Congestion in the transmission network prevents execution of the desired market transactions. This results in some of the market transactions having to be curtailed, which translates into a loss to customers. This paper suggests that the decision to expand transmission facilities will depend on the loss sustained by the customer due to curtailment of market transactions vs. cost of installing new transmission facilities over a planning period. Thus, in a power system, the sum total cost of investment to expand transmission facilities and cost of cumulative loss due to curtailment of transactions to all the customers is set up as a minimization problem, which results in optimal transmission expansion needed over a planning period. With this consideration, the Benders decomposition technique is used for transmission expansion planning by taking investment cost as the master problem and loss due to curtailment of market transactions as the slave problem. The Southern Brazil power system is used as a test case where this methodology has been employed.
In the past a single utility owned generation, transmission and distribution of electric power. Thus, traditionally, the objective of the utility's centralized transmission expansion planning was to make decisions on addition of new facilities in an economical way such that the transmission network supported the load requirements of the system. The operating philosophy of the utility would either be to minimize the total system production cost [1] or to minimize the system-wide load curtailment [2], [3], [4], [5] and [6].
The deregulated electricity market has created a new structure in transmission management and system operation criteria. Accordingly, new transmission planning techniques have evolved to suit the new transmission management and operating criteria. Several transmission expansion schemes have been proposed for deregulated markets. Two transmission management structures exist in the deregulated market, namely: centralized transmission planning, where system planning and operation is done by a single company as in England; or, decentralized transmission planning where competitive transmission services are encouraged as in Australia. Transmission planning under each of these management structures was compared in [7]. Under the centralized transmission planning framework the operating philosophy would be system-wide social welfare maximization problem [7], [8] and [9]. Under the decentralized transmission planning framework the objective would be to maximize the profits of the network investors [7] and [10].
Game theory application [11], uncertainty in the availability of data [12], probabilistic criteria and reliability [13], environmental factors [14] and trading of electricity [7], [8] and [9] are modeled in transmission expansion planning studies. Trading of electricity is usually modeled as generators and customers submitting the bids to the pool market and decisions to expand the transmission system would be based on the market clearing mechanism of the bids. This method needs detailed expected hourly bids from the market participants.
Trading of electricity can be in the medium- to long-term bilateral contracts or in the hourly spot market. The desired set of market transactions are the expected bilateral and spot market transactions of the participants. In this paper, the congestion in the transmission network that prevents the execution of the desired market transactions is taken as the driving signal for expanding the transmission network. Data required for this formulation is relatively easy to obtain. It does not require hourly bid data of generators and customers in the spot market. It only requires generators and customers percentage participation in the bilateral and spot markets.
Several mathematical and heuristic methods such as Linear programming [15], Nonlinear programming [16], Simulated Annealing [17], Genetic Algorithm [18], Tabu search [19], Dynamic Programming [20], Branch and Bound [21], Expert Systems [22], Fuzzy Set Theory[23], Benders decomposition [2], [3], [4], [5], [6], [7], [8], [9], [10] and [24] were applied to determine the optimal transmission expansion schedule. In this paper, Benders decomposition is used to solve the proposed transmission expansion planning problem. Investment costs are taken as the master problem and “loss due to curtailment of market transactions” is taken as the operational cost which forms the slave problem. The paper is organized as follows: energy trading model and the mathematical formulation for trading electricity are described in Section 2 and 3. Benders decomposition based transmission expansion planning algorithm is described in Section 4. The proposed framework is applied to the Southern Brazil power system, the test results of which are presented in Section 5, followed by conclusions in Section 6, Appendix and References.
A Benders decomposition based transmission expansion planning formulation with an objective to minimize the curtailment of market transactions is proposed in this paper. The proposed method is analyzed on a Southern Brazil power system. In the spot market any generating unit can serve the load hence cheaper transmission line additions can be considered. Bilateral contracts exist between a specific Genco and customer so the choice of transmission line additions are limited and may result in more investment costs. The investment costs may further increase if more reserves are to be considered than curtailments.
