Power in pure inductive circuits:

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

V=Vm sin(wt+90°) and i = Im sin wt

The instantaneous power is given by

p = vi

=(1/2) Vm lm Sin (wt+90°) sin wt

=(1/2) Vm lm (2cos wt sin wt)

= (1/2)Vm Im Sin 2wt

Active Power or Avg Power:

Therefore, in a pure inductive circuit, the active supplied over a complete cycle average out to zero.

Reactive power:

The power supplied to a reactance (inductive or capacitive) is termed reactive power. Unlike active power denoted by symbol P, the reactive power is denoted by symbol Q and given the name volt-amp-reactive (var). Let us now see how the reactive power is calculated.

The peak value of instantaneous power is given by

For a Pure Inductive circuit

Here Q is the rate of change of reactive energy between the load and the source. By convention, Q is taken as positive and is called the lagging reactive power.


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