Hi,
I'm struggling with calculating the current from per unit voltage and power values. I can do it one way but get a different result when doing it another way. Here are the values I'm using:
This is for 3 phase.
VAbase = 1000kVA
VAload = 750kVA
Voltage base = 415V
Line voltage = 415V
Power factor = 0.96
I need to find the per unit load current. The way I've done it first to get the correct answer is:
Find the load current = I = (VAload)/((root3)*(Line voltage)) = (750kVA)/(root3)*415 = 1043.4
Find base current = (1000kVA)/(root3)*415 = 1391.2
Divide load current by base current = 0.75 p.u.
Calculate angle from power factor = 16.26 degrees.
So load current = (0.75<16.26) p.u. which is correct.
However, using the load VA and the line voltage with the equation S=(root3)VI, with a line voltage as the reference V=1<0 p.u.,
I = (S)/((root3)V)) = (0.75<16.26)/(root3)(1<0) = (0.433<16.26) p.u. which is wrong.
The only thing I can think of is that you're not meant to divide by (root3) in the above equation, but surely you have to because its 3 phase?
Thanks
I'm struggling with calculating the current from per unit voltage and power values. I can do it one way but get a different result when doing it another way. Here are the values I'm using:
This is for 3 phase.
VAbase = 1000kVA
VAload = 750kVA
Voltage base = 415V
Line voltage = 415V
Power factor = 0.96
I need to find the per unit load current. The way I've done it first to get the correct answer is:
Find the load current = I = (VAload)/((root3)*(Line voltage)) = (750kVA)/(root3)*415 = 1043.4
Find base current = (1000kVA)/(root3)*415 = 1391.2
Divide load current by base current = 0.75 p.u.
Calculate angle from power factor = 16.26 degrees.
So load current = (0.75<16.26) p.u. which is correct.
However, using the load VA and the line voltage with the equation S=(root3)VI, with a line voltage as the reference V=1<0 p.u.,
I = (S)/((root3)V)) = (0.75<16.26)/(root3)(1<0) = (0.433<16.26) p.u. which is wrong.
The only thing I can think of is that you're not meant to divide by (root3) in the above equation, but surely you have to because its 3 phase?
Thanks