Power in pure capacitive circuits:

The voltage lags the current by 90° in a pure capacitive circuit. Let the voltage and current at any instant t be represented respectively by

v = Vm sin wt             and

i = Im sin(wt+90°)

The instantaneous power can be written as

p = vi

= (1/2) Vm lm 2 sin wt sin (wt +90°)

=(1/2)Vm lm sin 2wt

Active power or Avg power:





Reactive power:

The peak value of instantaneous power can be written as

Pc=(Vmlm)/2 = (Vm/√2) (Im /√2)  =Vrms Irms

For a purely capacitive circuit,

Here, Qc is the rate of change of reactive power between the load and the source. By convention, Qc is taken as negative and is called the leading reactive power.

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