CFL's the next environmental disaster?

Tripp,

You have it about right. In most residential application PF is not really an issue. PF is the percentage of usable power a device uses. A Power Factor of 1.00 means that the device is able to use 100% of the power. Motor loads are really the thing in houses that are subject to poor power factor. In reality,, you pay for watts, (or kilowatts) not Kilovolt/amps. Kva is the true measure of power including PF. So a Cfl might draw 50 watts for example,, but at a PF of .5 the generator has to generate 100 watts to allow that bulb to light drawing 50. You don't pay for the lost 50% directly,,the power company does.

The reality is that while CFLs use ~1/4 as many watts per lumen as a incandescent,, it may burn 1/2 as much PF power net/net. In the off grid world, my bulbs may burn 15 watts @, but they cost me ~30 watts net/net out of the battery.

Does this make any sense?

Icarus

You are correct however that this is a phenomenon of AC power. I confess that I don't REALLY understand it all,, but it has to do with the ability of the device to "follow the phase" Add in RMS voltage and life gets quite confusing!

 

add in the 3rd phase and really get confused.

 

Add in Delta 277v 3 phase and I get lost!

Icarus

 

25 years ago, I understood 3 phase power and could tell you how it worked, that was when I used to do maintenance on Strippit turret punch presses. Today, I couldnt tell you how to plug the darn thing in anymore. Those thing had phase converters, step up, step down transformers, DC converters, all in one cabinet, which was scary to work on. It used PWM for the stepping motors that drove the XY table, and a big 3 phase motor on top that drove a heavy flywheel with an air driven clutch. I new those things inside and out, but today I couldnt tell you how to enter the programming, of course back then it was programmed with a tape strip that had holes punched in it.

 

KVA is a measure of power flowing in the lines, but not of the power needed to spin the power company's big rotating generators. The reactive power portion is bouncing back and forth between the generator and load, not being directly lost, but a small fraction of it is lost on each bounce as the extra current flows through the lines, which do have some resistance. That is why large industrial customers are charged for it, as a separate item in addition to the normal real power consumed.

The picture is more complicated because 60 Hz reactive current, commonly created by motors, causes different problems than harmonic currents, typically caused by electronic devices that pull peaky currents. But both cause excessive line losses for the power company in the same way.

I can't address how inverters respond to the reactive power issue.

 

Correct. The load is entirely resistive in nature

Correct. I found your statement a bit confusing, hence my question

I have posted links in earlier threads discussing power factor, power factor correction, etc. I realize they are a bit complicated, and I also realize I'm a poor teacher. Qbee42 tends to explain things better than I do, especially after a few drinks

Inductive and capacitive loads, correct. Older switching power supplies are pretty bad too, the newer ones have pf correction built in. Eg I have some OCZ GameXStream 1,100 watt computer power supplies that claim 0.99 pf

Correct. Of course, the power co *will* charge for pf correction, especially for large commercial users. The worst offenders I've worked with are the older 6-pulse thyristor UPS's. The input distortion was so bad, for such a given UPS you needed to size a backup generator 3-5 TIMES the rated UPS output, just to ensure the generator could run it!

Correct, but still overall better to run than an incandescent light bulb. Eg: that 15 watt cfl that "costs" you 30 watts, compare the overall lumens to a 30 watt incandescent light bulb

I suggest heavy drinking. That seems to work for me

Feh, what about Wye?

 

AHA so that is why half the Tripp Lites in the colo I built didn't work! Even with a 100 KW genset half of them would cycle through battery and not switch back to line.

Why oh why did you bring up Wye?!?! Now I have to go look that up because it rings a bell somewhere in my befuddled Cisco crammed workaholic mind.

 

I'll say it again:

Heavy

Drinking

Seriously, the behavior you described is what you would expect from the harmonic interaction of a 6 pulse thyristor system to a generator. You would have probably needed a 500-1,000 kw generator

 

Tripp, in a nutshell it works like this: voltage is a measurement of electrical potential, current is the flow of electricity. If we were talking about plumbing, voltage would be the pressure and current would be the gallons per minute. Power is the product of those two: the pressure (voltage) times the current. In the case of DC, the voltage and current are steady - they flow along like water from a faucet. In the case of AC, the voltage and current alternate back and forth, which is why we call it Alternating Current, or AC. If AC were used in plumbing, you would have a tank with an attached pipe. Water would surge into the tank from the pipe, then suck back out. In the case of U.S. house wiring, this in and out cycle is repeated 60 time per second, or 60 Hz.

Either system is able to deliver power. With DC it is a steady flow at a steady pressure. With AC it is a rhythmic in and out flow. You can imagine a turbine being powered by either method, although it would be more complicated with AC because of the in and out cycles.

You can get more power by increasing the pressure or increasing the current, or both. This is also true with electricity. Here is where it gets a bit tricky with AC: the pressure and current are both continuously changing: in and out, in and out, in and out. If the current and pressure change together, so that their maximum and minimum levels coincide, the power factor is one. If the current and pressure are exactly opposite, then the power factor is zero.

Thinking about this another way, if the current and pressure work together, you get maximum push along with maximum current. This gives you the most power you can possibly get with that current and pressure. If they are exactly opposite, the current goes in and out without any force behind it. There is just as much current, but no power. They aren't working together.

Power factor is just an expression of how well the current and voltage are working together. If they are right in step, you have a PF of 1.0. If they are completely out of phase, the PF is 0.0.

The issue with a poor PF is that it means a lot of electrons are going back and forth doing nothing but heating the supply wires. We want those electrons to work as hard as possible, so we want a good PF.

With inductive loads, such as motors, the voltage leads the current by 90°. With capacitive loads the current leads the voltage by 90°.

Tom

 

The reactive portion of the power is not actually LOST. It does have to be corrected for by the grid/generator though. Extra current must be maintained because of the power factor, but not extra power (at least not proportionally.) There is some additional loss due to the greater current though.

Say you have a PF of 0.5 and used 50 watts on the meter, that does not mean that 50/0.5 = 100 watts is effectively consumed. It does mean that extra current must be supplied. That extra current will result in higher line (resistive losses), etc. but much of the reactive load is recovered.

I'm still trying to understand how this works in the off grid case. What component would be absorbing all that power? I suspect that the PF is being corrected in the controller with only an incremental loss. Else there is a large amount of energy that needs a home...

 

Wow! Overall, excellent discourse! It's bringing back memories of the many electrical engineering courses I took in college and grad school.

One thing to clarify in your teaching, if my memory serves correctly, is that only for perfect inductive or capacitive loads are the voltage and current off by 90 degrees. Motors, which are the types of loads we generally see causing the power factor to be less than 1.0, are not perfectly inductive, just partially inductive, so their power factor that I've seen is generally around 0.85 (BIG 3-phase motors on ships).

 

Shawn,

Good question,

I am away from my off grid system for a bit,, but when I get home I will test it with the Kill-a-watt.

My guess is that when the .5 Pf light bulb draws 50 watts,, the inverter and the battery will have to put out 100 watt,, the rest lost in the wiring. I'll check it out on my solar forum.

Icarus

 

Inductive loads, by definition, are perfect inductors. Capacitive loads are perfect capacitors. The real part of the load is resistive. Obviously all real world devices are a combination of ideal devices.

Tom

 

Shawn,

I told you there are smarter folks than me around,
here is the proof from my solar forum: The question was if a CFL bulb off grid, was rated at 50 watts, with a PF of .5 how much would the inverter/battery have to supply.

"No, the CFL still draws 50 watts and the Inverter is still supplying ~50 watts...

However, it is 50 watts + a little bit more:

P=V*I
P=I^2*R

P=V*I; I=P/V= 50W / 120V = 0.42 amps
P=V*I*PF; I= P/(V*PF)= 50 W / (120 V * 0.5) = 0.83 amps

Ratio of increased power loss = P high PF / P low PF = (0.83a)^2 / (0.42a)^2 = 4:1

So--the I^2*R resistive losses are 4x higher because of the high power factor (as well as limitations of transformer saturation current, etc.)..."

Thank you, Bill!

Icarus

 

It is useful to separate the two main causes of power factors less than 1.0:

(1) linear devices (inductors, capacitors) that consume reactive power, sinusoidal currents at the same frequency as the AC source but out of phase;

(2) nonlinear devices (e.g. diode rectifiers charging storage capacitors of power supplies) that draw non-sinusoidal currents, peaky currents rich in harmonics of the AC source.

You are probably thinking of case #1, where the load is returning current to the generator during a portion of the AC cycle. I believe CFLs fall more into case #2. The current waveform is ugly but the load is not returning any significant current to the source, so there is no significant power left homeless.

 

I'm curious if you drive a car that burns gasoline, and if you are concerned about what that puts in the air for all of us to breathe.

I love that Wildcow has suddenly become so concerned for public health.

 

Well, on the topic of harmonics, especially 3rd and 5th order harmonics, that tends to play hell with other devices. Eg the "dirty" power we always hear about. Harmonics have no real impact on resistive loads, such as heaters and light bulbs, but a lot of electronic loads can glitch if the harmonics are bad enough

Most inverters do a poor job dealing with harmonics and loads that are mostly reactive or inductive. There can be a situation where the harmonics can go into an oscillation.

As an example, getting back to the older 6 pulse thyristors used in older UPS's. Typically large UPS's, the kind used to backup data centers and other large loads. Say the UPS is rated 50 kw

Normally, folks would size a generator to 1.5x the load, a 75 kw generator. Actually, that generator would probably not handle the load, and the UPS would stay on battery. A generator sized 2-3x would be needed

If there are many such UPS's hooked up to a generator, the problem is much worse. In that case, a generator 5x, even up to 10x the rated load, would be needed to ensure the UPS could transition off battery

 

That is pretty much what we discovered. The NOC I built was designed without a whole room UPS system, wasn't in the budget, and since it was rental space for customers to place their servers, they were required to have their own UPS systems. Those who had APC units, never had an issue switching back to line once the Gen kicked in, those with the small Tripp Lites, not the RM3000 units, but the smaller desktop size ones, would never kick into line, in fact they oscillated between battery and line while on the generator. We had a 100KW Kohler installed, that was more than enough for the amount of circuits we installed. They have since increased capacity by removing the shelf racks and installing more cabinets, and have had to increase the Genset and added a whole room UPS.


One thing I would like to add. DC seems to be a more efficient means of providing power for motors. It is what is used to drive trains, and can provide more power for hand held devices, like drills, on smaller voltages. Drawback is DC has a short life when it comes to transmission, you need substations to boost the power every few miles, which made it ineffective for mass distribution, which is why AC is the dominating power source. AC transmission, they boost the voltage up to 30K or more, shoot it across miles of lines, then step it down at the substations for local distribution. AC is also a bit more forgiving when you accidentally touch the conductors. DC at 120 volts can do some serious damage to you, where 120 AC will just give you a jolt. The power used for trains is 600 VDC, one touch of the overhead, or third rail and you wont even have time to blink before your dead. AC OTOH you fry a little bit before you die, don't know which one I would rather go down under if it were to come to it. Gruesome.

 

That behavior is entirely predicted. If the oscillation of a large number of 6 pulse thyristor UPS's are allowed to continue, you can expect a spectacular visual effects display from the generator

Well, a few corrections

Polyphase electric motors are the dominant source of industrial motive power. One must keep in mind the majority of motor duty is constant speed, either on or off

The locomotive example is different, as power must be controlled. The engine-generator set allows you to provide very finite control to the power applied, from zero to full forward, to even full reverse

I'm sure we've all seen locomotives joined, some running in reverse and some in forward, with no loss of efficiency

As far as long distance power transmission, only in the past 20 years or so have solid state devices been developed to allow practical HVDC power transmission. Particularly in the past 5-10 years, the cost of IGBT's and the like, have fallen to the point they are cost effective

HVDC dates back almost 100 years. Back then it required messy and inefficient motor-generator sets, liquid mercury valves and tubes, etc. In contrast, HVAC was downright simple

HVAC suffers from a number of line losses, such as "skin effect." There is the recognized danger from EMF from overhead HVAC lines. I'm sure qbee42 will chime in. There are I2R losses due to the 60 hz cycle - The conductors must be oversized as a result.

As HVAC is polyphase, you need 3 conductors. Over long distances, precise frequency synchronization is difficult to maintain

In a grid intertie scenario, if the two intertie points should happen to drift out of frequency synchronization, very bad things could happen. There are contraptions that allow matching frequency, but they are cumbersome and complex

GE Energy - Variable Frequency

Most modern HVDC systems use a bipole design, or two wire system. The inversion/conversion is done with 12 pulse systems, so no harmonics and high efficiency. Here is an example from what IMHO is the world leader in HVDC

ABB HVDC - Power T&D Solutions

So, ABB and also Siemens

https://www.energy.siemens.com/cms/00000029/Pages/products.aspx?lang=en&country=ZZ&partid=KN030112

have HVDC systems that are designed to be more efficient, safer, and cheaper than HVAC systems, depending on application and distance

So, modern HVDC power transmission is more efficient than HVAC. For longer distances, it's lower cost. No EMF to worry about. There are no issues with grid intertie synchronization. It's even thought the HVDC is a bit more resistant to solar flares

 

Excellent, You can see I haven't kept up on my electronics learning in quite some time. I gave it up when I left my RF Induction job back in the 80's. I always thought DC would be a more practical solution, but it has had it caveats. For example, cars used to use a DC generator to recharge the battery, but if the car idled too long, the battery would drain because the generator could not produce enough current to keep it charged up, which is why cars all now use an alternator with rectifier and regulator setup. An alternator can produce enough current at idle to keep the charge up on the batteries.

So with the new technology, would producing DC be more efficient than AC, be able to use existing transmission lines, and with a converter in the homes and plants be a more practical solution for energy production?