Plant Engineering: Mines s2

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Plant Engineering: Mines

GCC: Electrical & Mechanical Engineers

Past Examination Papers

June 1996

Question 1:

The static torque required by a double drum Ward Leonard rock winder is as shown:

A represents the start of wind

B represents the end of acceleration

C represents the start of deceleration

D represents the end of wind

The following information is available:

Skip mass …………………………………………….. 7 707 kg

Load mass ……………………………………………. 10 400 kg

Mean radius of drum and rope …………………….. 2,54 m

Moment of inertia of rotating parts …………………. 652 343 kg.m2

Rope mass ……………………………………………. 10,4 kg/m

Acceleration/deceleration …………………………… 0,914 m/s2

Maximum speed ……………………………………… 16,34 m/s2

Loading time ………………………………………….. 15 s

Motor efficiency ……………………………………… 90%

Length of wind ……………………………………….. 2 470 m

Effective cooling time

= ( x acceleration time) + (full speed time) + ( x deceleration time) + ( x loading time)

Calculate the RMS power of the motor.

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Question 2:

The electricity supply received from the supply company is 11 kV at a new mine. You are planning to install three consumer substations, one on surface with a demand of 2 MVA and the other two underground, each with a demand of 2 MVA, with a spacing of 500 m between the first and second and between the second and third substations consecutively.

Operating voltages of 525 V are required from all three substations, each having 2 x 1 MVA transformers.

Neglecting 380 V circuits which are fed from separate circuits, draw a sketch showing the flow diagram including all features necessary to ensure the following on both the HV and LV circuits.

(a) Safety

(b) Fault discrimination

Question 3:

(a) You are the appointed engineer, required to conduct a safety risk audit in the underground workings of your mine.

Explain the sequence of events from the points of deciding composition of the team to obtain optimum results, the ideal duration of each event, the reason for conducting such audit, the desired results and what you will do with the information obtained.

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(b) As engineer it is your duty to ensure that nothing can enter a vertical shaft unintentionally from any point, including self-propelled mobile machines. The shaft is equipped with 3 licensed winders. Explain, with the aid of sketches, the measures you would apply in order to comply with this requirement.

[10]

Question 4:

(a) You are required to build a concrete dam wall as shown in the sketch.

The height of the wall must be 5 m from the floor and the factor of safety against overturn is 2,5.

i. Determine the thickness of the wall per metre width of the dam to prevent overturn.

ii. If the ground bearing stress at the toe is 180 kPa, determine whether or not any tensile stress will occur in the wall.

[10]

(b) A slime pump delivery pipe has a diameter of 150 mm. The velocity of flow in the pipe is 2,4 m/s. If the specific gravity of the slimes mixtures is 1,4 and that of the solids alone is 2,65 calculate the quantity of solids delivered in t/h.

[10]

Question 5:

A belt conveyor is required to transport 1 kt of coal per hour in an inclined shaft. The length of the conveyor is 1,2 km and the slope of the shaft is 17°.

(a) If the belt speed is 2,5 m/s, calculate the following:

i. The belt conveyor width

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ii. The power required to drive the fully laden belt conveyor

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iii. Size and type of electric motors required if 4 identical motors are utilized

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iv. The maximum tension in the belt conveyor

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(b) Describe the following:

i. A means to accommodate belt stretch

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ii. An effective means of ensuring controlled start-up of the belt conveyor

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iii. The drive pulley configuration that you would use

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iv. The troughing idler configuration that will give the least spillage.

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Given:

Angle of wrap = 240°

Coefficient of friction between the drive pulleys and the belt = 0,7

= Wv

where:

= Capacity of the belt conveyor in kg/s

W = Belt width in m

v = velocity in m/s

= density of coal in kg/m3

Question 6:

(a) A centrifugal pump is required to pump 800 m3 of water per hour from one underground reservoir to another at a higher level, some distance away.

The water level at the lower reservoir may be taken as 9 m below datum and that at the higher reservoir as 64 m above datum.

The pipe from the pump at the lower reservoir is 2,4 km long with an inner diameter of 380 mm. This pipe then feeds two parallel pipes, each 1,5 km long, one of diameter 200 mm and the other 300 mm.

Ignore the frictional resistance of the suction pipe and of all elbows, bends and fittings.

Calculate:

i. The quantity of water delivered by each pipe at the higher reservoir

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ii. The power required to drive the pump if the pump efficiency is 76%

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Given:

(b) Against which problems would you be required to take precautions in a long pipeline installed on a gradient? Mention the precautions taken.

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Question 7:

(a) Calculate the area of copper conductors of an overhead line needed to transmit 1,3 MW at 3,3 kV with a frequency of 50 Hz over a distance of 8 km. The power factor is 0,75, and the volt drop at the receiving end is not to exceed 10%.

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(b)

i. What does the term “intrinsically safe” denote as applied to:

a) A circuit

b) Apparatus

ii. To which types of electrical equipment can “intrinsically safe” circuits and apparatus be applied?

iii. Under what conditions may extensions to “intrinsically safe” apparatus or circuits be made?

[10]

Question 8:

(a) The following figures give the operational characteristics of a fan used in a dust extraction plant:

Water gauge (mm) / 219 / 203 / 180 / 152
Air volume (m3/min) / 700 / 850 / 1 000 / 1 150

The quantity of air handled by the filter plant is 850 m3/ min.

At this quantity the ducting resistance is 76 mm water gauge and the filter resistance is 126 mm water gauge.

In order to increase the quantity of air handled a new filter unit with half the resistance of the old unit is fitted. The ducting remains unchanged.

Plot the pressure-volume curve of the fan on the graph paper and determine:

i. The new quantity of air handled

ii. The new water gauge

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(b) 15 m3/minute of air is compressed to 670 kPa absolute. The inlet pressure is 85 kPa at 20°C.

If the compression is done in one stage with an index of 1,25, calculate the following:

i. Final air temperature

ii. Final air volume

iii. Power required to operate the compressor

iv. Efficiency of compression

[10]

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Plant Engineering: Mines – Past exams: June 1996

Printed on 8/16/2005 12:37 PM