Usibelli Coal Mine Flywheel

The B.E. 1300W walking dragline
photo: Alaska Department of Natural Resources

Project Overview

In 1978 the Usibelli Coal mine in Healy Alaska commissioned a Bucyrus-Erie 1300W walking dragline. This is a machine used to move large quantities of material during mining operations by dragging a bucket that can hold up to 42 cubic yards of material. The dragline weighs 4 million pounds and has a 225-foot mast and a 325-foot boom which pulls buckets that scoop material, mud, clay, etc. clearing the the coal seams for excavators and trucks.1 The dragline is fully and electric and is connected to the Golden Valley Electric Association (GVEA) grid. During this the loading period, the dragline uses around 6MW. When the dragline is unloading it regenerates around 2MW of power. This cycle occurs approximately every 60 seconds.2 This fluctuation proved too great for the GEVA grid. When the dragline was in operation, lights in of other customers on the GVEA grid flickered. To alleviate the grid issues caused by operation of the dragline, in 1982 the Usibelli coal mine purchased and installed a flywheel to stabilize the load produced by the dragline. This flywheel, called the “Peak Shaver” allows the fluctuations from the dragline to be managed effectively with the grid.3


Usibelli Coal Mine Flywheel
Photo: Western Mining Electrical Association


The 40 ton flywheel consists of three one foot thick, eight foot diameter steel plates and is housed in a separate building unit, and is connected to the dragline and the GVEA grid. to level the load of the dragline, the flywheel can release 5.2 MW for three second bursts. When the dragline is pulling power, the flywheel slows down, when the buckets are unloading and swing, the flywheel accelerates to absorb the produce energy.4The system utilizes a GE silcomatic power converter.5Also installed is a supplemental 1.8MW generator. Since the installation of the flywheel fluctuation on the grid has decreased to only around 500 kW and there have been no issues for other customers.6

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