To study the heat transfer performance of a new natural ester, the temperature rise of the windings and oil in a transformer is simulated by a simple experimental setup comprising a coil immersed in the oil and powered by a 50 Hz A.C. supply for 30 mins. Because of the differences in the viscosities for various oils, as noted above, the heat produced by the coil will likely to be conducted and dissipated to the entire oil differently.