Introduction
The US has one of the largest mining industries in the world – an industry closely linked with the economy. In the past, the discovery of resources such as gold and oil resulted in a major population shift and rapid growth for formerly remote regions of the country, such as California, Texas, and Alaska. Extraction of these resources, and finding new deposits, continues to provide the foundation for local economies in some regions.
Some of the minerals mined in the US are coal, uranium, copper, gold, silver, iron, lead, zinc and others. Most of the mines in the US are highly automated and thus energy intensive. To provide an example, even in the last decade of the 20th century, iron ore mining alone consumed 62.3 trillion Btu of energy across a calendar year. Because mining is such a large industry and makes a sizable contribution to the national income, mines must have a dependable source of power – a crucial resource for mining processes.
The mining and mineral extraction sector both in the US and worldwide relies heavily on energy to harness natural resources such as aggregates, precious metals, iron ore, oil, gas, and coal. This energy is used to power shovels and drills for excavating these products, loading them into enormous mining trucks or onto conveyer belts, sorting, sifting and crushing ores, heating, and a hundred other functions. Both surface and underground mining operations rely on powered equipment to extract materials and load trucks. Overall, the mining sector could not flourish without the use of vast amounts of energy.
The Role of Transformers
Mine ‘Power Centers’ or ‘Load Centers’ are an essential system for underground and surface mining. Their primary function is to convert distribution voltage into utilization voltage for equipment operation, thus placing power transformers at the heart of the load center. Proper selection of transformers is imperative, and must fulfill safety, reliability, and efficiency requirements. Determining capacity rating is among the first steps for selection of a power transformer for a mining load center. A rule of thumb here is to allow 1 kVA for every horsepower of connected load. Most mining processes, however, do not produce constant loads – all machinery is not connected all the time – and therefore the 1 kVA per horsepower thumb rule will typically result in transformer oversizing. According to the SME Mining Engineering Handbook by Howard L. Hartmann, “Past experience and demand factors established by manufacturers and operators, along with the horsepower of the connected load, are essential for determining transformer capacity. For typical underground mining sections, the kVA rating may lie within the range of 50 to 80% of the connected horsepower.”
Transformer Losses
Standard transformers while under full load operate at 90 to 95% efficiency, with this figure dropping as the load lightens. This is due to inefficiencies in the transformer’s core, a main component of the transformer. The losses in the core remain the same throughout the transformer’s operating range. At 100% load, the amount of comparative loss is negligible. However, at reduced loads, the same amount of energy loss represents a higher percentage of energy being wasted. Unfortunately, average transformer loads run between 34 and 50% of the transformer’s total capacity. With the majority of the electricity used
in the US being run through transformers at these lower loads, massive amounts of energy are being wasted. This issue is of special relevance to the mining industry, simply because of its high energy usage. Mining operations also involve hostile environments full of dust, dirt, chemicals, moisture and airborne contaminants. Load center transformers need to function reliably and efficiently in these environments over a long term.
Without electric power at mining facilities, the natural materials extracted from the earth in the mining process would be much more costly than they are today. Thus, power transformers provide a lot of muscle, capacity, and stability to an essential industry. From drilling trenches to busting up rock, carting out huge loads of materials and pulling up heavy amounts of minerals, power transformers provide the strength and capability needed.
Liquid Filled and Dry Transformers: Performance Characteristics
1.Liquid-Filled Transformers
While there is still debate on the relative advantages of the available types of transformers, there are some performance characteristics that have been accepted: • Liquid-filled transformers are more efficient, have greater overload capability and longer life expectancy. • Liquid-filled units are better at reducing hot-spot coil temperatures, but have higher risk of flammability than dry types. • Liquid-filled transformers sometimes require containment troughs to guard against fluid leaks. • Liquid filled transformers are smaller in size than dry-type units for the same power rating capacity and have lower losses because of their better thermal dissipation characteristics.
2.Dry Type Transformers
Dry type Transformers are usually used for lower ratings (the changeover point being 500kVA to 2.5MVA). They are usually placed indoors, serving an office building/apartment. Dry type units typically come in enclosures with louvers, or sealed.
Dry type transformers use almost no flammable materials and therefore do not constitute a fire hazard when used underground in both coal and other mines.
Dry type transformers in the mining industry are housed in a steel tank and the core and windings are cooled by air circulating within the tank, transferring heat to the steel tank which is in turn cooled by the external air. In some compact designs for mounting on mining machines water cooling is added to further improve the performance of the transformers.
Correct choice of insulating materials and an understanding of the cooling system is imperative if the transformer is to be correctly designed. For example, a temperature rise test conducted on a transformer manufactured and sold as continuously rated, can reveal that the transformer only had a continuous rating of 65% of the nameplate rating.
The Need for Energy-Efficient Mining
With the current focus on climate change and reduction of environmental impact, government agencies around the world are making increasingly stringent demands on industries to reduce energy consumption and manage waste more effectively, among others. It is surprising how many mining operations still use twenty-year-old technology.
Regulatory pressures are already beginning to affect the mining industry – according to an article on ‘US Environmental Regulations and the Mining Industry’ on the International Development Research Center (IDRC) website, “Environmental regulations have had an effect on the US mining industry’s profitability. Companies have been forced to retrofit or renovate installations or leave the market. Increasing operational costs have affected their international competitiveness, and to some extent, this may be changing the world allocation of mining investment. Employment levels have fallen substantially, and local economies have borne part of this cost.”
Mining companies in the US are thus feeling the pressing need to be energy-efficient, simply to stay competitive. Reducing energy consumption by adopting customized, cost-effective solutions like NEMA-approved transformers and harnessing solar or wind energy to meet their future energy needs can be good ideas in the long run, especially since the alternate energy option will help mining companies keep away from fluctuating international fuel prices. Alternate sources of energy are still a very small blip on the graph, in terms of actual power provided for industries like mining, and thus the sector as a whole needs to come up with more immediate ways to conserve energy.
Various types of transformers for the mining industry:
Transformers can be used in various open pit and hard rock (subterranean) applications that range from auxiliary lighting loads to power for cranes, drag lines, conveyor belts and other miscellaneous dedicated variable speed drive applications.
Benefits of energy-efficient mining
• Reduced cost of production
• Opening up of new reserves for Conclusion
On one hand the mining industry is all set to grow to keep up with increasing demand; on the other it has to stay competitive as fuel prices zoom upwards. For an energy intensive industry, keeping a check on fuel consumption and cost is critical. Thus the mining industry as a whole is looking for energy efficient technology, including power transformers.