Torsional Vibrations in Electric Motor Driven Compressor Trains

Electric Motor Drives in the power range from 1,000 to 60,000 HP are often used to drive centrifugal compressors. One of the key reliability issues is the treatment and management of torsional vibrations. The torsional behavior impacts shaft endurance limits and operational flexibility. In this paper, a methodology used to ensure torsional integrity in standardized Electric-motor-driven gas compressor packages is described. The electric drive ("drive")may be a variable frequency drive (VFD), or a constant speed electric motor. In addition to steady-state torsional analysis, the drive harmonics from electrical sources (steady-state pulsation) and the drive’s characteristics at fault-events such as phase-tophase faults (transients) are incorporated into the torsional model to perform a complete torsional analysis. Shaft stresses are evaluated over a wide range of motor frame sizes, and consequently couplings and gearboxes. Couplings and gearboxes are designed to handle the mean torque and peak transient torques as appropriate.