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Figure 1.25. Productive power.
Power factor is known as cosine Ø(phi) where Ø is the angle shown on the vector diagram of
Figure 1.25 above, but it is more usually expressed as the ratio of useful power
to total power. For example, if a system needs 100,000W of productive power and the non-productive
power is 10,000W, then the total power is 110,000W
Power factor is 100,000/110,000 = 0.909.
Note the power factor will always be less than unity (1).
The non-productive power component is of no value to the user but still must be generated
and paid for. The objective of any electrical system, therefore, is to reduce the non-productive
component as much as possible.
As the non-productive power component is reduced the power factor increases. If the non-
productive power component of the above example is reduced to 1,000W, the power factor increases to
0.99 (100,000 / 101,000). Now only 101,000W of power must be paid for. The power factor of any
electrical system can be improved by the addition of special electrical devices.
From a purely technical standpoint, productive power is measured in watts, non-productive
power is measured in VAr (volt-ampere reactive) and total power is measured in VA (Volt Amps). For
large users the electrical supply company either sets a minimum requirement for power factor, say
0.9, or charges for total power.
Voltage Drop
Voltage drop is the measure of energy that electrons lose as they travel through a circuit.
Energy is dropped proportionately to all energy consuming components in the circuit so that the
total voltage drop always equals the source voltage.
Figure 1.26 shows the voltage drop in two series circuits. Note that both circuits
have the same 20V source.
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