184 SECTIONAL ADDRESSES. 
Main; three-phase power was transmitted, at 8,500 volts, from a water- 
power station at Lauffen to Frankfort, a distance of 110 miles. 
This development of the use of high-voltage alternating currents 
followed the development of the transformer. Gaulard and Gibbs patented 
a system of distribution involving transformers in 1882, and, although 
their patent was upset in 1888 on the ground of its impracticability, the 
_ present method of using transformers for the distribution of electrical 
power was introduced in 1885, and shown at the Inventions Exhibition 
in London in that year. Although from 1890 onwards there has been a 
steady increase in the size of alternators and transformers and in the volt- 
age employed for long-distance transmission, the last few years have seen a 
really amazing increase in thesize of the units employed. In 1913 the largest 
2-pole turbo-alternators had an output at 3,000 revolutions per minute of 
about 7,500 kilowatts; such machines are now made up to 30,000 kilo- 
watts, and 4-pole alternators are running at 1,500 revolutions per minute, 
with an output of 60,000 kilowatts. This increase in size and in peripheral 
speed has been made possible by improvements, both in the material and 
in the design. With a bursting speed 25 per cent. above the running speed, 
the peripheral speed can now be raised to 150 metres per second. Improved 
methods of cooling and a better understanding of the various causes of 
loss in the armature have enabled the materials to be used at higher 
current and flux densities. 
This great increase in the size of units is not confined to the steam 
turbo-generator, as can be seen from the water-turbine sets recently added 
to the Niagara installation. Whereas the original Niagara turbines were 
of about 5,000 horse-power, the new ones have an output of 70,000 horse- 
power at the low speed of 107 revolutions per minute. 
The importance of cheap electric power has led to this great increase 
in the size of the units in the generating stations. Any slight difference of 
efficiency between a 10,000-kw. and a 60,000-kw. alternator is of little 
importance, and would certainly not counterbalance the decreased factor 
of safety due to concentrating the whole power supply in three or four 
large units, instead of distributing it between a dozen or more units. 
The reason for the adoption of the smaller number of large units lies 
almost entirely in the decreased capital cost per kilowatt of plant. In my 
opinion, however, there are many cases in which too much consideration 
has been given to this factor, and too little to the importance of a 
guaranteed continuity of supply. 
Of even greater interest than the growth in the size of the units in the 
power station is the development of the switch control and protective 
gear, which is such an essential element in the success of the modern power 
plant. In the early days of electrical supply all the switch-gear was mounted 
on slate panels in the engine-room ; then, as the power and voltage in- 
creased, the switches were placed above, below, or behind the board and 
operated by mechanical links; then they were removed to another part 
of the building, each enclosed in its own fire-proof cubicle, and operated by 
means of relays. The modern high-power switch, like the transformer, 
is oil-immersed in its iron containing case, and is so robust and weather- 
proof that it needs no further protective covering, but can be placed in the 
open air. The insulated bushings through which the leads are taken into 
the case are the most vulnerable points, but constitute no insuperable 
difficulty at the present time. 
