Lifetime reduction of transformers and induction machines

Investigates aging and lifetime reduction of transformers and induction machines due to elevated temperatures caused by harmonics. The additional temperature rise caused by harmonics is defined by a weighted-harmonic factor function which has not yet been published in a textbook. The Arrhenius reaction rate equation is relied on to estimate the reduction in lifetime of motors and transformers due to harmonic voltage magnitudes. Harmonic limits within single- and three-phase power systems are proposed and rigid harmonic spectra are not recommended. The probabilistic and time-varying nature of harmonics and their incurred cost are reviewed. Various operating regimes of electric machines are investigated from a lifetime reduction point of view. Heat flow relations due to radiation and convection are given with their associated thermal equivalent circuits. 11 application examples with solutions and 11 application-oriented problems are included.