Which configuration is used to increase the starting torque of a three-phase motor?

The delta connection is commonly used to increase the starting torque of a three-phase motor. In this configuration, each winding of the motor is connected end-to-end to form a closed loop, allowing for higher phase currents and, consequently, a greater torque during startup. This is particularly advantageous in applications where motors face significant load at startup, as the increased torque helps to overcome initial inertia and start the motor effectively.

In contrast, a star connection (or Y connection) is typically associated with lower starting currents and lower starting torque. While this configuration helps reduce the overall current draw when starting, it does not provide the same level of torque output as the delta configuration. Therefore, while star connections might be beneficial for some applications, they are not ideal when high starting torque is critical.

Series connections, while relevant in other contexts, are not applicable to three-phase motors in the same way as star and delta configurations. They are used in different types of circuits, typically in DC motors, where they wouldn't be appropriate for the starting torque of an AC three-phase motor. Overall, the delta connection stands out as the suitable choice for enhancing starting torque in three-phase motors.