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How to select the right Variable Speed Drives?

In selecting a variable speed drive, consideration must be given to the load characteristics of the driven machinery. The three basic load categories can be summarized as follows:
  • Constant-torque loads require a constant motor torque throughout the operational speed range.
  • Loads of these types are essentially friction loads such as traction drives & conveyors.
  • Variable-torque loads require much lower torque at low speeds than at high speeds. Loads that exhibit variable torque characteristics include centrifugal fans, pumps, & blowers.
  • Shock (impact) loads require a motor to operate at normal load conditions followed by a sudden, large load applied to the motor. An example would be the sudden shock load that results from engaging a clutch that applies a large load to the motor (as it would during a hard start). This current spike could cause the variable speed drive to trip as a result an excessive motor current fault.