|
Geographic Location The main objective is to avoid schedule and daily variations of the river Limay flow originated by the fluctuations in the production of energy at El Chocón Plant, which is aim at satisfying the peaks in demand of the Argentine Interconnection System (SADI). The variations in flow caused by this plant are weekly compensated in Arroyito by regulating the discharges downstream, complying with the regulations for Water Use stated in the Concession Agreement.
Making use of the reservoir formation of weekly regulation, the Hydroelectric Power Plant of base was built at the dam toe, dam of fill materials. It has an installed capacity of 120.000 KW and a functional waste weir placed next to the plant. Reservoir The Arroyito reservoir is located immediately downstream from El Chocón and its characteristics can be described as follows:
Maximum Height above see lever 316.5 m
Surface 42.3 KM2
Total Volume 361 HM3
Variation of Level 5.35 m
Maximum Length 27 KM
Maximum Width 3.8 KM
Maximum Depth 16 m
Medium Depth 7.8 m
Coast Length 72 KM The first section of the reservoir, downstream from El Chocón Plant, has an approximate width of 1.2 KM and shows in general ravines of medium height -10 to 20 m- reaching in some sections 50 m. After turning a curve and shaping the form of the old river valley, the reservoir becomes wider until it reaches its overall width in the proximities of the Arroyito dam. The left margin mantains high ravines while the right margin present beach characteristics. Dam The Arroyito Dam is an embankment of about 3500m long, formed by a homogeneous and permeable section of sandy gravel. The left dam support is formed by sedimentary rocks (clay and sandstone) which are found at the side of the Limay river, while the support on the right is formed by natural sand and gravel of the river-bed until reaching crest level. The crest elevation is of 319.00 m above see level. The medium height of the dam, measured from its foundation, is of 13 m and the maximum of 26 m. The width of crest varies between 6 and 10 m according to the purpose of the road. The talus upstream is protected with a breakwater or balsatic rip-rap mantel from the erosive action of the waves, while the talus downstream is protected from the rain and wind erosion by a layer of selected granular material. The control of the embankment, foundation and abutment performance is conducted through different control instruments. It is fundamental to determine the volume of dam leakage measured by six (6) gagers at the dam toe. Spillway Placed adjacent to the plant, the structure of the spillway is formed by a block of monolitic base on which are erected the piles that constitute seven (7) vanes of 12.50 m each. Their discharge is regulated by means of radial sluices of 7.40 m height. The spillway profil corresponds to a Creager. The surfice among the vanes is curved and it adapts to the geometry of the falling crest and continues into a stilling pool of 30 m long provided with fourteen (14) energy disperser blocks. At the end of it starts the wasteway coated with concrete slab against erosion on its first 27 m. The hydromechanic equipment is composed by seven (7) radial sluices operated by an oleohydraulic system, four (4) maintenance cofferdams, a clamping beam and a gantry crane of 25tn. Hydroelectric Power Plant It is composed by four independent modules. In three of them were installed the groups of generators of 42.660 KW each. The fourth is used as sevice unit or dumping yard, assembly and maintenance.
Hydraulic design is typical of plants of low head hydroelectric station, intake and spiral casing integrated to the plant, without conductor pipeline, all in concrete. The soleplate of the suction pipe continues downstream into an upslope concrete slab until reaching the soleplate elevation level of the salvage drain. The structure is erected on sedimentary rocks. Downstream from the machinery room, at the same level and in the open are placed the head transformers, one per group and the outlet portals of tension lines of 132 KV which supply energy to the Comahue region. The gallery of mechanical service, the gallery of electrical service and the pannel and battery galleries are located there as well. In the extreme north, downstream of the service unit, there is the supervision room from where the local operation of the plant is conducted, through an informatic system headed by two computers of redundant configuration. The regular and standard operation is done by telecommand from El Chocón Plant. They were used 150.000 m3 of concrete and 8.000 t of steel during the construction of the intake work and of the plant Turbine The hydraulic plant is equipped with three turbines of 61.623 CV of nominal power each and with a nominal head of 16.85 m. The turbines are of Kaplan type of vertical shaft and rotate at 90.9 rpm clockwise. They also have two (2) bearings, an upper bearing of thrust and guide combined and a lower guide bearing located in the neck of the turbine and next to the turbine spiral casing. The emergency sluices of the turbine (two per each unit) is located in the suction pipe which enables the use of the machines as bottom dischargers and allowing for the control of the water flow accordint to the different percentages of opening. Under this condition, with the turbine rotating at a speed near nominal, the water discharge becomes effective through the turbine, dissipating all its energy at the emergency sluice (partial opening) the generator unit is disconnected from the net. The generators integrated to the turbines are of projecting pole type and their generation tension is of 13.8 KV. This tension is raised to 132 KV by the head transformers. These transformers are linked to the Sectioning and Maneuvers Station of 132 KV through an aerial line per each group.
|
