One of the world’s highest grade known tin deposits is being developed in the Democratic Republic of Congo, and dry-type transformers from specialist supplier Trafo Power Solutions are now integral to powering this effort. Two 3000 kVA, 400 V / 11 kV cast resin transformers – housed in 6-m containers – were recently delivered to Alphamin Resources’ remote Bisie mine site in North Kivu province. They will step up the supply from the operation’s diesel-powered generator plant from 400 V to 11 kV. Trafo Power Solutions also supplied two 100 kVA, 400 V / 400 V Dyn11 dry-type lighting transformers for outdoor applications.
Bisie is located about 180 km north west of Goma, in the Walikale Territory – some 60 km from the town of Walikale and 32 km from the national route linking Walikale with Kisangani.
“The mine’s remote position, and the difficult access road to the mining operation, made it essential for us to custom-design the substation and transformers to withstand the rough journey,” says Trafo Power Solutions managing director David Claassen.
According to Claassen, the complete solution was manufactured in a fast track project that took only 12 weeks. This included the in-house design of ventilation and airflow systems to deal with the extreme heat and humidity levels of over 90%, as well as lighting and small power equipment.
He highlights the suitability of dry-type transformers to the climatic conditions at the mine, especially their ability to remain cool with only minimal movement of air across the windings. Where necessary, extremely high ambient temperatures may require the employment of forced air options in the design.
“The cast resin design of dry-type transformers improves their efficiency and hence their heat losses, so cooling requirements are reduced,” he says. “Their efficiency also means they consume less energy, which in this application saves on diesel costs.”
Among the advantages of dry-type transformers is that they require almost no maintenance and can last up to 25 years without much attention. Oil-filled transformers, on the other hand, need regular maintenance and sampling of oil if they are to operate safely and consistently. In a remote location like Bisie mine, this advantage delivers particular benefits to the user. Dry-type transformers can also be installed indoors, without the need for their own civils infrastructure such as bund walls and structures – as there is no oil posing safety or environmental risks.
On December 5, Alphamin reported progress at its Bisie tin project. By then, the company’s 80.75% owned DRC subsidiary, Alphamin Bisie Mining SA (ABM) had received all approvals required to draw down the final $20 million of its previously announced $80 million credit facility.
Cold commissioning of the crushing circuit was expected to start in the first half of December, while the completion of construction of the gravity concentration building and tailings storage facility remain on track for Q1, 2019. Hot commissioning (first ore through the plant) is currently expected to commence in late March 2019.
Alphamin is assessing the impact of the likely change of mining method. Rock conditions underground have led management to review the suitability of sub level caving mining as previously planned at Bisie. A cut and fill mining method is being analysed and if approved, would result in changes to the operating costs, mined grade, recovery and mineral reserves.
