The 32.4-MW Vernon project began operating on the Connecticut River between Vermont and New Hampshire in 1909, to provide electricity to load centers in Massachusetts. A recent upgrade increased capacity of this historic plant and equipped it to operate for decades to come.
The 32.4-MW Vernon hydroelectric project is celebrating its centennial of operation in 2009. This project, which spans the Connecticut River between Vermont and New Hampshire, was built 100 years ago to provide electricity to meet growing demand in manufacturing centers in Massachusetts. To ensure the plant continues operating successfully into the future, perhaps for another 100 years, owner TransCanada conducted extensive rehabilitation and upgrading at the project. This work, completed in 2008, included upgrading four of the original 100-year old units at the plant to increase annual generation by more than 40 percent.
Planning to develop Vernon
The story of the Vernon project development begins in 1903. That year, the Massachusetts legislature recognized the need for alternative forms of energy to supplant expensive coal-based steam generation. This generation was needed to keep pace with ever-growing demand in manufacturing centers throughout the state. The state legislature passed a law allowing special permits for a new breed of utility companies that could sell electricity directly to bulk customers. In 1903, as a result of this legislation, Malcom Chace from Rhode Island and Henry I. Harriman from Taunton, Mass., formed the Chace & Harriman Company. The company's sole purpose was to develop remote hydroelectric generating facilities in northern New England that would deliver electricity via long-distance transmission lines to industrial customers in Massachusetts.
For five years, from 1903 to 1907, seven businessmen from Brattleboro, Vt., worked to convince the New Hampshire and Vermont legislatures to grant respective charters allowing water to be drawn from the Connecticut River and used to power a hydroelectric facility. This group came to be known as the Seven Original Incorporators. The charters were granted in 1907.
That year, the Seven Original Incorporators met with Harriman and Jeremiah Smith Jr., who was representing Chace, on a small island in the Connecticut River to launch construction of the Vernon project.
Design and construction of the facility
A fledgling engineering company, Charles T. Main Inc. of Boston, was chosen to design the Vernon project.
Overall, the Vernon project would create a 2,550-acre reservoir with a drainage area of 6,266 square miles. The project would raise the river 30 feet and flood more than 150 farms up to 28 miles upstream. The dam was a reinforced concrete gravity structure with an integral powerhouse on the western end. The concrete dam was to be tied to a solid bedrock foundation. This was a departure from the typical rock-filled timber dams that were common throughout New England.
Site preparations began in May 1907 with construction of a massive cofferdam. Later that year, a flaw developed in part of an underwater ledge of the bedrock foundation. Construction was delayed while the river bed was removed to a depth of 70 feet to reach a solid footing in that section. Then, in October 2007, the worst flood in 40 years swept through the site, taking with it structures, tools, and equipment. However, the cofferdam withstood the flood and construction resumed a week later.
When it was completed in 1909, the dam was 956 feet long, with a maximum height of 58 feet. The dam featured a 600-foot-long ogee spillway with a sluiceway to accommodate log drives. The concrete spillway section also contained ten 9-foot-wide by 7-foot-tall submerged floodgates operated by oil pressure cylinders accessible via a 250-foot-long tunnel within the concrete structure. The powerhouse was 216 feet in length and was constructed in a Renaissance Revival style with rows of floor-to-ceiling arched windows illuminating and ventilating the generator gallery. Reportedly, the dam and powerhouse contain more than 42,000 cubic yards of concrete. The construction of the Vernon facility required 450 men and cost about $1.5 million at the time.
Perhaps the most significant feature of the Vernon project was the use of vertical triple-runner technology for the eight 2-MW turbine-generator units. Horizontal turbine-generators were the norm in those days, as most generators were designed for that configuration. In addition, a reliable, maintenance-free vertical thrust bearing had not been developed. In 1905, designers of a hydroelectric plant in Sault Ste. Marie, Mich., used the first vertical-shaft, direct-connected turbine-generator units in its design. This application likely influenced the use of this "modern" technology at Vernon.
When it was completed in 1909, the Vernon hydro facility had a capacity of 16 MW and was the first plant in the northeastern U.S. to supply electricity across state lines.
Thus, all eight units incorporated 2-MW General Electric vertical shaft generators directly connected to triple-runner S. Morgan Smith waterwheels on a single shaft in an open flume (no scroll case). The lower two runners were 60 inches in diameter and were in a back-to-back configuration. These runners were used during normal water conditions. Under high flow conditions, the upper 57-inch-diameter wheel was operated. Lombard governors controlled the lower 60-inch turbines, while the upper turbine was controlled by a hand wheel.
Step-up transformers at the plant raised the voltage of the electricity produced to 66 kilovolts. Electricity traveled as far away as 60 miles, to the manufacturing centers in Gardner and Fitchburg, Mass. This was the first plant in the Northeast to transmit electricity across state lines, and it became the cornerstone of the modern interconnected transmission system in New England.
Operation through the years
The Vernon project began producing electricity on July 27, 1909. At that time, it supplied the Estey Organ Works in Brattleboro. By 1910, all eight units were operating, providing a total capacity of 16 MW and supplying electricity to load centers in Massachusetts.
The original eight units installed at the Vernon plant featured vertical-shaft triple-runner waterwheels.
By 1914, Chace & Harriman and its various associated companies, including the New England Power Company, became organized under the New England Company. From 1920 to 1925, the New England Company made significant improvements to Vernon. World War I caused energy consumption and coal prices to increase rapidly. In response to this opportunity and the call for additional energy, the New England Company initiated the so-called "White Coal Project." This project consisted of work on three hydro projects in Vermont, including an 8-MW expansion of Vernon.
This expansion, accomplished in 1920, involved adding two 4-MW vertical turbine-generator units to the project. This work required adding 112 feet to the length of the powerhouse on the Vermont end of the powerhouse. Unlike the original eight units, Units 9 and 10 consisted of two vertical-shaft generators directly connected to Francis-type single-runner turbines. General Electric supplied the generators, S. Morgan Smith the turbines, and Lombard the governors. These turbines were set in a concrete scroll case with a modern draft tube tailrace.
Between 1921 and 1922, Units 5 through 8 were upgraded with new waterwheels and wheel cases to improve efficiency. Chace & Harriman maintained the triple-runner configuration of these units. Then, between 1923 and 1925, Units 1 through 4 were completely replaced with single-runner turbines surrounded by a cast concrete scroll case. During the upgrade work, Units 1 through 8 were outfitted with oil pressure Gibbs-type vertical thrust bearings. High-voltage electrical switchgear and bus structures originally located inside the powerhouse also were relocated to various structures outside the building as additional transmission lines from Vernon were constructed.
For the better part of 60 years after these upgrades, Vernon remained in this configuration. The 1980s brought changes to the structural nature of the facility. Federal Energy Regulatory Commission (FERC) licensing proceedings, completed in 1979, mandated installation of an upstream fish ladder to pass Atlantic salmon and American shad. This fish ladder, completed in May 1981, was the first in Vermont on the Connecticut River.
In addition, New England Power Company rebuilt the spillway portion of the dam, adding crest control and a vehicular bridge deck to the structure. A total of six tainter gates, two bays of hydraulic flashboards, and three sections of stanchion flashboards were added. The steel deck across the entire spillway structure to the New Hampshire bank provided access to operate and maintain these improvements. Finally, in the early 1990s a large guidance louver and fish pipe was installed to facilitate downstream fish passage.
Starting around 1990, New England Power proposed to significantly increase the generating capacity at Vernon. However, for several reasons – including de-regulation of the wholesale energy industry in New England, an over-supply in capacity, and the divestiture of New England Power's generating assets to USGen New England Inc. – this upgrade was never started.
Then, in May 2005, TransCanada acquired the six former New England Power hydro facilities from USGen New England. TransCanada immediately began to re-examine the Vernon upgrade project. In the 1990s, Units 5 and 8 had been officially decommissioned due to mechanical failures. In addition, Units 6 and 7 were in "emergency run only" status, primarily because of repeated equipment problems and maintenance challenges related to confined space. However, hydroelectric generation was appearing to become an increasingly important source of renewable energy, both politically and from a market perspective. Rather than maximizing capacity, it now made more sense to maximize generation without changing operation of the project in terms of reservoir fluctuation or flow.
In late February 2006, TransCanada filed a license amendment with FERC to reduce the previously approved 44.4 MW of capacity to 32.4 MW. Instead of installing two 14-MW units to replace Units 5 through 8, TransCanada proposed to replace these four units with 4-MW axial-flow Kaplan type turbine-generators using the same basic footprint in the powerhouse. FERC approved the application within six months, and within another three months construction was authorized to commence.
This upgrade project began in 2006 with dismantling and removing the old units. TransCanada personnel and workers with general contractor Gerace Construction used tools and cutting torches and the original station crane to accomplish this task.
As a result of a recent upgrade project, the Vernon powerhouse now has a capacity of 32.4 MW and is poised to continue generating electricity for decades to come.
Once the old equipment was dismantled and removed, the silt had to be mined out of the base of the powerhouse. Because of difficult access conditions, much of the silt was removed using hand shovels. After extensive testing to ensure there was no contamination, the silt was taken to an authorized disposal site on company land.
The most difficult aspect of the upgrade project was the need to maintain powerhouse stability while removing large portions of concrete to accommodate the new units. This required a precise and repetitive sequence of removing specific sections of concrete and placing new concrete before moving on to the next structural portion.
Although the footprint of the new units basically would match that of the original units, the similarities ended there. The new units required flow to enter the powerhouse horizontally, then turn 90 degrees downward and drop vertically through a ring of guide veins located directly above the variable-pitch axial-flow Kaplan-type runner supplied by Litostroj. Bedrock was removed at the base of each unit alignment to accommodate a new, deeper concrete draft tube. In addition to modifying each unit's supporting powerhouse superstructure, an access shaft to the base of the powerhouse was constructed between Units 6 and 7. Using the station crane, each runner would be lower or removed for future maintenance onto a rail-mounted carriage and rolled to each turbine pit for assembly. In addition to the upgraded units themselves, the original powerhouse crane, head gates, and draft tube gates were replaced.
By May 2008, the upgrade project was completed and all four new units were operating. As a result of this $55 million investment, Vernon's future average annual energy production is expected to increase more than 41 percent, or about 56,000 megawatt-hours. This incremental energy will earn Internal Revenue Service production tax credits of about $500,000 a year for ten years. Additionally, in June 2009 the Vernon facility was certified by the Low Impact Hydropower Institute. This certification will enable incremental energy produced at this plant to qualify as renewable energy credits in state programs that require a renewable portfolio standard to be met.
Celebrating a centennial
The Unit 5 through 8 upgrade coincides with Vernon's centennial. Many changes have been made over the past 100 years to upgrade and modernize the plant; improve environmental effects; manage flow; and improve worker, public, and dam safety. But the primary purpose of the plant remains. Just as it developers envisioned, Vernon will continue to serve and provide a clean renewable alternative to other energy sources in New England for decades to come.
John Ragonese is FERC license manager for TransCanada. He is responsible for all Federal Energy Regulatory Commission licensing and compliance requirements for TransCanada's hydro facilities in the U.S., including those associated with the amendment for the 32.4-MW Vernon project that enabled the recent upgrade.