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MINE SERVICES |
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Electric Power |
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MINE SERVICES
Electric Power
The majority of Australian coal mines have power supplied by another entity to a surface substation on site. Power is fed through switchgear to main feeder(s) to required locations around the surface and to underground, at most modern mines at 11kV (even higher at new mines). The feeder(s) to underground may be suspended in a shaft or hung in a drift but increasing use is being made of boreholes to carry services. This is because use of a borehole for cables may allow them to be located more conveniently, may be shorter (vertical borehole versus length of inclined drift) and will be better protected. In a deep mine, cables will not be able to support their own weight if hung vertically and will require other support such as a catenary wire to support them.
Electric power is reticulated around a mine in roadways and may be exposed to damage. The cables are therefore "armoured" (where the live cores are heavily protected by sheathing and earthed wire) to minimize risks associated with the potential damage of the cables.
The underground reticulation system is sectionalized by isolators and switchgear with power being transformed to operating voltages near the equipment being powered, in most cases to 1100V (or 415V for some older equipment, to 240V for special circuits such as lighting and increasingly for use at 3300V as higher capacity equipment is being introduced).
Individual equipment is usually connected through a distribution box (often called a "load centre" or "gate end box") or through a starter panel.
Where electric powered equipment is mobile (e.g. continuous miners, shuttle cars, longwall shearers, etc) special cables (referred to as "trailing cables") are used to power the equipment. Although heavily sheathed to protect cores from damage, the main protection for personnel in the event of trailing cable damage is by the use of fault detection and trip devices.
There are quite severe restrictions on the use of electric power within what is referred to as a "hazardous zone" in a coal mine, which means anywhere on the return ventilation side of a point 100m before a pillar where mining operations are taking place all the way back to where the ventilation exhausts to surface (see relevant Mining Regulations for the full definition). Within such a zone all equipment must be either "flameproof", which means enclosed within a container able to prevent any internal explosion being transmitted to the external atmosphere, or be "intrinsically safe", which means that the power is too low under any conditions to produce a spark of sufficient power to ignite methane. There are extensive additional requirements regarding the use of electrical equipment in hazardous zones and for its inspection and testing. Note that cables cannot be made flameproof.