Power factor correction

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leafminer

Bloody H E L L !
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I am not sure if the power companies bother with domestic circuits, but it occurs to me that running large inductive ballasts (would need to be a few KW) would cause a large power-factor lag on the incoming AC line. It might be a good idea to install power factor correction capacitors if you're in that situation.

Running digitals causes a different problem: the amount of switching noise on the line will increase to the point where it could cause problems. The reputable manufacturers should have incorporated sufficient filtering to ameliorate this problem.
 
leafminer said:
I am not sure if the power companies bother with domestic circuits, but it occurs to me that running large inductive ballasts (would need to be a few KW) would cause a large power-factor lag on the incoming AC line. It might be a good idea to install power factor correction capacitors if you're in that situation.

Running digitals causes a different problem: the amount of switching noise on the line will increase to the point where it could cause problems. The reputable manufacturers should have incorporated sufficient filtering to ameliorate this problem.

I'm confused :confused:...Could you expound on this in language that idiots can understand? Are you saying that magnetic ballasts and digital ballasts draw electricity differently than other high wattage appliances? That the power company can tell that I running say 4 1000W ballasts, rather than say my water heater or hot tub that are over 5000W?
 
I'll try. Hard to explain in simple terms.

Let's say for instance you connect a mag ballast across the supply and remove the lamp, replacing the lamp with a piece of wire.
The ballast is a pure inductance (almost). It looks like a REACTANCE not a RESISTANCE.
Current will flow through the ballast - and the same current will appear to any line monitor - but NO POWER will be drawn. This is because the current occurs at the moment when the voltage is zero, and as you probably know, power = current x voltage. When voltage is zero the power must also be zero. We call this an OUT OF PHASE current (technically it is at an angle of 90 degrees to the voltage. Take your hand and stick the thumb in the air with the fingers flat. The voltage is the fingers, the current is the thumb. For any actual power to be drawn they must both be in the same plane.)

In industrial premises, if you buy for instance a 3KW motor, it is also inductive and so causes a lagging power factor (the current pulses lag behind the voltage pulses.) So the power companies hate this and ask industrial consumers to correct for this problem by installing capacitors (big, paper dielectric, oil filled ones) across the incoming line. Capacitors cause a LEADING power factor and cancel out the lag caused by the inductive load.

Of course, people in domestic premises don't usually run large inductive loads in their houses. Your average Joe doesn't have a 5HP motor in his basement.

But growers using inductive ballasts . . . aha! Yes, 5KW of inductive lamp ballasts are going to cause a highly lagging load on the power line.
The reason electricity companies hate this is simple: Your electricity meter records only "true watts" of power. But the lagging power factor causes additional losses (current * current * resistance) in the power line that feeds your property. And they don't get paid for it - it's wasted power. If the lag gets to a certain point (if you visit a power station or substation you can clearly see the power factor meters on the supply panels) then they'll want to investigate why that's happening.

Digitals cause an entirely different problem. There is NO lag at all with digitals. But instead, you get another problem. The digital box controls the current through the load using a 'chopper' device, typically a triac. This is a semiconductor switch that is rapidly 'chopping up' the waveform into a series of sharp-edged pulses. The sharp edged pulses cause a high amount of HARMONICS to be reflected back up the power line. This can adversely affect all sorts of things: especially medical equipment. And it tends to radiate interference to TVs, stereos, radios . . . the level of harmonics is regulated by standards and if the power company sees too high a level of switching pulses on the line, again they will investigate.

(A harmonic is a multiple of the original frequency. The US standard being 60Hz, commonly the highest radiated harmonic from these digital boxes is 180Hz, followed by the 5th harmonic (300 Hz) and so on.)

If you are running more than a couple of KW of lighting you should load balance: bring both phases into the grow room and run half the lamps off one phase and half off the other.
 
BTW I could also add:
The power people can also see when electricity is being stolen, because their total KWH from the domestic meters would be less than the indicated power consumption as recorded by the power substation. I know how to turn meters backwards, for instance, but if done as a regular practice it is likely to bring people to your door.
 
LOL--I know to turn meter backwards, too. However, you lost me on the rest of the stuff. Thanks for trying, though.:48:
 
I dunno brother... think the problem is more theoretical than real world. You can run 6 1000 watt ballasts from a single 40 amp 220/240v circuit and still draw no more at startup or operation than a large inductive heater, furnace, clothes dryer, AC welder, etc. If you were running 60 of them then life with electrons would change... heh...

Have I missed your point?



leafminer said:
I am not sure if the power companies bother with domestic circuits, but it occurs to me that running large inductive ballasts (would need to be a few KW) would cause a large power-factor lag on the incoming AC line. It might be a good idea to install power factor correction capacitors if you're in that situation.

Running digitals causes a different problem: the amount of switching noise on the line will increase to the point where it could cause problems. The reputable manufacturers should have incorporated sufficient filtering to ameliorate this problem.
 
Yes, I'm afraid it is not quite as simple as that. Let me see if I can do it using math as an example. You know that if you square a number, say 2, you get a positive number always? Like for instance -2 times -2 = +4. OK.
Now think about square roots. I can take the square root of +4 and get +2 right? OK.
But what is the square root of -2? Can't be done because it results in what's called a 'non-real' number.
If you imagine a simple plane, like a graph, it's got two axes, right? An X and a Y. You can plot any point simply by taking the X coordinate and the Y coordinate and finding where the two lines meet. I'm sure you all did this in school . . .
Now, imagine a point that lies not ON the paper but, say, behind it or in front of it. That would be an 'imaginary' number.
The current flow in an inductor - like a lamp ballast - if you connect it straight across the supply, with no load (no lamp), would be like the point that's not on the plane but behind it.

From Wikipedia:
The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts). This increases generation and transmission costs. For example, if the load power factor were as low as 0.7, the apparent power would be 1.4 times the real power used by the load. Line current in the circuit would also be 1.4 times the current required at 1.0 power factor, so the losses in the circuit would be doubled (since they are proportional to the square of the current). Alternatively all components of the system such as generators, conductors, transformers, and switchgear would be increased in size (and cost) to carry the extra current.

Utilities typically charge additional costs to customers who have a power factor below some limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.


Now, if you are running say 3KW of inductive ballast lamps in your house and the rest of your load is say 3KW, then I can say for sure your power factor is not 0.9 or 0.95!
I could calculate it for mine, if I am not too lazy. But I only run 300W of lamp loads via inductors, so I am not bothered.
By the way, fluorescent lamps also are inductive loads. CFLs are not.

All the above is only really of interest to those who are running large lamp loads, say 4 KW or more. YOU might not worry but if there are neighbours with grow setups also running inductive ballasts . . . it all adds up.
 
Holy cow leafminer...this took me straight back to first year electrical engineering 20 years ago! Great explanation...but boy, it gotta tell you, it makes my brain hurt. :holysheep:

I hated EE so much that after I left, I never used my degree, and went into computers instead! :D

Thanks for the explanation though, leafminer...I can tell somewhere, you took the same classes I did.
 

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