Electrical Power & Protection


Better transformer design improves safety

October 2019 Electrical Power & Protection

As electricity utilities and users worldwide look to become more safety conscious and efficient in their use of electrical energy, it is important to leverage the improvements that have been made in the design of transformers.

According to Trafo Power Solutions managing director, David Claassen, there have been considerable strides in technology, surpassing both the efficiency and the reliability of the traditional oil-filled transformers that are predominantly used in power grid systems.

These high efficiency solutions include open-wound transformers (OWTs), vacuum-pressured impregnated transformers (VPIs) and cast resin transformers (CRTs). Traditional oil-filled transformers use paper saturated in oil wrapped around the winding material as an insulation medium. If not maintained correctly, insulation degradation will occur, with the oil posing both a safety and environmental risk.

“OWTs are constructed by dipping preheated windings into a high temperature varnish bath and then baking them,” says Claassen. “This replaces the need for oil and paper, so only a small amount of material is flammable.”

In VPI construction, layers of polyester resin are applied to the windings, which are subjected to interchanging cycles of pressure and vacuum that ensures deeper penetration and reduces the chances of air voids.

“With CRTs, windings are placed in a mould which is filled under vacuum with resin epoxy,” says Claasen. “Fibreglass mesh is used to strengthen the windings, which are cured in a heat-controlled oven. This process also prevents air voids, and the resin in CRTs is non-flammable.”

These designs have also made advances in reduced electrical losses, thereby improving efficiency. The use of OWTs, VPIs and CRTs offer considerable savings in energy costs over their life-spans, which for CRTs averages about 20 years. Despite the slightly higher capital cost (around 20%), these technologies can repay the price differential in just four years.

Claassen concludes that low loss cast resin transformers are being used in many parts of the world including Europe and North America because, although there is an initial premium, the payback period is between two and four years. These are now available for the African market from Trafo Power Solutions.




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