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Fig. 14. Connections Of A. C System With
means of the alternating-current system with static transformers, connected as shown in Fig. 14, energy can be transmitted at a much higher voltage from the station. The higher the voltage of transmission, the smaller will be the current (amperes') for a given energy (watts) : therefore, with the high-voltage system, a given energy can be transmitted over a much smaller wire than would be required for that same energy at a low voltage. In the transformers placed at or near the point where the current is to be used, the pressure is "stepped down" to the voltage of the lamps on the circuit.
The regulation—that is, the steadiness and constancy—of the voltage of these alternating-current lines, was.very much poorer than that of the direct-current system. This was largely due to the effects of self-induction, which is ever present with alternating currents. The early incandescent lamp used on the directcurrent no-volt systems was rather delicate, and had only a short life when burned on a circuit in which the pressure fluctuated very much. Consequently it coidd not economically be used on the existing alternating-current lines. A 50volt lamp could be made far more stable, and, largely because of this, the secondaries of the early transformers were ■wound for 50 volts. The primaries were
wound for use on 1,000-volt circuits— which was then considered as high as desirable, because of the difficulties of insulating the line, the transformers, and other apparatus on which this voltage was applied. Rapid advance, however, was made in the art of insulating, and soon this primary pressure was doubled. Most of the city A. C. distributing systems now have a primary pressure of about 2,300 volts. It is interesting to note that the insulators used on the early European high-tension lines were constructed with a trough along the edge on the inner side, which was filled with oil in order to prevent current leaking over the surface of the insulator to the pin and thus to ground, by way of the cross-arm and pole, on wet days.
One of the larger of the early stations for the generation and distribution of alternating current was built in St. Louis, Mo., in 1889. The system adopted was single-phase, 1,200 volts, 60 cycles*, with a three-wire Edison system for the secondaries. These secondaries were tied together at street crossings, forming
* A current which alternates 120 times per second has 60 double alternations or "cycles" per second.
formers, the latter being treated as part of the feeders. Pressure wires were connected to the secondaries of the transformers, and were run back to the station voltmeters to be used by the switchboard operator in regulating.
An interesting alternating-current line was built between San Bernardino and Pomona, California, in 1891. Here a transmission pressure of 10,000 volts was used, obtained by means of connecting the 500-volt primaries of twenty transformers in series. Thus each transformer had to have insulation for a working pressure of only 500 volts, which was comparatively easy to produce.
In 1891 the celebrated three-phase transmission line from Lauffen to Frank
fort, in Germany, was operated. Originally this was intended for transmitting energy generated by water power at Lauffen, to the city of Heilbron, six miles away; but it was first used in the now famous transmission to Frankfort, a distance of no miles, at the time of the Frankfort Exhibition. The .dynamo, built at the Oerlikon Works in Switzerland, was star-connected, and generated a star pressure of about 50 volts.
In a three-phase star-connected generator, the armature windings consist of three branches which are connected together at one end to a common point. These branches are so placed on the armature core that the wave of the alternating pressure is set up in one coil a little later than is the wave of pressure set up in the coil immediately ahead of it, and a little sooner than the wave in the coil immediately back of it. These three pressures then follow each other in regular succession, the phase difference (the time between similar values of the different waves) being equal to one
third period.* The wires leading from the other ends 6i the three armature coils are called the "phase" wires, while the one connecting to their common join is the "neutral" wire. The pressure between a phase wire and the neutral is called the "star" pressure, while that between any two phase wires is the "delta" pressure. This latter is 1.732 times as great as the star pressure. For greater safety in operation—principally to prevent abnormal rises in pressure between a phase wire and earth—the neutral wire is thoroughly "grounded" by being connected to a plate embedded down in the moist earth.
The 50 volts' pressure generated at Lauffen was "stepped up" in transformers to 8,000 volts, delta, at which pressure the current was transmitted.
Development of Water Powers
After the success of polvphase transmission was thus established, a great impetus was given to the development of water powers, and the following years found this system adopted by many companies. One of the first of these in America was built at Telluride, Colorado, in 1892. The original pressure used here was 3,000 volts, three-phase, straight from the generator. As a result of an extended series of experiments made on this line in 1896, much valuable data was obtained regarding high-tension transmission ; and to-day there are many such systems, some operated at a pressure as high as 40,000 volts, which is the pressure now used at Telluride, while a few others are going still higher. The limit to-day seems to be about 60,000 volts, but even this may be increased as the art advances.
The Sacramento-Folsom line, in California, built in 1895. originally transmitted 1,000 H. P. at 11,000 volts, threephase. The generators were wound to give a pressure of 800 volts, and this was raised in transformers to 11,000 volts.
The Mechanicsville, N. Y., and the Snoqualmie Falls. Wash., plants are the most important three-phase transmission systems built in 1898. In the former, a
* A "period" is the time, in fractions of a second, for one complete cycle of the alternating wave—that is. for one double alternation; or, in other words, a period is the time taken by the coil in passing one pair of poles of the field.
Mr. Charles F. Scott. This connection is shown in Fig. 16. In this diagram, T, and T2 are two transformers, the primaries of which have the same number of turns and are connected to the two phases of the two-phase circuit. The secondary of T, has only .866 times the turns of the secondary of T2. By connecting one end of the secondary of Tt to the middle of the secondary of T2, as shown, three-phase currents of equal pressures on each phase are obtained from these secondaries.
The best known example of this is the system at Niagara Falls, N. Y., where 25-cycle two-phase currents, generated at 2,200 volts, are transformed to three-phase currents at 22.000 volts, at which pressure the energy is transmitted to Tonawanda and to Buffalo, the latter
Function of the Storage Battery
While these important developments in cross-country transmission were under way, the engineers of the urban stations also had new problems to solve. The convenience and other desirable features of the use of electric light and power were now being widely appreciated, especially when the cost of the lamps was reduced, and electric motors also were being used more liberally, in sizes from one-fourth horse-power to 300 H. P. and larger. This meant a big increase in the load on the station, as well as in the size of the district to be served. How to meet this increase economically, required an intelligent study of the problems of current distribution. As already noted, the distance over which it is economical to transmit current at a low volt
to the regular load, can be sent over these feeders, and if this current can be stored in some way in a location within but near to the economical limit, so that it can be used at the period of heavy load, this storage substation will in turn become a point of distribution from which current can be sent out as far again as the economical limit. Here is where the storage battery filled the want. In 1894 we find storage-battery substations installed in Boston and New York, and soon thereafter companies in other cities adopted them. In Boston a number of battery substations were installed in the nearer outlying districts, all of them being connected with one another and with the steam station. The batteries are charged during the hours of light load by means of boosters, which form part of the substation equipment. Their usefulness, however, is not by any means limited to outlying districts. As an auxiliary to a generating station, it is considered good practice from the standpoint of economy to install a storage battery if the peak of the load does not exceed two and one-half hours. As a safeguard against interruption of service, and as a help in maintaining a uniform pressure on the system, they have been found almost invaluable.
(To be Concluded)
Mechanical Appliances in Modern
Modern Devices that are Working a Revolution in the Shipbuilding Industry
By WALDON FAWCETT
IN THE COURSE of his testimony at the recent Congressional hearing relative to the condition of American shipping and shipbuilding, Mr. Cramp, probably the best known shipbuilder in the United States, made the statement that in this industry the advantage conferred by the superiority of the American workman is a thing of the
past. His explanation of this surprising statement was, that in this age speed and economy in shipbuilding are secured largely by the employment of the wonderful time-saving and labor-saving machinery introduced during the past few years, and that these products of Yankee ingenuity are being installed in foreign shipyards just as rapidly as the manufacturers can turn them out. Since these highly perfected automatic machines can be operated by any workman of average intelligence—by the poorly paid labor of Europe quite as well as by the highpriced American artisan—-it is claimed that vessel construction all over the world will ere long be on one basis.
Steam and Electric Cranes
Of all the classes of mechanical appliances which are serving as factors in inducing the new status of steel shipbuilding, unquestionably the most important
the shipyard, is placed a high trestle upon a track, on top of which is mounted one of the cranes. The horizontal boom of the crane is high enough above the shipways to pass over the highest point of the ships being built, while the arms of the cantilever project over the full width of the ship on each side of the trestle. The cantilever of the crane is equipped with a trolley and hoist block, whereby the load can be hoisted from the ground and traversed from one end of the cantilever to the other. Thus, inasmuch as the crane travels up and down the trestle, the en
is that made up of the various kinds of cranes. Chief among these are the steam and electrically operated balanced cantilever cranes—one of the American inventions which has of late been most extensively adopted in the shipyards of the Old World. These giant burdenbearers, unquestionably the most perfect machines yet devised for handling material about ships in course of construction, embody new features in crane construction which allow the long spans and high speeds for.which they are designed and equipped.
All the cranes of this type in use either in the United States or abroad are the invention of Mr. Alexander Brown, the well-known engineer, and all have the same plan of operation. Between each pair of shipways or building berths in
tire length and width of the two ships are covered, and materials may be handled and delivered to any part of the ships under construction. The trolley will attain any speed desired on the tramway, while the crane is capable of traveling along the track at a speed of 750 feet per minute. ,
One pair of engines, or an electric motor controlled by a single operator; drives all functions of one of these large cranes. The engines or motor and the machinery are located in the pier, and there is no dead weight carried either on the bridge or on the trolley. This allows the lightest form of bridge construction and very quick movement of trolley, and, especially, allows the trolley to be started, run at full speed, or stopped instantly. The cantilever cranes are equipped with