"The Interborough Subway's Power House" (1904)

Scientific American · October 29th, 1904, pp. 297-298.

The Great Subway Power Station, with Five of the Eleven Engines and Generators In Place. Ultimate Capacity, 132,000 Horse Power. Scientific American, October 29, 1904.

The present article is devoted more particularly to the great power station, which has been built at Fifty-ninth Street and the North River, the spot being chosen for its central location with regard to the distribution of the current, and because of the facilities afforded for water transportation, and transportation by rail on the New York Central Railroad tracks, which run past the power house. The building occupies an entire block, and measures 200 feet in width by 694 feet in length. It is divided longitudinally by a central wall into two portions. The northern half, 117 feet in width, is known as the operating room, while the southerly half, 83 feet in width, is the boiler house. As will be seen from our accompanying sectional drawing, the operating room or engine house is built with galleries extending the whole length on each side, those on the northerly side containing the electrical apparatus, those on the southerly side being occupied chiefly by the steam-pipe equipment. When the plant is entirely completed, it will contain six sections. Each section, with the exception of the turbine section, consists of twelve boilers, two engines, each connected to a 5,000-kilowatt alternator, together with the necessary condensing and boiler feed equipment, and a chimney, there being six chimneys in all. A novelty in respect of the last named is that they are carried on the steel structure of the building, upon a platform at an elevation of 76 feet above the basement floor. The supporting columns for carrying the chimneys form part of the regular system of columns of the boiler house. The top of each chimney is 225 feet above the gratebars, or 162 feet above the top of the supporting platform, and each weighs 1,200 tons. The obvious advantage of this arrangement is that the brick portion of the chimney extends only from about the level of the roof upward, the interior of the, boiler house being thus entirely free from brickwork, and the space thus saved is available for boilers. This enables the line of boilers to extend continuously through the whole length of the house, and preserves the general symmetry of the installation. Above the boiler house, extending the full length thereof, is a coal bunker capable of holding 18,000 tons of coal. Immediately below the bunkers, and all on the same floor, are the boiler economizers, and below these again are the boilers, which are arranged in two long lines confronting each other, with a central platform between them, from which they are fired. The ashes are dumped by gravity into hoppers, which deliver them to small ash dump cars running on tracks in the basement. The cars are drawn out by a small electric locomotive to the waterfront, where they are dumped into a 1,000-ton bin, to be subsequently disposed of by barge or otherwise.

Sectional view of the subway power station. Scientific American, October 29, 1904.

The coal is brought in barges or vessels to a pier on the water front, where it is unloaded by coal-unloading towers, crushed, weighed, and carried by belt conveyors to a system of 30-inch elevating belt-conveyors, by which it is elevated to the top of the boiler house and delivered to a system of 20-inch, horizontal belt-conveyors, for even distribution throughout the bunkers.

The boiler room will ultimately contain seventy-two Babcock & Wilcox boilers, with an aggregate heating surface of 432,576 square feet. They will operate at a working steam pressure of 225 pounds to the square inch. It is ultimately intended to apply superheaters to the whole boiler plant, but before doing so a trial is being made of two well-known makes or superheaters built in this country. Special attention has been paid to the design of the steam piping, and all fittings are made somewhat heavier than is customary in ordinary practice, and they are all of special design. The line and bent pipe is of wrought iron, with loose flanges made of wrought steel rolled at the Krupp works. The engine equipment when all is completed will consist of eleven 7,500-horse-power Allis-Chalmers engines of the same general type as those installed in the 76th Street power station of the elevated road of this city, which have already been described in this journal. As these are capable of working at overload up to 11,000 or 12,000 horse-power, the total horse-power of the plant for traction purposes alone will aggregate say 121,000 horse-power. To this must be added four steam turbines used for electric lighting and two exciter engines, which would bring up the total horsepower for this station to a maximum capacity, when pushed to the utmost, of 132,000.

The main engines are each made up of two component compound engines, driving a common staff, upon which is carried the 5,000-kilowatt generator. The high-pressure cylinders are placed horizontally and the low pressure vertically, each pair connecting to a common crankpin. The high-pressure cylinders are 42 inches in diameter, the low-pressure 86 inches in diameter, and the common stroke is 60 inches. This is for each cylinder, as compared with the Manhattan engines, a reduction in diameter of 2 inches, the stroke being the same and the revolutions per minute, 75, being also similar. The steam pressure of the Rapid Transit Subway engines is 175 pounds, as against 150 pounds for the earlier engines. The low-pressure and the high-pressure piston rods are both 10 inches in diameter, and the crankpin is 20 inches in diameter, an increase of 2 inches over the dimensions of the Manhattan engines. The low-pressure valves are single-ported Corliss, and the high-pressure valves are of the poppet type. At the journals the shaft is 34 inches in diameter, and the length of the journals is 60 inches.

One of the Engines, Showing the Barometric Condensers. Scientific American, October 29, 1904.

The guarantees of the engines specify that they must be capable of operating continuously, when indicating 11,000 horse-power, without producing abnormal wear, jar, noise, or other objectionable results. They are to he so proportioned that if desired they can be operated with a steam pressure at the throttle of 200 pounds above atmospheric pressure. They must also operate successfully under 175 pounds pressure, should the temperature of the steam be maintained at the throttle at from 450 to 500 degrees. Finally, the engine must not require more than 12.25 pounds of dry steam per indicated horse-power per hour when indicating 7,500 horse-power at 75 revolutions per minute, with a vacuum of 26 inches at the low-pressure cylinders, with a steam pressure at the throttle of 175 pounds, and with saturated steam at the normal temperature due to its pressure.

The turbo-generators for electric lighting consist of four Westinghouse-Parsons multiple-expansion, parallel-flow turbines, each consisting of two turbines arranged in tandem-compound. The alternators will run at a speed of 1,200 revolutions per minute, and produce current at a pressure of 11,000 volts. Each unit will have a normal output of 1,700 horse-power, and it is guaranteed to operate under 450 degrees of superheat. The guarantee under a full load of 1,250 kilowatts is 13.8 pounds per electrical horse-power hour, which, it will be seen, is considerably lower than the guarantee for the reciprocating engines. There are also two exciter engines of the compound type, direct-connected to 250 kilowatt generators.

In view of the fact that the efficiency of the engines depends so largely on the vacuum, particular care was given to the design of the condensing plant. Each engine is supplied with two Alberger barometric condensing chambers, each attached as closely as possible to its respective low-pressure cylinder. The circulating pumps are vertical, cross-compound, Corliss engines. Their foundations are on the basement floor; but their steam cylinders are above the engine floor and are, therefore, under the eye of the engineer. The normal capacity of each pump is 10,000,000 gallons per day; therefore, the total pumping capacity of the station is 120,000,000 gallons per day.

The 5,000-kilowatt alternators, like the engines, closely resemble those of the Manhattan Railway Company. They deliver 25-cycle alternating three-phase current at a pressure of 11,000 volts. The revolving part is 32 feet in diameter, and it weighs 332,000 pounds. The machines stand 42 feet in height, and the total weight of each is 889,000 pounds. The revolving parts have been constructed with a view to securing ample ability to resist the centrifugal forces which would be set up should the engines, through some accident, run away. The hub of the revolving field is of cast steel, and the rim is connected to the hub by two huge disks of rolled steel. The alternators have forty field poles, and they operate at 75 revolutions per minute. Field magnets form the periphery of the revolving field, the poles and rim of which are built up of steel plates, dovetailed to the driving spider. The armature is carried outside of the field and is stationary.

Current is delivered at 11,000 volts to eight substations, where it is transformed and converted to direct current at a potential of 625 volts, at which it is delivered to the third or contact rails. As explained in our article of September 10, the third rail is protected by a lateral and overhead shield, which should prove fully effective in safeguarding the workmen or passengers from injury.

We take this opportunity to express our indebtedness to Mr. George S. Rice, the Chief Assistant Engineer of the Rapid Transit Commission. for his invariable courtesy and assistance. in the preparation of the many articles that we have published during the construction of the Subway.

The New York Times · October, 1904

New Power Plant of the Interborough Rapid Transit Company

One of the most interesting and instructive power plans in the world is the new one recently constructed by the Interborough Rapid Transit Company of this city for the operation of the Subway trains. From this one station is to be derived the power needed to run some 800 trains on the thirteen miles of three ad four track road now built or in the process of construction. This tremendous plant is situated on Eleventh Avenue and extends from Fifty-eighth Street to Fifty-ninth Street, being about 700 feet in depth measured back from the avenue. The skeleton of the building is of steel, but the other loads which will have to be supported are so great that the side walls have been made entirely self-supporting.

The steel work is extremely strong, its heavy sections coming in the class of bridge girders rather than ordinary structural shapes. The floors are made of I-beams, connected by plate girders, and the interstices filled with concrete arches. The concrete is reinforced with expanded metal to give it greater stiffness and tenacity. The floors have been designed to stand safely under the following maximum loads: Two hundred pounds per square foot on all flat parts of the roof; 500 pounds in the engine room, and 300 pounds in the boiler house. In the latter part of the building, in the parts directly in front of the boilers, where the wear will be greatest, heavy cast-iron plates with rough, checkered surfaces are made into the floor. These plates extend across the entire front of the boiler, and are three feet wide.

Most of the columns are built up of plates and channels, the latter being 12 inches deep and the former 18 inches wide. The wall columns are of the "box" type of plate and angle construction.

As the layout of the boiler room, putting all the boilers on one floor required that exceptional care be taken to economize space as far as possible, the novel expedient was adopted of raising the the stacks and building them on steel legs and platforms instead of solidly on the ground, as has heretofore been almost the universal practice. These platforms are about the level of the roof of the building, saving thereby a large amount of space in the boiler room and the economizer room, which is on the floor above. The platforms on which the stacks rest are extremely heavy, being made up of 24-inch I-beams, on which the brickwork is directly placed. The beams are supported by a bracing made up of plate girders eight feet deep. The columns supporting this weight are of box pattern, made up of angles and plates, and are about 10 by 20 inches outside. These columns are stiffened by girders and braces, and are practically separate from the building proper.

The columns rest on cast iron bases large enough to distribute the weight and bring the unit pressure down to the limit prescribed by law. The cast iron bases are supported on granite blocks, which are set on leveled concrete beds built on the bedrock.

The inside arrangement of the building is substantially that which has grown into general use from its practicability and convenience. A transverse wall of brick divides the building into two great divisions, the boiler house on the south and the engine room on the north.

The northern half is divided into three bays by partitions parallel to the main dividing wall. The central and largest bay is the operating room and contains all the engines and dynamos. The southern bay is called the steam pipe area and contains the feed-water pumps, vacuum pumps, circulating pumps, and steam pipes, with their multiples. This bay is quite shut off from the rest of the building, so that in the event of a steampipe bursting in it, steam will not enter the operating room. The northern bay is made up of galleries which are given up to the electrical equipment. The southern half contains on the first floor two unbroken lines of boilers, extending the entire length of the building. The floor above this is devoted to smoke flues, economizers, and the coal-distributing system.

The coal bunkers are above the economizer floor, and the chutes are so arranged that the coal can be fed from any bunker to any battery of boilers without the use of any more hand labor than is necessary to adjust the conveyors and chutes properly. The bunkers are made of heavy I-beams and plate girders so arranged that the pressure on the four sides tends to neutralize itself, and that the bunkers, whether full or empty, exert no pressure on the structural frame of the building. The bottoms of the bunkers are sloped so that they will completely empty by gravity. They are lined throughout with cement to prevent the wear of the iron members. The handling of the immense quantity of coal necessary for the operation of a plant of this magnitude was a problem that had to be worked out with great care, and the solution is interesting for the completeness with which it dispenses with hand labor. The coal is received at the Fifth-eighth Street pier in barges and unloaded by a tower unloader with a capacity of 125 tons per hour. This tour contains rolls for reducing the coal to uniform size and automatic scales to weigh it. From this stage the coal passes into a conveyor tunnel leading under the sidewalk in Fifth-eighth Street. From the end of this tunnel it is raised by a series of elevator conveyors, which deliver the coal to the conveyors running the length of the building above the bunkers. These are so arranged that they may be unloaded into any one of the bunkers. Each conveyor is arranged to run a little faster than the one preceding it, so as to insure all the coal getting cleared away and avoid any possibility of congestion, the capacity of the last conveyors being, at normal rate, about 200 tons an hour.

Each bunker is about 80 feet long by 60 feet wide, and their aggregate capacity is estimated to be between 12,000 and 16,000 tons. From the bottom of the bunker the coal passes through a cast iron hopper into a cast iron pipe chute, and a gate is provided where the hopper joins the pipe. Thence, through a system of gravity and mechanical conveyors, it is delivered into the boiler room almost directly in front of the door into which it is to be fed. The stoking, for the present, will be by hand, but the boilers are so constructed that any one of several makes of mechanical stokers can be installed when desired, with only very minor changes.

The six chimneys are of what is known as the the Alphonse-Custoids type. The inside diameter of each is 15 feet, and their greatest height is 225 feet above the grate. The bottom thickness of the sides is 24 inches, gradually reducing to 8 5/8th inches at the top. In each is a baffle wall 21 feet high to prevent the gases of one boiler from affecting the drought of its mate. The stacks weigh about 1,160 tons.

The steam pipes have been arranged with a view to the greatest possible symmetry and simplicity, and all sections have been made as nearly as possible alike, so that a man familiar with one set of pipes could go to another and find the valves in the same relative positions. The main steam piping is of the best wrought iron or steel lap-welded pipe. A general steam header is provided, but only for use in the case where an engine is to be operated by a set of boilers other than its own. The eight water storage tanks each have a capacity of 38,040 cubic feet. In case it is necessary to use river water, provision has been made by means of a salt water pump with a 12-inch suction pipe drawing from a well situated low enough to always be flooded. The water for the condensers is always the river water, and the pumps are designed to deliver 7,000,000 gallons per day of twenty-four hours, with a possible capacity of 10,000,000 gallons if it becomes necessary.

The electrical generator of the power plant consist of nine engines and alternators, four turbine alternators, and five exciter units. The main reciprocating engines are of the cross-compound type, the high-pressure cylinders being horizontal and the low-pressure cylinders vertical. Both pistons of each engine are connected to the same crank pin. The normal rating of each engine is 8,000 horse power, with a possible capacity of 50 per cent. overload. The generators are of the Westinghouse revolving-field fly-wheel type, directly connected to the engines. They have a capacity of 5,000 kilowatts each and furnish 25-cycle three-phase alternating current at 11,000 volts. Each generator has forty poles and revolves at seventy-five revolutions per minute. In the turbine section three steam turbines have been erected, and provision is made for a fourth. These turbines are of the Westinghouse-Parsons type, and each is direct-connected to an 11,000 volt, 1,250 kilowatts 60-cycle generator. These supply power to light the stations and the Subway. The exciter units are in this same section and consist of five 250-volt 250-kilowatts direct-current generators, three of them direct-connected to motors and two to 400 horse power vertical, cross-compound engines.

In order to obviate the possibility of a stoppage from the breaking down of any or all of the exciters, a storage battery has been installed, capable of supplying 3,000 amperes for an hour. These would give time for any necessary repairs in the exciter plant.

The switches are great interest. The problem of being able to break a circuit carrying 100,000 horse power was not in any sense merely a question of magnifying the ordinary hand switch that is used in small work. The switches are broken by motors, so connected through a powerful spring arrangement that the circuit is broken with great rapidity. The break is made under oil, and each conductor is inclosed in a special box and separated from the others by partitions of brick and soapstone. The current may be carried by either of two complete sets of bus bars, or main feeder conductors, so that one breakdown or overload fusion could not disturb the system. Each bus bar is made up of three sets of triple cables, each set having one cable for every 2,000 horse power of current. Some idea of the magnitude of the amount of electric power to be handled may be gathered from the fact that nearly $2,000,000 has been invested in cables and conductors alone. For example, a complete system of return circuits to the sub-stations has been provided, instead of letting the current find its way back to the transformer through the ground or whatever other path it may find easiest.

The danger signals are the most complete ever installed. The block system is so arranged that if the track is clear for three blocks ahead, the train runs free. If the free track is only two blocks, the motorman of the second train receives a danger signal and must run slowly. If the distance narrows to one block an automatic trip throws the current off the second train and it simply cannot run until the track is free. If an accident occurs, such as a derailment, the first thing the train operator does is run to the nearest emergency box, break the glass, and pull the handle. This does a number of things at once. The ticket agents at the two adjacent stations are told that something has happened in that particular section. The entire current is thrown off from the whole district of several miles. This is to minimize the danger of shock from the third rail to those are working to repair the damage and to prevent other trains passing. Arrangements have been made with the Fire Department and special signals installed in every station, so that there may be no time lost in the event of the almost inconceivable fire.

The Interborough management is entitled to a compliment for the civic spirit shown in adopting a design for the power house which makes it an ornament to the neighborhood in which it is placed. By reason of the attention given to the chaste and admirable scheme of decoration and the building of its stacks of the kind of bricks employed in its facades, the necessarily large cost of the plant was increased some $55,000. It can not be doubted, however, that this liberality was repaid. The building is an ornament to the west side and enhances rather than diminishes the value of surrounding property. But for its stacks, it might suggest an art museum or public library rather than a power house. The unsightliness to which we are accustomed in buildings of this character usually represents an economy of thousands of dollars secured at a cost of millions in the depreciation of adjacent property and contiguous neighborhoods. -- J.C. BAYLES.