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Introduction to Three-Phase Power

Introduction to Three-Phase Power. Typical Transformer Yard. Basic Three-Phase Circuit. What is Three-Phase Power?. 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.

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Introduction to Three-Phase Power

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  1. Introduction to Three-Phase Power ECE 441

  2. Typical Transformer Yard ECE 441

  3. Basic Three-Phase Circuit ECE 441

  4. What is Three-Phase Power? • 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). ECE 441

  5. Three-Phase Power ECE 441

  6. 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 441

  7. Phasor (Vector) Form for abc Vc=Vm/+120° Va=Vm/0° Vb=Vm/-120° ECE 441

  8. Phasor (Vector) Form for abc Vc=Vm/+120° Va=Vm/0° Vb=Vm/-120° Note that KVL applies .... Va+Vb+Vc=0 ECE 441

  9. Three-Phase Generator • 2-pole (North-South) rotor turned by a “prime mover” • Sinusoidal voltages are induced in each stator winding ECE 441

  10. ECE 441

  11. How are the sources connected? • (a) shows the sources (phases) connected in a wye (Y). • Notice the fourth terminal, known as Neutral. • (b) shows the sources (phases) connected in a delta (∆). • Three terminals ECE 441

  12. Look at a Y-Y System ECE 441

  13. Definitions • Zg represents the internal generator impedance per phase • Zl represents the impedance of the line connecting the generator to the load • ZA,B,C represents the load impedance per phase • Zo represents the impedance of the neutral conductor ECE 441

  14. Look at the Line and Load Voltages ECE 441

  15. Phase Voltages Line Voltages ECE 441

  16. Vector addition to find VAB=VAN-VBN -VBN ECE 441

  17. Using the Tip-to-Tail Method -VBN VΦ = Line-to-Neutral, or Phase Voltage VAB = VAN – VBN = √3VΦ ECE 441

  18. Conclusions for the Y connection • The amplitude of the line-to-line voltage is equal to √3 times the amplitude of the phase voltage. • The line-to-line voltages form a balanced set of 3-phase voltages. • The set of line-to-line voltages leads the set of line-to-neutral (phase) voltages by 30°. ECE 441

  19. Summary ECE 441

  20. Look at the Delta-Connected Load ECE 441

  21. ECE 441

  22. Phase Currents Line Currents ECE 441

  23. Vector Addition to find IaA=IAB-ICA -ICA ECE 441

  24. Using the Tip-to-Tail Method -ICA IaA = √3IΦ/-30° ECE 441

  25. Conclusions for the Delta Connection • The amplitude of the line current is equal to √3 times the phase current. • The set of line currents lags the phase currents by 30°. ECE 441

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