6.8 Wattless and Wattful Current:

The average power over a cycle of AC is given by,

$P_{av} = V_{rms}. I_{rms} . Cos\phi$ .......... (i)

Here $Cos \phi$ is the power factor and $\phi$ is the phase factor.

In pure inductor or an ideal capacitor, $\theta = 90^0$. So average power consumed in a  pure inductor or ideal capacitor is,

$P_{av} = V_{rms}. I_{rms} . Cos 90^0 = 0$

Therefore, Current through pure 'L' or pure 'C' which consumes no power for its maintenance in the circuit is called Wattless Current.

At resonance $X_L = X_C$ and $\theta = 0$

∴ Cos $\theta =$ Cos $0^0 = 1$

Therefore Maximum power is dissipated in a circuit at resonance.

The Current through resistance (R), which consumes power for its maintenance in the circuit is called Wattful Current.

Return to Main Menu