From the available inputs;
let us see how to determine the 'smallest allowable cross sectional area' of the circuit conductors.
Available inputs;
|
Load Current
|
200 A
|
|
THDi
|
48 %
|
|
Conductor Insulation*
|
XLPE
|
|
Conductor Type
|
Multi-Core Cable
|
|
Conductor Material*
|
Copper
|
|
Installation
|
Directly in Ground
|
|
Soil Resistivity*
|
2 Km/w
|
|
Soil Temperature*
|
40*C
|
*Some of the inputs are assumed to provide in this example; and they were neither received from the user, nor from the environment.
Procedure:
- Determinant conductor : Neutral
As the THDi is > 33 % (that is THDI = 48 %). So, the Size-determining" live conductor is Neutral
- Neutral Current : 3 × 0.48 × 200 = 288 A
- Correction factor K3 : The factor based on the overload protection device.
This circuit is assumed to be protected by the circuit-breaker.
So that the K3 =1.0
- F1 Temperature : Table B.52.15
For 40°C and with the insulation XLPE. F1 = 0.85
- Installation method : 72 (Sheathed single-core or multi-core cables direct in the ground - without added mechanical protection) Reference method : D2
There is no additional touching circuits i.e. total no. of circuits is 1
F2group = 1.00
- Correction factor F3 : Table (E.52.1)
THDI >45 % = THDI = 48 % à f3NeutralTHDI = 1.00
Installation method = in Ground -> Rth = 2.0 K.m/w
f3RthSoil = 1.12
Correction factor f
f = 0.85 × 1.00 × 1.00 × 1.05 × 1.00 = 0.952
The overall correction factor is determined by multiplying all 'the available correction factors."
Theoretical Iz’ = (K3 x IB) / (F x N live) = (1.0 x 288) / (0.952 x1) = 302.52 A = 303 A
The conductor selection is done from the given Table B.52.5 Column 8
185 mm2 will be able to carry 324 Amps
240 mm2 will be able to carry 375 Amps
Considering the +5% of tolerance, It would be recommended to consider the size as 185 mm²
|
K3(Correction Factor based on Protection Device)
|
1
|
|
F1(Correction Factor based on Temperature)
|
0.85
|
|
F2(Correction Factor based on Group of conductors)
|
1
|
|
F3(Correction Factor based on THDi)
|
1
|
|
F3(Correction Factor based on Soil Resistivity)
|
1.05
|
|
K user(Correction Factor defined by the user)
|
1
|
| |
|
|
Iz’(A) Theoretical
|
303 A
|
|
Iz (A) considered from the table
|
324 A
|
|
Theoretical cross sectional area Ph (mm²)
|
1 x 185 mm²
|
|
Theoretical cross sectional area Neutral (mm²)
|
1 x 185 mm²
|
|
Theoretical cross sectional area PE (mm²)
|
1 x 95 mm²
|
