International Journal of Electrical Power & Energy Systems
Value-based distributed generator placements for service quality improvements
Introduction
The electric power industry is under deregulation in response to changes in law, technology, market and competition. One of the main advantages of deregulation is that it can increase the efficiency of the industrial sector and reduce the cost of electrical energy for all customers. Deregulated power systems can no longer bundle the generation, transmission, distribution and retail activities, which were traditionally carried out by vertically integrated utilities. Therefore, different pricing policies will exist between different power companies. Many contributions in deregulated electric power industries such as establishing ISO’s, and providing a fairer and more competitive generation market have been developed. However, some believe that the most significant changes yet to come will occur in distribution business since the cost to serve commercial and residential customers is higher than the cost to serve industrial customers. Therefore, the applications of DG – the small, self-contained electric generating plant that can provide power to homes, businesses, or industrial facilities in distribution feeders – will be important and helpful. Moreover, a more comprehensive distribution system with higher reliability, efficiency and power quality can be obtained if distribution automation, demand-side management and DG can be combined together. Nowadays, most types of DG utilize traditional power generation paradigms such as diesel, combustion turbine, combined cycle turbine, low-head hydro or other rotating machinery. However, DG also includes fuel cells and renewable power generation methods such as wind and solar [1], [2], [3], [4], [5], [6].
Generally, the planners can evaluate DG’s performance from two aspects: cost and benefit. Cost is one of the most important elements in nearly all DG evaluations, but is insufficient for complete evaluations. In addition to DG cost, reliability enhancements, power cost saving and power loss reduction are also essential elements in determining whether DG should be installed. The costs of DG placement can be classified into investment, maintenance and operating costs. Investment cost includes cost of the DG unit, DG site, site preparation, fuel delivery system, electric system interface, SCADA system, protection system, and so on. Maintenance cost includes the repair, scheduled maintenance cost, and so on. Operating cost includes the labor cost for service, taxes, fuel cost, and so on [6]. The benefits of the DG placement can be classified into power cost and power loss reduction, and reliability enhancement. The benefits for power cost and power loss reduction are quite straightforward, since the DG can inject its power into distribution feeders. The merit of reliability enhancement has received considerable attentions as it provides an opportunity to reduce the costs or losses incurred by utility customers as results of power failures. To render reasonable means of decision making on the necessity of changing service continuity levels experienced by customers, the cost incurred by customers associated with interruptions of service must be incorporated in planning and operating practices [7], [8], [9], [10]. The valued-based planning method can be used to find the best balance between costs and benefits, such that an optimal DG placement can be derived in terms of the costs and benefits to the customers and utility.
There are many methods available for DG planning [11], [12], [13], [14]. In [11], some successful experiences of DG in Central Virginia Electric Cooperative were reported. Ref. [12] proposed a method for DG planning based on genetic algorithm. The paper is aimed towards the cost evaluation, benefits for customers and utility such as reliability enhancement, customer interruption cost reduction and peak load cost reduction have not been included. Ref. [13] proposed some processes for DG planning that also permit the incorporation of distribution automation and demand-side management. Ref. [14] proposed some guidelines for DG planning. From those papers, it can be found that in a deregulated power system, each individual distribution company may wish to determine the costs and benefits of DG planning in different manners and decisions. It is difficult to find a single configuration and consideration planning method that satisfies each company. In this paper a value-based planning method for DG placement is proposed. The proposed method takes the benefits and costs of DG placement into account and tries to find the optimal location and sizing for DG placement. Test results show that with proper types, sizes and installation site selection, DG placement can be used to improve service reliability, reduce the customer interruption costs and save the power cost.
Section snippets
Basic concepts
Value-based planning methods are based on balancing the costs to a utility and the benefits received by the utility and its customers. The costs of DG placement include the investment, maintenance and operating cost. The benefits of DG placement include the power cost and loss reduction, and reliability enhancement. A value-based planning method attempts to locate the minimum cost solution where the total benefits can be maximized. Fig. 1 illustrates how utility costs and benefits of utility
Solution algorithm
The main problem studied in this paper is to find the optimal types of DG and their corresponding sizes and locations in distribution feeders. The objective function of the valued-based DG placement problem iswhere BenefitDG and CostDG are the benefits and costs of DG placement, respectively. NG is the total number of DGs installed in the feeder. KA is the cost
Test results
The proposed algorithm was implemented with Borland C++ on a Pentium-III PC. Some of the test results obtained by the proposed algorithm are presented. The test feeder is shown in Fig. 5. The candidate locations for DG placement are also shown in Fig. 5. The parameters used in this test case are:
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Outage rate: 0.04 failure /mile-year.
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Outage duration: average repair time is 2.0 h and the average duration to perform the necessary fault isolation, switching and load transfer activities from
Discussions and conclusions
In a deregulated power system, each individual distribution company may wish to determine the costs and benefits of DG from different points of view. It is difficult to find a single configuration and consideration planning method that satisfies each company. In this paper, a value-based planning method for DG placement has been proposed. The proposed method has taken the benefits and costs of DG placement into account and tried to find the optimal types, locations and sizes for DG placement
Acknowledgement
This paper was sponsored by National Science Council, Taiwan, under research grant NSC 90-2213-E-214-052-.
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