| Chapter 23 - Electrical |
| Number |
Topic |
Rule of Thumb |
| 23.01 |
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 |
| 23.02 |
Power Consumption |
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 |
| 23.03 |
Power Consumption |
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 |
| 23.04 |
Power Consumption |
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 |
| 23.05 |
Power Consumption |
To estimate annual power cost for shaft horsepower, divide the hourly cost by 3 and multiply by 20,000. For example, a typical rate of $0.075/kWh equates to approximately $500/HP-year. Source: Dave Hamel |
| 23.06 |
Power Consumption |
Power consumption (energy portion of utility billing) for a mine hoist approximately 75% of RMS power equivalent. Source: Unknown |
| 23.07 |
Power Consumption |
Power consumption (external work) for a mine hoist is 1 kWh/tonne for each 367 m of hoisting distance at 100% efficiency (no mechanical or electrical losses). In practice the efficiency is approximately 80%. Source: Sigurd Grimestad |
| 23.08 |
Motors |
AC motors operate very well at 5% over-voltage, but are likely to give trouble at 5% under-voltage. Source: George Spencer |
| 23.09 |
Motors |
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 |
| 23.10 |
Motors |
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 |
| 23.11 |
Motors |
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. |
| 23.12 |
Motors |
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 |
| 23.13 |
Motors |
The difference between a service factor of 1.0 and 1.15 on the nameplate of a motor is a 100C higher allowable temperature rise for the latter. Source: W. MacDonald, M. J. Sheriff and D. H. Smith |
| 23.14 |
Motors |
For a DC hoist motor, the peak power should not exceed 2.1 times the RMS power for good commutation. Source: Tom Harvey |
| 23.15 |
Motors |
For a DC hoist motor, the peak power should not exceed 2.0 times the rated motor power for good commutation. Source: Sigurd Grimestad |
| 23.16 |
Motors |
An AC cyclo-converter hoist motor can have a peak/RMS rating as high as 3. Source: E A Lewis |
| 23.17 |
Motors |
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 |
| 23.18 |
Motors |
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 |
| 23.19 |
Motors |
The shaft-mounted cooling fans are bi-directional on AC motors up to 50 HP. Larger motors may be directional and, therefore, rotation should be specified. “Normal rotation” is clockwise facing the non-drive end. Source: H. A. Simons Ltd. |
| 23.20 |
Motors |
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 |
| 23.21 |
Motors |
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 |
| 23.22 |
Motors |
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 |
| 23.23 |
Motors |
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 |
| 23.24 |
Belt Drives |
The lower side of the belt loop should be the driving side. Vertical belt drives should be avoided. Source: General Electric |
| 23.25 |
Belt Drives |
2½ times the diameter of the larger pulley will normally provide a safe working distance between centers. Source: General Electric |
| 23.26 |
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 |
| 23.27 |
Primary Power |
For a proposed mining operation it is best to design primary transmission lines for a 5% voltage drop at rated capacity, which should be taken as the maximum 15-minute integrated peak (maximum demand). Source: Charles M. Means |