Publication: American Electrician
New York, NY, United States
THE DEVELOPMENT OF THE HYDRAULIC POWER OF THE
HUDSON RIVER AT MECHANICVILLE
The development of the power of St. Anthony's Falls on the Mississippi at Minneapolis, Minn., is followed closely by the utilization of the power of the upper waters of the Hudson River at Mechanicville, N. Y., where an undertaking of no less magnitude has, within the past few days, been completed. Five to seven thousand h.p. is available at the power house and the use of high tension current permits of its distribution over a wide territory.
As in the Mississippi, the waters of the Hudson above the present point of development have been, to some extent, employed by factories using low head turbines directly driving their machinery, but not until the undertaking just concluded was decided upon had any very serious effort been made to take advantage of the great amount of power which has run to waste for ages down the stream of the main waterway of the Empire State.
Early in 1897 the attention of Mr. R. N. King, President of the Stilwell-Bierce & Smith-Vaile Company, of Dayton, Ohio, was drawn to this water power. His long experience with water powers and their development, led him speedily to recognize the possibilities which were presented. The site is but two miles from Mechanicville, eleven miles from Troy and eighteen miles from Albany, in each of which towns large quantities of power would doubtless find a market. But, most important of all, it lies only seventeen miles from Schenectady, where, covering not less than 130 acres of ground, the largest electrical works in the world are operated from an extensive steam plant, with which the electrical power from the Mechanicville cataract could readily compete.
After consultation with the chief engineers of the General Electric Company, in which the necessary assurances were given, Mr. King formed the Hudson River Power Transmission Company.
The hydraulic engineering features of the development were carried out in their entirety by Mr. A. C. Rice, Chief Engineer of the Stilwell-Bierce & Smith-Vaile Co., and it may be said that in the completed work as it stands to-day little or no departure from the plans laid down by Mr. Rice has been made. As the General Electric Company was to purchase the largest amount of power, its advice as to the electrical equipment was naturally closely followed. The result brought about by the harmonious co-operation of both hydraulic and electrical engineers is a power transmission plant in every respect strictly representative of the most modern hydraulic and electrical practice.
At the point chosen for the hydraulic development the physical conditions make the location an ideal place for a dam and power house. The banks and bottom of the river are of rock, as is Bluff Island, immediately adjacent, which divides the Hudson into two channels. During the greater part of the year there is water sufficient to produce from 7000 to 10,000 h.p.
The island is about one-third of the distance across the river from the western bank, the combined width of the two channels being about 1200 ft. The western channel is used for the head and tail races.
In order to make the excavations for the power house and the main dams, heavy cofferdams were built across both streams. The work would have been completed well within the time at first specified had not an extraordinary freshet swept away part of the cofferdam, necessitating long delay. The rock and shale resulting from the excavations proved unsuitable for incorporation into concrete, and the broken rock used was brought over a special track from the neighborhood of Schenectady.
The power house, extends from the western bank about 215 ft. into the river and is connected with Bluff Island by a concrete dam, 26 ft. high above the bed of the river, 10 ft. wide on top and 18 ft. wide at the base. The upstream face is vertical and the downstream face is sloping. The top of this dam is at an elevation that the water will never reach; thus no provision is made to take care of falling water on the down stream side, but the dam is provided with four arch waste gates, 4 ft. wide and 6 ft. 9 ins. high, operated in the same manner as those in the main dam.
The main dam is on the eastern side of the island. It is built entirely of concrete, asindeed, is the entire construction with the exception of the upper walls of the power house. The upstream face is vertical, the downstream face is curved and provided with a horizontal apron 14 ft. wide, which throws the falling water off horizontally, and thus effectually prevents wash or scour of the toe of the dam. The dam is 16 ft. high above the river bed, 8 ft. thick immediately below the crest, 16 ft. thick through the base and 30 ft. thick through base and apron. The dam is set between massive abutments anchored to the rock sides of the river bank and island. The eastern is 20 ft. long, 26 ft. high above river bottom, 16 ft. thick at the top and 34 ft. wide at the base. The western abutment is 100 ft. long, the other dimensions being similar to those of the eastern abutment. The length of the spillway between abutments is 800 ft. In the western abutment are twelve arched waste gates of ample proportions. Each waste gate is 4 ft. wide and 6 ft. high, and is opened and closed by a heavy iron hoist operated by rack and pinion. The eastern dam is practically a solid rock wall capable of safely resisting any flood. It was severely tested in the spring of 1898, when a flood of extraordinary proportions came against it, yet, notwithstanding the fact that the dam was green, the flood in no manner injured it. To prevent any floating rubbish, ice, or logs reaching the rocks or choking the waste gates, a floating wooden boom stretches from the western end of the spillway diagonally for a distance of 400 ft. to the edge of the normal river bank, and then for a distance of 1000 ft. to the main embankment of the Mechanicville highway. It is anchored to a line of stone-filled cribs.
Between the west end of the power house and the Mechanicville highway a broad roadway has been built of earth and slate rock.
To avoid any possibility of water finding its way through the embankment in case of very high water a concrete core was put in the center, starting at the solid rock and finishing 2 ft. below the surface of the road. The embankment forming the roadway is 40 ft. wide on the top, 124 ft. at the base and 18 ft. high at the deepest point.
The power house lies between the west bank and the short concrete dam, nearly filling the space between the island and the west bank of the river. It is practically a continuation of the dam, and, like the main dam, is of concrete with the exception of the upper walls. Its construction is of the most substantial character, the foundations are carried down to bedrock, and the house is carried on heavy steel box-web girders resting upon steel I-beam columns. The latter are imbedded in concrete walls carrying arches which form the floor of the generator room and the floor on which the wheel flumes rest. The walls form a separate and distinct tail race 22 ft. wide for each set of turbines, from which the water may be shut out at will.
The house is divided into two parts by a thick head wall. The upstream part contains wheel chambers for seven 1000 h. p. wheels, of which five only are at present occupied. The downstream portion contains the wheel governors and the electrical apparatus. The length of the power house proper is 257 ft. 6 in.; the width of the dynamo room between head wall and south wall 34 ft., and the width of the wheel chamber portion 32 ft. 6 in. The total width of the power house is 66 ft. 6 in. At the western end an L extension runs up stream 87 ft. 5 in. long and 44 ft. 10 in. wide. This portion of the power house is of brick. A retaining wall runs down stream from the power house along the western bank a distance of 50 ft. The western stream running between the bank and the island forms the forebay, 300 ft. long. The main tail race is 205 ft. wide and joins the main stream 750 ft. below the power house.
Arched chambers are provided for seven main wheels and two exciter wheels. Each main wheel chamber is 32 ft. 6 in. long, 22 ft. wide and 17 ft. 5 in. high and is provided with two 6-ft. manholes. Each exciter wheel chamber is 32 ft. 6 in. long, 17 ft. 5 in. high and 10 ft. wide. The head wall of the chambers is 6 ft. thick, the wall on the upstream and both sides 3 ft. thick. In the head wall of each main chamber is set a heavy cast iron cover through which the the turbine shaft passes in a water-tight packing box, carrying the ring oil bearing for the shaft. The saving in space effected by the new arrangement of housing and coupling together of the turbines, patented by the Stilwell-Bierce & Smith-Vaile Co. has tended to diminish considerably the size of the power house.
A 20-ton crane from the works of Pawling & Harnishfeger, Milwaukee, runs the entire length of the dynamo room.
In front of the wheel chambers and running the entire length of the power house is a trash rack of steel bars supported on a framework of steel channel and I-beams. This rack effectually prevents the access to the wheels of any rubbish or floating material that may escape the boom.
The main wheel plant consists of ten pair of 42 in. horizontal Victor turbines of the latest type, built by the Stilwell-Bierce & Smith-Vaile Co., of Dayton, Ohio. Each main turbine consists of two pair of wheels which, at the normal speed of 114 revolutions is rated at 250 h. p. The wheel power of each set of turbines is therefore 1000 h. p. Five units are now in position; the two additional turbines will be installed shortly. The head under which the water wheels are operated is 18 ft.
The turbines for the exciters consist of three 18-in. Victor cylinder gate wheels, having, at 259 revolutions per minute, a total of 300 h.p. The quarter turns and packing boxes of these wheels are brought through the wall beneath the station switchboard.
Two draft tubes lead from each main turbine, the forward tube descending; straight into the tail race beneath the power house, the rear or upstream tube curving and flaring downward and outward. Each tube is 9 ft. 6 in. in diameter at the bottom. Two draft tubes are also allotted to each set of exciter wheels, the setting following a similar arrangement. The rear tube is 4 ft. in diameter, the forward tube 3 ft.
The speed of each set of main wheels is regulated by a Geisler electro-mechanical governor, mounted on a platform directly over the turbine shaft, and between the head wall and the generator.
The use of electricity renders the mechanism of this governor extremely sensitive and effective, and the gates can be entirely opened or shut, should the full current be thrown on or off, in six seconds. The driving pulley is replaced by a rawhide pinion, giving a rigid connection between the governor and the wheel, and making 400 r.p.m. The speed may be increased to shut off or throw on in less than six seconds, if necessary. The Geisler governor is now in use in many of the most important electric power transmissions in this country, including those of Columbia, S. C.; Pelzer, N. C.; Lachine, Que.; West Kootenay, B. C.; Montmorency, Que.
The governors controlling the exciter wheel gates are improved "Snow" governors, which rapidly bring the speed to normal when changes are neither frequent nor heavy. They are especially adapted to the regulation of water wheels driving exciters and are provided with adjustable stops which limit the hoisting action on the gate as soon as the gate is fully open.
The dynamo room is a spacious chamber well lighted by windows on all sides. It is 255 ft. long and 34 ft. wide, 30 ft. 5 in. in the clear from floor to roof truss and 22 ft. from floor to crane. The ultimate generator capacity of the station is 7000 h.p. in seven generators each of 750 k.w. capacity. Five have been installed and are now running. They are unitooth, three phase, fortypole 750-k.w. 114-revolution, alternating current machines, having revolving fields and stationary armatures, and wound to deliver 36 amperes of current at a periodicity of 38 cycles and a pressure of 12,000 volts to the transmission lines. They are arranged for operation in parallel at constant voltage. By using the revolving-field type of generator and thus securing this pressure directly from the machine the use of step-up transformers to raise the voltage for transmission purposes is avoided. As the current is to operate synchronous and induction motors, to operate lights and to be converted into direct current through rotary converters, the frequency of 38 cycles was selected as most suitable for the different conditions required.
The alternators are similar in their main characteristics to those successfully used in the development of the power of the Lachine Rapids at Montreal. The armature frame or ring is of the box type, 15 ft. 4 in. in diameter and 36 in. wide. It is bolted to a base 18 ft. 2 in. long by 10 ft. wide,. along which it may be moved parallel with the shaft, in order that the revolving field spider and poles may be uncovered should occasion require. The armature winding is protected on each side by iron shields. The pillow blocks are also bolted to the base and the bearings are of the spherical seated self-oiling type used in all General Electric generators.
The field ring is bolted to the spokes of the spider. It carries forty poles, each securely fastened by two bolts to the ring. The whole revolves on a shaft 15 in. in diameter provided with a rigid coupling on the turbine shaft. The dynamo shaft is extended for coupling to a vertical steam engine in case of necessity. The following reasons for selecting this type of alternator have been given by Mr. C. P. Steinmetz, of the General Electric Company:
In addition to the advantage which the stationary armature type has over the stationary field type in allowing a high transmission voltage to be taken directly from the armatures, it allows of a fairly low saturation of the magnetic circuit, giving an almost straight saturation curve. This is preferable in power transmission, since a considerable increase in the voltage may be obtained if needed to cover excessive drop in the lines, due to heavy loads, etc., and the voltage may be maintained even if the speed remains low.
The exciters are placed one on each side of the stairway leading to the switchboard gallery. They are 6-pole 100-k.w. 125-volt standard General Electric machines with ribbed field frame and iron-clad armatures.
The switchboard, erected on a gallery on the north wall of the dynamo room, is built up of nine highly polished panels of blue Vermont marble, each panel 7 ft. 6 ins. high, 3 ft. wide, and 2 ins. thick. Of these nine panels five are used for the generators and two for the feeders; one is the total out-put panel and the last is for the control of the exciters. The generator panels occupy the left side of the board, and room on the gallery is left for two additional panels. The feeder panels are on the right hand side; the total output panel is between these and the generator panels and the exciter panel is the third panel from the left-hand end of the board.
Each generator panel is equipped with the following instruments: One inclined coil alternating am- meter reading to 75 amperes for the generator, and one direct current ammeter reading to 150 amperes for the field. Above each of these is a pilot lamp, and between each pilot lamp is a synchronizing lamp. Beneath the two ammeters is an inclined-coil voltmeter reading to 15,000 volts, and beneath this instrument are three single-blade double throw, quick-break, high-tension switches, which, seen from the front of the board, are each mounted upon pyramids of corrugated hard rubber. Similar pyramids intervene at the back of the board between the bus bars and the board. The corrugations give a total distance of about 8 ins. of surface between the metal clips and hinge, and the surface of the marble on each side. As these switches are to break a current of 12,000 volts, they are tested to break without difficulty currents of 21,000 volts. The switches are without handles. An eye is made in the end of each blade, into which a hook at the end of a stick may be inserted and the switch opened by the attendant from a sate distance. Further, to prevent any dangerous arcing from blade to blade, marble barriers 1 1/4 ins. thick, 3 ins. long and 12 ins. wide from the face of the board are erected between each blade.
On the left-hand side oi each