Calculation of the forced, directed oil-circulation rate through a transformer cooling system

On the basis of hydrodynamic theory and of data obtained by measurement on largescale models, a method is presented for calculating the overall oil flow and its components through the individual transformer cooling ducts in the case of forced, directed oil circulation. Following a preliminary hydraulic calculation it is possible to suggest suitable design adjustments so as to render the temperature-rise increments in the individual ducts mutually equalised, thus achieving optimum utilisation of the circulating oil. The calculated oil velocities in the individual ducts permit the heat-transfer coefficients to be determined reliably; the oil/air temperature gradients can be established from the known rates of oil flow through the ducts of the coolers.