AC Inductance

The following figure shows an inductor in an AC circuit. When an AC supply is connected to an inductance, an emf is induced into the coil as the current is varying continuously.

FIGURE

        The following is the waveform diagram and the phasor diagram that represents the inductance in an AC circuit. The back-emf opposes the rise of current thus delaying its rise. In a pure inductive circuit, V leads I by 90^o or I lags V by 90^o. It is similar to AC resistance, but is identified here as the reactance (X_L).

FIGURE

FIGURE

        The inductive reactance of a coil depends of the rate of change of current and the inductance value, which is calculated using the formula below.

X_L = inductive reactance (ohms)

f = frequency (Hertz)

L = inductance (Henrys)

        As the current and voltage are 90^o out of phase, both positive and negative powers are produced. The circuit gets positive power from the power supply on one half cycle and the negative power is returned to the supply source on the other half cycle. Since positive and negative powers cancel, the net power is zero for a complete cycle. The power in a purely inductive circuit is shown in the figure below.

FIGURE