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ECE201_Lecture38

# ECE201_Lecture38 - ECE201 Linear Circuit Analysis I Lecture...

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1 ECE201 Linear Circuit Analysis I Lecture 38 Topic: Complex Power: Reactive & Apparent Power; Conservation of Power 1. Real Power P ave = V eff I eff cos θ Z = V rms I rms cos θ Z What are the meanings of P ave , V eff (V rms ), I eff (I rms ), and θ Z ? What are their units? P ave is also called the Real Power , its unit is watts , or W . 2. Apparent Power The quantity V eff · I eff is called the Apparent Power , its unit is volt-ampere , or VA .

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2 3. Complex Power (1) Complex power is a phasor: eff v eff V V = ∠θ i eff eff θ I I = * eff eff I V S × (Definition of complex power) ( ) eff v eff i eff eff v i eff eff z eff eff z S V I V I V I cos jV I sin = ∠θ × ∠ − θ = ∠ θ − θ = θ + θ 1442443 1442443 P ave + jQ (2) complex = average + j reactive power power power ( ) ( ) 2 2 eff eff z eff eff z eff eff S S V I cos V I sin V I = = θ + θ = Therefore, the magnitude of the complex power is the apparent power in unit (VA). The reactive power: { } Q Im S = (VAR) volt ampere reactive P ave = Scos θ z ( W ) Q = Ssin θ z = P ave tan θ z