ارزیابی امکان سنجی تراکنش های همزمان دوجانبه و چندجانبه

The main aim in this paper is to develop algorithm for assessment of the feasibility of simultaneous bilateral and multilateral transactions and if they are not feasible then to find out the minimum amount of transacted power to be curtailed in order to make them feasible. This analysis will be a great help for the generations-loads pairs to decide whether to withdraw the unfeasible transaction completely or to make it feasible by reducing its size optimally. The proposed algorithm can also be used for determining the transfer capability and hence feasibility of a single bilateral transaction at a time. In addition to above algorithm an efficient, repeated Newton–Raphson power flow based algorithm is also developed to determine transfer capability and hence feasibility for single bilateral transaction. The results of the proposed algorithm have been compared with a method proposed by Hamoud in his paper [6]. In this paper, based on the proposed algorithm and with the extension of Hamoud’s method, different feasibility evaluation procedures for simultaneous bilateral and multilateral transactions are suggested, analyzed and applied.

All the transactions need to be evaluated ahead of their scheduling time to check their feasibility with regard to the system conditions at the time of scheduling. ISO would have to honor and execute only those proposed transactions as far as the system design and operating conditions permit. So before we go for cost analysis, it is important to analyze the feasibility of all proposed firm transactions for a particular transmission network under prevailing system constraints. Only after passing the feasibility test the proposed firm transactions are scheduled for dispatch. This analysis will be required not only by ISO, but also by the end users of the systems to make proper decisions regarding the generations and loads to be connected at different buses of the power system. A transaction is deemed to be feasible if it can be accommodated without violating any of the system operating constraints such as equipment ratings, transmission interface limits, voltage limits etc. The feasibility of a single bilateral transaction can easily be determined from the available transfer capability (ATC) of the network between the buses where a transaction power enters and leaves the network. ATC is a measure of the transfer capability remaining in the physical transmission network for future commercial activity over and above already committed uses [1]. Transfer capability evaluation is a very wide area of research. Extensive work has already been carried out in this direction and more research is in progress in this field in order to increase its accuracy considering various factors and margins [1], [2], [3] and [4]. The transfer capability has been defined in the literature [1], [5] and [6] in many ways depending upon the requirements and accuracy required for a particular analysis. It may be defined as amount of power, incremental above normal base power transfers that can be transferred over the transmission network, with all facility loading are within normal ratings and all voltages are within normal limits [5]. The literature survey [7] reveals that most of the work has been done related with determination of ATC. Ou and Singh [8] have presented a probabilistic based method to assess various factors and procedures to incorporate them into ATC. Christie et al. [9] have suggested power transfer distribution factor and line outage distribution factor for determination of transfer capability from one bus to another bus of the power system. But this method provided only the approximate results. The Information Technology applications for determination of ATC have also been given in some research papers [10]. Application software [11] is also available for ATC calculations. To render the ATC as a more realistic measure of transmission availability, a stochastic calculation of ATC has also been explained in the literature [12] and [13]. But most of calculation procedures reported in the literature for ATC will be useful for feasibility assessment of only bilateral transactions. But in this paper methods are proposed for feasibility assessment of simultaneous bilateral as well as simultaneous multilateral transactions. Available transfer capability is required to be posted on Open Access Same-time Information System (OASIS). The generation-load pair can make reservation for the bilateral transaction whose size should be less than ATC between the points where transaction power enters and leaves the system. After including one transaction in the system, ATC between all the buses changes and reevaluated. Same procedure is repeated for second transaction. Similarly all the feasible bilateral transactions are added to the system one by one. But this procedure cannot be applied directly to simultaneous bilateral and multilateral transactions. Because the transfer capability of a transaction in a group of simultaneous transactions will depend upon the order in which the transactions are considered to be added to the transmission network.

In this paper a new optimization based algorithm has been proposed for assessment of feasibility of simultaneous bilateral and multilateral wheeling transactions. The results are compared with the existing method. It has been observed that the proposed method is fair in assessment of feasibility. It is simple and efficient to apply even when there are large numbers of bilateral and multilateral transactions. This analysis provides the information that if all simultaneous transactions are not completely feasible, then how much minimum possible curtailment of size of the transactions has to be done in an optimal manner, in order to make them feasible. The proposed algorithm has also been applied to single bilateral transaction, simultaneous bilateral transactions, multilateral transaction as well as to a combination of simultaneous bilateral and multilateral transactions. This work is a useful contribution not only for Scheduling coordinators (SCs) for scheduling various firm transactions but also for independent power producers (IPPs), bulk load centers, gencos as well as for discos to plan transfer of power from one place to other in an optimal manner. This work will also be useful for power systems of those developing countries, which are not completely deregulated, but are moving towards deregulation.