110 
The N.Z. Journal of Science and Technology. [June 
ELECTRIC POWER FOR MILKING-PLANTS. 
By L. Birks, B.Sc., M.Inst.C.E., &c. 
Dairying promises to develop into the main industry of the Dominion. 
Already the exports of dairy-produce for the year ending the 31st March, 
1921, have amounted to £12,628,983, out of total exports of £48,199,359— 
i.e.> over 26 per cent. At present prices this year’s proportion will be very 
much higher, and the higher proportion will probably be maintained for 
some time. On the 30th April, 1920, there were 35,643 milk-suppliers to 
the dairy factories, and the number is increasing at the rate of about 
10 per cent, per year. Of these 8.806 were using milking-machines requiring 
2 to 3 horse-power each. This number is increasing at the rate of 16 per 
cent, per year, and will grow rapidly until it approaches the number of 
milk-suppliers. The total demand for this purpose alone will thus run 
into tens of thousands of horse-power, and will constitute a large proportion 
of the total demand for hydro-electric power in the Dominion. In fact, 
it is becoming clear that the milking-machine motor will be the main 
justification for a large proportion of the country reticulation. A revenue 
of £24 to £30 is available from the average dairy farm for the milking- 
machine alone. This justifies the line ; and when the line is once run to 
the farm all kinds of other uses are found for electricity—lighting, ironing, 
cooking, heating, and power generally. But the peak load on the farm 
service in the dairying districts will be at ; the milking-hours, morning and 
night. 
In view of the difficulty of making country lines pay their way it is 
important to keep down the size of wire— i.c., the current and power con¬ 
sumption—and with the object of investigating this matter a series of 
meter tests have been made on five typical milking-plants in the Canterbury 
District. These tests are intended to determine—(«) The power required 
to drive the average milking-plant; (h) the consumption of energy in such 
a plant over an average season. 
No attempt is made in this article to differentiate between the energy 
taken by different makes of milking-machine on the market. This is an 
important investigation which will be undertaken in due course, but it 
is only reasonable that the makers should submit plants for this purpose 
in the best working-order in each case for comparative purposes. The 
object of the present investigation is rather to determine not the lowest 
consumption under the best conditions in each case, but the general 
consumption of power under ordinary working-conditions, and for this 
purpose the plants were selected at random. A 3 h.p. motor is employed 
in each case, although the tests indicate that a 2 h.p. would have been 
sufficient for at least four out of the five, and probably, with a little 
improvement in the conditions of operation, for the fifth as well. This 
is important from the point of view of the economy in the mains, as 
the idle magnetizing-current for a 3 h.p. motor will be approximately 
50 per cent, greater than for a 2 h.p. motor, and this magnetizing-current 
has to be supplied continuously as long as the motor is running, whether 
there is anv load or not. 
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