esidual lifespan estimation index in power transformers based on condition

Abstract

Oil-immersed power transformers are highly reliable electrical machines, designed to achieve a lifespan of 20 to 35 years, for which it is necessary to assess their condition based on international standards. There is evidence that some transformers have reached up to 60 years of operation, including proper maintenance. In general, based on historical data, a power transformer is expected to operate satisfactorily up to 40 to 45 years. The assessment of a power transformer based on recognized international standards has not considered the operating context and the possible repairs carried out on this. For this reason, a certain uncertainty is generated for those responsible for the operation, in relation to the life expectancy and the progressive deterioration of the machine in accordance with what different manufacturers offer. Therefore, having a non-invasive assessment methodology is becoming increasingly necessary in order to consider factors related to: i) the power transformer insulation system; and, ii) historical data collected from condition-based maintenance, both dielectric and online condition monitoring. The methodology must consider that deterioration due to the thermal effect has been the main failure mode, since the increase in temperature progressively deteriorates the insulation system, irreversibly, mainly in the dielectric paper (which can cause premature aging). This work presents a new methodology based on calculating a residual life span considering its dielectric condition and operational aspects. The results obtained showed that the residual life of a power transformer must be estimated including its operating context in the calculation, in order to consider its effects on the estimated values.