

Power Factor>Rob Sedgwick wrote at 11:38 AM 3/4/2013: > > Hi, > I feel I have a valid and major concern regarding some universal energy > measurement standards that are used in certain consumer devices, > residential service meters and potentially (as my inquiry is yet > unanswered) appliance ratings, (such as 'Energuide' in Canada). > > Todays existing, typical energy consumption measurements use a watthour > (Wh) or kilowatthour (kWh) unit. Although the Wh or kWh unit is accurate > for 100% linear (resistive) loads or the resistive portion of all loads, > accurate and true measurements will need to calculate the total flow of > electrons (amperage) through both the resistive and reactive portions of > loads. > > The reactive portion of inductive loads (most electronics, microwaves, > fluorescent lights, refrigerators/freezers, pumps, etc) will increase the > current flow to the load based on the power factor (electrical efficiency) > of the load. Adding a capacitive load (such as a capacitor) can offset the > increased current flow by improving the power factor. > There is no 'freelunch' when using the 'watt' consumption of a load and > not accounting for any extra energy consumed from its inefficiency
Hi Rob!
Here's the central issue: Power Factor is not electrical efficiency.
The two are distantly related, but PF and efficiency are entirely
different concepts.
Because of Power Factor effects, any voltamp meter measurements will
often be wrong. Voltamps gives an incorrect OVERestimation of the rate
of actual energy consumption.
What's Power Factor? It's based on the idea that an (ideal) inductor
consumes zero energy... yet whenever we plug inductors into
AC outlets, the inductors draw
significant current. (Same applies to capacitors.) If we multiply their
voltage
and current measurements, we'll see major watts of energy flow. But this
wattage is wrong, and for ideal or nonlossy coils and capacitors, the
actual energy consumption is zero.
The problem is that inductors do draw energy from the utility grid
...but then they turn around and give back every bit! During each cycle
of AC, the
electrical energy will be "sloshing" back and forth between the distant
generator and the inductor. Resistors don't act like this. A resistor's
current alternates, but the voltage alternates at the same time, so the
energy flows in just one direction: from generator to load. With
capacitors and coils, this doesn't happen.
Let's take a straightforward view which avoids imaginary numbers. We can
investigate zero Power Factor by driving an
inductor with a battery, then instantly swap the battery leads back and
forth to create
AC square waves.
What happens?
[Diagram, four simple schematics 1a, 1b, 1c, 1d]
When first connected in [1a] above, the current rises smoothly, and the
battery is dumping energy into the inductor as expected. In [1b] we flip
the battery instantly. Since inductors act like "electricity flywheels"
they have a
large "inertia effect" on the flowing charges within them. The voltage
polarity reverses, yet the direction of
current does not. In [1b], the battery terminals have swapped, and the
energy stored in the inductor flows back into
the battery, charging it up.
If we leave the inductor connected, the current decreases, eventually goes
through zero, and
becomes negative, as in [1c]. The reversed battery voltage is driving a
negative current, and negative times negative gives positive watts:
this means that energy is again
flowing from the battery into the inductor. Next, flip the battery again
in [1d]. Again the current stays momentarily the same. But reversing the
voltage has reversed the energy flow, and the inductor's stored energy is
again being dumped back to the battery.
Finally, wait until the current goes to zero, and we've created one
complete "AC cycle."
See the problem? A large current exists in the power line, but our
inductor uses up zero energy. On each halfcycle of AC, the inductor first
draws some electrical energy from the power supply, but then it dumps it
all back again. Voltamperes remains large, yet energy consumption is
zero, so PF is zero. We can't just look at voltamperes, since it
wrongly predicts that inductors consume immense energy. In fact,
inductors consume very low energy (ideally it's zero.)
> > For the purpose of illustration, let's look at nonlinear loads that > basically have static consumptions (fluorescent lights, televisions). > Let's neglect cyclic, variable or high starting loads such as > refrigerators or pumps for now. > I've used my 120VAC circuit measurement device (a standard tool on the > consumer market) to read the energy consumption of a staticload > appliance. This device is simply taking the measured_wattage_ of the > appliance and multiplying it by the cumulative time recorded in the > device. Although this same device has the capability to measure current, > voltage and power factor it isn't using these values for proper energy > consumption calculations. > I believe this results in very inaccurate readings and misleading > information for the consumer.
Nope, the energy meter is doing it right.
When connected to an inductor,
it ignores the voltamperes and the reversing energy flow. We don't want
to measure the "sloshing energy" created by an inductor or a capacitor.
We only care about the total energy which moves, on average, from generator
to appliance. (And, if the capacitor or inductor is getting hot, that
heat is caused by genuine oneway wattage being drawn from the power
grid.) 