

Cabiing	Chapter 6

Appendix E

Rating factors for variations in thermal parameters

Rating factors for variation in ambient air temperature

(a) Maximum conductor temperature 70 ° C

Air temperature, ° C	25	30	35		40	45	50	55

Rating factor (maxhnum	1.00	0.94	0.88		0.82	0.75	0.67	0,58
conductor temperature
70 ° C)

Lb) Maximum conductor temperature 90 ° C

Air temperature, ° C	25	30	35		40	45	50	55

Rating factor (maximum	1.00	0.95	0.91		0.86	0.80	0.75	0.69
conductor temperature
90 ° C)
				-

Rating factors for variation in ground temperature for cables buried direct in the ground.

(a) Maximum conductor temperature 70° C

Ground temperature, ° C	20	25	30	35	40

Rating factor (maximum	0.95	0.90	0.85	—	—
conductor temperature
70 ° C)

(b) Maximum conductor temperature 90 ° C

Ground temperature, ° C	20	25	30	35	40

Rating factor )maximum	0.97	0.93	0.89	0,86	0.82
conductor temperature
90 ° C)

612

Appendix E

Appendix E (cont'd)

Rating factors for variations in thermal parameters

Rating factors for variation in ground temperature for cables laid in ducts

(a) Maximum conductor temperature 70 ° C

Ground temperature, ° C	20	25	30

Rating factor (maximum	0.95	0.90	0.85
conductor temperature
70° C)

lbl Maximum conductor temperature 90 ° C

Ground temperature, ° C	20	25	30

Rating factor (maximum	0.97	0.93	0.89
conductor temperature
90°C)

Note: The rating factors in the following tables may be taken to be the same for maximum conductor temperatures of 70 ° C and 90 ° C respectively.

Rating factors for variation in depth of laying direct in the ground

		415 Volt cables		3.3 kV and 11 kV
Depth of		415 Volt cables		cables
				cables

laying, m	Up to		Above	Up to	Above
	Up to		Above	Up to	Above
	50 mm 2	70-300 mm	300 mm 2	300 mm 2	300 mm 2

0.50	1.00	1.00	1.00	-	-
0.60	0.99	0.98	0.97	-	-
0.80	0.97	0.96	0.94	1.00	1.00
1.00	0.95	0.93	0.92	0.98	0.97
1.25	0,94	0.92	0.89	0.96	0.95
1.50	0.93	0,90	0.87	0.95	0.93

613

Cabling	Chapter 6

Appendix E (cont'd)

Rating factors for variations in thermal parameters

Rattng factors for variation in soil thermal resistivity

(a} Cables laid direct in the ground

Nominal area of			Ground thermal resistivity			K.m/W
Nominal area of
conductor		0.8	0.9	1.0	1.5	2.0	2.5
		0.8	0.9	1.0	1.5	2.0	2.5

Multicore cables
2.5 mm 2		1.09	1 07	1.04	0.94	0.86	0.80
4.0 mm 2		1.10	1.07	1.05	0.94	0.85	0.79
6.0 mm 2		1.10	1.07	1.05	0.93	0.85	0.79
16	mm 2	1.12	1.08	1.05	0.93	0.84	0.77
35	mm 2	1.13	1.09	1.06	0.92	0.83	0,76
70	mm 2	1.14	1.09	1.06	0.92	0.83	0.75
120	mm 2	1.14	1.10	1.06	0.92	0.82	0.75
150	mm 2	1.14	1.10	1.06	0.92	0.82	0.75
185	mm 2	1.14	1.10	1.06	0.92	0.82	0.74
240	mm 2	1,15	1,10	1.07	0.92	0.81	0.74
300	mm 2	1.15	1.10	1.07	0.92	0.81	0.74
Singlecore cables
300	mm 2	1.17	1.12	1.07	0.91	0.80	0.73
400	mm 2	. 1.17	1.12	1.07	0.91	0.80	0.73
500	mm 2	1.17	1.12	1.07	0.91	0.80	0.73

614

Appendix E

Appendix E (cont'd)

Rating factors for variations in thermal parameters

Rating factors for variation in soil thermal resistivity fbi Cables laid in ducts

Nominal area of						Ground thermal resistivity, K.m/W
Nominal area of
conductor				0.8		0.9	1.0	1.5	2.0		2.5
_				0.8		0.9	1.0	1.5	2.0		2.5
_
Muir/core cables
2.5 mm 2				1 03		1.02	1.02	0.98	cDo	49	0.91
4.0 mm 2				1.04		1.03	1.02	0.97	cDo	49	0.90
6.0 mm 2				1.04		1.03	1.02	0.97	.		0.90
6.0 mm 2				1.04		1.03	1.02	0.97	.		0.90
16	mm 2			1.04		1.03	1.02	0.97	.		0.88
35	mm 2			1.05		1.03	1.02	0.96	o CD 49COCOCD		0.87
70	mm 2			1.05		1.04	1.02	0.96	o CD 49COCOCD		0.86
500	mm 2			1.11		1.08	1.05	0.93	oo	RES%88	0.78
120	mm 2			1.06		1,04	1.03	0.95			0.85
150	mm 2			1.06		1.04	1.03	0.95			0.85
185	mm 2			1.07		1.05	1.03	0.95			0.84
240	mm 2			1.07		1.05	1.03	0.95			0.84
300	mm 2			1.07		1.05	1.03	0.95			0.83
Single-core cables
300	mm2			1.11		1,08	1.05	0.93			0.79
400	mm 2			1.11		1.08	1.05	0.93			0.78

Rating factors for variation in depth of cables laid in ducts

Depth of			415 Vo t cables				3.3 kV and 11 kV cables
Depth of
laying, m		Single-core			Multicore		Single-core	Multicore
		Single-core			Multicore		Single-core	Multicore

0.50			1.00		8RER ci		_	_
0.60			0.98				-	-
0.80			0.95				1.00	1.00
1.00			0.93				0.98	0.99
1.25			0.91		TA O		0.95	0.97
1.50			0.89		TA O		0.94	0.96

615

Cabling

Appendix F

Cross-sectional area of armour wire

475 V 3.3 kV and 17 kV single-core power cables

Nominal cross-sectional	Cross-sectional area of
area of conductor	armour wire, mm 2

11 kV Cables
Single-core 300 mm 2	103
Single-core 500 mm 2	169
3.3 kV Cables
Single-core 400 mm 2	153
415 V Cables
Single-core 400 mm 2	153

All cable sizes have round aluminium armour wire

415 V and 3.3 kV mutt/core power cables to 8S6346

Nominal cross-sectional		Cross-sectional area of
Nominal cross-sectional		armour wire/strip mm 2
area of conductor
mm	2	2-core	3-core		4-core
		mm 2	mm	2	mm2

2.5		17	19		20
4		21	23		35
6		24	36		40
16		23	26		29
35		24	30		34
70		56	67		78
120		N/A	117		136
185		N/A	143		214
300		N/A	237		271

2.4 mm 2 , 4 mm 2 and 6 mm 2 cable sizes have steel wire armour

16 mm 2 and above cable sizes have aluminium strip armour

Chapter 6

.. .....M1

616

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