Basic AC Reactive Components CAPACITANCECAPACITANCEThere are many natural causes of capacitance in AC power circuits,such as transmission lines, fluorescent lighting, and computermonitors. Normally, these are counteracted by the inductorspreviously discussed. However, where capacitors greatly outnumberinductive devices, we must calculate the amount of capacitance to addor subtract from an AC circuit by artificial means.EO 1.5 DEFINE capacitive reactance (XC).EO 1.6 Given the operating frequency (f) and the value ofcapacitance (C), CALCULATE the capacitive reactance(XC) of a simple AC circuit.EO 1.7 DESCRIBE the effect on phase relationship betweencurrent (I) and voltage (E) in a capacitive circuit.EO 1.8 DRAW a simple phasor diagram representing ACcurrent (I) and voltage (E) in a capacitive circuit.CapacitorsThe variation of an alternating voltage applied toFigure 3 Voltage, Charge, and Current ina Capacitora capacitor, the charge on the capacitor, and thecurrent flowing through the capacitor arerepresented by Figure 3.The current flow in a circuit containingcapacitance depends on the rate at which thevoltage changes. The current flow in Figure 3 isgreatest at points a, c, and e. At these points, thevoltage is changing at its maximum rate (i.e.,passing through zero). Between points a and b,the voltage and charge are increasing, and thecurrent flow is into the capacitor, but decreasingin value. At point b, the capacitor is fullycharged, and the current is zero. From points bto c, the voltage and charge are decreasing as thecapacitor discharges, and its current flows in adirection opposite to the voltage. From points cto d, the capacitor begins to charge in theopposite direction, and the voltage and current areagain in the same direction.Rev. 0 Page 5 ES-08
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