Tredyffrin Easttown Historical Society
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Source: October 1995 Volume 33 Number 4, Pages 131–146


Conowingo: The Source of Our Electric Power

Robert E. Geasey

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When I was a boy my family made an annual motor trip from our house in suburban Washington to visit my grandparents in North Philadelphia. They lived in Hunting Park, right next to the Edward G. Budd plant. What wonderful things were to be seen in a city that made everything, and the Franklin Institute held more wonders yet! But the high point of the trip was crossing the Susquehanna on Conowingo Dam. The control of so much raw power, the spidery support of the high-voltage lines, the huge insulators were all the ice cream and cake to a lad who wanted to be an electrician. Today, looking back from a more sophisticated technical era, it is still a fascinating view; a time of great technical achievement as astonishing as our modern space program, and every bit as satisfying as the Little Engine that Could.

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Prologue

In the last two decades of the 19th century five men were singularly influential in the business community of Philadelphia: Thomas Dolan, P. A. B. Widener, William L. Elkins, Martin Maloney, and William G. Warden. Dolan achieved a virtual monopoly in knit textiles, then played a major role in organizing and directing gas and electric companies. Under his leadership United Gas Improvement (UGI) was formed, consolidating the gas utilities, and leasing the city gas works. Widener made a fortune in the meat business during the Civil War, then turned his interest to street railways, learning how to manipulate city government and state politics. Under his leadership Philadelphia's street railways were consolidated into a unified utility. Elkins started in the grocery business, then became interested in oil, winning a partnership in Standard Oil.

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For a time he controlled the Philadelphia oil refining business. He also manufactured illuminating gas, bought gas works, and joined with Widener in buying up street railways. Maloney, born in Ireland, was brought to Scranton at an early age and apprenticed to become a plumber and gas fitter. He saw the potential of gasoline as an illuminant, perfecting a gasoline burner for that purpose. Moving to Philadelphia, he obtained the contract for lighting the grounds of the Centennial Exposition. Within ten years his Penn Globe Gas Light Company was supplying street lighting for 137 cities and towns, making him a leading figure in large-area illumination. Warden was a pioneer oil man. Coming to Philadelphia in 1865, he formed the Petroleum Storage Company, built the world's largest refinery, formed a company to ship oil across the Atlantic, and served as president of Atlantic Refining Company.

These five men, bound by interlocking interests in illumination by oil and gas, in 1882 formed the United Gas Improvement Company. The initial purpose was to introduce a new process for the manufacture of artificial gas; the company eventually became one of the largest gas holding and operating companies in the world. The founders were men of diversified interests who could see the future for electric lighting; the year before they organized UGI they entered the electric field by forming Philadelphia's first two electric light companies.

Electric lighting came to Philadelphia in 1878 when John Wanamaker put 28 arc lamps in his Grand Depot. It is believed to be the first commercial installation in the country, and throngs gathered outside to gaze at this latest technological wonder. A few Philadelphians soon followed, notably merchant Thomas Dolan. In 1881 Dolan, together with other wealthy merchants, formed the Brush Electric Light Company to provide free lighting for Chestnut Street, and to manufacture, procure, and own various equipment to produce heat, light, and power by electricity. This company built a steam generating station of 360 horsepower capacity at 20th and Ranstead streets.

The popularity of electric arc lighting soon spread, albeit rather slowly in conservative Philadelphia, but no large company dominated operations, for several reasons. First, there were many "systems" of arc lighting, and although the influential Franklin Institute had declared the Brush system to be superior buyers were free to choose among many, and choose they did. Second, wide-area power distribution was difficult. The arc lamp is essentially a series-connected device, so power distribution tended toward radial loops rather than networks. Furthermore, the citizenry had become aroused by the proliferation of poles and overhead wiring engendered by the telegraph. (South Broad Street, for example, in 1895 had poles with as many as 21 cross-arms on them, 16 lines on an arm, with poles on each side of the street. Overhead electric distribution was simply not condoned.) And third, and of greatest import, City Council received a fee from each company franchised: the more companies, the more fees. Even overlapping franchises were not proscribed. City Council also believed, and the public agreed, that competition was the only way to keep rates down.

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By the middle of the 1890s Philadelphia was the best lighted city in the nation. More than twenty electric light companies served the city, with a like number of electrical systems. There was direct current at 100, 220, and 600 volts; single-phase, two-phase, and three-phase alternating current at 40, 60, 66, 125, and 133 cycles. It was readily apparent that the growth of the electric industry in Philadelphia could not progress unless some standardization could be effected. As early as 1886 steps were taken toward consolidation through the formation of the Electric Trust by Dolan, Widener, and Warden. The Trust, operating as a holding company, began buying up operating companies. However, it was a sub-rosa organization, and when its existence became common knowledge contemporary crusaders accused it of all the miseries associated with monopolies, some true, some not.

Perhaps public opinion would eventually have killed the Electric Trust, but competition was faster. In 1879 Thomas Edison invented the incandescent lamp. It was more safely manageable, in many respects, than the arc lamp, especially after he, with Francis Upton, developed an electric generator with a startling efficiency of 90%. The Edison Electric Light Company was formed, and in 1882 the first truly central station went into operation at Pearl Street in Manhattan. In 1886 the Electric Light Company of Philadelphia was chartered. A central station with a generating capacity for 84,000 lamps was built at 9th and Samson streets. This station, which went operational in 1889, was an immediate success, principally because of the popularity of the incandescent lamp, but also because the Edison franchise permitted distribution in underground conduits. Edison also believed that his low rates would stifle competition; in short time Philadelphia Edison's net profit nearly equaled that of all the Trust's companies combined.

In the meantime, Widener and his syndicate had introduced the electric trolley car. By 1897 electricity had taken over. Horse cars had disappeared. Willow Grove had been created to attract transit business. At the same time, Martin Maloney had re-entered the electric lighting business with the Pennsylvania Heat, Light and Power Company, franchised in the same area as Edison. There was a natural synergism with Edison: Maloney could use the exhaust steam from the Edison plant to supply his heating customers, and Edison could use the PHLP franchise to enter the arc lighting field. The merging of interests was effected by Maloney's buying stock control of the Edison company. Maloney became president of PHLP, and Dolan and Elkins became directors. The company then also bought the Electric Trust. Consolidation had begun. The administrative, purchasing, engineering, and sales staffs of the Brush and Edison companies were combined, and expansion and standardization were started.

On January 1, 1899 the City Hall tower clock went into operation, its dial lighted by 600 incandescent lamps. It was the start of a year of turmoil. In January the Electric Company of America was chartered to buy electric companies outside the city area; UGI held a large interest in it, with Elkins, Widener, and Dolan serving on the board. In May the National Electric Company was chartered, entering the Philadelphia market by purchasing stock in several of the local companies which were not under the control of PHLP.

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Maloney's last contribution toward consolidating the city's electric companies was to persuade National Electric to merge its holdings with his. In October the two companies were brought together with the formation of a New Jersey holding company called Philadelphia Electric Company.

During its first year of operation Philadelphia Electric increased its output by nearly 35%, and bought a large property at Christian Street and the Schuylki 11 River. There it planned to build a central station of very large capacity. As the holding company had consolidated only ownership, not operations, the various companies had to operate separately within the limits of their ordinances, however. This problem was overcome in 1902 by an ordinance granted to a new Pennsylvania corporation, entirely owned by Philadelphia Electric (of New Jersey). This ordinance granted the right to erect and maintain an electric system throughout the entire city, and the further right to acquire by purchase or lease existing light companies within the area. The new company was named The Philadelphia Electric Company, and thus PECO was born.

Of course, Elkins, Widener, and Dolan were members of the board of the holding company, though Maloney, having made a fortune, decided to retire. Joseph B. McCall, who had risen to various executive positions under Maloney's tutelage, was named president of PECO, Walter H. Johnson became the chief financial officer, and W. C. L. Eglin became chief engineer. (The latter two had previously held significant positions in Edison Electric.) This triumvirate led PECO into an era of expansion and unification within the city.

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The Developing Need

At its founding PECO had 12,090 customers who were using 17,188 arc lights, 440,698 incandescent"lamps, and 11,868 horsepower in motors. Generating capacity for the new company was initially provided by standardizing and networking the many small stations which had been purchased, by expanding the Edison station to its full capacity, and by converting a former traction company plant on Callowhill Street. Still, the capacity was not enough, so nine acres on the Schuylki11 at 28th and Christian streets, serviced by coal barges and rail lines, were purchased. Here, in 1903, Schuylkill Station A went on line with a 5000 Kw alternator, the largest in the state, built by the 11-year-old General Electric Company. This station, after further expansion, for several years was to be the principal generating location for the company.

The earliest years of World War I had little effect on Philadelphia Electric. The Schuylkill station, now Station A-1, had been upgraded and expanded to 81,000 Kw capacity, and in 1915 Station A-2, co-located, went on line with an additional 65,000 Kw. When the war caused a huge expansion of manufacturing in the area, particularly along the Delaware, and a concomitant increase in the need for power, PECO responded by constructing Chester generating station and purchasing land for Delaware Station on the waterfront at Beach and Palmer streets.

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Nonetheless, the company faced a severe power shortage for the peak loads of 1919-1920. During the last two years of the war the central stations needed frequent help from the five local stations obtained with the consolidation. These stations were highly inefficient; while Schuylkill A-2 burned 1 3/4 pound of coal per Kwh, the Callowhill Station used 9 pounds and the old Edison Station used 13 pounds. More efficient capacity clearly was needed.

Although the end of the war brought some relief, industrial requirements continued to mount. The Pennsylvania Railroad began electrified operation on the Paoli line in 1915, and on the Chestnut Hill branch in 1918. These were precursors of the wider-scale electrification of the late 1920s, and the railroad bought its power from the local utilities. Furthermore, in 1910 Philadelphia Rapid Transit (PRT) had come under the control of financier E. T. Stotesbury, who brought in Thomas E. Mitten to run the system as managing director. Within a year Mitten had executed a contract with PECO to furnish power to the traction system. As PRT expanded, its need for power also increased; by 1919 the PRT load alone was 40,000: Kw, and rose even more in 1922 with the advent of the Frankford elevated line. (PRT was PECO's largest customer, but it was a love-hate relationship with PRT's demand for lower rates and Mitten's desire to take control of PECO.)

When industrial plants replaced manual labor with machines the prime mover was steam. As electric motor design matured, it was common to power the motors with a generator attached to the steam prime mover; Wanamaker's pioneering arc lights, for example, were powered by a generator attached to the elevator's steam hoist. Thus, before the first World War, many industries had generated their own electric power. During the war, these plants experienced many difficulties: trained operators and/or mechanics, spare parts, and fuel were all hard to obtain. And so, in the years following the war, many plant managers were very ready to buy their power from PECO. Demand continued to rise.

Another result of the war was a revolution in the domestic scene. The wages of servants had risen so high that thousands of homemakers were now doing their own domestic work, and the seduction of the new electric washing machines, irons, and cleaners had wide-spread acceptance. PECO embarked on a program in which they would wire a house, time-financing the costs, if a customer purchased an electric washer or iron. A phalanx of men, my father included, sold the program by day and wired the houses by night. The wiring of old houses and the proliferation of electric appliances mushroomed. And the demand for electric energy continued to rise.

Even with the completion of Chester Station, near the end of the war PECO saw demand far outpacing capacity. Delaware Station was built in 1920, expanded in 1922, and again in 1923. Chester Station was also expanded in 1923, yet two or three more generators would be needed for peak loads by 1925. In that year, at Lewis Street and Delaware Avenue, the 100,000 Kw Richmond Station went on line ... and still it was not enough. Not only was the peak load rising, but there was no reserve. And the generating equipment, stressed by the war years, was beginning to fail, sometimes with disastrous consequences and power outages lasting several days. More power obviously was needed.

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The war also provided a most distasteful experience for the company: fuel shortages. All the PECO plants, except Edison, burned bituminous coal, mined in central Pennsylvania, shipped by rail to Port Richmond, and then moved by barge to the waterside stations. The winter of 1917-1918 saw the development of a serious coal shortage, due principally to a shortage of railroad cars. Although PECO bought a tract of land on Petty's Island for stockpiling coal, many restrictions had to be placed on the use of electricity to conserve the fuel supply. Additionally, the quality of the coal declined, doubling consumption, while the price rose from $2.75 to $5.40 a ton.

But this was only the start of coal problems. In 1918 a bill was introduced in the Congress to reduce rates by building power stations at the centers of coal production, a reprise of Martin Maloney's 1895 idea, and failed only upon the realization that there would be insufficient water for steam generation. In 1919 John L. Lewis took the bituminous miners out on strike; within a month Philadelphia was hurting. PRT cut off the heat in its trolleys, train service was reduced, manufacturers went on a one-day week, and so on. When the strike was settled, there was a blizzard in the coal regions, a shortage of coal cars, a railroad strike, a tugboat crew strike, and a pier strike. By early 1920 there was only a 24-hour supply of coal at the generating plants. Then in 1922 another strike shut the mines in twenty states, and the car shortage continued unabated. As a consequence, the cost of fuel continued to rise.

By 1926 the capacity of PECO's six steam stations was 529,000 Kw, with an additional 15,000 Kw in reserve ... and demand was still rising. Since there was no space for further expansion of the existing plants, Eglin, the engineering vice-president, was preparing plans for a new generating station which would be the largest steam plant in the world.

At the same time, reflecting on the cost and vagaries of the coal supply, another source of power was also being considered: hydroelectric power from the Susquehanna River.

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Getting Started

As early as in 1884 the Susquehanna Water Power and Paper Company of Harford County (Maryland) built a small wing-dam to power its paper mill at Conowingo, which means "at the rapids". The company was later sold to another corporation, eventually to become the Susquehanna Power Company, which, in 1905, decided to build a hydroelectric plant. During the development phase the project came into conflict with the Susquehanna Electric Power Company and the McFall Ferry Power Company, each of which also had hydroelectric rights on the lower river.

In 1908, to avoid litigation, the three companies consolidated their interests under the leadership of the Susquehanna Electric Power Company, which was under the control of Bertron, Griscom & Co., investment bankers of New York and Philadelphia. However, the power company was unable to obtain financing.

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Meanwhile, in 1910, the Pennsylvania Water and Power Company built a hydroelectric dam across the river at Holtwood, Pennsylvania [Note 1]. It began to transmit power to Baltimore and York, and the Holtwood dam demonstrated the practicality of hydroelectric generation on the Susquehanna. Bertron, Griscom reacted by funding serious engineering studies and collecting data at five sites in the Conowingo area.

The means by which PECO gained control of these activities is highly convoluted, so only the highhlights will be described.

During the war the Federal government had considered the Conowingo area in its search for additional power, and discussed the possibilities with PECO in 1918. Further pursuit at that time was abandoned because of the long development time, but the proposition was again taken up by Eglin in 1921. To keep the project alive, banker Rodman Griscom offered McCall, PECO's president, an informal option on the Susquehanna Power Company, whose tangible assets included 5424 acres and the control of eight companies that owned part of the river land. During 1922 Eglin, PECO's vice-president for engineering, assisted by the engineering firm of Stone & Webster and by a battery of lawyers, conducted a plethora of preliminary studies. Their findings, presented to the board of directors in 1923 by financial vice-president Johnson, were that it was economically feasible to build a dam and power plant there capable of generating 237,500 Kw for an estimated cost of $45 million and to transmit the power to Philadelphia at a lower cost than it could be manufactured by the system's steam plants [Note 2]. Johnson also stressed the importance of protecting the company from adverse interests who might develop this cheap power source for themselves.

A clause in the option Griscom offered PECO, however, was not popular with the PECO directors. It guaranteed to United Gas and Electric, the owners of 50% of the Susquehanna Power Company stock, twenty-five per cent of the project's output at a rate less than the cost of production. Therefore, the directors rejected the proposal, hoping that someone else, from whom PECO could buy cheap power, would underwrite the project. To protect the company's interest, and perhaps to make a buck, one of PECO's directors, W. E. Long, representing Drexel & Co., acquired the option from Bertron, Griscom. In these negotiations the clauses which favored United Gas and Electric were eliminated, and it was understood that the option could be exercised in favor of Philadelphia Electric.

Meanwhile, further engineering and economic studies were made. Although the projected cost had risen to $59 million, it still would represent a saving of $21 million over building steam plants of equivalent power, would allow 36,000 Kw to go into emergency service in one minute, rather than one and a half hours for a steam plant, would save 750,000 tons of coal yearly, and would provide water power most abundantly at the times of year when coal deliveries were most troublesome. Accordingly, in July of 1924 PECO authorized preliminary work at Conowingo and advised Drexel & Co. of its desire to exercise the option on the stock of the Susquehanna Power Company.

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There still were problems. Since Conowingo lay in Maryland and since the head pond would lie mostly in Pennsylvania and since the War Department had ruled that the Susquehanna was navigable, the project required approval from two state power commissions and from the Federal Power Commission. Engineering plans, cost estimates, financing, and the corporate structure all had to be developed in detail for presentation to these commissions [Note 3]. With the plans firm, PECO officials appeared before the three bodies in March 1925. As the hearing was being called to order, the entire legal staff of PRT walked in; Thomas Mitten was out for blood.

In its opening attack PRT claimed that Drexel & Co. would make exorbitant profits from the financing, that the project was not sound, that it could not be completed in time, that rates would rise, &c. &c. (Mitten also attempted to gain control of PECO by soliciting proxies, offering to increase the dividend from 8% to 10%, but at the April 1925 PECO annual meeting 95% of the stock was voted for McCall's administration.) Mitten's attacks continued for another year, but eventually, after some of his objections as to the interest rates were sustained by the commissions, he withdrew from the battle. In March 1926 Drexel & Co. formed a syndicate to market $36 million of 5 1/2% Philadelphia Electric Power Company bonds; with an additional issue of $12 million in 8% preferred stock the project at last became alive.

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Construction

The specific location for the dam had two limiting constraints. First, it was desirable to develop the maximum hydraulic head by locating the dam downstream as close as possible to the Chesapeake tidewater. However, the Columbia and Port Deposit branch of the Pennsylvania Railroad [Note 4] ran along the east bank of the river and would have to be relocated. The farther downstream the dam would be located, the greater the ruling grade on the railroad. And second, the dam could not be placed too far upstream as it could not flood the tail-race of the existing dam at Holtwood. Five possible sites were examined, with extensive studies of head and power available and of the cost of development.

The site chosen was about two miles below the original village of Conowingo. The hills on either side of the river form natural abutments, 250 feet above mean sea level (MSL) on the Cecil County, or east, side of the river, and 155 feet MSL on the Harford County, or west, side. The test borings showed hard rock to a depth of more than 100 feet.

The site is nine-and-a-half miles from tidewater. The foot of the dam is ten feet MSL: A head pond surface elevation of 108.5 feet was adopted. (At this depth, although the pool did not reach the existing Holtwood tail-race, it did flood a planned future excavation and limited power expansion there; the problem was solved by an arrangement, wherein the Holtwood company would share in the Conowingo generation.) At the site selected, at full flow the normal tail-race level was to be 19 feet, leaving a net head of 89.5 feet. The ultimate capacity was to be 400,000 Kw; the installation was to provide about 2/3 of this capacity initially.

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On either side of the river camps to house 3800 workers were erected. On the east bank heavy transportation was provided by a spur from the Columbia and Port Deposit branch line. The main channel of the river lay along the west bank, so the power house was to be located at that end of the dam, although there was only limited space available for the construction site. To supply transportation for the construction of the power house a connection was made with the PRR at Havre de Grace, which was run nine miles along the towpath of the old Tidewater Canal. The old bridge over the river at Conowingo had very limited capacity, so no effective direct construction route existed between the two shores; accordingly, a three-track construction trestle was built across the river. Here there were three gantry cranes, each carrying a concrete hoist and a derrick. Electric power was provided by running a transmission line from Holtwood to the construction site.

Concurrent with the beginning of construction, eight miles of the Baltimore Pike were relocated, since the road would eventually run across the top of the dam, with the old bridge crossing destroyed. Telephone and telegraph lines which paralleled the original road, and crossed on the old bridge, were replaced with submarine cable, A major project was the relocation of the Columbia and Port Deposit, which otherwise would have been submerged by the head pond. This relocation, which provided right-of-way for two tracks, involved the excavation of 1.46 million cubic yards, 900 feet of tunnel, 42,000 cubic yards of concrete masonry in bridges and tunnels, and the laying of 20 miles of single track. It was an impressive project in itself!

The dam is a gravity-section, concrete masonry structure, with its base on the river bed 10 to 15 MSL, rising to an elevation of 86 feet at the main spillway [Note 5]. In overview, the dam is constructed as a sequence of piers on 45-foot centers, each rising to an elevation of about 115 feet, carrying the highway on top. The piers are then joined by concrete masonry having different length cross-sections. Beginning at the east bank abutment, for a length of 1190 feet the piers carry only the highway and illumination standards. Between these piers the dam has no opening to the water; the section resembles a buttressed wall. The piers for the remaining length of the dam have additional width for the tracks for three large gantry cranes, a visible characteristic peculiar to Conowingo. These cranes lift the various "gates" which control the water level in the head pond; that is, they control the flow over the spillways. The next 2250 feet of the dam contain the main spillway and its "crest gates". Here the cross-section between the piers is ogee-shaped, following a long reverse curve which crests about 20 feet below the highway, providing openings for water to flow over the dam. The ogee shape essentially follows the stream lines of water flowing over the spillway, minimizing erosion of the concrete. The crest gates, fifty in all, are plate-like metal structures which slide in grooves in the sides of each pier. When closed, each gate rests upon the crest of its spillway section; to adjust the flow of water over the spillway the gantries raise or lower the crest gates. The gates are held in vertical position by large "pawls", which are painted black and easily seen from the highway. With all the gates closed, the maximum elevation of the head pond is 108.5 feet.

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In the next 135 feet of the dam are three regulating sections. They have cross-sections similar to the spillway sections, except that they crest somewhat higher. Each is topped by a "regulating gate", also adjusted by the gantry cranes, which provide a finer adjustment of the flow rate over the dam. All the gate guides are electrically heated to keep them free of ice.

The next 950 feet comprise the "headworks" section of the power house; that is, it is the part of the dam proper where the water is taken from the head pond and is channeled into the power house. As do the other sections, the headworks carry the highway and gantry tracks. At the upstream edge, a concrete curtain extends 40 feet below the pond surface as a protection against the entry of ice. At the base of the section are intake openings to the tunnels through which water is carried through the dam to the entries of each water wheel. (Immediately upstream from the intakes are trash racks, which slide in vertical guides for cleaning, and additional guides for service gates to close the intake ports for maintenance.) There are two intake ports for each of the eleven water wheels, or turbines [Note 6] and each pair of water tunnels, or "penstocks", is merged into one before leaving the dam section. There are no gates in the headworks for control of the intake water flow. Downstream, this section of the dam forms a sort of ledge, above which part of the power house is constructed, with vaults for transformers, bus-bars, and circuit breakers located here. Immediately under the roadway is a railed transfer gallery along which heavy transformers can be moved.

The final portion of the dam is the western abutment section, which joins the headworks to the west bank. It is about 100 feet long, and is similar in construction to the eastern abutment.

The pond formed by the dam is a bit over 14 miles in length, 0.5 to 1.3 miles in width, and 9000 acres in area. The energy storage capacity is slightly over five million kilowatt-hours. In later years the Muddy Run pumped power station and the Peach Bottom atomic power station, together with thousands of fishermen and nature lovers, would all take advantage of the reservoir provided by Conowingo. (The original design of the dam provided fishways to bypass the obstruction, but at government request these were substituted for by an annual payment for stocking the pool, and within a few years 25 million perch and bass had been placed in the pool. Today the dam is equipped with elevators to service spawning shad.)

The power house is located at the western end of the dam on the downstream side. On overview the power house is a high-bay concrete building with the elongated windows that have become characteristic of generating stations. The "basement" contains the tail-race penstocks, which carry water from the turbine exits to the tail pond outside and downstream from the building. The water wheels are at the same elevation as the entry penstocks. The main floor is about two stories above the water wheels. Outside the building, at this elevation, on the downstream side is a ledge which carries the rails for a gantry for lifting the tail-race service gates. (At present this area is open to visitors, and to fishermen who regularly work the tail pond.)

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The generator room occupies the majority of the power house building. The generator floor is about six stories above the base of the dam, with the roof yet another six stories higher but only eight feet above the surface of the highway. Beyond the upstream side of the generator room are several vaults which run the length of the building, and which appear at several levels. At the main floor level is a vault which contains the low-voltage (13.8 Kv) oil circuit breakers. At the level of the generator floor is a vault which contains the low-voltage connecting buses. And above this vault are located the low-voltage to high-voltage (220 Kv) transformers, together with handling apparatus [Note 7].

The top of the vault complex contains the control room, located at about the center of the ultimate station length. This room contains three semi-circular switchboards, one behind the other. The first is a low-profile console, on which are mounted control switches and indicator lamps for the main generators, transformers, and circuit breakers. Next is a ceiling-high metering panel, containing voltmeters, ammeters, wattmeters, and strip-chart recorders for the main circuits. The third panel contains the protective relaying for the hold instrumentation for the various station utilities. (The original instrumentation was Victorian: knife switches, inch-thick slate switchboards, and meters the size of small hatboxes. As visitors are not permitted in the control room, one is uncertain as to later modernization, but on the generator floor one still sees original instrumentation, huge, bulky, but still working.)

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Producing the Power

The flow of power at Conowingo begins, naturally, with the entry of water at the intake penstocks. As they leave the headworks the two penstocks merge into one, and enter the steel plate scroll case. It is at this point that the water flow is controlled by a large butterfly valve [Note 8]. With a diameter of 27 feet, these were the largest ever made at the time; they were designed to open or close in five minutes against maximum water flow. From the scroll case the water enters a turbine, or water wheel. The turbine speed is slow, due to the modest pressure head of the water. The water exits from each turbine axially downward into the tail-race and thence out to the tail pond.

Each turbine drives three generators, each mounted coaxially with the water wheel and stacked one atop the other. At the lowest level is the main generator. (Because of the low speed, these are dimensionally the largest generators built at the time [Note 9].) Atop the main generator is the auxilliary generator, which supplies power to run a motor-generator set, which, in turn, is the exciter for the main generator. The third generator, at the summit of the stack, is the exciter for the auxilliary generator.

The output power of each main generator goes through low-voltage circuit breakers, then on to low voltage buses. In normal operation, two main generators are connected in parallel, and their combined output is raised by three-phase transformer banks. The transformer output is fed upward to the switchboard on the roof. The lines next go through high-voltage circuit breakers and lightning arresters. Throughout, a plethora of disconnects provides alternative paralleling arrangements of the circuits.

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Perhaps the most spectacular exterior sight at Conowingo is the extensive high-voltage switchyard which surmounts the power house. At the ground level of the switchyard (that is, the roof of the power house) are located the high-voltage oil circuit breakers, high-voltage lightning arresters, and handling rails. Since the output power is three-phase alternating current, each of the power-handling devices, which are extremely large, appears in triplicate. Above these devices, supported by vertical structural sections and horizontal truss work, are the many disconnects through which the various generators are connected to each other and to the output buses. Still higher, again on structural sections, are located two three-phase output buses, to which the cross-country high-voltage transmission lines connect. The superstructure is topped by numerous lightning rods which reach to a height of 226 feet above the base of the dam.

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Transmission to Philadelphia

The Conowingo project included the construction of two transmission lines and two substations to link the project to the users.

One transmission line was built from Conowingo to Plymouth Meeting. This line, which operates at 220 Kv, was provided with a 315-foot right-of-way to accommodate three circuits, each with individual tower suspension. Only the two extreme positions were constructed with the dam project, with the central position, which was never built, available for future expansion. This twin-tower line lies mostly in Chester County. It passes through Tredyffrin contiguous with the Trenton cut-off, passing over the Little League field, the squash club, and Teegarden Park. As built, the line ran uninterrupted from Conowingo to Plymouth Meeting, but more recently substations have been added which tie in with Peach Bottom and Pennsylvania Power and Light (PP&L) and several substations for local distribution, such as at Exton and Paoli.

Plymouth Meeting substation, the line's terminus, was also built as a part of the Conowingo project. It is located between the Trenton cut-off and the Reading Railroad, with access from Gallagher Road. The substation provides for interconnections with a line to PP&L at Siegfried, Pa., and with a line to Public Service and Gas at Roseland, N. J. These interconnections were included in the original construction, and are effected by a small forest of buses, switchgear, and circuit breakers. The main purpose of the substation, however, is to enter the Conowingo power into the Philadelphia network. Two three-phase transformer banks step the voltage down to 66 Kv, the voltage that PECO uses to interconnect its generating stations. Thus, Plymouth Meeting makes Conowingo appear to the system as just another station.

Also constructed at this time was the Westmoreland substation, located in the city between Westmoreland Street and the Reading Railroad. Here the 66 Kv line from Plymouth Meeting is interconnected with lines from the Richmond and Schuylkill generating stations.

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(It should be remembered that one objective of the Conowingo development was to provide rapid emergency power to the Philadelphia network in the event of a breakdown or during maintenance work; the tie at Westmoreland provides this capability.)

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Concluding the Work

Compared to more recent projects, particularly highways, the Conowingo project was completed with blazing speed. Some of the highlight dates are

Construction started, site clearing, &c. March 1926
First concrete poured August 1926
Power house superstructure started June 1927
C&PD railroad in operation at relocation October 1927
Highway bridge opened to public November 1927
Power house concrete work completed December 1927
Dam concrete work completed January 1928
Main generators #1 & #2 in commercial service March 1928
Main generators #3 - #7 in commercial service June 1928

Two years: amazing! The dam impounded 150 billion gallons of water, had a generating capacity of 252,000 Kw, and generated an average of 1.3 billion Kw-hours a year.

Conowingo's original construction comprised seven generating units, each of 36,000 Kw capacity, with space and headworks provided for four additional units. By 1965 advancements in the technology of electric genertation made possible the installation of 60,000 Kw units in each of these spaces. Thus, four new additional units have increased Conowingo"s capacity by 240,000 Kw, an increase of 95%.

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Epilogue

Although Joseph McCall, while president of The Philadelphia Electric Company, was responsible for many progressive innovations, among them the Conowingo project, he believed that the Company's operations should be confined to the City of Philadelphia. Yet as early as in the 1890s United Gas Improvement had been interested in the development and consolidation of electric companies outside the city and in our area; indeed, principals of UGI were, as noted earlier, instrumental in the formation of Philadelphia Electric of New Jersey. While McCall concentrated on developing electric service within the city, UGI was active in the rest of south-eastern Pennsylvania. Talk of merger of the two companies began in 1904, and was a perennial topic of conversation. When S. T. Bodine replaced Thomas Dolan as president of UGI in 1913 and promptly attempted to lease Philadelphia Electric, rumors intensified.

Still McCall sat idly by while UGI bought the suburban utilities ringing Philadelphia. To the north lay an extensive area served by Philadelphia Suburban Gas & Electric, bought by UGI in 1925. In 1927 UGI bought control of Day & Zimmerman, construction engineers and operators of public utilities in fifteen states. UGI owned Counties Gas & Electric, which operated in Montgomery County and owned a modern steam plant on Barbadoes Island at Norristown, and UGI supplied power to the Main Line, the Schuylkill valley, and the territory from Coatesville to Trenton. The advantages of consolidation were evident to almost everyone but McCall.

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McCall died in early 1926, and Eglin, the engineering vice-president, in March 1928; neither was to see the completion of Conowingo. Walter Johnson, the financial vice-president and last of the Conowingo triumvirate, took over at McCall's passing.

By this time it was obvious that consolidation was inevitable. The UGI companies were buying much of their power from PECO, and PECO was about to enjoy a major increase in generating capacity from Conowingo, with its consumer market still limited to the city. Bankers from the influential Drexel & Co. sat as directors for each of the two companies. Public opinion had become favorable, and the respective stockholders were overwhelmingly for it. Accordingly, over 95% of PECO common stock was exchanged for UGI shares, and in February 1928 control of The Philadelphia Electric Company passed to UGI. The city and suburban operations were gradually combined and in October 1928 the two companies were formally merged into the newly incorporated (no "The") Philadelphia Electric Company.

Thus the expansion of The Philadelphia Electric Company begat the need and drive for the construction of the Conowingo hydroelectric station, and the success of Conowingo was instrumental in creating the Philadelphia Electric Company as we have come to know it.

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Notes

[1] Holtwood dam, built in 1910 and now owned by Pennsylvania Power & Light, is still operating with a capacity of 102,000 Kw. A steam plant has been built next to the original power house. The dam is about 15.5 miles upstream from Conowingo. State route 372 crosses the river just below the dam. On the east bank, shortly before the crossing, a road leads down to the edge of the tail pond, apparently a good fishing spot. On the west bank, also accesible from route 372, PP&L has built a small park with fishing access to the river, and which contains the remains of Lock 12 of the old Susquehanna Canal. This is a nice "day trip"; on the west side one can then go down to Peach Bottom and return with a visit to Conowingo.

[2] Considering the erratic flow of the Susquehanna, sometimes heavy, sometimes light, it could be effectively used for hydroelectric purposes only in conjunction with a highly developed system of steam plants. When the river was running strongly, Conowingo would carry PECO's base load, the steam plants furnishing peak demand. When the river was low the strategy would reverse. The general idea was to maximize the saving of coal; in its initial years the plant saved 750,000 tons of coal annually.

[3] The corporate structure created for the Conowingo development was a new company, the Philadelphia Electric Power Company, which was to be a subsidiary of The Philadelphia Electric Company. This company was to own the hydroelectric property in Pennsylvania, including the majority of the reservoir and the transmission lines to the point where they entered PECO territory. The new company would also own the Susquehanna Power Company, a Maryland corporation, which was to hold title to properties in that state, including the dam and parts of the reservoir and transmission lines.

[4] The Columbia and Port Deposit Railroad was originally incorporated in Pennsylvania in 1857 as the Washington and Maryland Line railroad, apparently a local enterprise to form a route from Harrisburg to the Chesapeake Bay and thence to Baltimore, the preferred market for much of that section of Pennsylvania.

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For seven years little was accomplished, except name changes, until the C&PD was incorporated in 1864. In subsequent years construction was started, and over a million dollars in bonds were issued, all owned by the Pennsylvania Railroad. In 1877 construction was completed on the 40 miles, which connected the PRR main line at Columbia with tidewater at Port Deposit, also connecting there with the Philadelphia, Wilmington and Baltimore (later the Washington Division of the PRR). These were years of intense competition among the PRR, B&O, New York Central, and Reading railroads to seize the traffic between "the West" and tidewater. This same rivalry, during this period, led the New York Central to build the tunnels through which the Pennsylvania Turnpike now runs.

[5] A gravity dam is a structure which is held in place by its own weight. Although poured directly onto bedrock, to which it gains some adhesion, there is no mechanical attachment to its surroundings. It has been reported, perhaps apocryphally, that there was concern for the dam's stability during the Hurricane Agnes flooding, but it is, truly, still in place.

[6] The headworks of the dam were built with penstocks for eleven water wheels. The initial construction of the power house was sized for seven turbines, the remaining four to be for future expansion.

[7] A bus is an electrical connection to which various devices are attached. In low-voltage devices, such as a computer, it is simply a wire; in a residential fuse box, it is a copper strap; in a high-voltage switchyard it is a large copper beam supported by substantial truss-work and very large insulators:

Three specifications are used to express the capacity of large electrical equipment. The voltage rating, expressed in kilovolts (Kv, thousands of volts) determines the maximum voltage which can be applied without danger of a breakdown of the insulation which could result in a short-circuit and/or fire. The power capacity is given as the product of voltage and current; that is, as kilovolt-amps (Kva, thousands of volt-amps). Of this capacity, only 70% to 80% is useful energy, measured in kilowatts (Kw, thousands of watts).

A disconnect is a switch that performs the same function as a household light switch. They are unenclosed, and are built more like an old-fashioned knife switch than a household toggle switch. At high voltages they are quite large. They proliferate in switchyards because of the necessity for rearranging circuits as load and/or supply conditions change -- which is the basic purpose of the switchyard. Circuit breakers provide protection from excessive current, exactly as in the home. The interrupting capacity, however, is very much higher, 1000 amperes at Conowingo. The opening of a circuit at such high current would be followed by an intense arc were it not for a magnetic quenching device invented by Elihu Thompson, a Philadelphia high school teacher who later became one of the principal founders of General Electric Company.

Transformers are used to change the voltage; in a home, for example, they step down 110 volts to 12 volts to operate doorbells or high-intensity lamps. The principle of the transformer is that no matter what is done to the voltage, the product of voltage and current, or volt-amps, remains constant. Since the losses in a transmission line depend upon the square of the current, at the start of the line a transformer raises the voltage, lowering the current, and lowering the losses by the square of the voltage. At the terminus another transformer lowers the voltage to the level appropriate for the next level of distribution. At the residential level, a "pole-top" transformer, usually rated at 25 Kva, will supply two or three homes; many of them can be seen in nearly every suburban block. High-voltage transformers are cooled by oil, and are very heavy. (The 220 Kv transformers at Plymouth Meeting weigh 185 tons with oil.) Handling them is a major consideration, and until recently all high-voltage switchyards were located for railroad service. In fact, when the old Chester Valley branch of the Reading was abandoned, PECO acquired a section to move transformers into its Berwyn maintenance complex on Swedesford Road. Today specially-designed high-capacity trucks move these monsters. (For years the oil used in transformers and circuit breakers was laced with PCBs as a fire-retardant, a practice which led to much environmental contamination.)

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[8] The water enters the water wheel along the entire periphery of the wheel, passes through the blades, then leaves axially downward from the center. The water is conducted from the penstock to the turbine by the scroll case. This is a very large circular pipe, 27 inches in diameter, made of steel plate. The entrance end connects directly to the penstock in the concrete headworks. The scroll case then bends around the periphery of the water wheel. Beginning at the point of tangency to the wheel, the scroll case is open to the wheel, allowing for the transfer of the water. To maintain pressure as the water volume decreases, the diameter of the scroll case continually decreases as it wraps around the wheel. Thus, while the inside radius is constant, the outside radius forms a spiral, and so the scroll case resembles the shell of a very large snail.

Water flow is controlled by a butterfly valve at the entrance to the scroll case. This is a circular disk, of steel construction, having the same 27-foot diameter as the scroll case. The valve is pivoted and actuated on an axis through its vertical diameter so that it can assume any position between parallel to the stream line (fully opened) and perpendicular to the stream line (fully closed), thus controlling the flow rate. At the time of construction these were the largest butterfly valves ever built.

[9] Every generator is based on the principle that a conductor within the field of a moving magnet will have a voltage developed in it. In an alternating current generator the magnet is rotated (this part is called the rotor) by the prime mover, with the conductors coils of wire wound around a metal salient, or pole, of the frame (this part is called the stator). In very small generators the rotor is an electromagnet. The power required to energize this electromagnet is supplied by the "exciter"; in many generators the exciter is mounted on the same shaft as the main generator. At Conowingo the main exciter is a separate motor-generator set; its power comes from the auxilliary generator which is coaxial with the main generator. In turn, the power for the exciter for the auxilliary generator comes from a small direct current generator which is also coaxial with the main generator. This arrangement may appear awkward, but it provides a high degree of sensitivity for control of the main generator's output voltage.

Meanwhile, back at the stator, the voltage developed in the wire around each pole increases with the number of turns in the coil of wire; high voltage means lots of turns. The current that can be drawn is proportional to the cross-sectional area of the wire; lots of current means heavy wire. Thus a generator of high voltage and high current (high Kva) has very large poles on the stator. One complete revolution of the rotor generates one electrical cycle in one pair of series-connected poles. Since the low-speed Conowingo turbine turns at only 81.8 rpm, or 1.36 rev/sec, to generate 60-cycle current requires 60/1.36, or 44, pairs of poles per phase. Thus, a high-voltage, high-current, low-speed generator has a very great number of very large poles on the stator. The main generators at Conowingo were, at the time, the largest ever built. (Three were built by Westinghouse and four by General Electric.)

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Sources

Conowingo Hydro-Electric Development of the Philadelphia Electric System. A collection of technical papers written by various engineers for PECO, contractors, and manufacturers, published in various technical journals.

History of the Philadelphia Electric Company 1881-1961, Nicholas B Wainwright. Philadelphia Electric Co., Philadelphia, 1961

Centennial History of the Pennsylvania Railroad 1846-1946, George H. Burgess, Miles C. Kennedy". The Pennsylvania Railroad, Philadelphia, 1949

Men and Volts, The Story of General Electric, John Winthrop Hammon. Lippincott, Philadelphia, 1941

 
 

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