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Power Electronics and Motor Drives
book

Power Electronics and Motor Drives

by Bogdan M. Wilamowski, J. David Irwin
October 2018
Intermediate to advanced content levelIntermediate to advanced
1015 pages
40h 24m
English
CRC Press
Content preview from Power Electronics and Motor Drives
Three-Phase Electric Power Systems 34-11
If the system is balanced, it is straightforward to show that (Figure 34.10)
p t p t p t p t
V I V I t
V
an bn cn3
2
φ
θ ω α β
( ) ( ) ( ) ( )
( ) ( )
= + +
= + + +
+
cos cos
II V I t
V I V I t
+ + + °
+ + +
cos cos
cos cos
( ) ( )
( ) (
θ ω α
θ ω α
2 240
2 240°°
=
)
( )3V I cos θ
(34.28)
Hence, we see the second advantage to balanced three-phase systems. The three-phase instanta-
neous power is constant!
Contrast this with the single-phase instantaneous power, which is oscillatory with radian frequency
2ω. Continuing, it is straightforward to show that
S V I
S V I
V
I
V I
P V I
an a
L
L
L
L L
L L
3
3
3
3
3 3
3
3
3
φ
φ
φ
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Publisher Resources

ISBN: 9781439802861