It has been five years since Trafo Power Solutions supplied Alphamin’s Bisie tin mine in the Democratic Republic of Congo with two dry-type transformers; they have performed so well that another three of these modular substations equipped with dry-type transformers will soon be on their way, to keep up with the mine’s expansion.

“This latest order is testament to the operational performance of our dry-type transformers at Bisie mine over the past five years,” says David Claassen, Managing Director of Trafo Power Solutions. “There were numerous challenges that our design had to accommodate, not least of which is a very arduous section of road in the journey to the mine.”

The mine’s location in the Walikale Territory of DRC is remote, being about 180 km north west of Goma, and more than 30 km from the national route linking Walikale with Kisangani. Like the initial order, the three 3000 kVA, 400 V/11 kV substations will be supplied in standard six metre containers to facilitate transportation. However, specialised steel bracing is required – to withstand the challenging road conditions, especially over the last part the journey.

“These conditions make the road almost impassable by any vehicle other than a six-wheeled Unimog,” says Claassen. “There is intense vibration and tilting of the cargo on these trailers, so our design and bracing is done with this in mind.”

He notes that the mine had considerable foresight in specifying the first dry-type transformers, especially given the relative novelty of this option at the time. At that stage, it tended to be standard practice to use oil-filled transformers for this type of application. Apart from the logistics, the substation solution also had to withstand the equatorial climate and frequent lightning strikes.

“The region where the mine is located is ranked in the top five most vulnerable to lightning strikes, so there is a high risk of damage to equipment related to electrical surge,” he says. “We therefore designed robust surge protection solutions on both the medium voltage and low voltage sides of the substations, and for the transformers.”

Given the warm climate, Trafo Power Solutions designed a fully redundant N+2 cooling system for the transformers; this means that each transformer is cooled by two fans, with another two fans on standby. Among the advantages of dry-type transformers in this climate is that the MV winding is completely cast in resin, so is highly resistant to humidity.