Page images
PDF

it to the cargo space by easy stages and with practically no breakage. Some of these car-dumping machines will handle upward of 200 loaded cars in an ordinary working day, not only actually transferring the coal, but handling the loaded and empty cars to and from the machine, and obviating all necessity for the employment of a shifting engine and traincrew.

Coal-Loading Machines An ingenious type of coal-loading machine is found at Fairport on the south shore of Lake Erie, and at several other points in the United States. By its operation the coal to be loaded on a boat is dumped from the hopper-bottomed railroad cars into a large receiving hopper underneath the car. From this hop

per the fuel is delivered to a carrier of the continuous type, which hoists it up to an incline spout down which it passes into a telescope spout and thus directly into the boat. This telescope spout is drawn out to its full length at the commencement of operations, and is then gradually taken up or shortened as the boat is filled. By this means the spout is kept constantly full of coal, and the breakage of the fuel is reduced to a minimum. It requires but two men to operate such a machine, which is driven by a 50-horse-power engine. The cost of an installation of this kind is much less than in the case of some of the other types of coal-handling machinery, and yet such a machine is capable of loading from 600 to 900 tons of coal per hour.

[graphic]

A Quarter-Century of American
Central Station Engineering

The Marvelously Rapid Progress in Electrical Engineering -which has
Revolutionized Industrial Conditions

Part III.

By R. F. SCHUCHARDT. B. S.

Testing Laboratory, Chicago Edison Company

Consolidation of Plants

THE NEXT STEP in the development was one of consolidation. Many cities had been liberal in granting franchises to lighting companies, and as a result there were built within the same city many systems of various excellence and stability. To the engineers of the consolidated company was then presented the problem of unifying the systems; but the changes to the new sys

tem had to be made without sacrificing the value of the investment represented by the generating apparatus and lines of the existing stations. Such a change, naturally, was made step by step, and thus required several years. In addition to providing for the existing load, the new system had to be designed for the future; and the probable development in the line of various classes of electrical apparatus had to be considered.

In our larger American cities, the load

[merged small][merged small][graphic][merged small]

30 per cent of the load goes to power users; therefore the system had to be adapted to all classes of motor service, as well as for lighting. For this service in such a district, the Edison direct-current three-wire system is certainly the most satisfactory, and this system has been pretty generally adopted. It permits the use of storage batteries; requires less copper than does the alternating-current system, because in it there is no loss due to inductance; gives better regulation; and is far better for general all-around power service.

To consolidate several systems of this class was a simple matter. It required merely that the separate networks of mains be tied together, and a uniform pressure kept on the system by each station feeding into it. In the outlying districts, however, the problem was more

ondary pressure ranged from 104 to i-S volts, while some of the earlier systems still maintained a secondary pressure of 50 volts. A few of the later stations had 2,000-volt lines, with a frequency of 60 cycles; and there were also polyphase (generally two-phase) lines for serving a motor load. A view of some of these earlier alternating-current stations is given in Figs. 19 and 20.

High-Voltage Polyphase Systems

This conglomerate mass, then, had to be unified. A careful study of various systems showed the four-wire threephase system, with a frequency of 50 to 60 cycles, to be the best suited to the distribution of such a load ; and this system is being freely adopted. Good examples of it are found in Chicago, Milwaukee,

[merged small][merged small][graphic][merged small]

and the single-phase lighting feeders are switched on to this 2,300-volt connection. The various feeders are connected each to one of the phases and the neutral, so that the three phases are aproximately balanced. For a power load, then, connection is made to all three phases; and the motor is usually of the polyphase induction type, of which one is shown in Fig. 21. Where the capacity of the motor is very small—say under 3 H. P.— the single-phase type of induction motor, equipped with some special starting device, is often used. Stepdown of the voltage to the service pressure is, of course,

pole line carrying principally alternatingcurrent primaries. Transmission to substations, which in this case are merely distributing centers, is then done over the three phases at 4,000 volts, the neutral preferably being carried along also. At the substation, only feeder regulators are required beside the switching apparatus; and the feeders here also are connected between a phase wire and the neutral, 2,300 volts. A diagram of a four-wire three-phase distribution is shown in Fig. 24(p. 154) ; and in Fig. 25(P-T55)'s seen a switchboard installed for such a system.

[merged small][graphic][merged small][merged small]

a neutral conductor is not used and all load is connected between phase wires). Brooklyn has a two-phase 2,300volt 60-cycle system in the residence section; Philadelphia also, though in the latter city the current is generated at 5.500 volts and stepped down to 2,300 volts for alternating-current distribution. A 500-volt two-phase generator is shown in Fig. 26. For higher voltages the revolving-field type is used, thus avoiding collector rings and brushes for the high-voltage current. At the South Boston station of the Boston Flectric Light Company (now part of the Boston Edison Illuminating Company), the generators are wound for 2,300-volt threephase 60-cycle currents.

[merged small][graphic][merged small][merged small][graphic][merged small]
[merged small][graphic][merged small][ocr errors][subsumed][merged small][merged small][merged small][graphic][merged small]
« PreviousContinue »