# Design of a Rotary Transformer for Installations on Large Shafts
## 6 Conclusions  
Among all the possible applications of rotary transformers, their installations on relatively large shafts are of great interest, since they allow us to use those devices in aerospace applications, such as helicopters, trains, cars and ships, as well as in many industry applications. This paper proposes an example of a preliminary design for a transformer that should transfer around 4 kW from primary to secondary, considering a resistive load of 20 \(\Omega\). To this aim, three cascaded optimization procedures were carried out. The grid-search and the genetic optimizations were aimed at finding the best geometrical and electrical arrangements for the rotary transformer by applying some constraints on its size. Because of its installation on shafts, one goal of these procedures was the minimization of the weight of the device, which translates to a minimization of the additional inertia applied on the rotating part of the system. In these optimizations, special attention was also paid on setting sufficiently conservative limits on the current density on the coils and saturation of the two magnetic cores. The third step was meant to reduce the weight of the magnetic core, in addition to limiting the risk of cracking the bulk ferrite. These two goals were achieved by slicing the cores. This design choice of splitting the main structure using small C-ferrite cores was validated using a reduced-scale prototype. Moreover, this new design was realized following the same procedure reported in this paper. Therefore, this validation is intended both to check the actual possibility to transfer power from primary to secondary using sliced cores and to prove that the developed design steps provide the desired results. Additionally, the verification highlights that the models developed during this study provide accurate predictions despite all the uncertainties encountered in the modelling phase. This can be realized comparing simulation and measurement results. ANSYS Maxwell was used mainly to estimate the inductance matrix of the device; however, it had a great mismatch in the prediction of the harmonic content of each waveform. This deviation was mainly due to the impossibility of imposing the same input voltage adopted in the real system. Conversely, this constraint can be set in Simulink(r); in this framework, the identified inductance matrix can be combined with working conditions which can deviate from the nominal conditions, allowing us to predict voltages, currents and transferred power for a wide set of working points, reducing the simulation time (compared to 3D FEM co-simulation runs). Future work can focus on the realization of a prototype able to transfer 3-4 kW from primary to secondary tailored for a specific application and on the validation of the prediction on the full-size device.  
Conceptualization, M.B., F.C.D. and M.M.; Formal analysis, N.T. and M.M.; Funding acquisition, M.B., F.C.D. and M.M.; Investigation, N.T.; Methodology, M.S.C.; Project administration, M.B.; Supervision, M.B., M.S.C., F.C.D. and M.M.; Validation, N.T.; Writing--original draft, N.T.; Writing--review and editing, M.B., M.S.C., F.C.D. and M.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Frequency** & **Quantity** & **Measurement** & **Simulation** & \(|\Delta|\) \\ \hline \multirow{3}{*}{5 kHz} & \(i_{1}\) RMS & 2.333 A & 2.251 A & 3.64\% \\ \cline{2-5}  & \(i_{2}\) RMS & 0.909 A & 0.945 A & 3.83\% \\ \cline{2-5}  & \(v_{2}\) RMS & 4.543 V & 4.724 V & 3.83\% \\ \hline \multirow{3}{*}{20 kHz} & \(i_{1}\) RMS & 0.938 A & 0.997 A & 5.86\% \\ \cline{2-5}  & \(i_{2}\) RMS & 0.537 A & 0.574 A & 6.53\% \\ \cline{2-5}  & \(v_{2}\) RMS & 2.684 V & 2.871 V & 6.53\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Measured vs. simulated RMS values for currents and voltages. Simulations were carried out in Simulink®, see Figures 13 and 14.