pit or slot has been sunk, which at present is 140 feet in length, 21 feet in width, and 178 feet in depth, having room for four turbines. It will be extended in length as required. Over this the first section of the power house has been erected, and it contains a 50-ton electric travelling crane, commanding the whole floor, which is being used in erecting the machinery.

The 5,000 h.p. Turbines.-Soon after the meeting of the Commission it was decided that the first turbines for the power

FIG. 80.

slot

station should be of 5,000 h.p., running at 250 revolutions per minute, to suit the requirements of the electrical engineers. It was decided to place the turbines at the bottom of an open or wheel-pit, 175 feet in depth, and transmit the power to the dynamos at the ground level by vertical shafts. Designs by Messrs. Faesch & Piccard, who conjointly with Messrs. Cuenod Sautter & Co. sent in the combined project which received the highest award of the Commission, were selected. The first three turbines have been constructed by Messrs. J. P. Morris & Co., of

the superintendence of Messrs. Faesch & Pic

card, and they are now being erected.

Hasty critics have assumed that, whatever difficulty there may be about the transmission of the power, the hydraulic part of the problem is of a very ordinary character. That is not so, and the way in which the essential conditions have been met, without sacrifice of efficiency and by arrangements of very great simplicity, reflects great credit on the mechanical skill judgment

and

of

Messrs. Faesch & Piccard. The water descends the wheel-pit to each turbine, fig. 81, in a supply pipe 7 ft. 6 ins. in diameter. The supply pipe bends at right angles at the bottom and delivers the water between a pair of twin outward flow turbines. The hydraulic pressure on the top cover of the wheel chamber, amounting to 60 or 70 tons, is used to support the

weight of the vertical shaft and the revolving field magnets of the dynamos, while the pressure on the bottom of the wheel chamber is supported by the foundations. No mechanical arrangement of footstep which could have been designed would have supported so great a weight, on a shaft running at 250 revolutions. One considerable difficulty of the mechanical problem is thus met by means involving absolutely no expense, and perfectly permanent in action. The adjustment of the exact amount of unbalanced upward force can be left to be decided at the last moment. Collar bearings on the shaft support the small difference of load and upward thrust which may unavoidably arise.

The turbine wheels are of bronze, 6 ft. 2 ins. in diameter, and by adopting twin turbines the whole arrangement is made compact, and the double condition of supplying the necessary power at the required speed has been met, without sacrifice of the hydraulic requirements on which the efficiency of the turbines depends. Efficiency at 'part gate' is not important at Niagara, and two ring sluices, on the outside of the turbine wheels, have been adopted for regulating the power. The pressures on these being balanced, they are without difficulty put under the control of a relay speed governor, notwithstanding their great size. To give the governor time to act on the sluices, a fly-wheel of considerable power is necessary. This fly-wheel has been obtained by making the field magnets of the dynamos the revolving part, the comparatively light armature being stationary. The speed regulation of turbines driving dynamos is of the greatest importance, especially as alternating dynamos in parallel are to be adopted. Experience has shown that the speed regulation of turbines of large size by governors presents a mechanical problem of considerable difficulty. The speed governor is a relay governor of a type used by Messrs. Faesch & Piccard in other installations on a smaller scale. They have so much confidence in its action that they have given a guarantee that when a quarter of the load, that is 1,250 h.p., is suddenly thrown off, the speed variation will not exceed 2 per cent.

The relay is a mechanical relay. A shaft geared to the turbine sluices carries two pulleys, ordinarily running loose and driven by an open and crossed belt. Either pulley can be geared instantly to the sluice shaft by a friction brake, which

X

holds one of a train of three bevil wheels. The brakes are put in action by a sensitive pendulum governor, acting on ratchet gear. The governor merely puts the ratchet click in gear. Hand regulation is provided.

The Electrical Installation.'-At the time of the meeting of the Niagara Commission, the continuous current method of working was the only one which had been practically used in any large distribution of motive power. The gradual growth, subsequently, of a conviction that distant transmission was of the greatest importance at Niagara led to a decision, in 1893, to adopt an alternating current system. For the Niagara work, continuous current methods involved too great a limitation of the electrical pressure for economical distant transmission. The alternate current method has one special advantage, in the possibility of varying the electrical pressure by statical transformers. Initially, the adoption of an alternate current method was open to the objections that it involves greater stress on the insulation, and that motors for alternate currents were not altogether satisfactory for general use, and were almost untried. Progress in the construction of such motors has been made in the last year or two, and the objection now has less force. Some doubt also existed at first as to the satisfactory working of alternate current generators in parallel. It would be extremely inconvenient if the generators could not be used in groups according to the demand for current. Later experience shows that alternate current generators can be constructed to work synchronously, in parallel, in a perfectly satisfactory way. The success of the three-phase motor at Frankfort, and of the twophase motors of Tesla in America, has led to the selection of a two-phase system of working. Such a system with two independent circuits is equally available for working two-phase and one-phase motors, and for the distribution of part of the current at any point for ordinary alternate current lighting. There remain certain applications, such as tramway working, where continuous currents are most suitable. It appears probable that methods will be perfected for commutating alternate currents after their transmission and transformation to

1 See, for much fuller details, the paper by Professor G. Forbes, Electrical Transmission of Power from Niagara Falls,' Journal Inst. of Electrical Engineers, vol. xxii.

low tension. In any case, motor transformers can be used to obtain continuous currents when necessary.

Acting on the advice of their electrical adviser, Professor G. Forbes, a departure is to be made from previous practice in the electrical system by reducing the frequency of the alternations.' Hitherto, alternating currents have been used almost exclusively for lighting, and high frequency (100 to 133 periods) has been commonly adopted, partly to avoid flicker in the lamps, partly because it reduces the cost of transformers. Messrs. Ganz have for some time adopted 42 periods per second. Professor Forbes proposed to use 163 periods per second; but, after negotiation with the constructors of the dynamos, a frequency of 25 periods has been selected. Professor Forbes believes that low frequency will make parallel working of the dynamos more easy, and improve the efficiency and facilitate the construction of motors. It will reduce the loss due to the unequal distribution of the current in the section of the transmitting conductors, a matter of importance with the large conductors required at Niagara.

Professor Forbes is prepared to construct dynamos to work up to 20,000 volts, in which case step-up transformers would be unnecessary for the transmission to Buffalo. But, proceeding more cautiously, it has been decided that the three first 5,000 h.p. dynamos, now being constructed by the Westinghouse Company, shall work at 2,000 volts, and deliver a two-phase current. For the district at Niagara, electricity will be distributed at 2,000 volts; for transmission to Buffalo it will be transformed to 10,000 volts.

A subway large enough to walk through has been constructed for a third of a mile through the land of the Company. Beyond that the transmission to Buffalo will be by bare copper conductors on insulators carried on posts.

The Scheme on the Canadian side. The idea of utilising power on the Canadian side was first discussed some years ago. Plans were prepared in which Pelton water-wheels driving dynamos were to be placed in rock chambers underneath the river, just above the Horseshoe Fall, and the tail-water discharged by tunnels, directly on the face of the escarpment forming that fall. Various vague statements were made as to transmitting

1 Mr. Tesla is also an advocate of low frequency for motor work. See Inventions, Researches, and Writings of Nikola Tesla; New York, 1894; p. 8.