Rutland, Vermont is probably not a place one would expect to be in the forefront in new technology in power generation, unless perhaps it was in mountain stream hydropower. Even less likely is this town‟s involvement with one of the first land-based gas turbines to drive an electric generator. But that is just what happened sixty years ago. In 1951, three new gas turbine plants manufactured by General Electric (GE) in Schenectady, NY were installed on the west end of Rutland, elevating this New England city to the leading edge of power technology. The owner and operator of these plants was Central Vermont Public Service (CVPS).
GE called this design combustion turbine a frame size 3. There were only ten turbines of this design ever manufactured by GE. According to their published records, all were installed in the early 1950s in such diverse locations as Maine, Texas, Connecticut and the aforementioned Vermont.
Note: The very first GE installation in power generation was at Belle Island Station of Oklahoma Gas and Electric Company was two years earlier. It was a Frame 3 but a simple-cycle, single- shaft generator drive, with the model designation 3001.
Fig. 6-1 below shows a colored cross-sectional view of the Rutland gas turbine. As depicted in the rendering, there are compressors at each end. The low-pressure (LP) axial-flow compressor is on the right; another axial-flow compressor (so called high-pressure, HP) is on the left. Air from the LP compressor is intercooled before going to the HP compressor. Air discharging from the HP compressor is then pre-heated by regenerators before going the combustors. There will be more on this later in the chapter.
Fig. 6-1: Cutaway of the 5000 KW “Kilowatt Machine at Rutland, VT
According to the CVPS unit operator log books, the first of three plants went into commercial operation on October 1, 1951. The three units were installed side by side in a building that is now an electrical repair shop for transformers, since the last gas turbine plant was retired in 1987. Unit #1 is shown in Fig. 6-2 below.
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Fig. 6-2: Elevated view of plant operators recording data on Unit #1 at Rutland, VT (circa 1951) The Rutland plants were very advanced for their time. In fact, they would be considered extraordinary even by today‟s standards. Unlike the simple-cycle, peaking gas turbine power plants that became popular in the late 1960s, in reaction to the great Northeast Blackout of 1965, these first gas turbine power plants were very complex. Dubbed the “Kilowatt Machines” by GE engineers, the indoor in power stations in Rutland were both inter-cooled and regenerative cycle. See Fig. 6-3 below. Each plant could develop approximately 5,000 kilowatts when operating at an ambient inlet temperature of 80 degrees Fahrenheit at the Rutland elevation.
Crisp and clean mountain air was sucked into the inlet of the LP compressor. The LP compressor was driven by the LP turbine stage. Air from the discharge of LP compressor was not only higher in pressure but at an elevated temperature, which hurt overall performance. GE used twin intercoolers (in parallel) to reduce the temperature at the LP compressor discharge (while maintaining the pressure) before piping it into the high-pressure (HP) compressor for further compression.
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Fig. 6-3: Cycle Diagram of the CVPS plants
The HP turbine provided the power to both the HP compressor, and through a speed reduction gear box, the AC generator. The air from the HP compressor discharged into twin regenerators. Installed in parallel to divide the airflow, the regenerators transferred heat from the turbine exhaust to the air from HP compressor discharge. This compressed and pre-heated air was then directed into the six combustors where fuel was burned adding additional heat.
Fig. 6-4: The late Norton Mark Cobb, CVPS Superintendent of Gas Turbines, kneels to take readings next to a “Kilowatt Machine” (circa 1951)
CVPS would start a plant on #2 diesel oil and later transfer to the heavier Bunker “C” fuel. The ultra-hot combustion gas, firing at 1500 degrees Fahrenheit when at base load, was then expanded through the two sections of the turbine. Approximately two-thirds of the power
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developed was needed to drive the two compressors. The remaining one-third was used to develop electrical power. Finally, after transferring most of the heat to the air from the HP compressor through the regenerators, the gas was discharged the exhaust back into atmosphere. Even by today‟s standards, the gas turbine power plants installed by CVPS at the end of Greens Hill Lane in Rutland six decades ago would be considered advanced and sophisticated. The plants are now retired. According to the logbooks, the last of the three plants to be retired (Unit #1) ran its final time in 1987. I saw it run around that time. It had over 100,000 operating hours when mothballed and later sold for scrap. Note: GE was offered the units at museum prices but declined. A shame.
48 Specifications
Item Description
1 9-stage, axial-flow LP compressor, 7200 rpm (driven by LP turbine) 1 11-stage, axial-flow HP compressor, 8694 rpm, (driven by HP turbine),
variable inlet guide vanes (VIGV) 6 Combustors (liquid fuel)
1 2-stage LP turbine (7200 rpm when at 100% rated speed) 1 1-stage HP turbine (8694 rpm when at 100% rated speed) 1 Reduction gear (8694 rpm to 3600 rpm) driven by HP turbine 1 5000 KW generator, 6250 KVA, .8 power factor, 3-phase, 60 cycle,
3600 rpm driven by HP turbine 2 Regenerators (connected in parallel) 2 Intercoolers (connected in parallel)
2 Starting motors for both for LP and HP compressor
Fig. 6-6: The late Ira “Chick” Evens of CVPS measures compressor blades during an inspection in 1951.
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Fig. 6-7: Basic Control and Protection System for the “Kilowatt Machines”
General Electric sold many regenerative cycle plants over the years, mostly to gas pipelines and process plants where the load device was a compressor rather than a generator. The main advantage of regeneration was to reduce fuel consumption (resulting in a lower heat rate) for plants that operated continuously for thousands of hours per year, as was often true in the industrial market. In the power generation field, however, this cycle lost its popularity, primarily due to the high repair costs associated with the regenerators. Regenerators that are started and stopped frequently can experience tube cracking that can be costly to keep in good operating condition. Inter-cooled gas turbines, on the other hand, became even less popular probably because GE was able to manufacture more efficient axial-flow compressors with more stages. Typical GE compressors today have 17 or 18 stages with discharge pressures exceeding 175 pounds per square inch (psig).
Long before waxed hickory boards with bear trap bindings helped put Rutland, Vermont on the map for skiing at nearby Killington, this city was truly a proving ground for a new means of electrical power production. The three old “Kilowatt Machines” are gone now from the building at the end of Green Hills Lane, but their contribution to the application and development of gas turbine technology should never be forgotten.
Tags: Blackout, Central Vermont Public Service, Combustion, Compression, CVPS, Gas turbine generators, gas turbines, Great Northeast Blackout, inter-cooled, Kilowatt Machine, regenerative cycle, Rutland, Schenectady
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