Detection of mechanical imbalances during transient torque operating conditions

Mechanical rotor imbalances and rotor eccentricities give rise to specific mechanical vibration, and certain electric, electromagnetic and mechanical harmonics. The extent and location of these harmonics depends on the actual severity of the imbalance, machine supply and load torque. Many fault detection techniques evaluate the spectral components of any of the mentioned electric or mechanical quantities. Such techniques are therefore usually only applicable for steady state operating conditions. To realize an imbalance detection technique working under transient conditions, load dependencies have to be taken into account. In this contribution a technique is used that employs a phase locked loop to track the imbalance-specific harmonics of the electrical power. This technique, therefore, overcomes the slip and load dependency of the imbalance-specific harmonics. The proposed imbalance detection technique is applied to measured data. Results for steady state and transient operating conditions are then compared.