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Experiment_2_Phase_Angle

# Experiment_2_Phase_Angle - Experiment 2 Phase Angle Active...

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2 1 Experiment 2 Phase Angle, Active, and Apparent Power OBJECTIVE To study the meaning of phase angle. To study the relationship between active and apparent power. DISCUSSION In DC circuit, with a resistive load, as the voltage across the resistor increases, the current through the resistor increases. This is also true in an AC circuit with a resistance load. If a sinusoidal voltage e is applied across a resistor R, the instantaneous variations of current i through R follow exactly the instantaneous changes in voltage e . Thus, at the instant e is going through zero, i is going through zero. When e is at maximum, i is at maximum. When the voltage and current are “in step” with each other, they are said to be in phase. This relationship is shown graphically in Figure 2-1. However, it only occurs when the circuit load is a pure resistance.

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2 2 Figure 2-1 There are conditions under which the current is not “in phase” with the voltage. Such a condition is shown in Figure 2-2 (a) where the current attains its maximum value some 30 electrical degrees after the voltage. The current is said to "lag" behind the voltage by 30°. On the other hand, the current waveform shown in Figure 2-2 (b) attains its maximum value 30° ahead of the voltage. The current is said to “lead” the voltage by 30°.
2 3 (a) (b) Figure 2-2 To complete the picture, the current in Figure 2-3 (a) lags behind the voltage by 90°. (We would also be correct in stating that the voltage “leads” the current by 90°). In Figure 2-3 (b), the current leads the voltage by 90°. (We could also say that the voltage “lags” the current by 90°). Here we find the interesting condition where the current is zero at the instant when the voltage is maximum and vice-versa.

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2 4 (a) (b) Figure 2-3 Although this would appear quite improbable, because we have been told that the voltage causes the current until this point. How then can we have maximum current when the voltage is zero? It occurs when a load (such as on containing an inductor or capacitor) which is capable of storing energy is connected to an AC source. The load absorbs energy during part of the cycle and,
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Experiment_2_Phase_Angle - Experiment 2 Phase Angle Active...

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