Page images
PDF
[merged small][graphic][merged small]

of the best in the world, and, in some respects, resembles that of Paris. Figs. 2 and 3 show typical scenes during the construction of these canals.

Pumping to Higher Levels

The waterways are divided into eight groups, each being served by a set of pumps operated by electric power. In all, 26 pumps are in service, having a total discharging capacity of 7,600 cubic feet per second, with an average lift of 12 feet. They are connected by a system of wires with the generating station from which all of the power is secured. This building (Fig. 4) is 181 feet in length, 140 feet in width, and two stories high. An interior view is shown in Fig. 5. The building contains an equipment of 7 units, each consisting

[graphic]

INTERIOR OF CENTRAL POWER STATION. NEW ORLEANS DRAINAGE SYSTEM. One-half of engine room is here shown.

Fig. 5.

brick arches to uphold the roadway. Considering the difficult character of the work, the svstem is considered to be one

of a steam engine direct-connected to a generator, and each unit developing 2,000 horse-power. Steam is suppliednel, to be pumped into the outlet canal and finally discharged into Lake Borgne, a large inlet from the Gulf of Mexico, 12 miles east of the city.

[merged small][merged small][graphic]

FIG. ti. SUCTION BASIN AND PUMPING STATION NO. 7. PARTIALLY COMPLETED.

[merged small][merged small][graphic]

FIG. 7. DISCHARGE BASIN AND PUMPING STATION NO. 7. PARTIALLY COMPLETED.

Sewerage Below Water-Level

Realizing the need of adequate sewers in connection with the drainage system, a portion of the fund which has been provided is being expended for this improvement. Only a beginning has been made; but about five miles of sewers have thus far been completed, and it is intended to have the principal streets in the 560 miles of thoroughfare that traverse New Orleans, properly sewered within the next decade. Contracts have already been let for an extensive area. Provision has also been made for an ample supply of pure water, so that the people in future will not have to depend upon wells for their supply of this necessary of life.

New Activity in Building

One of the results of the extraction of the moisture from this great "sponge" upon which the city rests, is the activity in building. Already the business section of New Orleans has undergone a remarkable transformation. Since the principal canals have been completed, it has been found possible, in these districts, to erect buildings of brick, stone, and iron, which compare favorably with those to be found in other large cities of the country; and the area of one-story and two-story buildings appears to be at an end. Contracts have recently been let for a hotel which will be twelve stories high—a remarkable altitude for a New Orleans building. Although this building will contain several thousand tons of steel, the site upon which the structure is to stand has become so firm that architects say it can be built with entire safetv and with but little difficultv.

[graphic]

A Quarter-Century of American Central Station Engineering

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

Part II.

By R. F, 5CHUCHARDT, B. S.

Testing Laboratory. Chicago Edison Company

Alternating-Current Systems

SO MUCH for the early development of the direct-current systems, of which the cities cited are characteristic examples. Let us see when the alternating current entered the field. The development of the alternating-current system in America is due largely to Mr. George Westinghouse, who, in 1885, had built at Pittsburg, Pa., an experimental plant to work out the system devised by Gaulard and Gibbs in England. The first commercial result of the Westinghouse investigations, car

ried on by Shallenberger, Stanley, and others, appeared in the plant installed at Buffalo, N. Y., in November, 1886. The following year, 65 plants, with a total capacity of 125.000 lights, were built; and the increase thereafter was rapid.

With a direct-current three-wire system using 230 volts between outside conductors, it is uneconomical to transmit current much farther than one and a-half miles, because of the prohibitively large amount of copper necessary to keep down the loss in the feeders. The resistance of a conductor varies with theformers, 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.

[merged small][ocr errors][ocr errors][ocr errors]

Fig. 14. Connections Of A. C System With
Static Transformers.

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

[ocr errors][graphic][merged small]

* A current which alternates 120 times per second has 60 double alternations or "cycles" per second.

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

[graphic][merged small]

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.

« PreviousContinue »