Three-Phase Power

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

Phasor Diagram

Delta-Connected Sources

VLINE = V

Phasor Diagram, VAB as reference

Look at the Currents

I = ILINE / 3

Y-Connected Sources

Phasor Diagram with A as reference

Complete Phasor Diagram

VLINE = 3V

Look at the Currents

I = ILINE

Three-Phase Bridge Rectifier

Conduction Sequence

Average Output Voltage, Vdc

0

6

0

1( )

23 cos ( )

26

3 31.654

T

dc

dc m

dc m m

V f t dtT

V V td t

V V V

rms Output Voltage1

2

62 2

0

1

2

23 cos ( )

26

3 9 3

2 4

1.6554

rms m

rms m

rms m

V V td t

V V

V V

Diode Currents

1

26

2 2

0

3

4cos ( )

2

0.5518

mm

r m

r m

VI peak

R

I I td t

I I

Transformer Secondary Current1

26

2 2

0

1

2

8cos ( )

2

2 1 2sin

6 2 6

0.7804

s m

s m

s m

I I td t

I I

I I

Instantaneous Output Voltage

0

2 2( ) 0.9549 (1 cos(6 ) cos(12 ) ...

35 143mv t V t t