Economical and Reliable Transformer Maintenance by Holistic Interpretation of Insulating Oil Condition
A few misconceptions about the transformer industry: – “If my old transformers are still in good condition, it is not necessary to worry about replacing...
byMarius Grisaru
A few misconceptions about the transformer industry:
– “If my old transformers are still in good condition, it is not necessary to worry about replacing them.”
– “Transformer technology is the same as it was 50 years ago; same steel, same oil and same cellulose.”
– “We intend to keep an old transformer in operation without maintenance until it fails, than replace it with a new one.”
– “The testing guidelines published in some of the standard guides also apply to my transformers.”
All those misconceptions can lead to very costly outcomes, e.g. replacement of a good quality old transformer by a less robust new transformer, or a dramatic failure scenario.
Transformer maintenance is commonly compared to medicine, and as such, it has to be based on reliable tests and diagnoses which must be carried out by a specialist who is familiar with the latest technologies and issues regarding transformers and who is able to recognise specific conditions of the specific piece of equipment. Like human beings, transformers differ one from the other, even the ones made by the same manufacturer and in the same housing, and the twins.
All those parameters impose a real dilemma for the transformer owners and contribute to discrepancies in proper maintenance, reliable electricity supply and shareholders’ profits.
The transformer technology and demands change dramatically these days and the transformers are no more “low tech”.
Today a much more compact transformer has to transform more energy at higher voltages and in significantly less space. These requirements impose a continuous search for new materials, new designs and new maintenance strategies to enable longer transformer operation.
This paper will focus on insulating materials inside the transformers. Those materials are responsible for the majority of failures and catastrophic events but, nevertheless, can be monitored during transformer operation:
1. Choosing the right oil type for each transformer type. The variety of insulating oils increase and change constantly. 50 years ago, users had access to a very limited assortment of oil types, such as the well known PCB. Inhibited mineral oil with non-strict demands, such as low oxidation stability and lower breakdown voltage, was also available. At this time, the oil test limits were not mandatory, e.g. the former IEC60422 allowed 0.5, acidity. Back then, almost all oil types were suitable for any transformer.
2. With such variety of insulating oils today, it is very difficult to establish the differences and advantages of so many oil types and liquids. Of course, the oxidation stability coupled with potential of sulfur corrosion and additives are the main concerns for all industries due to too many recurring incidents related to these problems. The transformer purchaser chooses the liquids manly according to the initial price which can lead to very costly outcomes. However, the price is not a good criterion as some of the most expensive insulating liquids can also damage transformers. The only solution is to have the correct unbiased knowledge.
3. Solid insulating materials are also challenging to implement. Although there are very durable insulation materials, this is not always the best choice pricewise. The designer and the transformer owner have to know and understand the needs and problems of all materials and their compatibility.
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