تخصیص هزینه های تلفات انتقال

An analysis of the performance of six major methods of loss allocation for generators and demands was conducted, based on pro-rata (two), on incremental factors (two), on proportional sharing (PS) (one), and on electric circuit theory (one). Using relatively simple examples which can easily be checked, the advantages and disadvantages of each were ascertained and the results confirmed using a larger sample system (IEEE-118). The discussion considers the location and size of generators and demands, as well as the merits of the location of these agents for each configuration based on an analysis of the effect of various network modifications. Furthermore, an application in the South-Southeastern Brazilian Systems is performed. Conclusions and recommendations are presented.

In the present economic environment, electric energy transmission companies must deal with significant changes, and various new challenges have arisen. One of these is the need to determine the optimal available transfer capacities, and another is the determination of the responsibility for energy loss in relation to generators and demands. This paper deals with the determination of the loss allocation for generators and demands starting with the most prominent methods in practical applications and the ones with higher future potentials. Since energy losses originate from the power injection in various buses and they are non-linear functions, the analysis of these phenomena should consider various options. The allocation of the cost of these losses certainly does not affect directly the functioning of the existing electrical systems, since the calculation of the costs is computed after the dispatch of the demand. However, the size and the location of generators and demands does influence these losses, some more than others. This piece of information can thus be a determining factor in the definition of the most adequate location for the insertion of new generators in a system, as well as in the decision regarding the expansion. Loss allocation methods are designed to evenly distribute the responsibility of transmission losses between generators and loads. Various factors must be considered for an equitable allocation, including the injection of power at each bus, the relative location of each bus in the transmission network, consistency of the power flow solution, stability in relation to alterations in network parameters, and effectiveness of calculation of financial incentives to individual generators and demands as a function of its relative location in the network and of its magnitude. The present paper was oriented towards presenting an analysis of the performance of the major methods used in the allocation of losses to generators and demands. After using simple examples which are easy to check for advantages and disadvantages, the results were checked on larger systems. The results presented and discussed in this article consider the location and size of generators and the demands involved, as well as the merits of these locations in the network configuration. The sensitivity of the methods to alterations in the electric network was also investigated in an attempt to provide effective alternatives for the solution of a problem expansion transmission planning. The methods discussed are the following: • Z-bus (a method based on circuit theory using a Z-bus matrix); • Incremental transmission loss (ITL), including negative allocation (compensation for efficiency) and without such allocation (U-ITL); • Proportional sharing (PS); • Pro-rata method (P) based on active power injection, and (I) based on the current injection. The analysis of energy losses is essential since losses can involve an amount of hundreds of millions of dollars per year. For instance, the power losses in the South-Southeastern Transmission Brazilian System can reach up to 2200 MW during the peak load period.

This paper has presented a critical analysis of the results obtained by the most commonly used techniques for the allocation of losses in transmission networks. One of the objectives of this paper is to give additional contributions in relation to the previous comparative publications. All of the methods are user-friendly and easy to implement, although the pro-rata, P and I methods work independently from the specific network, which could be a disadvantage. The ITL and Z-bus methods, however, provide both positive and negative allocations, although the more frequent negative allocation suggested by the Z-bus method is a definite advantage. One problem found in methods is to make the allocation in a discriminatory fashion. Methods providing negative allocation tend to have the most discriminatory policies, since the buses receiving positive allocations must pay for the incentives as well as the global losses. The negative allocations resulting from the ITL and Z-bus methods, however, provide information about the merits of the location of these buses in the network, and this can be quite useful for indicating where the generation and demands should be or are concentrated. This kind of negative allocations can be very useful for generator, demand and transmission agents. The analyses conducted here suggest that allocation of losses using a single method may not be a very good solution for all generators, demands, and transmission systems since discriminatory allocation may appear. One suggestion would be to work with more than one method of cost allocation. One possibility could be to work with two methods, one that produces unsubsidized allocation and less discriminatory behavior to allocate the losses for payment purposes (pro rata, for example), and another, like Z-bus, that attributes negative allocation in order to indicate the buses with favorable locations. However, such analyses require further investigation, and the definition needs to be accepted by all of the agents. Allocations procedures based on bilateral contracts, like [16], was not considered in this work.