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This paper proposes an adaptive protection scheme for distribution systems with distributed generations (DGs). To mitigate the influences on the protection devices by DGs, an online calculation method of fault current under various system operation conditions is presented. By sampling local available measurements in the buses, a proposed optimized estimation method is used to calculate the Thevenin equivalent circuit parameters of the system dynamically. Moreover, the short-circuit current can be calculated accurately to set the overcurrent relay protection value considering the behavior of DGs during the fault. To ensure the accurate operation of the protection devices, a coordinated protection scheme, including primary and backup protection is presented. Performances of the proposed method and scheme have been verified by simulations on a sample distribution system based on PSCAD/EMTDC. The sensitivity and selectivity of the coordination between primary and backup protection are satisfied under different system operation conditions, fault locations, and types. [ABSTRACT FROM AUTHOR]

A new reclosure scheme applied to parallel transmission lines with shunt reactors is proposed to improve the adaptability of the autoreclosure. Detailed analysis of the fault phase voltage is performed to derive the criteria to distinguish the temporary fault from the permanent fault. For different types of ground faults, the integral of the fault phase's recovery voltage is used to identify the permanent grounded faults. For different types of cross-line ungrounded faults, the integral of the \beta modulus of the fault phase's recovery voltage is used to identify the permanent cross-line ungrounded faults. Besides, the phase reclosure sequence principle is used for all fault types. The performance of the proposed scheme is verified by the digital and analog simulation test for a 500-kV parallel transmission line with shunt reactors for several cases on different fault types and fault conditions. The Electromagnetic Transients Program-based and physical analog simulation results show that the proposed scheme is effective. [ABSTRACT FROM PUBLISHER]

Provides information on a study which developed an electric charge-pumping method to characterize the hot-carrier induced local damages. Basic principles; Critical surface electron and hole concentration; Results and discussion.

The rapid development of microgrid (MG) has made it ready to connect multiple MGs for providing regional power supply. The energy management of a multi-MG (MMG) system is the key to the reliable, economic operation of the interconnected power system. The MMG system is rich in distributed generation sources. The intermittence and volatility of renewable energy sources (RESs), such as wind and solar, cannot be ignored in a large-scale hybrid power system. Therefore, the energy management of a MMG system is a complex problem that coordinates distributed generation units within individual MGs, the power exchange among MGs, and the power trading between the grid and MGs. System of systems (SoS) has been identified as an effective way of forming a MMG system and coordinating the participating MGs for energy management. This paper proposes a hierarchical decentralized SoS architecture for the energy management of a MMG system and, accordingly, formulates it as a bilevel optimization problem. Energy management at the level of individual MGs is modeled as a multiple-stage robust optimization to handle the issue of RES uncertainty. Energy management at the level of MMG system further addresses the problem of spatially unbalanced demand and generation in the area. The proposed MMG energy management is further verified through a case study. [ABSTRACT FROM AUTHOR]

This paper researches on the implementation of an ultrasonic time-of-flight (TOF) measuring system by the difference of the peak time sequences (PTSs) of dual frequencies. The process to develop appropriate implementation parameters was demonstrated. Critical characteristics of the transient behavior of the PTS were studied, and their counteracting data processing measures were devised in the process. Obtaining the PTS by averaging repeated test data and the linear regression on the PTS was found to be effective in uncovering the actual TOF of the first wavefront with high precision. A PC-based test bench was built to test the characteristics and to verify the performance of the new TOF measurement system. In our TOF measurement over the distance of 145 cm, a standard deviation (STD) of 0.0113 of a period was achieved by a nominal driving wave period of 25.6 \mu\s (39 kHz) and a frequency difference factor of 0.0048. When applied to a distance measurement, the worst STD of 0.097 mm was achieved with a relative distance ranging up to 1450 mm, given the nominal driving wavelength of 8.6 mm. This new dual-frequency PTS-based TOF measurement system can be economically embedded in a microcontroller, together with a field-programmable gate array, and some simple transistors that are suitable for positioning mobile units indoors or in small open-field environments. [ABSTRACT FROM AUTHOR]

In this paper, the light emission performance from nonpolar a -plane gallium nitride (GaN)-based photonic crystal (PC) slabs with line-type defect cavities has been investigated. Via the focused ion beam milling technique, thin membrane structures of the nonpolar GaN PC defect cavities were engineered, exhibiting one dominated resonant mode occurred at 419.3 nm with a high quality factor of 1.9\times 10^{3} in the photoluminescence emission characterizations. In the far-field region, light emission performance shows a high polarization degree of 50% with the beam direction perpendicular to the defect cavity. Compared with the PC defect cavity patterns fabricated on c$ -axial oriented GaN materials, the $a$ -plane PC defect cavities display not only the linear light output–input power dependence, but also an invariant resonant mode of constant light emission behavior with increasing the injection carriers, therefore providing a new perspective for the future development of promising optoelectronic devices. [ABSTRACT FROM AUTHOR]