Rating considerations for squirrel cage induction motors operated with variable frequency drives

The author addresses rating considerations for squirrel cage induction motors operated with variable-frequency drives. The motors addressed are assumed to be larger than 20 HP and of three-phase design. It is shown that for the majority of applications, consisting of centrifugal fans or pumps, standard motors with 1.15 to 1.2 service factors can be rerated for inverter use with 1.0 service factors. For more rigorous applications, such as constant torque, constant horsepower, or reciprocating loads, the selection of motors more suited for inverters has been gaining popularity.<>