Star and Delta Connected 3 Phase Supplies

Star and Delta Connections

• Used in transformers for 3-phase supplies.

• Choice depends on application, load requirements, and desired electrical characteristics.

• Common to use both in different parts of systems to utilize their advantages.

• Example: Delta connection on primary side, Star on secondary side.

Key Differences

Star Connection (Y)

• Voltage Levels: Line voltage = √3 x Phase voltage ; higher voltage transmission, reduces losses.

• Neutral Point: Provides a neutral point for grounding and single-phase supply.

• Reduced Phase Voltage: Phase voltage is lower, beneficial for equipment needing lower voltages.

• Load Balancing: Helps maintain stability and efficiency by balancing loads across phases.

• Starting Torque: Used in motors for reduced starting torque, allowing lower starting currents.

Delta Connection (Δ)

• Higher Current Capacity: Line current = √3 x Phase current ; suitable for heavy loads.

• No Neutral Requirement: Simplifies design, useful in industrial applications.

• Torque Characteristics: Provides higher starting torque, advantageous for electric motors.

• Phase Voltage Equalization: Each load phase directly connected across line voltage for equal voltage drops.

• Reduced Harmonics: Improves power quality by reducing certain electrical harmonics.

Current and Voltage in Star Connection

• Current in Star:

  • Line current (IL) flows through the cable for each load.

  • Phase current (IP) is the current through each load.

• Voltage in Star:

  • Line voltage (VL) between line conductors.

  • Phase voltage (VP) across any load.

Current and Voltage in Delta Connection

• Current in Delta:

  • Line current (IL) flows through the cable supplying each load.

  • Phase current (IP) is the current flowing through each load.

• Voltage in Delta:

  • Line voltage (VL) between line conductors.

  • Phase voltage (VP) across any load.

Additional Notes

• Delta connections do not have a neutral, balancing automatically in delta motors but may face issues with complex and unbalanced loads.