Okuyahagi Pumped Storage Power Station

Okuyahagi Pumped Storage Power Station
Okuyahagi Pumped Storage Power Station
Country	Japan
Location	Toyota, Aichi Prefecture; Ena, Gifu Prefecture
Coordinates	35°13′56.03″N 137°25′42.95″E / 35.2322306°N 137.4285972°E
Status	Operational
Operator(s)	Chubu Electric Power Company
Upper reservoir
Total capacity	9,900,000 m3 (8,000 acre⋅ft) (Kuroda Dam lake, effective)
Lower reservoir
Creates	80,000,000 m3 (65,000 acre⋅ft) (Yahagi Dam reservoir)
Power Station
Hydraulic head	Okuyahagi 1: 161 m (528 ft) ; Okuyahagi 2: 404 m (1,325 ft)
Pump-generators	3 x 116 MW reversible Francis turbines (Okuyahagi 1) ; 3 x 260 MW reversible Francis turbines (Okuyahagi 2) ; 2 x 31 MW Francis turbines (Yahagi 1) ; 1 x 32 MW Francis turbine (Yahagi 2)
Installed capacity	1,160 MW (1,560,000 hp)

The Okuyahagi Pumped Storage Power Station (Japanese: 奥矢作発電所, Hepburn: Okuyahagi Hatsudensho) is a group of large pumped-storage hydroelectric power plants and smaller conventional plants located in Toyota, Aichi Prefecture, and Ena, Gifu Prefecture, Japan. With a combined installed capacity of 1,160 megawatts (1,560,000 hp), it is among the largest pumped-storage power stations in Japan.

The facilities are run by the Chubu Electric Power Company. The station includes 4 distinct power plants. The first two power plants, Yahagi 1 and 2 are conventional power plants.^[1]^[2] The other two plants, Okuyahagi 1 and 2 are pumped-storage plants. Yahagi 1 uses water from the Yahagi Dam (矢作ダム)^[3] and has a capacity of 60 MW.^[4] Yahagi 2 uses water from the Second Yahagi Dam (矢作第二ダム),^[5] a smaller dam downstream of the main one, and has a capacity of 31.2 MW.

The pumped-storage station has an unconventional configuration, with three reservoirs at different heights.^[6] The lower reservoir is created by Yahagi Dam on the Yahagi river. The upper reservoir is the Kuroda Dam lake, an artificial lake created by the Kuroda Dam. A third reservoir, in between the two at an intermediate elevation is formed by the Tominaga Dam. The two Okuyahagi power stations work in tandem between the three reservoirs.^[6]^[7]^[8] This configuration was necessary because of the geological conditions in the area, with a fault that prevented the safe construction of a single connection between upper and lower reservoirs.^[6] Okuyahagi 1 is the upper power plant, operating between the upper and the intermediate reservoir using 3 units with a combined capacity of 323 MW.^[4] The first unit started operation in September 1980, while the second and third units became operational in February 1981. The Okuyahagi 2 is the lower power plant operating between the intermediate reservoir and the lower reservoir employing 3 units with a combined capacity of 780 MW.^[4] Okuyahagi 2 became operational together with the first plant, with the first unit online in September 1980 and the other 2 in February 1981.^[6] The two plants operate as a single power station.^[6] Both station have a maximum water flow rate of 234 cubic meter per second.^[6]