Whatever
or how perfect the conductivity of a cable, we will still faced a voltage drop
problem caused by natural characteristics, which the impedance exist along the
cable when convey currents. Based on certain resource, the voltage drop from
the origin source must not be more than 4% of the supply.
Consequently, if we need to
deliver supply to long distance, voltage drop calculation must be considered.
This will help us to choose the appropriate cable’s size for our design, and to
avoid the voltage drop more than 4%.
For this topic, I have approached
formulas for the appropriate calculation on voltage drop. What I can conclude
from this study is shown below:
VOLTAGE DROP
- Cause by impedance exist in cable
- Can be ignored if the cable length is
short
Maximum
voltage drop tolerate is 4%:
(a) For three phase = 415 x 0.04 = 16.6V
(b) For single phase = 240 x 0.04 = 9.6V
Voltage
Drop = (M.D x D x mV/A/m)
1000
Where: M.D is Maximum Demand (Ampere)
D is Distance (meter)
mV/A/m is milivolts / A / meter which is cable impedance value obtain from
IEE cable voltage drop Table
Voltage drop from EMSB to ESSB-LP:
Maximum
Demand (MD) = 600A
Distance
(D) = 30m
mV/A/m Z = 0.175
mV/A/m
(for 4/1C 400mm2
XLPE/PVC cable. Refer to
Table4E1B)
Voltage
Drop = (MD x D x mV/A/m)
1000
= 600A x 30m x
0.175
1000
= 3.15V
% Voltage Drop = 3.15V x 100
415V
=
0.76%
Voltage drop from ESSB-LP to SUBMAIN
5:
Maximum
Demand (MD) = 200A
Distance
(D) = 75m
mV/A/m Z = 0.45
mV/A/m
(for 1 x 4C 95mm2 XLPE/ PVC cable. Refer to Table4E1B)
Voltage
Drop = (MD x D x mV/A/m)
1000
= 200A x 75m x
0.45
1000
= 6.75V
% Voltage Drop = 6.75V x 100
415V
=
1.626%
IEE Wiring Regulations (17th Edition)
