power factor

Power factor - Wikipedia, the free encyclopedia

hello,

capacitor provides a leading current which reduces the angle between voltage phasor and current phasor and hence by reducing angle value of cos angle is also increasing and power factor is going to increase.

by increasing the power factor less part of power is converted into the reactive and more is converted into useful power so wastage is less so capacitor is providing any energy or so.

you can also go to the link given by the above CR4 user.

by increasing the power factor less part of power is converted into the reactive and more is converted into useful power.

Controversial statement. _{I disagree}

why you disagree?

power factor is the cosine of angle between voltage phasor and current phasor

and when you increasing the value of power factor the value of cosine of angle is going to increase and value of sine of angle is going to decrease ok.

now useful power = v x i x cos(angle)

reactive power = v x i x sin(angle)

so, as you can see from the expression when the value of cos(angle) is increases and value of useful is going to increase and at the same time value of reactive power is going to decrease

i hope now you dont need any more explanation???????

There is a good article in Wikipedia on this topic.

How many more times are you going to resurrect this subject?

Get an engineer in that knows that he's doing!

What does it "convert" energy from? Where is the energy input in that equation?

The Guru's have got it right - do your home work or get an engineer who understands the subject.

The first thing you need to understand is that reactive power is what causes the power factor to deviate from one - and reactive power is "imaginary". It is not real power and it is only a temporary storage situation - the two forms are capacitive (which gives leading currents) and reactive (which results in lagging currents)...and there are lots of both of these in a typical induction motor.

The main reason for being concerned about poor power factor is that it increases line current and hence line losses because a greater current that has to be transported for a given job when the power factor is lower. - though there are other situations, a long lightly loaded line for example, where the higher delivery voltage that arises from this is undesirable.

I cannot imagine why anyone who understood the maths of the situation would be fussed about correcting a power factor of 0.99 as one recent post was concerned about.

Trev "..the two forms are capacitive (which gives leading currents) and reactive (which results in lagging currents)...and there are lots of both of these in a typical induction motor."

I teach my students that inductive circuits give lagging current. We use the mnemonic CIVIL. So in parallel systems Voltage is reference, IC phasor leads and IL phasor lags. Inductive currents tend to derive from motor windings, whereas Capacitors provide compensation, returning to a more resisitive load. I'm very interested to understand the lag in flourescent tube circuits = plasma.

Must admit to being more electronic experienced, so I'm fine with what is real world terminology!

When you install a capacitor into a "lagging power factor circuit", you do not change anything at the supply.

What is changed is at the load side (which also implies you should install power factor correction devices nearer to the load side). The original reactive power (X) consumed by the load is supplemented by the capacitor's ability to produce reactive power (Y), thereby reducing the total reactive power required of the supply by (X-Y).

Now, having less reactive power to supply into the load, the total apparent power is less than the original's. This implies that less total current is supplied by the supply reducing the losses and also capacity of the supply is increased and you can add more load to it.

Red Triangle (has worse power factor) and consumes more reactive power than Blue Triangle (has better power factor). Therefore, Blue Triangle need less apparent power which means less current flow in the Blue Triangle circuit, reaping the benefits mentioned above.

Cheers,

Versalite

Power factor is INDIRECTLY related to system efficiency. If pf is low then it means that ACTIVE power ( read usable power ) delivered to load is low & vice versa.

Ashok Toshniwal

You are confusing the issue more...

the PO Thinks that the P.F. is related to the efficiency of the motor where he has added the capacitor to improve the P.F. (!?).

All that is happening is an improvement of power transmission in the power line to the motor, by reducing the reactive current flow in the line, therefore reducing heat loss in the line. The Electric motor will still consume the same Active power as before, i.e. the Watts are the same.

My limited understanding is that our power utility companies measure electricity consumption by metering the current. So it pays to reduce the (lagging, reactive) current as much as possible.

For those living on generated supplies, eg our boys in Afghanistan, the power factor needs to be monitored to avoid overloading generators.

"My limited understanding is that our power utility companies measure electricity consumption by metering the current. So it pays to reduce the (lagging, reactive) current as much as possible."

Nope. That's just plain wrong. Utilities measure consumption of ENERGY, as measured in kWh, which can be broken down into Watts for Hours. Current is only a component of Watts. But the difficult thing for most people to understand is that reducing measurable current does not necessarily reduce the kWh.

People. The ONLY thing that PF correction capacitors do is allow a delivery system to get more equipment capacity from the same amount of current flow, by storing and releasing REACTIVE power into INDUCTIVE loads. That's it. No "conversion", no reasonable "energy reduction" etc. etc.

When you reduce the current in a set of conductors, you are thereby reducing the I²R losses in the conductors, the heating of the conductors, by an infinitesimal amount. If your conductors are properly sized, as they should be, then the amount of savings is so small as to be barely measurable. If you own the utility supply transformer, and it is rated for XX kVA of delivery, and the PF is poor, then you are energizing that transformer while not being able to collect revenue on the load side via kWh charges, because the kWh charges are not reflective of the poor PF. So the main beneficiaries of PF improvement are the delivering utilities, because they are absorbing the overall larger scale costs of having a set of components that must be sized for the apparent power but can only charge for the real power.

If, by virtue of the utility's cost of operation, they assess penalties on those of their users contributing too much to the overall power factor issues for them, then you can often AVOID those penalties by improving your own PF. But if they are NOT assessing penalties to YOU, then there is almost no justification for installing PF correction capacitors. Such is the case with the vast VAST majority of residential users because the PF costs are built-in to the kWh rate we pay to the utility.

As this is an international forum, I understand that this issue is not necessarily universal and some smaller utility suppliers do in fact assess penalties for poor power factor on small users. In those rare cases MAYBE there is justification for it. But for the rest of us, anything that does not SPECIFICALLY and SIGNIFICANTLY reduce the kWh use will have NO APPRECIABLE EFFECT on reducing the cost of energy. Power Factor Correction Capacitors fall into that category. Plain and simple.

Your response is factually correct but does not really recognise the principal issue in Cigarshaped's post. The real question is about whether power is measured correctly by the meter - clearly, if only current were measured this would not be the case.

What Cigarshaped needs to know, is that the typical old fashioned electro mechanical power meter has two coils - one for current and one for voltage.....and without going into any more detail, pretty obviously so these are multiplied together via eddy currents in the Aluminium disc so that, as required, watt hrs and not amp hrs is being measured.

ACTIVE power ( read usable power ) delivered to load is low & vice versa.

No in general.

Usually the load demands power - both active and passive (or reactive) depending on its drive configuration (electrical portion)

Teh active power is any way treated as a fairly constant and the reactive power is add on.

Even if you change the drive/ compensation, the active power will remain same (and will not reduce as your post implied) the ractive portion will change.

The only (and in majority of the case) effect the extra or lesser reactive power will have is in line losses (and in a few specific extremes to bring down the voltage at load drive terminal to unacceptable value)

But Note the active/reactive power ratio will not change the active power by itself (except the effects as mentioned above and it's effect on efficiency wont be even in percentages usually)

The main affected is the generator which has to supply the extra active power (through field compensation) and also the extra effort in maintaining the voltages in network and that's why the penalty for poor pf.

Agreed, Thanks and regards

Ashok Toshniwal

Power Factor can not be used as a measured of systems efficiency, rather a better way of conserving and improving systems efficiency in terms of cost and adequate ratings, size of plant, cables,switch gears etc. The capacitors are usually connected in delta and in parallel with the supply. The discharge power of the capacitor in Kvar at zero points crossing of the alternating cycle, enables it to adequately compensate for energies in inductive loads and there by improving the phase angle towards unity and at same time reducing the Kva. Since ur aware that the capacitor stores energy, the energy stored is a leading one that acts vectorially to reduce the Kva by as much energy discharged from the capacitor. A vectorial summation of the Kva and the Kvar will reduce the Kva and relocate the PF angle towards unity. Take care.