Introduction to Three-Phase Power
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Three sinusoidal voltages that are equal in amplitude but out of phase by 120 degrees make up a balanced three-phase system. The phases are labeled A, B, and C and arranged either as A, B, C or A, C, B. A three-phase system uses four wires - three for the A, B, and C phases colored red, black and blue, and one neutral wire colored white or gray. The voltages of the three phases are shown as Va, Vb, and Vc where Va is 0 degrees, Vb is -120 degrees, and Vc is +120 degrees, following KVL such that Va + Vb + Vc = 0.
Introduction to Three-Phase Power
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- 4. Three sinusoidal voltages of equal amplitude and frequency out of phase with each other by 120°. Known as “balanced”. Phases are labeled A, B, and C. Phases are sequenced as A, B, C (positive) or A, C, B (negative). 4
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- 6. 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 6
- 8. 8 Va=Vm/0° Vb=Vm/-120° Vc=Vm/+120° Note that KVL applies .... Va+Vb+Vc=0
- 9. 2-pole (North-South) rotor turned by a “prime mover” Sinusoidal voltages are induced in each stator winding 9
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- 11. THANK YOU… 11