Resumo:
In this work, the thermal behavior of a 5 kVA three-phase dry transformer was analyzed
when subjected to the application of distorted loads and the efficiency of a forced cooling
system was obtained using the ®software. Experimental tests showed
temperatures above the transformer insulation limit. The emissivity of the core surface
was determined with a thermal imager. The ® program was also used to model
the fluid in the numerical simulation of the heating of the transformer core under the effect
of loading and cooling. Comparisons were made between experimental and numerical
temperatures to validate the methodology. Values of local and average convective heat
transfer coefficients and local and average Nusselt numbers were calculated numerically
and compared with the literature. The results obtained showed that the temperature
residues showed average differences of less than 1% after 300 min of testing. An
improvement was observed, compared to the literature, in numerical results when
modeling the fluid. As no empirical correlations for Nusselt number and heat transfer
coefficient that approximated the core geometry were found in the literature, this work
was a great contribution to making up for this lack. The experimental and numerical
temperatures reached 20 °C above the transformer insulation limit, confirming the need
to use an efficient cooling system.
