Turbine Hall Chester Electric Power Station - PECO Energy, Chester Pennsylvania
On October 1, 1918, a distinguished crowd that included Pennsylvania Senator William C. Sproul attended a ceremony to place the first turbo-generator at Chester into operation. Despite the presence of a rather incongruous temporary wood shed that sheltered the unit while work continued on the roof, the design of the great turbine hall unmistakably communicated the importance of the turbo-generator as the technical centerpiece of the plant. Although the turbines appeared remarkably small in the vast space created by pilastered walls and a sky-lit, barrel-vaulted ceiling, the sense of immense power contained within the steel shells conveyed a technical sublimity that complemented the architectural design. One female observer likened the view of similar turbines under steam to "the sensations experienced when first looking into the Grand Canyon from the front of the El Tovar Hotel." The attention drawn to the steam turbine by architecture was in part warranted by the machine's pivotal role in the growth and success of central station power generation. Since the first large-scale application of turbines to electricity generation in 1903, astounding increases in power output and economies of scale had been realized, ensuring the machine's continued use in American power stations.
Many of the early steam turbines ordered by utilities in the United States were based on a design conceived by Charles G. Curtis and further developed by the General Electric Company. After purchasing the Curtis patents, G.E.'s research department devised a vertical-shaft turbine that offered a substantial reduction in the initial cost and space required for conventional reciprocating steam engines. Despite the absence of an extended field service, Philadelphia Electric embraced turbine technology in its early stages of development, installing a vertical unit in 1905 at the Tacony Station. Two more units arrived in 1906: a General Electric 500 kW unit at the Beacon Light Station and a larger 5,000 kW unit at Schuylkill A-l. Despite occasional trouble, the Curtis vertical turbines performed well, and Philadelphia Electric ordered several additional machines, including two 15,000 kW units for A-l in 1913. These two machines turned out to be some of the largest of their type constructed by G.E., because the increase in shaft length and weight associated with the steady rise in turbine capacities presented problems for the vertical arrangement of the G.E. design. Between 1912 and 1914, a horizontal-shaft design rapidly supplanted the vertical machines, and turbine capacities continued to grow.
For Philadelphia Electric, acceptance of the turbine over the steam engine came at considerable cost. By 1913, Philadelphia Electric had replaced two large and relatively modern steam engines, the 2000-kilowatt and 5000-kilowatt "monster" units, with vertical turbines in the 15,000-kilowatt range. But economies of scale gained from the growth of steam turbine capacities and improved boiler designs more than offset the price of steam engine obsolescence, allowing Philadelphia Electric to keep pace with burgeoning demand for electricity without having to build numerous or overly massive generating stations. During the transition from steam engines to turbines, the company signed its first large contracts to supply the Pennsylvania Rapid Transit Company (PRT) and the Pennsylvania Railroad with electricity. The 25-cycle loads for streetcar and railroad companies presented technical problems for Philadelphia Electric but led to the placement of an order for the largest turbines ever built for the new A-2 Schuylkill station in 1914.
After nearly ten years of operating experience with G.E. turbines, Philadelphia Electric remained a loyal customer. In 1916, the utility ordered two of the four machines intended for Chester Station, selecting units of slightly smaller capacity than the one recently installed in A-2, but of an innovative design. Turbines of this type, first shipped to the Wheeling Electric Company in 1917, constituted the first large-scale embodiment of the conical-flow type eventually approached in one way or another by every manufacturer of large efficient turbines... [The design's] importance can hardly be overestimated. The change was so radical in comparison with types that had previously been manufactured that the plans were laid before E.W. Rice, then president of the General Electric Company.
Philadelphia Electric's expectations for the new units were high. Equipped with the latest
generating technology, Chester was supposed to provide sorely needed base-load power for a
system stretched dangerously thin by wartime demand for electricity. But confidence in
General Electric was eroded by a rash of postwar turbine failures that afflicted generating
stations across the United States. Under the stress of meeting orders from utilities,
shipbuilders, the Navy, and other wartime customers, G.E. had shipped its new turbine
without proper testing. Engineers later found that vibration and bending fatigue in the rotors
was causing destructive wheel and bucket failures. Power generation periodicals and utility
industry groups focused on the crisis. The problem was so severe that the AEIC assembled an
emergency committee in March 1919 to examine the failures. Horace P. Liversidge of the
Philadelphia Electric Company chaired the committee, and sent a copy of the confidential
report to President Joseph McCall in June 1919. The findings amounted to a direct
indictment of G.E.:
As a result of this study of the situation, the Committee is firmly of the opinion that the serious turbine failures which have been reported upon are directly attributable to three fundamental causes, viz.: (1) Improper design. (2) Poor workmanship. (3) Demoralization of manufacturer's plant due to war conditions.
So far as the Committee is able to determine, the responsibility for failures due to the above causes rests wholly with the manufacturer. The machines in question embodied radical departures in a number of features from previous design; marked reductions having been made in weights, overall dimensions, and working clearances for the evident purpose of obtaining better economies of operation and production costs. However, with the full knowledge of the important bearing these changes would have on operating performances, a large number of these machines were sold and allowed to go into operation before a few units of this newer design had been tried out and their reliability definitely established. This action, and also the evident lack of adequate consideration of the details of design and construction which seriously affect the reliability of these large units, are open to severe criticism.
The report included a "List of Turbo-Generators Now in Operation, Which are Considered Doubtful, and On Which Wheel or Diaphragm Changes Will Be Made." Both units ordered by Philadelphia Electric for Chester were listed.
G.E. reacted immediately to the crisis by working with the AEIC committee to address the problems, and ordered an emergency testing and analysis program. The research produced a seminal paper presented to the ASME that greatly advanced understanding of wheel vibrations and bending stresses in turbines. Additional research and exhaustive tests in the early 1920s led to successful new designs. Thus, when Philadelphia Electric ordered two new 30,000-kilowatt units in 1923 to bring Chester Station up to full capacity, the turbines were similar in appearance and rating to the original units, but differed internally.
Such design improvements, however, could do little to remedy a series of problems that plagued older equipment in Philadelphia Electric's system during the early 1920s. In 1920 alone, a breakdown at Chester halted operations at Hog Island, Station A-2's 35,000-kilowatt failed, and other turbines at A-l had to be taken out of service. A more spectacular breakdown occurred in September of the following year, when A-2's 30,000-kilowatt turbine (of the defective variety) virtually self-destructed. The service disruptions were serious blows to the company's image as a reliable supplier of electricity, and were particularly costly for industrial customers. Although the growth of turbine capacities generated economies of scale, multiple equipment failures exposed the risks of relying on a few, large prime movers. To handle such failures, utilities serving large urban territories with diverse customer bases needed flexible connections between stations and substations - networks that would permit the rapid re-routing of electricity. The turbine troubles provided further stimulus for developing a solid system of interconnection and securing adequate reserve capacity.
The 1924 installations at Chester Station reflected these concerns. In 1923, Philadelphia Electric President Joseph McCall reported to the Board of Directors and recommended purchase of the new turbines for Chester. He noted that a high peak load forecast for 1924, a request by the New Jersey utility PSC for power from the Philadelphia Electric system, and possible expansion of electrification efforts of the Pennsylvania Railroad would result in an inadequate system reserve capacity. Earlier in 1923, Philadelphia Electric had completed its first interstate tie line to another utility, the Public Service Company of New Jersey (PSC), to sell excess capacity. This inter-utility link occurred during a period of agitation for some form of regional interconnection between electrical producers, and presaged a more comprehensive and path-breaking arrangement worked out between Philadelphia Electric, PSC, and the Pennsylvania Power & Light Company (PP&L) in 1927.
The development of new designs and materials permitting higher steam and pressure temperatures during the last half of the 1920s brought turbine capacities to heights thought far in the future just five years earlier. Output was also improved by hydrogen cooling, which allowed generators to reach higher rotational speeds (previously limited by the capacity of conventional air-cooled designs to dissipate heat). Philadelphia Electric's 1932 order for Richmond Station, a 165,000-kilowatt turbo-generator of record size, was indicative of the strides made in turbine output since 1924. Moreover, high-pressure turbines could be superposed with existing low-pressure units, as occurred at Chester. The 1925 success of G.E.'s first commercial-service superposed unit at Boston's Edison Electric Illuminating Company led to the widespread use of superposition in the United States during the 1930s. When experts predicted that loads in Chester's highly industrialized service would exceed the station's capacity by 1940, Philadelphia Electric considered superposition among the options for averting crisis.
The rapid changes in turbine technology between 1920 and 1940 complicated decisions about adding capacity to aging facilities. Electrical World's survey of design trends in 1940 investigated different approaches, asking, "Who is venturing into the highest pressures and superheats? Who is still finding opportunity and justification for superposition? Who prefer to continue on the pressure levels already well established in their plants? Which stations reflect a multiplicity of lesser advances in equipment and technique, while adhering to conventional trends in major matters?"
Elements of each of these trends were manifest in the 1938-1942 construction project at Chester. Philadelphia Electric forayed into high pressures and superheat temperatures by installing a 50,000-kilowatt, 3600-r.p.m., hydrogen-cooled, superposed unit with inlet steam conditions of 1,250 psi and 950 degrees Fahrenheit (and two new boilers to supply steam at these conditions). At the same time, the company reinforced the existing low-pressure system by adding a low-pressure, 80,000-kiIowatt turbo-generator set. Global politics motivated this latter project. Following Germany's 1939 invasion of Poland, Philadelphia Electric had re-evaluated power needs in its service area. The resulting proposal to install a low-pressure Westinghouse unit at Chester was implemented even though it required building a major addition to the downriver side of the turbine hall. Electric Light & Power noted that "On completion of this project, there will be installed at Chester Station the largest concentration of generation on the Philadelphia system with an effective peak capacity of 272,000 kw."
In conjunction with the major equipment installations, Philadelphia Electric incorporated several new auxiliary systems - a "multiplicity of lesser advances in equipment and technique" -- to improve the thermal efficiency of the plant. As far back as the early 1920s, Chester designer W.C.L. Eglin had recognized the importance of auxiliary equipment such as that used for heating feed water by steam bled from turbines, reheating the steam between pressure stages in turbines, and purifying feed water with evaporators and deaerators. Nonetheless, the original feed water auxiliaries at Chester were minimal. Internal corrosion found in the economizers during the mid-1920s prompted the installation of deaerators, which remedied the problem, but by 1939, what few auxiliaries existed were in need of an upgrade. The 1939-1942 construction program added the latest in deaerator, evaporator, and cascading feed water heater technologies, and multiple pumps and by-pass piping to enhance flexibility and allow full operation during periodic equipment maintenance.
Excepting a brief slump following World War I, Philadelphia Electric faced a steady increase in the demand for its service. In the years separating the installation dates of the first Beacon Light Company turbine and Chester's 80,000-kilowatt unit, the remarkable growth of turbo-generator capacity helped Philadelphia Electric keep pace with consumption of electricity in Philadelphia, but also raised distinct problems. The high-output turbines forced utilities to cope with rapid cycles of technological obsolescence and concerns for turbine reliability became paramount. Philadelphia Electric protected itself from turbine failures by interconnecting its own transmission network, tying into those of other utilities, and extensively designing redundancy and by-pass piping into its steam systems.
While demand for electricity drove the development of more powerful turbines, the demand itself assumed many forms in the early years of the electric utility industry. As railroads, street cars, factories, stores, and households began to adapt electricity for their purposes, the resulting multiplicity of needs and equipment complicated the task of electricity producers. Philadelphia Electric reacted to these technical exigencies by rationalizing and standardizing its electrical system, particularly through a path-breaking conversion to alternating current.