Switch House Chester Electric Power Station - PECO Energy, Chester Pennsylvania
Railway and Streetcar Electrification
Analysis of the first two decades of electrification in Philadelphia reveals many of the
technological reasons why electricity was labeled a "natural monopoly" in the twentieth
century. Like other metropolises of the era, Philadelphia passed ordinances for separate
distribution rights in the different wards and suburbs. Between 1881 and 1891, some
seventeen companies divided the greater Philadelphia area into distinct operating territories,
creating chaos by their use of different frequencies and voltages. Looking back at the
situation with over two decades of hindsight, Philadelphia Electric managers pointed to the
need to standardize electrical generation and distribution, justifying consolidation as
a necessary step in the technical evolution of electrical systems:
Territories overlapped and controversies were frequent. Some measured the current in ampere hours, some in lamp hours and some in watt hours. Voltages ranged from 55 to 120, and cycles from 45 to 133. With these variations in all the essentials of the service, customers who removed from one section of the city to another often found their equipments of dental motors, fans, coffee grinders, etc., to be useless.
Absorption of the Philadelphia area operating companies in 1902 left Philadelphia Electric with an assorted inventory of equipment, including direct current plants, several types of steam engines, various switch gear and transformers, and transmission lines rated for different phases, frequencies, and voltages. Although the utility began rationalizing its system by implementing two-phase alternating current, commercial consolidation was to precede technological standardization by several years. The "battle of the phases," and the "battle of the frequencies," waged since 1886, had not produced a victor in the first decade of the twentieth century, and direct current systems were still a mainstay in downtown districts. Philadelphia's direct current, three-wire system, inherited from the Edison company, was a case in point. Attempts to establish uniformity of service were further complicated by customer requirements. Philadelphia Electric obtained its first large power contract in 1911 to supply single-phase, 25-cycle-, 13.2-kilovolt electricity for the Philadelphia Rapid Transit Company (PRT) - a departure from the two-phase, 60-cycle system adopted as Philadelphia Electric's standard in 1902. To accommodate the 25-cycle load, the utility adapted its 60- cycle current with frequency converters rather than generate at the lower frequency. At the same time, the company embarked on a larger campaign to improve the efficiency of its distribution system by upgrading well-placed substations, abandoning obsolete ones, and builing new high-voltage transmission lines. And in a third major push, Philadelphia Electric engineers set out to standardize the bulk of their company's territory on the higher voltage (13.2 kV) required by the PRT, but with three-phase electricity delivered at 60 cycles.
Another large rail contract prompted a reassessment of plans to standardize on 60 cycles. The Pennsylvania Railroad launched an experimental electrification program in 1913 by ordering electricity from Philadelphia Electric for the Paoli and Chestnut Hill rail lines. This time, instead of relying on frequency converters, Philadelphia Electric planned to supply the 25-cycle railway load with a dedicated turbo-generator in a massive new central station proposed as an addition to the 1903 Schuylkill A-l station. The new station, designated A-2, would contain the largest turbo-generators yet constructed with separate electrical buses for each frequency (25 cycle for the rail and streetcar load, 60 cycle for general power and lighting service), and require special phase converters and voltage-balancer sets (designed by Charles Steinmetz at the General Electric Company).
Electrification of the railroad and streetcars proved a significant force behind the early development of the Philadelphia Electric electrical system. Rail loads shaped the evolution of a comprehensive transmission and distribution network in Philadelphia, while rail-related frequency differences impeded attempts to standardize that system. Despite corporate claims that consolidation would eliminate the disorder created by numerous operating companies in the nineteenth century, the diversity of customer demand prior to World War I continued to prevent an easy transition to uniform service. The initial response of Philadelphia Electric to the dual-frequency demand problem was to move away from a standardized generation of electricity and instead build a state-of-the-art facility (A-2) that utilized two separate production structures: one for 25 cycle frequency, the other for 60 cycle. Two years later, Eglin and other Philadelphia Electric engineers made a different choice at Chester.
Switch House, Part II
Chester Station was designed to generate a single type of electricity: three-phase, 60-cycle, alternating current at 13.2 kilovolts. Future Philadelphia Electric power stations also generated this type of current, and relied on convertors or substations to make the necessary adjustments for different users. The original switch house at Chester was, in effect, an internal substation. It housed the equipment needed to step up electricity to higher voltages for long distance transmission, and directly connected certain large industrial customers such as Sun Ship Yards to the main station bus.
The bus connected all incoming and outgoing electrical transmission lines. Its structure reflected Philadelphia Electric's growing experience with central station design and increasing success in standardization. In several respects, the main bus in Chester's switch house resembled that of Schuylkill A-2. Yet the single cycle bus configuration differed from Schuylkill's two separate-cycle buses, and the structural separation from the turbine hall was more fully articulated at Chester. Physically, the bus originally consisted of a large loop or "ring" of several flat strips of copper bolted together, housed in a long compartment that occupied the third and fourth floors of the switch house. The sectionalized, double "Hconnected" ring bus design at Chester combined flexibility for system maintenance with reliability. Each generator and outgoing feeder had tie lines to either bus, which could be used interchangeably in the event that a problem disabled one bus. Disconnects allowed operators to isolate sections of the bus without impeding the rest of the system for maintenance work or line failures. Directly under the control room, a "pipe room" connected the switching controls and instrumentation to the main circuits. The pipe room was designed for easy access to the control lines and for future expansion. It was first used at Chester, and later employed with success at the Delaware and Richmond stations.
Feeder lines from the generators carried three-phase, 60-cycle electricity at 13.2 kV into the switch house under the main floor, through oil-filled circuit breakers and connected to the main station bus on the fourth floor. Each floor of the switch house generally contained equipment for a specific task: potential transformers, cable disconnecting switches, and the test bus were located on the ground floor; reactors and current transformers on the first floor; circuit breakers on the second floor; bus disconnects on third floor, and the main bus on the fourth floor. The design of the later switch house at Delaware Station mirrored Chester's, but Philadelphia Electric changed to a new vertical phase isolation arrangement at Richmond Station in 1925. Whereas the three-phase circuits were previously mounted adjacent and parallel to each other, the Richmond bus design separated the phases by floors, virtually eliminating the potential for phase-to-phase faults.
The Chester design also incorporated several safety procedures for accessing the lines, including the "Cory scheme" based on an interlocking system of keys. All buses, switches, transmission circuits, generator leads, and reactors were enclosed in compartments, protected from human contact by locked doors. The switchboard operator supervised access to the compartment keys. Chester followed a "red tag" system of blocking procedures for installation and maintenance of equipment; developed at Schuylkill, this system provided a model for permits and blocking procedures at Philadelphia Electric. Remote-controlled oil-filled circuit breakers handled disconnections of the high-voltage system under load.
Aside from substation function, the switch house served as the nerve center and control point for station operations. Control of the electricity generated at Chester ultimately rested in the hands of the switch house control room operators. From a desk in the control room, an operator monitored an assortment of switches, gauges, and controls laid out in concentric, semi-circular panels and instrument boards. Behind the desk, a series of windows opened onto the turbine hall, providing a commanding view of the equipment and personnel from the third floor. The operators worked in relative serenity, insulated from the noise of the turbine hall, the heat of the boiler house, and loud hum of the electrical circuitry in the lower levels of the switch house. The comfortable environment was sometimes a place of emergency action, as millions of dollars invested in station equipment depended on the quick response of control room operators to station crises.
The confinement of the major switch gear equipment to an integrated interior space within the station eventually presented problems that led to the use of outdoor substations. Progress in power distribution transformer technology between 1920 and 1940 produced larger units with higher volt-ampere ratings and improved methods of dissipating the resulting heat. Increased station capacities also required the use of electrical equipment (circuit breakers, relays, fuses, etc.) with commensurately higher load ratings. The physical limitations of the switch house gradually began to show as station capacity grew. In 1924, Philadelphia Electric doubled the station's transformer capacity by installing two internal, water-cooled units, but after 1940 such additions occurred outside.
The 1939-1942 plant upgrade presented engineers with the difficult task of adapting the switch house to handle twice the capacity for which it was originally designed. The new turbo-generator sets necessitated extensive modifications to the switch house, including the replacement of the original multiple-bar bus with a new, hollow-channel design shown by studies to handle the higher capacity safely. A few months prior to this phase of construction, Philadelphia Electric executives expressed a concern about the potential spread of damage in the event that an overloaded oil-filled circuit breaker exploded. Accordingly, a partial replacement of Chester's oil-filled breakers with a recently developed air-blast design less prone to explosion began in 1939. By this date, the long-apparent drawbacks of integrating the substation function in the switch house led to the location of related electrical equipment outside.
By 1945, only a few hundred yards separated the rows of cylindrical transformers, now placed outside and isolated by a high chain link fence, from Chester Station. Aesthetically, the difference was stark. Private ownership of electric utilities was firmly established, and architecture had ceased to serve as an important public relations tool for the industry. The new outdoor substations, with their equipment exposed to the elements and devoid of any embellishment, marked the start of an entirely machine-based aesthetic in electric utility design. Gone was the neoclassicism of Philadelphia Electric's Chester, Delaware, and Richmond stations, replaced by the blunt functionalism of post-World War II construction.