CAPACITANCE Basic AC Reactive ComponentsAt point d, the capacitor is fully charged, and the current flow is again zero. From points d toe, the capacitor discharges, and the flow of current is opposite to the voltage. Figure 3 showsthe current leading the applied voltage by 90°. In any purely capacitive circuit, current leadsapplied voltage by 90°.CapacitiveReactanceCapacitive reactance is the opposition by a capacitor or a capacitive circuit to the flow ofcurrent. The current flowing in a capacitive circuit is directly proportional to the capacitance andto the rate at which the applied voltage is changing. The rate at which the applied voltage ischanging is determined by the frequency of the supply; therefore, if the frequency of thecapacitance of a given circuit is increased, the current flow will increase. It can also be said thatif the frequency or capacitance is increased, the opposition to current flow decreases; therefore,capacitive reactance, which is the opposition to current flow, is inversely proportional tofrequency and capacitance. Capacitive reactance XC, is measured in ohms, as is inductivereactance. Equation (8-3) is a mathematical representation for capacitive reactance.(8-3)XC12pfCwheref = frequency (Hz)p = ~3.14C = capacitance (farads)Equation (8-4) is the mathematical representation of capacitive reactance when capacitance isexpressed in microfarads (µF).(8-4)XC1,000,0002pfCEquation (8-5) is the mathematical representation for the current that flows in a circuit with onlycapacitive reactance.(8-5)IEXCES-08 Page 6 Rev. 0
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