DOL (Direct On Line) starter and Star-Delta starter are two common methods used to start induction motors.

Direct On Line (DOL) Starter

• Principle: The motor is directly connected to the power supply from the start.
• Starting Current: The starting current is typically 6-7 times the full-load current, causing a significant voltage dip and potential mechanical stress on the motor and connected equipment.
• Applications: Suitable for applications with low to moderate starting torque requirements and where voltage dips are acceptable.

Star-Delta Starter

• Principle: The motor is initially connected in a star configuration, reducing the starting current to about 1/3 of the DOL starting current. After a short time, the motor is switched to a delta configuration, increasing the voltage and torque.
• Starting Current: The starting current is significantly lower than DOL, reducing the impact on the power supply and mechanical stress on the motor.
• Applications: Ideal for applications with high starting torque requirements or where voltage dips are a concern.

Key Differences:

In summary, DOL starters are simpler and less expensive but can cause significant voltage dips and mechanical stress, especially for large motors. Star-Delta starters, on the other hand, offer a more controlled start and are suitable for applications with high starting torque requirements. The choice between DOL and Star-Delta starters depends on the specific needs of the application and the desired trade-offs between starting current, voltage dip, and cost.