“…It was further confirmed through applications that solar radiation can lead to transformer top oil temperature rise by about 3.7 °C, [ 17 ]. Other variables considered by different researchers in thermal dynamic model modifications for TOT and HST estimation to improve on adequacy and accuracy are not limited to tap-changer position, oil viscosity, harmonics in loading, insulation water content, constant or variable thermal resistances taking into account the type, design and capacity of the transformer [ 5 , [16] , [17] , [18] , [19] , [20] , [21] ].…”