The is a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

on the

Tenryū River The is a river in central Honshū, Japan. With a length of , it is Japan's ninth longest river. Its source is Lake Suwa in the Kiso Mountains near Okaya in Nagano Prefecture. It then flows through Aichi Prefecture and western Shizuoka Prefect ...

, located on the border of Toyone, Kitashitara District, Aichi Prefecture on the island of Honshū, Japan. It is one of the tallest dams in Japan and supports a 350 MW hydroelectric

power station A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...

. Nearby a frequency converter station is installed, allowing interchange of power between Japan's 50 Hz and 60 Hz AC networks.

History

The potential of the Tenryū River valley for hydroelectric power development was realized by the

Meiji government The was the government that was formed by politicians of the Satsuma Domain and Chōshū Domain in the 1860s. The Meiji government was the early government of the Empire of Japan. Politicians of the Meiji government were known as the Meiji o ...

at the start of the 20th century. The Tenryū River was characterized by a high volume of flow and a fast current. Its mountainous upper reaches and tributaries were areas of steep valleys and abundant rainfall, and were sparsely populated. However, the bulk of investment in hydroelectric power generation in the region was centered on the

Ōi River The is a river in Shizuoka Prefecture, Japan. Geography The Ōi River flows from the Akaishi Mountains, the branch of the Japanese Southern Alps which form the border between Shizuoka, Nagano and Yamanashi prefectures. These mountains, with p ...

, and it was not until the Taishō period that development began on the Tenryū River. Private entrepreneur Fukuzawa Momosuke founded the , which later became before it was nationalized into the pre-war government monopoly in 1938. The first dam on the main stream of the Tenryu River, the Yasuoka Dam was completed in 1935. This was followed by the Iwakura Dam in 1938. The Hiraoka Dam was started in 1938, but not completed until 1951 due to the start of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. After the end of World War II, the American occupation authorities ordered the dissolution of Nippon Hassoden, which was divided into regional power companies. Central Japan came under

Chubu Electric Power , abbreviated as Chuden in Japanese, is a Japanese electric utilities provider for the middle Chūbu region of the Honshu island of Japan. It provides electricity at 60 Hz, though an area of Nagano Prefecture uses 50 Hz. Chubu Electric ...

, which inherited the various dams and projects on the Tenryū River, all of which were located in Nagano Prefecture. To tap into the hydroelectric potential of the river in Shizuoka Prefecture, the government turned to the

Electric Power Development Company The , operating under the brand name J-POWER, formerly , is an electric utility in Japan. It mainly produces electricity from coal and hydroelectric power stations. It also has a few wind farms and is currently building a nuclear plant in Ohma ...

. The new company, in part through foreign aid loans from the

United Nations The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmoniz ...

, began work on a new dam in 1952, based on plans which had begun as early as 1921. The main contractor for the project was Hazama Corporation, and construction was completed in 1956. Construction was facilitated by the steep V-shaped walls of the site, and its proximity to the

Iida Line The is a Japanese railway line connecting Toyohashi Station in Toyohashi, Aichi with Tatsuno Station in Tatsuno, Nagano, operated by Central Japan Railway Company (JR Central). The line links eastern Aichi Prefecture and southern Nagano Prefe ...

train (several stations of which had to be relocated once the reservoir began to fill. Construction also involved the relocation of 240 households with 296 families. The official opening ceremonies on October 28, 1957 were attended by

Emperor Hirohito Emperor , commonly known in English-speaking countries by his personal name , was the 124th emperor of Japan, ruling from 25 December 1926 until his death in 1989. Hirohito and his wife, Empress Kōjun, had two sons and five daughters; he was ...

and Empress Kojun and was the occasion for the issuance of a

commemorative postage stamp A commemorative stamp is a postage stamp, often issued on a significant date such as an anniversary, to honor or commemorate a place, event, person, or object. The ''subject'' of the commemorative stamp is usually spelled out in print, unlike de ...

Design

Sakuma Dam is a hollow-core concrete gravity dam with several central

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure th ...

s. It supplies water to both the Sakuma Hydroelectric Power Station and serves as the lower reservoir for the Shin-Toyone Hydroelectric Power Station, with a rated capacity of 350,000 kW and 1,200,000 kW respectively.

Surroundings

The Sakuma Dam Reservoir is a popular attraction for canoeing and camping, due to its proximity to downtown Hamamatsu and ease of access. The surrounding area is part of the Tenryū-Okumikawa Quasi-National Park.

HVDC frequency converter

The western part of Japan uses 60 Hz and the eastern part uses 50 Hz as power grid frequency. In 1965 an HVDC back-to-back station was installed in the city about 1 kilometre south of the power plant (). It was rated 300 MW with an operating voltage of ±125 kV. The converter station is connected to the 275 kV 50 Hz grid and the 275 kV level of the 60 Hz grid. Initially the converter used mercury arc valves manufactured by

ASEA ''Allmänna Svenska Elektriska Aktiebolaget'' (English translation: General Swedish Electrical Limited Company; Swedish abbreviation: ASEA) was a Swedish industrial company. History ASEA was founded in 1883 by Ludvig Fredholm in Västerås a ...

. In 1993 it was converted to use light triggered

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...

s, which were installed in the same valve hall that had contained the mercury arc valves. Each inverter consists of two series-connected six pulse inverters forming a twelve pulse inverter. As in many other HVDC facilities, quadrivalves (serial connections of four valves forming a unit) are used. Each valve consists of 7 series-connected thyristors designed for a current of 2,500 A and a blocking voltage of 6 kV. Each of the two inverters uses 84 thyristors. The station has three transformers on the 60 Hz side. One transformer is the power supply of the station, and two 275 kV/55 kV transformers feed the valves. The transformers have their low-voltage windings connected one in a delta and other in a wye. All these transformers share a common tank. On the 50 Hz side, two 275/54 kV transformers, in separate tanks, feed the valves, again with one in delta and the other in star connection of the low-voltage windings. The DC smoothing reactor has an inductance of 0.12 H and is designed for a current of 2,400 A. On each side filters for the 5th, 7th, 11th and 13th harmonic exist, which consist of a series connection of a capacitor, an inductor and a resistor. In addition, a high pass filter is used, which consists of a capacitor switched in series with a coil to which a resistor is switched in parallel.

References

*Japan Commission on Large Dams. ''Dams in Japan: Past, Present and Future''. CRC Press (2009).
Sacuma HVDC-back-to-back station

Sacuma HVDC-back-to-back station scheme
{{Dams in Aichi Prefecture Converter stations Gravity dams Dams in Shizuoka Prefecture Hydroelectric power stations in Japan Dams in Aichi Prefecture Dams completed in 1957 Energy infrastructure completed in 1957