Assessing DP value of a power transformer considering thermal ageing and paper moisture

ANDRES ARTURO ROMERO QUETE; DIEGO XAVIER MORALES JADAN; RICARDO DAVID MEDINA VELECELA; GIUSEPPE RATTA; ENRIQUE ESTEBAN MOMBELLO

Power Transformer Condition Monitoring and Diagnosis

The Institution of Engineering and Technology

Lugar: Londres; Año: 2018; p. 87 - 124

Current power transformer (PT) ageing models are approximations to reality basedon experimental and theoretical evidence; these models are simplifications ofcomplex interactions inside units, because of that loss-of-life results could be presentedin a wide range. In PT decision-making context?investment, replacementor maintenance, this amplitude could lead inadequate actions and, in extreme cases,might compromise technical operation and profitability.Solid insulation failure is the leading cause of end-of-life of PTs, insulationpaper is composed by long fibers of cellulose; the average length of these fibers iscalled degree of polymerization (DP), it is widely accepted that DP value is a goodindex of PT loss-of-life.Considering the above, this chapter presents a holistic methodology for solid insulation ageing assessing based on all thermal degradation process (oxidation, hydrolysis and pyrolysis) and the influence of paper moisture dynamics.Paper moisture is estimated using as input external variables such as hot-spottemperature, transformer technical data and measurements regarding oil moisture,in order to consider uncertainty in oil moisture growing, arithmetic-Brownianmotion(ABM) algorithms are presented.For illustrating the application of this method, DP value of two units isassessed; available information for this example are hourly profiles of load andambient temperature and yearly moisture in oil samples for a period over 15 years.