Voltage Rise Rate Research Articles

Bubbles in Transformer Oil: Dynamic Behavior, Internal Discharge, and Triggered Liquid Breakdown

It is generally accepted that the presence of bubbles severely degrades the electric strength of liquid dielectrics, but the influencing factors and mechanisms have yet to be elucidated. Dynamic behavior, partial discharges (PDs) inside bubbles, and their effects on the breakdown of transformer oil are investigated experimentally and theoretically in this study. The results show that, under a nonuniform electric field, the presence of bubbles does not significantly affect the PD inception voltage (PDIV) and breakdown voltage (BV) of the liquid, as bubbles migrate to the region with lower field strength under dielectrophoretic force. In a uniform electric field, conversely, bubbles greatly reduce PDIV and BV; an increase in the number of bubbles or a slower voltage rise rate appears to exacerbate this effect. The PDIV observed in the experiment is much higher than the theoretical value calculated by the Townsend theory or streamer criterion, which may be due to the lack of free electrons inside the bubble, thus resulting in scarce internal discharge. The addition of X-rays enhances the radiation ionization and then eliminates the inconsistency between the theoretical and measured values of PDIV, which supports our hypothesis. The bubble-triggered breakdown of liquid dielectrics, namely, once a discharge occurs inside the bubble, likely triggering the breakdown of the liquid gap, is observed. The electric field enhancement caused by surface charges and the instability of the gas–liquid interface may account for this.

Influence of Trigger Pulse on the Trigger Characteristics of Surface Flashover Trigger Vacuum Switch

Surface flashover triggered vacuum switch (STVS) working performance mainly depends on the electrical characteristics of trigger pulse. This article presents an experimental investigation of the trigger process. The influence of the electrical properties of the trigger pulse on the trigger characteristics is focused. Based on the self-developed high-performance STVS product, the experimental test platform was established. The experimental results show that a shorter delay time of STVS can be obtained by heightening trigger voltage. However, the effect of trigger voltage on time jitter is not obvious. The slight increase in trigger current has evident influence on trigger delay time. It also does not affect the stability of trigger delay. With the increase in trigger voltage rise rate, the trigger delay time and time jitter can be optimized. Finally, the long-term stability of STVS is discussed. After 300 trigger times, the delay time changes from about 140 ns to more than 150 ns and the jitter changes from about 5 ns to more than 10 ns. In the design of STVS products, it is recommended to adopt a trigger system with a fast rise rate of trigger voltage and trigger current.

ФАКТОРЫ, ВЛИЯЮЩИЕ НА ЭЛЕКТРОМИГРАЦИЮ ПРОКАИНА ГИДРОХЛОРИДА В УСЛОВИЯХ КАПИЛЛЯРНОГО ЭЛЕКТРОФОРЕЗА

The article discusses the influence of various factors on procaine hydrochloride electromigration under conditions of electrophoretic separation by capillary electrophoresis. The rate of voltage rise in the capillary electrophoresis system has been studied and a device making it possible to measure the potential in the system independent of the program software has been developed. The influence of the difference in hydrostatic pressure at the inlet and outlet of the quartz capillary and the difference in the approach to the analysis when changing the base electrolyte are investigated. The influence of the sample injected zone length on reproducibility of assay results of procaine hydrochloride has been studied. In order to improve separation efficiency and reproducibility of quantitative analysis results it is recommended to replace the base electrolyte after each analysis, as well as to inject the sample avoiding short injection values and high pressure. The values of apparent mobility of the test substance which can be used in the development of methods for procaine hydrochloride assay by capillary electrophoresis are calculated. The research results obtained can be applied in chemical and pharmaceutical laboratories as well as in scientific research.

Study of Influential Factors on the Dielectric Strength of [UPE/BaTiO3] Nanocomposites

Unsaturated polyester resin (UPE) was used as a base material and barium titanite nanoparticles (BaTiO3) (50-7-nm) as a support material, with different weight ratios (0.25,0.75,1.25,2 wt%), to prepare a nanocomposite material. The research models were prepared according to the standard specifications and with different thicknesses (≈ 1.1,1.8,2.2,2.7 mm) to show the effect of thickness, number of cycles, percentage of addition and voltage rise rate at (5 kv/s and 0.5 kv/s) on the dielectric strength (Ebr) of the prepared material. The results showed that Ebr decreased with increasing the thickness of the material, BaTiO3 additive rate and the number of cycles. Dielectric strength (Ebr) increases with increasing of voltage rise rate.

Critical study of partial discharge inception in voids: statistical behavior to stochastic nature

Although many studies have been done and advanced progress has been made in understanding partial discharge (PD) behavior in the void, this is not the case firinception of PD, especially its stochastic nature. The statistical behaviors of PD inception voltage (PDIV) and inception time delay (PDTD) inside the void were investigated in this study through repeated tests to observe the stochastic nature of PD inception. The results show that the PDIV and PDTD of the void are highly dispersed and obey Weibull and exponential distributions, respectively. The significant dispersion of PDIV can be attributed to the statistical time delay of PD inception. The lengthy inception delay is attributable to a lack of free electrons. The exponential distribution of PDTD indicates that free-electron generation is completely random; further, the stochastic nature of void PD inception is determined by the supply of free electrons. The test method (voltage rise rate, test time, and test time interval), void parameters (size, material, and surface condition), and background radiation determine PD inception by affecting the volume ionization or surface-emission process providing free electrons. Enhanced background ionization or significant increase in test voltage and test time allow for the effective detection of void defects during PD tests. This work contributes to an empirical understanding of the physical process of PD inception in voids and improving existing PD testing technologies.

Impact of Superconducting Current Limiter on the Gaseous HVDC Circuit Breakers Characteristics

This article combines a mechanical DCCB and commutation circuit charged by resistive superconducting element to study the HVDCGCB arc interruption process during fault occurring and to investigate the transient behavior of the HVDCGCB during switching phenomena using the tools of black box arc model and EMTP-ATP simulation software. at the instant of short-circuit fault occurring, the superconducting resistance becomes a great interrupting resistance to supply the commutation capacitance by the required voltage to drive discharge current through the fault current for obtaining artificial current zero instantly. Developed model has been used for investigating the impact of uncontrolled and controlled parameters such as the factor of power cooling, the arcing time constant and the capacitance and inductance of the commutation element values on the circuit breaker arcing time in the presence of resistive SFCL and in its absence, in order to verify the differences. Results proved that the HVDCGCB with resistive (SFCL) can interrupt the fault current successfully. Arcing time of the fault interruption is reduced to several milliseconds and the interruption capability is extremely improved through commutation capacitance charging voltage and it's discharging current. From the study carried out in the article it is found that the superconducting resistance provides high discharge current leading to improve in the CB interruption process and the rise rate of the re-striking voltage between the circuit breaker contacts decreases with the use of the resistive SFCL, which reduces the likelihood of insulation failure of the circuit breakers. Moreover the impact of resistive SFCL on the HVDCGCB current, re-striking voltage and currents of resonance and absorber elements are investigated. The impact of current limiting resistor on the capacitor's charging current and voltage, is also presented in the article.

Streak investigations of the dynamics of subnanosecond discharge developing in nitrogen at a pressure of 6 atm with the participation of runaway electrons

The results of an investigation of a self-sustained subnanosecond discharge in nitrogen at a pressure of 6 atm are presented. A high voltage pulse with a front of approximately 770 ps at the level of 0.1–0.9 in amplitude was applied to the studied gas gap. In this case, the voltage rise rate in the discharge gap at the prebreakdown stage was 1.45 × 1014 V s−1. A breakdown occurs at the end of the front of the voltage pulse. The cathode geometry used provided a 3.3-fold enhancement of an electric field in the near-cathode spatial domain. It is shown that at the initial stage the discharge is of a volumetric form which turns into a spark form further. The discharge contraction starts from a cathode and an anode almost simultaneously. The propagation rate of ionization waves accompanying the spark channel development is 4.2 × 108 cm s−1. The initial volumetric form of the discharge is provided by preliminary ionization of a gas medium by runaway electrons. The generation of runaway electrons takes place in the enhanced electric field area formed near a microprotrusion on the cathode surface, while the macro-geometry of the discharge gap does not ensure enhancing of the electric field up to the value which is sufficient to the implementation of the runaway electron generation criterion. Numerical simulation of a formation process of the electron avalanche initiated by an electron field-emitted from the top of the cathode microprotrusion was carried out taking into account the motion of each electron in the avalanche. To simulate electron motion through the discharge gap, the 3D Monte-Carlo technique was employed. The following runaway electron parameters were calculated: characteristic runaway electron trajectories; runaway electron energy gained during the motion through the discharge gap; and times required for runaway electrons to reach the anode.

Streamer propagation in atmospheric-pressure air: effect of the pulse voltage rise rate from 0.1 to 100 kV ns−1 and streamer inception voltage

This study investigates the effects of voltage rise rates from 0.1 kV ns−1 to 100 kV ns−1 on streamer discharge in air at atmospheric pressure using numerical simulation. The curvature of the needle electrode is also used as an input parameter to change the streamer inception voltage and the average voltage, V ave, during streamer propagation. The results show that the streamer propagation velocity, v pri, the electric field strength at the streamer head, E h, the diameter of the streamer channel, and the O radical production characteristics during the primary streamer propagation are dependent on V ave. v pri and E h exhibit different effects on V ave/d, where d is the gap distance of the electrode, which indicates that the streamer remains in the transient state from the filament-type discharge to the diffuse-type discharge. The comparison between the simulation and experimental results shows that the simulated v pri characteristics are in good agreement with the experimental results, regardless of the voltage waveform and electrode configuration, which indicates that V ave/d has a strong correlation with the primary streamer characteristics.

Performance Evaluation and Limitations of Overvoltage Suppression Circuits for Low- and Medium-Voltage DC Solid-State Breakers

This paper presents a design and performance evaluation of three different overvoltage suppression circuits employed in a solid-state circuit breaker for medium- to high-power and low- to medium-voltage DC grids. The evaluated criteria are the requirements for passive components, as well as the breaker performance in terms of peak switch overvoltage, peak short-circuit current, fault clearance time and rate of voltage rise during the fault clearing process. Additionally, the impact of the stray inductance in the solid-state breaker design on the anticipated overvoltage is also investigated. Design and operating limitations of each configuration from an application perspective are also discussed. From simulations of a 1.8 kV and 500 A breaker for high-power medium-voltage DC applications it is shown that the most effective overvoltage suppression is achieved by means of using a metal-oxide varistor and a snubber capacitor connected in parallel with the main switch at a cost of high fault current. A medium-power solid-state DC breaker prototype rated at 1.5 kV and 50 A was also designed and constructed. The experimental results reveal that using only a metal-oxide varistor can be sufficient when the breaker employs high-voltage discrete semiconductors with long current falling time and is used in medium-power medium-voltage grids.

Picosecond solid-state generator with a peak power of 50 GW.

This article describes a picosecond solid-state pulsed system, where the input pulse from the generator with a semiconductor opening switch (SOS) is amplified in power and decreases in duration by ferrite gyromagnetic lines. The lines operate in the Magnetic Compression Line (MCL) mode, which occurs at close values of the input pulse duration and the period of the oscillations generated in the line. The energy compression system contains three successive stages-MCL1-MCL3 lines. For an input pulse power of 6 GW (490 kV, 40 Ω) and a duration of 7 ns, pulses of 54 GW (1.62 MV, 48 Ω) and a duration of 170 ps have been achieved at the MCL3 output. Compared to the parameters of the input pulse, the voltage rise rate has been increased ∼130 times up to 14.8 MV/ns, and the power rise rate has been increased ∼350 times up to 0.7 TW/ns. A numerical simulation of the MCL3 line operation in which the maximum electric and magnetic fields are realized (>2 MV/cm and >500 kA/m, respectively) has been carried out. The inner structure of the process of power amplification during the electromagnetic wave passage along the line has been demonstrated. First, the front of the input pulse is sharpened, and then, after the excitation of the oscillations, the process of power amplification begins, followed by the pulse amplitude reaching the saturation region.

Electric Breakdown in Long Discharge Tubes at Low Pressure (Review)

The review is devoted to studies of the processes and mechanisms of ignition of a glow discharge in tubes whose length significantly exceeds their diameter (long discharge tubes) at low pressures (~10 Torr and lower) and moderate voltage rise rates (~1 kV/μs and lower). The electric field in such tubes before a breakdown is substantially nonuniform. Therefore, a breakdown occurs after an ionization wave (or waves) passes through the discharge gap at a speed of ~105–107 cm/s. This makes the characteristics of the breakdown in long tubes significantly different from the breakdown between large and closely spaced electrodes, where the electric field is uniform before the breakdown and where the Townsend or, under strong overvoltage, streamer mechanism is realized. On the other hand, the nature of these processes is very different from those occurring in nanosecond discharges, which arise at voltages with a steepness of ~1 kV/ns and higher and are associated with high-speed (~109 cm/s) ionization waves. The review is based on the materials of experimental and computational works published from 1938 to 2020. Breakdown processes, optical and electrical characteristics of the discharge gap during breakdown, and the influence of the external circuit parameters and external actions (shielding and illumination by external sources of visible radiation) are analyzed.

Measuring Setup for Investigation and Visualization of the Percolation Phenomenon in Non-Оrdered Models of Metal-Dielectric Nanocomposites

The study uses the phenomenon of high voltage partial discharge to investigate the phenomenon of percolation and visualisation of the percolation channel. The phenomenon of partial discharges is very similar to the quantum tunneling phenomenon observed in metal-dielectric nanocomposites. In both cases the flow of alternating current occurs in the absence of direct contact between the metallic phase particles.A measuring stand was developed and constructed to test models of metal dielectric nanocomposites using high voltage partial discharge. The stand consists of a 110 kV high voltage transformer, a voltage regulator protecting the constant rate of high voltage rise, a measuring system consisting of a measuring probe, voltmeters and a computer. The communication between the measuring probe and the voltmeter was made in digital technology with the use of fiber optic technology, which allowed the meter to communicate with the computer without any errors and eliminated the interference caused by a strong electromagnetic field resulting from the use of high voltage.Systems modelling metal-dielectric composites were built, consisting of metallic elements in the form of disks, randomly distributed on the surface of the dielectric matrix. The number of disks was increased in series of 40 in each. The maximum number of disks was 1520. The dependence was determined of one of the important parameters characterising an partial discharge, i. e. the initial voltage, at which an electric current starts to flow between electrodes, on the concentration of the metallic phase. On the basis of these results, a percolation threshold was established for a matrix with a random distribution of metallic phase elements, the value of which is about 50 %. Films and pictures of partial discharges with visible percolation channels were taken with the camera with which the stand was equipped.

How short is the runaway electron flow in an air electrode gap?

We present and analyze characteristics of the runaway electron flow in a high-voltage (the voltage rise rate of up to 1.5 MV/ns) air-filled electrode gap with a strongly nonuniform electric field. It is demonstrated that such a flow contains a high-energy electron component of duration not more than 10 ps. According to numerical simulations, runaway electron generation/termination is governed by impact ionization of the gas near the cathode and switching on/off a critical (sufficient for electrons to run away) electric field at the boundary of the expanding cathode plasma. The corresponding characteristic time estimated to be 2–3 ps is defined by the ionization rate at a critical field.

Неодномерный эффект dU/dt в мощных тиристорах

The method allowing to take into account the influence of the design peculiarities of a power thyristor on its dU/dt parameter is described. A simple model is proposed, that makes it possible to find the parameters of the auxiliary thyristor structure that belongs to the regenera-tive control gate and provides the given value of the thyristor dU/dt parameter. The minimum possible value of turn-on current of the thyristor, limited by a given value of the maximum rate of voltage rise, is found.

The effects of voltage rise rate on structure and corrosion resistance of PEO coatings

ABSTRACT 6061 aluminium was treated by Plasma electrolytic oxidation (PEO) where a new experimental method was introduced: the applied voltage of the PEO process was quickly increased to 486 V by different voltage rise rates (13.5, 27 and 54 V/s). Scanning electrochemical microscopy (SEM) and Energy-dispersive spectrometer (EDS) and X-ray diffraction were performed to investigate the effect of different voltage rise rates on the structure and the distribution of element and the phase composition of coated 6061 aluminium. Electrochemical impedance spectroscopy (EIS) was employed to further research corrosion resistance of PEO coatings. The results show that the corrosion resistance becomes poorer and the compactness of the outer layer becomes worse with the increase of the voltage rate. As the PEO time prolonged, the inner layer of coatings with higher voltage rise rate would be destroyed.

Pulse generator of a polygonal design with a high rate of voltage

The paper discusses the results of experimental studies of pulsed generators based on a drift diode with a sharp recovery (DSRD) and inductive energy storage of standard and polygonal structures. For the first time the generator of a polygonal design is presented. It is shown that when the generators are working on an active-capacitive load, the rate of voltage rise on it at the generator of a standard construction is lower. The generator of a polygonal design has high characteristics for the rate of increase of voltage and its amplitude. This article will discuss the effect of capacitive load on the rate of voltage rise and the way to increase it.

Effect of electrical polarity on dielectric breakdown in a soft magnetic fluid

In this paper, we focus on a dielectric breakdown in transformer oil and three magnetic fluid samples. The magnetic fluids contain iron oxide nanoparticles sterically stabilized with oleic acid. The nanoparticle volume concentration ranges from 0.05 vol% to 0.35 vol%. The breakdown tests are carried out in the needle-sphere electrode geometry with the high negative electrical potential applied once to the needle and then to the sphere. The breakdown voltage was found to increase not only due to the increasing nanoparticle concentration, but also due to the increasing voltage rise rate. The experiments revealed a remarkable polarity effect on the dielectric breakdown voltage of the transformer oil and the magnetic fluids under both above mentioned influencing factors. A significant increase in the breakdown voltage was measured with the negative high potential applied to the needle electrode, as compared with the high potential on the sphere. To provide the explanation of the observed effect, the electric field distribution, space charge and a potential effect of local magnetic fields in the vicinity of the magnetic nanoparticles are considered.

Dependence of the Breakdown Potential on the Voltage Rise Rate in a Long Discharge Tube at Low Pressure

We have measured the dynamic breakdown voltage in a long (80 cm) discharge tube in neon, argon, their mixture, and in argon with mercury vapor at pressures of 80–400 Pa in a wide range of anode voltage rise rates (dU/dt ~ 10–4–102 kV/ms). We have detected a nonmonotonic dependence of the breakdown voltage on dU/dt with a minimum in the region 0.1–10 kV/ms. The breakdown voltage rise in the range of low voltage growth rate can probably be explained by the specific features of breakdown in long tubes and is associated with the accumulation of a surface charge on the tube walls. The charge reduces the potential difference between the anode and the wall and complicates the primary breakdown between them. The results of additional experiments with pulses superimposed on a constant bias voltage confirm the admissibility of such an explanation.

High-Voltage Diffused Step Recovery Diodes: II. Theory

Approximate analytical formulas are derived to evaluate the main characteristics of diffused step recovery diodes, which operate as current interrupters in high-power nanosecond pulse generators with intermediate inductive energy storage: the spurious prepulse voltage, characterizing the resistive loss in diffused step recovery diodes; amplitude; front duration; maximum voltage rise rate, and duration of the pulse formed on an active load. Similar formulas for epitaxial step recovery diodes, partially obtained for the first time and partially refining previous results, are given for comparison.

Stepwise propagation of a guided streamer along a DBD helium plasma jet fed by biased oscillating voltage

A stepwise propagation of a guided streamer along a helium atmospheric pressure plasma jet driven by a dielectric barrier discharge was recorded. To feed the plasma jet, we used a power supply generating an output voltage signal consisting of a superposition of 41.6 kHz bipolar square pulses and 300 kHz oscillating signals. At a positive half a period of the output voltage signal, a step-by-step propagation was observed for the ionization wave along the plasma jet. The streamer head stops with the decrease in voltage in the first cycle of oscillations and then restarts its motion at the voltage front of the next cycle of a voltage oscillation. The streamer propagation velocity and plasma jet length are likely to be controlled by varying the gas flow rate, bias voltage, voltage rise rate, frequency of oscillations in the pulse, and other parameters.