50 The N.Z. Journal of Science and Technology. [Jan. 
a movement is now on foot in Great Britain to interconnect a number of 
existing power-supply undertakings and large municipal stations at present 
working independently, proving that there are still advantages to be gained 
by further aggregation. 
Advantages of Electric Distribution outlined. 
The gain to the community as a result of concentrating the power plant, 
generating electricity therefrom, and distributing it over a large area, may 
be conveniently summarized under the following heads, viz. : (1) A saving 
in capital; (2) a saving in fuel; (3) a saving in labour involved in operating 
and maintenance ; (4) a higher efficiency and an increased production, 
which accrues to the power-user by the employment of a more manageable 
and flexible agent; (5) the use of the power-lines as a vehicle for conveying 
and utilizing surplus power derived from industrial operations, or power 
from lesser water-power sources ; (6) the establishment of new industries 
as the result of the facilities offered. 
Economy of Capital. 
Economy of capital expenditure is rendered possible owing to the fact 
that when a large number of power-users are supplied from a common 
source the maximum power is usually only a fourth or a fifth of the aggregate 
of the power of the segregated plant, for the reason that each power-user 
if generating* power for himself has to provide a power plant of a size 
necessarily adequate for the maximum of his requirements, which is seldom 
reached. Moreover, it is found as a matter of experience that the incidence 
of the power requirements of the individual power-user, and of a class of 
users, and of the different trades, and of different localities, is so diverse 
that the load on the common supply-station is only a fraction of the sum 
total of the individual loads if assumed to be coincident. 
In the case of the Lake Coleridge works the maximum load at the 
present time is 6,000 horse-power, whilst it is estimated that the total 
power connected to the circuits amounts to 18,000 horse-power. In the 
case of the Dunedin municipal works the maximum load recorded for the 
year ended March, 1917, was 6,200 horse-power, whilst the load connected 
to the circuits amounted to 20,500 horse-power—a ratio of 3 to 1 in the 
former case and over 3 to 1 in the latter case, which may be taken as a 
rough measure of the ratio of total power of plant when segregated to that 
of a centralized plant. The economy in capital which results from the 
concentration of the power-generating plant is, however, partly offset by 
the expenditure upon transmission, distribution, and conversion ; but in 
spite of this the net gain is considerable, and may be approximately ap¬ 
praised thus : The capital cost of an electric-power-supply system, including 
generating plant, transmission, distribution, and transformation, is about 
£40 per horse-power of generating plant when fully developed, whilst the 
capital cost of the self-contained power-user is certainly not less than £20 
per horse-power; and if the aggregate power be taken at three times the 
power of the centralized plant we reach an expenditure 50 per cent, in 
excess of the total expenditure upon an electric-power-supply system. The 
full benefit of economy in capital is not, of course, realized except in regard 
to new industries. Even then the gain is a substantial one, and the 
greater the measure of it the greater the magnitude of the power-supply 
undertaking. 
