Power Factor Correction

But why are PF and cos φ different? I thought they were different ways of saying the same thing. Is that wrong?

The meter uses cos as a phase shift between current and voltage waveforms only, PF takes in to account all usable power so harmonics play a key in determining that number.

With a very clean waveform PF would equal cos.

OK thanks

Normally there is no penalty for PF less than 0.95, you have a risk using capacitors correcting even up to 90%. If you over-excite the equipment, you risk damaging equipment, much more costly than your credit for correction.

Also, if you switch these capacitors on & off accounting for load, office building is typically cyclical load due to ambient and occupancy, the voltage spike you can generate during switching can damage equipment or trick it into shutting down.

There is an economic balance point somewhere between paying extra for reactive power and paying to invest in power factor correction.

Although there are many things that can be done, only the economics will dictate whether or not they should be done. The forum is not privy to the commercially-sensitive information that would determine the balance point, nor should it be.

What PF correction unit did you purchase? Was a harmonic study completed first?

You can have a good cos PHI between your current and voltage (they are close to being in phase) but if you have very high harmonics it can cause your overall PF to be lower.

cos PHI can also be used in the PF triangle to represent the difference between apparent and active power but I do not think the Fluke uses it in this context.

The Fluke 435 gives you harmonics as a percentage of the fundamental frequency, that would tell you if the waveform is extremely distorted.

Did you look at the phase balance as well? A major phase balance issue can cause very dirty power in your building. I have troubleshoot facilities with a 50% greater load across 2 phases which lead to early transformer failure.

I have looked for phase balance, there is no significant changes in PF, Low power factor mostly contributed by harmonics. I plan to install Harmonic filter.

The issue they were having was large phase imbalance caused delamination of the core in their transformer which led to large amount of harmonics on incoming power. Showed up as high THD on voltage waveform (12% if I remember right)

Thanks for sharing

Problem of power factor is only with AC appliances. Do DC appliances also have this problem ? I am sure they do not have. Except that transmission over long distances is possible with AC (now high voltage DC transmission was also found as effective).

AC has harmonics, frequency, which ion real terms is going from high to low every second, 50 or sixty times, and thus inefficient, and many other problems.

Why does not community shift to DC, as Edison propounded ?

Because whlie both have merits, on balance AC has advantages over DC. That's why it took over worldwide.

The concept of power factor in DC applications is a non-starter.

To be effective for long distance transmisdion, DC voltage must be very high but not safe in your home or business. If the DC voltage is low enough to be relatively safe, transmission distances would be very short compared to AC. If Edison had won out, there would have needed to be DC generating stations within 5 miles of users and at the time, all using DC generators for which Edison owned the rights to. Only the rich could have afforded electricity and he liked it that way because he intended to soak them. Tesla was much more egalitarian in that regard, he wanted electricity for everyone, even free electricity.

A transformer cannot pass DC and during that time period there were no efficient DC to DC converters so to step voltage up for transmission and back down for use in house was inefficient.

Also rotating motors used in most power generation make AC by default which can be easily rectified to DC but still requires more components.

Cost and efficiency of equipment is what made AC so popular.

With smart and more efficient DC to DC voltage converters it is becoming more popular. It also allows "storage" of a type on a central buss where power can be injected into multiple separate AC power systems in-phase quickly without having to phase all the separate systems.

This makes DC good for large scale shared transmission systems but still poor for final use transmission as the roll out of the system and upkeep of the more complicated equipment (transformer vs. DC to DC voltage converters) is prohibitive.

Lets not start killing elephants and dogs in public displays again to show how "deadly" AC is :)

Simply because AC systems have been active all these years, thanks to the 'Egalitarian Tesla' who seems to have a second innings by his namesake company, via, Elon Musk, please don't wish away DC. In fact, it is DC motors and DC storage, what he is harping on.

Almost every natural electric circuit s DC, we, animals have DC circuit inside, eels have DC, lightning, thunder are all made of DC. Computers run on DC and DC only.

OK. AC had some glaring advantages, when DC- DC converters did not make their appearance. Please do not malign Edison, and glorify Tesla.

Point is about efficiency of conversion of energy into motive force. Let the discussion be on that aspect and not on animals and individuals.