Additional Losses of Electrical Machines Under Torsional Vibration

Abstract

Electric drive trains have a torsional rigid-body vibration mode at a small, non-zero frequency. If an excitation occurs close to this frequency, the vibration amplitude may grow large and the electrical machine may suffer from significant additional losses. Standards set constraints on the oscillating torque in the shaft coupling and on the harmonics of line current. They indirectly limit the vibration amplitude and losses of the machines.Time-discretized finite-element analysis was used to study the losses of six induction and six synchronous machines under torsional vibration restricted by the constraints above. All the machines were supplied from sinusoidal voltage sources. In the worst cases of the induction motors, the vibration increased the electromagnetic total loss by about 20%. The constraints on synchronous machines are milder than those for induction machines. In this case, the maximum increase of the loss was 75%. The limit on the harmonic currents is essential from the loss point of view. Without this limit, the additional loss at the rigid-body resonance would lead to a temperature rise high enough to destroy the insulation system of the machine.The method of loss analysis was validated by measured results.

Torsional Vibration Mitigation by Harmonic Inversion through SPWM Carrier Signal Control

“…In addition, even mild vibrations can cause an increase in the additional losses of synchronous machines, which depend on the vibration amplitude and frequency. Moreover, the thermal status can reach critical high levels because of vibrations [1].…”

Reducing the Losses of Electrical Machines Under Torsional Vibration

“…The induction machine is small for compressor applications. It is included as it was earlier tested under torsional vibration to validate the loss computation methods [3]. The synchronous motor was specially designed for a compressor drive.…”

“…The method of loss analysis was validated for the 37 kW motor in [3]. No further validation is given in the present paper.…”

“…The natural frequency of the rigid-body mode is typically some Hertz for large-power drives and some tens of Hertz for smaller ones. At such a rigid-body resonance, the electrical machine may suffer from significant additional losses [3].…”

Review of Medium Voltage High Power Electric Drives

“…Critical operation points, where the rotational speed of the motor causes harmonics and interharmonics coincident with one of the shaft torsional natural frequencies, can cause resonance and lead to system failure (174) (175) . Beside the conventional losses, a recent study shows that additional losses are introduced in the electric motors under torsional vibration (184) .…”