As compared to across-the-line starters, reduced voltage starters:

As compared to across-the-line starters, reduced voltage starters:

• A. Increase starting current inrush
• B. Reduce starting current inrush
• C. Have no effect on current
• D. Increase energy consumption during start

Answer: (B)

Reduced voltage starters limit the voltage that reaches the motor during start-up. An induction motor draws a large inrush current when started with full line voltage because the rotor is stalled and the impedance is low. By lowering the applied voltage, the current needed to start the motor is reduced, so the inrush is much smaller. This helps protect the electrical supply and reduce mechanical stress on the drive. At the same time, starting torque also drops (torque is roughly proportional to the square of the applied voltage), so acceleration is gentler. Because the current during start is reduced, energy used in the starting interval is typically lower, not higher. The other statements don’t fit, since reducing voltage does not increase inrush or leave current unchanged, and it does not typically increase start energy.

Reduced voltage starters limit the voltage that reaches the motor during start-up. An induction motor draws a large inrush current when started with full line voltage because the rotor is stalled and the impedance is low. By lowering the applied voltage, the current needed to start the motor is reduced, so the inrush is much smaller. This helps protect the electrical supply and reduce mechanical stress on the drive. At the same time, starting torque also drops (torque is roughly proportional to the square of the applied voltage), so acceleration is gentler. Because the current during start is reduced, energy used in the starting interval is typically lower, not higher. The other statements don’t fit, since reducing voltage does not increase inrush or leave current unchanged, and it does not typically increase start energy.