Question

Find the current rating for the following system.

An outdoor pole-mounted 11 kV / 415 V substation has to be installed for supply to an area having a load of 63 kVA.

1. 50 A
2. 88 A
3. 72 A
4. 65 A

Answer 1

Correct Answer - Option 2 : 88 A

Concept:

Power in 3-phase transformer (P) = √3 V_LI_L

V_L = Line voltage

I_L = Line current

Calaculation:

​Given

Power (P) = 63 kVA

Line voltage (V_L) = 415 V

Line current (I_L) = P / √3 V_L = 63000 / √3 × 415 = 87.65 A

Current rating = 88 A