External diagnosis of Gas Circuit Breaker contact wearing
The internal inspection for a GCB (gas circuit breaker) is regularly performed to check and change contact parts in the case that the number of times of fault current breaking reaches a specified number, because TBM (time based maintenance) criteria is generally applied. Our new system, however, can change maintenance criteria to CBM (condition based maintenance). Current interval for internal inspection may be, however, redundant compared with the actual amount of contact wearing, because it is difficult to estimate the actual amount of contact wearing correctly from the outside. Then, in order to evaluate the precise amount of contact wearing from the outside, we developed a sophisticated system which can presume the accurate amount of contact wearing by using real breaking current and arcing time. Furthermore, this new system can evaluate the precise amount of contact wearing even if CT (current transformer) is saturated by DC in fault current and regardless of the current phase at the breaking. Therefore, the internal inspection period to replace contact materials can be extended up to nearly three-fold length compared with the traditional way.
The least squares method for VCB electrical endurance parameters predicting research based on breaking current weighted cumulative method
Calculating method of the current index alpha and the theoretical total wear Q is emphatically analyzed based on the electrical endurance curve, which adopt advanced breaking current weighted cumulative method (BCWC) used for predicting the remaining electrical endurance of vacuum circuit breaker (VCBs) contact system. The purpose of this work is to provide a clear and concise engineering description for VCBs contact system on-line monitoring practically. The mathematical and theoretical model of electrical endurance for VCBs contact system is established. The current index alpha and the theoretical wear Q are analyzed in detail based on the method of least squares. Then the parameters predicting method used for prognosticating remaining electrical endurance is proposed. Comparative study was carried out, through which the validity and feasibility of researched method can be verified. The results of this work show that the achievement and the researched procedure are correct and reasonable, which indicate the total wear of a VCB contact system is certain once contact material and structure type is determined. Moreover, based on the method provided, the relation between breaking current and already operation time is also can be gained. So the current index alpha and the theoretical wear Q applying to the advanced breaking current weighted cumulative method are obtained. Finally, the hardware and software for VCB contact system electrical wear on-line monitoring device is fulfilled based on the research results mentioned above. This work can provide some reference for engineering application for electrical endurance on-line monitoring of VCBs contact system.
Child Poverty in the United States: A Tale of Devastation and the Promise of Hope.
The child poverty rate in the United States is higher than in most similarly developed countries, making child poverty one of America's most pressing social problems. This article provides an introduction of child poverty in the US, beginning with a short description of how poverty is measured and how child poverty is patterned across social groups and geographic space. I then examine the consequences of child poverty with a focus educational outcomes and child health, and three pathways through which poverty exerts its influence: resources, culture, and stress. After a brief review of the anti-poverty policy and programmatic landscape, I argue that moving forward we must enrich the communities in which poor families live in addition to boosting incomes and directly supporting children's skill development. I conclude with emerging research questions.