Let's continue our discussion on this topic, focusing on basic operating principles of alternating current (ac) variable-speed drives (vsd's) as applied to three-phase, ac induction motors.
Vsd's have become an important component in building power systems from the standpoint of energy savings. Centrifugal pumps, as well as centrifugal and vaneaxial fans, have variable torque loads. The torque required to drive the fan or pump is proportional to the square of the speed. Since torque and horsepower (hp) are related to each other as a function of speed, the hp requirement is proportional to the cube of the speed.