Pulsed Electrical Breakdown Research Articles

Criterion of the incubation time in the problems of pulsed fracture and electric breakdown

The problems of a pulsed strength of continuum media are considered in terms of the structural-time approach that is based on the concept of the incubation fracture time. This approach makes it possible to describe phenomena that arise under high-velocity external effects. A limiting condition that determines the instant of rupture or breakdown is proposed on the basis of the structural-time approach. A way to interpret and to determine the incubation time is proposed. A phenomenological model of an electric breakdown of solid dielectrics is formulated. Examples are considered where the structural-time approach is applied to problems of spall fracture, crack initiation, and a pulsed breakdown of dielectrics. A procedure for describing the time dependence of the electric strength (volt-second characteristic) is described in detail. The results of the calculations are found to be in good agreement with experimental data.

Transient regime of pulsed breakdown in low-conductive water solutions

The transient regime of pulsed electrical breakdown in both distilled and low-conductive water (σ<15 µS cm-1) has been investigated in a point-to-plane electrode system using quasi-rectangular voltage pulses with a repetition frequency of 25 Hz. Two individual current pulses were observed within the interval of voltages of 18.5-20 kV. The appearance of the transient regime was limited by the minimal capacitance of the storage capacitor C≅4 nF. While the time lag of the first current was not apparently affected by the capacitance of the storage capacitor, a growth in time lag of the second current pulse was observed as the capacitance was increased. The distortion of the electric field at the head and an increase of the leader channel resistance due to accumulation of the electrostatic charge on the inside wall of the gaseous channel are two most likely mechanisms effective in the transient regime. The enhancement of OH radical production in such a regime can be surmised from spectroscopic observations.

An experimental system for studying the dynamics of the pulsed subnanosecond electric breakdown of gas gaps

In order to study pulsed gas breakdown initiation dynamics, a subnanosecond voltage pulse with a width of 0.2–4 ns and a height of 20–150 kV is applied to a gas-discharge gap. The voltage rise rate ranges from 6×1013 to 7.5×1014 V/s. The amplitude and duration of subnanosecond high-voltage pulses are adjusted continuously, as well as the magnitude and profile of the discharge current. The glow accompanying prebreakdown and breakdown processes in the gap is registered by a high-speed electron-optical camera.

Use of inductive energy storage for electric pulse destruction of solid materials

An inductive energy storage switch system for the destruction of solid materials is reported. This is based on creating a pulsed electric breakdown in the solid dielectric, which then propagates in the specimen. This scheme provides a higher destruction effectiveness compared to a capacitive energy storage system. The higher energy efficiency is attributed to a different discharge behavior during the discharge build-up in the solid material. A higher applied voltage causes a breakdown of a larger number of voids in a heterogeneous solid dielectric. The energy transfer to partial discharges, when using the inductive storage system, is faster than for the capacitive energy storage system, due to a shorter risetime of the discharge current.

Pulsed electrical breakdown from superconducting electrodes in vacuum diodes

Results are presented of investigations of the pulsed electric strength and threshold current densities of YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb cathodes at cryogenic temperatures. It has been shown that the cooling of a Nb cathode from 300 to 4.2 K leads to a 1.5 to 2.5/spl times/ increase of pulsed electric strength and that the transition of the cathode from the normal to the superconducting state has no effect on either the breakdown delay time or the threshold current density of cathode micropoints. An analysis is made of the process of heating of cathode micropoints from cryogenic temperatures under the action of high-density field emission current. Experiments have shown that the atomic structure and electronic properties of Nb cathode micropoints and the dynamics of their heating are the same for Nb cathode tips having an atomically smooth and clean surface. We did not observe this effect for YBa/sub 2/Cu/sub 3/O/sub 7-x/ single crystal cathodes. That is why the prebreakdown phenomena in diodes with YBa/sub 2/Cu/sub 3/O/sub 7-x/ electrodes are similar to those in diodes with metallic ones. Data are presented of the work function, limiting current densities, and tensile strength of YBa/sub 2/Cu/sub 3/O/sub 7-x/ single crystal cathode tips. >

Pulsed electrical breakdown in liquid helium in the μs range

Information about breakdown time-lags under pulsed voltage stress is prerequisite to the insulation design of superconducting devices. Experiments have been carried out using a pulse generator which provides a step voltage with 200 ns rise time and a long decay time constant of more than 1 ms. The present experiments may bridge the information gap between time lag measurements in the ns range using extremely high field strengths, and existing data found with usual lightning impulse voltage. The test device is described in the paper, and some typical results are discussed in detail.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characteristics of the explosive action associated with the pulsed electrical breakdown of hard materials

Characteristics of the explosive action associated with the pulsed electrical breakdown of hard materials

Electrical Breakdown Characteristics of Soil

The pulsed electrical breakdown characteristics of soil between a hemispherical and a planar electrode have been measured in meter-size geometries for three soil types with water contents from 1 to 7% by volume. The threshold electric field for breakdown is a function of the soil type and the water content, varying from about 1 to 2 MV/m locally near the hemispherical electrode. The delay time (tD) between application of the voltage and the occurrence of the breakdown is primarily a function of the applied voltage, which varies approximately as tD-3/8 for these samples. After breakdown, the impedance of the soil decreases with time until it reaches a minimum impedance of 0.2 to 5 Ω/m for these meter-size samples, depending on the current that the pulser can drive through the arc. The discharge arc prefers to travel underground rather than on the surface of the soil unless there is some low-impedance object on the soil surface.

Effect of lamination on the pulse breakdown of mica

1. The important role of closed laminations in the pulsed electric breakdown of mica has been established. 2. Electrical strengthening of mica due to the effect of a one-sided pressure has been observed.

156. Determination of the velocity of expansion of plasma of a cathode torch at pulsed electric breakdown of millimeter vacuum gaps: C P Vavilov, Izv VUZ Fiz, 9, 1972, 139–140

Differential and total cross sections of the optical (radiative) collision process with an asymptotically forbidden transition He(11S) + Ne + ℏω→ He(21S) + Ne have been calculated in the framework of exact quantum mechanical and uniform quasi-classical approaches in the energy range 1–220 cm−1. The dependence of the total and differential cross sections on the frequency and polarization of light has been investigated. Although the process involves only atoms in symmetric S-states the results demonstrate the azimuthal scattering asymmetry. The disagreement between the quantum and quasi-classical approaches does not exceed 10% for collision energies ⩾50 cm−1, but increases up to 25–40% with collision energy decreasing to 1–10 cm−1 with a very similar functional dependence on the scattering angle. The reason for the disagreement here mainly is the loss of accuracy of the WKB approximation for the ground state wave function at low energies.

Rate of expansion of the plasma of a cathode flare with pulsed electric breakdown of millimeter vacuum gaps

Rate of expansion of the plasma of a cathode flare with pulsed electric breakdown of millimeter vacuum gaps

Polarization effects in pulsed electrical breakdown of suspensions

The effect of conductivity and polarization of the solid and liquid phases on the pulsed electrical breakdown of suspensions was investigated. The variation of the suspension breakdown voltage with concentration of the disperse phase is attributed to distortion of the internal field due to impurity polarization and space-charge formation.

Destruction of the stronger component during the pulsed electric breakdown of a multilayer material

Destruction of the stronger component during the pulsed electric breakdown of a multilayer material

The influence of several factors on pulsed electrical breakdown in rocks

1. The breakdown voltages of the rocks studied are comparatively low and do not exceed 270 kV for a 1 cm thickness. This means that electrical methods based on technically available energy sources can be used for rock breaking. 2. With voltage durations of 2·10−7 to 2·10−6sec, the breakdown voltages of wet rocks do not exceed those of dry rocks by more than 25%. 3. Impregnating rocks with an insulating liquid (transformer oil) increases their breakdown voltages. The relative increase in breakdown voltage depends mainly on the structure and porosity of the rock.