Operating strategies to preserve the adequacy of power systems circuit breakers

The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. These temporary power system operating strategies address circuit breaker adequacy issues, and overstressed breakers can be operated longer and more reliably until they are replaced with adequate equipment.;The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit (fault) currents levels. A number of circuit breakers do not have sufficient ratings to interrupt these increased faults currents. These breakers are said to be overstressed (underrated, inadequate). Because of their insufficient ratings, overstressed breakers are subject to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To avoid outages and system unreliability, overstressed breakers must eventually be replaced.;The replacement of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers, using the substation reconfiguration and generator commitment strategies described in this study.;The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) more reliable network operation, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enable improvements in power systems planning.;The proposed work is illustrated using a three-phase, breaker-oriented 24-substation test system that extends the existing IEEE Reliability Test System.