The Interborough Power Plant
The Interborough Subway's Power House
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.
New Power Plant of the Interborough Rapid Transit Company
The New York Times · October 1904
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.
Interborough Power Plant Enlargement
Electric Railway Journal · Vol. 45, No. 16 · April 17, 1915 · pp. 1063-1064.
One-Half of the Seventy-Fourth Street Power Station, Which Supplies Power to the Elevated Railways, Is Being Remodeled, Increasing Its Capacity by 300 Per Cent on the Same Floor Space.
[Left] FIG. 1-VIEW OF SEVENTY-FOURTH STREET STATION [Right] FIG. 2-INTERIOR BEFORE ALTERATIONS.
On account of the prospective increase in the demand upon the power-generating plants of the Interborough Rapid Transit Company in New York, due to the third-tracking of the elevated lines, the Seventy-fourth Street station is being remodeled. The changes are now approaching completion, two out of three new 30,000-kw turbo-generator units being in operation, and carrying all of the load except during the peaks when the remaining 7500-kw turbine and four reciprocating engines are sometimes called upon for assistance. One unit, shown in Fig. 3, is finished complete, and the second is undergoing an exhaustive series of tests. The foundations for the third unit are under construction. The remodeling, which is being done with a view to the ultimate installation of a total of eight 30,000-kw units, is being carried on within the original building. For the present it involves principally the substitution of three turbine generators for four engine generators (see Figs. 4 and 5); the making over of one-half of the boiler plant opposite the turbines by replacing Roney stokers with Taylor underfeed stokers, adding superheaters and removing the economizers; the partial replacement of motor-driven triplex, with turbine-driven centrifugal boiler-feed pumps, and the complete rearrangement of the electrical switching system with the addition of current-limiting reactors.
The Power Plant of 1901
The old power plant, built during 1901 [fully described in the issue of the Street Railway Journal for Jan. 5, 1901], was the model steam power plant of that time. Its appearance is shown in Fig. 2. It contained eight Reynolds, Allis-Chalmers double, horizontal-vertical, cross-compound engines of 12,000-hp actual or 8000-hp normal rating each, driving 11,000-volt, revolving-field Westinghouse alternators, the largest built to 1901. Each engine unit was essentially two separate compound engines at the ends of the shaft, each having a 44-in. high-pressure cylinder and an 88-in. low-pressure cylinder and of 60-in. stroke, the speed being 75 r.p.m. By the 135-deg. setting of the cranks eight impulses per revolution were obtained.
The revolving weight on the bearings of each of the engines was 439,000 lb., and an allowance of 70,000 lb. more was made to provide for magnetic pull between field magnet and armature. The shaft itself weighed 63,000 lb. On account of the great mass of the revolving field magnet it was possible to dispense with the flywheel, a notable advance in slow-speed generating-unit design. To these engines was later added a 7500-kw Westinghouse turbine unit.
The engines exhausted into Worthington jet condensers with triplex motor-driven circulating pumps. These were changed, about 1903, to the barometric type.
The boiler house consisted of a basement, two boiler floors and a row of coal bunkers, the height from the basement to the top of the monitor being 128 ft. The basement was divided into three longitudinal compartments for the purpose of protecting the pumps from the dust produced by the ash-handling machinery. On each boiler floor were thirty-two B. & W. boilers, with Roney stokers, each rated at 520 nominal horse-power and containing 5200 sq. ft. of heating surface. These were arranged in batteries of two, eight boilers to an engine, the whole forming a generating unit. The boiler house was provided with four Custodis brick stacks of 17-ft. flue diameter at the top and 18 ft. at the bottom, 278 ft. high above the basement floor, the tallest stacks of the kind constructed in this country to that time. A Green economizer was provided for each four boilers, as it was deemed necessary to have these to heat the feed water, all of the auxiliaries being electrically driven. Each unit was served by an electrically-driven Goulds triplex boiler feed pump. Above the boiler floors was a row of three coal bunkers, separated by 35-ft. spaces for fire protection, having a total capacity of 7500 tons, a ten-day supply.
The building housing this plant, seen in Fig. 1, extends from Seventy-fourth to Seventy-fifth Street along the East River, with a width of 204 ft. 4 in. and an average length of 404 ft. It is divided by a longitudinal wall into engine and boiler houses, respectively 93 ft. 6 in. and 104 ft. 2 in. wide. The basements of these are on the same level, 4 ft. 6 in. above high water and 2 ft. 6 in. below Exterior Street, which lies between the plant and the river. Extending across the west end of the building is a vault 18 ft. wide divided into two parts, one for oil storage and the other for switch control storage batteries. The roof of this vault serves as a roadway from street to street on the level of the lower boiler-room floor.
The coal and ash-handling plant consists of two towers on the river bank for unloading coal and storing ashes, connected by bucket and belt conveyors with the power plant, distributing and collecting in the manner now standard in such plants. A feature of the tower design was the provision for hoisting coal from barges with a 1-1/2-ton shovel just high enough to give the fall necessary for passing it through the crushers and weighing hoppers.
In the engine house were the basement, 21 ft. 6 in. high, the operating floor, 107 ft. to the roof, and on one side three switchboard galleries, under the lower-most of which the engine-driven exciter sets were placed. A 50-ton electric crane traversed the length of this house.
The important features of the switching apparatus were the layout of group switches and the use of General Electric motor-operated switches. There were two complete sets of busbars connected by bus junction switches to permit of the operation of the alternators in either two or four batteries. The feeders from one substation formed one group controlled by a group switch in addition to the individual feeder switches. On the benchboard dummy busbars were placed to give the operator a graphic representation of the connections.
The Power Plant of 1915
The changes listed in the second paragraph, together with incidental changes, will be discussed in the order therein followed. The turbines, fully lagged, will appear as shown in Figs. 3 and 5. They have been rather fully described in the technical press so that only a few salient features need be mentioned. Each cross-compound unit consists of two turbines, a 1500-r.p.m. single-flow reaction turbine, and a 750-r.p.m. double-flow reaction turbine connected as a compound machine with a large receiver between elements. This novel arrangement was chosen to simplify design problems, particularly those relating to temperature range, blade speeds and steam congestion. At the same time the reliability of comparatively small units was secured. The efficiency guaranteed is higher than any heretofore obtained. Taking the amount of heat available in the steam between the conditions of admission and exhaust as a basis, the engines will deliver in electrical form 75.75 per cent of this energy. The total weight of the complete unit is 1,500,000 lb.
The turbine rests upon a foundation consisting of a steel frame encased in concrete, leaving most of the space below available for condensers, receiver and pumps.
The Worthington surface condenser, of 50,000 sq. ft. cooling surface for each unit, is of the twin-shell type, of simple construction and practically self-contained. The tube arrangement is as shown in Fig. 7, passages being provided by "gashing" to give the freest possible access of the steam to the tubes. The condensers are hung directly from the turbine bedplates, a novel arrangement but one conducive to the elimination of stresses due to temperature changes. The weight of the condenser is, however, not carried by the turbine foundation, but upon a number of spring jacks, adjusted to properly share the load. The receiver is a vertical cylinder, of 7 ft. 9 in. inside diameter and 21 ft. long inside, placed symmetrically with respect to the condenser shells as shown in an accompanying plan. This is as large a receiver as could be accommodated in the available space.
Below each condenser shell and forming an integral part of it is a sump 4 ft. in diameter and about 4 ft. high, into which the condensate drains. This is designated as a "hot well" on the drawing, but there is no hot well in the new plant, using the term in its usually accepted sense, that function being performed by the feed-water heater.
The piping to and from the condenser is of unusual construction, designed to minimize the number of bends. As shown in Figs. 7 and 9, the water enters the condenser at the bottom through a 60-in. pipe, which dips under the nearer shell to reach the farther one. A baffle inside deflects a share of the circulating water into its proper channel. A similar outlet pipe above takes care of the discharge flow. This is the simplest possible piping layout for a twin shell condenser. Short rubber sleeve expansion joints are inserted in the intake and discharge pipes near each shell. These joints con- sist of tubes of 1/2-in., 5-ply-insertion rubber, 12 in. long and of 42-in. and 60-in. inside diameter, each clamped between an outer flange and an inner ring.
Circulating water for each pair of condensers is supplied, as shown in several illustrations, through a pair of tri-rotor, centrifugal pumps having a combined capacity of 75,000 gal. per minute. These discharge through separate motor-operated gate valves, the discharge pipes uniting beyond the valves. The full capacity of the pumps will be required in summer when the circulating water temperature is high, but one pump will be sufficient in winter.
The pumps are driven by steam turbines rated at 240 hp each. The pumps draw from a new tunnel 12 ft. 6 in. X 12 ft. 6 in. in section. They discharge into two tunnels, one 8 ft. 6 in. x 12 ft. 3 in., and one, 5 ft. x 12 ft. 3 in., which is the combination of the original intake and discharge tunnels. These will supply condensing water for eight units. The mouth of the intake tunnel is about 150 ft. upstream from the nearer discharge tunnel. New motor-driven revolving screens of the type shown in one of the illustrations have been installed near the river end of the intake tunnel, the driving motor being housed in a small building at the right, not shown. The screens are rotated for cleaning purposes daily. The location of the condensers with respect to the river level makes it possible to circulate the condensing water readily, the power required being only that necessary to overcome a small amount of friction, principally the friction head of the condenser and piping.
The condensate pumps for each unit are of the centrifugal type, turbine driven and of 800-gal. per minute capacity each. One pump is sufficient, the second being a reserve. One reciprocating dry vacuum pump is provided for each unit, with a capacity for two. The vacuum pumps are cross-connected between units.
The general turbine-room piping scheme is shown in Fig. 10. It comprises duplicate 15-in. mains for the turbines and 8-in. auxiliary mains, all suspended overhead in the basement, and provided with long radius curves and goosenecks where necessary. Twelve-inch condensate lines unite in a 16-in. main to the heater, as do 28-in. exhaust lines into a 36-in. main. The illustration shows the essentials of one unit with the exception of the atmospheric exhaust, an important feature on account of the large sizes of pipe involved.
This atmospheric exhaust system is combined with the auxiliary exhaust in the following fashion. From each receiver is a 30-in. line into which the auxiliary exhaust lines are connected. An atmospheric relief valve is in each line near the receiver. This is a standard relief valve weighted to open on about 28 lb. per square inch absolute pressure by means of a hydraulic piston and standpipe accumulator. The three lines lead into a tapered header, from which two 30-in. risers, sealed with back pressure valves, extend above the roof. From the header a 42-in. pipe leads to the feed-water heater. This is also protected with a riser and valve.
Between the receiver and the feed-water heater is a "thermal" or "heat-balance" valve for equalizing the distribution of heat in the system. This valve is shown in cross-section in Fig. 11. Its function is to bleed steam from the receiver into the heater when there is a deficiency of supply to the latter from the auxiliaries, or vice versa. At about 27,000 kw the receiver pressure reaches atmospheric pressure, continuing to rise until at 32,000 kw it is about 8-lb. gage.
In the figure the left-hand opening in the chamber leads to the heater, the right-hand one to the receiver. There are two piston valves, A and B. When heater pressure is above atmospheric, the latter being applied to the upper side through a pipe connection, A rises and bleeds steam through port C to the receiver. Whenever the receiver pressure is higher than that of the heater, B rises, admitting steam through port D to the heater. A dashpot at the top of the upper valve chamber prevents sudden acceleration of A, and through A provides a cushion for B. In action the valves do not lift very high off their seats.
Above the valve is an auxiliary cylinder E with live steam above its piston and with pressure controlled by the turbine automatic stop governor below. The piston is loosely packed and leaky and ordinarily floats. When the automatic stop governor operates, pressure is reduced below the piston which is forced down, restoring A and B to the positions shown and cutting off connection between receiver and heater. Another valve, which has been developed by the company's engineers, is one for shutting off the supply of steam in case the vacuum falls below a predetermined value. It consists of a float, the level of which is controlled by the height of a mercury column connected to the condenser. The valve is adjusted to trip the pilot valve of the actuating piston on the main throttle when the vacuum falls to, say, 15 in.
In the boiler house the original boilers are being retained, but one-half are being rebuilt to the extent of adding standard B. & W. superheaters to give 200 deg. of superheat when the boilers are delivering three times their rated output. The Taylor underfeed stokers which are being installed under one-half of the boilers are standard, but on four of the boilers air tuyeres have been installed along the side walls, directing jets over the fires and protecting the side walls.
One Hoppes open-type feed-water heater 9 ft. in diameter and 21 ft. long, with a capacity of 1,600,000 lb. per hour has been added to do the work of the displaced economizers, there being now a good supply of steam from the turbine-driven auxiliaries. It contains 240 pans, each 4 ft. long, having a total area of 3400 sq. ft. In this heater the surplus heat is being absorbed to such an extent that an occasional gentle puff of steam from the relief valve on the heater indicates how little heat is wasted in this part of the system.
As the remodeled boiler plant provides only superheated steam, provision had to be made for the auxiliary supply of saturated steam for the reciprocating engines. In the line connecting the old and new boiler plants is connected a receiver from one of the old engines. This is placed in a vertical position and the superheated steam is led in at the top, passing downward nearly to the bottom through a 15-in. tube. Near the top water is sprayed into the steam through a spraying nozzle, the surplus collecting in the bottom from whence it is returned to the water system. The wet steam rises in the space between the tube and the casing, drying as it rises, and saturated steam is taken off near the top. This device is known as an "attemperator."
In the boiler-room basement much space has been saved by the removal of four triplex pumps, accommodating three turbine-driven centrifugal pumps sufficient in capacity for the entire plant, and the stoker fans and turbines. For each pair of boilers there is one turbine driving two stoker fans direct and the stokers also through helical reduction gears from the blower shafts. In the ashpit section of the basement, ashpits of expanded metal plastered with cement have been recently put in.
The electrical distribution of the plant has been entirely remodeled with a view to providing adequately large switches, feeders, etc., and to protecting the underground cables from damage due to the large amounts of power which will now be concentrated on short-circuit. There are two sets of buses, main and auxiliary, to which each old and new generating unit is connected. Between the generator and the main bus is a reactor with 5 per cent reactance, and between it and the auxiliary bus is one with 2 per cent reactance. The main bus is sectionalized through oil switches, groups of feeders being taken off from each section.
The reactance coils are placed on the exciter gallery conveniently located with respect to the generators. The 5 per cent coil is about 4 ft. 6 in. in diameter and 8 ft. 6 in. long, and the 2 per cent coil is about 4 ft. 6 in. in diameter by 3 ft. 6 in. long.
The oil switches are of standard General Electric manufacture, type H6, with 10-in. pots.
The generators have been designed for their rated capacity, 30,000 kw, with 55 deg. Cent, temperature rise. They are ventilated by means of fans which form part of the revolving field. The air is taken in through the openings below the bedplates, shown in Fig. 5, and is discharged through ducts to the boiler house, eventually reaching the stoker fans. The generators have about 8 per cent reactance, and the armature windings are braced with extraordinary firmness to withstand the mechanical effects of short-circuits.
The changes described in this article were designed and carried out by the engineers of the Interborough Rapid Transit Company, under the direction of Henry G. Stott, superintendent of motive power. Those in responsible detail charge were Reginald J. S. Pigott, mechanical construction engineer, and Gaylord C. Hall, electrical engineer.
FIG. 3-NEW TURBINE UNIT
FIG. 4-CROSS-SECTION OF ENGINE ROOM BEFORE REMODELING
FIG. 5-CROSS-SECTION OF ENGINE ROOM AFTER REMODELING
FIG. 6-GENERAL LAYOUT OF TURBINE UNIT
FIG. 7-CONDENSER AND SECTIONS OF PIPING
FIG. 8-TRI-ROTOR CIRCULATING PUMPS
FIG. 9a-PLAN AND ELEVATIONS OF CONDENSER
FIG. 9b-PLAN AND ELEVATIONS OF CONDENSER
FIG. 10-PIPING FOR ONE UNIT
FIG. 11-HEAT-BALANCE VALVE
FIG. 12-REVOLVING INTAKE SCREEN
Tests on 30,000-Kw. Turbine
Electric Railway Journal · Vol. 47, No. 20 · May 13, 1916 · p. 903.
Tests on 30,000-Kw. Turbine. The Most Recent Units for the Interborough Rapid Transit Company, Reaching a Thermal Efficiency of 25 Per Cent, Have Made the Gas Engine Obsolete in Large Stations.
At a meeting of the American Society of Mechanical Engineers in New York on May 9 a paper was presented by H. G. Stott and W. S. Finlay, Jr., in which were given the results of a series of elaborate efficiency tests on one of the 30,000-kw. cross-compound steam turbines recently installed in the Seventy-fourth Street power station of the Interborough Rapid Transit Company of New York. Before the paper was read Mr. Stott made some preliminary remarks on the development of prime movers since the year 1900, when the Seventy-fourth Street station was installed.
At that time the plant was equipped with reciprocating engines of 5000-kw. rating and a maximum capacity of 50 per cent overload. The water rate was 17-1/2 lb. per kilowatt-hour, and the cost of the engine, generator and condenser approximated $40 per kilowatt of rated capacity. The plant was of the unit-type arangement, and 4000 hp. of boilers were furnished for each 5000-kw. turbine. When the new turbines were installed, each one occupied the same floor space as one of the original reciprocating engines, although the turbines was of six times greater capacity. The new machine had a water rate of ll-1/2 lb. and cost about $9 per kilowatt, including generator and condenser, being operated by the same eight boilers that had originally supplied steam for the 5000-kw. reciprocating unit.
INTERBOROUGH TURBINE TESTS — WATER-RATE CURVE.
This extraordinary development of the turbine, Mr. Stott said, had caused it absolutely to have displaced the gas engine for power station work. The thermal efficiency of the turbine now approximated 25 per cent, as good a figure as could be obtained from the gas engine, while the latter involved very much higher overhead charges and maintenance costs. For the same reason, hydroelectric power, which looked like a gold mine fifteen years ago, even when the cost of development ranged between $200 and $300 per kilowatt, was to-day not a good investment. Even at Niagara Falls, where the development charge is at a minimum, and where the supply of water is practically unlimited, hydroelectric power cannot compete with that obtained from a modern steam-turbine station when the load factor is less than 50 per cent.
The paper of the evening was then presented by Mr. Finlay. This gave a brief description of the installation and presented in detail the results of the tests. From the figures, it appeared that the maximum efficiency was attained with a load approximating 90-per cent capacity, the water rate at this point being 11.25 lb. per kilowatt-hour. Throughout all of the tests, the operating conditions were approximately the same, the figures for the test giving the lowest water rate being as follows: Absolute steam pressure at throttle, 224 lb.; steam temperature at throttle, 500 deg. Fahr. ; superheat, 108.5 deg. Fahr.; absolute steam pressure at primary inlet, 215 lb.; absolute steam pressure at low-temperature inlet, 15 lb. Vacuum referred to 30-in. barometer, 28.86; average load, 26,740 kw.; water per hour, 301,035 lb. The water rate for this test was 11.258 lb. per kilowatt-hour, this figure being corrected to meet standard conditions involving 215 lb. absolute primary-inlet pressure, 120 deg. superheat and 29. in. of vacuum. The Rankine-cycle efficiency under these same conditions was 75.84 per cent and the thermal efficiency was 24.81 per cent.
The load under which the turbine was tested took the swings as normally produced by the railway substations which were being supplied with power, but a number of tests were also made under throttle control to show the influence of the swings upon the economy. The latter results, however, did not differ from the former, showing that swings even amounting to more than 30 per cent of the average load made no appreciable difference in the performance.
In the discussion which followed F. Hodgkinson, of the Westinghouse Electric & Manufacturing Company, who had designed the turbine, discussed the irregularity that appears in the water rate curve above loads of 22,000 kw., this having been found definitely to be due to some other cause than errors in the readings. He ascribed it in part to the action of the separator that was installed between the high-pressure and low-pressure elements for the purpose of removing the water that otherwise would be carried over into the low-pressure blading. This separator was of the centrifugal type, and it was found at times to be inefficient, the removal of the collector plates actually reducing the amount of water carried over at certain loads. R.J.S. Piggott also commented upon this phenomenon, stating that it is impossible to remove the last few per cent of moisture in steam with baffles. It is best to slow down the velocity of the steam below 3000 ft. per minute, at which point the "fog" coalesces into drops which will separate themselves from the flow of steam.
In answer to a number of questions that were raised during the course of the discussion, Mr. Stott stated that the maximum capacity of the turbine was between 33,000 kw. and 34,000 kw., it being rated at 30,000 kw. and guaranteed for a load of 32,000 kw. Beyond this point, the turbine lost speed, so that an addition of 25 per cent overload would produce a slowing down of about 15 per cent from normal speed. The monthly average coal consumption of the plant approximated 1.5 lb. per kw.-hr. With the original reciprocating engine displaced by the turbines, the coal consumption had been 2.5 lb. The thermal efficiency of the station as a whole averaged 17 per cent throughout the month at the present time.
Data of New Interborough Turbine
Electric Railway Journal · Vol. 57, No. 21 · May 21, 1921 · p. 945-946.
Data of New Interborough Turbine. Water Rate of 11 Lb. per Kilowatt-Hour for 30,000-Kw. Turbine Shown by H. B. Reynolds, Research Engineer Interborough Rapid Transit Company, to Have Been Attained in Test — Facts Contained in A. S. M. E. Paper.
In a paper scheduled for presentation at the spring meeting of the American Society of Mechanical Engineers, to be held in Chicago, May 23 to 26, 1921, Herbert B. Reynolds, research engineer, Interborough Rapid Transit Company, New York City, gives information regarding the several types of turbine which have been installed by that company during the past dozen years. He also includes the results of tests on the latest unit installed, namely, the three of 30,000-kw. capacity, the installation of which was completed during the past year.
Mr. Reynolds said that in order to provide additional power capacity for the new subways constructed in New York City during the period from 1913 to 1921, and operated by the Interborough Rapid Transit Company, additional turbine units were installed in both the Fifty-ninth Street and Seventy-fourth Street power stations. He reminded his readers that the original engine-room equipment of the Fifty-ninth Street power plant consisted of nine 7,500-kw. maximum capacity Manhattan-type Allis-Chalmers double-angle compound engine units and three Westinghouse 1,250-kw. turbines, the latter driving 60-cycle generators which supplied current for subway lighting. Later 25-cycle current was adopted for this lighting, the current being taken from the main units. During 1909 and 1910 five low-pressure 7,500-kw. maximum capacity General Electric turbine units were added, taking exhaust steam from five of the engines at atmospheric pressure.
Two of the new 30,000-kw units in the Fifty-ninth Street plant were installed in the space formerly occupied by the three lighting units, while the third turbine was installed at the western end of the station. The concentration of power possible with modern turbines is strikingly shown by the space they require as compared with that for reciprocating engines. The maximum capacity of the engines visible in the background in the photographs reproduced is but 26,250 kw., while that of the turbine in the foreground is 35,000 kw.
The three 30,000-kw. Westinghouse cross-compound turbines which were completed in 1915 were among the new units installed at the Seventy-fourth Street power station.
In the paper Mr. Reynolds gave structural and design details of the new turbines. Among other things, he said that they are of the straight Curtis impulse type, having twenty pressure stages, each consisting of one velocity stage. The normal steam pressure at the throttle is 225 lb. per square inch, abs., with a super-heat of 150 deg. F., exhausting into a vacuum of 29 in. referred to a 30-in. barometer at 58.1 deg. F. The speed is 1,500 r.p.m.
In addition to the primary steam inlet, a secondary valve is provided which opens after the load reaches 24,000 kw. and which enables the turbine to carry a load of 35,000 kw. As all auxiliaries in the station are steam driven, a connection has been provided in the turbine through which any excess auxiliary exhaust steam may be injected. This is at the sixteenth stage of the turbine.
The generators are three-phase, star-connected, generating 25-cycle current at 11,000 volts. The excitation is at 250 volts. The generators are cooled by circulation of air maintained by a fan which forms an integral part of the generator. The air is drawn from the turbine-room basement and discharged from the top of the generator into the turbine room through a short stack.
Each unit comprises one single-shell two-pass Worthington condenser, two Worthington centrifugal circulating pumps, each driven through reduction gears by Kerr turbines; two Worthington centrifugal condensate pumps, each driven by a General Electric turbine, and one Laidlaw-Dunn-Gordon dry vacuum pump. Each condenser contains 50,000 sq.ft. of tube surface in 10,760 tubes 18 ft. long, 1 in. in outside diameter and of No. 18 B.W.G. thickness. The condenser is of the two-pass type, the water entering at the bottom and passing out at the top. As the condensers are mounted on springs, rubber expansion joints are inserted in the circulating water lines.
Adjustment of Spring Condenser Supports
As no expansion joint was provided between the turbine and the condenser, it was necessary to mount the latter on springs, so as to provide for expansion and contraction. The spring supports are shown in one of the illustrations. To facilitate the setting of the springs and provide a means for detecting and adjusting for fatigue in them, hydraulic jacks were incorporated in the condenser supports.
Mr. Reynolds gave some detail of the procedure followed in setting these springs. He said that after the erection of the condenser and circulating water pipe had been completed, with the exception of making the joint between the condenser and the turbine, the condenser was raised while empty by means of the jacks, leaving 1/2 in. clearance between the face of the turbine outlet and the face of the condenser inlet. The load on each of the four supports was then determined by noting the oil pressure in the jacks. It was decided that with the condenser empty and cold the downward pull on the turbine should not be less than approximately 17 tons. The distance that the joint between turbine and condenser would have to be pulled in order to give this load was estimated from the modulus of elasticity of the turbine and condenser metal. The condenser was then raised to within the predetermined distance of the turbine outlet, which was found to be 0.231 in., after which the lock nuts on the jacks were screwed home and the condenser bolted to the turbine. The load on the springs was then determined with the condenser still empty by noting the pressure required just to raise the lock nuts. Every few months the load carried by the springs will be determined in this manner and compared with the load which existed when the condenser was first bolted to the turbine. Any fatigue which may develop in the spring will be compensated by screwing the lock nuts down.
It was found that the minimum condenser load carried by the turbine with the condenser shell empty was approximately 17 tons. As the water required to fill the condenser weighs about 60 tons the load on the turbine increases to 77 tons when the circulating water pumps are started. This is reduced to about 70 tons due to the compression of the springs under the expansion of the condenser during warming up. Immediately after shutting down, and while the condenser is still warm but drained, the load on the turbine is reduced to 10 tons. Thus, the condenser load on the turbine varies from 10 to 77 tons, out of a total condenser weight varying from 180 to 240 tons.
Tests Showed High Thermal and Mechanical Efficiency
The equipment used for conducting the turbine tests consisted of two large water-weighing scales for measuring steam consumption, three single-phase rotating standard watt-hour meters for measuring the output, and the necessary thermometers, gages and mercury columns for determining temperatures, pressures and vacua. Most of the tests were of three-hour duration and, with the exception of a few special tests, the turbine was operated under conditions normal as to the type of load.
The results of the tests, in so far as the water rate is concerned, are given in the accompanying curve. The lowest rate obtained while operating under normal conditions was 11.03 lb. per kilowatt-hour. The thermal efficiency, or ratio of the output to the energy in the steam, was 25 per cent. The Rankine efficiency; that is, the ratio of the energy developed to that available within the working range of temperature and pressure, was 75.5 per cent.
In the paper the results of various auxiliary tests were also given, but it is impossible to summarize these within the space limitations of the present abstract.
ONE OF THE THREE 30,000-KW. TURBINES INSTALLED AT THE FIFTY-NINTH STREET POWER STATION OF THE INTERBOROUGH RAPID TRANSIT COMPANY IN 1920.
A COMPLETE TURBINE AND CONDENSER UNIT.
DETAILS OF THE SPRING SUPPORTS FOR THE CONDENSER.
WATER-RATE CURVE FOR NEW INTBRBOROUGH RAPID TRANSIT TURBINE. Dotted line shows results that would probably have been obtained if steady-load tests had been conducted within this range of load where the secondary valve is continually opening and closing.
Interborough Commissions 60,000-Kw. Turbo-Generator Unit
Electric Railway Journal · Vol. 53, No. 19 · May 10, 1919 · pp. 906-908.
Interborough Commissions 60,000-Kw. Turbo-Generator Unit. Attention Is Directed in This Article Particularly to the Automatic Control Features of the Installation.
By W. S. FINLAY, JR., Superintendent of Motive Power, Interborough Rapid Transit Company, New York City.
The Interborough Rapid Transit Company, in its Seventy-fourth Street power plant in New York City, has the largest prime mover now in service in the world. The machine is the first of the three-cylinder type of turbine to be put into operation, one of the elements being the high-pressure section and the other two the low-pressure sections. The combined unit has a maximum continuous capacity of 60,000 kw., or 70,000 kw. for two hours. It occupies a floor space of 52 ft. x 50 ft. and at maximum load requires 826,000 lb. of steam per hour.
The unit is designed on what is known as the cross-compound principle. Each element is coupled direct to its electrical generator, and all three elements when in normal operation are tied together electrically. The steam path is such that all of the steam passes through the high-pressure element, then divides equally and flows through the two low-pressure elements. This principle of design, by dividing the work done into separate cylinders, allows the use of smaller individual elements which are inherently stronger than large cylinders; it makes possible an outfit considerably more flexible than a single large unit and more reliable because the turbines are smaller and there is less temperature difference in any one cylinder; and it permits the use of commercially common materials with moderate blade speeds and stresses.
NORMAL LOAD ON EACH ELEMENT IS 20,000 KW.
The high and low-pressure turbines are proportioned so that with a total load of 60,000 kw. the load will be equally divided among the three elements. In case of failure of one of the low-pressure elements, it would be called upon to carry an abnormal load since all of the steam from the high-pressure element must pass through one low-pressure turbine. To provide against injury to the generator from this cause there is provided a back pressure valve on the exhaust of the high-pressure element which, when the pressure has reached a given amount, will permit steam to exhaust direct to atmosphere. The pressure selected is that which corresponds to a load of 30,000 kw. on the low-pressure turbine, which it is well able to sustain for a half hour. One half-hour is regarded as sufficient time in which to get other units onto the system, when the load on the high-pressure and one low-pressure element of the triple unit may be reduced to the limits of the continuous capacity of the low-pressure generator.
40,000 KW. IS THE MAXIMUM-ECONOMY LOAD
The high-pressure element contains fifty rows of blades, the height of the first row being 4 in. and that of the last row 9 in. The journals are 10 in. in diameter, and the rotor is equipped with a Kingsbury thrust bearing the function of which is to prevent any axial movement of the rotor. Each low-pressure element contains forty-four rows of blades, the height of the first row being 6 in. and that of the last row 15 in. In this element the turbine rotor journal is 12 in. in diameter. The rotor is, like the high-pressure element, equipped with a Kingsbury bearing.
In connection with the turbine there are four surface condensers installed, two being connected to each one of the low-pressure elements. The total area of cooling surface is 100,000 sq.ft.
The turbine is designed to operate with steam at 220 lb. per square inch, absolute pressure superheated 150 deg. Fahr. and to exhaust into a 29-in. vacuum. At a load of 40,000 kw., which is the point of best economy of the unit, the high-pressure element will exhaust into the low-pressure element at 29.7 lb. per square inch, absolute pressure, at a temperature of 250 deg Fahr. This turbine unit is estimated to operate at load between 30,000 kw. and 60,000 kw. at a water rat which is not more than 5 per cent greater than the minimum.
Each turbine runs at 1500 r.p.m. and its generator delivers three-phase power at 11,000 volts, 25 cycles. Each element has its individual busbars with separate feeders. Installed in the connections between the bus-bars are reactance coils to limit the flow of current between generators.
Although the unit consists of three separate elements the method of starting the elements from rest preparatory to synchronizing is essentially the same as for single-shaft units. First the field current of all three generators is applied; then the throttle valve on the high-pressure element is partially opened. As soon as the high-pressure rotor starts to revolve it will, through the applied field current, set the rotors of the two low-pressure elements revolving. This causes all three elements to come up to speed together and in correct phase with each other, so that when synchronized with the system they can be connected to the main busbars by closing a single circuit breaker.
The new Interborough turbine unit is of interest not only on account of its size but because unusual attention has been given to the development of automatic features by means of which in the event of trouble with any of the elements it will be automatically cut out of service, the remaining two elements continuing to carry the load.
By the use of an ingenious governing arrangement means have been provided that will permit uninterrupted operation of each individual element, should one or the other two be taken out of service by tripping the automatic stop from any cause not affecting all three elements.
For example, if the high-pressure element is shut down, each low-pressure element will automatically receive high-pressure steam direct from the boilers through its own individual high-pressure steam system, whereas in normal operation the low-pressure elements do not receive any high-pressure steam direct. Vice versa, if the two low-pressure elements be shut down, from any cause not affecting the high-pressure element, the high-pressure element will continue operating and automatically exhaust its steam into the atmosphere. Should only one low-pressure element be removed from service, the high-pressure element will exhaust into the remaining low-pressure element. All this governing arrangement is entirely automatic.
THE GOVERNORS SEEM ALMOST TO HAVE INTELLIGENCE
Since the governing mechanism must control three units, not only when operating together but also when operating separately, several features novel in steam turbine practice are involved. Each unit is provided with an over-speed stop governor which will immediately shut off the steam from that unit if the speed rises above a predetermined amount. Each unit is also equipped with a speed regulating governor of which that on the high-pressure unit is of the customary form. The speed-regulating governors on the low-pressure units are somewhat more complicated.
A butterfly valve, capable of automatic operation, is provided at each connection between the high and low-pressure units which will be automatically closed should the low-pressure turbine speed exceed a predetermined limit. This is tripped shut first by the speed regulating governor should it go to the outer position, and in the event of its failing then by the automatic stop governor. The high-pressure turbine is provided with another exhaust, having a back-pressure valve, so that when necessary the exhaust from ths high-pressure turbine may pass to atmosphere and the high-pressure turbine continue to carry its load.
Similarly, if the high-pressure turbine loses its load its governor will cut off steam to the whole system. If the governor does not control the turbine and the speed reaches the predetermined limit, then the stop governor on the high-pressure will close the automatic throttle, similarly cutting off steam from the whole system. The whole system will then slow down until it reaches a predetermined speed lower than normal, when the governors on the low-pressure turbine will cause live steam to be admitted directly to them.
A DIFFERENTIALLY-OPERATED VALVE CONTROLS THE LOW-PRESSURE LINE
There is a butterfly valve in the low-pressure line which is controlled from the governor of the corresponding low-pressure turbine. Each valve is operated by a differential piston to both sides of which steam pressure is admitted. One end of this cylinder is connected to a valve trip mechanism located at the low-pressure governor and so arranged that when the governor reaches a prescribed position a valve will be tripped open, thus releasing steam from that side of the differential position. Steam pressure on the other side will then quickly force the butterfly valve closed. If the turbine is to be shut down the gate valve is then closed by hand. The butterfly valve may be opened or closed also by a hand-controlled valve.
The valve controlling live steam direct to the low-pressure turbine will begin to open when the low-pressure governor reaches a prescribed position. This valve mechanism does not differ in principle from the main high-pressure valve controlling steam in the system, and is in conformity with ordinary practice for such purposes.
The overspeed stop governor on the high-pressure turbine will close the main throttle valve and the main regulating valve, while that on the low-pressure turbine will bring about the closing of the butterfly valve and the governor and throttle valve, admitting high-pressure steam to the low-pressure turbines.
As part of the throttle valve there is a switch which, when closed, will open the main circuit breaker. Should some accident happen to one of the turbine elements, it may be instantly cut out by operating the emergency stop, which will cause the immediate closing of the automatic throttle. This in turn causes the closing of the switch, which opens the circuit breaker.
The new unit was built by the Westinghouse Electric & Manufacturing Company, but unlike most Westinghouse turbines of moderate capacity it is built entirely on the reaction principle, whereas the custom of this company has been to build its turbines with an impulse high-pressure section. This change is due to the enormous volumes of steam which are to be handled and it permits the use of relatively long blades in the first rows of the high-pressure element.
TURBINES HAVING A NORMAL CAPACITY OF 150,000 KW. IN INTERBOROUGH POWER PLANT. New 60,000-kw. unit in foreground, three 30,000-kw. units in background.
CIRCULATING WATER PUMP IN INTERBOROUGH POWER PLANT.
PLAN AND ELEVATION OF 60,000-KW. TURBO-GENERATOR UNIT.
Power Distribution in the Interborough
Electric Railway Journal · Vol. 67, No. 4 · January 23, 1926 · pp. 152-156.
The Contact Rail Sections Are Interlocked and Connected by Electro-Pneumatic Circuit Breakers and All Are Under Control from a Centralized Station. In Consequence, the Circuit Breakers Controlling an Entire Substation Section Can Be Opened Through an Emergency Alarm Whose Boxes Are Distributed Along the Walls of the Subway.
[Left] Circuit Breakers in Boxes on Columns, with Boxes Open at 156th Street and Alexander Avenue. [Center] Circuit Breakers in Boxes on Columns with Boxes Closed at 129th Street and Lexington Avenue. [Right] Front View of Group of Circuit Breakers in Chamber at 79th Street and Lexington Avenue.
Articles in this paper last year discussed the numerous safety features and other improvements applied to the rolling stock of the Interborough Rapid Transit Company and other phases of its New York subway rapid transit service. Equal care has been used in the installation of the electrical distribution system to protect against accidents and electrical disturbances, as well as to safeguard passengers against possible delay through interruption.
Primarily the safety features of the system depend upon the sectionalizing of the third rail, the sections being electrically connected by electro-pneumatic circuit breakers, which are under remote control from a centralized control station. In consequence, the circuit breaker controlling a section, besides automatically opening in case of a super-current flow, will open if an emergency alarm is sent from one of the alarm boxes mounted on the subway wall in that section. Reference to this emergency alarm system in connection with the sectionalized distribution system has been made in previous articles in this series, particularly in that in the issue of July 25. In this article an account will be given of the method by which the contact rails are sectionalized and connected up and supplied with energy from the substations, as well as how the emergency alarm works.
CABLE CONNECTION TO CONTACT RAIL
The contact rail in the tunnels is protected from the adjacent structures, and particularly from the steel columns, by means of a specially prepared board carried over the top of the rail and supported by properly insulated posts. The cables which furnish power from the substations to the contact rails are of the concentric type that is to say, there is an inner core that is positive, then a layer of insulation, then a layer of wires forming the negative conductor, then more insulation, and then an outer covering of lead. The purpose of this type of cable construction is to localize any trouble caused by short circuits.
At its outer end this cable terminates at a manhole in the side wall of the tunnel where the positive and negative portions of the cable are separated, the negative lead being connected to a bus and the positive lead carried to a circuit breaker. The circuit breaker is of 3,000-amp. capacity and is equipped with an electro-pneumatic valve for the closing operation and a trip coil for the tripping operation. The circuit breaker is mounted on an extra heavy panel. In some cases, these circuit breakers are housed in fireproof boxes and mounted on the columns, as shown in the left hand drawing on page 153, but wherever possible, a separate concrete and steel chamber is constructed as part of the subway structure, as shown in the right hand drawing on page 153.
The negative bus is mounted in a separate chamber immediately adjacent to the circuit breakers. The negative cables are then run from this negative bus to the track rails in fiber conduit, with a sufficient thickness of concrete around the conduit to prevent water from entering it and to protect it from damage that might be caused by its coming in contact with any heavy object, as well as to afford protection against fire.
The positive connection from the circuit breaker to the contact rail is made by means of 2,000,000-circ.mil cable, insulated by an extra heavy thickness of Kerite insulation, and where it is necessary to install this cable on the steel beams it is further insulated by porcelain insulators. This 2,000,000-circ.mil cable is terminated in a specially devised pothead, constructed of concrete where it is changed to four smaller cables more easily to permit of its being bonded into the contact rails to its full capacity. This change in the size of cables is made by a mechanical connector that permits of ready disconnection whenever necessary.
At all locations where it is possible the positive cables are run underneath the track bed in the way already described for the negative cables, except that as a further insurance against the collection of moisture in the conduits under the track the conduit is filled solidly with a cable compound. Some idea of this detail may be gained from a study of the drawing above, which shows one of the several methods of making the connection, the one used depending upon conditions.
CONTROL OF ENERGY SUPPLY
Power is furnished to the contact rails from substations located approximately 2 miles apart. The contact rails within the section supplied by power from a substation is in full control of the operator of that particular substation, and he is under the direction of a system operator located in the main power station. This arrangement has been made possible by the control system in use by which each track section receives power through separate feeders and circuit breakers, and it permits the localizing of any trouble to the track section on which the trouble occurs. The contact rails are further sectionalized for reasons of operating facility during times of emergency, particularly at places where crossovers are located and where it may be necessary to turn or divert trains from one track to another around sections where trouble exists. This is accomplished by creating a gap in the contact rail, around which gap cables are inserted for continuity of power, the cables being in series with a circuit breaker.
In the design of this system, one of the fundamentals observed was the elimination wherever posible of any material of an inflammable or combustible character that would tend to create smoke or fumes. Where this was not possible extraordinary preventive measures were followed for the protection of materials of a combustible or inflammable character.
CIRCUIT BREAKERS AND WIRING
The contact-rail sections fed from each substation are terminated at points midway between adjacent substations by gaps in the contact rail, around which are cables connected to a group of circuit breakers in sufficient number to provide separate and distinct circuit breakers for each track and for each substation. That is to say, at the dividing point between substations each substation has its own set of circuit breakers. These circuit breakers are all bus-connected so that the load in all rails will be equalized. Therefore, each contact rail section generally consists of a section of tunnel in sole control of a substation operator and furnished with power from this substation, with each track and section independently operated and controlled by dovetailing into the adjacent substation feeding section, as shown in the diagram on page 154.
Each section of contact rail between the gaps is designated by a series of letters and numbers for the purpose of ready identification. So far as is possible, the designating letters employed are related to the location of the limits of the section.
The wiring system for the control of the circuit breakers is shown in the large drawing on page 152. Its operation is as follows: In times of emergency, the emergency alarm boxes located throughout the tunnels are operated by any employee at or near the trouble. Operation of this emergency alarm causes the main feeder breakers in the substation to open and simultaneously to open the equalizing circuit breakers at each end of the substation feeding section. The result of this operation is that the supply of power is then discontinued within the limits of the line fed by the substation. Properly authorized officials in the field are then placed in communication with the system operator, when the proper procedure is decided upon for the resumption of operation. On receipt of these instructions the system operator issues the necessary orders to the substation affected.
This system of control wiring involves the use of control cable throughout the entire length of the subway. This cable is carried on the walls of the tunnel, so that in event of electrical disturbance in cables in the duct line it will be as far removed from trouble of this sort as possible. It is of a rubber-covered type, with specially designed outer covering and support, and of necessity is made up of many conductors, the number of conductors depending upon the number of circuit breakers to be controlled by a particular substation.
The description of the contact rail system just given applies only to the tunnel portions of the Interborough Rapid Transit Company. While the general features of the contact-rail system on the elevated structure of the company are somewhat similar they differ in a number of particulars, especially on the outlying sections of the elevated structure.
Typical Wiring Diagram of Remotely Controlled Circuit Breakers Controlled from a Substation (No. 23).
At Left, Pillar Support and Housing; for Circuit Breaker In Subway. At Right, Pit Location for Circuit Breakers with Typical Cable Run.
Detail of One Method of Making Contact Rail Connection.
Cable Connections at 82nd Street Lower Level, Lexington Avenue Line.
Portion of Positive D.C. Feeder Layout Showing Location of Substations, etc.
Electric Railway Journal · September 2, 1916 · p. 5.
Three 30,000 kw. Westinghouse Cross Compound Turbines, 74th St. Station, Interboro Rapid Transit Co. (Click to enlarge.) [These turbines were not at the main IRT powerhouse but the image is included here for reference.-Webmaster]