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from a battery of 11 boilers arranged in a separate compartment, the entire set of boilers representing about 15,000

FIG. 6. SUCTION BASIN AND PUMPING STATION NO. 7, PARTIALLY COMPLETED.

horse-power. The boilers are of the tubular type, and are provided with chaingrate mechanical stokers. In addition to the generating units and boilers, the station also contains two small steam engines for auxiliary use.

The canals are so arranged that a pumping station of sufficient capacity is connected with each level. This is usu

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ally located at the terminus of the principal receiving canal in the locality, the water draining by gravity into a suction basin (Fig. 6), from which it is forced. by the pumps into a discharge basin (Fig. 7), thence passing through another chan

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

nel, 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.

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 safety and with but little difficulty.

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.

Oth

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, SCHUCHARDT, B. S.
Testing Laboratory, Chicago Edison Company

Alternating-Current Systems

S

O 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 the

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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 secondaries of the early transformers were wound for 50 volts. The primaries were

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

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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.

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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 Switzer

land, 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 of 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 transform ers to 8,000 volts, delta, at which pressure the current was transmitted.

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 to-day seems to be about 60,000 volts, others are going still higher. The limit 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 cycles, was adopted; while in the latter, the generated pressure of 1,000 volts, 60 cycles, was stepped up to 25,000 volts.

Many of the polyphase stations built in the early nineties were equipped with two-phase generators. The two-phase currents were then stepped up and transformed to three-phase currents by means of a scheme of connections devised by

Mr. Charles F. Scott. This connection is shown in Fig. 16. In this diagram, T1 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 T. By connecting one end of the secondary of T, to the middle of the secondary of T2, as shown, three-phase currents of equal pressures on each phase are obtained from these secondaries.

FIG. 17. WESTINGHOUSE 2-PHASE 2,200-VOLT 20-CYCLE TURBO-ALTERNATORS AT NIAGARA FALLS. POWER HOUSE NO. 1.

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

being about twenty miles from the station. When this station was first operated, in 1896, the transmission pressure was 11,000 volts. Since that day many high-tension transmissions have sprung into existence; and the increase in voltage is keeping step with the improvement in insulators, as already noted. An interior view of Power House No. I at Niagara Falls is shown in Fig. 17.

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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

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