Thermal Performance of Ester Oil Transformers with Different Placement of Cooling Fan

Ester oil is becoming a substitute to replace mineral oil for transformers due to higher fire safe, environmental friendly, higher thermal stability and or longer insulation life (transformer life). The chemical composition and molecular structure of ester oil groups of natural ester oil and synthetic ester oil are entirely different from commonly used petroleum based mineral oil. The higher viscous nature of ester oil will increase the oil temperature rise, winding temperature rise, winding gradient and hot-spot temperature due to less convective heat transfer. Hence, the internal and external cooling modes of transformer needs to be analyzed extensively by transformer manufacturer to get an advantageous of ester oil for transformer applications. In this paper, Thermal Hydraulic Network Model (THNM) is effectively utilized to predict top oil temperature rise, bottom oil temperature rise, winding temperature rise, oil flow rate and hot-spot temperature on 12.5/16MVA, 132/11kV transformer winding geometry with different types of ester oil and comparing its results with mineral oil under steady state conditions. In addition, effect of different types of cooling fan mounting arrangements (vertical and horizontal manner) on 4 radiators with 3 cooling fan and 4 radiators with 4 fan are analyzed and its results are compared for ester oil and mineral oil. Temperature rise test is also performed to validate the THNM results.