Continuing trend towards deregulation and unbundling of transmission services has resulted in the need to assess what the impact of a particular generator or load is on the power system. A new method of tracing the flow of electricity in meshed electrical networks is proposed which may be applied to both real and reactive power flows. The method allows assessment of how much of the real and reactive power output from a particular station goes to a particular load. It also allows the assessment of contributions of individual generators (or loads) to individual line flows. A loss-apportioning algorithm has also been introduced which allows the break down of the total transmission loss into components to be allocated to individual loads or generators. The method can be useful in providing additional insight into power system operation and can be used to modify existing tariffs of charging for transmission loss, reactive power and transmission services.

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Tracing the flow of electricity

This paper introduces a simple novel method of transmission supplement charge allocation based on topological analysis of power flows in the network. The method uses the MW-MILE methodology but analyses the share, not the impact of, individual loads and generators in line flows. This results in positive contributions from all the users hence rescinding the problem of counterflows.

Topological generation and load distribution factors for supplement charge allocation in transmission open access

The application of marginal costing to transmission pricing in open access schemes requires the collection of a supplement to finance the transmission systems. The paper describes the application of marginal cost based pricing in the Chilean power system and the difficulties faced in allocating the supplement among parties involved. Alternative methods for defining the allocation are formulated. Generalized generation and load distribution factors for cost allocation are formulated and implemented. The methods are applied to allocate payments for transmission services provided by the transmission network and by a distribution company. >

Marginal pricing and supplement cost allocation in transmission open access

In this paper, the authors describe the basic technical concepts involved in developing cost based transmission prices. They introduce the concepts of transmission pricing paradigms and methodologies to better illustrate how transmission costs are transformed into transmission prices. They also briefly discuss the role of these paradigms and methodologies in promoting "economic efficiency" which is narrowly defined in this paper. They conclude the paper with an example of the application of some of these paradigms and methodologies for pricing transmission services in Brazil.

Some fundamental, technical concepts about cost based transmission pricing

This paper presents an overview of usage-based methods of transmission cost allocation under open access. Allocation of transmission costs involves both technical and regulatory issues, and as a result, the methods available in the literature differ in their definition and measure of the "extent of use" of transmission resources. The primary objective of this paper is to provide a summary of techniques used for designing fair and equitable access fees for the recovery of fixed transmission costs. The discussion is thus organized under two major subtopics: algorithms for transmission usage evaluation and alternative pricing strategies. Numerical examples are provided to show the results using different methods.

Review of usage-based transmission cost allocation methods under open access

The authors describe the principles and the implementation of a methodology to evaluate the transmission network capacity use for firm transmission services including wheeling transactions. In this methodology, transmission network capacity use of a transaction is a function of the magnitude of electric power, the length of the transmission lines, and the type of facility involved in the transaction. This capacity value provides an equitable means of allocating the cost of transmission facilities among users of the firm transmission service. Through examples, it is shown that this methodology, called the MW-mile methodology, is more reflective of the actual usage of the transmission network in allocating the transmission network capacity cost than the now widely used postage stamp rate procedure. Also indicated is the potential for realizing greater economic efficiencies through the use of this methodology. >

Evaluation of transmission network capacity use for wheeling transactions

This paper presents a new approach implemented in MISO day-ahead and real-time energy and ancillary service market clearing processes to address the reserve deliverability issue In this approach, MISO enhanced the co-optimization process to incorporate post zonal reserve deployment transmission constraints Reserves are procured within the co-optimization to meet both market-wide reserve requirements and ensure their deliverability on a zonal basis As a result, zonal market clearing prices (MCPs) for reserves can properly reflect the effects of zonal reserve deployment on transmission constraints under consideration

Incorporating Post Zonal Reserve Deployment Transmission Constraints Into Energy and Ancillary Service Co-Optimization

In the U.S. electricity markets, locational marginal prices (LMPs) are obtained in economic dispatch with fixed commitment decisions. The costs of committing or dispatching fast-start units at their minimum limits may not be covered by LMPs and significant uplift payments are thus needed. Extended LMPs (ELMPs) were established by MISO to appropriately reflect these costs, but are computationally expensive for market implementation. The approximate ELMP (aELMP) model is then developed with reduced complexity. An important design issue that highly affects aELMPs is to allocate commitment costs of fast-start units over time. However, it is difficult to obtain an allocation for the simplified model to effectively approximate the complex ELMPs. In this paper, allocation guidelines are derived in the day-ahead energy market without considering transmission capacity constraints for simplicity. The idea is to separate the ELMP problem into individual-hour problems resembling the aELMP model by using Lagrangain relaxation. Karush–Kuhn–Tucker (KKT) conditions are then innovatively used to derive guidelines for an easily implementable allocation that utilizes the commitment and dispatch results. To examine effectiveness of the guidelines, aELMPs are compared with ELMPs and LMPs. Numerical results show that the resulting aELMPs effectively approximate ELMPs and reduce uplift payments.

Commitment Cost Allocation of Fast-Start Units for Approximate Extended Locational Marginal Prices

In current electricity markets of the USA, locational marginal prices (LMPs) are obtained from the economic dispatch process and cannot capture costs associated with commitment decisions. The extended LMPs (ELMPs) were established as the optimal Lagrangian multiplier of the dual of the unit commitment and economic dispatch problem. Commitment related costs are included and uplift payments are minimized. To obtain ELMPs, the dual problem should be solved with multiplier optimality and computational efficiency. Subgradient methods suffer from the multiplier zigzagging difficulty. Cutting plane methods encounter computational complexity issues in calculating query points. In this paper, a subgradient simplex cutting plane method is developed to obtain ELMPs. Transmission is not considered for simplicity, while key features of ELMPs are still captured. By innovatively using subgradients and simplex tableaus, query points are efficiently obtained through an adaptive three-level scheme. A query point along the subgradient is easily calculated at Level 1. As needed, Level 2 obtains Kelley's query point and Level 3 obtains the Chebyshev center, both by pivoting simplex tableaus. Numerical results show that the optimal multiplier is efficiently obtained.

The Subgradient Simplex Cutting Plane Method for Extended Locational Marginal Prices

In current deregulated power markets, prices are determined in the economic dispatch problem with fixed unit commitment decisions. Start-up and no-load costs are not included in the prices and significant uplift payments have to be paid to generators. The convex hull pricing model was developed to include the fixed costs in setting prices by solving the dual of the unit commitment and economic dispatch problem. The optimal multipliers are the convex hull prices, and the prices minimize the uplift payments. The optimal multipliers can be obtained by using cutting plane methods that iteratively shrink the feasible polyhedron in the dual space to the optimal point. The calculation of query points is a key step for cutting plane methods and centers such as center of gravity and analytic center are reported as the query point. To calculate the convex hull prices in a more efficient way, this paper develops a subgradient-simplex based cutting plane method to find a query point along the subgradient. When the query point is not deep inside, a sphere inscribed in a corner or the Chebyshev center is calculated by the use of simplex tableaus to ensure the query point is always deep inside. Redundant constraints are also pruned based on the tableaus.

Paul Gribik

Papers

Evaluation of transmission network capacity use for wheeling transactions

Incorporating Post Zonal Reserve Deployment Transmission Constraints Into Energy and Ancillary Service Co-Optimization

Commitment Cost Allocation of Fast-Start Units for Approximate Extended Locational Marginal Prices

The Subgradient Simplex Cutting Plane Method for Extended Locational Marginal Prices

The subgradient-simplex based cutting plane method for convex hull pricing