These nutehhtes are built in sizes ranging fro in a few horse-power to over 250 horse-power, and the following data refer to three sizes, the /17. W., or Kilowatt, being equivalent to 1.33 horse-power : Fig. 53 shows the general type of Weston machine for are and incandescent lighting. Probably the most strikingly distinctive feature of the Weston machine is the sectional arma tore. The armature-core (Fig. 54) is built up of iron disks of the form shown. These are secured together upon the armature-shaft. but separated somewhat from each other, so as to leave spaces between them. These spaces serve to break up the continuity of the core, and thus prevent the formation of induced currents; they also form ventilating spaces. By a very ingenious arrangement, the armature is made to act as a centrifugal blower, to main tain a circulation of air through the core and about the coils, and thus whatever heat may be generated in them is dissipated. The coifs are spread apart, where they pass across the heads of the armature, by flanged plates (shown somewhat removed from the head of the armature in Fig. 54). so as to leave an opening about the shaft for the admission of an•, which is taken into the interior of the armature and thrown out between the coils by centrifugal force. With a sectional arm ature and this system of ventilation, no trouble whatever is experienced from heating of the core or coils. The armature complete is shown in Fig. 55.
The cores and pole-pieces of the field-magnets are made very heavy, so as to maintain an extremely intense field with comparatively little expenditure of current-energy, and the pole projections on the armature being almost directly in contact with the pole-pieces, concentrate the lines of force of the field directly upon the armature. All of these features of construc tion contribute to produce the requisite electromotive force with very low internal resist ance and low speed.
In a Weston machine, de signed for 200 incandescent lamps. 199 could be turned out without materially affecting the brilliancy of the remaining one. The data of this machine are as follows: Weight. 2,836 lbs.; length. 62.5 in.; breadth, 53 in.; height, 2515 in.: resistance of external circuit, ohm: resistance of nrma ture,'008 ohm ; resistance of field-coils, 24.1 ohm ; E. 31. F., 67 volts; uum ber of revolutions per min., 960; diameter of armature - wire, 0.24 in.
The ratio of armature to shunt resistance in this ease was therefore 1 to 3,000. This high into is. however, rarely at tained.
Fig. 56 illustrates the Thomson - Hmodon Dy namo for incandescent lighting. It resembles in general design the are machine its distinguish ing feature, however, is the method employed for obtaining constant poten tial automatically without the use of external resist ances. This is accom plished by means of a set of - series - coils " placed nt an inclined position around the armature, as shown, which react upon the armature so as to maintain the point of commutation fixed at all loads.
Fig. 57 shows the Eickemeyer Dynamo, which claims attention on account of its novel construction. The object sought to be obtained by the inventor is to concentrate the full excit ing force of the field-coils upon the armature-core. and he ac complishes this by encircling the armature-core with an ex citing helix. and then inelosing the whole within an iron shell, The latter is provided with pole-faces. and thus completes the magnetic circuit which in eludes the armature-core and the cheeks.
Fig. 58 shows a longitudi nal section of one form of the machine, and Fig. 59 a Intim: verse section wit h the armature removed. It will be seen that the shell of iron inclosing the armature is built np of at lami nated mass of sheet-iron. to which end-pieces of cast ism are added, the whole being bolted together. The iron sheets are stamped out cirem larly with a longitudinal exten sion On the limier and lower halves. The rectangular space thus formed is occupied by the field-coils, which are W01111(1 in same direction as the wires of I he armat ore. and are divided so as to leave a space for the passage of the armature-shaft. The armature is placed within the exciting (.oils, and is completely surromaled by the coils above and below and by the iron al the side. The imignelie circuit thus formed is a complete one, and not Ilse slightest of is pereeptihk. As regards t he output of this machine, it may be remarked that JIr. Eicketneyer has made the experiment of plae ing the armature of an old form of machine within the field, such as he uses, and by employing the same amount of field-wire as was used on the older form he succeeded in increasing the out-put of the armature nearly twice. More recent machines are built of solid east steel.
In the Kennedy Dynamo (Fig. GO) the field-magnet is made of three pieces. with only one field-bobbin. The core of the bobbin is mode of hammered scrap-iron, and measures 10 in. in diameter and 14 in. in length ; the pole-pieces are of soft cast iron, and are of much greater cross-section than the core of the bobbin, This construction has the advantage of simplicity. et4nbined with compactness and low magnetic resistance. The armature is built of iron disks, and the core is turned true, outside and inside, and mounted on metal spokes on it steel shaft. The outsides of the armature are usually turned up true on the shaft. The armature-core of this machine is 12 in. long, 10 in. in diameter outside, and 0 in. inside diameter, the depth of core being thus 2 in. The arma ture is wound with fiat wire 5 nun. by 3.5 mm., one layer outside. The current allowed for this armature running constantly for long runs is amperes. The commutator is made of solid drawn copper sec tions, insulated with mica. and is of large size. The brushes are adjust able in all directions, and the press ure on the commutator is adjusted by springs. The brushes require a slight adjustment for varying loads, but at a speed of about :100 revolu tions t he machine gives 102 volts at the terminals. According to the tests of Prof. Andrew Jamieson, the dynamo gave an output of 10.850 watts, or 108.5 amialres, and 100 volts at 020 revolutions per minute. The peripheral speed of the arma ture is 1,900 ft. per minute. The following are the data of construc tion and operation of the machine : Resist once of armature. warm. ='04 ohm ; resistance of magnet-shunt, warm, = 20 ohm : resistance of mag net main coil, warm, = -03 ohm ; current in working circuit = 108-5 ampIres; current in shunt-magnet coils = 5 ampGres; difference of potential at dynamo-ter minal = 100 volts; difference of potential at brushes = 10:1 volts; speed in revolutions per minute = 030: temperature of air = 60' F.: highest temperature of armature = 140° F.: highest temperature of magnet-coils = 125° F.