The Mather and Hopkinson Dynamo, an excellently designed machine, is illustrated in Figs. 61 and 62. The armature, designed by Dr. J. Hopkinson. F. R. S., and Dr. Edward Hopkinson, is a modified Gr£11/1111C, with low resistance and careful ventilation. The collector is unusually substantial. and consists of 40 bars of toughened brass insulated with mica. It is usual in these machines so to shape the pole-pieces that there is a smaller clearance oppo site the highest and lowest points of the armature; this concentrates the magnetic field, and helps to prevent its distortion by the armature-current. In a 24-unit machine (designed for 300 lamps) of this pattern the armature-cores are 12 in. long and 12 in. in diameter, with 120 turns of wire. The resistances are: Armature, -023 ohm ; shunt, 19.30 ohms: series-coil, -012 ohm. With a speed of 1.050 revolutions per minute the current was 220 amperes. the machine being nearly self-regulating for 111 volts. This machine is known as the -Man chester " dynamo. Its efficiency is 90.9 per cent.
The Brown Dynamo (Fig. 63), designed by C. E. L. Brown, of the Oerlikon Works, near Zurich, Switzerland, closely resembles the Manchester " type (Fig. 62), but is even more massive. The illustration represents the ma chine designed to give 450 amperes at a 115 volts at 150 revolutions per minute. The di mensions of it are as follows : Diameter of ring, 61.4 ems.; length of ring, 55 ems. ; length of shaft, 100 ems, ; total height of machine, 120 ems.; wrought-iron cores, 00 ems. long, 40 ems. diameter ; cast-iron yokes, 30 ems. thick, 44 ems, broad ; diameter of pulley. 60 ems.; total weight, 6.5 tons; ampere turns at full ex citation, 35,000.
The armature of Brown's dynamo differs in one respect from those of the loreeeding ma chines. It is built up of thin iron disks, but these, instead of being toothed as in the l'aci notti forms, are perforated with a peripheral series of holes, as in the Wenstrilin dynamo, to receive the armature conductors, which lie thus about 1 mum. below the periphery. This construction reduces the magnetic resistance of the air-gap to an exceedingly small quantity, and there is no tendency, as with most toothed armatures, to undue heating of the pole pieces.
Fig. (U represents the general type of incandescent machine designed by Mr. William loehhausen for the Excelsior Electric Co. The armature is supported by two arms, which project from the neutral points of the mag net-frame at its base. The magnet-cores are composed of solid wrought iron. The following data give a idea of the elec trical design of the machine capable of feediiig 600 incandescent lamps: Current, 360 amperes; K 31. E.. 110 volts; resist ance of field. 18 ohms: resistance of arma ture, .005 ohm; ampere turns in field, 22, 420; ampere turns in armature, 8,820 ; size of conductors on field, No. 10 B. & S.; size of conductors on armature, bundle of four No.5 B. & S. wires; number of sections on armature, 49, of one turn each ; speed, 750 revolutions per minute; weight. 6,500 lbs.
Dynamos for Electrolytic These machines do not differ materially from the general type of generators, lint are specially constructed for delivering heavy eurrents at very low voltage. In these machines it is specially desirable to obtain a, low an internal resistance in the armature as pus:title, and frequently they are wound with heavy copper bars. The latest form of 1 lochhausen's plating-ma chine resembles closely the type of his in candescent nmehine, 04. The machine is so wound and mimeo/41 that it can be made to deliver two potentials with corresponding strengths of current. The following table gives the capacity and dimensions of these ma chines in inches: The following data relate to a Hochhausen machine capable of reducing and depositing 7,000 lbs. of copper per day of 24 hours: Current, 2,400 amperes; E. Al. F., 16 volts; resist ance of field, .285 ohm ; resist ance of armature, •000°_5 ohm ; ampere turns in field, 39,300; ampere turns in armature, 10. 800 : number of sections in armature. 9, of one turn each ; size of conductors on field, No. 10 B. & S. wires in multiple; size of conductors on armature, 36 No. 8 11. & S. wires in mul tiple : speed, 700 revolutions per minute; weight, 600 The Gener ator of :Messrs. Clarke, Chap man & Parsons has been spe cially designed for compact ma rine installations. The combi nation consists of a steam-tur bine, or rotary engine, of novel construction, connected directly with a dynamo. Fig. 65 shows the machine in perspective, and Fig. 66 shows the engine taken apart. so as to expose the interior of the turbine." As will lie seen, the steam enters the barrel at the center, passes through the succession of turbines to either end, whence it passes through a steam-way cast in the lower part of the barrel, and finally exhaust$ at the center just below the admission port. The spindle is of steel and carries a number of brass disks, reduced near the periphery, where the blades are cut to half the thickness they possess at the center. The projecting ring thus formed has
helical teeth cut upon it, Constituting the moving blades, the pitch of the teeth varying along the length of the barrel to al low of the expansion of the steam. The disks are made of such diameter as just to turn freely with the spindle within the barrel without risk of con tact with the interior of the rings which carry the fixed blades. The spindle is made very stiff, so as to allow the clearance to be made exceeding ly small, as it is found that the loss of power due to the fric tion of the spindle and its bear ings is exceedingly small, and it is very desirable to prevent, as far as possible. the passage of steam between the barrel and the disks. Between each of these disks there is an annu lar wheel, with helical teeth, corresponding to those on the disk. but sloping in the other di rection. These form the fixed or ;aide Wades. The annular wheels are fitted closely within the barrel, the teeth projecting from one half of their width only. and it is within the smooth cylindrical portions of these annular wheels that the moving blades or teeth of the disks actually turn. The barrel thus contains a double series of sirens very similar in principle to Helmholtz's double siren. only that the axis is horizontal instead of vertical. The holes in the disks are cut around the periphery, and there are a great number of pairs of disks, sometimes 45 or more, on each side of the center. One of the most ingenious features of the generator is the magnetic governor. Tlx field-magnet is shunt-wound, but not nearly saturated. Hence. any increase of the E. 3I. F. of the dynamo increases the magnetism of the field-magnet- Above the yoke is pivoted a bent iron bar, which is attached to a spring similar to the hairspring of a Watell, so that this bar is mounted exactly like the balance-wheel of a watch. Projecting from this iron bar. at an nug,le of 45', is a gun-metal fork, the extremities of which are formed with sharp edges and move immediately in front of the opening of the small copper tube which is seen in the upper part of the figure. This tube communicates with a small circular bellows, shown above the left end of the turbine barrel. The bellows are kept distended by a spring, but a small turbine on the spindle of the motor tends to exhaust the air and make the bellows collfipe under the atmospheric pressure. The throttle-valve which regulates the steam-supply is connected with the movable back of the bellows, the rod passing through a gland in the fixed front. When the iron bar above the field-magnet is inclined about 45° to the axis of the machine, the end of the copper tube is folly open. and air enters the bellows as fast as it is exhausted hr the turbine, and the throttle valve remains fully open. If the E. M. F. increases, the iron bar turns in the direction of the lines of force against the constraint of the hair-spring." the end of the fork closes the air pipe, the bellows collapse under this exhaust of the little turbine, and the steam is shut off by the throttle-valve. The action of this governor is so prompt, the moment of inertia of the moving parts of the machine being so small that nearly all the load may be turned off the machine With scarcely a perceptible change in the brightness of the lamps remaining. It will be seen flout the figure that the ColnInut ator is made of very great length. The brushes are of wire and press nearly •• end on" to the commutator. The four brushes can be shifted into any position, so as to keep the wear of the commutator even. The armature is of the cylin der type. The core is built up of thin charcoal-iron plates, separated from each other by thin disks of paper. The disks are clamped up tight by two brass disks threaded on the shaft. The coils, which are laid in channels cut in the iron. are 30 or 40 in number, of stranded or solid copper wire, and each makes one complete turn. The whole is bound round with steel piano-wire. The commutator-segments are connected each to the ends of two ad jacent coils, connected up in parallel. There are, therefore, 15 or 20 commutator-bars. The speed varies, according to the size of the machine. from 9.000 to about 10,000 revolutions per minute. The loss of power in the armature and field-magnet coils on the large machines amounts to only about 11- per cent, the high speed allowing exceedingly small resistance to be employed in the armature. A machine with an output of 32 electrical horse-power in the outer circuit is about 10 ft. C in. in length and 1 ft. 6 in. in breadth. A small machine, run ning a lamp of 1,000 candle-power, besides a number of smaller lamps, was exhibited in the Newcastle Exhibition, 1888, suspended by three wires. The exhaust-pipe was of India-rubber, and the steam-pipe was provided with a flexible joint, so that the machine could be about while running.