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POWER FACTOR
If a load is partly capacitive or partly inductive then the current will lead (capacitance) or
lag (inductance) the load voltage.
When this occurs on a large scale, say in a factory with many highly inductive machines,
much fluorescent lighting or many electric welders then this part of the power station’s
load will be highly inductive and therefore the current will lag the voltage by a significant
amount, and since the cosine of the angle between voltage and current is one definition of
Power Factor then in this situation the Power Factor will be significantly less than 1
which can be a problem. (Strictly speaking this cosine definition of Power Factor only
holds true if the voltage and current waveforms are sinusoidal).
Power factor can be lagging or leading depending on whether the current lags or leads the
voltage. That is to say whether the load is largely inductive or capacitive.
Ideally the load current and voltage should be in phase, which by the above definition of
Power Factor gives a Power Factor of 1.
Another definition of Power Factor is: Power Factor = True Power/Apparent Power
Where True Power is the actual power used to perform work or dissipated as heat in the
load.
True Power is measured in Watts and would register on a Wattmeter.
Apparent Power is what you would calculate if you measured the actual current and the
actual voltage and multiplied them together.
Apparent Power is the vector sum of True Power and Reactive Power (I haven’t
mentioned Reactive Power before now). I.e. Square True and Reactive Powers add them
together and take the square root.
Apparent power is measured in VAs or Volt Amperes.
Reactive Power is the power being transferred backwards and forwards between the load
and the Grid and not actually being used in doing any real work.
Reactive Power is the part of the Apparent Power that is only used to repeatedly generate
an electric field in the capacitive part of a load or the magnetic field in the inductive part
of a load.
Reactive Power is measured in VARs or Volt Amps Reactive.
So if the reactive power is large this means that the Apparent Power is large and if the
True Power is relatively small then the result is an undesirably low Power factor.
In this situation a large fraction of the power is being transferred back and forth between
the load and the grid. This Reactive fraction of the power is not actually doing any work.
Electric Companies have to upgrade their infrastructure to cope with this extra power
which costs money and they therefore place a surcharge on companies whose Power
Factor is small enough to cause this problem.
A low factory Power Factor caused by highly inductive loads can be increased towards
the ideal value of 1 by installing a calculated value capacitor bank. This is known as
Power Factor Correction. This means that the Reactive Power is only transferred locally
between the inductive loads and the added capacitor bank and is not then transmitted over
the Electric Company’s infrastructure. Therefore a surcharge cannot be levied.
To get back to a Nicholas Vinnen type transformerless power supply. This type of power
supply is highly capacitive giving a low Power Factor as much of the power is transferred
back and forth between the dropper X2 capacitor and the grid and isn’t actually doing any
real work.
However the amount of power utilised in such a small-scale operation is very small and
therefore wouldn’t cause the above-described problem with the Electric Company’s
infrastructure unless, I suppose, a very high number of them were used together.