composite insulator has been widely used in highvoltage electric power transmission system owing to its advantages such as light weight, anti-pollution flashover and less routine maintenance. With the increasing number of compositor insulators and their running years, the aging of compositors draws attention to the related industries. Considering the aging problems of composite insulator, the material performance of a silicone rubber composite insulator which has worked for more than 10 years on a 500KV transmission line at Guangzhou in China has been analyzed. Judged from the surface, a non-uniform aging characteristic on the different surfaces of the insulator sheds and sheathes exists. The contact angle measurements made on surfaces from different positions confirm the visual aspect of non-uniform aging. In order to explain the phenomenon, the electric field of different positions is computed through finite elements methods. Then the shed and sheath samples on the insulator's various positions were analyzed with Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). At the same time, Thermally Stimulated Current (TSC) was used to find the inner charge difference of both sides of sheds from differentpositions. It is found that electric field intensities and ultraviolet of sunlight are the main factors influencing the aging of the silicone rubber composite insulators. The results will be helpful to the researches of aging problems from composite insulator and its antiaging optimization design.
High voltage direct current (HVDC) transmission lines fault location is extremely important in repairing the fault line timely and reducing outage losses, so as to guarantee the reliability of power supply and to improve the stability of power system. Traveling wave, which is a kind of non-stationary signal with mutation, spreads along the line when HVDC transmission line fault happens. The feature of the traveling wave with mutation contains the fault time, fault location. By analyzing the traveling wave, accurate fault location can be derived. In this paper, an HVDC transmission line fault localization algorithm based on radial basis function (RBF) neural network with wavelet packet decomposition (WPD) is proposed. For the sake of simplicity, the proposed algorithm is shorted for WPD-RBF in the rest of this paper. By using WPD algorithm, the feature of the traveling wave can be extracted from the voltage and current signals. These features are then used as the training input sample of RBF neural network to mapping to the line fault location. Simulation result indicates that, line fault position can be accurately localized by the proposed algorithm. Keywords-HVDC; transmission line fault location; wavelet packet decomposition; RBF neural networkI.
ZnO varistors are wildly used in power system and electronic system to protect equipments against surges and overvoltage. As there is none series gap in ZnO arresters, the ageing phenomenon of ZnO varistors has attracted great attention. In order to study the principle of pulse degradation of ZnO varistors, the thermally stimulated current (TSC) characteristic, voltage-current (U-I) and pulse electro-acoustic (PEA) characteristic of aged ZnO varistors have been investigated. The experimental results show that the trap level and trap charge increase as the impact time or impulse current increased; the TSC results show that there is ion migration during pulse degradation process of ZnO varistors, which is account for the drift of U-I characteristic curves. Based on the research results, a conclusion can be drawn that the pulse degradation of ZnO varistors is the consequence of thermal ageing and ion migration. The space charge characteristics of ZnO varistors provide a new view to study the pulse degradation mechanism of ZnO varistors.
ZnO varistors have high nonlinearly which are widely utilized in protecting power systems and electronic devices against the dangerous over-voltages or surges. In this paper, the thermally stimulated current (TSC) characteristic and U-I characteristic performance of aging ZnO varistors had been investigated in different aging conditions(impulse current amplitude, impulse time). Based on the experimental results, with the increase of impulse time, U-I characteristic drifts. It was found that the trapped charges would be increasing with the increase of impulse time, and this might bring the decrease of the Schottky barrier height aggravating, which would lead to the impulse aging of ZnO varistors. In addition, the trend of U-I characteristic is consistent with the trend of TSC characteristic. Consequently, the thermally stimulated current experiment is an effective method to present the impulse aging degree of ZnO varistors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.