MechChem Africa September-October 2022

⎪ PowerGen,PetroChem and Sustainable energy management ⎪

flash. Dry-type transformer construction increases robustness under these conditions and they are able to withstand a high level of short-circuit current,” he explains. As a result , Trafo Power’s dry-type transformers have class F1 Fire Protection certification, which means that under short circuit or external fire conditions, the trans former will neither cause nor exacerbate a fire. All the materials and resins used are flame retardant and no harmful gases will be produced. “Because of poor oil containment on an oil-filled transformer, a relatively small fire in the switchgear can often ignite the transformer oil, which then makes that fire bigger and bigger. Using a dry-type trans former completely overcomes this problem,” he notes. Describing a recent success where cus tomisation played a critical role, Claassen tells of an installation at an underground goldmine to supply power to a refrigeration plant via MCCs. “We supplied three trans formers for the applications, a 250 kVA, a 630 kVA and a larger 3 150 kVA unit. These are all going underground and, due to the dimensional and weight constraints of the cage and the access limitations through the underground decline shaft, our standard 3 150 kV transformer geometry wouldn't fit into the cage from a height or width perspective. So we've custom-designed and manufactured a transformer with a unique geometry and with a purpose-built skid base so we can get it down the mine and slide it along the decline shaft,” Claassen explains. Compared to an oil-filled design, this was much more easily achieved. More im portantly though, an oil-filled transformer would have been a fire hazard and, while they are not yet illegal in our mines, from an insurance perspective an oil-filled trans former can cost more than double to insure. Also, operators need to comply with a whole lot of extra fire suppression, detection and other requirements. “This is an excellent example of how we prefer to operate, where clients comes to us with their power requirements and voltages, along with their access or site constraints and their specific ambient conditions. We then customise a solution to best suit all of these conflicting needs,” says Claassen. The cost advantage In comparing the costs of dry-type versus oi l -f i l led transformers, Claassen says, because they were less common, dry-type transformers used to be much more costly than traditional oil-filled equivalents. This has changed dramatically in recent years and, while the upfront investment in a typi cal dry-type transformer solution might still

Left: Rigging into position of a cast resin transformer within an enclosure for a commercial building. Right: Containerised dry-type transformer solutions, ideal for the challenging terrain of African mines.

be slightly more expensive, this premium is quickly swallowed up by the additional infrastructure costs of isolating an oil filled transformer in its own building or in a purpose-built bay with a bund wall. In addition, maintenance requirements and costs for dry-type transformers are sig nificantly lower. “On dry-type transformers there's very little maintenance and service intervals are much longer. The only things that we tend to look at are the terminations and cabling, possibly once every year or so, and to use a leaf blower to clear any build-up of dust that might be affecting the cooling. Oil-filled transformers require repairs of oil leaks and regular oil sampling to monitor gas and moisture build-up and oil degrada tion – and this is essential to minimise fire risks. Fire detection and onsite fire suppres sion equipment is also usually required. So the additional costs of the ‘cheaper’ oil-filled unit are almost always far higher than the slightly increased purchase price of a dry type transformer.

“In some cases there seems to be a disconnect between keeping the project outlay low and minimising running costs and investment returns,” Claassen argues. “In the mining industry and in data centres, however, where end users are a lot more in volved in the project development process, dry-type transformers have proved to be a safer, better and much more cost-effective choice. “For anyone charged with the responsi bility of keeping a facility’s equipment op erating safely, reliably and cost effectively for the next 30 years, it makes a lot of sense to get involved in the discussions with the project developers at an early stage so that their future ongoing operations become easier to manage. “And dry-type cast resin transformers, custom-built to suit specific onsite needs and conditions, make total sense in that regard,” he concludes. https://www.trafo.co.za

A custom-built enclosure housing a dry-type transformer for specialised mining application.

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