APPARENT CURRENT COMPONENTS 2

[ZOBLITZ]

Hi Everybody!

I took some measures from a 1250_kW@480_V generator:

P:941_kW
PF: 0.87

I know that the apparent power has two components (active and reactive power) is why I am assuming that the current measured with a clamp, TC, etc. is the apparent current so if I multiply the apparent current for power factor I can get the current active component and using the triangular relationship IQ = √ ((Is ^ 2) -ip ^ 2) we can find the reactive current.

I'm pretty sure I'm doing something wrong here because:

S=P/PF=1081.6_kVA
Q=√((1081.6_kVA)^2-(941_kW)^2)=533.27_kVAR
Is=1081_kVA/(√3*480_V)=1300.9_A
IP=1300.9_A*0.87=1131.78_A
IQ=IQ=√(1300.9^2 )-(1131.78^2)=641.41_A

(IP:1131.78_A)+(IQ:641.41_A)=1773.19_A are components of IS=1330.9_A?

I appreciate any help in this regard, Greetings.

 

[bwen08]

To be short: Ip + Iq does not equal your measured current Is. Ip is a real value, Iq is an imaginary one. That is violating your first equation: Iq = √( (Is^2) - (Ip^2) )

The correct form would be Is = Ip + j*Iq, Iq will be positive or negative depending on the power factor.

 

[wroggent]

Correct:
Is=(Ip^2+Iq^2)^0.5

Incorrect:
Is=Ip+Iq

 

[ZOBLITZ]

Thanks guys,

Following the comments of brian134 what I get is = (1131.78 + j641.41) when I transform it to polar, what I get is 1300.9 = 29.54 °, and COS (29.54 °) = 0, 87 which coincides perfectly with the vectorial composition of the active current, reactive and apparent, no problem with that.

I still wonder a few things about the subject, but I guess I have to compare the measured parameters with those resulting from mathematics because yesterday a new power factor correction panel was commissioned, the PF was directed at 1 and the current from the bank was 638_A value very close to the 641.41_A resulting from the calculation.

Thank to brian134 and wroggent for your kind help.