[Trade Journal]
Publication: Electrical World
New York, NY, United States
vol. 60, no. 26, p. 1365-1372, col. 1-2
ELECTRIC DEVELOPMENT IN NEW ENGLAND
The Four-Million-Dollar Initial Project of the New England Power Company on the Deerfield River in Massachusetts and Vermont.
A Description of the Four Generating Stations, Storage Reservoir and Transmission Lines of the System, Which Reaches Many Important Industrial Cities in Central New England and Ties Together for Co-operative Service the Deerfield and Connecticut River Transmission Systems.
A HYDROELECTRIC development of profound industrial significance is rapidly approaching completion on the historic and beautiful Deerfield River, in Massachusetts and Vermont, with comprehensive plans for future expansion of storage and generating facilities which rival many of the water-power enterprises of the Far West. From the economic, hydraulic and electrical standpoints the work now in progress is of broad interest, for it marks the advance of low-priced energy into new manufacturing and transportation fields in Massachusetts hitherto unreached by marketed power. It insures the efficient interchange of electricity between the Deerfield and Connecticut River systems of electrical generation and transmission, and furnishes, both in the standardization of plant designs adopted and the storage facilities under way, a convincing illustration of the possibilities of conservation of capital and natural resources attainable by modern engineering practice.
CONNECTICUT RIVER TRANSMISSION COMPANY.
The realization of the commercial benefits of hydroelectric power distributed over large areas received a marked stimulus in Massachusetts in 1909, when the 66,000-volt system of the Connecticut River Transmission Company was placed in operation. The developments of this company were described in the Electrical World of Sept. 9, 1909, and consist in brief of a 20,000-kw water-power plant located on the Connecticut River at Vernon, Vt., and a steel-tower transmission system extending southeast through the Gardner, Fitchburg, Clinton, Marlboro and Worcester districts. The company operates in general as a wholesaler of energy and supplies electricity at an average rate of slightly under 1 cent per kw-hr. Prior to the advent of this system hydroelectric developments in New England were rather restricted in scope, and central stations serving comparatively limited areas sought with few exceptions the small-power market. The electrification of large industrial plants and the arrangement of reciprocal power contracts between these plants and the transmission company followed the introduction of the electrical service, and the latter has increased so rapidly that its present yearly output exceeds that of the combined central stations of Massachusetts with the exception of the Boston Edison Company.
Through the reciprocal power contract, the steam generating plant formerly used by the consumer is held in reserve as an auxiliary capable of supplying energy to the circuits of the transmission company in an emergency, and by this means an investment in steam-plant equipment by the latter is avoided. The Connecticut River Company's development has been carried out under the general direction and control of the Chace-Harriman interests of Boston, and these interests are closely identified with the Deerfield utilization under the corporate organization of the New England Power Company. The entire work of engineering and construction is being handled by the Power Construction Company, of Shelburne Falls, Mass., an organization created about eighteen months ago to engage in engineering and construction work in general, and headed by Mr. George W. Bunnell. Messrs. J. G. White & Company, of New York, and Charles T. Main, of Boston, were retained as advisory engineers in connection with the general project, but all designing and the immediate supervision of construction has been handled by the Power Construction Company.
The present development comprises the building of a storage reservoir at Somerset, Vt., which will hold 2,500,¬000,000 cu. ft. of water, the construction of a power house -building to- be used as a temporary substation near the Hoosac Tunnel and of three 6000-kva generating stations in and near Shelburne Falls, and the erection of transmission lines connecting the Shelburne Falls plants with the Vernon plant of the Connecticut River company by direct tie and by a high-tension cross-country steel-tower installation be-tween the Shelburne Falls and Worcester districts. This will form a double-line loop through the latter district back through Clinton to Vernon and Shelburne Falls. Right-of-way has been secured from the Worcester district southeastward through the Blackstone Valley in anticipation of an early extension of the system into Rhode Island and the Providence market. The estimated cost of the initial development is about $4,250,000. The Shelburne Falls-Worcester district line, terminating at Millbury, Mass., has been designed for ultimate operation at 120,000 volts, while the remainder of the system is designed for 66,000 - volt transmission. At Millbury power will be delivered to the Worcester Consolidated Street Railway Company's transmission system through a frequency - changer substation which is to be located near the existing steam-turbine generating plant of the railway company. A corresponding delivery of power will be made to the Boston & Maine Railroad in the western part of the State for the operation of electric train service in the Hoosac Tunnel and lines of the Berkshire. Street Railway Company, the present Zylonite steam plant being utilized as an auxiliary. At Ware energy will be delivered to a branch transmission line owned by the Central Massachusetts Electric Company for supplying electricity to the Warren-Palmer district, and similarly energy will be delivered from the Vernon plant and its interconnecting lines to the Keene (N. H.) Gas & Electric Company, over a 19,000-volt branch running northeast from the Vernon station to the latter company's district. With the extension of the 120,000-volt lines from Millbury to the Providence district, the construction of a second loop transmission line through Danielson and Putnam, Conn., is planned, with connection back to Millbury through Webster, Mass. Further proposed extensions cover the territory including Bennington, North Adams and Pittsfield, with a branch transmission line from Fitchburg to Nashua, N. H., and Lowell, Mass. With the completion of these lines the system will extend from a point near the New York state line on the west to the Boston Edison Company's territory on the east, supplying power in four of the six New England States and placing the whole problem of electrical distribution in the populous municipalities of central Massachusetts upon a new footing.
DRAINAGE AREAS UTILIZED.
The Deerfield River, which is the principal tributary of the Connecticut, rises in the southwestern part of Vermont, being formed by the conflux of a number of small streams draining an area of about 189 sq. miles. The only outlet of the stream is through a single narrow valley at the south. The branch of the river which retains the name of Deerfield rises in the town of Stratton, Vt., and flows south through Somerset into Searsburg, where its volume is considerably increased at its junction with a large brook called the East Branch, which rises in the town of Somerset. Near the headwaters of this brook the first reservoir is to be built in connection with the development. From the town of Searsburg the Deerfield River flows easterly into Wilmington, where it receives another notable addition from the North Branch. From Wilmington it flows south into Whitingham, westward into Readsboro, and thence across the Massachusetts boundary. In the latter State the river flows several miles through the narrow valley above mentioned, where the elevations of the hills at the sides vary from 800 ft. to 2000 ft. above sea level.
At Hoosac Tunnel the river makes a sharp bend eastward and flows rapidly for a few miles through a hilly valley, which gradually becomes more level upon approaching Charlemont. The valley again narrows about 2 miles west of Shelburne Falls, where the town boundaries of Charlemont, Colrain and Buckland meet. The river here takes a sharp turn around a hill, flows north through a deep ravine, and then bends to the east, receiving the waters of the North River. In southern Vermont, from Davis Bridge to the state line, and thence to Scott's Bridge, west of Shelburne Falls, the drainage area of the river is 229 sq. miles, and the drainage of the North River, also extending northward into Vermont from the Shelburne Falls district, covers an area of 100 sq. miles, making a total watershed of 518 sq. miles between the extreme headwaters of the Deerfield River and the generating plants in the neighborhood of Shelburne Falls. East of Shelburne Falls the river flows for to miles through a precipitous valley, then passes through wide meadowlands and discharges into the Connecticut River southeast of Greenfield. The drainage area of the Connecticut River at Vernon is about 6300 sq. miles.
SOMERSET RESERVOIR.
The Somerset reservoir is now under construction and will be formed by the erection of an earth dam built across the East Branch at the terminus of a narrow-gage lumber railroad connecting the site with the main line of the Boston & Maine Railroad at Zoar. The height of the dam above extreme low water will be 100 ft., producing an available storage capacity of 2,500,000,000 cu. ft., with the water at the level of the spillway crest. With 4 ft. of flashboards on the dam, however, this storage can be raised to 2,700,000,000 cu. ft. The downstream face of the darn is to have a slope of 2.5 to 1, the upstream slope being 3 to the top width being 20 ft. and the length of the dam about 2000 ft. The dam is to be paved on its upper slope to prevent damage due to wave action. The reservoir above will have an area of about 3 sq. miles.
Like many other New England streams, the Deerfield suffers from extreme variations in its flow, which ranges from a normal discharge of about 1300 second-ft. at Shelburne Falls in an average year to a maximum of 28,000 second-ft. under flood conditions. It is estimated that with the completion of the four hydroelectric plants above outlined and the filling of the Somerset Reservoir 112,000,000 kw-hr. of salable energy can be produced on the Deerfield River even in a dry year.
As shown in the accompanying drawing, the Somerset dam will be about 48o ft. thick at the base and will be provided with a concrete pipe tunnel about 12 ft. in diameter carrying two delivery pipes each 4 ft. in diameter, to facilitate drawing water from the reservoir for power service. Gates are to be furnished at the upstream end, and these will be equipped with operating mechanism permitting the use of the water in part before the completion of the reservoir. About 30 sq. miles are immediately tributary to the latter. At a later date a second storage reservoir, which will contain 4,500,000,000 cu. ft. of water, is to be built at Davis Bridge, about 4 miles from the Massachusetts boundary, in Vermont, and this storage basin will be operated in series with the Somerset reservoir. This will require a dam about 195 ft. in height, and when completed and used in conjunction with the final development of seven water-power sites on the river, with an average gross head of 1050 ft. total, it is estimated that the plants of the New England Power Company will produce 236,000,000 kw-hr. per year. With the present development of three generating stations in the Shelburne Falls region, supplemented by the Somerset dam and not including the Hoosac hydroelectric station, an aggregate net head of 386 ft. being utilized, the output attainable even under the conditions of a dry year will be 70,000,000 kw-hr. The construction of the Hoosac hydroelectric plant, with the installation of the waterwheels planned for that station, will add 12,000 kva to the generating capacity of the present Deerfield plants of the New England company, making a total of 30,000 kva installed in the four stations.
TYPICAL PLANT DESIGN.
A striking feature of the development is presented in the similarity of the design employed, both from the hydraulic and electrical standpoints, in the generating stations now under construction. Each of the three plants at Shelburne Falls is equipped with three 2000-kva units, consisting of a 2300-volt, three-phase, 60-cycle General Electric revolving-field alternator driven through a horizontal shaft by a 3000-hp double-runner, central-discharge Wellman-Seaver-Morgan turbine operating at 257 r.p.m. The heads at Stations 3 and 4, in Shelburne Falls, are the same, 64 ft., and the head at Station 2, east of Shelburne Falls, at a point on the river known as Upper Bardwell's, is 6o ft. In general, each station consists of a brick and steel building with concrete foundations erected at the lower end of a row of penstocks delivering water to the wheel casings, which are located outside the station and connected by short shafts with the generators. The latter are mounted in an operating room which extends the entire length of the building. The switchboard in each case is installed on the operating floor opposite the wheel-shaft entrances. At one end is a 2300-volt bus structure, with low-tension oil switches installed in concrete cells having asbestos intermediate barriers, the cables from the machines being run to the cells in conduit which is laid in the floor. A gallery is provided at the end of the operating room above the bus cells to carry a storage battery for operating switch and other minor equipment. In the upper story extending along the station over the operating room is a transformer and high-tension oil-switch room designed for 66,000-volt service and equipped with a 50.000-lb. chain hoist for handling transformers between this room and the operating floor below. Upon the tar and gravel roof is mounted a steel and pipe frame structure supporting the insulators which carry the incoming and outgoing lines, with horn-gaps and lightning-arrester connections.
Below the station the turbines discharge through draft tubes into a tailrace connecting directly with the river, as shown in the accompanying drawings. The chief differences between the three plants in the Shelburne Falls district lie in the arrangements made for the supply of water to the penstocks and the local relations of the high-tension wiring to the transmission lines of the system. All penstocks are built of riveted steel varying in thickness from 5-1/4 in. at the upper ends to 5/16 in. at the bottom. Lombard governors with 30,000-lb. rating are used in all stations, a short lever and rocker-arm connection being made between the governor and the spindle controlling the gate movement within the wheel casings.
STATION 4.
Plant No. 4, located about IA miles above Shelburne Falls, is the first station of the present development encountered in descending the Deerfield River. The station is located on the east side of a hill around which the stream sweeps in approaching the plant, and the water supply is drawn from the river on the further side of the hill by a tunnel 1580 ft. long, the intake being built at one side of the solid concrete dam which has been constructed across the river goo ft. below Scott's Bridge. The river surrounds the hill on three sides, flowing north, east and south until it reaches the power-house site, directly opposite the first bend at the dam, and the difference in altitude made possible the development of a 64-ft. head through the use of a tunnel, and with 4 ft. of flashboards on the top of the dam a pondage of 320 acre-ft. is secured. The dam is about 235 ft. long at the crest and is built at an angle with the stream to give a greater length of spillway in times of high water. It is anchored in solid rock, has a maximum height of 50 ft., a thickness at the base of 28 ft. and a width at the top of the spillway of 4 ft. At the lower end of the dam an installation of sluicegates 42 ft. in width has been made, and the water for power-plant service is drawn through an inlet chamber with stop logs, gate and screens into the tunnel on an axis at right angles to the flow of the river.
The gate equipment was supplied by the Exeter Machine Works, of Pittston, Pa. The gate weighs 38,000 lb. and is built of steel plates and 26-in. I-beams and is raised and lowered past a 3/4-in. bronze wearing plate on the side by a pair of 5-in. steel screw steams terminating at the top in a horizontal bevel gear meshing with a shaft which is driven by a 15-hp motor. The gate is 13 ft. 8 in. high and 14 ft. wide, and the driving motor is a 2300-volt induction machine mounted on an I-beam framing at the top of the gate shaft.
THE TUNNEL.
The tunnel is a concrete-lined bore through the rocky hillside and has a horseshoe section equivalent in area to a circle 13 ft. in diameter. The inside diameter of the tunnel is 13 ft., and the use of Blaw steel forms was a feature of its construction. The tunnel is built with its highest point near the middle, in order to facilitate complete drainage in case the water is shut off. The normal capacity of the tunnel is 1650 second-ft., and it discharges into a .forebay located on the east side of the hill. The forebay is provided at its eastern side with screens and gates and is connected with three penstock intakes as shown in the accompanying plan. A 2oo-hp motor-driven air compressor supplied with power from the Vernon plant of the Connecticut River Transmission Company was used in the excavation of the tunnel, and electrically operated contracting equipment was employed wherever possible in the work on the three stations in the Shelburne Falls district. The energy consumption reached a maximum of about 85,000 kw-hr. per month during the height of the construction period.
THE PENSTOCKS.
The penstocks at all three stations each have an inside diameter of 10 ft. and in Stations 3 and 4 they are about 160 ft. long and are anchored into the hillside by concrete piers 26 ft. apart. Two gates about 7 ft. x 12 ft. in size are provided for each intake, provision being made for the use of stop logs and double sluicegates in the dam at Station 3, as shown in the accompanying drawing.
From the penstock intakes to the switchboard, Plants 3 and 4 are practically identical in design. The turbine casings are located outside the station buildings, as stated, but are designed so as to admit of handling the runners and shafting through the end which projects into the power house. Access to the interior is had through a manhole in the casing outside the building in addition to the end plate construction in the power house wall. A 15-ton hand-operated traveling crane of Northern manufacture serves the entire generator room, which is about 31 ft. wide by 94 ft. long inside. The governors are operated under oil pressure supplied by a 4-in. by 6-in. triplex pump, which is belted to the wheel shaft inside the generator room, and the governor rotation is effected by a belt connection to the wheel shaft. The generators are installed along the middle of the operating room with about 22 ft. between shaft centers and deliver energy directly to the low-tension switches and buses as outlined above. Each of the three plants is provided with two too-kw, 125-volt exciters, and each is direct-connected on a horizontal shaft to a 2300-volt General Electric induction motor running at 900 r.p.m. The transformer equipment of each of these stations consists of two 3000-kva General Electric oil-insulated, water-cooled units wound with 2300-volt primaries and 66,000-volt Y-connected secondaries, with solenoid-type oil switches of the same make for both low-tension and high-tension service. The former are provided with series relays and an associated tripping rod in place of series transformers.
FURTHER ELECTRICAL DETAILS.
None of the plants is provided with a turbine-driven or a steam-driven exciter, since energy is available either from the transmission lines connected with other plants for the operation of the motor-generator exciters or temporarily from the small storage batteries supplied for the oil-switch service. The main generators deliver 503 amp per terminal at full load and are designed for a maximum temperature rise of 4o deg. C. when carrying full load for twenty-four hours at 8o per cent power-factor, and with a maximum rise of 5o deg. C. when operated at 25 per cent overload for two hours. The high-tension oil switches are of the remote-control type, having a rating of 150 amp at 70,000 volts, and are mounted on the floor of the transformer room below the steel structure supporting the incoming and outgoing leads, and are connected by short leads run overhead to the transformers.
Copper tubing has been largely used in the inside wiring of the high-tension sections of the stations on account of the tendency of solid leads to sag and get out of line even in moderate spans. In each station the transformers are installed upon rails leading to a central opening about 9.5 ft. by it ft. in dimensions. The rails are carried in the opening by steel I-beams which can be removed after a transformer has been raised from them by the hoist, so that the unit can then be lowered to the room below. Cooling water for the transformers is provided at each station by a 1-1/2-in. Lawrence centrifugal pump which is connected with a 1-1/2-hp, 110-volt induction motor running at 1800 r.p.m. Around each transformer is built a wall of concrete 8 in. deep, with a short brick section which can easily be knocked out on the side nearest the hatchway leading to the operating room. This basin serves as a temporary receptacle for oil in case of leakage. In addition to this each transformer is equipped with a 3-in. pipe and quick-acting lever valve by which the inclosed oil can be discharged into the river in case of an emergency.
The operating rooms in these stations are lighted by eighteen too-watt tungsten lamps with prismatic reflectors carried in pairs on pipe-frame brackets as shown in the accompanying photograph, the lamps being located about 16 ft. above the floor. In each station the switchboard is installed in front of a row of auxiliary panels placed 37 in. behind the former, allowing a clearance of 33 in. between the latter and the wall. All field rheostats are mounted on angle-irons which are carried on the top of the switchboards. The auxiliary panels are fitted with integrating wattmeters, testing jacks, transfer switches and potential plugs.
TYPICAL SWITCHBOARD STATION.
A typical switchboard controls three 2000-kva generators, wound for 230o volts, two too-kw exciters equipped with speed-limiting circuit-breakers, two 3000-kva transformers and four outgoing 66,000-volt transmission lines. The operating board is 16 ft. 4 in. long and contains ten panels, with the usual synchronizing bracket and switch plugs, a Tirrill regulator, a high-tension feeder, recording and meter panel and remote-control switches, reed-type frequency indicator, power-factor indicators, wattmeters and ammeters. The generator switches are equipped with instantaneous overload relays and differential relays are placed in the circuits of the oil switches controlling the transformers. Graphic recording voltmeters are installed in each station. The switchboard in Station 3 includes a panel for service to a local cutlery mill which was changed to electric drive when the hydraulic development was made at the generating station. At Plant 2 only two high-tension feeders are to be installed at present, but with these exceptions the operating switchboards are closely alike. All alternating-current instruments are equipped with transformers so that not more than 250 volts is taken into the cases. Electrolytic lightning arresters with horn-gaps, disconnecting switches, choke coils and alarms are provided in each plant, the arresters being placed in the transformer room opposite the high-tension oil switches.
All relay and instrument circuits are equipped with standard testing jacks, transfer switches and potential plugs mounted on the auxiliary panels and so arranged that standardizing meters can be connected without interfering with operation. All automatic switches are equipped with alarm-bell relays. They neutrals of auxiliary transformers and switchboard meters are tied into a separate ground plate and into the steel frame of the building. The main transformers are connected in delta on the low-tension sides, and the neutrals on the high-tension sides are carried on insulators for a short distance away from the transformer cases so that they may be disconnected and the system operated ungrounded if necessary. There are two barriers provided for each set of three 2300-volt disconnecting switches, 34-in. outer asbestos panels being used, with Win. asbestos sheets between buses. On the main switchboard panels is installed a dummy bus showing connections between machines, buses and outgoing lines, with the usual pilot lamps. In addition to the latter, pilot lamps are provided for indicating the position of disconnecting switches in the high-tension wiring and in the 2300-volt circuits within the stations, the lamps being cut in and out by hand switches located near the disconnectors.
HIGH-TENSION ROOF STRUCTURES.
The accompanying illustration shows the mechanical arrangement of high-tension lines on a typical station roof. All lines are dead-ended on strain insulators fastened to the station wall, and from these lines taps are carried to insulators supported on steel framework as shown in the photograph. The insulators taking the taps from the incoming lines are built with four petticoats and are mounted on horizontal framing consisting of steel I-beams installed in pairs latticed together by diagonal bracing on both top and bottom. In general, these lines are spaced about 8 ft. apart horizontally and are carried transversely across the roof between frames at a height of about 10 ft. The horizontal framing is supported at its ends in each case by steel uprights fastened into the concrete of the transformer room ceiling. All posts are provided with copper flashing and asphaltum sealing against the leakage of moisture into the building. As the high-tension lines cross the roof taps are taken off and lead to the transformer and oil-switch room below, these lines, placed with centers 5 ft. apart, being carried through the roof by Thomas five-part roof bushings. Transverse high-tension leads are carried along the roof above the incoming (or outgoing) lines, and selector knife switches are installed at various points to enable the lines to be paralleled or the station cut out of service without carrying the high voltage into the transformers. On the opposite side of the roof from the entering conductors are installed the horn-gaps, with operating rods extending through the roof to hand levers placed in the transformer room. From the horn-gaps short vertical taps are carried through Thomas bushings to the electrolytic arresters inside the building, the verticals being provided with additional insulators in the course of the drop to obviate the possibility of cumulative vibration. A brick parapet is provided on three sides of the roof, and the whole area is illuminated by 16-cp incandescent lamps installed in waterproof sockets and supplied with energy through auxiliary station leads. The transformers in all stations are provided with General Electric "capillary" thermometers giving the temperature of the windings with much greater accuracy than was possible with the mercurial equipment. As shown in the photograph, the roof is pitched to drain directly into the river. Access to the roof in the various stations is had by an iron ladder leading from the transformer room to a small penthouse placed near the parapet wall which is farthest away from the high-tension lines.
STATION 3.
Station 3 is located in the heart of Shelburne Falls, about 1500 ft. from the Boston & Maine Railroad station and at the foot of a conduit, canal and penstock system which starts from a dam crossing the river just above a large cutlery plant, which formerly utilized a portion of the stream. The stream passes over a ledge at this point and has been utilized since the latter part of the eighteenth century for saw-mill, grist-mill and other work. At the crest of the falls part of an old crib dam was used by the construction company in the building of a new concrete dam 12 ft. high, 17 ft. thick at the base and 46o ft. long, extending diagonally across the river. An intake delivers water to a 17-ft. by 12-ft. tunnel passing under the cutlery factory, discharging into an open canal and terminating in a forebay above the power house, which is about 1800 ft. downstream from the dam. The capacity of the conduit is 1650 second-ft. Gates and screens are provided at the intake and also at the lower side of the forebay, where the penstocks start downward to the wheels. The tunnel section is of reinforced-concrete construction and is about 600 ft. long. The power house is situated at the head of a pondage belonging to the Shelburne Falls plant of the Greenfield Electric Light & Power Company, the tailwater of the former being immediately utilized by the latter within the limits of its capacity. The penstocks at Station 3 are 160 ft. long and the general design of the plant is similar to that of Station 4.
STATION 2.
About 2 miles below Shelburne Falls a concrete dam has been constructed across the river in a narrow gorge, and on this site Plant 2 is being built. Except on its hydraulic side and in minor details, the station practically duplicates the two others just described. The dam has a height of 6o ft. and is 5o ft. thick at the base and 5 ft. wide at the top, its length being about 375 ft. The spillway is of an ogee shape, and the power house is located at one end of the dam on the downstream side. Short penstocks connect intakes on the upstream side of the dam with the wheels, the intakes being equipped with screens and gates to meet all anticipated operating conditions, while the dam is provided with sluicegates which facilitate the discharge of water, ice and debris. The location of this station at the bottom of the gorge greatly facilitated handling materials during construction by gravity, and an extensive sand-washing and stone-crushing plant was a feature of the work. Electric power was used widely in the operation of the field machinery, including hoists, compressors, cableways, etc.
FUTURE STATION.
The site of the so-called Station I is near the outlet of Dragon Brook, on the Deerfield River and about 2 miles below Station 2. Preliminary work on this site indicates that an initial development of about 4000 kva may be desirable, but for the present this will be held in abeyance.
STATION 5.
Station 5, the so-called Hoosac plant, is located about 3 miles north of the southern terminus of the Hoosac Tunnel & Wilmington Railroad at Hoosac, Mass. Although this plant will be used at present only as a frequency-changer substation, in the near future it will be equipped with complete hydraulic power-producing facilities. Water will be conducted to the power house from a concrete diverting dam located in the Deerfield River about 1/2 mile below Monroe Bridge, a conduit and canal 13,800 ft. long being required. The canal will have a capacity of 750 second-ft. and will deliver water at an average net head of 200 ft., and the conduit will be a reinforced-concrete flume of rectangular cross-section. At the generating station three 4000-kva units will be installed, each equipped with a 25-cycle generator and a 60-cycle generator, so that the requisite interchange of frequencies may be made between the transmission system and the distribution circuits and power plant of the railway company operating through the Hoosac Tunnel.
FREQUENCY-CHANGING UNITS.
The present equipment of the Hoosac station will consist of three 3000-kva transformers, which will reduce the potential from 66.000 volts to 2300 volts, three 150-kw exciters, switching apparatus, lightning arresters of the aluminum type and three frequency changers, each consisting of a 3000-kva, three-phase, 6o-cycle, 2300-volt generator direct-connected to a 3000-kva, single-phase, 25-cycle, 11,000-volt alternator. These 6o-cycle generators will be operated as synchronous motors in supplying power to the railway company and later, when the waterwheels are installed in this station, both machines can be run as generators if desired, or one as a generator and the other as a motor. This gives a highly flexible interconnection between the systems and will enable the Zylonite plant to feed back into the Connecticut River Company's system in case of a shortage of water at any of the hydroelectric stations in other parts of its territory. The waterwheels to be installed later will be rated at about 6000 hp each. The 11,000-volt machines are designed so that either single-phase or three-phase energy may be obtained from them. Both generators are mounted on a common bedplate, with three bearings. The winding of this three-phase-single-phase machine is star-connected, with one terminal arranged for grounding, and the rotor is provided with a damping device. The regulation specified is such as to give not over fifteen times normal current on dead short-circuit with normal no-load field current, the short-circuit to be placed directly across one phase without the interposition of reactance coils. The machines are designed to operate in parallel with the generators now in the Zylonite station in either single-phase or three-phase service. The latter regulate for sudden changes of load substantially as if provided with constant field strength, uninfluenced by armature reaction. When used in conjunction with a Tirrill regulator the machines will not vary 5 per cent above or below normal voltage. The alternating-current generators in the Hoosac station, No. 5, are to be provided with adjustable resistance to give a 15 per cent voltage variation by hand control. Inverse time element relays are provided in the generator circuits. A Tirrill regulator is being installed in this station for the purpose of keeping the power factor of the alternators run as synchronous motors at from 80 to 100 per tent.
To meet the requirements of heavy freight service in the Hoosac Tunnel, the 25-cycle machine in each unit is to be capable of delivering 4300 kva for twenty minutes of each hour at 70 per cent power-factor and during the remaining forty minutes of each hour the machine is to be capable of operating at a load of moo kw at 90 per cent power-factor, with a final temperature rise not exceeding 50 deg. C. by thermometer or 6o deg. C. by resistance measurement. The 60-cycle machines are designed to deliver 3000 kva at 8o per cent power-factor with a maximum temperature rise of 4o deg. C. after twenty-four hours' run and a 50-deg. C. rise after two hours run at 25 per cent overload. When running as a synchronous motor, the machine is to be capable of driving the 25-cycle generator with a temperature rise not exceeding so deg. C. when operated at 8o per cent power-factor leading. In order to facilitate the installation of conduits in the floors of the various stations, the switchboards are mounted on channel irons and the conduits are brought in through the floor to nipples and insulated bushings connected with previously prepared holes in the framing. The termination of each lead or wire is properly marked and the location of the holes at the proper points along the switchboard base insures rapid and reliable work by the interior wiring forces.
TRANSMISSION LINES.
The present transmission system, including lines now under construction, comprises two three-phase circuits of No. I copper between a point opposite Station 4 on the Deerfield River and Shelburne Falls and the Vernon station of the Connecticut River Power Company, a distance of 16 miles; two similar lines each 1/3 mile long, extending from the former point to Station 4; two No. I copper lines extending a distance of 14 miles from Station 4 to the Hoosac plant (Station 5); two lines extending from the junction opposite Station 4 down the river 94 miles to Station 2, with two 72-mile taps to Station 3; two lines of No. 00 copper extending 6o miles from Station 2 eastward to Millbury, Mass.; two tie lines extending 14 miles from Millbury to the vicinity of the Greendale substation of the Connecticut River Transmission Company, outside of Worcester, and the existing double three-phase lines of the latter between Worcester and Vernon, with the branches previously mentioned. The Shelburne Falls-Millbury line, designed for I20,000-volt operation, will be equipped with 75-ft. steel towers supplied by the American Bridge Company of New York. A transformer station will be erected for this service at Shelburne Falls.
Between Station 2 and Millbury there is a No. 4 copper-clad telephone circuit carried on separate poles. The line between Shelburne Falls and the Hoosac station is carried on pin-type insulators supported on 75-ft. Milliken towers, with 475-ft. spans. Two circuits of No. 2 copper form the tie lines between Millbury and Greendale. Another tic line is to be installed at Leverett Junction, Mass., connecting the Deerfield system with that of the Amherst Power Company.
WIRING SCHEME.
The general wiring scheme followed in the construction of Station 4 is typical of that used in the remaining plants. Two sets of 2300-volt buses are provided, the selection being made by disconnecting switches without going to the expense of installing oil switches, although a single oil switch is provided in each generator circuit. The low-tension sides of the step-up transformers are provided with a 2300-volt oil switch and two knife-switch selectors, so that any generator or transformer may be operated on either 2300-volt bus in parallel or independently. Each high-tension circuit passes from a transformer through an oil switch to a bus section interconnected with that of the other unit by a tie switch of the oil type. From the oil switches the high-tension leads pass to the roof structures, where provision is made for by-passing the station and for connecting the lightning arresters. A 2300-volt auxiliary bus for supplying induction motors driving exciters, lighting and small power transformers in the station is also installed with provision for taking this service from either of the main 2300-volt buses. Switches between the generator buses and the transformer primaries, between the main buses and the 2300-volt service bus and between the transformer secondaries and the outgoing lines are automatic.
The principal sub-contractors of the work are F. T. Ley & Company, Springfield, Mass., who are building Station 3. and the Vernon-Shelburne Falls line; Fraser, Brace & Company, New York, for Stations 2 and 4, and the B. F. Smith Company, Pawtucket, R. I., for Station 5. The Chicago House Wrecking Company, Chicago, Ill., supplied materials for the erection of seven six-room bungalows for the use of operators employed at generating stations outside the center of Shelburne Falls. These homes are wired for electrical service and are as complete in all the details as comfortable residences of moderate cost. The main office of the Power Construction Company is at Shelburne Falls, Mass., the branch offices in Boston being combined with those of the Connecticut River Transmission Company at 50 Congress Street.
