Consider an AC circuit in which there is a phase angle of ϕ between VRMS and IRMS and voltage is assumed to be leading the current by ϕ as shown in the phasor diagram (Figure 4.55).
Now, IRMS is resolved into two perpendicular components namely, IRMS cos φ along VRMS and IRMS sin φ perpendicular to VRMS as shown in Figure 4.56.
(i) The component of current ( I RMS cos φ) which is in phase with the voltage is called active component. The power consumed by this current VRMS IRMS cos φ . So that it is also known as ‘Wattful’ current.
(ii) The other component ( I RMS sin φ) which has a phase angle of π/2 with the voltage is called reactive component. The power consumed is zero. So that it is also known as ‘Wattless’ current.
The current in an AC circuit is said to be wattless current if the power consumed by it is zero. This wattless current happens in a purely inductive or capacitive circuit.