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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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ECE 441

ECE 441

• 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

ECE 441

• 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

Vc=Vm/+120°

Va=Vm/0°

Vb=Vm/-120°

ECE 441

Vc=Vm/+120°

Va=Vm/0°

Vb=Vm/-120°

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

ECE 441

• 2-pole (North-South) rotor turned by a “prime mover”

• Sinusoidal voltages are induced in each stator winding

ECE 441

• (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

ECE 441

• 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

Line Voltages

ECE 441

Vector addition to find VAB=VAN-VBN

-VBN

ECE 441

-VBN

VΦ = Line-to-Neutral, or Phase Voltage

VAB = VAN – VBN = √3VΦ

ECE 441

• 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

ECE 441

Line Currents

ECE 441

Vector Addition to find IaA=IAB-ICA

-ICA

ECE 441

-ICA

IaA = √3IΦ/-30°

ECE 441

• 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