Fig. 14.
The potential ordinarily employed in the main circuits of the Westinghouse installations is about 1000 volts, and that in the lamp circuits 50 volts, the ratio of conversion, therefore, being as 20 to 1; the dynamos are manufactured, as a rule, in three sizes, No. 1 for 650, 16 candle-power lamps; Nos. 2 and 3 for respectively 1300 and 2500 lamps. The converters are also made in three ordinary sizes to supply 20, 30, and 40 lamps of 16 candle-power each. A 40-light converter contains about 85 pounds of iron and 25 pounds of copper, so that the total weight of metal is less than 3 pounds per lamp; the electrical efficiency of the converter is said to exceed 95 per cent. when the potential is reduced from 1000 volts in the primary to 50 in the secondary. “It is claimed that the trifling loss of energy in conversion from high to low potential at the point of consumption is made up for by gain at other points, especially in the increased efficiency of the lamps, so that an alternating current plant may be counted on to give 10-16 candle-power lamps per indicated horse-power, as against 7 with the direct system;” the comparative gain is doubtful, but by using 50 instead of 100 volts the life of the lamps is increased, the former having a much stronger filament and consequently a longer life.
Electric Motors.
Having slightly diverged from the original lines by describing a system which is at present not introduced into Europe, a few remarks on the subject of electric motors may not be inappropriate, as they are almost universally worked in the United States, from the installation which supplies electric light. There is a considerable profit to the electric company if electric power is taken in the district, the wires conveying the lighting current are thus economically employed during the day. In the diagram, [Fig. 15], which represents a district at Boston, the curve on the right principally represents the demand for power which takes place between the hours of 8 a.m. and 3 p.m. A circular was addressed to all the leading electric companies in America a short time ago, asking if they supplied power as well as light, also for what purposes it was used.
Answers were received from 56 companies, who stated that the motors were employed for:—driving ventilator fans, collar-and-cuff machines, printing-presses, various apparatus in repair-shops, sewing-machines, coffee-mills, gun-shop tools, sausage-machines, elevators, lathes, pumps, saws, ice-cream freezers, organ-bellows, and washing-machines. The size of motors varied from one-eighth to 15 horse-power; 26 companies have supplied motors from arc light circuits, 14 from arc and incandescent, and 16 from incandescent circuits alone. The motors are principally owned by the subscribers, and are charged for at a rate varying from £3 to £15 per horse-power per month. The motor business is still in its infancy, but is cited to show how Electric Power can supplant the steam-engine, especially for those purposes in which the power required is small and complete control is desirable.
Fig. 15.