Transmission Loss Allocation Research Articles

Optimal compensation of transmission losses in a multiple-transaction framework

This paper presents an optimal power flow formulation in which the generation is dispatched in order to compensate for losses allocated to different transactions. Since the loss allocation itself depends on the solution, the two problems are combined and solved together. Loss allocation scheme developed by the authors earlier [Ding Q, Abur A. Transmission loss allocation in a multiple-transaction framework, IEEE Trans Power Syst 2004;19(1):214–20] is used in this formulation. It is assumed that each transaction is entitled to select its own designated generators to compensate for its allocated losses. The case where some transactions prefer instead to let the independent system operator (ISO) to provide the loss compensation service is also considered. An optimization procedure, which yields the least-cost compensation from participating generators, is developed for this purpose by using an OPF model. Several numerical examples are included to demonstrate the proposed procedures.

A Comparative Analysis of AC and DC Incremental Methods for Transmission Loss Allocation

This paper intends to analyze the accuracy of incremental DC methods for loss allocation in electricity markets. The model under implementation at the Brazilian electricity market is one of this kind and has motivated this investigation. The model to be used in Brazil is based on incremental methods and defines loss factors for generators and loads. This technique uses a DC load flow to calculate the loss factor, and so it does not consider the complete power flow equations. Consequently, this method may provide unfair loss allocation depending on the system operation condition. Hence a method is developed to calculate the loss factors, based on incremental methods but using an AC load flow that takes into account the system nonlinearity. Both methods are applied to a small system for conceptual discussions and to a version of the Brazilian North-Northwest system for the validation of the results by using a real system. The results demonstrate the limitations of the DC method for loss allocation, justifying the use of an AC load flow to calculate the total system losses and the loss factors. The loss factors calculated by both methods depend on the choice of the slack bus. In order to overcome this limitation, the concept of distributed slack bus is included into the AC power flow, and new slack-bus independent results are obtained.

Transmission Loss Unbundling and Allocation Under Pool Electricity Markets

This paper presents a methodology based on the circuit theories for unbundling and allocation of transmission losses among the participants of a pool-based electricity market. Starting from a known operation point and using the basic network equations without additional assumptions, an expression of the branch losses based on nodal current injections is derived. Since the power flow equations and circuit theories are satisfied, the methodology turns explicit, in a natural way, separating the losses at each system branch and assigning the responsibility to the respective market participants. It means that the loss allocation of each branch, which is produced by each generator and consumer, is obtained. Extensions and strategies considering unsubsidized and predefined proportion-based loss allocation as well as issues related with the allocation fairness and transparency are also included. Comparisons with previous methods and validation tests of the proposed method are reported by using the IEEE Reliability Test System.

Transmission loss allocation in a deregulated electrical energy market

This paper presents a new method for transmission loss allocation in a deregulated electrical power market. The proposed method is based on physical flow through transmission lines. The contributions of individual loads to the line flows are used as basis for allocating transmission losses to different loads. With minimum assumptions, that sound to be reasonable and cannot be rejected, a novel loss allocation formula is derived. The assumptions made are: a number of currents sharing a transmission line distribute themselves over the cross section in the same manner; that distribution causes the minimum possible power loss. Application of the proposed method is straightforward. It requires only a solved power flow and any simple algorithm for power flow tracing. Both active and reactive powers are considered in the loss allocation procedure. Results of application show the accuracy of the proposed method compared with the commonly used procedures.

Transmission Loss Allocation Through Equivalent Bilateral Exchanges and Economical Analysis

A new loss allocation (LA) scheme based on the principle of equivalent bilateral exchanges (EBEs) is presented and compared with other available techniques. Formulation and results from extensive simulations including consistency tests show that the suggested methodology has several desirable properties: It is flow-based, requiring only a solved load flow for its implementation; it is not dependent on the choice of a slack bus; it is straightforward to apply; undesirable negative loss allocation is not produced; and low volatilities are shaped. An economic analysis with various LA methods is also carried out when these are integrated into a combined economic dispatch/load flow dispatch strategy, a likely scenario for LA in a real system. This combined dispatch strategy yields prices charged to the loads and rates received by the generators that account for loss allocation and loss supply. Results show that these economic indexes are very close to the marginal costs derived from an optimal power flow (OPF) approach with the advantage of reducing volatility.

Modified Topological Generation and Load Distribution Factors

In this paper, a modification of the topological generation load distribution factor method of power flow tracing is reported. The modification is needed since the existing method introduces additional fictitious nodes on system lines in order to take into account the transmission losses. Due to the expansion of a system, the existing algorithm based on the augmented matrix equation requires more mathematical effort and memory and longer calculation time to obtain a solution. The new approach successfully avoids the matrix expansion by introducing matrix decoupling, which is its main improvement. The second novelty is an introduction of an equivalent model of a line that unites the nodal reactive power with the power produced by shunt admittances. Thus, the modified method can be also applied to the reactive power flows and transmission-loss allocation.

A transaction-based method for allocation of transmission grid cost and losses

The problem of grid cost and losses allocation may be divided into independent subproblems: allocation of branch flow and losses to transactions, definition of these transactions and cost allocation to transactions. From this final allocation, the charges to participants in transactions may be made straightforwardly. A differential, slack-invariant method for the allocation of flow and losses to transactions that makes use of the AC load flow equation is presented here. The definition of transactions must be addressed using a non-discriminatory rule in pool systems. There are many possible options for this definition, and the choice made has great influence on the results. Cost allocation, on the other hand, may be made in different ways, as well. The paper presents an allocation process that addresses all these issues. Results for the IEEE-RTS96 test system are obtained and discussed.

Comparação de propostas para alocação dos custos de perdas na transmissão

Uma análise de desempenho dos principais métodos de alocação de perdas para geradores e cargas é realizada. São discutidos dois métodos baseados na técnica pro-rata, três procedimentos baseados em técnica incremental, um método baseado em participação proporcional e mais um método baseado na teoria de circuitos elétricos. Os algoritmos são testados, primeiramente, com exemplos didáticos de fácil verificação de potencialidades e desvantagens, para em seguida avaliar resultados com sistemas de porte maior (IEEE 118). Os resultados apresentados e discutidos verificam: a localização e a magnitude de geradores e cargas; a possibilidade de se ter agentes bem ou mal localizados em cada configuração da rede; o desempenho com alterações na rede elétrica; e o comportamento discriminatório. Conclusões e recomendações são apresentadas.

Transmission loss allocation through a modified Ybus

A methodology to allocate the active power transmission loss among agents of a power pool is proposed. The approach is based on the inclusion of the admittances equivalent to bus power injections in the bus admittance matrix. For a given power-flow solution, the relationship between the branch currents and the load/generator current injections is determined using a modified bus admittance matrix, which allows the power loss of each transmission line to be expressed in terms of bus current injections. The proposed technique is simple to implement and flexible enough to allow the assignment of loss parcels to a preselected set of buses. An example, with a six-bus system illustrates the main steps of the proposed allocation strategy, and numerical results obtained with the IEEE 57-bus system are used to assess the quality of the loss allocation.

An Empirical Formula for Transmission Loss Allocation of Power Systems

This paper presents an empirical formula for preliminary loss allocation to each generator in a network. From the relationship of Incremental Transmission Loss (ITL) and the power outputs of generators, we have derived a preliminary loss allocation formula for each generator. To get the allocated losses to generators, the preliminary losses have been adjusted according to the correction factors calculated from them. Preliminary losses are adjusted so that the sum of allocated losses equals the total loss calculated by DC Optimal Power Flow (DC-OPF). Using DC-OPF the procedure for loss allocation including the preliminary loss calculation formula has been tested for 6-bus-3-generator and IEEE 118-bus-36-generator model power systems. Allocated losses calculated by our procedure have been compared with those of incremental method for the both model power systems and the features of the proposed method have been discussed.

Generation Scheduling and Economic Estimation of Power Systems Including Bilateral Contracts

The electric power transactions are classified into pool transactions and bilateral contracts as well as security transactions. A certain transaction level of, for example, bilateral contracts may affect pool transactions by causing transmission congestion etc. In this paper, we will discuss how both the market and the bilateral transaction participants share the operation cost and charge for using network in consideration of power transmission loss allocation among generators. Following these discussions, we present an optimal scheduling method for pool participants. To ascertain the effectiveness of the proposed scheduling algorithm and to show how the bilateral contract level affects the pool operation, we will demonstrate various simulation results for a model power system of 8 units 44 bus power system.

Closure to discussion of "Transmission loss allocation: part I - single energy market"

For original article by A. M. Leite da Silva and J. G. de Carvalho Costa see ibid., vol.18, p.1389-94, Nov. 2003 and for discussion by A. J. Conejo and F. D. Galiana see ibid., vol.19, no.4, p.2111, Nov. 2004.

Discussion of “Transmission Loss Allocation: Part I— Single Energy Market”

For original article by A. M. Leite da Silva and J. G. de Carvalho Costa see ibid., vol.18, p.1389-94, Nov. 2003.

A Methodology for Allocating Transmission Losses Due to Cross-Border Trades

Transmission pricing of cross-border trades is often difficult since individual countries may use incompatible internal transmission pricing regimes, and they are usually unwilling to disclose any sensitive information about their own systems. In this paper, the use of a tracing methodology is proposed to overcome these problems using loss allocation problem as an example. Firstly, a modification of the tracing methodology is presented in which the loss is allocated in a direct way. Then a unifying tracing-based methodology of transmission pricing for cross-border trades is proposed. The only data required are the flows in the tie-lines and the charges to be applied to the border nodes in each country. No information is required about individual transactions, load/generation profiles or internal networks. The methodology is illustrated on the IEEE 118 node network divided into four areas, each with a different internal transmission pricing methodology. The proposed methodology is shown to be simple, transparent and very fast and it can deal effectively with cyclic flows.

04/01873 Reviewing strategies for active power transmission loss allocation in power pools: Salgado, R. S. et al. International Journal of Electrical Power & Energy Systems, 2004, 26, (2), 81–90

04/01873 Reviewing strategies for active power transmission loss allocation in power pools: Salgado, R. S. et al. International Journal of Electrical Power & Energy Systems, 2004, 26, (2), 81–90

Transmission Loss Allocation in a Multiple-Transaction Framework

A new method, which allocates losses to individual power transactions in a multiple transaction setting, is presented. The derivations for the allocated losses directly follow the system loss formula and do not make any simplifying assumptions. It explicitly expresses the losses in terms of individual transactions, and this leads to a natural separation of system losses among all transactions in the system. A transaction-loss matrix, which illustrates coupling effects between any pair of transactions taking place in the system, is also introduced. Several numerical examples are presented to demonstrate the application of the proposed approach to power systems with multiple transactions.

Transmission loss allocation: part II-multiple interconnected energy markets

For pt.I see ibid., vol.18, no.4, p.1389-94 (2003). This paper presents a new methodology based on the incremental transmission loss concept for allocating electric losses to generators and loads, participating in multiple interconnected energy markets. The main objective is to generalize the formulation proposed in the companion paper, Part I, in order to identify through a decomposition technique, the amount of losses that each participant in the market causes on all system areas. The concept of interchange losses is introduced: the total amount of losses that occurs outside a given market whose agents are responsible for causing them. Some criteria to share these losses among the market agents are presented and discussed. The IEEE Reliability Test System is used to illustrate the proposed methodology.

Transmission loss allocation: part I-single energy market

This paper presents a new methodology for allocating transmission losses to the participants of a single energy market. The proposed approach is based on the incremental transmission loss concept and is implemented through two models: basic and extended. In the basic model, the total system losses are estimated through the linear DC load flow equations, while the extended model uses the exact AC formulation. The concept of center of losses is used; a fictitious bus in the system network where all transactions are compensated for transmission losses. Both models provide a sharing of transmission losses among generators and loads based on a predefined proportion, for instance 50%:50% for each participant class. Some important aspects related with the allocation fairness and transparency are illustrated by numerical applications with the IEEE Reliability Test System. The extension of this methodology to interconnected energy markets is treated in a companion paper.

Reviewing strategies for active power transmission loss allocation in power pools

Transmission losses have a considerable effect on the active power generation cost and thus, a strategy to allocate them fairly among the power system agents is essential to economic efficiency of the electric energy market. The present work focuses on the allocation of the active power transmission losses among the buses of a power system operating under pool condition. Three types of approaches, based on extensions of the conventional and optimal solutions of the power network equations, are analyzed here: (1) direct use of sensitivity relationships between the transmission losses and the bus power injections; (2) use of participation factors obtained from power flow solutions; and (3) integration of sensitivity relationships mentioned in the previous item. Numerical results obtained with a 19-bus power network are used to illustrate the main aspects of the loss allocations based on the application of the selected techniques.

Transmission loss allocation under combined pool and bilateral operation

The allocation of transmission losses in an open system operating under both pool and bilateral contracts is analyzed using the method of differential loss allocation. This approach allows to consider loss supply as marketable product since each bilateral contract can chose its more appropriate loss supplier. The relative time-dependence of the various contracts including those with the pool are shown. It is also studied the relative influence of implementing bilateral contracts on the pool dispatch performance. The theory is presented together with a number of numerical examples.