The Westinghouse Allernaling-Current Dynamo (Incandescent).—The machine at present very largely employed in the United States for incandescent lighting on the alternating sys tem is that of the Westinghouse Electric Co., shown in perspective, with its exciter, in Fig. 83. The Westinghouse Co. makes five sizes of dynamo, of which the following particulars are of interest : The No. III has an armature about 2 ft. in diameter and 2 ft. long. It has 16 poles, and rims at 1,100 revolutions per min. The arm:1litre plates have each six large holes for ventila tion and lightness. The weight of armature is 2,000 His. The insulation is mien and copal varnish, which is found to he much superior to shellac or any other material tried.
Fig. ll is n :410 view and Fig. 85 is an enil view, front which the construction will be a fly understood. The field-magnets, bolted to the external frame of the machine, form circle, radiating inward toward the armature, which is mounted in the center on from the base. They are of idhp, kid the longer axis of a cross-section of each core being parallel to the armature-shaft, as shown at f ;Ind g g, Fig. 84, the edges of the cores tieing shown at Fig. 8:6. The winding of each magnet is opposite to that of the adjacent one, so as to produce north and south polarity. The coils are slipped on the cores after being wound. The arm ature-core is composed of sheet-iron disks, insulated by paper. and having tnladar openings fur ventilation pa rallel to the axis a great number of these being laid together, the openings regis tering to form the tubes. and then bolted together by end plates, as shown. The wind ing differs from that of the Granu»e armature in no interior wire. The coif's consist of single layers of wires wound on the external surface of t he core and looped around projections 41 at the ends, attached to non magnetic rings a', so that the planes of the coils are at right angles to the radii of the armature, and there arc no crossing wires at the ends, as in the Siemens, nor wire in the interior of the ring, as in the Gramme : the ends being exposed for ventilation through the tubular open ings in the core. Adjacent coils being wound ly, as in the field-magnets, as shown in Fig. 87, generate alternating, opposite cur rents. The coils are insu lated from the core with no ea, and also covered exter nally with the same material, and firmly bound with t-he bands jl ji. The space between the armature and the field-mag nets being only in., and there being only a single laver of wire On the armature surface, both the coils and the core are in close proximity to field-magnets, and hence the mag retie and electric reciprocal actions are at. the maximum, and there is no dead or partially
inactive wire in the interior ; all the wire, except a very small percentage on the ends, exposed to the full action of the magnetic field. A Stanley direct-current, shunt-wound dynamo is used as an exciter.
The Machine of the Thomson llouston Electric Co., designed by Prof. Elam Thom son, is illustrated in Fig. 88. Its distinguishing feature is its self-regulating property, by which a constant po tential is maintained at all loads. This isaccomplished by an arrangement of the coils on the field-magnets of the dynamo, called a " composite field," in which prac tically the same methods are employed as in the direct current incandescent dynamo of Prof. Thomson (see above). As shown in the diagram (Fig. 89), a part of the magnetic field is maintained by means of current from a separate exciting dynamo. If the load upon the outside circuit is increased, it is necessary to in crease the magnetism of the field in order that the ma chine may, in turn, supply the increased demand in the circuit, and .the lights remain steady. This is usually accomplished by varying the current on the field-mag nets by a rheostat or variable resistance operated by hand. In the dynamo under consideration, however, the same result is obtained entirely automatically by passing the greater portion of the main current through the field-magnets, thus energizing the machine in exact accordance with the demands made upon it. As an alternating current is not suitable for magnetizing the fields, it is necessary to change the character of the current produced in the armature to a direct current before passing it through the special winding on the field, and this is done by a commutator at the end of the shaft. By this regulation the attention required at the dynamo is reduced to a minimum, while at the same time the efficiency of the machine is increased, and any number of lamps from one to the full capacity may be thrown on or off without in any way affecting the steadiness and brilliancy of those remaining. To allow for a predetermined percentage of loss in the wiring, it is necessary, as the load is increased, that there should he a definite amount of increase in potential, which is accomplished by placing around the field-winding for the main current a resistance which shunts that portion of current not required for regulation.