Three – Phase Power System

Three-Phase Power

Definitions 4 wires –3 “active” phases, A, B, C –1 “ground”, or “neutral” Color Code –Phase ARed –Phase BBlack –Phase CBlue –NeutralWhite or Gray

Balanced Three – Phase System

Phasor Diagram Positive Phase Sequence abc

Phasor Diagram Negative Phase Sequence acb

Delta-Connected Sources V line = V  Line Voltages V line V ab V bc V ca Phase Voltages V Φ V a V b V c

Currents for the Delta Connection Line Current I line Phase Current I Φ I line = √3I Φ

Y-Connected Sources Line Voltages V line V ab V bc V ca Phase Voltages V Φ V a V b V c V line = √3V Φ

Currents for the Y - Connection Line Current I line Phase Current I Φ Line Current = Phase Current ----I line = I Φ

Power in a Balanced Three – Phase System Total Power is equal to 3 times the power per phase!

Power in a Balanced Three – Phase System (Continued) For a Balanced Y – Connected System

For a Balanced Δ – Connected System,

Three-Phase Bridge Rectifier

Conduction Sequence

Average Output Voltage, V dc

rms Output Voltage

Diode Currents

Transformer Secondary Current

Instantaneous Output Voltage