Environment Influence on Lifetimes of Power Transformers

Abstract

This paper presents a study on the influence of the environmental factors (respectively, ambient temperature and solar radiation) on hot spot temperatures and the consumed and remaining lifetimes of power transformers. In this regard, 15 identical 105 MVA distribution transformers are considered, loaded with the same load, and operating in 15 areas of Romania (with different climatic characteristics). Using the equations recommended by IEC 60076-7 (modified in the case of the presence of solar radiation) the values of oil temperature, hot spot temperatures and consumed and remaining lifetimes in two days from July 2020 are calculated, both in the presence and in the absence of solar radiation. It is shown that the values of the hot spot temperature and of the consumed lifetimes differ from one locality to another and that they increase with the increase of the ambient temperature and the intensities of the solar radiation. Finally, it is shown that the results obtained can be used to develop more efficient maintenance programs for distribution power transformers.

A New Hybrid Model to Evaluate the Loss of Life of Power Transformers

“…The relative aging of the transformer is determined using eq. (2). It shows the equivalent aging factor at the reference temperature for the specified time and temperature [11]:…”

“…If the temperature variation curve is unknown, eq. ( 9) can be used to determine the relative loss of life (Dcr) in the range ∆t [2,11,14,15]:…”

“…The hot-spot temperature of transformers is used in these standards, which define the thermal models, to assess the loss of life. However, these models only apply to temperatures reached at nominal loads and overloads, not the entire temperature range [2].…”