23 April 2018

The Impact of Laminated Cellulosic Products on Transformer Lifetime

In today’s power transformers, two types of laminated cellulosic products are predominantly used: laminated pressboard (made from high-density pressboard) and laminated wood or ‘plywood’ (made from wood veneer). These are mainly used for thick and thin beams of the cleat system, winding clamping rings and platforms, threaded rods and nuts, and for thick boards of various functions.

Weidmann performed an investigation to determine potential aging behaviour differences between the two laminated types, particularly whether aging by-products would interact differently with the paper in the system. This would then possibly impact the paper deterioration process and therefore would eventually have an influence on the transformer lifetime. The aging experiment was performed according to IEC 62332-2 using sealed glass tubes that were filled with kraft paper and thin pressboard with either laminated pressboard or laminated wood as well as copper and magnetic steel.

The experiment showed that the decomposition of the paper was significantly increased in the presence of plywood. By extrapolating the small-scale experimental results, it is concluded that using laminated insulation products from wood veneer instead of pressboard of high purity, kraft pulp can shorten transformer lifetime drastically as the conductor paper becomes brittle in half the time.