The title says it all.

I realize why it's important to the power company, but when we design circuits, are there any advantages to trying to keep the PF at unity? Do high frequency circuits make it any more or less important?

 

P.F. correction as far as incoming power is concerned is usually a concern for larger industrial users, where the cost factor can be considerable.
For the average residential user, it is most likely not practical to try and correct any small difference that may occur at the supply level.
Max.

 

Thanks. That's what I thought. I was reading a pdf file put out by one of the chip manufacturers on SCRs and Triacs. In it they were speaking specifically to how one goes about designing a circuit for a light dimmer to keep the PF high. It's actually a benefit to the consumer, as I understand it, to have a low PF. The way they described it, it was an essential design element. I guess they're just being responsible corporate allies.

 

The title says it all.

I realize why it's important to the power company, but when we design circuits, are there any advantages to trying to keep the PF at unity? Do high frequency circuits make it any more or less important?

Not a fvreq issue. Unity power factor significantly reduces the AC RMS current drawn from the mains for a given amount of load power.

 

Many countries now have requirement for the minimum power factor of home appliances and electronics that are sold. That's the reason for the dedicated chips to help power factor, it's a created market.

Sorry to disappoint but few companies are so responsible that they design chips from the goodness of their heart. The only do it if there's a profit to be made.

 

P.F. correction as far as incoming power is concerned is usually a concern for larger industrial users, where the cost factor can be considerable.
For the average residential user, it is most likely not practical to try and correct any small difference that may occur at the supply level.
Max.

Power companies "correct" commercial users PF by putting large capacitors on the power poles. Most homes look inductive.

 

Sorry to disappoint but few companies are so responsible that they design chips from the goodness of their heart. The only do it if there's a profit to be made.

That's because they learned from experience that consumers won't pay a nickel more for a product that is "green" or "environmentally friendly" if there is a cheaper one.

 

Power companies "correct" commercial users PF by putting large capacitors on the power poles. Most homes look inductive.

There must be nice power companies where you work. My company just had to do your own.

 

That's because they learned from experience that consumers won't pay a nickel more for a product that is "green" or "environmentally friendly" if there is a cheaper one.

There are alway A few people willing to buy a hybrid so they look environmentally friendly (because neighbors and customers can see their cars). Very few will pay extra for renewable sourced electricity.

 

Power companies "correct" commercial users PF by putting large capacitors on the power poles. Most homes look inductive.

I just attended a seminar put on by the Provincial service supplier in order to educate local industries to encourage them to have an evaluation done of the plant, and show the potential saving, often the ROI of PF equipment is recouped in the 1st year. But it is the companies responsibility to have the evaluation.
A large culprit now is the prevalence of VFD's and other high frequency switching power devices.
I was asked to attend by one of my customers in order to establish a plan.
Max.

 

There must be nice power companies where you work. My company just had to do your own.

They aren't nice, it saves them money. Keeping the PF closer to unity makes their transformers RMS current go down, and keeps the power delivcered a lot more Watts and less VARs. Most commercial users get billed for the Watts only, so the power company gets more money by correcting the PF. I have heard of cases where they installed a VAR meter when the user was running way off, but not typically.

 

They aren't nice, it saves them money. .

The saving is by the customer, not the service company.
Max.

 

A large culprit now is the prevalence of VFD's and other high frequency switching power devices.

As far as power switchers: the ones we built to run off AC mains single phase typically had PF's about 0.58 ballpark, the ones with three phase AC input got up to close to 0.85 so that was a big advantage for users who had three phase AC available. Any power supply above about 2kW had to use 3 ph because the input current would have been too high otherwise.

 

The saving is by the customer, not the service company.
Max.

No actually, the power company saves too. As the power factor goes off unity, the RMS current you have to draw from the transformers increases substantially to support a given amount of load Watts. That RMS current is what heats the transformers and causes power losses and limits the power that can be delivered.

You are correct the power company usually gives a customer a break on the bill if he will implement better power factor: and they do it because it saves them money. The power company would prefer unity PF, most residential homes are in the 0.85 - 0.9 ballpark. But commercial can drop a lot lower because they have so much inductive hardware running, so power companies incentivize them correcting the PF because it saves them money.

 

Of course the power company saves also, but the incentive for companies to employ PF correction has to be seen in real $$ and it is not because of a 'break' by the power company it is because of Real metered savings in the cost of power.
Max.

 

Not a peep (from the power company) about PFC here in Florida.
Once upon a time, I tried correcting a 1/4 HP refrigerator compressor. It needed about 80uf. Then I wondered how long it would be until the relay contacts welded shut, so I removed the capacitors.

 

LED lights and switchers. Imagine the usage.

 

Of course the power company saves also, but the incentive for companies to employ PF correction has to be seen in real $$ and it is not because of a 'break' by the power company it is because of Real metered savings in the cost of power.
Max.

The "incentive" for the the customer company to save $$ is very simple: the power company is going to charge a lot more when their PF drops too low because it causes power losses at the source end and they are going to charge for that. The power savings at the customer end isn't really that much, the cost savings is from avoiding being socked with the low PF surcharges by the power company and getting a VAR meter installed:

Q: How significant is power factor correction in industrial settings?
A: Power factor is low in industrial settings where most of the plant energy is used to power electric motors. It is lowest when the induction motors tend to be oversized and under-loaded. A lagging (less than 1.0) power factor causes some additional energy loss because more current is required – compared to an in-phase sinusoidal current – to deliver a certain amount of power. Correcting power factor can be an appropriate and cost-effective measure, but not because of energy savings.




Q: How much energy can be saved by installing correction capacitors?
A: Power factor correction does not save much energy – usually less than 1 percent of load requirements – but even that benefit depends upon how low the power factor is to begin with and how heavily loaded are in-plant distribution system conductors. Note that power supplied to your motor driven-equipment is proportional to Volts × Amps. Energy losses in your in-plant distribution system coincide with your voltage drop. If your transformer supplies power at 480 volts and the voltage at your motor terminals is 470 volts, you have a voltage drop of 10 volts, or approximately 2 percent of 480 volts. The total power loss in the in-plant distribution system upstream of connected load equipment seldom exceeds 2 percent of the load requirement.


Q: Under what circumstances are capacitor corrections warranted?
A: Despite the slight energy savings, correcting power factor can bring significant savings in energy bills when the utility imposes a low power factor penalty in their rate structure, as most utilities do for industrial customers. The simplest penalty is imposed through basing demand charges on kilovolt-amperes (kVA) instead of measured kilowatts (kW). Another penalty approach is to calculate a billable monthly demand charge that is equal to the measured demand times the ratio of the desired power factor (often 95 percent) divided by the measured power factor. How much you can save through installing capacitors depends upon your initial power factor, the level you correct to, motor horsepower rating and loading, and how the penalty charge is calculated by the utility.
Keep in mind that power factor correction reduces currents in conductors and transformers ahead of where the capacitors are installed. Simply correcting power factor does not change the current or operating condition of motors or other loads. Depending upon their location, installing capacitors can free up system capacity, and reduce voltage drop somewhat, but significant energy savings do not occur. The utility benefits because the current reductions decrease electrical energy losses in their transformers and transmission and distribution lines.

http://www.reliableplant.com/Read/13339/power-factor-correction

 

ronv... that photo's a fake!!

It's never night over the entire EARTH at the same time! Plus, you'd have to have an awful long arm for a selfie THAT big!

 

At least it proves the earth is flat.