Starting now-a review of reduced voltage AC motor starters

The wide acceptance of variable frequency (VF) AC drives in textile, fiber and film applications has led to their use to control motor starting performance, even where the motor is run at a constant speed. The benefit of a VF drive in such applications lies primarily in its ability to provide a gentle start, in which the torque applied to the load and the inrush current from the power line are not allowed to interfere with the process or with adjacent equipment. The technology used in a VF drive, which draws power from the line, converts it to DC and inverts it to AC at a different voltage and frequency, can also control voltage alone. The author describes solid state and electromechanical starters, and VF drives. Performance during and after a start are discussed, as is performance when stopping. A brief overview of available accessories for overcurrent protection diagnostics and enclosures is given. General trouble-shooting and spare parts issues are also noted. Applications and future trends are briefly considered.<>