Chicago Worlds Fair electrical subways

WORLD'S FAIR ELECTRICAL PLANT.*

BY R. H. PIERCE.

Of all the cities that have ever been built, there has never been one in which electricity has played such an important role as in the White City. The present exposition is the first international exposition in which electricity has been recognized as one of the great departments, and no previous electrical exhibition has equalled the electrical exhibit of the World's Columbian Exposition. Volumes have already been written upon the various electrical exhibits, and all that will be attempted in this brief paper is a description of the great plant which furnishes the electrical service of the exposition. The electrical plant comprises a local telephone exchange, complete system of police signal and fire-alarm service, and the plant for furnishing electric power and light.

Telephones. — The telephone exchange is a regular exchange of the Bell system. It comprises at present 130 telephones. It supplies sevice for the offices of the officials, the engineers, and superintendents. It forms an adjunct to the fire-alarm service, and connects the head-quarters of the police department, the department of admissions, and of the secret service with all gates and with all portions of the grounds. It contains no points of novelty, but is an interesting exhibit of a great private exchange. It is installed with complete metallic circuits of double and twisted rubber-covered conductors. The circuits comprise 160 miles of No. 18 B. & S. wire, and the service is practically unaffected by the proximity of the immense number of circuits carrying currents, both direct and alternating, and all degrees of current strength.

Police and Fire Signals. — The police signal and fire-alarm systems comprise 137 fire-alarm boxes of the Gamewell Fire Alarm Telegraph Company, and 137 police boxes, and 60 watchmen's patrol boxes of the Police Telephone and Signal Company. These systems are two well known to need even comment, and make the service uniform with that of the city of Chicago, to which it is connected. The boxes are distributed about the grounds and buildings in pairs, each fire-alarm box having a corresponding police box. The number of boxes is estimated to be sufficient for protecting a city of 150,000 inhabitants, and its installation consumed 80 miles of No. 14 B. & S. rubber-covered wires. The watchmen's patrol boxes are located under the floors of the main buildings, and enable the guard to send in an alarm direct to headquarters without even the loss of time required to reach the nearest fire or patrol box.

Light and Power Plant. — The portion of the plant which especially oommends itself to the interest of both the engineer and the architect is the plant for electric lighting and electrical transmission of power. All the electrical machinery for furnishing light and power is located in Machinery Hall, so that the power plant in Machinery Hall is a great central station. I say "central station," but, in fact, the plant is divided, as far as operation is concerned, into nine distinct central stations, each of which, under normal working conditions, is entirely independent. The plant comprises 98 direct-current series arc dynamos, having a total capacity of 5,230 lamps of 2,000 nominal candle-power each; 14 alternating-current incandescent dynamos, having a total capacity of 128,000 lamps of 16 c.p.; one direct-current incandescent dynamo, having a total capacity of 800 kilowatts; and 20 direct-current power generators, having a combined capacity of 2,936 kilowatts, or 3,936 e.h.p. In addition to these there, are also four direct-current generators having a total capacity of 600 kilowatts, or 804 e.h.p., which serve the double purpose of supplying current to operate the electric fountains and to charge the storage batteries for the electric launches. There are also one direct-current generator of 700 kilowatts, or 938 e.h.p., which operates both arc and incandescent lamps; and, finally, one direct-current generator of 180 kilowatts, and one of 45 kilowatts, a total of 225 kilowatts, or 300 e.h.p., which supply the current for search-lights. The entire plant has a generating capacity of 14,916 kilowatts, or 19,989 e.h.p., so that it would require not less than 25,000 i.h.p. to operate all the dynamos to their full working load.

Circuits. — The circuits from all dynamos are carried under the floors of the power plant to the several switchboards, and thence under the floor to the gallery, which runs the entire length of the power plant, and under the aisle directly north of the plant. This gallery is for the greater part of its length 13ft. wide and 9ft. high, and is shut off from the rest of the basement on both sides by walls of expanded metal and cement. Along each side of the gallery is a row, and down through the centre are two rows of cast-iron uprights placed 30ft. apart. These uprights have sockets into which are driven oak cross-arms. These arms carry from four to six pins, and have, in all, sufficient pins and insulators for 280 wires, allowing but one wire to an insulator, but, by the use of a special two-wire insulator designed for this purpose, the capacity of the gallery is greatly increased. From this gallery, the circuits are carried out of Machinery Hall in the main subway and the duct trunk line. All the circuits feeding the east portion of the park are carried in an underground tunnel called the main subway.

Subway. — The main subway, as it passes under the east end of Machinery Hall going north, is a double tunnel, each half of which is constructed as follows: A series of frames are built of 3 in. by 8 in. timber, and are covered on the outsides, on the top and sides, with 2in. plank. On the inside the top and sides are covered with expanded metal and plaster, and the floor is formed of Portland cement This forms a practically fireproof tunnel, 6ft. 6in. wide and 6ft. 5in. high. To the timbers on both sides of each tunnel are legged cast-iron uprights 30ft. apart. These uprights carry on each side of the subway 12 five-pin cross-arms 2ft. 3in. long, so that one can walk in a 2ft. passage having on either side a regular underground pole line. Conductors are carried on double petticoat insulators, there being capacity in the entire subway for 250 insulators. Here, as in the gallery, many two-wire insulators are used. The subway is lighted by incandescent lamps and drained by hand pumps located at low points. When single insulators are used, all wires are rigidly separated and not less than 5in. of air space is allowed. The main subway runs due north to Electricity Building, where the west half enters the building, and then branches, running to the Mines Building, and the east half makes a right-angled turn, running east to the bridge over the north canal. The circuits are then carried under the bridge, and on the east of the bridge the subway is continued to the south-west corner of Manufactures Building, whence, decreased in section, it runs north the entire length of the Manufactures Building, under the West Loggia. It then runs east to a point north of the centre of the Manufactures Building, thence north to the Government Building. Under the Government Building it is constructed with a covering of expanded metal and plaster, both inside and out, and from the Government Building it is continued to the Fisheries Building, where it ends.

Duct Trunk Lines. — The circuits feeding the west half of the park and Midway Plaisance, with the exception of the power circuits, are carried from the gallery under Machinery Hall to the north side of Machinery Hall in a conduit of 3in. and 4in. vitrified tile ducts. Thence the duct trunk line is continued by 30 ducts of pump log of 2 1/4in. bore. Large manhole boxes, 30in. by 36in. are set every 150ft. This trunk line runs under the terminal tracks to the south-west corner of Transportation Annex, whence it runs parallel to the fence, to a point near the north end of the California State Building. From the main subway and duct trunk line, the circuits are distributed throughout the grounds in wooden ducts of 2 1/4in. bore. These ducts form a network all over the park, and are intersected at angles and convenient points by manholes with cast-iron covers. There are in all about 100 miles of these ducts, and about 3,500 manholes. Thus all circuits are carried underground except those south of Machinery Hall and along fences. These are carried on poles, while the power and telephone circuits on the west side of the park are run under the structure of the elevated intramural railway.

(To be continued.)

*Paper read brfora the World's Congress of Architects, Chicago, August 2, 1893.