One of the functions of the electricity sector operation planning is the coordination of the operation of reservoirs' system, minimizing the risks of thermal generation or supply deficits in interconnected systems. This coordination includes the use of part of reservoir capacity during the rainy season as waiting volumes to reduce damages caused by flooding in areas downstream from reservoirs. The maintenance of these volumes implies a reduction in energy availability and increased risk of relying on thermal generation or undergoing supply deficits in the future. Therefore, the contribution of the electricity sector for flood control is of conjuncture nature. Each year, the allocation of waiting volumes is based on Flood Prevention Studies where risks of future thermal generation and supply deficit are calculated using simulations of the operation of interconnected systems under different scenarios of waiting volume corresponding to given flood return periods (risk).
SPEC - System for Flood Prevention Studies: DIANA, CAEV and VESPOT
In order to support Flood Prevention Studies done within the scope of Yearly Operation Plans of the Brazilian Electricity Interconnected Systems , Cepel has developed several softwares that were incorporated in the SPEC System. The SPEC focuses on analysis of Multi-reservoir/ Multi-Flood-Control-points, considering intra-annual hydrologic variations, and includes the following modules:
• DIANA: It is a stochastic model for generation synthetic multivariate daily inflow scenarios. It has seven functions: ENSOCLAS, AUXAJUS, EPN, EEN, GEP, COMPARA and SIMRESC. ENSOCLAS considers the influence of the ENSO phenomenon (El Niño - Southern Oscillation) on the generation of synthetic scenarios; AUXAJUS performs automatic adjustment of the models parameters; EPN and EEN estimate model parameters; GEP generates the synthetic daily inflow scenarios; COMPARA performs statistical analysis on the daily flow scenarios generated by GEP; and SIMRESC is used when there are reservoirs without outflow control in the river basin.
• CAEV: The reservoir system is decomposed into partial systems (set of reservoirs upstream of a flood control point), for which an upper rule-curve is calculated for the whole rainy season (waiting volume curve). To calculate these curves we use the theory of controllability conditions, and uses only inflow scenarios generated by DIANA.
• VESPOT: The model spatially disaggregates the waiting volume curves of the partial systems, defining the waiting volume that must be allocated in each reservoir of the river basin. It uses a linear stochastic formulation. This module was structured to avoid imbalanced waiting volume allocations and exaggerated reservoir depletions that may compromise the system generation capacity. It uses Benders decomposition and network flow algorithms as solving techniques.
SPEC - System for Flood Prevention Studies
Software for Flood Control Operation: OPCHEN, OPCHEND and OPCHENS
Volume flexibility may be necessary during a flood. OPCHEN software is a Short-Term Planning tool used to help the weekly planning of the filling/emptying of waiting volumes defined in Flood Prevention Studies. The methodology is based on the solution of a linear programming problem, subject to the current hydrologic situation and to meeting at the end of the corresponding week a set of waiting volumes curves, in ascending order of flood risks. The outflow defined by hydrothermal coordination studies performed with the DECOMP program is considered in this model as the minimum outflow. The time horizon may be up to five weeks. OPCHEN software is also a tool used in studies to verify the possibility of relaxing waiting volume constraints during the final months of the rainy season, with the aim of increasing the probability of reaching the end of the rainy season with full reservoirs.
The OPCHENS software is based on the OPCHEN model, but its purpose is to carry out studies to statistically evaluate the operation of flood control rules and the degree of protection (risk) provided by the waiting volume curves calculated in the Flood Prevention Studies. These studies are performed through simulations of the weekly flood control operation during the whole rainy season using historical or synthetic inflow scenarios.
Set of envelops organized in ascending order by flood risks, considered as constraints in the LPP solved in OPCHEN
Similarly to the OPCHEN model for short term planning, the OPCHEND plans the filling/emptying of the system's waiting volumes for the next day by solving a linear programming problem similar to the one used in OPCHEN. Its operation horizon is up to 15 days and it considers travel time of water in river courses that connect power plants. Another difference is that daily programming also requires verification of the possibility of emergency situations. In these cases, necessary outflows to protect the hydropower plant must be programmed using Emergency Diagrams. The methodology of these diagrams is implemented in the OPCHEND software.
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