Improving Motor Quality by Trim Balancing

Large electric motors 1,000 horsepower and up are often difficult to balance effectively, even with the sophisticated hard bearing machines of today. Typically, large wound rotors or migrating barred rotors with sleeve bearings will exhibit different characteristics at actual running speed as compared to slow turning balancing machines. Forces on rotor components at running speed, uneven thermal growth and bearing clearances can contribute to unexpected shaky test runs. It is especially a concern with two-pole sleeve bearing motors. A reasonably quick and simple motor quality procedure is to perform a balancing routine at running speed to trim out the effects of what the balancing machine may have missed.