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

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

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

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

At 575 volts, a 3-phase motor draws 1 amp per horsepower.

At 460 volts, a 3-phase motor draws 1.27 amps per horsepower.

At 230 volts, a 3-phase motor draws 2.5 amps per horsepower.

At 230 volts, a single-phase motor draws 5 amps per horsepower.

At 115 volts, a single phase motor draws 10 amps per horsepower.

* These above are approximations.

746 watts = 1 HP


How to figure out what phase is a certain circuit number for 3 phase:

A easy way to figure what phase a circuit number is to divide it by 6. If it divides evenly it is always "C" phase.

Lets say you have circuit number 27. Divide it by 6. Six will go into 27 four times with a reaminder of 3. Normally panels are labeled with the odds on the left and the evens on the right (see Panel layout example below). So 3 is the second one down from the top on the odd side, so therefore it will be "B" phase. Let's try another one; Say your circuit number is 50. Divide it by 6. Six will go into 50 eight times with a remainder of 2 . So the correct phase for circuit 50 will be "A" phase. This is taken in consideration if the the 3 phase system is phased A,B,C left to right, top to bottom. This is the normal phasing of a system.

Example of Panel Layout:

A - ckt 1 A - ckt 2
B - ckt 3 B - ckt 4
C - ckt 5 C - ckt 6
A - ckt 7 A - ckt 8
B - ckt 9 B - ckt 10
C - ckt 11 C - ckt 12

Left Hand Generator Rule:

Can be used to to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current. To use the left hand rule, place the thumb, forefinger, and center finger at right angles to each other. The forefinger points in the direction of the field flux, assuming that magnetic lines of force are in a direction of north and south.. The thumb points in the direction of thrust, or movement of the conductor, and the center finger shows the direction of the current induced into the armature.

Here is a easier way to remember this:

Thumb = Thrust

Forefinger = Flux

Center finger = Current


Right Hand Motor Rule:

Used to determine the rotation of the armature when the magnetic field polarity of the pole pieces and the direction of current flow through the armature is known. The thumb indicates the direction of thrust or movement of the armature. The forefinger indicates the direction of the field flux assuming that flux lines are in a direction of north to south, and the center finger indicates the direction of current flow through the armature.

Here is a easier way to remember this:

Thumb = Thrust (direction of armature rotation)

Forefinger = Field (direction of magnetic field)

Center finger = Current (direction of armature current)

This post was last modified: 05-24-2009 01:28 AM by chpkkr.