Kingdon Inductor dynamo (Fig. 101) has been designed to meet the wants of electric-supply stations employing the alternating transformer, or the alternating direct system. The main feature of the " inductor" dynamo is that all the bobbins of electric con ducting wire are fixed ; there are therefore no brushes or loose contacts. The number of bobbins in use may be easily varied to suit the requirements of the supply ; another ad vantage is that, owing to the bobbins being fixed, even with high-tension currents, there is very small risk of destroying the insulation of the machine. An "inductor" dynamo of normal size—i. e., 50 kilowatts—has 32 coils wound, and mounted on 32 cores (radial), which are composed of plates of thin, very soft charcoal-iron, magnetically insulated one from the other. Sixteen of these coils represent the field-magnets of the dynamo, while the remaining 16 intermediate ones correspond to the armature-bobbins of other machine~. The cores and poles of both field-magnets and armature-bobbins are arranged radially, surrounding the only moving part of the dynamo, which is called thu "inductor-wheel" (Fig. 105), which is the rotating part of this dynamo. It consists of 10 musses of laminated soft charcoal-iron, called inductor-blocks, also meehanically insu lated, which are mounted on the circumference of gun-metal fliers or wings. which in turn are clamped between two steel plates, mounted on a boss keyed on to the main driving-shaft. Each indicator-block is jest long enough to be embraced by the poles of one field-magnet and one armature-bobbin. The field-magnets are separately excited. The energv consumed for this purpose does not, as a rule, exceed 2 per cent of the maximum output of the machine. By rotating the soft-iron inductor-blocks be fore the respective poles of the field-magnets and armature-bobbins, rapid periodic rever sals of the polarity of the armature bobbin pole are effected. This produces alternating currents in the armature-coils. Between the in ductor-blocks and the above-mentioned pole-pieces there is only just sufficient clearance to allow of free rotation ; consequently the resistance of the magnetic circuit, of the air-space is a minimum, while the soft character of the iron in the inductor-blocks and the magnet and armature-cores tends also to make this loss as small as possible, thus producing a very efficient machine at a km speed.
Fig. 106 illustrates the Kennedy alternator. The machine very much resembles a trans former in its parts, and is about as simple in construction. The iron field-magnet portions snrroillld the en !Ter coils. which are simple rings of insulated wires the inductors are carried on gun-metal wheels, and in revolving alternately open and elose the magnetic circuit the rapper coils, t1111. indneing current in them. There is no reversal of magnetism in any part 4.1 the Iperntiiii Of the only a simple rising and falling of the magnetic flow without reversal. The iron is made of very ample sections, so that the induction is never high, and falls to zero. The excitation is constant, lint the induction varies with the position of the inductors. There are two pairs of coils in the machine, and two sets of in ductors, placed as shown in Fig. 107. The generating coil is wound first and insulated, then
the exciting coil is wound over that, and the whole is insulated and fixed in the machine in the recesses formed in the field-blocks. By using two pairs of coils and two sets of inductors, and exciting the coils so that the field-blocks are magnetized with a pole in the middle and similar poles at each end, when the two exciting coils are in "series" with each other, any inductive effects on the one exciting coil are exactly and entirely neutralized by those effects on the other exciting coil. The two generating coils can be coupled either in series or in parallel, but the exciting coils must always be in series. This machine is very simple and inexpensive to build, and there is no difficulty with insulation or in constructing them for any pressure or frequency required. In large dynamos there are four pairs of coils and four sets of inductors. In the machine illustrated the inductors are 21 in. in diameter. the coils being 21+ in. inside diameter ; the electromotive force of the generating coil is about 1.35 volts per ft., working at very moderate inductions and at moderate speed, and this can be safely raised to 2 volts per ft. For low-pressure alternating currents this machine is equally applicable. A machine with inductors 4 ft. in diameter gives an output of 150.000 watts (100 volts 1,500 amperes) at a speed a little over 2-00 revolutions per min. This is suitable for low-pressure distribution near the station, and high-pressure at a distance by means of step-up trans formers.
Machines in which iron masses alone and no conductors are moved have also been con structed by Wheatstone, Henley, Elihu Thomson, Forbes, Klimenko, and others.
The OerliAoss Three-Phase Allernalor.—This machine (Fig. 108), designed by Mr. C. E. L.
Brown, was employed as the generator in the celebrated installation of power-transmission between Frankfort-on-the-Main and Lauffen-on-the-Neckar, 1891, a distance of 112 miles. The machine was designed for 300 horse-power, running at a speed of 150 revolutions per min. The armature-circuits are arranged to give three alternating currents, lagging one behind the other. Each of the three circuits of the machine is wound for a pressure of 50 volts and a current of 1,400 amperes. The current output being large, rubbing contacts have been avoided by making the armature stationary and the field-magnets revolve. The arma ture-conductors are 29 nun. in diameter, and consist of massive bars of copper, insulated inside with asbestos tubes, and buried in holes punched out of the iron close to the internal periphery. Foucault currents, which would values in such large clipper con ductors, if they were arranged in the ordinary way, are by this device avoided; in fact, experiments made with "buried" conductors, 50 non. in diameter, did not show that any power was lost by Foucault currents. This method of arranging the armature conductors Is mechanically strong, and, as it enables asbestos to be used as an insulator, results in an iirmature which is absolutely incombustible. Moreover, the reduction in the air-space, and the consequent improvement of the magnetic circuit, reduces the exciting current.