still on power factor correction

[ammarawadallah]

i need some one to comment on my obsecure understanding of power factor correcting capacitors:

1- voltage is impressed upon both inductor and capacitor since both connected to common point
2-current will flow across the capacitor line at 90 d a head of source voltage and supply current to the inductor
3-inductor opposes source voltage current by 90 d while allowing capacitor current\ reactance that is opposite to inductor reactance
4-capacitor reactance canels inductor reactance(originated due to inductor cemf), since both are opposite in direction ,therefore source load current flow without delay as seen by the source.
5- is the above true ? if not how?
6-if above is near true and currents cancels out in the inductor ,where from do we get magnetizing current necessary to drive the load since it should also cancels out to zero due to the 2 opposing reactants :weeping:.

 

[GoldDigger]

In the case of a motor, the current consists of an inductive component as well as a resistive component.
The power factor correction capacitor cancels the inductive component only, letting the resistive component flow unchanged.
The net result is less current flowing in the supply wiring, in theory all the way back to the POCO generating plant.

In the case of a transformer, the capacitor partially supplies the non-linear magnetizing current in the primary while any resistive component of load on the secondary will cause a resistive component of current in the primary.

 

[ammarawadallah]

In the case of a motor, the current consists of an inductive component as well as a resistive component.
The power factor correction capacitor cancels the inductive component only, letting the resistive component flow unchanged.
The net result is less current flowing in the supply wiring, in theory all the way back to the POCO generating plant.

In the case of a transformer, the capacitor partially supplies the non-linear magnetizing current in the primary while any resistive component of load on the secondary will cause a resistive component of current in the primary.

ok understood ,but in the text book they tel you capacitor supply magnatising cuurent and free the source line current from supplying it but still suply the resistive one only, we seem to agree on opposite reactances cancels out at the inductor and therfore,ends cuurent delay,but my question is who supply the magnatizing current ? ?

 

[GoldDigger]

ok understood ,but in the text book they tel you capacitor supply magnatising cuurent and free the source line current from supplying it but still suply the resistive one only, we seem to agree on opposite reactances cancels out at the inductor and therfore,ends cuurent delay,but my question is who supply the magnatizing current ? ?

The magnetizing current (steady state after inrush) circulates back and forth through the inductor and the capacitor as a parallel resonant circuit, leaving little net current on the supply line.
Because of the hysteresis of the magnetic material the magnetizing current curve is not sinusoidal, so the cancellation via a capacitor cannot be complete.
The initial (<2 cycles) of inrush magnetizing current on turn on ends up coming pretty much entirely from the supply line.

 

[ammarawadallah]

The magnetizing current (steady state after inrush) circulates back and forth through the inductor and the capacitor as a parallel resonant circuit, leaving little net current on the supply line.
Because of the hysteresis of the magnetic material the magnetizing current curve is not sinusoidal, so the cancellation via a capacitor cannot be complete.
The initial (<2 cycles) of inrush magnetizing current on turn on ends up coming pretty much entirely from the supply line.

sounds good,but why they tell people in the engineering litreture that the capacitor is supplying leading current to the inductor to establish it's magnatic field and relief the source ,also there is little to non mentioning of cemf and cancelling reactances ,and that kind off unsolve the ambiguty associated with this topic to many people at least to me? am i right golddigger??

 

[GoldDigger]

sounds good,but why they tell people in the engineering litreture that the capacitor is supplying leading current to the inductor to establish it's magnatic field and relief the source ,also there is little to non mentioning of cemf and cancelling reactances ,and that kind off unsolve the ambiguty associated with this topic to many people at least to me? am i right golddigger??

Well first of all counter EMF is seen in motors where the rotation establishes a voltage which opposes the applied voltage. That means that the driving voltage across the motor is different from the voltage across the capacitor. This makes it impossible for s fixed value capacitor to compensate over both the starting and running regime, but it does not negate the basic principle.
IMO it does mean that you cannot calculate the correct value of the capacitor based on the stationary inductance of the motor.
Which brings us to your second point. .

 

[Besoeker]

A picture that might help.
The blue is the load current. I've used per unit values for the graph. Any multiplier can be applied.

The PFC does two things. It significantly reduces supply current and improves supply power factor.
The currents, being out of phase means there is cancellation.
I've deliberately chosen a poor power factor load, 0.5 in this case, to illustrate what happens. But it's not unrealistic for a lightly loaded motor.

For existing installations that reduces supply losses and potential penalties for low power factor.
For new installations, smaller conductors can be used.
Reduced costs...........