Due to the complex and integrated nature of power systems, failures in any part of the system can cause interruptions which range from inconveniencing a small number of local residents to a widespread catastrophic disruption of supply. For this reason, the transmission reliability margin must be provided for the system to be operated at all times in such a way that the system will not be left in a dangerous condition even though unpredictable events occur. In this paper, Kirschen's tracing method is employed to find the usage contributions of individual generators to the line flows under normal conditions. Apparently, it seems plausible to compute the reliability contributions of all market participants based on the probabilistic approach which takes notice of the forced outage rate for each transmission line as well as the line outage impact factor and then to allocate the transmission reliability cost among all the system users in proportion to their “extent of use” of reliability reserves in transmission facilities.
The electricity transmission system is an extensive, interconnected network of high-voltage power lines that pass electricity from generators to customers. Such a transmission system must be flexible enough, every second of every day, to accommodate the growing demand for reliable and affordable electricity.
Nevertheless, rapid growth in electricity demand and new generation, lack of investment in new transmission facilities, and the incomplete transition to fully efficient and competitive wholesale markets have allowed transmission bottlenecks to emerge. These bottlenecks increase electricity costs to consumers and increase the risks of blackouts. Today, power failures, close calls, and near misses are much more common than in the past. The transmission systems of tomorrow must be operated in ways that maintain adequate safety margins for reliability and allow customers to follow strict tariffs for reliability with appropriate penalties for non-compliance.
Despite the fact that transmission charges account for a small percent of operating expenses in utilities, we cannot afford to allow the relatively small transmission costs to prevent customers from enjoying the reliable and affordable electricity service that the properly managed competitive forces will deliver to our nation. Therefore, transmission pricing should be a reasonable economic indicator used by the market to make decisions on resource allocation, system expansion, and reinforcement [1]. The first step toward increasing the role of market forces in managing transmission system operations efficiently and fairly is increasing the role of price signals to direct the actions of market participants toward outcomes that improve operations. Improving operations by relying on accurate price signals may, by itself, alleviate the need for some construction of new transmission facilities. Moreover, when new construction is needed, price signals will help market participants identify opportunities and assess options to address bottlenecks. Several aspects of transmission operations, including congestion and losses, could be effectively addressed by pricing based on the principle that if market participants see the true costs of transmission services reflected in prices, they will use or procure these services efficiently. Thus, reliance on uplift charges, in which costs are recovered from all transmission users on an equivalent basis, should be minimized.
In the past few decades, many researchers have devoted themselves to achieving an efficient transmission pricing scheme that could fit all market structures in different locations so that participants in markets can see and respond to the true costs of using the transmission system. Generally, the transmission charge is grouped into the following parts: transmission line usage charge, system reliability charge, access charge, and so on [2]. Any transmission tariffs should be able to reflect these respective cost components without any distortion.
Particularly, this paper suggests a probabilistic approach to allocating the reliability cost of the transmission system to each market participant. Based on the transmission line utilization of all market participants under normal conditions, this paper provides a helpful comparative framework for allocating the reliability cost in the context of a competitive electric market by taking care of the forced outage rate as well as the line sensitivity factors after a loss of one single circuit or (n − 1) criteria and then calculating the reliability contributions of all generators to the transmission lines. Finally, the case study exhibits the applications of the proposed methodology on a simple 6-bus test system.
This paper has examined an alternative mechanism to allocate the transmission reliability cost to market participants in a more equitable manner. In fact, we have attempted to fully quantify the relative influences of each outage in network on a particular transmission line by taking advantage of changes in flow on that line for all the outages analyzed and the forced outage rates of the failed lines as well. Finally, the reliability cost allocation is achieved by the reliability contributions of individual entities to the corresponding transmission line which consist of the normalized relative reliability evaluation factors and their “extent of use” of the line under normal conditions.
