An advanced model-based diagnosis system for online detection of the moisture content of power transformer insulations

Abstract

It is a well known fact that the moisture content of a power transformer insulation system is a key parameter for the estimation of its aging condition and operation reliability. Therefore detection of the moisture content is a very essential task within power transformer diagnostics. While conventional methods for estimation of the water content of the insulation system require a transformer shutdown for several hours, the proposed method calculates the profiles of water concentration in the cellulosic part of the insulation system, as well as the concentration of water in transformer oil from operational parameters. An advanced model for the moisture diffusion in paper estimates the temperature dependent moisture distributions in the paper for non-uniform temperature distributions along the transformer winding. The model covers temperature dependent diffusion coefficients and acts as a non-linear control loop for the water concentration in transformer oil. Moreover the water concentration at the oil-paper interface, which is a measure for the risk of surface discharges, is computed. The identification procedure for the models is based on nameplate data and dielectric response measurements. Sensors for temperatures and relative water concentration of oil provide the possibility to integrate the models into a framework of model-based diagnosis using structured residuals. The models have been verified with a laboratory setup consisting of a power transformer, equipped with sensors for temperature, load current and oil humidity.

Study on Correlation Among Oil Dielectric Characteristics, Dissolved Gases, and Operating Life of 150 kV Power Transformer

“…Insulation attacked by ageing will work ineffectively and is likely to be failed. An effective assessment method is urgently needed to extend transformer lifetime and prevent the failure [3][4].…”

Verification of a model-based diagnosis system for on-line detection of the moisture content of power transformer insulations using finite element calculations

“…In order to study the interaction of oil and paper during diffusion processes and to solve the problem with a ordinary differential equation (ODE) solver such as MATLAB TM , a one-dimensional model of an enclosed transformer insulation system is proposed and experimentally verified in [1]. The model is based on a layer of paper of thickness d P that is on both sides surrounded by an oil volume.…”

“…Power transformers belong to the kind of equipment with comparable long lifetime (30 -50 years and above) and high reliability. This implies the need for a self supervising diagnosis system, in order to avoid a decreased reliability of the overall system (transformer and diagnosis system) [1].…”

“…Details for such a thermal model are given in e.g. [1], [4] and shall not be discussed here in any further detail.…”

Aging Assessment of Power Transformer Using Multi-parameters

“…As the most expensive and important equipment in electric power system [1][2], power transformer plays a vital role in maintaining reliable and efficient electricity supply. However, as the population of transformers in service is increasing and growing older, much and much attention has been paid on their aging condition and life assessment than ever.…”