Introduction to Three-Phase Power

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# Introduction to Three-Phase Power - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about ' Introduction to Three-Phase Power' - consuela-arcelia

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Presentation Transcript
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).

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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

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Phasor (Vector) Form for abc

Vc=Vm/+120°

Va=Vm/0°

Vb=Vm/-120°

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Phasor (Vector) Form for abc

Vc=Vm/+120°

Va=Vm/0°

Vb=Vm/-120°

Note that KVL applies .... Va+Vb+Vc=0

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

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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

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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

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Phase Voltages

Line Voltages

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Using the Tip-to-Tail Method

-VBN

VΦ = Line-to-Neutral, or Phase Voltage

VAB = VAN – VBN = √3VΦ

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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°.

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Summary

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Phase Currents

Line Currents

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Using the Tip-to-Tail Method

-ICA

IaA = √3IΦ/-30°

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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°.

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