258.1

The shaft bearings, bearing standards, base plate, and armatureslides are cast in one piece. The shaft carries two heavy cast-iron yoke-pieces 27 inches in diameter. To each of these are screwed, at equal radial and circumferential distances, the wrought-iron cores of 12 magnets of alternating polarity. Thus the whole rotating mass acts as a fly-wheel, tending to neutralize any variation in the speed of the prime generator. As the nominal speed of the machine is less than 1,100 revolutions per minute, the structural strength is more than sufficient to meet all demands made by cen. trifugal force. Further than this, the mechanical stress is less when the magnets are excited than when the alternator is running without load, as the lines of magnetic force between the faces of opposing poles tend to counteract centrifugal force. In machines

silver frame consisting of two semicircles bolted together on the line of the vertical diameter. Into the slots of the frame slip the six mounted armature-coils, the tongue on the edge of the one engaging with the groove on the edge of the next. The coils thus thrust into the intense magnetic field constitute a disk nine-sixteenths of an inch in thickness, and with an opening in the centre through which passes the revolving shaft. As there is no magnetic metal in the armature, there are no local currents to waste the energy.

The several coils are insulated carefully; and the stationary armature, as a whole, is insulated from the bed-plate on which it rests. The coils are joined in series, the binding-posts adjacent to any radial line of division between the two coils constituting fixed

of larger size, as usual, the speed is less, that of the 150,000-watt dynamo being not more than 700 revolutions per minute.

The most interesting part of the alternator is the fixed armature, shown in Fig. 2. The vertical disk is occupied by flat armaturecoils made of insulated copper ribbon wound on porcelain cores. The copper ribbon of each coil is re-enforced on either side with strong insulating material of the same thickness as the porcelain. One of these re-enforcements is grooved, and the other tongued. The coil, consisting thus of core, ribbon, and re-enforcements, has an angular width of 60 degrees. The upper part of each face of each coil is covered with an insulating plate five-sixteenths of an inch thick. The coil thus built up and insulated is set in Germansilver holders, cut from turned rings, and held together by sunkheaded screws. Each terminal of the copper ribbon connects with a binding-post, as shown.

The six armature-coils thus mounted are carried in a German

FIG. 8.

terminals for the main line. There is no commutator, and there are no collecting brushes to take the alternating current from the rotating parts.

The low resistance of the armature-coils is evident. It would seem impossible for one of them to burn out. None ever has burned out; but if one should, it may be removed, and a new one readily put in its place, in three minutes, or the injured coil may be shunted out of the circuit and the dynamo kept running with the other five until the time for shutting down. The coil section complete weighs only about 20 pounds. The whole armature may be removed by loosening the coupling-bolts, and sliding each half of the frame from between the field-magnets (Fig. 3).

In action, the 24 field-magnets of the alternator are excited by the direct current from a Brush dynamo of the well-known form. This exciting current is carried to the brushes that rest upon the two uncut insulating rings (shown at the left of Fig. 1), and thence

oped to the place where it is to be used, the form given to it for economy of transportation may be changed so as to adapt it fully to the uses for which it is intended. High tension may be exchanged for greater current, volts for ampères. This transformation is accomplished by the converter shown in Fig. 6. In this converter, the core consists of a polygonal ring made of insulated iron wire, so wound as to leave several concentric air-spaces in the In the converters of the smaller sizes, the core is built up of

core.

Over each of these single-layer parts of the secondary coil ar bound a few layers of smaller copper wire to form a corresponding part of the primary coil. These corresponding parts of the, sec ondary and primary coils are separated from each other by insu lating pads at the corners and intervening air-spaces in the sam manner and with the same advantages as previously described.

The ventilation of these converters is specially provided for, and the insulation resistance is exceedingly high. It is impossible to so overload the wire of the primary circuit as to force its current into the secondary circuit: in other words, the high-tension curren cannot pass the converter. The converters are tested at the fac tory with double load, and, though no one has ever given out, over loading is made impossible by the use of safety-fuzes for the pri mary coils. These are extra long, and so mounted on slate or porcelain strips that they may be removed or replaced with the fingers merely, and without touching any metallic part of the con

verter.

The converter-coils, with safety-fuzes, etc., are placed in wind and weather proof cast-iron boxes of pleasing design (Fig. 8) and may be placed wherever most convenient; the governing

FIG. 4. BRUSH ALTERNATING SYSTEM.

perforated thin iron plates (Fig. 7). In either case, the iron is so divided that the efficiency of the converter is little less with half than with full load. Upon each side of this core or iron ring is wound a single layer of heavy copper wire. The four or five single-layer coils carried by each half of the core are joined in series; and the two groups, borne by the two halves of the core, are joined in multiple, the whole constituting the secondary coil. The terminals of this secondary coil connect with the secondary main line running into houses and supplying current for the lamps. Most of the converters are wound so as to give a secondary current of

about 100 volts, but may instantly be connected to give 50 volts and twice as many ampères as before. They are made in sizes that supply each from 5 to 250 16-candle-power lamps, or more.

Between the fine iron wire of the core and the heavy copper wire of the superposed secondary coil, insulating pads one-eighth of an inch thick are placed at the corners of the core. Between these insulating corner-pieces are insulating air-spaces. Thus the copper and the iron are separated from each other at the corners of the core by their respective coverings and the insulating pads, and at all other points by their respective coverings and open airspaces, the latter affording ample ventilation and facility of examination.

FIG. 9. BRUSH ALTERNATING SYSTEM.

principle being to do as much work as possible with the less expensive primary wire, and to shorten the more costly secondary main. These converters are now made in sizes ranging from 2-lamp to 250-lamp capacity. With converters, as with dynamos, the larger sizes are the most economical. With a 100-volt converter fed by a 2,000-volt primary current, it is more easy and profitable to run a short secondary main to supply several consumers than to provide a converter for each consumer.

Fig. 9 represents the ammeter, which is placed in the main or feed circuit, wherever it is desirable to measure the strength of the current. It is a compensated expansion device, acting on the principle of one type of Brush arc lamp. It is free from any magnetic action, the simple compensating arrangement insuring the normal working of the apparatus at all temperatures. It is equally efficient with direct and with alternating currents.

The alternating-current apparatus of the Brush Electric Company here described is based on the patents of Charles F. Brush and Gustav Pfannkuche, the latter having the supervision of this branch of the Brush Electric Company's business.

THE heat in Russia and other parts of northern Europe has been intense of late. The Central Observatory at St. Petersburg has not recorded such a high temperature at the same time of the year since 1774.