March 22, 1894] 



NA TURE 



4B5 



in connection with the conductors for the transmission 

 of the power. There are many difficulties experienced 

 with high frequency currents which are either largely 

 mitigated, or entirely removed, by the adoption of a low 

 rate of alternation. There is, first, the tendency of 

 alternating currents to confine themselves to the outside 

 of the conductors carrying them, thereby increasing the 

 resistance, an effect increased by augmenting the fre- 

 quency ; secondly, there is the impedance of the line, 

 due to the magnetic field formed between the go and 

 return wires of a circuit, which is also increased by rais- 

 ing the frequency ; another is the tendency to discharge 

 from a conductor, shown so well by Dr. Lodge's ex- 

 periments with extremely high rates of alternation, which 

 is less marked the lower the frequency ; a fourth is that 

 tendency to break down solid insulators, shown by Mr. 

 Tesla, again using currents of extremely high frequency, 

 which is reduced the lower the rate ; and lastly there is 

 the loss due to capacity, both owing to static charge, and, 

 combined with the self-induction of the circuit, resonant 

 eftects, which is reduced more and more the lower the 

 frequency is made. There is one important objection, 

 in general, to the use of a slow period of alternation, and 

 this is that, with the frequency to be used at Niagara 

 Falls, flickering of lamps, both arc and incandescent, 

 is perceptible. But this objection is very easily overcome 

 by changing the alternating current into a continuous 

 current, as will have to be done for other purposes at 

 Niagara Falls, which may be accomplished in one or two 

 ways, to be mentioned later. This objection, too, had 

 not the same weight at Niagara Falls as it might have 

 at other places, as most of the power transmitted will 

 be used for motive-power purposes. 



The electric pressure selected for use in the neigh- 

 bourhood of Niagara Falls, and for transmission to 

 Buffalo — one of the first more distant places to be supplied 

 with power — will be 2000 volts at first, for the former, 

 and probably 20,000 volts for the latter. As regards the 

 means of obtaining the 20,000 volts, it is much to be re- 

 gretted that the inability to obtain from American manu- 

 facturers a guarantee for machines constructed for such 

 a pressure, they having never supplied machines at a 

 higher pressure than 2000 volts, has necessitated the 

 adoption of step-up transformers. The consequence is 

 that economy has had to give way to expediency, and this 

 has again made itself felt in the pressure of 2000 volts 

 decided upon, as probable, for the local distribution. 

 The use of the extra high pressure, even here, would have 

 obvious advantages. One would be the resulting uni- 

 formity in the whole system, local and distant ; and a 

 second, the saving to be effected in the amount of copper 

 in the conductors. It is a significant fact in support of 

 this contention that, to put in the most economical sec- 

 tion, using 2000 volts, will require 3 sq. in. of copper for 

 each conductor, or 12 sq. in. for each 5000 horse-power 

 dynamo. 



The dynamos for generating the power in two alter- 

 nating currents differing in phase by 90", at 200J volts, 

 will be mounted directly on the top of the turbine shafts. 

 They will be of 5000 horse-power each, and were 

 designed specially for the work by Prof. George Forbes, 

 as the Company's electrical consulting engineer, three 

 being now made by the Westinghouse Electric and 

 Manufacturing Company, of Pittsburgh, Pa. In them 

 the armature is fixed, the field magnet, formed of a nickel- 

 steel ring, 12 ft. 9 in. in diameter, 4ft. 2 in. high, and 6 in. 

 thick, with the pole-pieces pointing radially inwards, 

 revolving outside. In this way the pole-pieces are well 

 held in against centrifugal force, and, moreover, the 

 magnetic pull between the pole-pieces and armature 

 opposes the centrifugal force of the revolving field 

 magnet. The nickel-steel ring with the pole-pieces is 

 suspended from a steel spider with eight arms, which 

 spreads over the top of the armature like an umbrella, 



NO. 1273, VOL. 49] 



being keyed to the solid steel shaft- passing through the 

 centre, and attached to the ring by studs and nuts. The 

 attendants will be able to enter the interior of the arma- 

 ture at all times, whether the machine be running or not, 

 for the purpose of attending to the two bearings inside, 

 and the collecting rings on the under side of the spider 

 and the brushes, for passing the current to the exciting 

 coils, &c. 



From the dynamos conductors will be led, in conduits 

 in the floor of the power-house, to a large subway running 

 the whole length of the house and opening into a large 

 cellar underneath it, in which will be placed the trans- 

 formers for raising the pressure for the transmission of 

 the power outside, and other apparatus. 



The means adopted for running the conductors between 

 the power-house and the spots where the power is to be 

 utilised is of the most satisfactory description. Bearing 

 in mind the very real troubles likely to arise with a pole 

 line from lightning, wind, and frost, including the formation 

 of sleet upon the wires and insulators, the Cataract Con- 

 struction Company abandoned this cheapest form of 

 construction, and decided to build a subway large enough 

 to carry the conductors, and allow of a man walking or 

 travelling on a trolley along the whole length. The 

 length built up to the present extends from the power- 

 house to the Pittsburgh Reduction Company's works, 

 to be devoted to the production of aluminium, and 

 one of the first places to be supplied with power, a dis- 

 tance of 2500 feet. This subway, which may eventually 

 be extended to Buffalo, is built after the design of the 

 Cataract Construction Company's electrical consulting 

 engineer, and is of concrete 9 or 10 inches in thickness. 

 The height inside is 5 ft. 6 in. It is of the horse-shoe 

 shape, as shown in Fig. 4, which is from a photograph 

 of the actual work. Iron castings are embedded in the 

 sides every 30 ft., on which are bolted brackets carrying 

 oil insulators to carry the bare copper conductors. In 

 front of the conductors, on each side, will be placed screens 

 formed of wooden frames 10 ft. long, on which will be 

 stretched open metal, covered with plaster to within 

 about a foot of the top, which will there be left open to 

 allow of inspection of the conductors behind. Down the 

 centre space, 22 inches wide, will be a track for an elec- 

 tric trolley, with a conductor between the rails. Drain- 

 age, &c., has been well provided for, manholes built to 

 the surface of the ground, and each casting carrying 

 insulators is put to earth. The subway will probably be 

 artificially dried by forcing a current of dry air through 

 it. In this way a very satisfactory piece of work, both 

 from the point of view of efficiency, and that of safety, 

 has been undertaken and practically completed, making 

 this part of the work of the same permanent character 

 given to the rest of the undertaking. 



It only remains to say a few words with regard to the 

 motors to be used for converting the electrical power 

 into mechanical power at the far ends of the lines, and the 

 other purposes to which it will be put. 



For electric lighting the current, as already stated, 

 will have to be transformed into a continuous current on 

 account of the low frequency of alternation adopted ; a 

 continuous current will also be required for other pur- 

 poses, such as street railways, metallurgical works, and 

 probably the working of the canal boats on the Erie 

 Canal running from the Niagara River above the Falls to 

 the Hudson River at Albany, 350 miles distant. This 

 continuous current can be obtained in several v/ays, one 

 being the well-known method of driving a continuous 

 current dynamo by an alternating current motor ; a 

 second by using a commutator, placed where the con- 

 tinuous current is required, and there rotated. With 

 this latter method, besides all the advantages of the alter- 

 nating current being retained up to the point where 

 the continuous current is required, the rectification can 

 be effected with very inexpensive machinery and without 



