This paper presents a thermal study to define the appropriate correlations allowing the determination of the convective heat transfer coefficient over large parallel rectangular fins for a permanent magnet synchronous generator coil. For this purpose, an experimental setup is developed for both horizontal and vertical orientations and different input currents. The experimental results are compared with the analytical method, based on correlations proposed in the literature, which are generally limited for a small range of heat sinks. The results show that the analytical calculation based on Jone's correlation for the horizontal case and Tari's correlation for the vertical case, have good agreement with the experimental data. These correlations are experimentally validated for the calculation of the natural convection coefficients of large rectangular fins arrangement too. (C) 2018 Elsevier Ltd. All rights reserved.