Development of computer models for design and economic analysis of lighting systems in surface mines

Category Mine
Group GSI.IR
Location 20th WORLD MINING CONGRESS 2005
Author M. Aruna N. C. Karmakar Y. V. Rao
Holding Date 14 January 2006
 
ABSTRACT
 
Artificial lighting is very important in night shifts to provide safe and efficient working condition. The illumination design should fulfil the minimum lighting standards, specified by various regulatory bodies. This is possible with scientific design of lighting system. A computer model has been developed in MATLAB for deign of illumination system, which incorporates all the design parameters such as height of pole, tilt angle, overhang and type of source. The cost model computes the total annual cost of the lighting system. In this paper 1.0 km length road is designed for three different types of sources at five stages of pole heights. The designed systems were compared for optimum annual cost. The results of the study show that 100 W HPSV source offers minimum-operating cost compared to other sources, considered in the present design.
 Key words: design, source, lighting standards, spacing, pole height, illumination level.
 
 

INTRODUCTION
 
Haul roads within the pit are one of the critical areas in surface mines where lighting installations are not permanent due to regular advancement of the working face (Bandhopadyay, 1989). Due to this reason it is very difficult to maintain the lighting standards, specified by various regulatory bodies. As per Director General of Mines Safety (DGMS) guidelines minimum horizontal illuminance level of 0.5 lux should be maintained in haul roads (CMR, 1957). The uniformity ratio in the design of illumination is also essential for uniform distribution of light. In mines design is based on overall uniformity ratio, which is ratio of minimum to the average illuminance level.  Though Indian mining regulations do not mention about uniformity ratio, International Commission on Illumination (CIE), Austria stresses upon uniformity ration as well. It is suggested that for uniform distribution of light, overall uniformity ratio should be at least 0.3 for haul roads (CIE, 1998). CIE also suggests for the average light level instead of minimum light level. As per Indian Bureau Standards, average illumination level to be maintained in any light traffic roadways is 4 lux (IS, 1991). In this paper all the above three parameters were considered for lighting design of haul roads.
 
DEVELOPMENT OF DESIGN MODEL
 
Two fundamental laws in lighting design are inverse square law and cosine law. According to this law, horizontal (Eh) illumination at any point is given by
 
                                      (1)  
where,
Eh = horizontal illuminance (in lux) at the point of measurement,
I(C, g) = intensity (in candela) from the source to the point of measurement
م = angle between the vertical and the line joining the source to the point of  measurement , and
r = inclined distance from the source to the point of measurement.
 
In Fig. 1,
             (2)                                                                                                       
 
                                    (3)                                                                                 
 
where,
h = vertical height of source from the measurement surface.
a = distance from the source to the point of measurement along م – plane, and
b = distance from the source to the point of measurement along C-plane
 
From equation (2) and (3), horizontal illuminance at any point P is given by
 
                                   (4)                                                                                     
Considering utilization factor (UF) and inverse maintenance factor (IMF), the equation (4) can be re-written as
                      (5)                                            
Using above equation, program has been developed in MATLAB for performing basic luminance and illuminance calculations.  Because the MATLAB commands are similar to the expression of engineering steps in mathematics, writing computer solution in MATLAB is much quicker than using a high level language such as C or Fortran (Etter, 1997). Many MATLAB features and virtually all tool boxes are implemented in programmable “M-files” that gives the user access to the source code and algorithm.
 
 
    
Figure 1: Illuminance on a horizontal plane.

DEVELOPMENT OF COST MODEL
 
The cost of any lighting project is calculated under three major heads i.e. fixed annual costs, running costs and maintenance cost. The fixed annual cost consists of annual depreciation and annual interest on luminaires, poles and cables. Running cost is the sum of lamp cost per year, energy cost per year and labour cost for lamp replacement. Maintenance cost is the total sum of cleaning charges of lamps and luminaires per annum. The total annual cost (TAC) is given by
TAC = Fixed annual cost + Running cost +    
            Maintenance cost                                      (6)
Using the above equation a computer model has been developed in MATLAB. This model can be utilized for calculation of total annual cost of lighting system, which may involve different types and wattage of lamps. 
 
DESIGN OF HAUL ROAD ILLUMINATION
 
In this study three different types of sources [250W high pressure sodium vapor lamps (HPSV), 250 W high pressure mercury vapour lamps (HPMV) and 2 x 40 W twin tube fluorescent lamps (FTL)] were considered, at five stages of pole heights, for illumination of a haul road of length 1.0 km.  The width of the road is 12 m. Using developed design model maximum pole spacing was determined, for a given pole height and luminaire distribution, in compliance with the required lighting standards (minimum illuminance level - 0.5 lux; average light level - 4.0 lux; overall uniformity ratio - 0.3). Fig. 2 shows typical output of design model for 250 W HPSV lamps at 12m height poles. Table-1 represents the details of the lighting installations. By knowing pole spacing, minimum number of poles needed for illuminating total length of haul road was calculated. The total annual cost of lighting systems was computed using cost program, the results of which is presented in Table-2. Table-3 shows typical output of cost model for design with 250 W HPSV lamps.       
 

Source
Height of pole (m)
Pole spacing (m)
No. of poles
Minimum illuminance (lux)
Average illuminance
Uniformity ratio
250 W HPSV
8
34
30
5.69
18.95
0.30
10
55
19
3.25
11.20
0.29
12
62
17
2.66
9.05
0.29
14
70
15
2.27
7.35
0.30
16
80
14
1.76
5.90
0.29
250 W HPMV
8
25
41
2.91
9.79
0.29
10
38
27
1.86
6.02
0.30
12
47
22
1.36
4.49
0.30
14
46
23
1.73
4.05
0.42
16
40
26
2.28
4.06
0.56
2 x 40 W FTL
8
16
64
1.64
5.28
0.31
10
18
57
1.78
4.16
0.42
12
15
68
1.96
4.02
0.48
14
10
101
2.25
4.10
0.54
16*
51
21
0.51
1.12
0.45
*Not acceptable as the values are less than the minimum standards of 4 lux.
Table 1: Design parameters satisfying minimum lighting standards.
 
Source
Pole height (m)
8
10
12
14
16
Total annual cost ( Rs.)
250 W HPSV
2,56,364
1,71,170
1,57,683
1,43,283
1,37,450
250 W HPMV
3,43,845
2,38,544
2,00,343
2,15,304
2,49,719
2 x 40 W FTL
2,37,391
2,35,609
2,97,814
4,67,404
-
Table 2: Cost calculation for different illumination design parameters as given in Table 1.

Table 3: Cost calculation for 250 W HPSV lamps
at 12 m height poles.
 
DISCUSSION AND CONCLUDING REMARKS
 
As observed from Table-2, the annual cost for design with 250 W HPSV lamps at 16 m height poles is the lowest (Rs. 1,37,450) where as it is the highest with 2 x 40 FTL lamps at 10 m height poles. In general, it is observed that total annual cost incurred by 250 HPSV lamps is the minimum at all the five stages of pole heights. A close look for comparison of sources reveals some interesting points. The performance of fluorescent lamps is better at lower heights, where as HPSV and HPMV lamps are showing good performance at greater heights. However annual cost with HPSV lamps is less compared to HPMV lamps. It is mainly because of longer


lamp life (15,000 hrs for HPSV and 5,000 hrs for HPMV) and high lumen output (25,000 lumen for HPSV and 13,500 lumen for HPMV).
 
It has to be borne in mind that optimum design achieved by this study is valid only for the chosen illumination standards. In fact the design parameters i.e. spacing and number of poles will vary with the change in standards. In overall the study reveals that height of mounting is very important to achieve all the required lighting standards at the same time.  
 
REFERENCES
 
1.        Bandhopadhyay, P. K., (1989): Lighting of Opencast Mines, Proceedings of National Conference on Lighting for 21st Century, Bangalore.
 
2.        Bureau of Indian Standards, (1991): Indian Standard Code of Practice for Lighting of Public Thoroughfares, IS:1944 (Parts I and II) – 1970, Fourth reprint, April. 
 
3.        Coal Mine Regulations (CMR) (1957): India.
 
4.        CIE (1998): Guidelines to the Lighting for Opencast Mines, Publication No. 128 (T.C. 5-03). 
 
5.        Delores, M. Etter, (1997): Engineering Problem Solving with MATLAB, Published by Prentice-Hall, International, Second Edition.  

ROAD LIGHTING
 
Figure 2: Spot horizontal illuminance levels for 250 W HPSV sources

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