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.
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."
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.
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.
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