RESONANCE Basic AC Reactive ComponentsParallelResonanceResonance in a parallel R-C-L circuit will occur when the reactive current in the inductivebranches is equal to the reactive current in the capacitive branches (or when XL = XC). Becauseinductive and capacitive reactance currents are equal and opposite in phase, they cancel oneanother at parallel resonance.If a capacitor and an inductor, each with negligible resistance, are connected in parallel and thefrequency is adjusted such that reactances are exactly equal, current will flow in the inductor andthe capacitor, but the total current will be negligible. The parallel C-L circuit will present analmost infinite impedance. The capacitor will alternately charge and discharge through theinductor. Thus, in a parallel R-C-L, as in Figure 10, the net current flow through the circuit isat minimum because of the high impendence presented by XL and XC in parallel.SummaryResonance is summarized below.Resonance SummaryResonance is a state in which the inductive reactance equals the capacitivereactance (XL = XC) at a specified frequency (fRes).Resonant frequency is:fRes12p LCR-C-L series circuit at resonance is when net reactance is zero and circuitcurrent output is determined by the series resistance of the circuit.R-C-L parallel circuit at resonance is when net reactance is maximum andcircuit current output is at minimum.ES-08 Page 20 Rev. 0
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