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, G.—ENGINEERING. 119 
highest as yet utilised is at the Fully installation in Switzerland. Here 
‘the working head is 5,412 feet, corresponding to a working pressure 
of 2,360 lb. sq. in. The pipe line is 19.7 in. in diameter and 1{ in. 
thick at its lower end, and each of the three Pelton wheels in the power 
house develops 3,000 horse-power, with an efficiency of 82 per cent. 
Until comparatively recently the Pelton wheel was looked upon as 
the only practicable turbine for high heads, and the use of the Francis 
turbine was restricted to heads below about 400 feet. This was due 
partly to the fact that a reaction turbine of comparatively small 
dimensions gives a large output under a high head, and except in 
turbines of comparatively large power the water passages become very 
small, and the friction losses in consequence large. 
A further and more important reason for the general choice of the 
Pelton wheel for high heads was the fact that in the earlier Francis 
turbines, when operating under heads involving high speeds of water 
flow, corrosion of the runner was very serious. ‘This corrosion is now 
generally attributed to the liberation of air containing nascent oxygen, 
at points where eddy formation causes regions of low pressure. Careful 
design of the vanes has enabled this to be largely prevented in modern 
runners, and in consequence the field of useful application of the Francis 
turbine has been extended until at present turbines of this type are 
operating successfully under a head of 850 feet, and this limit will 
‘probably be exceeded in the near future. 
The great increase in all constructional costs since 1914 has 
increased the cost of the average hydro-electric plant by something 
of the order of 150 per cent., and since the cost of energy produced by 
such a plant is mainly due to fixed charges on the capital expenditure, 
this cost has gone up in an even greater proportion owing to the higher 
interest charges now demanded. 
It is true that the same increased cost applies within narrow limits 
to the output from every steam plant erected since the War, and the 
relative position of the two types of power plant with coal at about 25s. 
per ton is much the same as before the War. 
The fact remains, however, that a newly constructed hydro-electric 
plant has often to compete in the market with a steam plant built in 
pre-war days whose standing charges are comparatively low, and in 
order to enable it to do so with success the constructional cost must 
often be reduced to a minimum compatible with safe and_ efficient 
operation. With this in view many modifications in design and con- 
struction have been introduced in recent plants, but there would still 
ppear to be ample scope for investigation into the possibility of reducing 
the first cost by modifying many of the details of design and methods 
of construction now in common use. 
Among recent modifications in this direction may be mentioned— 
1. The elimination of the dam in storage schemes in which 
natural lochs or reservoirs are utilised, this water level being 
drawn down in times of drought instead of being raised in 
times of flood. This reduces the cost of construction 
appreciably in favourable circumstances, and eliminates the 
necessity for paying compensation for flooding of the land 
surrounding the reservoir. 
