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| Mining Field: Electrical |
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Area: Power Consumption |
| | • | The power consumption for a typical open pit mine, including the concentrator (mill) will be approximately 60 kWh per tonne of ore mined and processed. While that of a typical underground mine including the concentrator will be approximately 100 kWh per tonne. Source: Jack de la Vergne |
| | • | The scale up factor for the power requirement at an underground mine is 1.85 for a doubling of mine capacity. Source: Jack de la Vergne |
| | • | Good demand factors for power systems range from 0.7 to 0.8, depending on the number of operating sections in the mine. Source: Morley and Novak |
| | • | The power consumption for a concentrator (mill) can be roughly approximated by adding 15 kWh/tonne to the Bond work index of the ore (determined by laboratory testing). Source: Jack de la Vergne |
| | • | Power consumption (energy portion of utility billing) for a mine hoist is 75% of RMS power equivalent. Source: Unknown |
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Area: Motors |
| | • | AC motors operate very well at 5% over-voltage, but are likely to give trouble at 5% under-voltage. Source: George Spencer |
| | • | At 10% under-voltage, the life of fractional horsepower motors will be reduced to three years and the life of 3-phase motors reduced to five years. Source: Klaus Kruning |
| | • | For an AC motor, torque varies with the square of the voltage – a 10% loss in voltage is a 21% loss in torque (this is an important consideration for the head of a pump and the rope pull of a mine hoist). Source: Jarvis Weir |
| | • | A typical AC induction motor for regular mine service is supplied with a 300% breakdown torque. It operates at nearly constant speed within its normal working range, develops rated horsepower at approximately 97% of no-load speed, and a maximum torque of approximately three times full-load torque at about 80% of no-load speed. Source: Domec Lteé. |
| | • | A typical AC induction hoist motor is supplied with a 250% breakdown torque. In application, this means that the peak horsepower of a hoist motor should not exceed 1.8 times the RMS power. Source: Larry Gill |
| | • | For a DC hoist motor, the peak power should not exceed 2.1 times the RMS power for good commutation. Source: Tom Harvey |
| | • | An AC cyclo-converter hoist motor can have a peak/RMS rating as high as 3. Source: E A Lewis |
| | • | To permit overhung motors, the air gap for large direct drive DC hoist motors is typically 6mm (0.25 inch). Comparable cyclo-converter drives can have similar or larger gaps. Source: E. A. Lewis |
| | • | In operation, a typical 575-V AC motor will draw one amp per horsepower. A similar 440-V motor will draw 1¼ Amps per horsepower. Source: Bill Forest |
| | • | The brushes on an AC machine should be first set at a pressure between two and three pounds per square inch (15-20 kPa). Source: General Electric |
| | • | The brushes on a DC machine should be maintained at a pressure between three and five pounds per square inch (20-35 kPa). Source: General Electric |
| | • | The peak inverse voltage from a DC mine hoist motor will be approximately twice the supply voltage so the thyristor bank is designed accordingly. Source: Jim Bernas |
| | • | The rate of brush wear on DC motors and generators can be kept to an acceptable level if the air has a water vapour density above 5 mg/l. The sensitivity to atmosphere humidity increases at least proportionately to the speed (of rotation of the armature). Source: Gerald Tiley |
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Area: Belt Drives |
| | • | The lower side of the belt loop should be the driving side. Vertical belt drives should be avoided. Source: General Electric |
| | • | 2½ times the diameter of the larger pulley will normally provide a safe working distance between centers. Source: General Electric |
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Area: Transformers |
| | • | For a typical mine circuit with multiple components, the capacity required for a transformer, measured in kVA, is approximately equal to the load expressed in horsepower. In other words, a load of 500HP normally requires a transformer with 500-kVA capacity. Source: Bill Forest |
Mining Rules of Thumb have been gathered over 30 years of hard rock mining service provided by Stantec / Mining and predecessor firms.
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