Life cycle management of power transformers: results and discussion of case studies

The knowledge of a current state of running machines is of high importance for users and producers of transformers; especially the knowledge of the present state of their priority component - insulation system. The article deals with methodology of creating and utilization of the information about the condition of insulation system of transformers database as a tool for the transformer life management. The post-mortem analysis of the insulation systems condition of transformers that have already grown old and are intended for liquidation were used a source for the database. The procedure of sampling is described. Analytically determined values of degree of polymerization (DP) and tensile strength (R) are accompanied with information from running history of a transformer (especially DGA and 2FAL values). Individual case studies, whose results are shown in the article, are realized in most cases for transformers with the highest voltage 400 kV but they differ in type (power transformers, autotransformer), manufacturer (4 providers) and also in construction. The study deals with generalization of reciprocal relationships of analysed quantities for typical representatives of individual machine groups as well as with the impact of non-standard events during the running of particular transformer.