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

the carth. To prevent leakage, the bottoms of the canals are lined with concrete, while the side walls are of brick.

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


POWer 15 secured.

Inis Duilding (Fig.


THE SEVERAL PUMPING STATIONS IS GENERATED. Those which are constructed beneath the streets (Fig. I have roofs formed of steel framework, which in turn support



One-half of engine room is here shown. brick arches to uphold the roadway. of a steam engine direct-connected to a Considering the difficult character of the generator, and each unit developing 2,work, the system is considered to be one 000 horse-power. Steam is supplied

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

FIG. 6. SUCTION BASIN AND PUMPING STATION NO. 7, PARTIALLY COMPLETED. horse-power. The boilers are of the tu ally located at the terminus of the princibular type, and are provided with chain- pal receiving canal in the locality, the grate mechanical stokers. In addition water draining by gravity into a suction to the generating units and boilers, the basin (Fig. 6), from which it is forced station also contains two small steam by the pumps into a discharge basin (Fig. engines for auxiliary use.

7), thence passing through another chan



nel, to be pumped into the outlet canal

New Activity in Building and finally discharged into Lake Borgne, One of the results of the extraction a large inlet from the Gulf of Mexico, 12 of the moisture from this great “sponge” miles east of the city.

upon which the city rests, is the activity

in building. Already the business secSewerage Below Water-Level

tion of New Orleans has undergone a Realizing the need of adequate sewers remarkable transformation. Since the in connection with the drainage system, principal canals have been completed, it a portion of the fund which has been has been found possible, in these disprovided is being expended for this im- tricts, to erect buildings of brick, stone, provement. Only a beginning has been and iron, which compare favorably with made; but about five miles of sewers those to be found in other large cities of have thus far been completed, and the country; and the area of one-story it is intended to have the prin- and two-story buildings appears to be cipal streets in the 560 miles of thor- at an end. Contracts have recently been oughfare that traverse New Orleans, let for a hotel which will be twelve properly sewered within the next decade. stories high-a remarkable altitude for Contracts have already been let for an a New Orleans building. Although this extensive area. Provision has also been building will contain several thousand made for an ample supply of pure water, tons of steel, the site upon which the so that the people in future will not have structure is to stand has become so firm to depend upon wells for their supply of that architects say it can be built with enthis necessary of life.

tire safety and with but little difficulty.

A Quarter-Century of
American Central Station Engineering

The Marvelously Rapid Progress in Electrical Engineering which has

Revolutionized Industrial Conditions

Part II.

Testing Laboratory, Chicago Edison Company

Alternating-Current Systems O JUCH for the early development of the direct-current systems, of which the cities cited are char

acteristic 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 the

length; and as it requires the expenditure of energy to send a current over a resistance, obviously a high resistance means a large amount of energy lost in the transmission. By increasing the cross-section of the feeder, this resistance can be kept low; but the cost of the feeder would then be prohibitive. By


wound for use on 1,000-volt circuitswhich 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





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 110-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 could 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 second anes of the early transformers were wound for 50 volts. The primaries were


Three-wire Feeders. - Three-wire Mains. 0 Junction boxes, where mains connect with feeders. a complete network similar to that described for the direct-current system and shown in Fig. 15. In this case the feeders of the D. C. system were replaced by the high-tension A. C. feeders and trans

+ A current which alternates on times per second hoe 60 double alternations or "cycles" per second.

« PreviousContinue »