Koviljka Stankovic

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.

Calculation of impulse characteristics for gas-insulated systems with homogenous electric field

The possibility of generating a statistical sample of the pulse breakdown voltage random variable numerically is examined for arbitrary shaped pulses. Impulse characteristics are then determined on the basis of the generated statistical sample. Numerically generated statistical samples of the pulse breakdown voltage random variable are compared to the corresponding experimentally obtained statistical samples. Impulse characteristics obtained from the numerically generated statistical samples are compared to the corresponding impulse characteristics derived from the semi-empirical Area Law and the Time Enlargement Law. The set of impulse characteristics obtained in this way is compared to the results obtained experimentally for different shapes of the pulse voltage load. Gases used in the experimental and numerical models include SF6, N2 and Ar. Gas pressures range from 1 × 102 Pa to 6 × 102 Pa, and inter-electrode gaps from 0.1 to 10 mm. A homogenous electric field is considered.

Simulated Effects of Proton and Ion Beam Irradiation on Titanium Dioxide Memristors

Effects of titanium dioxide memristor exposure to proton and ion beams are investigated. A memristor model assuming ohmic electronic conduction and linear ionic drift is used for the analysis. Simulations of particle transport suggest that radiation induced oxygen ion/oxygen vacancy pairs can influence the devices operation by lowering both the mobility of the vacancies and the resistance of the stoichiometric oxide region. These radiation induced changes affect the current-voltage characteristic and state retention ability of the memristor.

Conditions for the applicability of the geometrical similarity law to impulse breakdown in gases

This paper investigates the conditions for the applicability of the geometrical similarity law to impulse breakdown in gases, using statistical methods necessitated by the stochastic nature of the impulse breakdown voltage. Theoretical analysis in the paper is accompanied by experimental results obtained for geometrically similar systems, i.e. for systems with equal shapes of the macroscopic and microscopic electrical field. The experiments were conducted in controlled laboratory conditions, for a wide range of gas pressure and inter-electrode gap values. Two-electrode systems were used, with both homogeneous and non-homogeneous electrical fields, utilizing SF6, N2 and He gases as insulators. Standard lightning and switching voltage impulses were applied, as well as ramp-shaped impulses with different slopes. On the basis of the statistical processing of the obtained experimental results, conclusions regarding the conditions for the applicability of the geometrical similarity law to impulse breakdown in gases are drawn.

Surface-time enlargement law for gas breakdown

This paper investigates, through theory and experiment, the applicability of the results obtained in laboratory tests of relatively short duration performed on model structures, as a part of the process of designing high-voltage equipment intended for lasting exploitation. Possibilities and limitations of applying these results to practical structures are examined using the methods of mathematical statistics. Special attention is devoted to the influence of electrode surface enlargement and pulse load (overvoltage) prolongation on the statistical behaviour of the pulse breakdown voltage random variable, expressed in the form of the enlargement law. In the theoretical part of the paper, the general four-dimensional (space-time) enlargement law is derived, along with its simplified three-dimensional (surface-time) variant. In the part of the paper related to the experiment, performed with the aim of testing the applicability of the derived surface-time enlargement law to SF6 gas-insulated two-electrode systems, a description of the experimental equipment and procedure is provided, along with the details of measurement data processing. Comparison of experimental results with those predicted by the surface-time enlargement law proved its validity for a two-electrode configuration with a homogenous and radial electric field, insulated by SF6 gas under pressure (with gas pressure as a parameter).

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.

Determination of Pulse Tolerable Voltage in Gas-Insulated Systems

In this paper we expound on the procedure of determining the pulse tolerable voltage characteristic in the voltage-versus-time frame, by applying the time enlargement law to the breakdown time random variable, and using a single statistical sample for this variable, obtained through experiments with a predefined shape of the voltage load. The suggested algorithm has been experimentally tested for Ar, N2, and SF6 gases, in the pd product (pressure × interelectrode gap) range from 10-4 to 300 bar mm. The testing was performed by comparing the pulse tolerable voltage characteristic of a two-electrode configuration obtained by applying a particular shape of the pulse voltage load with the values corresponding to other pulse voltage shapes, covering a wide range of frequencies. Satisfactory results have been obtained concerning the applicability of the procedure, with certain minor limitations, which are pointed out.

Influence of

This paper investigates the synergetic effect of the SF6-N2 gas mixture, taking the effective temperature of the free electron Maxwell spectrum at the time of breakdown as an independent parameter. In this way, a direct link between a macroscopic variable (dc breakdown voltage of the mixture) and a fundamental microscopic variable (effective temperature) is established. Derivations are presented of expressions that relate the streamer mechanism breakdown voltage in an SF6-N2 gas mixture to the pd product (pressure×interelectrode distance), the percentage contribution of the N2 gas (χ), and the effective temperature of the spectrum of free electrons in the mixture (Td) at the time of breakdown (breakdown temperature). A new theoretical model for the dependence of the electron attachment coefficient (effective cross section) in the electronegative SF6 gas was used, which resulted in the final expression being different from the corresponding expressions obtained from other models. The obtained results were verified by experiments, under well controlled laboratory conditions. There was a high degree of agreement between the experimental and the theoretically calculated results.

{\rm SF}_{6}\hbox{--}{\rm N}_{2}

Two types of three-electrode gas-insulated spark gaps have been investigated in this paper: one with the third electrode located inside the main electrode, and the other with a separate third electrode. Three types of insulating media have been used: vacuum, SF6 and N2. Additionally, three different electrode materials have been implemented: copper, steel and tungsten. The following characteristics have been tested experimentally: the influence of insulating gas parameters on spark gap operation, the influence of the polarity of working and trigger voltages on spark gap operation, and the influence of the rate of rise of the trigger voltage on spark gap operation and the degree of spark gap irreversibility. A theoretical model of the spark gap is presented in the paper, which provides a basis for explaining experimental results depending on specific characteristics of the spark gap.

Gas Mixture Parameters on the Effective Breakdown Temperature of the Free Electron Gas

This article presents the experimental results of DC dynamic breakdown voltage Ub for small voltage increase rates and electrical breakdown time delay td of commercial gas discharge tubes. It was shown that Ub is a stochastic value with Gauss distribution for voltage increase rates ≥2 V/s. In order to determine the static breakdown voltage Us as a deterministic quantity, the mean values of the dynamic breakdown voltage Ub as a function of voltage increase rate k were extrapolated until the intersection with Ub axis using linear fit. The intersection point (for k = 0) correspond to Us value. Additional experiments were performed in order to verify the temperature stability of these components over the wide temperature range from 25 to 250 °C. The experimental results of electrical breakdown time delay are also presented in the paper. Electrical breakdown time delay if often refereed as delay response and it is also very important parameter of gas filled devices. It was shown when the voltage higher then 310 V is applied to those components, the mean value of electrical breakdown time delay td insignificantly varies to the value of relaxation time τ≈1 s, while the breakdown probability is close to one for the voltages higher then 380 V. These facts show that the commercial gas discharge tubes are very reliable for the protection for voltages higher then 380 V.