Energy Saving Through PF Improvement

Tornado, you are basically correct, however, bear in mind that pf is used primarily for inductive loads. Any induction motor needs a small current, we call it eddy current(or wattless current), to setup the magnetic field. Only once this magnetic field is established, can the "working" current setup rotation. This wattless current still has to be paid for but it really does no work. The correct caps installed will take care of this current. Remember rule of thumb is that a cap will increase voltage by 1.4 times? Without boring everybody with calcs, this increased voltage is basically also useless but sufficient to induce the fields required for rotation. Running a number of large motors, 45 -200kw, will save you a lot of money if Pf is correctly applied.

I think the first post says it all. If you're interested the subject has been discussed on a previous thread.

http://cr4.globalspec.com/thread/18626

You can also read this good article on PF.

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

In theory, you should have a power factor of unity or 1.00.

This means that the load appears to the AC drive energy as a purely resistive load = PF 1.00

http://en.wikipedia.org/wiki/Power_factor

In larger motor sizes, it can pay to have a power factor corrector. As the article says, excess circulating current is charged on most large meters in industry, which read kilowatt hours used, peak load and power factor average. As you drop below 1, you are charged extra. Why? they need bigger wires and have larger losses due to the reactive current.

A small motor at home might not be corrected by this device sold in Taiwan. I think they are for suckers. The web is full of self serving adverts for these things. They are also sold at multi level marketing shows where people buy them for $25 to sell at $50 for $2 or less worth of parts.

You are right. PF improvement results in less penalization by electrical energy supplier. Low PF calls for unnecessary large conductor size; because the low PF consumer draws large amounts of currents but do not spend it and returns back forcing electrical energy provider to have huge dia cables, big distribution transformer, etc. Energy loss will be to the power provider as he has to unnecessarily keep big transformer and more no-load losses.

Power factor correction for domestic installation (single homes or small complex, not requiring maximum demand metering or at least less than 50 kVA installations), are irrelevant. You will gain almost nothing and definitely no reduction in cost from the power supplier. At best you might contribute to improve slightly (not very significant) the grid voltage up to your point of connection.The benefit will be for the power company!

The domestic power meter measures active power only (kW) and this will not change when pf correction is applied.

Maximum demand charges are on KVA for many power supply units. So PF improvements help reduce energy costs. Secondly there are many ac/dc drives with SCR's. They generate harmonics and can cause harm to electronic equipments. A PF correction device can reduce the effect of harmonics.

You are not concentrating on the question asked by NTNAIR.

He is interested whether a PF correction will improve and save him 30% on his DOMESTIC electricity bill.

The key word is DOMESTIC here. No kVA max demand is charged on a domestic consumer as far as I know. Therefore, correcting the pf from let us say 0.7 to near 1.0 will not reduce his kWh metering and his bill will remain the same.(at least nothing near a 30% reduction by a light year).

Concerning harmonics generated by electronic devices like converters etc..., sometimes a pf correction might increase their production especially if the correction is overdone! In any case this is only relevant when concerning an industrial like installation. For domestic installations, filters and suppressors of reasonable quality will protect their installation from harmonics and other interference...

When power factor isn't part of the domestic tariff calculations, there are negligible savings to justify the investment needed to correct it!

Respected sir,

Power= Voltage *CURRENT* (POWER FACTOR)

Power is constant.

VOLTAGE is constant.

If power factor is increased then current can be reduced

So current becomes optimum rather than expanded vallue.

This reduces the heating of cable.

This reduced heating contributes saving

of energy.

Guest,

Yes, the current is reduced when improving pf.

The Power consumed is, however, the same and the meter will bill the same kWh.... which is the subject matter of the initial question: does he get a 30% economy on consumed power?

The Power Supply company will benefit from an improved pf, but the tarif is normally worked out to take care for a pf of 0.80 and that is why they encourage consumers to keep within that pf.

You can decide to improve it for your premises but the economy to the user is not there for a domestic installation (this is the question for an answer...)

Thanks

.....and most of the time on a domestic supply, the incoming cable is operating nowhere near its maximum current capacity. Increases in power factor in the cable by some new-fangled widget therefore increase the voltage on the appliance terminals, which then consumes the power that has been saved in heating the cable, thereby obviating the savings that are desired by buying and installing the widget....

Surely a combination of thrift/meanness, timeswitches, occupancy detectors for lighting and high-lumens-per-watt lighting are the more obvious way to go in the domestic environment?

You are wright, I will advice you remain not convinced at least for now.

power factor correction for domestic and hotels environment are not adequately remunerating as not more than 5% and 10% savings respectively can be realized in each case.

The reason being that virtually all cooling systems used in houses and hotels except central chiller cooling, have a power factor correcting item. The ceiling fan used in houses also has a split phase capacitor in the fan circuit. The window and split units air conditions are all fractional horse power motors involving capacitors in the split phase circuit. Mercury, sodium vapour and indelux lamps are all equipped with capacitors that helps to improve the pf value of the respective device.

Better correction at 30% or 40% can only be achieved in factories where there are inductive loads. palm canel crushing, wire drawing, nail machines, mixers, extruders etc. requires 3-phase motors of various sizes and introducing a power factor improvement system here will be highly remunerating.

In all, it is recommended to check your phase angle to know if correction will be rewording or not.

DICKSON

Dear All ,

Remeber P.F. improvement only gives benfit at source and not at load .

1- For residential setups , P.F. is already good ( around .95) so there is nothing to be gained .

2- For industrial and commercial setups P.F. is poor ( around 0.8 ) due to a lot of induction motors , special illumination equipment etc. Rule is that

KVA released = KVA ( 1/P.F.1 - 1/P.F. 2 ) { Electrcial power distribution by Turan Gonen Chapter 8 )

so for a 50 KVA load a P.F. increase from 0.8 to 0.95 will result in 9.86 KVA saving at source . So if you are paying for KVA then you will gain abount 20% . Reason is that since KW remain same , KVAR requirements of circuit are fulfilled by capacitors .

It should also be remebered that getting too close to unity is very risky and such system tend to have voltage rises in low or no load conditions and this can damage equipment .

Nadeem Aziz