The Okukiyotsu Pumped Storage Power Station (Japanese:, Hepburn: Okukiyotsu Hatsudensho) No. 1 and No. 2 are two large pumped-storage hydroelectric power plants in Yuzawa, Minamiuonuma, Niigata Prefecture, Japan. With a combined installed capacity of 1,600 megawatts (2,100,000 hp),[1] the system is the third largest pumped-storage power station in Japan.
The facilities are run by Electric Power Development Company (J-Power).[1] Like most pumped-storage facilities, the power station uses two reservoirs, releasing and pumping as the demand rises and falls. Tashiro lake, formed by the Kassa Dam, is the upper artificial reservoir, while Futai Dam on the Kiyotsu river forms the lower reservoir.[2] Both dams are rockfill type dams, with a height of 90 m and 87 m, respectively.[3] The reservoirs were built between 1972 and 1978.
Okukiyotsu No. 1 is the first plant to be built on the site, and employs four 260 MW pump/generator units, for a total net capacity of 1000 MW.[4] The maximum water flow is 260 cubic meters per second. Construction on the plant started in 1972 and it became operational between 1978 and 1982.[1]
Okukiyotsu No. 2 is a later addition to the site. The plant is composed of two adjustable speed pump/generator units for a combined power capacity of 600 MW and a maximum water flow of 154 cubic meters per second.[4] Adjustable speed units allow for a rapid variation of power levels during both pumping and generation. These were the highest hydraulic head adjustable speed units in the world. Construction of the second plant started in 1992 and it became operational in 1996.[1] Both plants have an effective head of 470 m.[1]
Some of the interior of the second power plant can be visited by the public. The Okky Museum, managed by J-Power, also provides models of the station and explicatory panels and media.[2]
Serving the hydro power and dam construction industries since 1949
Prior to construction a six-year study of the plant was started in 1981. Analytical studies, experiments and computer simulations addressed potential problems within a saltwater environment and how they may affect civil structures, electrical equipment and environmental consid-erations. Work on the seawater pumped storage plant began in 1987, with con-struction getting under way in 1991.
The unique feature of this scheme is that it is actually a demonstration project which, since commissioning, has entered into a five-year period of testing. So far, the plant has been operating successfully with over 3500hr of generation and pumping in the first year. The main areas under examination are:
•Infiltration and dispersion of land-stored seawater.
•Seawater corrosion of power plant materials.
•Fouling by marine creatures.
•Operation of a pumped storage plant in various sea conditions.
The above subjects were categorised into those which can be dealt with by existing engineering methods, and those for which solutions will have to be provided by new technology. The object of the testing is to verify the application of the new technological solutions to a commercially sized plant through the design, construction and operation of a demonstration plant.
An example of the innovative solutions applied to the demonstration plant included addressing the problem of storing seawater in a land environment. Remedies included lining the entire surface of the reservoir with a synthetic rubber sheeting to prevent seawater infiltrating the surrounding land strata. In addition fibre reinforced plastic (FRP-M) pipes were used for the penstock which is subjected to a high pressure, high speed flow of seawater, while improved austenitic stainless steel was used for the pump turbine runners and guide vanes to prevent corrosion.
The plant has been in operation almost every day since March 1999 and provides electricity for the power system on Okinawa main island. Operation, inspection and monitoring of the plant during the first year (April 1999 to March 2000) were carried out as follows:
Demonstration operations and monitoring of the plant were carried out throughout the year.
•Maintenance and inspections:
Periodic inspection and maintenance were carried out on 14-30 June 1999, and on 19 January-14 February 2000. Routine inspections of electrical equipment took place once a week, and civil inspections twice a week.
•Environmental monitoring:
Land environment surveys were carried out twice a year. There was observation of plants (June, November-December), animals (June and September), birds (November) and noise levels (June and October).
•Seawater dispersion/infiltration survey: Water quality surveys were carried out regularly throughout the year while marine environment surveys were done in August and January.
•Meteorology/hydrograph monitoring:
Meteorology and hydro-graph observations were done throughout the year.
•Routine inspections during normal operations consist of equipment performance checks, performance checks of sensors and monitoring equipment, and analysis of the data collected by automated sensors and recorders.
•Periodical plant inspections will be performed twice a year during normal operating conditions. In addition detailed inspections will be performed in the second and fifth years of the demonstration plant''s life.
•Monitoring will be performed using various types of measuring instru-mentation. Environmental monitoring will be carried out annually to determine any environmental impacts of the plant.
•Operating results during typhoons will also be considered.
Infiltration and dispersion
Seawater infiltration and dispersion under normal operations are observed by daily monitoring and inspection. To prevent seawater infiltrating into the surrounding land strata, the entire reservoir surface is lined with rubber sheeting. Assessment of the impervious nature of the sheeting started when reservoir inundation began in August 1998. No water leakage has been detected within the upper reservoir for nearly two years, including the test inundation period. However, if seawater leakage does occur it will be detected and collected in the inspection gallery.
To observe the effect of ozone, ultraviolet rays and seawater on the rubber sheeting, test samples attached to the sheets are collected regularly and their physical changes observed.
No substantial change has been observed during routine inspections and at reservoir draining.
Seawater dispersion is regularly checked by measuring the salt content in the surrounding atmosphere, rainwater and soil. As Okinawa main island is surrounded by the sea the salt content is usually high. So far, there is no sign of an increase caused by the operation of the upper reservoir. To confirm the effect of seawater infiltration and dispersion the flora and fauna in the surrounding environment, and the water quality in nearby streams and ponds, are also being monitored. No substantial changes have been observed so far.
Periodic inspections were performed in June 1999 and January 2000. The pump-turbine was pulled out for the inspection. The level of the upper reservoir was reduced virtually to the low water level. The intake, penstock, discharge tunnel and tailrace were left full of water and could be inspected by divers.
Condition of civil structures
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