The star-delta connection, also known as the wye-delta connection, is a common method used in electrical engineering to connect three-phase electrical motors. It involves changing the motor's configuration from a star (Y) connection during starting to a delta (Δ) connection during normal operation. This transition helps to reduce the starting current and torque while maintaining efficient operation.

Here's how the star-delta connection works:

1. Star Connection (Y Connection):

   • In the star connection, each terminal of the motor winding is connected to one of the three phases of the electrical supply, and the other ends of the windings are joined together at a common point known as the neutral or star point.
   • This configuration is typically used during the starting phase because it allows the motor to draw less current from the supply, reducing the initial starting torque and preventing excessive stress on the motor and the electrical system.

2. Delta Connection (Δ Connection):

   • Once the motor has reached a certain speed (usually around 80% of its rated speed), the connection is switched to a delta configuration.
   • In the delta connection, the ends of each winding are connected together in a loop, forming a triangular configuration. This arrangement allows the motor to operate at its full rated voltage and provides higher torque for normal operation.
   • While the delta connection increases the voltage and torque, it also increases the current drawn from the supply compared to the star connection.

The switching between the star and delta connections is typically achieved using a special starter or contactor called a star-delta starter. This starter initially connects the motor windings in star configuration for starting and then switches to delta configuration once the motor has gained sufficient speed.

Benefits of Star-Delta Connection:

1. Reduced Starting Current: The star-delta connection reduces the starting current drawn by the motor, which helps prevent voltage dips and minimizes stress on the electrical supply system.
2. Smooth Starting: By gradually increasing the motor's speed and torque, the star-delta connection provides a smoother and controlled starting process, reducing mechanical and electrical stress on the motor and the connected machinery.
3. Energy Efficiency: While the star-delta connection initially reduces the starting torque and current, it still provides efficient operation during normal running conditions in the delta configuration, ensuring energy-efficient performance.

Overall, the star-delta connection is a widely used method for starting three-phase induction motors efficiently and reliably in various industrial applications.