An Overview of Techniques for Measuring Residual Stress in Metal Matrix Composites

Measurement of residual stress is significant to ensure safety, reliability and the life of composites, and currently has been a hot issue in scientific research. The fabrication processes such as machining, and heat treatment inherit either kind of residual stress which had either positive consequences or negative ones, for example, the fatigue limit of a component enhances by compressive stress, whereas corrosion resistance gets reduced by tensile stress. This study is aimed at a brief overview of the recent advancement in this field to help researchers in the in-depth study of measuring residual stress. It helps them in selecting the most appropriate techniques among destructive methods i.e., mainly Contour, ring core, deep hole-drilling method, and non-destructive techniques i.e., diffraction, ultrasonic method, depending on their requirements and applications. For each available technique, working methodology, physical limitations, and applications are discussed. At the end of this paper, future trends regarding an assessment of residual stress have been forecasted.

Integrated Wide Area Protection and Control for Power Grid Security

The traditional“three defense lines”for power systems are based on local information and static protection&control strategy,which are not suitable to modern large-scale power systems.In order to improve the security of UHV hybrid power grids,the Integrated Wide Area Protection&Control(IWAPC)is proposed in this paper by applying the new technologies of synchronized high-speed communication,which integrates“three defense lines”and promotes existing wide area protection only for security control.The IWAPC is the hierarchical protection and control system which provides the protection and control for wide area power networks to improve their reliability and security.It is divided into three levels,the local bay level,the substation integrated protection level and the wide area protection level.The wide area real-time protection and control information platform is the most important part of the IWAPC,which is based on a synchronized wide area communication network.The key technologies and new development trends include network topology analysis,wide area backup protection,wide area intelligent reclosing,wide area load shedding,wide area auto-switching,overload cutoff and transfer,transmission section protection,intelligent system splitting and dynamic stability control.It cannot only integrate three lines of defense for power system protection and control,but also improve security of the power grid.

Integrated protection based on multifrequency domain information for UHV half-wavelength AC transmission line

Half-wavelength AC Transmission(HWACT)can improve capability of AC transmission significantly.According to the basic principle of HWACT,the electromagnetic transient model of HWACT is built to analyze the fault transient process of transmission line.Based on fault characteristics of HWACT,the adaptability of traditional protections for transmission lines is analyzed briefly,such as current differential protection,distance protection and over current protection.In order to solve the problems of conventional protection caused by HWACT,a novel integrated protection based on multi-frequency domain information is proposed in this paper,which uses both the power frequency information and transient information.The integrated protection based on multi-frequency domain information takes advantages of power frequency and transient protections,which can not only improve the performance of traditional protection of AC transmission line but also realize fast fault judgment by transient travelling wave protection.