Experimental Characterization of Rotary Transformer Prototypes for Wireless Power Transfer on Helicopters

Wireless power transfer is an attractive solution for applications which require strong continuity of the service, high reliability, and low maintenance. Rotary transformers represent a practical embodiment at electrical machine level in all those situations where power needs to be transferred across moving parts, in relative rotation (such on a shaft), by inductive coupling of two separate circuits. For this reason, the use of rotary transformers was investigated from first principles, as a direct replacement of conventional "sliprings", in helicopter rotor blade ice protection systems. The idea is to use one transformer to supply the heaters embedded into the blades, and another one to interface with the temperature sensor in bundle with heaters. In this work, the full-scale prototypes of a power and signal transformer are presented. Their characterization in terms of electrical parameters and power transfer efficiency is summarized, when operated within an equivalent circuit at the nominal frequency, but reduced voltage. The experimental results are then compared with the numerical predictions and the discrepancies analyzed to draw a conclusion on the accuracy of the adopted model, the effectiveness of the implemented solution and the feasibility of the final helicopter application.