Choosing the Right Transformer for the Mining Industry

2

Executive Summary

The mining industry occupies a significant position in the US economy. With no shortfall in the demand for

minerals and ore, one can only expect the industry to keep growing.

One worrisome aspect of the mining industry in the US, however, is its excessive demand and

dependence on energy. Highly automated, the industry demands trillions of Btu (British Thermal Units) of

energy every year; the industry’s high demand for energy has also made it easily affected by the

fluctuating international prices of fossil fuel. While other sectors of the US economy are searching for

greener, more cost-effective energy options, the mining industry has also come under pressure to follow

suit.

Transformers are a key element in collecting and transporting energy on the national grid and their

efficiency has always been a source of debate. This whitepaper seeks to address this crucial question of

selecting the right transformer for the mining industry.

While the mining industry is critical to the economy, it is, by its very nature, full of hazards for both

manpower and machines. The transformers used have to be robust and technologically advanced to

function in dust, dirt, chemicals, and in the presence of high levels of moisture both above and below

ground. Despite the high levels of automation in this industry, it is also manpower intensive in certain

areas, which means that people are often working around all kinds of dangerous machinery; transformers

should not have to be included in that category.

This whitepaper delivers useful information about the role of transformers in the mining industry, the

various types of transformers and some tips on how to select the right one. The whitepaper also takes a

look at the need for energy-efficient mining, and Pacific Crest Transformers’ offerings to the industry.

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.

3

Energy Requirement for a hypothetical Iron Ore Mine

Process Btu/ton of Ore

Drilling 1,707

Blasting 2,901

Loading 6,315

Haulage 50,859

Miscellaneous 6,485

Total 68,267

Source: U.S Department of Interior, Office of Surface Mining, The Effects of Increasing Costs on the Future Relation Between Open

Pit and Underground Mining, Michigan Technology University, Department of Mining Engineering

Electrical systems for this industry must meet some basic standards, as stipulated by the Institute of

Electrical and Electronics Engineers (IEEE):

• Safety to personnel and property

• Reliability of operation

• Simplicity

• Maintainability

• Adequate interrupting ability

• Current-limiting capacity

• Selective-system operation

• Voltage regulation

• Potential for expansion

• First cost

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

4

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.

5

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.

Pacific Crest Transformers and the Mining Industry

Pacific Crest Transformers (PCT) has been providing solutions to the mining industry since its inception in

1919. Over the last 90 years PCT has had over a 100 clients from this industry across the world. PCT has

experience in building Padmount, Station and Secondary Unit Substation Transformers, and today

specializes in environmentally friendly and efficient liquid-filled distribution transformers.

PCT designs custom transformers after elaborate consultative process with clients. PCT transformers are all based on client specifications and are designed to fit into existing infrastructure.

PCT custom builds various types of transformers for the mining industry:

PCT 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. PCT also ensures reliable

transformer operation in hostile environments

containing moisture, dust, dirt, chemicals and

other contaminants.

Benefits of energy-efficient mining

• Reduced cost of production

• Opening up of new reserves for mining

• Positive response to new government regulations on improving safety performance

• Reduced impact on climate

PCT Transformers can be:

• Designed to operate on a tilt

• Designed for skid mounting

• Designed for movement over rough ground

• Designed for severe motor starting

• Designed for harmonic loads

• Designed for corrosive atmosphere

• Designed for high elevations

• Designed for special impedance

6

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.

As companies in the mining industry explore more energy-efficient possibilities, PCT has the expertise and long experience to provide custom-designed energy-saving transformers for all load center requirements.