II. Complete the following terms with suitable adjectives:

gravity, mining, pulp, support, pressure, manshift, pipe, jet, hose, development, loader, deposit, conditions, combus­tion, cutter

Electricity in collieries

The many advantages of electricity as a medium of power supply, its economy and ease of generation and transmission, its convenience of application and its versatility led to its early adoption in the mining industry and to its increasing use throughout the years.

Before considering in detail the various applications of electricity to mining, it is desired to consider briefly other forms of power available for use in mines and the reasons why electricity is rapidly replacing these. So far as underground plant is concerned¹, the only two main forms of power em­ployed are electricity and compressed air. Compressed air is used in places where, because of gassy conditions, electricity cannot be used. The transmission of energy in the form of compressed air over long distances underground is, however, extremely uneconomic compared with electricity and the quantity which can be so transmitted is limited by the size of mains which can be installed in roadways underground. There are also considerable difficulties in operating large-power consuming units such as modern cutter loaders by com­pressed air.

At the surface of the mine, a third source of power is avail­able, namely, steam. Although many collieries are completely electrified underground, steam still provides a considerable portion of the surface power requirements, particularly for the larger units, such as win'ding engines, main ventilating fans and reciprocating or turbo-compressors.

In general, electrical transmission and utilization is much more efficient and much easier in application than other means.

The amount of electrical energy required at a colliery depends primarily upon the extent² to which the colliery is electrified and upon the tonnage produced.

The consumption of electricity in terms of units per ton raised³ varies considerably throughout the coal-fields, depend­ing largely upon the depth of the shafts (where electric wind­ing is practised), the amount of pumping and the extent to which electrically-driven compressors are employed.

Notes

1. So far as underground plant is concerned — что касается подземной установки

2. depends primarily upon the extent — зависит, главным образом, от масштаба

3. in terms of units per ton raised — в единицах на тонну добытого угля

Exercises

I. Answer the following questions:

1. What are the main advantages of electricity as a medium of power supply in collieries?

2. What forms of power avail­able for use in mines do you know?

3. Where is compressed air used?

4. What does the amount of electricity required at a colliery depend upon?

5. Where is steam used as a sourer of power?

The importance of light in mines

Light is an essential requirement in all industrial enter­prises and- the provision of adequate artificial lighting below ground is a prime necessity because of the complete absence of natural lighting. Lighting has an important effect upon safety, health and productivity. Bad lighting results in acci­dents.

The provision of adequate light in mines presents special problems and difficulties. The chief difficulties arise from the presence in most mines of inflammable gases which require special apparatus.

The second difficulty is most apparent at the coal face, and is associated with the dark colour and the light-absorbing properties of the coal and the surrounding strata. Coal absorbs 95 per cent of the light falling upon it compared with only 40 to 50 per cent for white-washed surfaces.

Roadways are comparatively narrow, and long tunnels are not easy to illuminate uniformly. Coal faces are frequently low in height and the presence of props and machinery, which cast shadows, makes even illumination impossible.