Page 224 - Handbook of Electrical Engineering

208 HANDBOOK OF ELECTRICAL ENGINEERING

Table 9.22. Land based Installations. 3800/6600 V. 6350/11,000 V. 8700/15,000 V. Cu/XLPE/PVC/SWA/
PVC three cores
Nominal conductor Air Ducts Direct Notes
2
area (mm ) buried
◦
25 145 125 140 Thermal resistivity of soil is 1.2 Cm/W
35 175 150 170
◦
50 220 180 210 Ambient air temp. is 25 C.
70 270 215 255 Depth of laying cables is 0.5 m
95 330 255 300
◦
120 375 290 340 Standard ground temp. is 15 C
150 430 330 380
◦
185 490 370 430 Conductor surface temp. is 90 C.
240 570 425 490
300 650 470 540
400 740 530 600
◦
Ambient air temperature C 25 30 35 40 45 50 55 60
Rating factor K air for cables laid in air 1.0 0.96 0.92 0.88 0.84 0.79 0.73 0.68
◦
Ground temperature C 10 15 20 25 30 35 40
Rating factor K grd for cables laid in the ground 1.03 1.0 0.97 0.93 0.89 0.86 0.82
Table 9.23. Marine and offshore 600/1000 V Cu/EPR/CSP/GSWB or PBWB/CSP or PVC
installations. Cables run on open trays or enclosed in air. 1 to 6 × single, 3 or 4 cores
Nominal conductor Single 3and4 Notes
2
area (mm ) cores cores
◦
1.0 17 12 Ambient air temperature is 45 C
1.5 21 15
2.5 30 21
◦
4 40 29 Conductor surface temperature is 90 C.
6 51 36
10 71 50
16 95 67
25 125 89
35 155 105
50 190 135
70 240 170
95 290 205
120 340 240
150 385 270
185 440 305
240 520 365
300 590 415
400 670 470

Ambient air tem- 35 40 45 50 55 60 65 70 75 80
◦
perature C
Rating factor for 1.11 1.05 1.0 0.94 0.88 0.82 0.75 0.69 0.58 0.47
cables laid in air