Cable Sizing Calculator [PDF]

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Cable sizing and Voltage drop Calculation of Cable sizing and Voltage drop with an assumed example • • • • • • • • •

Power of Load P = 80kW Length from Source L = 200m System Voltage V = 415V Power Factor pf = 0.8 Ground temperature = 35oC Permissible Voltage drop = 5% Soil = Damp soil (thermal resistivity of soil) Burial depth = 1m Demand factor = 1

Cable Sizing: 𝐹𝐿𝐴 = 𝐹𝐿𝐴 =

𝑃𝑜𝑤𝑒𝑟 𝑖𝑛 𝑤𝑎𝑡𝑡 1.732 ∗ 𝑉 ∗ 𝑝𝑓 80 ∗ 1000 1.732 ∗ 415 ∗ 0.8

𝐹𝐿𝐴 = 139 𝐴 𝐾 = 𝐶𝑎𝑏𝑙𝑒 𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 𝐾 = 𝐾1 ∗ 𝐾2 ∗ 𝐾3 ∗ 𝐾4 ∗ 𝐾5 ∗ 𝐾6 ∗ 𝐾7

K – Factor

Thermal Resistance of soil

𝐶𝑎𝑏𝑙𝑒 𝐷𝑒𝑟𝑎𝑡𝑖𝑛𝑔 = 𝐹𝐿𝐴 = 139 𝐴

𝐹𝐿𝐴 𝐾

Underground Cable correction factor:

𝐾 = 1.05 ∗ 0.96 ∗ 0.97 𝐾 = 0.9776 𝐴 𝐹𝐿𝐴 =

139 0.9776

(𝐶𝑎𝑏𝑙𝑒 𝑑𝑒𝑟𝑎𝑡𝑖𝑛𝑔) 𝐹𝐿𝐴 = 142 𝐴 142 A is minimum current carrying capacity of the cable. Refer to cable datasheet more than 142 A 70𝑠𝑞. 𝑚𝑚 = 164 𝐴

Voltage Drop:

𝑉𝑜𝑙𝑡𝑎𝑔𝑒𝑑𝑟𝑜𝑝 =

=

1.732 ∗ 𝐹𝐿𝐴 ∗ (𝑅𝑐𝑜𝑠∅ + 𝑗𝑋𝑠𝑖𝑛∅) ∗ 𝑐𝑎𝑏𝑙𝑒 𝐿𝑒𝑛𝑔𝑡ℎ ∗ 100 𝐿𝑖𝑛𝑒 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 ∗ 𝑁𝑜 𝑜𝑓 𝑟𝑢𝑛𝑠 ∗ 1000

1.732 ∗ 139 ∗ (0.56 ∗ 0.8 + 𝑗0.074 ∗ 0.6) ∗ 200 ∗ 100 415 ∗ 1 ∗ 1000 𝑉𝑜𝑙𝑡𝑎𝑔𝑒𝑑𝑟𝑜𝑝 = 5.71%

The voltage drop obtained is more than the permissible value 5% the voltage drop should be below the permissible value. So, to reduce the Voltagedrop, the Size of the cable is increased by decreasing the resistance and reactance (taken from the catalogue). =

1.732 ∗ 139 ∗ (0.41 ∗ 0.8 + 𝑗0.0724 ∗ 0.6) ∗ 200 ∗ 100 415 ∗ 1 ∗ 1000 𝑉𝑜𝑙𝑡𝑎𝑔𝑒𝑑𝑟𝑜𝑝 = 2.2%

2.2% voltagedrop is within the permissible level. So, 95sq.mm is preferrable for the system.