Assessing the reliability of distribution systems

Since a typical distribution system accounts for 40% of the cost to deliver power and 80% of customer reliability problems, distribution system design and operation is critical for financial success and customer satisfaction. To address this situation, Commonwealth Edison is integrating reliability assessment techniques into distribution planning and engineering. Just as equipment loading and voltage regulation are treated with analytical rigor with power flow models, interruptions and outages can be treated with analytical rigor with reliability models. This is made possible through the use of predictive reliability assessment tools that are able to predict customer reliability characteristics based on system topology and component reliability data. Reliability software predicts expected interruption frequencies and duration in a manner analogous to current and voltage evaluations in traditional power flow models. This article describes the distribution system's reliability assessment model jointly developed by Commonwealth Edison and ABB. This effort modeled, calibrated, and assessed the reliability of more than 3300 feeders. After completing the model, an intelligent system was used to automatically identify potential reliability problems and recommend reliability improvement projects based on expected benefits and costs.