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formers, the latter being treated as part third period.* The wires leading from of the feeders. Pressure wires were the other ends of the three armature connected to the secondaries of the trans coils are called the "phase” wires, while formers, and were run back to the station the one connecting to their common join voltmeters to be used by the switchboard is the “neutral” wire. The pressure beoperator in regulating.
tween a phase wire and the neutral is An interesting alternating-current line called the “star" pressure, while that bewas built between San Bernardino and tween any two phase wires is the "delta" Pomona, California, in 1891. Here a pressure. This latter is 1.732 times as transmission pressure of 10,000 volts was great as the star pressure. For greater used, obtained by means of connecting safety in operation-principally to prethe 500-volt primaries of twenty trans vent abnormal rises in pressure between formers in series. Thus each trans
a phase wire and earth—the neutral wire former had to have insulation for a is thoroughly "grounded" by being conworking pressure of only 500 volts,
nected to a plate embedded down in the which was comparatively easy to pro moist earth. duce.
The 50 volts' pressure generated at In 1891 the celebrated three-phase Lauffen was "stepped up" in transformtransmission line from Lauffen to Frank ers to 8,000 volts, delta, at which pres
sure the current was transmitted.
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 110 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
Development of Water Powers After the success of polyphase 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.
transmission pressure of 12,000 volts, 38 being about twenty miles from the stacycles, was adopted; while in the latter, tion. When this station was first opthe generated pressure of 1,000 volts, 60 erated, in 1896, the transmission pressure cycles, was stepped up to 25,000 volts. was 11,000 volts. Since that day many
Many of the polyphase stations built in high-tension transmissions have sprung the early nineties were equipped with into existence; and the increase in volttwo-phase generators. The two-phase age is keeping step with the improvement currents were then stepped up and trans in insulators, as already noted. An informed to three-phase currents by means terior view of Power House No. I at of a scheme of connections devised by Niagara Falls is shown in Fig. 17.
Mr. Charles F. Scott. This connection is Function of the Storage Battery shown in Fig. 16. In this diagram, T, While these important developments in and T, are two transformers, the pri cross-country transmission were under maries of which have the same number way, the engineers of the urban stations of turns and are connected to the two also had new problems to solve. The phases of the two-phase circuit. The convenience and other desirable features secondary of T, has only .866 times the of the use of electric light and power turns of the secondary of T. By con were now being widely appreciated, esnecting one end of the secondary of T, pecially when the cost of the lamps was to the middle of the secondary of T,, as reduced, and electric motors also were shown, three-phase currents of equal being used more liberally, in sizes from pressures on each phase are obtained one-fourth horse-power to 300 H. P. and from these secondaries.
larger. This meant a big increase in The best known example of this is the load on the station, as well as in the the system at Niagara Falls, N. Y., size of the district to be served. How where 25-cycle two-phase currents, gen to meet this increase economically, reerated at 2,200 volts, are transformed to quired an intelligent study of the probthree-phase currents at 22,000 volts, at lems of current distribution. As already which pressure the energy is transmitted noted, the distance over which it is ecoto Tonawanda and to Buffalo, the latter nomical to transmit current at a low volt
age is limited ; and, when the area to be to the regular load, can be sent over these served exceeds this limit, recourse must feeders, and if this current can be stored be had to more stations or to a higher in some way in a location within but near distribution pressure.
A study of the to the economical limit, so that it can load curve of an average central station be used at the period of heavy load, this in a large city (Fig. 18) shows that the storage substation will in turn become feeders are carrying their heavy current a point of distribution from which cur
rent 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 con
sidered good practice from the standfor only a short time each day. During point of economy to install a storage batall the remainder of the day, then, the tery if the peak of the load does not excurrent in these feeders is comparatively ceed two and one-half hours. As a safesmall; also, much of the generating ca guard against interruption of service, and pacity of the station is idle, representing as a help in maintaining a uniform presjust so much investment inactive and sure on the system, they have been found earning no returns. If now, during the
almost invaluable. period of light load, a current, additional
(To be Concluded)
Fig. 18. TYPICAL LOAD CURVE OF CITY CENTRAL STATION.
Mechanical Appliances in Modern
Modern Devices that are Working a Revolution in the Shipbuilding Industry
By WALDON FAWCETT
N THE COURSE of his testimony past. His explanation of this surprising at the recent Congressional hearing statement was, that in this age speed and relative to the condition of Ameri economy in shipbuilding are secured
can shipping and shipbuilding, Mr. largely by the employment of the wonderCramp, probably the best known ship ful time-saving and labor-saving machinbuilder in the United States, made the ery introduced during the past few years, statement that in this industry the ad- and that these products of Yankee invantage conferred by the superiority of genuity are being installed in foreign the American workman is a thing of the shipyards just as rapidly as the manu
facturers can turn them out. Since these the shipyard, is placed a high trestle upon highly perfected automatic machines can a track, on top of which is mounted one be operated by any workman of average
of the cranes. The horizontal boom of ir telligence-by the poorly paid labor of the crane is high enough above the shipEurope quite as well as by the high ways to pass over the highest point of the priced American artisan—it is claimed ships being built, while the arms of the that vessel construction all over the world cantilever project over the full width of will ere long be on one basis.
the ship on each side of the trestle. The
cantilever of the crane is equipped with a Steam and Electric Cranes
trolley and hoist block, whereby the load Of all the classes of mechanical appli can be hoisted from the ground and ances which are serving as factors in in traversed from one end of the cantilever dlucing the new status of steel shipbuild to the other. Thus, inasmuch as the crane ing, unquestionably the most important travels up and down the trestle, the en
MONSTER CANTILEVER CRANE AT ORAMP SHIPYARD, PHILADELPHIA, PA.
is that made up of the various kinds of tire length and width of the two ships are cranes. Chief among these are the steam covered, and materials may be handled and electrically operated balanced canti and delivered to any part of the ships lever cranes-one of the American in under construction. The trolley will atventions which has of late been most tain any speed desired on the tramway, extensively adopted in the shipyards of while the crane is capable of traveling the Old World. These giant burden along the track at a speed of 750 feet per bearers, unquestionably the most perfect minute. machines yet devised for handling ma One pair of engines, or an electric terial about ships in course of construc motor controlled by a single operator; tion, embody new features in crane con drives all functions of one of these large struction which allow the long spans and cranes. The engines or motor and the high speeds for which they are designed machinery are located in the pier, and and equipped.
there is no dead weight carried either on All the cranes of this type in use either the bridge or on the trolley. This allows in the United States or abroad are the the lightest form of bridge construction invention of Mr. Alexander Brown, the and very quick movement of trolley, and, well-known engineer, and all have the especially, allows the trolley to be started, same plan of operation. Between each run at full speed, or stopped instantly. pair of shipways or building berths in The cantilever cranes are equipped with
an automatic counterweight running on a track located on the bridge, above the hoisting-trolley tracks, and connected by ropes to the trolley so that whatever position the hoisting-trolley may occupy on one arm of the crane, the counterweight
Entire crane along trestle, on track of 20foot gauge-400 to 700 feet per minute, depending on load and wind-pressure. The minimum of 400 feet is with full load and against a wind pressure of 30 miles per hour.
Recently this crane placed in position on shipboard, a battleship sternpost weighing eighteen tons, and, with the assistance of but a few men, conveyed it from the cars at the opposite end of the yard, an operation never accomplished under the old plan in less than two or three days nor without a large force of workmen engaged.
Derricks Ranking with the cantilever cranes for marvelous achievement are the monster derricks to be found at several American shipyards. The best example is afforded by the “Atlas” at the Cramp yard—the largest and most powerful floating derrick in the world. The pontoon of the structure is 73 feet in length, 62 feet in width, and 13 feet deep. When carrying the maximum load of 125 tons at the boom end, and with water ballast aft sufficient to bring her to an even keel, the “Atlas” has a freeboard of 16 inches and a displacement of 1,563 tons. The cone has a diameter of 40 feet at the base; the length of boom from the axis is 5812 feet; and the boom swings 36 feet clear of the pontoon. The height from deck to masthead is 116 feet; and from deck to boom, 65 feet. The maximum hoisting height is 50 feet. The pontoon is of iron, while the boom, mast,
at all times automatically keeps a similar position on the opposite arm.
Probably the best exemplification of the possibilities of these adjuncts of twentieth century shipbuilding is afforded at the Cramp plant at Philadelphia, where there are several of these cranes, all driven by electricity. Each crane is mounted on a steel trestle of special design and construction, about 600 feet long, and of sufficient height to bring the under side of the crane-girder 105 feet above the ground. One of these cranes, which may be considered as representative of its class, is 102 feet long from end to end of girders, with 190 feet effective travel of trolley. It will lift 30,000 pounds at 60 feet either side of the center, and 9.000 pounds at either end of bridge. A single electric motor operates all functions of the crane at the following speeds:
Hoisting a full load of 30,000 pounds—125 feet per minute.
Trolley across cantilever-400 to 800 feet per minute.
A LOCOMOTIVE CRANE.
and all lifting and traversing gear are of steel. The up-to-date shipyard also has a full equipment—there are twenty in the Cramp yard alone - of locomotive cranes, which are mounted upon box cars traveling on standard-gauge tracks, and