Abstract:
The stability of any distribution network is very much dependant on the performance of the
power transformers. These transformers need to be monitored to ensure that any unwanted
conditions, including high risk defects, are detected. The previous and current transformer
failures in the Northern Cape Operating Unit show that the health status in the Plant Health
Indicator of the transformers was on category A. Category A status means the transformers
were healthy. The root causes of failure were that only some of the Dissolved Gas Analysis
parameters were monitored. The transformers were shown to be healthy by the Plant Health
Indicator at the time of the failure. Parameters such as cooling, bushings, tap changers,
operating temperatures, ageing and loss of life were not monitored. The majority of
transformer failures recorded were affected by the parameters mentioned above, of which
some are not monitored in the Plant Health Indicator.
This research study discusses the application of integrated online condition monitoring for
power transformers as one of the techniques to assess the condition of the power transformer
during operation. The integrated online condition monitoring allows for transformer
condition assessment without having to switch off the transformer, thereby minimising power
supply interruptions. The integrated online condition monitoring system is unique technology
that monitors the condition of various parameters of the power transformer such as the
cooling fans, on-load tap changer, bushings, transformer operating temperatures, dissolved
gas analysis, transformer ageing and loss of life. The research design is quantitative with data
analysis retrieved directly from the online condition monitoring server. The results from the
bushings, cooling fans, tap changer and temperatures form part of the analysis. Data analysis lead to a discussion of these parameters, which highlights the problems
currently experienced with transformer failures in the Northern Cape Operating Unit.
The research study revealed that, although Eskom is having the best maintenance practices in
power transformers, there is a need to improve and save costs, as the current maintenance
strategies of power transformers are expensive. The results of the study should be regarded as
exploratory, and provide directions to researchers for further, more in-depth studies in this
field. The cost analysis was performed over a period of ten years, as compared to the current
costs of maintenance/monitoring and asset replacement strategies of power transformers. The
total saving per year was a great benefit for tasks such as inspections/maintenance/monitoring
and asset replacement. This was validated by the results from the proposed transformer
online monitoring technology that can predict the defects which may result in catastrophic
transformer failures.
