Numerical investigation of influences of coolant types on flow distribution and pressure drop in disc type transformer windings

In this paper dimensional analyses of flow distribution in and pressure drop over disc-type transformer windings in an oil forced and directed (OD) cooling mode are presented. Computational fluid dynamics (CFD) parametric sweeps were conducted to quantify the dimensionless relationships obtained from the dimensional analyses to form predictive correlation equation sets. With the help of the correlation equation sets, the influences of coolant types including a mineral oil, a gas-to-liquid (GTL) oil and a synthetic ester on flow distribution in and pressure drop over a winding model were investigated. It was found that the synthetic ester, which has a higher viscosity than the others, could be advantageous in terms of suppressing reverse flow and getting a relatively more uniform flow distribution at the cost of a higher static pressure drop.