Report on technical feasibility of underground pumped hydroelectric storage in a marble quarry site in the Northeast United States [report]

1982 unpublished
Pacific Northwest Laboratory Richland, Washington 99352 :PNL-4248 UC-94e r FOREWORD Underground pumped hydroelectric storage (UPH) is a technique for supplying electric power to meet peak load requirements of electric utility systems. Using low-cost power from base load plants during off-peak periods, pumps raise water to a surface pond from an underground reservoir, a mined out space in competent hard rock. During subsequent peak load periods, the surface pond water drops to the lower
more » ... through turbines to generate peak power. This relatively new adaption of pumped storage technology offers significant potential for reducing costs and improving efficiency of electric peak power generation, as well as reducing utility petroleum fuel consumption. Based on these potential benefits, the U.S. Department of Energy's (DOE) Electric Energy Systems Division sponsors programs and projects to accelerate commercialization of UPHS technology. The Pacific Northwest Laboratory (PNL) is the designated lead laboratory role for the UPH activities, but many other laboratories and contractors have been involved. DOE and the Electric Power Research Institute (EPRI) recently completed a major design study on UPHS, published as EPRI EM-1589, and there are major pump turbine development programs underway throughout industry for the high head application of the concept. An important element of DOE's effort is to promote commercialization of UPH technology through the transfer of research results and experience to interested utilities. Toward this end Chas. T. Main of Boston, Massachusetts, a previous contributor to UPH development, was selected to perform a preliminary study aimed at examining UPH feasibility on the Northeast Power Pool. Conducted for the Central Vermont Public Service Corporation, a member utility actively planning a UPH facility in the U.S., the study resulted in this report. iii • , EXECUTIVE SUMMARY The marble quarries at West Rutland have been mined for architectural and monumental stone since 1807. With' the market for such products diminished in recent years, production essentially ceased in 1972. Consequently the present owners are attempting to develop the site for other uses, among them oil storage and as a hydro-electric pumped storage site. The unique feature of using the marble quarries as a site for a hydro-electric pumped storage plant is that a substantial amount of the excavated material from construction of the project has' some commercial value in the production of ground products as fillers for paints, toothpaste and other items. Sale of the excavated material would therefore affect the total capital cost of the project and make it a more attractive investment. Although construction of a conventional pumped storage scheme was originally investigated, using the existing quarries for the lower reservoir, economy of scale and recent technological advancement in the development of very high head pump-turbines suggest that an underground pumped storage facility could prove feasible especially if some of the excavated material from construction could be sold. As a result, this report has been directed to examining the technical and economic aspects of construction of a very high head, underground hydro-electric pumped storage project at a prefeasibility level. The capacity of the project was selected to be consistent with the conventional pumped hydro-electric plant sizes currently under study by the New England System. Since this would be the third pumped storage plant on the system, this plant would be tentatively placed below the other two on the wider part of the load curve, depending on efficiency, and would operate for longer periods of time. For the purpose of this study, a capacity of 1200 MW and 12 hours of continuous operation at rated capacity were chosen. v Geology In an underground pumped storage facility, the complexities of stratigraphy and structure play an important role. Although more than a century has been spent on investigation of the general area by numerous geologists, individual interpretations of both structural deformation and stratigraphic sequences vary widely. The source study included a number of publications of the Vermont Geological Survey and communication with a number of geologists who have worked in the area but the most significant results to date appear to be the cores from the logs of one boring made at the site to a depth of 2422 feet. It appears that some marble of varying quality exists to an elevation just below about 1000 foot depth but it is questionable whether any of it has any value. Below that to the bottom of the hole, the rock is mostly schistose interspersed with various other minerals. Barring any unforseen circumstances however, it is judged that this material is strong enough to support the excavations contemplated for the project. With the total amount of storage fixed at 12 hours or 14,400 MWh the head has direct influence on the amount of excavation required for the reservoir. As a consequence, the highest head pump-turbine expected to be available in the mid 1990's was used in evaluation of the project. At present this appears to be approximately 4000 feet. To accommodate the storage, the lower reservoir was designed as 25 parallel tunnels, oriented in an east-west direction 50 feet in diameter connected at the ends by transverse tunnels. Live storage capacity is about 6.7 million cubic yards or 4150 acre-feet. A vertical shaft on the west transverse tunnel is vented to the surface near route #4. Two configurations were studied for the upper reservoir, one at the top of Clark Hill to the southwest of the site and the second, enlargement and connection of the existing quarries. Since the excavated material at the lower reservoir depth appears to have little or no commercial value and yet must be disposed of in some way, Scheme 1 utilizes all of the excavated material in construction of an impounding dike at the top of the hill. vi • The second, by enlarging and extending the quarries into one reservoir, recognizes the value of some of the excavated material and utilizes the remainder in construction of a dike surrounding it. In this case, excavation from the lower reservoir must be spoiled in the swampy area adjacent to the Castleton River. The powerplant complex, consisting of the powerplant, transformer gallery, and the draft tube gate gallery, is located at the lower reservoir level. It is connected to the surface by several service shafts and the intake shaft, manifold, and penstocks carrying water to and from the upper reservoir. The pump turbines are connected to the lower reservoir by means of the draft tube tunnels and the draft tube collector tunnel which intersects the east transverse tunnel. The powerplant cavern contains the four vertical shaft two stage reversible pump turbines, each capable of producing 415,000 H.P. at 720 R.P.M. Each is directly connected to a vertical shaft generator-motor capable of producing 300 MW at .9 power factor with a maximum of 60° Crise. Electrical and mechanical equipment necessary to the operation of each unit is arranged in galleries on the upstream side of the units. Those appurtenances common to the operation of the total plant are arranged on floors under the erection bay. An erection and service bay is provided at the end of the unit blocks for erection and service of the rotor and major turbine parts. A 250 ton bridge crane for handling major equipment and a 25 ton bridge crane for handling equipment of lesser weight are provided in the powerplant cavern. The transformer gallery is located directly above the powerplant cavern and connected to it by a series of adits and shafts to contain the low voltage bus ~onnection to the transformers. Because of weight limitations in the heavy hoist shaft, single phase transformers were selected for this project. Output from two units is fed to one bank of three single phase transformers. vii Two banks of single phase transformers are arranged in the transformer gallery, each separated by concrete firewalls with a common transfer way on the downstream side. Isolation walls adjacent to the transformer are designed to contain transformer fires which could occur. C02 fire protection is provided for each transformer and an isolated exhaust system provided as well.
doi:10.2172/5273227 fatcat:fours62dzjfjljyjl5sfzrb4ky