Recent Question/Assignment

Assignment 1
The purpose of this assignment is for the student to design an electrical distribution system for the coal mine illustrated in Figure 1.

Figure 1: schematic diagram of underground workings.
The mine is to operate a single retreating long wall coalface at any one time. Whilst this face (panel 1 on the figure) is in production the next panel is under development. The physical dimensions of each airway in the system are as listed in Table 1. All airways excepting the drift and shaft are developed fully within the flat coal seam of 3m thickness. A ventilation fan is located at the top of the return ventilation shaft that can in emergency situations act as a second means of egress.
Coal clearance is undertaken by conveyor, conveyors are located in airways 1-2, 2-5, 5-7, 5-6, 7-10, 10-11, 11-12, 12-13 and 7-14 with an armoured face conveyor located on ht face 6-8. Development is undertaken using continuous miner. Table 2 lists the electrical machine requirements and location for the time frame under consideration.
Distribution voltage at the mine is 13.2 kV.
The purpose of the exercise is to devise an electrical distribution system to service the current and possible future requirements of the mine. The student is to consider the following:
• Cables and cable couplings
• Switchgear
• Transformers
• Power centres
• Distribution and utilisation systems
• Electrical safety
• Control requirements
• Any other requirements
• Power factor correction (if required)
All assumptions need to be detailed and justified. The results should be presented as a report; no page limit is specified, with diagrams and other data as required. Students should note that there is no single answer to this design, marking will be based on the robustness of the system, the inherent safety of the system and the ability of the system to be expanded. In order to aid on the last criterion it is expected that the life of an individual panel is of the order of 6 months under the current production schedule, the extracted length of all panels in the mine is 1950m, i.e. a 50 m barrier pillar is required.
Table 1: Dimensions of mine.

Table 2: Major items of electrical equipment to be considered within the exercise

Assignment 2
If required it may be assumed that g = 9.81 m/s2, Density of water = 1000 kg/m3,
You are a mine planning engineer at a medium sized operation producing 1.5 mtpa of coper ore at 3% Cu. The mine was originally designed using a bench height of 15m. Footwall benches were 15 m wide to give a slope angle of 45°, but on the hanging wall side alternate benches are only 10m wide to produce an angle of about 50°.

You are required to design a drainage and pumping system to deal with the mine water for the next 10-15 years based on the data in the following sections. As the mine grade is low and power costs are high every effort should be made to minimise the operating costs of the pumping system. Describe your proposed drainage and pumping system with the aid of diagrams where required and explain the general philosophy behind the system. Detail and assumptions made and make comments and conclusions as required.
Data
Mine water
Ground water: currently averages 1,000,000 litres/day and is expected to increase at a rate of 5% per year as the mine deepens.
Mine water: averages 50,000 l/day with small variations in use on an hour by hour basis.
Water Quality: Run of mine water is expected to be slightly acidic due to the formation of sulphuric acid from sulphides within the rock
Rock properties: SG of 2.9 for all rocks. Hanging wall and ore have moderate strength, footwall is very strong.
Mine Selection

Rainfall: the average annual rainfall s 740 mm, the average monthly figures are as follows

10)For the system indicated below determine the following:
d) The Average Power on the low winding side of the transformer kW
e) The reactive power kVAR
f) The effective power kVA
g) The power factor
h) The Current I1

26) The following data presented is from a nest of piezometers installed side by side at a single site.

If A, B and C refers to the points of measurement of piezometers a, b and c, determine:
a) The hydraulic head, pressure head and elevation head at A, B and C
b) The vertical hydraulic gradients between A and B, and between B and C if they are spaced 200m apart
36) A 100 kW, 450V AC shuttle car uses a flat cable. Two layers of the cable will remain on the shuttle car’s reel at all times. What is the required ampacity for the cable if efficiency is 80%, a power factor of unity also applies.
17. For the ventilation network shown on the next page, determine the flow and pressure drop in each branch of the network.

18) For the following
Face dimensions 5.5 m high by 6 m wide
Face advance 3.5 m
Length of development before blast 250m
Rock density 3 tonnes/m3
ANFO factor 2.5 kg/m3 rock broken
Face ventilation 30m3/s
NO2 gas production rate 3.5 kg per tonne of ANFO
NO2 TWA is 3 ppm
Determine
1. Volume of rock to be blasted
2. Tonnes of rock to be blasted
3. ANFO used
4. Fume throw back distance
5. Volume of fumes immediately after the blast
6. Volume of NO2 gas produced
7. Concentration of NO2 in fume throw back zone immediately after the blast
8. Concentration of fumes after they have spread throughout the drive but before they have entered the decline
9. Time for diluted fumes to fill the drive
10. Time for fumes to be diluted below TWA concentration
11. Total time for fumes to clear