Design and Testing of Large 2 Pole Variable Speed Pump Motors with Well Damped Rotor Natural Frequency

High-speed induction motors are widely used in conjunction with frequency inverters to operate in different speeds and operating points. This solution is commonly found in the oil and gas industry and more particularly on liquid pipelines since it allows huge operational flexibility. However, on large electric motors many times it is not possible to avoid critical speeds within the operating range. Once these frequencies are excited, the vibration response of the equipment is high leading to mechanical and human risks. In these cases, the resonance region must be well damped to meet the API 541 5th Edition vibration levels. This paper will also highlight the importance of the multi-plane balancing as defined in ISO 21940 and a real example of an 7,300 HP 2-pole pump motor applying sleeve bearing.