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Understanding Star and Delta Connections

May 10, 2025

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Easy Guide to Star and Delta Electrical Connections

Understanding Sine Waves and Three-Phase Supply

  • Single Phase Supply

    • Example: 230V UK 50Hz
    • Shape of voltage: sine wave

  • Three-Phase Supply

    • Involves three identical sine waves: L1 (brown), L2 (black), L3 (gray)
    • L2 starts 120 degrees after L1; L3 starts 120 degrees after L2
    • Generated by coils displaced by 120 degrees

Adding Up Sine Waves

  • Phaser Addition
    • Representation of sine waves
    • Example: 230V supply drawn to scale (1cm = 20V)
    • L1 and L2 are 120 degrees apart; total length ~19.9cm
    • Resulting ratio: 19.9/11.5 = 1.73 (root 3)
    • Root 3 (1.732) is standard in three-phase installations

Star (Y) Connection

  • Configuration

    • Consists of three coils connected to a central point (star point)
    • Lines L1, L2, L3 connect to the coils

  • Currents and Voltages

    • Phase Current
      • Flows in the phase windings (coils)
      • Equal across all windings if balanced load
    • Line Current
      • Flows in the external lines L1, L2, L3
      • In star connection: IL = I_phase
    • Phase Voltage
      • Measured across each winding to the star point
      • No need for a neutral, just access to star point
    • Line Voltage
      • Measured between any two external lines
      • Relationship: VL = V_phase * root 3*

Delta (Ξ”) Connection

  • Configuration

    • Three coils connected in a triangle shape
    • No central point, thus no neutral possible

  • Currents and Voltages

    • Phase Current
      • Flows through the coils
    • Line Current
      • Measured in lines connected to the triangle
      • IL = I_phase * root 3 (after considering phase angle)
    • Phase Voltage
      • Measured across each coil
    • Line Voltage
      • Measured between any two external lines
      • VL = V_phase (no difference between line and phase voltage)*

Conclusion

  • Star and Delta connections each have unique characteristics and applications
  • Understanding phasor relationships and root 3 factor is critical for calculations
  • Watch related video for in-depth calculations and applications

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