TRANSACTIONS OF SECTION G. 505 
produced by each mine or group of mines laying down its own plant, or by 
means of centralisation of generation in works serving a number of mines. 
In the United Kingdom a great extension in the application of electricity has 
taken place since the report on the use of @lectricity in mines was issued by the 
Home Office in 1904. 
As regards the Rand, the author believes that almost every operation at present 
performed by steam could be more economically effected by electricity if the power 
were generated at a central power station supplying the whole of the mines. 
He pointed out as an instance of the economy effected by the use of electricity 
that in the case of drills worked by compressed air supplied from the surface an 
inevitable loss of from 50 to 75 per cent. of the power takes place owing to 
leakage and friction. Portable electrically driven compressors placed in ventilated 
positions close to the workings would result in a loss of only about 22 per cent. 
Turning to the question of whether the supply of electrical energy could be 
more cheaply obtained from one central station or from separate works supplying 
each group of mines, it must be considered whether the advantages of centralisa- 
tion do not outweigh the disadvantages arising from losses in transmission through 
long lengths of distributing mains. 
To take an extreme case, there would be no difficulty in supplying electrical 
energy to the mines of the Rand from a central power house at the Victoria 
Falls on the Zambesi; but, even disregarding the cost of the enormous works 
necessary for utilising the water-power, the annual capital charges on the cost of 
the transmission lines would far outweigh the annual outlay on coal used in works 
laid down close to the Rand. 
The costs of generation and distribution of electrical energy divide themselves 
as follows :—(1) Capital charges; (2) Working expenses, 
As regards capital charges the advantages gained by centralisation and the 
resultant diversity factor are that the plant required is reduced in total capacity ; 
also that plants of larger size can be used and the capital expenditure thereon 
minimised. 
As regards the effect of centralisation on working expenses, and considering 
steam-driven plant, the consumption of coal is reduced owing to the size of the 
generating plant. A saving is also made in water consumption, and in oil, waste, 
and stores, for the same reason. A great saving would be effected in wages, as 
the same number of men would be required to operate, say, six plants of 
1,000 kwts. as would be required to work the same number of plants ten times 
the size. Similar savings would be effected in the other items of working costs. 
As regards the size of a central station to supply the whole of the Rand the 
total consumption of power at present may be estimated from the amount of coal 
consumed annually. In the report of Mr. T, R. Price, the general manager of the 
Central South African Railways, for 1904 it is stated that the coal carried 
amounted to 1,864,926 tons. Assuming that 1,250,000 tons out of this total are 
taken by the mines on the Rand, and assuming that the coal had a calorific value 
of from 8,000 to 12,000 B.T.U.s per lb., and, further, that 6 lbs. of coal were 
used for every brake horse-power hour, the total power consumed on the Rand 
would be 416,666,666 horse-power hours, or, say, 400,000,000 horse-power hours 
per annum—equivalent to an average output throughout the area of over 45,000 
horse-power, working day and night without intermission. 
The above consumption of power is equivalent to 300,000,000 units (k.w. 
hours) of electrical energy per annum. 
In order to arrive at the total capacity of a central power house to deal with 
this output it is necessary to consider the load and diversity factors which would 
be obtained. 
As already indicated the extent to which the aggregation of output leads to 
economy in working cost practically turns upon the exccllence of the load and 
diversity factors which would result from the supply to a large number of con- 
sumers. The term ‘load factor’ is the name given to the ratio of the actual 
output of any works during a given period to what that output would have been 
had the works been operating at their maximum rate throughout that period, 
