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11.5 Complex Power (2)
P: is the average power in watts delivered to a load and it is
    the only useful power.
Q: is the reactive power exchange between the source and
    the reactive part of the load. It is measured in VAR.
•Q = 0 for resistive loads (unity pf).
•Q < 0 for capacitive loads (leading pf).
•Q > 0 for inductive loads (lagging pf).
S  =      P             +   j               Q