Papers by Keyword: Breakdown

Abstract: Zinc oxide (ZnO) crystals form are various applications could be created like in manufacturing ultraviolet laser and photodetectors. Zinc oxide (ZnO) crystals are synthesized by applying electric current on ZnO ceramic bar which are made using powder metallurgy method. By using Scanning Electron Microscope (SEM) and X-Ray Diffractometer (XRD) could be characterized of ZnO sintered bars easily. The different types of crystal are produced such as polygonal, broken stick, flowers, trunks and many more when applied the DC heating until the sample of ZnO will be glows and breaks apart. The loads or pressure and heating method to the sample of ZnO will be affected to the types of crystal growth. The optimum load is 3 metric tonne and will ease the ignition during DC heating due to less porosity of the samples.

Abstract: The effect of the termination structure on the unclamped inductive switching (UIS) failure is analyzed for two kinds of SiC MOSFET, where S-MOS and G-MOS termination structure are adopted. The MOSFETs are named as S-MOS and G-MOS according to the buses connecting with different electrodes in the termination region. The experimental results indicate that the avalanche energy G-MOS can withstand is 1.15 times larger than that of S-MOS. To understand what are the factors that lead to different UIS capabilities, further static measurements and hotpot mapping after UIS test are done, and technology computer aided design (TCAD) simulation also is done to further confirm the principle.

Abstract: This study focuses on the evaluation of different post-trench processes (PTPs) for Trench-MOSFETs. Thereto, two different types of inert gas anneals at process temperatures above 1250 °C are compared to a sacrificial oxidation as PTP. The fabricated 4H-SiC Trench-MOS structures feature a thick silicon dioxide (SiO₂) both at the wafer surface (‘top’) and in the bottom of the trenches (‘bottom’) in order to characterize only the thin gate oxide at the trenched sidewalls. It is shown that an inert gas anneal at a process temperature between 1400 °C and 1550 °C yields uniform current/electric field strength (IE) values and excellent dielectric breakdown field strengths up to 12 MV/cm using a SiO₂ gate oxide of approximately 40 nm thickness. Charge-to-breakdown (QBD) measurements at a temperature T of 200 °C confirm the necessity of a high temperature inert gas anneal after 4H-SiC trench etching in order to fabricate reliable Trench-MOS devices. QBD values up to 16.2 C/cm² have been measured at trenched and high temperature annealed sidewalls, which is about twice the measured maximum QBD value of the corresponding planar reference MOS structure. The capacitive MOS interface characterization points out the need for a sacrificial oxidation subsequent to a high temperature inert gas anneal in order to ensure a high quality MOS interface with excellent electrical properties.

Abstract: For oblique incidence of laser radiation on the target, the breakdown of air and erosive jet are separated in time and space. The electron density is higher in the air breakdown area while Al I density is higher in an erosive plume area. We also defined plasma expansion mechanism and estimate the time of erosive plume formation.

Abstract: According to a TOM bushing faults, three typical 220kV cable-conductor bushings (COT, TOM and BRDLW) widely used in the power grid are analyzed about diversion structure. Bushing diversion structure, diversion contact surface, current path and installation sensitivity are discussed in the paper. The study found that installation accuracy of TOM bushing has greater effect on contact resistance of diversion path than others. The improper installation of TOM bushing caused overheating defects and finally developed into this bushing fault.

Abstract: According to two typical COT bushing faults, three typical 220kV cable-conductor bushings (COT, TOM and BRDLW) widely used in the power grid are analyzed about bushing compact structure. Bushing pressing structure, installation clamping force, deformation deviation and sealing system are discussed in the paper. The study found that the installation clamping force and the reeds adjustment range of COT bushing is smaller than others. The manufacturability deviation and the poor condition will cause hidden trouble to the bushing sealing system. Last, several suggestions about bushing maintenance are given for the COT bushing.

Abstract: Some low purity alumina ceramics with an alumina content ranging from 86% to 93% were investigated, in order to explore the effects of microstructural parameters (grain size, intergranular phase) on mechanical (wear) and dielectrical parameters. The microstructure and worn surfaces were analysed using scaning electron microscopy. The correlation between microstructural, dielectrical properties and wear is discussed. It has been proposed that mechanical and electrical properties are two aspects of the same fundamental mechanism. Key words: Al2O3, Microstructure final, Wear resistance, Breakdown.

Abstract: The principle of laser induced air breakdown was introduced. The laser energy conversion in ionization process was studied. The phenomenon of laser induced air breakdown was observed by using high speed camera. It was found that a higher laser energy induced more laser energy to transfer into light and sound energy. The plasma reached maximum in shape in about 20 to 30 ns after laser excitation, and disappeared in about 16μs.

Abstract: Cross-linked polyethylene cables are widely used in power transmission system. In this work the effect of frequency and boost on the breakdown performance of XLPE cable with inserted needle defects was investigated by the frequency-tund resonant system with frequency ranging from 20Hz to 300Hz. The breakdown paths were observed by an optical microscope, and the fractal dimensions of the paths were estimated according to box-counting method. It was found that, with the increase of frequency, the variation of path fractal dimension as a function of frequency corresponded to that of breakdown voltage. Compared with the continuous boost method, the frequency, at which the fractal dimension of breakdown paths approached saturation and the breakdown voltage peaked, became lower under step test method. The increase of breakdown voltage is due to the increase of electrical power used for the initiation and development of dense discharge paths.

Abstract: This paper studies Optimal NT policies for a k-phase service M/G/1 system with Bernoulli vacation schedule. The system contains an unreliable server with a breakdown period and delaying period. The server determines to start service by the policy: the server reactivates as soon as the number of arrivals in the queue reaches to a predetermined threshold N or T time units have elapsed since the end of the completion period. There are k phases of service in the system. After the completion of k phases service, the server may take a short vacation or may remain in the system to serve the next unit, which is defined by Bernoulli vacation schedule. Moreover, we assume the server fails according to a Poisson process whose repair time follows a general distribution. In final, we analyze the system characteristics for each scheme and obtained the optimal NT threshold to minimize the cost function.