A. Vasić

Mechanism of electrical breakdown of gases for pressures from 10−9 to 1 bar and inter-electrode gaps from 0.1 to 0.5 mm

This paper discusses the mechanisms of gas breakdown at low values of pressure and inter-electrode gap, i.e. in the vicinity of the Paschen minimum. In this area of pressure and inter-electrode gap values, breakdown occurs either through gas or vacuum mechanisms, and also the so called anomalous Paschen effect appears. Electrical breakdown of electropositive, electronegative and noble gases has been investigated theoretically, experimentally and numerically. Based on the results obtained, regions in which particular breakdown mechanisms appear have been demarcated. Special attention has been devoted to the anomalous Paschen effect as well as to the avalanche vacuum breakdown mechanism.

Time enlargement law for gas pulse breakdown

This paper investigates the possibility of applying the time enlargement law for predicting how gas-insulated systems would behave when exposed to pulse voltage loads of different shapes. For this purpose, the validity of the time enlargement law in this case has first been tested and the most suitable theoretical distribution function of the breakdown time random variable established. Pulse characteristics of the investigated insulating system have subsequently been determined, by applying the time enlargement law to experimental values of the breakdown time random variable, obtained in measurements with predefined shapes of the voltage load. Pulse characteristics thus obtained were compared with the corresponding pulse characteristics derived from the area law. The results demonstrate the advantages of the time enlargement law method, especially in the case of a non-homogeneous electric field. The experiments were conducted with SF6 gas, at different values of the pd product (pressure × inter-electrode gap), in a wide frequency range of applied pulse voltages, for a homogeneous, radial and point–plane electrode configuration.

The influence of the electric field shape on the gas breakdown under low pressure and small inter-electrode gap conditions

The connection between nonhomogeneities of the electric field and the value of the breakdown voltage [direct current (dc), pulls] in gases (N/sub 2/, SF/sub 6/) under low pressure and small inter-electrode gap was investigated in this paper. The obtained results show that the values of the breakdown voltages for nonhomogenous fields are considerably higher than the values for homogenous fields. It was also established that there is some disagreement between experimentally and theoretically (numerically) obtained values of the dc breakdown voltages for nonhomogenous fields. These results could be explained by the small distance effect and by the combination of the gas and vacuum breakdown mechanisms.

The validity of the general similarity law for electrical breakdown of gases

This paper investigates the validity of the similarity law in cases of dc and pulse breakdown of gases. Geometrically similar systems insulated with SF6 gas were used during experiments. It is shown that the similarity law is valid for dc breakdown voltage if the electron mean free path is included in geometrical parameters of the system, but not for pulse breakdown voltages. The explanation for this is the mechanism of the pulse discharge. The similarity law was expanded to take into account mechanisms of pulse breakdown initiation. Thus, the general similarity law is obtained, the validity of which in case of a pulse breakdown is established experimentally.

The Validity of the Similarity Law for the Electrical Breakdown of

The aim of this paper is to investigate the justification and the limitation of the geometrical similarity law application on the electrical breakdown of SF6 gas. For this purpose, the measurements of the dielectric breakdown voltage for similar systems insulated with SF6 gas were done. The applied dc voltage source had an 8 V/s rate of rise. Standard double exponential overvoltage pulse (rise time T1=1.2 mus, fall time T2 =50 mus) of the amplitude U1 max=320 V, U 2 max=4.80 kV, and U3 max=640 kV was used. On the basis of the obtained experimental results and theoretical considerations, the conditions under which the geometrical similarity laws are applicable on discharges in gases are determined. It was concluded that there is no correlation between the geometrical similarity of the electrode surface topography and corresponding breakdown voltages. It was shown that the extension of the similarity law, introducing the electron mean free path as a linear dimension of the system, gives a good quantitative agreement. Also, in case of the pulse breakdown voltage, it is necessary to apply the breakdown possibility rise law

\hbox{SF}_{6}

This paper aims to find the possibility of stabilizing the gas-filled surge arresters (GFSA) static working point in gamma- and X-radiation fields by an appropriate choice of constructive parameters. The observed effects on some commercial components have been compared to the originally developed GFSA model with the aim of improving the characteristics of the commercial components. The type of noble gas, the pressure in the gas chamber, the inter-electrode gap value, the electrode material, and the manner of electrode surface processing are used as variable parameters. The obtained results are significant for a better understanding of the prebreakdown effects in gases at low pressures, but also have practical importance for the manufacturer of GFSAs

Gas

The most important output characteristics of solar cells, fill factor and efficiency strongly depend on fundamental physical properties of semiconductor materials, such as mobility, lifetime of charge carriers, diffusion length, as well as on the type of transport processes in the device. Ideality factor is considered the most direct indicator of the dependence of output characteristics of solar cells on the electrical transport properties of the cell, that is junction. The results obtained by investigating the influence of ideality factor values on the quality of solar cell as photovoltaic generator are presented in this paper. Since fill factor and efficiency are main indicators of solar cells quality, better understanding of the physical processes leading to their decrease with the increase of the ideality factor is crucial for optimization of the input parameters, and at the same time for obtaining high quality solar cells.

Influence of Gamma and X Radiation on Gas-Filled Surge Arrester Characteristics

The application of MOSFETs as detectors or device components in pulse power technique requires an investigation of their characteristics in radiation fields. Computing possibilities of the renowned programs FOTELP and PENELOPE for determining the energy deposited in MOSFET structure and dose distribution within microscopic dimensions of the dosimeter sensitive volume were presented in this paper. Based on the obtained results, qualitative conclusions were drawn about the values of energy deposited in different material zones having various dimensions. The difference between the two codes used for calculations in materials physics and semiconductor technics, basically originates from the different physical models for numerical simulation of photon, positron, and electron transport through various materials

The Influence of Ideality Factor on Fill Factor and Efficiency of Solar Cells

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.

Computer Simulation of Gamma Irradiation Energy Deposition in MOSFET Dosimeters

Faced with an alarming increase of energy consumption on one side, and very limiting amounts of available conventional energy sources on the other, scientists have turned to the most promising, renewable energy sources. Possibilities for the application of solar systems based on photovoltaic conversion of solar energy are very wide, primarily because of their relatively low cost and very important fact that solar energy is most acceptable source of electrical energy from the environmental point of view. Recently, increased investments in the development of PV technology are observed worldwide. Photovoltaic (PV) conversion of solar energy is one of the most up-to-date semiconductor technologies that enables application of PV systems for various purposes. The wider substitution of conventional energies by solar energy lies in the rate of developing solar cell technology. Silicon is still the mostly used element for solar cell production, so efforts are directed to the improvement of physical properties of silicon structures. Silicon solar cells belong to a wide group of semiconductor detector devises, though somewhat specific in its design (larger than most of the detectors). Basic part of solar cell is p-n junction, which active part is less that 0.2μm thick, so it could be treated as thin film. This photosensitive layer have the most important influence on solar cell functioning, primarily on creation of electron-hole pairs under solar irradiation, transport properties in cells, formation of internal field, and finally, output characteristics of the device such as short circuit current, open circuit voltage and efficiency. Furthermore, in order to function as a voltage generator with the best possible performances, beside p-n junction other thin films such as contact, antireflective, protective (oxide) thin films must be applied both on the front and on the back surface of solar cells. Also, in order to improve characteristics of the device, MIS structure (thin oxide layers) and back surface field layers are routinely used. Since thin films are very important in many fields of modern science (solar cell technology, for example), a large number of methods were developed for their characterization. Characterization of thin films includes investigations of physical processes in them, developing of the methods for measuring major physical and electrical properties and their