Which reduced voltage starter uses a switching arrangement to connect the windings of three-phase motors in different configurations during startup and normal operation?

Which reduced voltage starter uses a switching arrangement to connect the windings of three-phase motors in different configurations during startup and normal operation?

• A. Across-the-line starters
• B. Star-delta starters
• C. Autotransformer starters
• D. Soft starters

Answer: (D)

This question tests recognizing how some reduced-voltage starters achieve lower starting current by changing how the motor windings are connected. A star-delta starter switches the windings between two configurations. At start, the windings are connected in star, which reduces the voltage across each winding and lowers starting current and torque. Once the motor nears the desired speed, the connections switch to delta, applying full line voltage to each winding for normal operation. This winding-configuration switching is the key feature that defines star-delta starters. Soft starters, by contrast, use solid‑state devices to throttle voltage and ramp it up during starting but do not reconfigure winding connections. Autotransformer starters reduce voltage through transformer action, and across-the-line starters apply full voltage directly.

This question tests recognizing how some reduced-voltage starters achieve lower starting current by changing how the motor windings are connected.

A star-delta starter switches the windings between two configurations. At start, the windings are connected in star, which reduces the voltage across each winding and lowers starting current and torque. Once the motor nears the desired speed, the connections switch to delta, applying full line voltage to each winding for normal operation. This winding-configuration switching is the key feature that defines star-delta starters.

Soft starters, by contrast, use solid‑state devices to throttle voltage and ramp it up during starting but do not reconfigure winding connections. Autotransformer starters reduce voltage through transformer action, and across-the-line starters apply full voltage directly.