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The winding hot spot temperature of the oil-immersed power transformer is an important parameter factor in the long-term life of the transformer. It has a great influence on the transformer insulation aging and a close relationship to the transformer top oil temperature which is used to indicate the operating conditions of the transformer. In view of the hot-spot rise over top oil temperature is a function dependent on time as well as the transformer loading, this paper developed a simple thermal model to calculate transformer hot spot temperature based on thermal-electrical analogy, which incorporated the nonlinear thermal resistance and application of oil viscosity and winding losses changes with temperature. The model parameters are estimated by Levenberg-Marquardt method. In the end, The comparison of experimental data under various loadings and model outputs shows the accuracy and efficiency of the proposed model, which suggest that this presented model can describe the thermal behavior of oil-immersed transformer more accurately. [ABSTRACT FROM PUBLISHER]

Temperature, especially the hot spot temperature (HST) and top oil temperature (TOT), has played the important rule and became the most effective factor in determination of the insulation life of the transformer. The prediction of HST and TOT is very important for estimating the loss of life (LOL) of the transformer in power system. Therefore, an accurate technique is needed for solving the thermal models. This paper presents a numerical method which can accurately calculate the HST and thus provides an effective evaluation of LOL of the transformer. An alternative solution for solving the thermal model is proposed in this work and results are compared with the actual temperature, measured by fiber optic sensors and placed on the 30MVA power transformer. [ABSTRACT FROM PUBLISHER]

As the population of transformers in service increases and becomes older, more attentions are focused on their availability and reliability. Through decades' progress, it is undeniable that considerable advances have been achieved on the techniques of fault diagnosis and condition assessment for oil-immersed transformer, for its great importance in the whole transmission and distribution (T&D) system. However, still insufficient research work focused on how to evaluate transformer's aging condition. This paper represents Aging Index (AI) which is a practical tool that combines the results of routine inspections, and site and laboratory testing to estimate the aging condition. This Aging Index calculation considers not only typical test results such as dissolved gas analysis (DGA), oil quality, furan, and dissipation factor, but also other parameters such as top oil temperature and hot spot temperature estimating. And further, Frequency Domain Spectroscopy (FDS) is also introduced as a novel non-destructive testing technique to estimate remained life expectancy. Moreover, a software system based on transformer's electrical and thermal parameters is developed correspondingly, by using a multi-parameters analytic approach. This system is expected to help to decision-making and replacement planning and to have good application prospects. [ABSTRACT FROM PUBLISHER]

This paper reports the development of a numerical model which can predict the temperature distribution in a 5 kVA, 400/400 V, delta - star dry type three phase transformer. The numerical model has been developed using the Commercial Computational Fluid Dynamics Package FLUENT 6.3. Numerical simulations are carried out for different loads. In order to validate the numerical model, experiments are conducted by performing a short circuit test and the numerical results compare well with experimental data. Based on the numerically obtained hot spot temperature, the reduction of life of the transformer is determined using Montsinger Equation. [ABSTRACT FROM PUBLISHER]