oztules
Guru
Joined: 26/07/2007
Location: AustraliaPosts: 1686 |
| Posted: 10:28am 19 Apr 2009 |
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If you are not generating the power yourself, but are buying it on the grid, then there is no real difference to your pocket.
The two current's (.22 and .76) you are trying to reconcile are apples and oranges..... without the pf figure, you can't compare them.. the cost of the .76A pf.33 is actually .25A that you pay for. The other 500ma which is out of phase with your load, is returned? to the grid.... or so the story goes. That 500ma is stored in a magnet field, which when it collapses through the inductance that caused it, generates the current that gets put back into the grid... out of phase with the voltage (it has long gone and now looks at starting the whole thing over again)
There will be some losses via resistance in the line and the inductance, so not all the current is returned to the grid, and they will lose some getting it too you as well. So for the grids sake, pf=1=good for everyone.
I have no idea why the supplied capacitor didn't change the amps. It should have affected it... if the ballast was a transformer.
If it were a modern electronic ballast, then an inductor would have been necessary, as the modern electronic ballast tends to be capacitive and store energy in an electric field, and generate positive VARs...
The modern pwm 50khz units also distort the waveform, which can't be easily compensated for (perhaps toss out the filter capacitors in the pwm, and put up with the 100hz flicker) It does this by rectifying the wave, and the capacitor is used as a filter cap. This leads to situation, where for the first (most) part of the wave, we don't use anything, as the cap voltage is above most of the wave, We then hammer the top of it.
Now if we want the same RMS, but only use a small part of the wave, you can imagine how hard we have to hit it to get the same power from a small part of the wave. We must generate these peak currents, or the whole thing won't work, and average voltage will sag....... not good.
I will assume an older transformer ballast but there's something odd here.
It should have given you leading (positive) VARs to compensate for your lagging load, it would then not have to import them from the grid, as you would be generating them locally, and the current should have dropped to 250ma in the line.
One day I will understand this stuff.... I hope.
If you generate your own power, then there is a high price to pay for using low pf devices.... even though the extra VA's are wattless, it still means you have to generate the higher currents and voltages albeit at different times, and you wont get to use them, you still have to generate and transmit them.
The harmonic distortion poor power factor (lumped in together with/ but not traditional power factor..phase angle stuff) is costly in rectified and smoothed devices too. Try charging a big battery bank off a generator driving a charger.... it ain't pretty.... see explanation above Re: pwm, same sort of thing, the battery acts as the filter capacitor.....and the rest is history...
You will need a bigger genny than you calculate.
........oztulesEdited by oztules 2009-04-20
Village idiot...or... just another hack out of his depth |
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