Two Sinusoidal Waveforms
–
“in
-
phase”
Phase Difference of a Sinusoidal Waveform:
The voltage waveform above starts at zero along the
horizontal reference axis, but at that
same instant of time the current waveform is still negative in value and
does not cross this
reference axis until 30
o
later. Then there exists a Phase difference between the two
waveforms as the current cross the horizontal reference axis reaching its
maximum peak and
zero values after the voltage waveform.
As the two waveforms are no longer “in-phase”, they must therefore be “out-of-phase” by an
amount determined by phi, Φ and in our example this is 30
o
. So we can say that the two
waveforms are now 30
o
out-of phase. The current waveform can also be said to be “lagging”
behind the voltage waveform
by the phase angle, Φ. Then in our example above the two
waveforms have a Lagging Phase Difference so the expression
for both the voltage and
current above will be given as.
where, i lags v by angle Φ
Likewise, if the current, i has a positive value and crosses the
reference axis reaching its
maximum peak and zero values at some time before the voltage, v then
the current waveform
will be “leading” the voltage by some phase angle. Then the two waveforms are said to have
a Leading Phase Difference and the expression for both the voltage and the current will be.
where, i leads v by angle Φ
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