The objective any mining company like TATA STEEL is to reduce the amount of energy used in mining through the increase in employee productivity and safety. Mining operations consist of several tasks. The highest efficiency can only be achieved with full coordination among the persons carrying out these tasks and if the locations of vehicles and people are known by those who coordinate the activities. In addition, the large number of risks of explosion has the potential to cause a major accident. Therefore, the establishment of a better communication system for the mine underground is very important and significant to modernize the mine management, increase the labour productivity, and strengthen the security to protect the lives and property of the mines.
At present, cable telephone communication, power line communication, sensor communication, telecommunication, leakage communication, and radio communication are the main forms of communication in a mine. Our study shows that, a variety of mobile communication methods have their limitary application under coal mine. Some mines still use hardwired wall-mounted telephones. The disadvantage of this technology is the obvious necessity that the user cannot be mobile.
To reach this person, the caller must page the person who must then go to a wall-mounted telephone that may be a long distance away and in the case of an accident the telephone may be inaccessible to the injured person. Another popular technology , Leaky Feeder technology requires a relatively stiff,hard-to-install cable, about 5/8” in diameter, to be installed everywhere where communication is desired. To communicate the user must be in line-of-sight of the cable and not more than thirty or eighty feet away from the cable.
According to a survey conducted on how well current systems meet the needs for mining communication, 62 percent of Respondents replied negatively. None of them thought that mining communication needs were being met extremely well.
Some of their replies-
“Overall we cannot communicate well with miners.”
“There is the issue of battery, phone and wiring maintenance.”
“Safety in an emergency is still an issue.”
As the power lines in an underground mine cover a broad area, if we can make full use of power lines to communicate, then we can completely solve the problem underground communication. The use of power lines saves the cost of additional cable and the labour cost for system installation. Furthermore, power lines are built and installed in a rugged manner. Any underground wire or cable, when fed an RF signal, tends to distribute that signal throughout its length. Carrier current systems utilize this fact to establish communication paths using existing mine wiring.
Carrier current devices are basically FM radio transceivers that transmit and receive over existing mine wiring instead of using an antenna system. The LF (low-frequency) and MF (medium frequency)KP ranges propagate best in carrier current systems. A common example of a carrier current system is the trolley carrier phone systems presently used in many mines. Another example is the shaft communication systems that utilize the hoist rope itself to establish communications to and from the cage. The most modern system, based on MF, promises to be the most effective of a l l .
But there are lots of complex interference noises in power line communication under mine. More recently, the maturity of wireless as an accepted medium has increased the demand for instant, reliable, portable communication. Underground mines, however, have proved resistant to wireless communication due to environmental conditions that limit the transmission of radio waves. “Mines are looking to find such a system. It would become universal over time due to safety, a decrease in down time and an increase in productivity.”
This system may be further enhanced to A GPS-like (Global Positioning System) for underground mines which would serve an extremely useful function in saving energy in mining operations. Autonomous (i.e. unmanned) machinery has been a long-standing objective of the mining. This would move miners from underground mines to the surface from where they would
remotely control mining operations. Extremely important is to note that such a move would allow shutting off the energy-guzzling fans, which would result in large amounts of energy savings.
PLC is viewed as especially attractive because of several characteristics. Electricity services in most developing countries have higher reach than telephony. In addition, PLC can provide an elegant solution for in-home access and networking, since the signal can reach virtually any outlet in the home. However, there are several important technical issues in this simple scheme. The signal attenuates as it goes over the line, with higher losses at higher frequencies.
Given emission limits that restrict boosting the transmission signal, the only solution is the use of repeaters en-route, increasing the cost. Secondly, the LV transformers act as a low-pass filter, allowing electricity through with low losses but not higher frequencies. This is why most solutions rely on bypassing the distribution transformer. While an opportunity in terms of sharing capital equipment costs across users, shared infrastructures also lead to congestion, multiplexing, interference, and security concerns. To overcome these issues, PLC solutions rely on sophisticated signal processing and encoding.
For PLC to be successful, it must not only operate successfully from a technology point of view, but also present a viable business case. The market space consists of not only well-entrenched alternatives like DSL (Digital Subscriber Line) and cable, but also alternatives such as Fibre-To-The-Home (FTTH), Fiber-To-The-Curb (FTTC), and broadband wireless. Issues of telecom, regulation and competition play a vital role in deciding the future of PLC. Depending on the number of feeders emanating from the substation, different MV couplers are needed.
At every distribution transformer, a concentrator cum transformer bypass is required. This device transfers the signals to the medium-voltage line, bypassing the transformer. In addition, depending on the distances involved, repeaters might be needed to extend the signal. In addition to the one-time costs, which are amortized over specific periods, there are also explicit calculations of monthly operating costs.
After thorough estimation from various sources (web and consulting some industry people) the monthly costs of PLC is found to be around US$35 per month per user. Most of the values chosen are plausible, if not optimistic. In some hazardous locations, where specialized personnel are required, installation costs have been estimated at US$200–300. On the other hand, in normal cases, the installation would be somewhat over US$100 per user . The total capital costs per consumer (excluding Customer Premises Equipment (CPE)) average about US$85 , assuming an average of 6 homes passed per LV transformer. One result that is robust across most assumption ranges is that operating expenditures are about 45% of the total costs.
The most important variable, under the assumptions is the time period for paying off of the equipment. Given the fast changing nature of the telecom industry, the median value for economic purposes is assumed to be 5 years. In addition, within a region, the competitive pressures might be much lower, allowing for higher market share and greater sharing of equipment, marketing, and maintenance costs amongst subscribers. Given the estimated monthly costs of PLC it is almost clear that there is a gripping business case for PLC in the near term based on price for the end-user. Of course, economics is not the only factor in determining the success of PLC or any other broadband technology. User satisfaction, customer loyalty, branding, and competition (alternatives) are all important factors as well.
Courtney from Study Moose
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