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Originally Posted by michaellxv
Saw a story during the week on ACA about a device which would smooth out the typical dirty electricity supply we get thereby making appliances work more efficiently using less electricity.
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Hi Michael,
I am a Professional Electrical Engineer, so maybe I can help.
In the case of what we call "Power Factor Correction", this has nothing to
do with the electrical supply being "dirty".
Instead, power factor, which is the ratio of what is termed "real power" and
what is termed "apparent power", arrives from the fundamental laws of physics.
Suffice to say at university, to fully understand it at a grass roots level,
they instruct students in the mathematics of partial differential equations
and present them with Maxwell's equations and build up from there. We certainly
won't start from there in this brief response!
Instead, imagine if you will, AC power being a sinusoidal waveform that
can be split into two components, a voltage waveform and a current waveform.
Most people will be familiar with the equation in DC power systems that the
Power = Voltage x Current, or P=VI. Because of the sinusoidal nature of
AC, the equation is slightly different, but just keep the DC equation for
power in your head for one moment.
Ideally, to maximize the instantaneous power, the voltage and current
components in an AC supply would be in perfect synchronization so that the
voltage waveform peaks and troughs corresponded to the current waveform
peaks and troughs. In other words, they would be said to be 'in phase'.
However, due to the effects of capacitance and inductance, the current
waveform can lead or lag the voltage waveform. The waveforms are not
'in phase' and the two waveforms aren't delivering the same sort of
power 'punch' as if they were in phase. By how much they don't overlap
is the Power Factor. It can vary between 0 and 1 and ideally it has a value of 1.
For those who enjoy equations, if we go back to the original equation for DC
power and now present the equivalent equation for average AC power, we would write -
Pav = Vrms * Irms * PF
where Vrms is a measure of the average voltage, Irms is a measure of the average
current and PF is the power factor. By way of further background, the power factor,
PF, is equivalent to the cosine of the angle by which the voltage and current waveforms
differ in phase. Thus a power actor of 0.9 implies that the current waveforms lags
the voltage waveform by arccos(0.9) = 25.8 degrees.
In practical terms, an inductive load comes about from many common types of
motors, such as an air conditioner or washing machine.
What Power Factor Correction devices attempt to do is if the load is inductive,
they supply extra capacitance.
In may jurisdictions around the world, the power company dictates to the consumer
what the lowest power factor they are allowed to have is. However, this is in
almost every case only mandated to large industrial power consumers. For example,
if you and I were to open an aluminium smelting plant, the power company will
dictate to us the minimum power factor our load will present and we will then have
to take steps by buying and installing additional equipment or devices to ensure those
requirements are met.
For household consumers, the power companies don't generally come knocking
on the door for us to install power factor correction devices.
What is more, in Australia, the way that the meter measures the amount of power
you use at home means that if you were to install a power factor correction
device, it won't save you any money but the power company would love it,
as it would save them money.
Quote:
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3. If I get solar panels installed does this have the same effect? Do solar panels supply clean power. Does the whole setup smooth out the grid supply?
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If you want to save money, then you would need to talk with professional
consultants and weigh up the cost of installing solar panels amortized over
so many years compared to just using the mains. But like power factor correction,
solar panels don't "clean" anything with regards the electricity, though they
may help keep the air cleaner.
In fact, the solar power system which produces DC is often converted to
AC by an inverter, which is a type of electronic switch. If you were to look
at the waveforms from a typical inverter on an oscilloscope and compare them
with the waveforms from the mains, then generally the mains supply is
a purer sinusoid.
Anyway, hope this insight helps a little.
