Evaluation of Low-voltage Network Systems Reliability using Probabilistic Methods

Con Edison's distribution systems supply power to more than 3 million customers in New York City and Westchester County. About 85% of the load in the Con Edison service territory is supplied by underground low-voltage network systems. The reliability of underground low-voltage network systems is extremely high and Con Edison uses Network Reliability Index (NRI) programs the Contingency program and the AutoMonitor program to evaluate their overall reliability. The NRI programs use failure rates established for cable sections, joints, transformers, and other related equipment based on their age, temperature ranges, voltage levels, and loading. The programs simulate failures using the Monte-Carlo method. The Contingency program is a design tool used to compare the relative reliabilities of each network system, and rank them accordingly. The program runs long-range (20 years) Simulations to determine the NRI values for various design configurations. The AutoMonitor program is a real-time operating tool that provides operators with real-time and potential network system reliability information. This program runs short-range (up to 7 days) simulations. NRI programs have been in use in Con Edison for several years and the results of the programs are used to help Con Edison maintain its No. I position in providing electric power in North America.