Power Factor and how it diminishes LED lighting efficiency.

[Sorcerer]

I was reading through the wiki on LED lighting because my workplace is replacing many light bulbs in the warehouse and I was interested in how they could maximise capital while also reducing waste.

 

Reading through the comparison charts, I came across this quote below it :

 

 

Incandescent and Halogen have a natural Power factor of 1, but Compact fluorescent and LED lamps are using input rectifier and this causes high harmonics content in input current and also reactive power consumption. This causes extra loss (harmonics) and power transfer cost (copper usage) toward the power plant and energy cost will be distributed to all customers by rising energy bills. Future developments may implement PFC-circuits to bring the PF up to 1, but higher material cost and volume of electronics will result. Dimmable LED-Lamps typical have higher PF by using so called Valley-fill circuits, non-dimmable uses cheaperbridge rectifiers. The EU-Standard requires a PF better than 0.5 for power up to 25 Watt.^[32]

 

I tried to wrap my head around the word explanation for the mathematics describing what PF is, but failed. However keeping in mind that my lack of understanding of the topic is a recognised bias, the prior paragraph appears to me to be false information. How does Cu usage increase, when the infrastructure is already in place? If not then the alternative is they mean Cu is depleted overtime from this effect, how can this be? I've been LED (pun intended) to believe Cu is unaffected (a catalyst?) by the flow of electric current, what mechanism would remove Cu, is it electroplated onto the lighting terminals?

 

Although I recongnise "harmonics" as a genuine concept, it is also a red flag for bullshit in most pseudoscience. Can someone explain, "high harmonics". Are they singing a barber shop quartet on drugs? What is the quantifier used to give a value to lesser or greater harmonics?

Edited April 13, 2016 by Sorcerer

[studiot]

So often Wiki get too esoteric about a subject and does not offer a simple introduction/explanantion.

 

So here is my rough guide to power factor.

 

I would suggest that looking at power factor correction would suit you better.

 

https://www.google.co.uk/search?hl=en-GB&source=hp&biw=&bih=&q=power+factor+correction&gbv=2&oq=power+factor&gs_l=heirloom-hp.1.1.0i131l2j0l8.1141.3516.0.10344.12.8.0.4.4.0.125.969.0j8.8.0....0...1ac.1.34.heirloom-hp..0.12.1127.fuIIDDE7fDM

 

Things to note.

 

In DC electricity power equals the voltage x the current in all cases.

In AC electricity there may be a mismatch of timing between the current and voltage which means that the power you can extract from the supply is less than the product of voltage and current.

Thus in order to obtain a specific power, eg 1 kilowatt, you have to live with a higher value of voltage x current.

Since the mains voltage is fixed this means a higher current.

 

Thus the cabling has to be sized for this larger current.

 

The greater the mismatch the greater the cable size.

This is the reason for the extra copper.

 

Power factor is a measure of this mismatch. The ideal value is 1.

 

Power factor depends on the device connected, not on the supply.

 

There are two types of power factor, positive and negative.

This arises because there are two additional types of device in AC electricity over DC.

These are called capacitive and inductive devices and create power factors of opposite sign.

 

The main capacitive types are flourescent and more modern lights. the main inductive types are electric motors.

 

Industrially their two power factors can be used to cancel each other out, makeing the overall power factor closer to 1.

This is known as power factor improvement and many suppliers charge a premium the further your power factor is from 1.

 

I would say the two greatest faults with LED lighting installations ar.

 

1) They still generate much heat and insufficient provosion for dissipating this has lead to fires.

 

2) They have a very different light distrbution pattern, particularly compared to flourescent. They are a very concentrated, intense source.

as such they are unsuitable for recessed fittings, often favoured for flourescents. Many LED installations retro-fitted to recessed ceilings have proved a great disappointment as much of the light never leaves the recess and the lighting appears dim.

Edited April 13, 2016 by studiot

[Danijel Gorupec]

A funny post, Sorcerer

 

While I didn't check details from the paragraph you quote, to me it seems more or less right at first reading.

 

Harmonics: While we consider AC currents/voltages to be pure sine waves, this is practically never true. There is always some sort of distortion from the pure-sine form. A very important form of distortions are so called 'harmonics' - we call it that way because these are periodical distortions whose frequency is an integer multiple of the base frequency of the AC current. For example, a 60Hz AC current might have harmonics of 120Hz, 180Hz, 240Hz etc... Harmonics are unwanted and are often created as a result of non-linear loads, transmission systems and generation systems.... If you know something about Fourier analysis, you should be able to understand what harmonics are.

 

Power factor: The instantaneous power consumed by some load, is always equal to instantaneous current multiplied by instantaneous voltage. However in AC systems we rarely talk about instantaneous power (because it changes at 60Hz rate) but we are talking about average power (within one period). As a result we will calulcate the power cunsumed by a load as "average" current multiplied by "average" voltage multiplied by the power factor (I put the word average into quotation marks because it is actually RMS, root-mean-square, average)... Many times the power factor is not equal to one but is smaller - this means that power was delivered to the load during one part of one period, but is then taken back during the other part of that period. In an extreme case of power factor equal to zero you have a system that transfers lots of energy through wires, but no net power is actually delivered. The energy only goes back and forth.

 

Cu depletion: Now this is a word game - copper is not actually depleted. It just means that because existing wires only have so much current capacity, all this energy that goes back and forth (because the power factor is less than one) is just spending this capacity (and if we don't take care about power factor we are not using our expensive wires very efficiently).

[studiot]

 

Harmonics: While we consider AC currents/voltages to be pure sine waves, this is practically never true. There is always some sort of distortion from the pure-sine form. A very important form of distortions are so called 'harmonics' - we call it that way because these are periodical distortions whose frequency is an integer multiple of the base frequency of the AC current. For example, a 60Hz AC current might have harmonics of 120Hz, 180Hz, 240Hz etc... Harmonics are unwanted and are often created as a result of non-linear loads, transmission systems and generation systems.... If you know something about Fourier analysis, you should be able to understand what harmonics are.

 

I know it is difficult to use popular language and be precise at the same time,

It is all too easy to say or imply something untrue,so you have to be very careful to avoid this.

 

All harmonics are sinusoidal waves.

Power factor is just as important with a single frequency pure sine wave as with a distorted one.

It is not the distortion that lowers the power factor, it is the reactive components in the load.

With a purely resistive load the power factor would remain at 1, whatever the waveshape.

Edited April 13, 2016 by studiot

[Danijel Gorupec]

Absolutely.

 

Another example if imprecise wording in my post that I see now is when I say that instantaneous power in an AC system "changes at 60 Hz rate". The more precise wording would be 'continuously changes within one period'.

[studiot]

We discussed light sources in general and LEDs in particular a few years back, and I reported results of my trials of some LED lights.

 

Here is more gneral information

 

http://www.scienceforums.net/topic/67711-led-and-other-light-sources/

 

Here is a long thread pages3 and 4 are the most relevant.

 

http://www.scienceforums.net/topic/67073-cfls-not-a-bright-idea/page-3

[EdEarl]

The last line of the Comparison Table in the Wiki article shows total savings, which may be affected by rate changes due to power factor. However, such changes are unlikely to overwhelm your savings. Moreover, your warehouse can have an engineering firm balance its power factor by adding inductance or capacitance to you system.

[Sorcerer]

Thanks everyone.

 

So it is untrue that LED lighting causes more copper to be used, because that copper is already in place?

 

How does a PF less than 1 cause power to be wasted, if it remains in the line where does it go then? Is it lost as heat or does it leak through a larger EMF around the lines? Why does the PF need to be balanced locally, isn't the total networks average key. Aren't there industries with opposite requirements?

 

I've never heard of power suppliers charging a premium based on PF here in New Zealand, I'll have to look into it. As for balancing my workplace's PF, there isn't many other demands. Off the top of my head we have computers, A/C, roller doors, lighting and a waterblaster which are used daily.

 

Perhaps if we changed our fleet from diesel to EVs. But it seems years away.... hurry up humanity.

 

Thinking about it, there is a key card system with magnetic locks on 2 doors too, that runs 24/7. Is that a point of balance?

[studiot]

 

So it is untrue that LED lighting causes more copper to be used, because that copper is already in place?

 

 

 

Quite likely, since at least one purpose of using LED lighting is to use less electricity.

 

 

How does a PF less than 1 cause power to be wasted, if it remains in the line where does it go then? Is it lost as heat or does it leak through a larger EMF around the lines?

 

Power that is not drawn from the mains does not go anywhere, any more than power that is not drawn from an unused socket (wall outlet) goes anywhere.

 

Engineering is quite contrary to politics where they pay farmers to not grow turnips under a scheme called setaside.

 

Be glad of this because think how much your electricity company could charge if it could charge for power not drawn.

 

 

Why does the PF need to be balanced locally, isn't the total networks average key. Aren't there industries with opposite requirements?

 

 

 

That is done to some extent where the capacitive power factor of street lights is offset against the inductive pf of consumers.

 

However if your installation has a power factor of say 0.8, then as I already described, the power company's supply has to have a large capacity to supply you with say 25 kilowatts than it would if your power factor was 1.0, like say your neighbour enjoys.

 

Say you and a friend went to the ice cream van and each bought an ice cream, but you bought a double and he bought a single cone.

Would your friend be happy if the vendor said I'll average it and charge you both for 1.5 cones?

Edited April 13, 2016 by studiot

[EdEarl]

I think your electric meter is inaccurate with a PF different than 1; thus, you are charged too much for the power you really use. It is possible the meters have been changed since I studied power. It's also possible that different power companies use different kinds of equipment.

Edited April 13, 2016 by EdEarl

[Enthalpy]

When the power factor is bad it's almost always inductive. Not only does this increase losses in cables and transformers because the current is bigger for the same effect, it also lets alternators work under very unfavourable conditions - alternators are the main victims of the power factor. It results from the induction created by the stator as current is obtained from the alternator.

 

Because inductive load is very detrimental and nearly universal, regulations (in the EU) want all appliances of medium and high power (like computers) to have a good power factor. At electronic power supplies it means a power factor corrector at the input.

 

To compensate the big reactive power of a line, the traditional method was to free-run a synchronous machine. Meanwhile, big expensive capacitors are used but not universally; they improve the shape of the current too. Better means would be very useful, it's just that nobody knows how to.

 

Traditional electricity meters observe only the active power, so in a first approach the burden would be for the electricity supplier only, not for the consumer, but electronic meters do whatever they're meant for, and electricity suppliers want a minimum power factor from their customers.