Power Down Under
World’s largest mineral sizer powered by ABB
Derbyshire-based mineral sizer specialists Mining Machinery Development Ltd (MMD) have recently commissioned the world’s largest fully mobile mineral sizing station at an opencast coal mine in eastern Australia. The 1,760-tonne tracked machine — the MMD 1400 — was assembled from modules shipped out from the UK and manufactured in Australia using UK designs, and is now fully operational at BMA’s vast opencast site at Goonyella in Queensland. Designed for throughputs in excess of 10,000 tonnes/h, the machine is being used to clear overburden at the site.
The sizer operates alongside a mobile electric rope shovel which transfers 100 tonnes of overburden at a time into the machine’s feed hopper. From here an apron plate feeder lifts the material to the three-toothed mineral sizer which reduces it to lumps of rock around 350mm3 in size.
The material is then transferred by an outfeed conveyor to a slewing/elevating discharge conveyor which delivers it to the feed hopper of an existing overland conveyor. This carries the material up to 10km away to a spreader unit for disposal. When the rope shovel has cleared an area around the sizer, which is able to rotate through 270°, both machines move on to another location to clean further strips of overburden.
The MMD 1400 is completely electrically powered and driven, and can be supplied with power from either a 4MW, 6.6kV umbilical cable up to 1km long or a generator for maintenance purposes. The full electrification system, including the incoming 6,600V switchgear, outdoor-mounted Resibloc three-winding step-down transformer and low-power distribution, was supplied by ABB, specialists in industrial power and automation technologies.
The various components of the sizer are all powered by ABB drives and motors — two 430kW propelling drives with brake motors and shared inverters; two 430kW drives for the sizer; two 430kW drives for the apron plate feeder, with brake motors; one 430kW drive for the discharge conveyor, with brake motor; one 250kW drive for the transfer conveyor; and a 90kW hydraulic power AC drive.
All the drives are marine-standard ABB ACS 600 MultiDrives, designed to withstand any vibration effects caused by the mineral sizer. They incorporate an inverter supply unit to give them a regenerative capability, used to brake the machine and to allow it to move up and down inclines of up to 10°, and also have regenerative braking, allowing the discharge conveyor to carry material downward with running over speed.
Variable-speed drives were chosen for the sizer because of their soft-starting capabilities, as the electrical network at the mine does not have the capacity to supply the current that direct on-line starting would draw.
All motors used on the sizer were supplied by ABB and mainly comprise HxR machines with enclosed cast iron construction to withstand vibration and prevent the ingress of dust.
A major part of the electrical contract was the fitting of the drives and associated distribution equipment into air-conditioned housings. Based on three standard ISO shipping containers, these were customized for the application by coating them with a high-grade UV coating in order to withstand the 46°C ambient temperature experienced at the mine.
One of the containers houses a large MCC and MV switchgear, while the other two are stacked above each other and contain the ABB drives, connected by a 1kV DC busbar. These containers are fitted with an air-handling and cooling unit to deal with the 120kW heat load developed by the drives. In addition, all the containers are maintained at positive pressure to prevent the ingress of dust and all are fitted with filtered fans, fire detection and extinguishing systems, and small power and lighting systems.
ABB also supplied the control system for the mineral sizer, which can be operated manually through a SCADA system or remotely via radio.