26 September 2019

Save Cost, Buy Quality - Preserve Transformer Lifetime

“Save cost – buy quality” was a Weidmann slogan many years ago. Since then the cost pressure in the industry has increased dramatically; yet the slogan remains true to its word.

Stakeholders in the transformer industry are under substantial cost pressure, which in turn is passed on to suppliers. Participants in the supply chain do their best to minimize costs and present an attractive offer. However, this competition has led to a sharp drop in the price per MVA transformer rating. As in other areas of the market, the cost savings are not based solely on efficiency gains. Often it is sustainability that suffers.

Over the years it has become evident that IEC 61061 plywood, rather than IEC 60763 laminated pressboard, is increasingly being used as the base material for products such as clamping rings, press elements, beams, cleat systems and bolted joints. However, this apparent attempt at cost saving has revealed a negative side.

In 2017, a study presented at a CIGRE A2 Transformers Colloquium (*) shared the results of the accelerated ageing experiment which compared plywood with laminated pressboard (carried out according to the IEC 62332-2 standard). The insulating paper under investigation was aged in inhibited mineral oil together with copper and magnetic steel, along with either plywood or laminated pressboard and other insulating materials. It was observed that the paper aged significantly faster in the presence of plywood in comparison with laminated pressboard. When the results were converted into transformer operation according to the standard, the paper lifetime reduction using plywood was as much as 60–70 %. The difference is believed to be the formation and leaching of acids and water as plywood ages. In contrast, the high purity of laminated pressboard with its low lignin content and freeness of resins, means it was preserved for longer.

In summary, the savings that transformer owners gain by not specifying laminated pressboard in their products are negated over time by oil contamination through acids and associated accelerated cellulose aging, premature sludge formation and, ultimately, early transformer replacement.

(*) L. Dreier, M. Jashari, Ch. Krause, T. Prevost, “The impact of laminated cellulosic products on transformer lifetime”, Cigré A2 Transformer Colloquium, Cracow, 2017.