B Duncan LTD was approached to help commission new reclosers for upgrading the overhead network’s protection of the electrical supply at Macres Mine. These protection devices were installed on their overhead 11kV lines, which were used for both ring networks with directional protection running and radial networks with standard over current protection. This upgrade enabled the system to clear faults improving its reliability.

OceanaGold operates New Zealand’s largest gold mine, Macraes, located north of Dunedin. The Macraes goldfield includes the Open Pit gold mine and Frasers Underground mine. Macraes mine has been in operation since 1990, and has produced over 3 million ounces of gold. Macraes Mine’s operation also includes a processing plant near the Open Pit, for processing the ore into the final gold bars. As with any mining operation, there is a need for safe and reliable electric power; this is required for the power intensive daily operations of the mine and the processing plant.

Recent increases in plant through-put and mine life expectancy required Oceanagold to undertake a significant expansion to their Tailings Storage Facility at Macraes. A new tailings dam was constructed but these are 5km away from the ore processing facility. To transport the slurry this distance to the dam, a combination of up to 6 x 650kW centrifugal pumps have been installed whilst 2 x 450kW centrifugal pumps are used to return the decanted water back from the tailings ponds to the main processing plant. Due to the expansion, the power requirement was also increased, which warranted an upgrade of electrical supply system.

We reviewed and tested the protection settings to confirm the correct protection grading behaviour. This included calculating the vector sequence components for various distribution line faults, testing these fault scenarios with secondary current and voltage injection, and providing support services on the correct operation and setup of the new switchgear. We also provided training to ensure the commissioning of the new overhead protection system was a success.