THE USE OF RELIABILITY ECONOMIC ANALYSIS IN ALEXANDRIA DISTRIBUTION NETWORK

Modern competitive electricity markets ask for power systems with the highest possible economic efficiency. Higher efficiency can only be reached when accurate and flexible analysis tools are used. In order to relate investment costs to the resulting levels of supply reliability, it is required to quantify supply reliability. The calculation of performance indicators in respect to supply reliability is the task of the reliability assessment. This task can be divided into the calculation of interruption statistics and the calculation of reliability worth indices. The paper briefly illustrates the philosophies adopted by Alexandria Electricity Distribution Company (AEDC) in the collection of component and system outage data. A report of delivery quality in various distribution zones and in the whole company is presented. Interruption valuation enables the cost of interruption to be valued in a simplified manner. A calculation is made of the interruption cost. The customer outage model is evaluated. The outage cost is calculated using the Customer Damage Function. The concept of the Quality Function is discussed as an assessment of the company’s way of running its operations. INTRODUCTION Electric utilities have always been concerned with the need to provide a high level of continuity and quality of supply to their customers. This concern manifests itself in the planning, design and operation of their systems and the judicial selection of appropriate equipment. This can be achieved by quantitatively assessing the reliability of the power system. It is very important to analyse exhaustibly the statistics and the failure rates in order to direct with precision the investments to those installations which their marginal contribution to the indices of interruptions have more relative weight. In that line AEDC works with the continual improvement criteria in analyzing the interruption statistics supported by informatics tools that allow determining indicators with different criteria. Consistent collection of data is essential as it forms the input to relevant reliability models, techniques and equations. Consistent data are required to continuously monitor the performance of an electric power system and to measure its ability to provide reliable service to its customers. Equipment and system benchmarking cannot be performed in the absence of consistent data collected under comprehensive and agreed definitions and protocols. RELIABILITY EVALUATION CRITERIA AEDC created a system for collection, processing and reporting of reliability and outage statistics for the medium voltage distribution system. In addition to the equipment reliability information system, AEDC has also initiated an electric power system reliability assessment procedure that is designed to provide data on the past performance of the system. It contains systems for compiling information on system disturbances, system delivery point performance and customer service continuity statistics. In respect to the effects of interruption of supply on a customer, the interruptions are classified in planned and unplanned interruptions. A comprehensive report of delivery quality in various distribution zones and in the whole company is developed. The report includes the common practice reliability indices i.e. System Average Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI) and Customer Average Interruption Duration Index (CAIDI). These indicators are available for the whole company, for each distribution zone, both for planned and unplanned interruptions. The overall annual service continuity indices for the year (2005/2006) are shown in table 1. The major causes of interruptions to the system and to the customers are assessed; Figure 1 shows the classification of interruptions by cause. Figure 2 shows the relation between reliability of supply indices. TABLE 1Service continuity indices (2005/2006) Distribution zone Index Montaz a East Central West Coast AEDC Planned 1.812 1.143 1.83 1.72 0.45 1.44 Unplanned 2.28 1.16 2.04 2.54 1.63 1.87 SAIFI Overall 4.12 2.32 3.86 4.24 2 3.31 Planned 200.87 146.3 186.7 162.7 48.67 153.19 Unplanned 73.74 35.12 59.51 66.73 40.97 54.65 SAIDI Overall 274.64 181.4 246.33 229.4 89.65 207.84 Planned 110.85 128.0 102.02 94.64 108.1 106.62 Unplanned 32.34 30.28 29.17 26.27 21.23 29.22 CAIDI Overall 66.66 78.23 63.81 54.12 46.45 62.85 C I R E D 19th International Conference on Electricity Distribution Vienna, 21-24 May 2007