MechChem Africa September-October 2022

Customised dry-type transformer solutions for improved safety and lower costs

MechChem Africa talks to David Claassen, Managing Director of Trafo Power Solutions, about the cost, reliability and safety advantages of using dry-type/ cast-resin transformers, particularly in hazardous area applications such as underground mines.

of transformers – 66 kV in South Africa and 52 kV in Europe – make up our highest mar ket volumes and it has become a no-brainer to adopt this technology in preference to oil-filled technology,” he notes. “We at Trafo Power Solutions focus on customising the design of our transformer to bestmatch application and environmental requirements. So we don’t supply standard products that work for everything. There are always differences that need to be taken into account, depending on the load cycle and the ambient conditions, for example. If the transformer is being used in an industrial application, which typically has a lot of vari able speed drives that cause high non-linear loading on the transformer, the design needs to reflect that. “For a PV-plant, on the other hand, which will operate at 100% during the hot and sunny hours of the day but will be under no-load conditions during the cooler nights, different contraction and expansion consid erations need to be taken into account. In a nutshell, we can engineer a dry-type transformer for any appl ications where an oil-filled transformer is used, and these solutions will of fer significant advantages over the traditional technology,” Claassen tells MechChem Africa. Going back to the construction of the dry type transformers, he says that the medium voltage winding is typically sealed in a cast resin block, which gives the transformer a very high withstand capability against humidity and pollut ants. During manufacture, the winding is first wrapped with fibreglass mesh ing. When the resin is poured in, it binds into the meshing, which acts like rebar in reinforced concrete to create a very strong and robust containment structure. “Under short circuit conditions there is a requirement for the trans former to withstand the shock-loading caused by very high levels of current. On a traditional transformer, short circuit shock generates movement in the windings that can result in voltage

designed for optimal cooling around the transformer, either using natural ventila tion or by adding forced cooling fans when required," Claassen explains. "In every case, we will calculate the precise cooling require ments of a transformer based on the ambient air in the operating environment so that every transformer we supply will operate safely and reliably.” And while there is a limitation on the use of dry-type transformers for very large power transformers – very few dry-type manufacturers go above 20 MVA – for all applications around a sweet spot of 10MVA –which includes most data-centres, shopping centres, municipal distribution networks, motor control centres (MCCs) along with industrial power distribution centres for mines and oil and gas, chemical and petrochemical plants – dry-type/resin cast transformers are fast becoming the preferred option. “Globally, our Trafo distribution range

I n principle, the primary function of dry type power transformers is identical to traditional oil-filled transformers, begins DavidClaassenof TrafoPower Solutions. “Both are used to step up or to step down an incomingACvoltage tomatch the voltage and power rating requirements of an application. The primary difference is that oil-filled trans formers use oil as an insulation and cooling medium, whereas dry-type transformers use only air,” he says. Both types have a core, low voltage wind ings and medium voltage windings, with the turns ratio between these two windings governing the output voltage. But from a construction perspective, the windings are a combination of VPI (Vacuum Pressure Impregnation) and Cast Resin. “Each individual transformer is purpose

A Trafo dry-type transformer for a mining application that features an electrostatic shield for minimising higher harmonics.

30 ¦ MechChem Africa • September-October 2022