dc.description.abstract | In this thesis, a health index model for condition evaluation of power transformers
is proposed. A health index is a tool that processes service and condition data into
a score which describes the overall health of an asset. The motivation behind this
is to objectively and confidently assess the condition of power transformers so that
reinvestment and maintenance decisions might be justified. This way, the technical
lifetime of healthy assets might be safely increased, while risky assets can be identified
and taken care of before they fail. Health indexing is particularly useful for
evaluation of large transformer fleets, since it makes it easy to identify the assets
most in need of additional attention. An important prerequisite for a health index
to be useful is, however, that the availability of data is considered in the model
design. A health index intended for use in Norway will thus have to be customized
to the data availability faced by most Norwegian utilities and transformer users.
In order to identify which assessment methods that are suited for use in a Norwegian
health index, four existing health index models have been reviewed. Based
on these reviews and the general data collection practices of Norwegian utilities, a
health index model has been proposed. Its main inputs for assessment are: Dissolved
gas analysis, oil sample analysis, temperature or load history, maintenance
history and particular design data. This information is processed through assessment
modules that each evaluate different subsystems of the transformer. For these
assessment modules to reflect the degradation of transformers in a best possible
way, emphasis has been put on identifying the most important failure modes and
aging mechanisms.
In order to test the performance of the proposed model, it has been applied to
seven different transformers. The results from this analysis show that the model is
capable of differentiating between assets in different conditions and that the health
index score appears to be a rough, but reliable, indication of the actual condition
of a transformer. | |