Prediction of Synchronous Generator Fatigue Life in Islanded Microgrids With Harmonic Loads

This paper investigates the prediction of Synchronous Generators (SG) fatigue life span regarding current harmonic distortion in islanded microgrids. An analytical approach is proposed to calculate the harmonic components in the oscillating electromechanical torque of SGs feeding nonlinear loads in these microgrids. Moreover, a procedure is proposed to determine the damage of torsional vibration caused by these harmonics to the shaft of SGs. The proposed approach considers the cumulative effect of torque harmonics to predict the fatigue life. In a case study, the fatigue life span is calculated for an SG feeding a typical microgrid involving rectifier loads considering different loading and harmonic distortion conditions. Results show that harmonic distortion can consume the fatigue life of SGs significantly. Moreover, various effects of positive, negative, and zero sequence harmonics in the stator currents on the fatigue life of SGs are highlighted. The sensitivity of SG fatigue life to harmonic distortion magnitude, harmonic order, the shaft diameter, and windings parameters are also investigated.