Voltage Rise Rate Research Articles

Tunneling-assisted impact ionization fronts in semiconductors

We discuss a type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp (∼10 kV/ns) is applied in reverse direction to a Si p+–n–n+ structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds 106 V/cm. The front velocity vf is 40 times faster than the saturated drift velocity vs. The front passes through the n-base with a thickness of 100 μm within approximately 30 ps, filling it with dense electron–hole plasma. This passage is accompanied by a voltage drop from 8 kV to a voltage in the order of 10 V. In this way a voltage pulse with a ramp up to 500 kV/ns can be applied to the load. The possibility to create a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.

An overvoltage suppression scheme for AC motor drives using a half DC-link voltage level at each PWM transition

Passive filters are conventionally used to suppress overvoltage in the motor terminal, either by reducing the voltage rise rate at the inverter output, or by decreasing the motor terminal impedance. We propose an overvoltage suppression scheme that renders the use of passive filters unnecessary. This approach differs from general filter methods, in that it is independent,of d/spl upsi//dt and does not try to reduce d/spl upsi//dt. Our scheme utilizes the middle voltage level V/sub DC//2 at each pulsewidth modulation voltage transition, where V/sub DC/ represents the DC-link voltage. The duration of the middle voltage level is controlled in such a way that reflected voltages are cancelled out at the motor terminal. Optimal cancellation is achieved when the duration of V/sub DC//2 is equal to twice the transport delay of the cable. Further, if reflection coefficients at the motor terminal and the inverter output are equal to /spl plusmn/1, no overvoltage takes place. The proposed scheme requires the use of six auxiliary insulated gate bipolar transistor switches. Simulation as well as experimental results are presented here.

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.

A high-frequency model of an oil-immersed transformer, and its use in lightning surge analysis

A circuit model of an oil-immersed transformer for use in surge analyses in the high-frequency region is proposed, and its effectiveness is evaluated by comparison with measurements on a model winding. The circuit model is used for lightning surge analyses of a 500-kV substation, and the effect of transformer modeling on the lightning surge voltage at the transformer terminals is investigated. When the new circuit model is used for transformer modeling, the peak value of the surge voltage is lower but the rate of voltage rise is higher than in conventional transformer modeling by a lumped capacitance. This difference can be explained in terms of the charging of capacitances in the transformer model. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 28–35, 2001

Performance of pulsed power generator using high-voltage static induction thyristor

In a present pulsed power generator system using semiconductor switches, saturable magnetic switches are usually connected in series to compress the output pulse because the current rise-time of semiconductor switches are generally not short enough, However, the magnetic switches are heavy and they reduce the energy transfer efficiency. So we propose a pulsed power generator system using a 5500-V static induction thyristor (SI-Thy), a Blumlein line for pulse formation, and a step-up pulse transformer. The fundamental characteristics of the generator are evaluated. From experiments using only one SI-Thy, turn-on time of several tens of nanoseconds and the maximum rise rate of the output voltage of 115-kV//spl mu/s are obtained. It is confirmed that an SI-Thy will have sufficient performance as a main switch of the pulsed power generator for the flue gas treatment and decomposition of hazardous gases when several SI-Thys are connected in series.

An evaluation of mitigation techniques for bearing currents, EMI and overvoltages in ASD applications

With the increased application of adjustable-speed drives (ASDs) for the efficient speed control of AC motors, there has been a growing number of costly motor drive-related process failures. The popular ASDs consist of a pulsewidth-modulated inverter switching insulated gate bipolar transistors at 2-20 kHz, with rates of voltage rise (dv/dt) of 6000 V//spl mu/s. The high dv/dt has adverse effects on the motor insulation due to motor terminal overvoltages (exacerbated by longer cable lengths) and contributes to EMI and damaging bearing and leakage currents caused by common-mode voltages. In response to these problems, a variety of mitigation techniques have emerged. However, often-times the industrial user searching the literature for an immediate solution faces difficulties determining which mitigation technique is best for his/her application. Using laboratory measurements, this paper evaluates and compares various suggested mitigation techniques for bearing currents, EMI and motor terminal overvoltages in terms of their effectiveness and losses and provides practical application assessments for users.

A low-harmonic electric drive system based on current-source inverter

This paper presents a new electric drive system topology, which is based on a pulse width modulation (PWM) current-source inverter (CSI). It is aimed at reducing the current harmonics drawn from paper mill distribution systems and the electric utility. Additionally, the voltage harmonics feeding into the electric motors are significantly reduced. Furthermore, the voltage rise rate of the PWM-CSI drives is low compared to the currently dominant PWM voltage-source inverter (VSI)-based drive systems. This paper also presents a proposal to modify the current paper machine drive systems, in order to achieve an overall low harmonic level. The new topology is verified by computer simulations. The problems of the new drive system are also described.

Transient Voltage-Induced Leakage Current in Power Diode with Semi-Insulating Polycrystalline Silicon Resistive Field Plate

Leakage current of a power diode was found to flow at a much lower voltage than that of avalanche breakdown under the conditions of high voltage rise rate ( dV/ dt) and low frequency, and this leakage current was characteristic of a semi-insulating polycrystalline silicon (SIPOS) resistive field plate (RFP). This current, which we call transient voltage-induced leakage current (TVIC), has not been reported previously. TVIC can be suppressed by optimizing the reduced surface field (RESURF) structure. The electric charge for TVIC increased as both the applied voltage and the pulse time interval increased, whereas it decreased as the temperature increased. A possible model to explain the TVIC mechanism was presented.

Electrical breakdown of dysprosium oxide films

The principal laws governing the electrical breakdown of dysprosium oxide films in silicon metal — insulator — semiconductor structures are investigated. The dependence of the breakdown field Ebr on the rise rate of the voltage on the structure Kv, the temperature, the material and area of the electrode, and the humidity of the environment is studied. The dependence of the time delay of breakdown on the amplitude of a rectangular voltage pulse is investigated. It is established that the breakdown field increases linearly with log Kv for all insulator thicknesses, and the saturation of Ebr is observed at Kv>105 V/sec. It is found that Ebr does not depend on the electrode material and decreases as the area of the electrode or the temperature is increased. The maximum breakdown field is determined: E br max =14 MV/cm. The mechanism of the precursory stage of breakdown, i.e., the period of transient buildup of critical charge in the insulator, is discussed.

High Efficiency Electroluminescence from Porous Silicon during Anodic Oxidation

The Electroluminescence of p- type porous silicon during anodic oxidation (AO) in HCl solution has been investigated quantitatively. A typical EL peak wavelength at maximum intensity during AO was around 690 nm and the external light emitting efficiency at that time (ηm) was 0.12 %. The ηm was nearly proportional to anodic etching (AE) current density (DAE) and also increased with AE time (tAE). For the AO conditions, ηm increased abruptly as the AO current density (DAO) was reduced and it reached a maximum of 0.27% at minimum DAO condition. Furthermore, it was found that ηm was uniquely described by the AO voltage rise rate (dVAO/dt), which represents the effective injection current density into the PS microstructure surface.

Subthreshold rectification in neostriatal spiny projection neurons

Intracellular recordings from slice preparations were used to assess the subthreshold electrophysiological behavior of rat neostriatal projection neurons. Both current steps and ramp currents were used to estimate the current-voltage relationship (I-V plot). Inward rectification in the subthreshold range was a characteristic of most neurons. The amount of rectification varied greatly, and it was complex: membrane voltage trajectories in response to ramps were made up by almost piece-wise changes in the rate of voltage rise, suggesting that multiple conductances contribute to the subthreshold range. Inward current blockers such as tetrodotoxin (TTX) or Cd2+ decreased inward rectification, whereas outward current blockers such as tetraethylammonium (TEA) or 4-aminopyridine (4-AP) increased inward rectification. However, most inward rectification was due to TEA- and Cs(+)-sensitive conductances and not to TTX- or Cd(2+)-sensitive conductances. Cs(+)-sensitive conductances predominated at more negative membrane potentials, whereas 4-AP-sensitive conductances predominated at just +/- 10 mV below the firing threshold. In spite of a very slow activation, there was evidence for transient outward currents modulating the response, i.e., 4-AP-sensitivity, and voltage-sensitivity for firing frequency and threshold. TEA-sensitive conductances also contributed toward fixing the firing threshold. These results imply the contribution of various ion conductances on the shaping of the characteristic physiological firing recorded in vivo. Modulation of these responses by transmitters or peptides may help to understand neural processing in the neostriatum.

Influence of the rate of voltage rise on electrical forming and breakdown in a thin-film MIM system

An investigation was made of the influence of the rate of voltage rise on forming and breakdown in a thin-film metal-insulator-metal(MIM) system. It was found that an increase in the rate of voltage rise led to a reduction in the forming probability and consequently to an increase in the breakdown probability when the voltage exceeded a certain critical value, under otherwise identical conditions. Taking into account the known published data on forming and breakdown, the experimental results obtained were used as the basis for a qualitative model of electrical breakdown in the investigated MIM systems.

The electrical properties of some cordierite glass ceramics in the system MgO-Al2O3-SiO2-TiO2

The a.c. dielectric breakdown and electrical resistivity of glass ceramics in the system MgO-Al2O3-SiO2-TiO2 have been studied using three sets of samples having different crystallinity contents. Standard a.c. (50 Hz) breakdown tests were performed at room temperature (18 °C) using planar disc specimens and hemispherically-ended brass contact electrodes. The breakdown process caused the formation of a breakdown channel which terminated at the specimen surface in a crater. The breakdown strength was independent of the rate of voltage rise, but decreased exponentially (60 to 10 kV mm−1) with increasing specimen thickness. A high crystallinity content, good surface finish and a homogeneous microstructure yielded high breakdown strengths whilst poor microstructural development caused a reduction in breakdown strength. The breakdown mechanism is believed to be a combination of electronic, thermal and electromechanical processes.

The importance of the n-base in p-n-p-n-like structures subjected to dV/dt ramps

A simple yet thorough analysis of physical effects induced in p-n-p-n-like silicon structures by the high rate of the OFF-state forward anode voltage rise (dV/dt) is discussed. The importance of n-base parameters in shaping the faulty triggering of thyristors subjected to dV/dt ramps is clearly demonstrated. The main implications of the findings for thyristor physics and design are also outlined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impulse voltage withstand capability of rotating machine insulation as determined from model specimens

An evaluation of present-day turn and groundwall insulation is discussed. The surge breakdown voltage of unaged insulated specimens was evaluated at two rates of surge voltage rise; the values of breakdown voltage were compared to those obtained by direct voltage and 60 Hz alternating voltage. The insulations were then aged by voltage from conductor to ground and periodically evaluated for surge breakdown values. Finally, the specimens were tested for surge voltage endurance, and this endurance was compared to alternating voltage endurance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lightning Protection for Submergible Oilwell Pumps

Lightning protection for electric submergible pumps has long been an area of concern. Related insulation failures are costly and not altogether uncommon. These are due in part to poor-quality grounds and the tightly spaced geometry of submergible motor windings. An improved protection scheme is proposed wherein separate high-and low-current grounds are used, and the rate of voltage rise is limited. These techniques divert the major portion of lightning energy before it reaches the downhole equipment, thus minimizing coil-to-frame voltage stress. It also slows the rate of voltage rise to reduce turn-to-turn stress within a single motor coil. Design considerations are developed for the protection of an electric submergible pumping system, particularly as they relate to the value, quality, and reliability of individual protection components and various grounding systems. Laboratory test data are presented, showing the effects of motor impedance on performance when characteristic lightning transients are applied. Finally, available field data are reviewed.

Power drift step recovery diodes (DSRD)

Reverse recovery processes in diodes, leading to a high voltage rise rate, have been considered. A maximum voltage rise rate for silicon diodes as high as 2·10 12 v/s has been estimated. Power drift step recovery diodes for shaping 1 kV voltage steps with nanosecond fronts have been designed and investigated.

Spark Gap Breakdown at EMP Threat Level Rates of Voltage Rise

Electrical Surge Arrestors (ESAs) are used extensively for lightning and EMP protection on conductors which may be excited by these hostile environments. In-situ measurements of peak pulse voltage were performed at rates of voltage rise from 200 to 2000 kV/?s on several types of surge arrestors and combinations of spark gaps and filters. These data are presented along with samples of previous measurements. The effects of lead inductance and low impedance loading by the filter input capacitance are illustrated. Experimental results are compared to theoretical predictions of an ESA model used for EMP analyses.

The Lightning Arrestor Connector

A multipin connector has been modified to include lightning arresting features. A dielectric stimulated arc is used for rapid electrical, breakdown in the connector prior to any damage to downstream components. This report reviews the connector design basis and concept, and summarizes the electrical test results obtained during development and production. Electrical testing included insulation resistance, high voltage rise rate (to 500 kV/µs) tests and simulated lightning (over 200 kA) exposures. The lightning arrestor connector has been effective under all tests maintaining an insulation resistance over 100 M, and shorting fast rise lightning induced voltages to about 1000 V. A final test of a missile system showed the lightning arrestor connector effectively protected missile components against simulated lightning.

Dielectric Breakdown in Thin Evaporated Films of CaF2, MgF2, NaF, and LiF

Prebreakdown dc conduction and breakdown properties have been studied in thin-film capacitors with dielectrics of CaF2, MgF2, NaF, and LiF. The results are compared mostly with theory developed for electronic breakdown in ionic crystals due to Fröhlich, Callen, and Forlani and Minnaja. Capacitors were formed on glass substrates with dielectric thicknesses from 700 to 30 000 Å and electrodes of Al. Between −200° and 100°C prebreakdown and breakdown conduction appear to be independent. The transition time between prebreakdown and breakdown conduction is 10−8–10−7 sec. Except for some cases where the breakdown field Fmax (≈106 V/cm) displays an initial rise, an increase in temperature from −200 to 100 C is accompanied by a decrease in Fmax. Only the initial rise can be interpreted in terms of theoretical developments by Fröhlich and Callen. An increase in Fmax is observed as the rate of voltage rise varies from 15 to 15 000 V/sec. The breakdown field also varies in most cases as w1/2, where w is dielectric thickness. This behavior is in agreement with the theory of Forlani and Minnaja, implying that impact ionization plays an important role in breakdown. A voltage threshold (≈15 V) for the cessation of breakdown which is independent of thickness and temperature is found for each material studied. This is consistent with the notion that Vmin is the cutoff voltage of a gaseous arc. The above facts attribute an electronic nature to breakdown where, at the onset, the magnitude of current density is not altogether the critical factor. Evidence implies a period devoid of current enhancement just prior to breakdown during which the dielectric accumulates energy necessary to change to a gaseous state. It is the gas which affords the high conductance during breakdown.