Understanding Phasor Diagrams

The phasor diagram represents the voltage and current phasors for a three-phase electrical system. Here’s a general guide for understanding and documenting the diagram:

Key Components of the Phasor Diagram

1. Voltage Phasors:

   • Va (Red Solid Line): Represents Phase A voltage.
   • Vb (Green Solid Line): Represents Phase B voltage.
   • Vc (Blue Solid Line): Represents Phase C voltage.

2. Current Phasors:

   • Ia (Red Dotted Line): Represents Phase A current.
   • Ib (Green Dotted Line): Represents Phase B current.
   • Ic (Blue Dotted Line): Represents Phase C current.

Interpretation

• Voltage Phasors: These are represented as solid lines, indicating the three-phase system's voltages, with their respective magnitudes and phase angles.
• Current Phasors: These are represented as dotted lines and correspond to the currents for each phase.
• Angle Reference: Phase A voltage (Va) is used as the reference with 0° phase angle.
• Phase Relationships: The phase angles demonstrate the typical 120° phase shift between each phase for a balanced three-phase system. Any deviation indicates an imbalance.
• Magnitude: The magnitude of the phasors is proportional to their amplitude in the system.

Documentation Details

1. Title: Phasor Diagram for Three-Phase Voltage and Current

2. Legend:

   • Solid Lines: Voltage Phasors (Va, Vb, Vc)
   • Dotted Lines: Current Phasors (Ia, Ib, Ic)

3. Units:

   • Voltage Magnitude: Typically measured in volts (V).
   • Current Magnitude: Typically measured in amperes (A).
   • Phase Angle: Measured in degrees (°).

4. Key Observations:

   • The phase angles between the voltages and currents indicate the power factor and the type of load (resistive, inductive, or capacitive).
   • The diagram highlights any phase imbalance if the angles or magnitudes deviate significantly from expected values.

5. Applications:

   • Analysis of three-phase systems for load balancing.
   • Detection of harmonic distortions or system anomalies.
   • Power factor correction and energy efficiency optimization.

Example

• Voltage Phasors:

  • Va (Red Solid Line): magnitude of 122.86 and an angle of 0°.
  • Vb (Green Solid Line): magnitude of 122.41 and an angle of -119.8°.
  • Vc (Blue Solid Line): magnitude of 122.53 and an angle of -239.7°.

• Current Phasors:

  • Ia (Red Dotted Line): magnitude of 77.90 and an angle of -21.9°.
  • Ib (Green Dotted Line): magnitude of 78.63 and an angle of -143.5°.
  • Ic (Blue Dotted Line): magnitude of 78.20 and an angle of -262.3°
•  

Therefore, the power factor is (cosine of angle between voltage and current:

• PFa => cos(0° - (-21.9°)) => cos(21.9°) = 0.9278
• PFb => cos (-119.8° - (-143.5°)) => cos (23.8°) = 0.9146
• PFc => cost (-239.7° - (-262.3°)) => cos (22.6) = 0.9232