Modeling Power Transformer Field Drying Processes

Abstract

Power transformer field drying is becoming a habitual practice because water is damaging for transformer insulation, and its presence increases the probability of unexpected failures. Different drying methods are currently being used by electrical companies but sometimes without a profound knowledge of the drying processes involved, and consequently drying is not as effective as would be desirable.Physical models have been developed by the authors in order to study power transformer drying processes. The use of the models will help to plan more effective drying processes, tailoring the drying times and drying conditions for each particular case. The models have been tested in a test transformer fitted with sensors. In order to monitor the process, insulation samples were extracted from the transformer before and after the process.In this article, several transformer drying procedures are described. Theoretical models and their experimental validation processes are reported. Finally, some general recommendations about transformer drying in the field are provided.

Effect of Oil Regeneration on Improving Paper Conditions in a Distribution Transformer

“…It was decided to execute this stage at a system temperature of Normal industrial practice comprises of conducting the oil regeneration till satisfactory values for the oil parameters are reached. Previous studies [6,[15][16][17][18][19] have mainly focused on monitoring the condition of the oil. In order to gain a deep understanding of the effect of this process on the paper moisture and LMA, we chose to add an additional stage of processing beyond the 'cleaning of the oil'.…”

“…Interpreting this reduction along with the various experimental and simulation-based drying curves and models proposed in the literature [15,17,[22][23][24][25][26][27], it is possible that the moisture could reduce further with prolonged circulation. However, several factors could affect this, including the limitation of the off-line hot oil circulation process which does not heat the insulation from inside (i.e., affecting mainly the outer layers of insulation), and the thickness of the paper which directly affects the penetration of the drying.…”

Moisture sensor to characterize transformer solid insulations in transformers under non-equilibrium conditions

“…In the next stage of the work, the measurements will be processed by software to calculate the moisture distribution inside the insulation. To this aim, theoretical models of moisture diffusion in oil-paper insulation will be used [3], [4].…”

A review of moisture diffusion coefficients in transformer solid insulation - Part 2: Experimental validation of the coefficients

“…Moisture dynamics in cellulosic insulation can be estimated using a mathematical model of diffusion based on Fick's second law [1], [2]. The main parameter of this mathematical model is the moisture diffusion coefficient, and the precision of the model is dependent on using an accurate value of this coefficient.…”

“…The drying experiments were simulated using a diffusion model [2], solved by finite element analysis. The simulations were carried out using the diffusion coefficients proposed by the various researchers.…”