introduction to three phase power
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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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Presentation Transcript
what is three phase power
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
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
Phasor (Vector) Form for abc

Vc=Vm/+120°

Va=Vm/0°

Vb=Vm/-120°

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phasor vector form for abc1
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
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
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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definitions1
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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slide15
Phase Voltages

Line Voltages

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using the tip to tail method
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
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
Summary

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slide22
Phase Currents

Line Currents

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using the tip to tail method1
Using the Tip-to-Tail Method

-ICA

IaA = √3IΦ/-30°

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conclusions for the delta connection
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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