ECE 442 1
Three-Phase Power
ECE 442 2
Definitions
• 4 wires– 3 “active” phases, A, B, C– 1 “ground”, or “neutral”
• Color Code– Phase A Red– Phase B Black– Phase C Blue– Neutral White or Gray
ECE 442 3
Phasor Diagram
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Delta-Connected Sources
VLINE = V
ECE 442 5
Phasor Diagram, VAB as reference
ECE 442 6
Look at the Currents
I = ILINE / 3
ECE 442 7
Y-Connected Sources
ECE 442 8
Phasor Diagram with A as reference
ECE 442 9
Complete Phasor Diagram
VLINE = 3V
ECE 442 10
Look at the Currents
I = ILINE
ECE 442 11
Three-Phase Bridge Rectifier
ECE 442 12
Conduction Sequence
ECE 442 13
Average Output Voltage, Vdc
0
6
0
1 ( )
2 3 cos ( )263 3 1.654
T
dc
dc m
dc m m
V f t dtT
V V td t
V V V
ECE 442 14
rms Output Voltage12
62 2
0
12
2 3 cos ( )26
3 9 32 4
1.6554
rms m
rms m
rms m
V V td t
V V
V V
ECE 442 15
Diode Currents
12
62 2
0
3
4 cos ( )2
0.5518
mm
r m
r m
VI peakR
I I td t
I I
ECE 442 16
Transformer Secondary Current12
62 2
0
12
8 cos ( )2
2 1 2sin6 2 6
0.7804
s m
s m
s m
I I td t
I I
I I
ECE 442 17
Instantaneous Output Voltage
02 2( ) 0.9549 (1 cos(6 ) cos(12 ) ...35 143mv t V t t
ECE 442 18