Power Factor

Try this:

http://www.lmphotonics.com/pwrfact.htm

What power factor correction does is try to ensure that the optimum power is transferred between the supply and the load. To do that, the out-of-phase current has to be minimised.

In a perfect capacitor, current leads voltage by 90 degrees and the opposite occurs in a perfect inductor (voltage leads current by 90 degrees) thus, a capacitor resists any instantaneous change in voltage and an inductor resists any instantaneous change in current.

From an electric supply standpoint, the optimum is a ideal resistive load (voltage and current in phase). However most loads are inductive with associated inductive reactance so power factor correction capacitors are applied in various ways to compensate for the inductance (among other things). If the capacitive reactance equals the inductive reactance the circuit will appear resistive with a resultant power factor of 1. In terms of supply, reactive loads represent unmetered power that must be supplied to maintain voltage stability but for which no revenue is received directly.

I would think a google search would result in large quantities of information on power factor (or dissipation factor in the case of small loss angles).

In DC systems, the capacitor can be used to stor energy. In AC systems, this is not true. Your suggestion about capacitors storing reactive power is not correct, but the net outcome is similar.

The reactive current drawn by motors is 90 degrees behind the resistive current. This is described as a lagging power factor. With a capacitor, the current leads the voltage by 90 degrees. This is called a leading power factor. If the lagging power factor and the leading [power factor are equal, then they cancel out. The net reactive current is the sum of the capacitve current and the inductive current where the inductive current and capacitive currents have opposite polarity.

Both capacitors and motors draw VARs from the supply, but they are reverse polarity so they cancel.

Best regards,
Mark Empson
http://www.LMPhotonics.com | http://www.LMPForum.com

Hi Marke

Both capacitors and motors draw VARs from the supply, but they are reverse polarity so they cancel.

Both capacitors and motors draw VARs (individually) from the supply, but (if they are connected in parallel to the supply, the VAR is reciprocating between them, only the initial amount of VAR "transiently" is drawn from the supply. As a result, if a VAR.hr meter is connected to the supply, it will read nothing as inductive and capacitive VARs are equal.

Good Luck... Samak

I believe there is nothing so misunderstood in the field of AC power as Power Factor.

Imagine:

You want to move a heavy box on a floor for a certain distance, a plate is found between you and that box, the plate is connected to the box through some spring, only the plate you can touch.

1. You'll pay a certain amount of force (F1) on the plate to compress the spring a certain distance (X1) while the box is stationary. (Money payed)
2. You'll pay additional amount of force (F2) to move that box a certain distance (X2). (Money payed)
3. You'll release you hands and they will go backward a distance of (X1) absorbing that amount of work (F1.X1) of which consumed previously to compress the spring. (Money back)

And Hence:

the total amount of work = (F1.X1 + F2.X2) (Money payed)

the active part of work = (F2.X2) (Money lost)

the reactive part of work = (F1.X1) (Money back)

The active and reactive power are that simple.

The power factor is the ratio of the useful work to the total payment of work.

Thanks to all friends.

As Mr.Jraef stated that power factor concepts are very difficult to understand in Ac power. Hence I have some confusion and need to study the best articles in the links.

helloo

yes u r right It tells us about the angle between true power and apparent power

for any load their ar tow power consumption , active power and reactive power

the reactive power is like heat in motors we use it and consume it in the motor but we do not pay for it , we pay only the active power so we design the power factor and it is capacitors only to generate the required reactive power for the motors and electrical instruments

so we do not take that reactive power from the main power supply ,if it is transformer or generator we take only the active power and the reactive power we generate it locally by the capacitors

so when PF=1 THEN U DO NOT CONSUME ANY REACTIVE POWER FROM THE main POWER SUPPLY u take it from your capacitor in th unit of PF correction

then u can save nergy from the power supply (transformer or generator)

that is all as far as i knew

Old power factor visualization trick:

Go to a pub and order a glass of beer.

kVA is represented by the liquid beer.

kVAR is represented by the foam that came with the beer

kW is represented by how full the glass is.

Power factor is the relationship to foam vs beer.

Both the beer and the foam always comes from the tap, but you insist on only paying for the glass of beer if it is full to the brim, not half full of foam. Because of that, the barkeep keeps pouring until the glass is full of beer, allowing the foam to go to waste down the drain. So the foam represents a loss to the barkeep, not to you.

If the barkeep tilts the glass to stop it from foaming, you still get the same amount of beer, but he wastes less in the delivery process so he can sell more to others.

Tilting the glass is like correcting power factor. In the bar, the barkeep does it for you because he is the beneficiary. In the case of power delivery, the barkeep is asking you to tilt it for him, otherwise he will charge you more for the full glass of beer. That is because you don't want the utility coming in to your plant and telling you how much power you can use and when.

Automatic power factor correction is like an automatic glass tilter. Sure it saves losses for the barkeep and prevents him from charging you more for the beer you drink, but it does not create "negative foam" that waits for beer and negates the foaminess, it just reduces the foam losses when the beer is delivered.

Cheers.

You have a mixed up idea about this.Let me ask u the basic principle 2 u?Ok I suppose u know it.It works on the theory of mutual induction.So it must have a slip.So the stator power can"t be equal to the rotor power.This create the transient state.If we disconnect the field and connect it with some capacitor bank the power will be store in it,and the motor will continue to run untill the total power is dissapited.It is a type of braking used in EE drives.

In the power house the PF is restricted to 0.8 leading, this is influenced by inductive loading, (motor windings and the like), capacitive loading comes mostly from the reactiveness of the transmission lines. This is monitored by system control, and voltage adjusted as required.

Regards JD.