Congestion management enhancing transient stability of power systems

In a competitive electricity market, where market parties try to maximize their profits, it is necessary to keep an acceptable level of power system security to retain the continuity of electricity services to customers at a reasonable cost. Congestion in a power system is turned up due to network limits. After relieving congestion, the network may be operated with a reduced transient stability margin because of increasing the contribution of risky participants. In this paper, a novel congestion management method based on a new transient stability criterion is introduced. Using the sensitivity of corrected transient stability margin with respect to generations and demands, the proposed method so alleviates the congestion that the network can more retain its transient security compared with earlier methods. The proposed transient stability index is constructed considering the likelihood of credible faults. Indeed, market parties participate by their security-effective bids rather than raw bids. Results of testing the proposed method along with the earlier ones on the New-England test system elaborate the efficiency of the proposed method from the viewpoint of providing a better transient stability margin with a lower security cost.Congestion management Power market Corrected transient stability function Transient stability margin Security cost

Multi-objective congestion management by modified augmented [epsilon]-constraint method

Congestion management is a vital part of power system operations in recent deregulated electricity markets. However, after relieving congestion, power systems may be operated with a reduced voltage or transient stability margin because of hitting security limits or increasing the contribution of risky participants. Therefore, power system stability margins should be considered within the congestion management framework. The multi-objective congestion management provides not only more security but also more flexibility than single-objective methods. In this paper, a multi-objective congestion management framework is presented while simultaneously optimizing the competing objective functions of congestion management cost, voltage security, and dynamic security. The proposed multi-objective framework, called modified augmented [epsilon]-constraint method, is based on the augmented [epsilon]-constraint technique hybridized by the weighting method. The proposed framework generates candidate solutions for the multi-objective problem including only efficient Pareto surface enhancing the competitiveness and economic effectiveness of the power market. Besides, the relative importance of the objective functions is explicitly modeled in the proposed framework. Results of testing the proposed multi-objective congestion management method on the New-England test system are presented and compared with those of the previous single objective and multi-objective techniques in detail. These comparisons confirm the efficiency of the developed method.Multi-objective congestion management Augmented [epsilon]-constraint technique Efficient solution Solution preference Weighting method

Relationship between Ureaplasma urealyticum Colonization and Bronchopulmonary Dysplasia in Very Low Birth Weight Premature Infants: A Prospective Cohort Study

Background: Bronchopulmonary dysplasia (BPD) is the second prevalent lung disease and one of the care challenges of premature newborns. Different risk factors play an important role in the development of this disease. Therefore, the aim of the present study was to investigate the relationship between colonization with Ureaplasma urealyticum and BPD.Methods: This prospective cohort study was conducted in 2017 in the neonatal intensive care unit of Alzahra Hospital in Tabriz, Iran. The samples included newborns weighing less than 1500 g with the gestational age of less than 32 weeks who required intubation within 72 h after birth. Following recording the initial information, the secretions within the trachea were aspirated and Ureaplasma urealyticum was detected in reference laboratory by polymerase chain reaction. Afterwards, we completed a follow-up of 28 days after birth for BPD.Results: Our findings demonstrated that out of 82 infants, 21 cases (26.3%) were excluded from the study due to discharge from hospital or death before the age of 28 days. Among the rest (61 newborns), three cases (4.3%) were shown to have secretions infected with Ureaplasma and 33 cases (54.1%) suffered from BPD. All the three newborns infected with Ureaplasma had BPD. However, no significant relationship was observed between Ureaplasma infection and BPD (P=0.24).According to the analysis of data, the most important factors contributing to BPD among the patients were the gestational age and birth weight. In other words, for one week increase in the age of pregnancy and for each 100 g increase in birth weight, the likelihood of BPD is reduced by 55% and 1%, respectively. In the present study, no relationship was found between Ureaplasma infection and BPD, which might be due to the low prevalence of this infection. Nonetheless, prematurity and low birth weight could be regarded as the two considerable risk factors for BPD.Conclusion: In order to perfectly determine the role of bacterial colonization within the trachea in BPD, collecting and analyzing various samples for the existence of other bacteria are recommended