Torsional Analysis


Torsional Analysis of 10.65 MW Compressor-Gearbox-VFD Motor

DynoMech undertook torsional analysis of a 40 MW Turbine Driven Generator Unit. The torsional train consisted of a 4-pole alternator, with a rated speed of 1500 rpm, a gearbox, with a gear ratio 3 and a steam turbine, with a rated speed of 4500 rpm. The alternator is connected to the gearbox with a low-speed coupling and the steam-turbine is connected to the gearbox with a high-speed coupling. The objective was to ascertain the torsional critical speeds and torque amplification factor under 2-phase terminal short circuit. The criteria to meet safe field-operation were:</p>

The torsional critical speeds shall be at least 10% greater than the motor, compressor operating speeds and 50Hz electrical line frequency.

The torque amplification factor shall not exceed 5.

40 MW Motor-Compressor Torsional Analysis(Click to view)


  • First Torsional Mode – 15.1 Hz

  • Second Torsional Mode – 51 Hz

  • Third Torsional Mode – 199 Hz 





Share Tweet Pin it