Real / Reactive Current

[7Eggyjla4]

I'm trying to understand Active/Reactive/Apparent ampacities. A 415V3Ph 15kW load with 0.8pf, the Active Current : 15,000/(415*1.732*0.8) = 26A. How would I calculate the Reactive Current? Would the Reactive Current be calculated : 15,000/(415*1.732*sqrt(1-pf^2)) = 35A. The resultant current? : sqrt(26^2 + 35^2) = 43

 

[magoo2]

Your reactive current calc is wrong.

Before going to ampacities, start with kVA, kW and kvar.

kW = 15 given
pf = 0.8

kVA = kW/pf = 15/0.8 = 18.75

kvar = sqrt (kVA^2 - kW^2) = 11.25

Now you can get the ampacities based on 415 V.

 

[PeterVenkman]

S = apparent power
P = real power
Q = reactive power

P = pf*S
Q = (S^2 - P^2)^.5

Convert reactive power to amps

 

[LionelHutz]

You already had active power so you don't use power factor to calculate active current.

Active Current = W/V/sqrt(3) = 15,000/415/sqrt(3) = 21A

Total Current = VA/V/sqrt(3) = 15,000/0.8/415/sqrt(3) = 26A

Reactive current = VAR/V/sqrt(3) = sqrt((15000/.8)^2 - 15000^2)/415/sqrt(3) = sqrt(26^2-21^2) = 16A