A series RLC circuit will have unity power factor, when:

Concept:

In a series RLC circuit, the net impedance is given by:

Z = R + j (XL - XC)

XL = Inductive Reactance given by:

XL = ωL

XC = Capacitive Reactance given by:

\(X_C=\frac{1}{\omega C}\)

The resonance curve of the series RLC circuit is given as:

Observation:

• Below the resonance frequency, XL is low and XC is high → circuit behaves like a capacitive circuit (leading power factor)
• At the resonance frequency, XL equals to XC → circuit behaves like a purely resistive circuit (Unity power factor)
• At the above resonance frequency, XL is high and XC is low → circuit behaves like an inductive circuit (lagging power factor)