Table of Contents
What Is Three-Phase Power?
Three-phase power uses three AC currents offset by 120 degrees, delivering constant power unlike pulsating single-phase. It is the standard for power generation and distribution, using less conductor material and driving motors without starting capacitors. Star (wye) connects loads between line and neutral; delta connects between two lines.
Industrial facilities, data centers, and large commercial buildings use three-phase power. Understanding the relationships between line and phase quantities is essential for electrical design, motor selection, and power factor correction.
Formulas
P = √3 × VL × IL × cos(φ)
Star: Vph = VL/√3
Delta: Iph = IL/√3
Star vs Delta
| Property | Star | Delta |
|---|---|---|
| Phase voltage | V_L/√3 | V_L |
| Phase current | I_L | I_L/√3 |
| Neutral | Available | None |
FAQ
Why is 3-phase more efficient?
Delivers constant power (no pulsation), uses 75% copper of equivalent single-phase, and provides smoother motor operation without starting capacitors.