Electrical Basic Concepts
VOLTAGE DROP OF CABLE
Voltage drop is the losses of voltage due to cable impedance, the voltage at the end of a run of cable is lower than at the supply point.
The Voltage Drop play important role while selecting cable for an electrical dive , so below is given and example to understand the same.
Consider Actual Load=172 kw
Full load Current = Total load (KW)/( 1.732 x Motor eff. x P.F.x Voltage (KV) )
= 172/ (1.732 x 0.8 x 0.85 x 0.415)
= 352 Amps and Length of cable is 250 Mts.
Cable size selected is 3.5c x 300 mm² XLPE cable current carrying capacity is 461 Amps ) (
De rated capacity of cable
= 461 x 0.58= 267 Amps
Cable Runs
=352/267=1.31 (Say 2 runs ) ,
This cable can easily take the load of 352 Amps and is suitable.
Voltage Drop(%)
=1.732 x Full Load Current (A) x Cable Length (M) x 100 x ( cosᵩ x Resistance(ohms/km) + sin ᵩ x Reactance(ohms/km)) /(Rounded Cable Runs x 415 X 1000)
= 1.732 x 352 x 250 x 100 x (0.85 x 0.13 + 0.52 x 0.071)/(2 x 415 x 1000)
= 2.71 % (Well within permissible limit of 5%).