At low lagging power factor current increases but what happens to impedance it increases or decreases
1 Consider an ideal resistive circuit if it is supplied by AC voltage its power factor remain unity but when the same resistive load is added with some inductance so the power factor drops and as the inductance increases the more power actor drops so it means as impudence complex part is increasing the power factor is dropping.
But on the other hand we know current and impedance ae inversely proportional so am i wrong in these two interpretations or there is some explanation regarding these two opposite behaviors.
Low power factor would increased reactance, and hence would raised the impedance of circuit(Z=Sqrt(R)(R) +(X)(X), X= 2(pai)fL, L= do/di , variation of flux with variation of current). For the same load(W) the current would increased, would reduced the efficiency of system due to increased loss, with lowered power factor...
syed taha Ahmed
V=I*R (for dc) or V= I*Z (for ac). Z=R+j(XL-XC) , XL= Inductance, XC= Capacitance.
If inductance is increased, Z will increase too which means current will decrease if the voltage is remained fixed.
In case of AC current, "I" is not only 5A or 10A, it consists of an angle. The equation of power factor is, pf= cos ( θv - θi), where θv = Voltage angle , θi = Current angle.
So, when an additional inductance is added, the impedance will increase, the angle of current will change, the difference between voltage angle and current angle will be greater hence power factor will be decreased.
If the circuit had only resistance then in that case the difference between voltage and current angle would have been zero hence unity pf.
Dear Bhupendra and Mir Muntasir , Thanks for your answers and your valuable time.
So i would say that for complex loads current would increase with increase in impedance( R constant and increase in reactive load) hence low power factor .
But when we consider the transformer inrush current we say that at the instant when transformer is energizing the impedance is very low due to the fact that there is no load in secondary and that is acting like a short circuit so inrush current of transformer is high because impedance is low.
Summary would be like this
Transformer inrush or motor inrush current is high because of low impedance but on the other side current is increasing at low power factor provided the active load is constant because of increase in reactance .
syed taha Ahmed Current is not increasing. If impedance is increased, Current will be decreased and also, its angle will be changed.
Ok I think I got your concern. At low pf, due to voltage regulation the input voltage of a load is decreased. Hence to maintain the power requirement, the load draws more current.
- Badges
- Science topic
- Similar topics
- Entomology
- Resistance