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1.
Osmokrovic P. Petkovic D. Markovic O. 《IEEE transactions on instrumentation and measurement》1997,46(1):36-44
This paper describes the construction of four probes adjusted for fast transient monitoring in 123 kV SF6 insulated substations. The primary requirement was the ability to monitor without distortion very fast transients containing frequencies up to 200 MHz. The measuring system was tested and calibrated with the help of computer modeling techniques. The verified experimental apparatus was then used for testing and calibrating the measuring probes. During the test, various effects on the measuring system characteristics were analyzed with respect to materials used for the components of the system 相似文献
2.
Simple analytical expressions for the law of breakdown probability increase are suggested. They are tested by comparing with experimental data obtained by impulse and DC breakdown. The pressure 10-4 Pa and interelectrode gaps d<0.1 mm are used for vacuum, and the pressure 1 bar-5 bars and the interelectrode gaps 1 mm-50 mm are used for gas breakdown. The insulation gas was a SF6, N2 and gas-mixture: SF6-N2. It is concluded that such a simplified approach is not appropriate for vacuum. It is also concluded that, for gas, the BPI (breakdown probability increase) law, in the form of a simple expression, is valid in the considered range of relevant experimental parameters 相似文献
3.
Predrag Osmokrovic Boris Loncar Srboljub Stankovic Aleksandra Vasic 《Microelectronics Reliability》2002,42(12):1959-1966
The aim of this work is examining the influence of the number of the activation––over-voltage pulses to the aging of over-voltage protection elements. Both non-linear (gas-filled surge arresters (GFSA), varistors, over-voltage diodes) and linear (capacitors––constituents of filters) over-voltage protection elements were tested. The instruments employed allow reliable measurements, 1000 consecutive activation were tested. The double-exponential current pulse (amplitude I1max=13 A, I2max=16 A, rise time T1=8 μs, fall time T2=20 μs) for non-linear elements and a double-exponential over-voltage pulse (rise time T1=1.2 μs, fall time T2=50 μs) of the amplitude U1max=320 V, U2max=480 V and U3max=640 V for capacitors were used. The experimental results show that the over-voltage diodes are the most reliable elements in view of characteristic modifications that are consequence of aging. However, it was observed that varistors, GFSA and capacitors undergo noticeable changes in characteristics. 相似文献
4.
Jovalekic C. Pavlovic M. Osmokrovic P. Zdujic M. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1995,2(3):409-412
The effect of oxidation and reduction atmospheres on the ferroelectric behavior of bismuth titanate was investigated. The effective surface density σeff of free charges in samples polarized by applying an electric field Ep=1 MV m-1 at a temperature of 100°C for 90 min was determined by compensation voltage measurements. The thermally treated samples in oxidation atmospheres exhibit a significant decrease of σeff while those treated in a reducing atmosphere exhibit an increase accompanied by an improvement in the stability of the electret charge. Such observations indicate that the formation as well as the transformation of the electret state of Bi4Ti3O 12 ceramics may be related to the enhancement and diminishing of oxygen vacancies. In all cases homocharge with a time independent sign was obtained 相似文献
5.
The influence of switching operations on dielectric strength of vacuum interrupters is described. Detailed experimental procedure and numerical processing of experimental results are presented. The breakdown voltage and emission current before and after switching operations were experimentally determined for closing without current/breaking without current, closing without current/breaking with rated current, and closing without current/breaking of rated short-circuit current. The interconnect gap was varied, and DC lightning impulse voltage (1.2/50 μs) and AC 50 Hz voltages were applied. Three types of commercially available vacuum interrupter were tested, two with transverse and one with axial magnetic field and all having CuCr contacts. It was found which physical mechanisms determine the influence of switching operations 相似文献
6.
Osmokrovic P. Vujisic M. Cvetic J. Pesic M. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(4):803-812
This paper presents measurement results for the random variable "vacuum breakdown voltage", obtained by the application of pulse, dc, and ac voltage. Parameters varied during the measurements were: 1) vacuum pressure and 2) inter-electrode gap width. The measurements were performed under strictly controlled laboratory conditions. Conclusions about the influence that the variable parameters in the experiment exert on the parameters of theoretical statistical distributions have been drawn, based on the statistical analysis of the obtained experimental results. The obtained results have been explained by the mechanisms constituting the process of electrical breakdown in vacuum. 相似文献
7.
The breakdown of SF6 when static and impulse voltages are applied at small values (from 10-4 bar-mm to 1 bar-mm) of the product pd was investigated. It was found that the prevailing breakdown mechanism up to 8×10-3 bar-mm was the Townsend mechanism. Between 8×10-3 and 5.5 bar-mm the Townsend and streamers mechanisms combined, whereas from 5.5 bar-mm on the streamers mechanism took over. The Paschen law was found to hold for the points lying to the right of the minimum when static voltage was applied, whereas edge-type breakdown occurred on the points lying to the left of the minimum. When impulse voltage was applied, the Paschen law was valid only for the points to the right of the 1 bar-mm point. The electrode material affected the static and impulse breakdowns through the values of its work function 相似文献
8.
Lazarevic Z. Radosavljevic R. Osmokrovic P. 《IEEE transactions on instrumentation and measurement》1999,48(3):753-757
In this paper, the authors present a coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses. The effect of iron saturation, rotor parameter variation due to current displacement (skin-effect) and temperature variations of both stator and rotor resistances are taking into account simultaneously. A new device for the temperature measurement in the stationary as well as rotating parts of electric machines is built. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system, which is used for precise testing and investigating of a coupled thermal and electromechanical phenomena. An original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed 相似文献
9.
During the last eight years, 'VIN?A' Institute--Radiation and Environmental Protection Laboratory has performed environmental 'spot' broadband measurements of extremely low frequency (ELF-50 Hz) electric and magnetic fields and RF (100 kHz-3 GHz) electromagnetic fields in over 35 municipalities in Serbia. These investigations were motivated by the local population requesting information about levels of general public exposure to time-varying electric and magnetic fields in living spaces. This paper presents a summary of values measured in households under overhead power lines. These measurements will be useful in determining the exposure levels of the general public, which in turn determines whether the exposure levels are within reference levels recommended by International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines. It has turned out that measured values are far below the recommended safe levels. 相似文献
10.
This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards 相似文献