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Geographic Location The Hydroelectric Complex which holds El Chocón and Arroyito Hydroelectric Power Plants, is located in the region known as Comahue, which is formed by the Argentine provinces of Río Negro and Neuquén and the southern area of the Buenos Aires and La Pampa provinces. El Chocón is on the Limay River at about 80km upstream of its confluence with the Neuquén River.
General Characteristics of the construction works El Chocón consists of a Hydroelectric Power Plant, a dam of granular material and a water-proof core, a Spillway of four (4) radial sluices, an intake work and forced pipeline. The electricity is produced by six (6) generators of 200.000 KW each, with an overall maximum evacuation capacity of 2.400 m3/s. The annual average generation of proyect is of 3.350 millon Kwh. Reservoir The reservoir covers a surface of the valley of the Limay River of approximately 830 km2 and contains a gross volume of water of 20.000 Hm3. The total length of the reservoir is of 68 km and the overall width is of 20 km, the maximum depth is of 64 m, the medium depth is of 24 m and the coast length is of approximately 565 km. The seasonal variation of the reservoir level is of 3.5 to 4m. The grounds of the reservoir consist of aluvial deposit, which come from the bed of the Limay and from the aluvial deposit of the ancient terraces of the plateau. The modern alluvions are formed by round pebble of 5 and 10m thick. The alluvions of the plateau occasionally show a consolidation resulting from calcareous outcrops. Dam The dam is an embankment of gravel with a clay core and transition areas with filters. It has a crest length of 2.250 m and a maximun height over foundation of 87m, in the section of riverbed that covers 900m long. Most of the remaining length is on the left margin of the river where the dam has an overall height of 40 m. The right abutment is the highest and is here where the reservoir is placed. The core, centrally located, is erected on rock and most of its height is slanted downstream. The talus located upstream of the reservoir is protected from the erosive action of the waves with a mantle of valsaltic rip-rap. Spillway It is located on the right margin of the river and consists of a hood inlet, wing walls, a fast monitoring structure and a terminal structure of dissipation. The monitoring structure consists of four (4) vanes with radial sluices whose lights are covered with a bridge at the crest which is part of the path alongside the dam. Inside the monitoring structure a gallery has been built, the access to it starts at berm of elevation 356. The maximum evacuation capacity is of 8000 m3/s, and is conducted through four (4) radial sluices of 15.5m high, 16.5m wide and 80 t of weight. They are operated by motoreducer chains that activate a system of electrical axis. A protection consisting of a breakwater and an important amount of concrete plaques has been built on the bed of the river, on the spillway discharge. Intake Work and Forced Pipeline The structure of the intake work was built mostly by reinforced concrete in situ, although it was used some premoulded elements such as girders and plaques of the protection wall upstream above level 363.50 and in the plaques of the upper section of the intake structure. The equipment for the operation and monitoring of the sluice gates is located in the gallery. The forced pipeline includes six (6) water inlets that communicate with the turbines through tunnels. Each of these inlet openings has bars and sluice gates model waggon, which act as emergency sluices. They are automatically operated in case of urgent mechanical problems in the turbogroups. The emergency sluices are linked to oleohydraulic servomotors geared by a control system that enables proper surveillance of the pipeline.
Hydroelectric Power Plant
It is located on the left margin of the river immediately downstream of the dam. It has six (6) groups of generators of an overall istalled capacity of 1.200.000 KW. The turbines are Francis type of vertical shaft. It has three (3) monophasic transformer groups, each one of 540.000 KVA. They raise the tension of generation from 16 KV to 500 KV which becomes the tension of the Energy Transmission System. The Plant building is built on sandstone and the foundations are of reinforced concrete including the turbines, entrance tennels and suction pipes. The distance among the turbogroups is of 28 m and the length of the superstructure is of 225m. The machinery room’s width between the innner faces of the portals is of 24.50 m. In the extremes north and south there are two big service units or dumping yards meant for the discharge, assembly and maintenance of the equipment within the operating areas of the overhead travelling cranes of the plant. The plant has seven (7) joints that separate the concrete block bases of the machines from each other and they also separate them from the areas of assembly at the extremes north and south. Upstream from the machinery room and in the open, there are three monophasic groups of head transformers and the outlet portals of the transmission lines of 500 KV that link the plant with the Argentine Interconnection System (SADI)
The machinery cooling and pannel galleries of 13.2 KV and of 0.380 KV are found Downstream from the machinery room. In the upper section, there are the Monitoring Room, properly equipped with the necessary instruments for the operation of the generation units of El Chocón Hydroelectric Power Plant, and the telecommand of the genaration units of the Arroyito Plant.
Turbines The Hydroelectric Power Plant is equipped with six (6) turbines of 278.000 CV of nominal power each, with a nominal liquid fall of 58.4 m. The water ciming from the intake work through the reinforced pipeline enters the spiral chamber of each machine. The turbines are of Francis type with a vertical shaft, they rotate at 88.3 rpm clockwise and have two (2) bearings, an upper bearing of thrust and guide placed under the generator and a lower bearing of guide near the turbine spiral casing. The suction pipe that completes the hydroaulic circuit of the turbine is protected from erosion with armour in its lower section next to the generator spiral casing. The generators linked to the turbines are of projecting poles type and generate at 16 KV. This tension is raised to 500 KV in the head transformers.
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