Forecasting Transformer Reliability

Abstract

Abstract:In this paper the concept of an integral transformer lifetime model is presented. The model provides the best possible prediction of future behaviour given the data available. It treats remaining life in terms of future failure probability, thereby giving better support to the decision taking process than a mere remaining life estimate. The core of the model is a generic description of ageing processes, coupled to a probabilistic approach. The approach presented utilizes various techniques to reduce the uncertainty that is inherent to modelling processes with incomplete knowledge of the operational history. One technique couples the process model to externally measurable quantities; another technique involves a sensitivity analysis, which shows what additional input data gives the most efficient way to improve accuracy. We will illustrate the approach by applying it to a wellknown degradation process: thermal degradation of the transformer winding insulation.

Calculation of the remaining lifetime of power transformers paper insulation

“…Table I summarizes the quality parameter types [1,7,17]. Ideally, the value of a QP is Loss of life of the paper insulation Fig.…”

“…The results can even be fed back into the physical model to improve the accuracy of the modeling. The concept of QP was introduced for power transformers in [1,7,17] to obtain a measurable quantity which relates the degradation process to an observable quantity.…”

“…The probability of the threshold to have a value between x and x+dx is denoted as p DP_th (x, t)dx. The probability that the threshold is above a certain DP-value x is given by (12) [1,7].…”

“…In the USA, the winding insulation predominantly uses thermally upgraded paper [7]. Oil has a high insulating strength and at the same time serves as cooling medium by either natural or forced convection.…”

Remaining lifetime modelling of power transformers on individual and population level

“…We employ a predictive model which involves three essential ingredients: reliability engineering, physical understanding of the degradation process, and actual knowledge of the present condition [1]. The model is applied to the degradation of the transformer winding insulation [2]- [7].…”