Abstract: Power transformers are electrical machines that allow us to transport electric energy, with reduced losses, from generation stations to consumption points. This definition gives us an idea of the number of transformers that are used in power distribution systems worldwide. The main problem that may affect power transformers is the operation at high temperature. This paper summarizes the results of a postmortem temperature estimation carried out on an 800 kVA distribution transformer. Two methodologies are considered for estimating the temperature distribution in the windings of the machine. The first is based on the calculation of the degree of polymerization and the second is obtained from the tensile strength index. By knowing the value of these two magnitudes for a new and for an aged paper, and the period of operation of a transformer, the temperature distribution along the height of the windings can be estimated. None other previous works have used the tensile strength of winding paper for temperature distribution estimation. With these results and the loading regime records, similar transformers still in operation can be operated in an alternative manner and future designs can be improved.

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