14 - Single phase parallel a.c. circuits

Abstract

This chapter focuses on single phase parallel alternating current (a.c.) circuits. In parallel circuits, voltage is common to each branch of the network and is thus taken as the reference phasor when drawing phasor diagram. In the two branch, parallel circuit containing resistance R and inductance L, the current flowing in the resistance is in-phase with the supply voltage V and the current flowing in the inductance lags the supply voltage by 90°. The parallel resonant circuit is often described as a rejector circuit as it presents its maximum impedance at the resonant frequency and the resultant current is a minimum. The Q-factor of a parallel resonant circuit is the ratio of the current circulating in the parallel branches of the circuit to the supply current, that is, the current magnification. In a parallel circuit the Q-factor is a measure of current magnification, whereas in a series circuit it is a measure of voltage magnification.