Influência da carga não linear no resfriamento de transformador à seco por convecção natural e forçada

Abstract

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 ð€œ¥ð€œ±ð€œ¯ð€œµð€œ±ð€œ®Â®software. Experimental tests showed temperatures above the transformer insulation limit. The emissivity of the core surface was determined with a thermal imager. The ð€œ¥ð€œ±ð€œ¯ð€œµð€œ±ð€œ®Â® 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.