Page 239 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

AC power to a resistive load
In ac circuits, voltage and current are functions of time.
Power at a particular instant in time is given
P = vi= (Vmsinωt )(Imsinωt)
= VmImsin2ωt

=VmIm(1-cos2 ωt)

Power to capacitive

i=I sinat
m
v=V sin(at-90) 2 2
m
P
S
Q
p=vi=(V sinct-90°)(I sin at)=-V I cos at sinat
m m m m
V I V I
m m (Sin2ωS m m Sin2ω V I Sin2ω
2 2 2 RMS RMS

Load
Average power to a resistive load

Active power is the average value of instantaneous power

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CITS : Power - Electrician & Wireman - Lesson 38-40 CITS : Power - Electrician & Wireman - Lesson 38-40