Alternator delivers power to a system which has high speed operations such as aircraft, marine industry, and automobile industries. So, it is necessary to evaluate the performance of this alternator during high speed operations. Finite Element Analysis (FEA) is an effective tool to analyze the performance of electrical machines with certain boundary conditions. In this paper, the FEA analysis of the 5 KW alternator with two different rotor structures for high speed operation is presented. The transient electromagnetic FEA has been carried out which forms the basis for thermal modeling and thermal analysis of the alternator. Finally the overall electromagnetic and thermal performance of a prototype alternator with different rotors is compared experimentally. © 2017 Faculty of Engineering, Alexandria University