Numerical and Experimental Methods to Estimate Eddy-Current Losses in Grooved Solid Rotors as Used in Synchronous Machines

Large synchronous machines designed for high-speed operation often feature a solid rotor construction that guarantees the needed robustness against centrifugal forces. The rotor solid steel is exposed to air-gap field ripples due to stator slotting, which cause eddy currents possibly leading to overheating and efficiency issues. Milling circumferential grooves in the solid-pole surface is a common provision to limit such eddy currents. This article proposes a methodology to investigate the effect of grooving on rotor losses using either suited experimental tests or finite element analysis (FEA) of a 3-D model tailored to minimize the computational burden. Such methodology is applied to a custom prototype device, obtaining a good accordance between the results provided by the two independent approaches. This confirms the validity of the proposed solution, which can thus be used to investigate and optimize application-related designs.