No abstract

No abstract

This paper proposes a complete and effective smart over-voltage monitoring and identification system. In recent years, smart grids are of the greatest interest in power system research. One of the main features of smart grid is their self-healing, which can continuously carry out online self-evaluation, discover existing faults, and correct them immediately. The over-voltage smart monitoring-identification-suppression systems play a key role in the construction of self-healing grids. In this paper, eight kinds of common over-voltage are discussed and analyzed. The S-transform algorithm is used to extract features of over-voltage. Aiming at the main features of each kind of over-voltage, six different characteristic quantities are proposed. A well designed fuzzy expert system and a support vector machine are employed as the classifiers to build a two-step identification model. The accuracy of the identification system is verified by field records. Results show that this system is feasible and promising for real applications.

Abstract:A dielectric barrier discharge (DBD) produces a homogenous discharge with low energy consumption, offering broad developmental prospects, and this discharge process is also the mechanism through which charges are transported. Higher reaction efficiency is achieved when more charges are transported. Focusing on the electrode configuration of the multineedle-to-cylinder (MC) system, i.e., the structure of needles arrayed on the inner coaxial rod, the effect of needle arrangement, including needle length (NL), inter axial needle distance (ID), and inter axial needle rotation angle (INRA), on the transported charge per cycle and discharge power in DBDs is investigated. The finite-element method (FEM) and quasi-static field simulation are adopted to study the active region (AR) where the electric field strength exceeds the breakdown electric field strength between MC electrodes because this region plays a dominant role in DBD. The improvement of its volume ratio in the reactor allows an increase in discharge power. The simulation results are in accordance with the experimental results, which illustrate that quasi-static field simulation is effective and reliable. Simulation results show that mutual effects of nearby needles and between needles and the inner rod exist. As a result, shorter ID (1.5 mm), needles with similar lengths (3.5 mm) are arranged, and an INRA of 0° is proven to be the optimal structure because it produces the highest AR volume ratio. The result is experimentally validated by transported charges per cycle and discharge power obtained through Lissajous figures. OPEN ACCESSEnergies 2011, 4 2134

No abstract

No abstract

Abstract:Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high-and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis.

No abstract