Voltage Build-up Research Articles

An automated AC-DC transfer calibration system

Improvements in the National Research Council of Canada (NRC)'s ac-dc transfer capabilities have been achieved through full automation of the ac-dc transfer comparator, extensive redesign of the control software, and modification of the voltage buildup procedure. Hardware additions to the comparator design include stepping motor-driven switches and a range changer of a commercial electronic transfer standard. Redesigned software can be easily modified to accept new instruments and new procedures. The NRC voltage buildup procedure has been modified at the 500- and 1000-V levels. The expanded uncertainty assigned to the NRC working standard is given, and its components are briefly discussed.

99/01281 Hydroelectric generation scheduling an application of genetic-embedded fuzzy system approach : Huang, S.-J. Electric Power Systems Research, 1998, 48, (1), 65–72

This paper presents a critical review on the self-excitation process and steady state analysis of a self-excited induction generator driven by the wind turbine. The physics of self-excitation is crucial for the interpretation of the voltage build-up process of self-excited induction generators (SEIGs). During the initial phase of build-up the machine behaves as if it be a synchronous machine with weak permanent magnet in the form of remnant magnetization. In this paper the MMF approach as well as the synchronous resonance approach has been proposed to know the fact that how the machine relinquishes the initial synchronous mode and enters into the final asynchronous mode. The process of self-excitation is initiated by the resonating interaction between the terminal capacitor and machine׳s magnetizing reactance. The steady state analysis has been reviewed and proposed based on input/output impedance method to find the steady state reactive VAR need of the SEIG. The minimum and maximum critical capacitance has been evaluated theoretically. Finally the value of critical speed and critical load impedance has been evaluated.

Fast and slow voltage modulation of apical Cl- permeability in toad skin at high [K+

The influence of voltage on the conductance of toad skin was studied to identify the time course of the activation/deactivation dynamics of voltage-dependent Cl- channels located in the apical membrane of mitochondrion-rich cells in this tissue. Positive apical voltage induced an important conductance inhibition which took a few seconds to fully develop and was instantaneously released by pulse inversion to negative voltage, indicating a short-duration memory of the inhibiting factors. Sinusoidal stimulation at 23.4 mM [Cl-] showed hysteresis in the current versus voltage curves, even at very low frequency, suggesting that the rate of voltage application was also relevant for the inhibition/releasing effect to develop. We conclude that the voltage modulation of apical Cl- permeability is essentially a fast process and the apparent slow components of activation/deactivation obtained in the whole skin are a consequence of a gradual voltage build-up across the apical membrane due to voltage sharing between apical and basolateral membranes.

The effects of PWM voltage source inverters on the mechanical performance of rolling bearings

Modern power inverters provide the industrial control industry with significant advantages. The faster switching devices have increased drive performance, but with some disadvantages. One disadvantage, rotor shaft voltage and resulting bearing current, has become an industry concern. The oil film in a bearing acts as a capacitor and provides a charging mechanism for rotor shaft voltage buildup. Electrical breakdown of the film can damage the bearing. This paper examines the mechanical and electrical characteristics of the bearing and converts them into models. The mechanical model for the bearing contact area establishes an allowable bearing current density, which is used to estimate the electrical life of a mechanical bearing. The electrical model for the bearing provides a significant advancement, aids bearing design, and the analysis of electrically induced bearing damage. Finally, the paper presents quantitative results for one solution to the shaft voltage and bearing current problem.

An evaluation of the electrostatic shielded induction motor: a solution for rotor shaft voltage buildup and bearing current

This paper evaluates a new induction motor, the electrostatic shielded induction motor (ESIM). An ESIM reduces rotor shaft voltages to levels below the bearing lubricant's electric field intensity breakdown level and offers one solution to accelerated bearing wear caused by fluting induced by pulsewidth modulated (PWM) inverters. The paper begins by reviewing shaft voltages and the resulting bearing currents when operated on PWM voltage source inverters. An example of bearing fluting is shown, and system models are presented and discussed. The construction details and test results for several ESIMs are presented. Experimental results show the ESIM solves the electrostatically induced rotor shaft voltage and bearing problem without degrading the electromagnetic performance of the motor.

Plasma immersion ion implantation with dielectric substrates

Plasma immersion ion implantation (PIII) is a novel implantation technique for high-dose/high-current implants. Using the SPICE circuit simulator to model the PIII process, the sheath voltage and ion energy distribution are examined. Implanting into a dielectric substrate results in a significant voltage buildup in the wafer, reducing the effective implant energy. Increasing the pulse voltage raises the dose/pulse, but at the cost of an expanded implant energy spread. Increasing the plasma ion density also raises the dose/pulse, but at the cost of a wider implant energy spread and a lower coupling efficiency. Increasing the substrate thickness reduces both the coupling efficiency and dose/pulse while broadening the energy spread. The large voltage generated across the dielectric substrate decreases the charge neutralization time significantly, reducing the possibility of gate oxide damage.

A new SPICE subcircuit model of power p-i-n diode

A new modeling approach for the power p-i-n diode is proposed. The base region is represented with a two-port network, obtained by solving the ambipolar diffusion equation with the Laplace transform method, and by approximating the resulting transcendental functions in the s-domain with rational approximations. Two different networks have been obtained. The first one, based on Taylor-series approximation is shown to be a generalization of a two-port model already proposed in the literature for the nonquasi-static modeling of bipolar transistors. The second network representation is based on Pade' approximation and is shown to be more accurate than the Taylor-series approach, The obtained RLC networks are easily implemented in a PSPICE subcircuit which also takes into account the emitter recombination effects and the dynamic of the space-charge voltage build-up. Good agreement has been obtained by comparing the results of the proposed model with numerical device simulations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control of a polyphase induction generator/induction motor power conversion system completely isolated from the utility

Two squirrel cage induction machines interconnected via a 20 kHz parallel resonant high frequency (HF) AC link and associated switching pulse density modulated (PDM) power converters are investigated, one operating as a generator and the other as a motor. No capacitors are used for the excitation of the generator or motor. Instead, the real power of the generator is controlled so as to maintain the proper link voltage and match the power between the input and output, Current regulated PDM converters operating via field oriented controllers are used to control both machines. A zero voltage switching technique is utilized with the associated PDM converters. Low harmonic distortion waveforms have been obtained both at the input and output due to the high 40 kHz switching frequency. Link voltage build-up and excitation of the generator by an initial charging circuit, power matching between input and output, and peak link voltage regulation techniques are investigated. Both computer simulations and experimental results demonstrate the feasibility of the proposed system. >

Capacitance requirements of self-excited induction generators

A simple method for computing the minimum value of capacitance, C min. required for initiating voltage build-up in a three-phase self-excited induction generator (SEIG) is presented. Based on the steady-state equivalent circuit model, a consideration of the circuit conductances yields a sixth-degree polynomial in the per-unit frequency. The polynomial can be solved for real roots, which enables the value of C/sub min/ to be calculated. Critical values of load impedance and speed, below which the machine fails to self-excite irrespective of the capacitance used, are found to exist. Closed form solutions for C/sub min/ are derived for no-load and inductive loads. Using the same numerical approach, an interative procedure is developed for predicting the capacitance required for maintaining the terminal voltage at a preset value when the generator is supplying load. Experimental results obtained on a 2 kW induction machine confirm the feasibility and accuracy of the proposed methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modelling of deep-bar and double-cage self-excited induction generators for wind-electricity generation studies

The paper presents the derivation of a current state-space model of saturated deep-bar and double-cage induction machines. The approach adopted in the paper closely parallels that utilized in the derivation of the current state-space model of a saturated single-cage induction machine. The developed model is then adapted to the terminal conditions met in the self-excitation of induction generators. Simulation of voltage and current build-up during self-excitation is performed. Simulation results are confirmed by experimental investigation, thus providing verification of the derived saturated double-cage induction machine model. It is believed that the model could be very useful in transient studies concerning unconventional energy sources, especially wind-electricity generation.

Constant current corona charging as a technique for poling organic nonlinear optical thin films and the effect of ambient gas

Poling, which involves the alignment of nonlinear optical (NLO) dipolar molecules in the direction of the applied electric field, was carried out using constant current charging, a recently developed corona charging technique. Using this technique, the sample surface voltage buildup, and hence the efficiency of the dipole alignment, can be monitored during the poling process. In addition, it will be shown that this capability also provides a way to detect the end point of the dipolar orientation. Corona charging of the organic NLO film used in this study, however, needs to be done in an inert atmosphere. Results from in situ IR spectroscopy measurement during corona charging of the NLO film, ultraviolet and visible absorption spectroscopy and electron scattering for chemical analysis of this film before and after poling, indicated that exposing it to corona discharge in air ambient caused oxidation of the polymer surface. Various types of nitrogen oxides and carboxylic acids were found to be the products of this oxidation reaction. Finally, we also obtained evidence showing that the surface charging process of the organic NLO film is affected by this newly grown oxidized layer.

On the Return-Voltage Buildup in Insulating Materials

Charged capacitors which have been temporarily short-circuited display a "return voltage" buildup which may cause severe shocks. This old phenomenon has been reinvestigated on various materials (polyethylene, polyester, Kapton®, etc.) poled by different techniques (HV, corona, plasma, etc.) after different poling times. Return voltage buildup is observed on all insulating (polar and non polar) materials. A simple model based on the drift of charges in the material and the sign reversal of the Coulomb force acting on them is presented. Expressions for the total charge density, the depth of the charge centroid and the mobility of charges in the sample are derived in terms of measured quantities such as the initial rate of buildup and the maximum return potential. A confirmation of the model is obtained for the return voltage due to electrons injected at known depths in polymer sheets by an electron gun. As a consequence, the same technique might be used with electrode-poled samples, to assess the injecting character of the electrodes, and possible modifications produced by contamination, surface treatments, etc.

Prevention of current leakage in mass-transported GaInAsP/InP buried-heterostructure lasers with narrow transported regions

The use of narrow transported regions as a simple technique to minimize current leakage has been analyzed. In the present model, current leakage occurs when the voltage buildup in the p-region is sufficiently large to turn on the InP homojunction in the transported region. The voltage buildup, the injected electron concentration, the drift and diffusion of the electrons, and the resulting homojunction current have been analyzed in detail. A simple formula has been derived which allows for device design for operation at high currents without a significant leakage.

High field poling of poly(vinylidene fluoride) films using a current limiting circuit

A high field room temperature poling technique has been developed for preparing poly(vinylidene fluoride), PVDF, films with high piezoelectric activity. The technique utilizes a resistor (typically 5 × 107 to 1011 Ω) which is inserted between the power supply and the polymer film to control the voltage buildup across the polymer film and to limit the current flow through the film in case of incipient breakdowns. Application of the technique to 25 μm-thick biaxially oriented films (with provision to prevent edge flashover) showed that the films could be poled without breakdown failure for a period of one to 105 s depending on the external resistance and the applied field. The piezoelectric e31 coefficients of the poled films were comparable to those obtained with the breakdown field poling method recently developed by Wang and West; however, the values obtained with the present method were in general more consistent and reproducible than the values obtained with the latter method. It is shown that physical...

Integrated cascade of photovoltaic cells as a power supply for integrated circuits

ICs can be powered directly when a supply voltage source capable of generating a multiple of the open circuit voltage of one pn-junction is available on a chip. Two schemes have been investigated for cascading photovoltaic cells on the chip. The structures can be made compatible with standard bipolar processes. Deep ion implantations have been used here to realize the multiple-junction structure. Power losses due to photocurrents originating from insulation junctions in the cascade can be kept to a minimum. The surface areas of two adjacent cells have to satisfy a definite relation to ensure the build-up of output voltage. Operating under sunlight conditions, 0.6 mW/cm 2 has been generated in a cascade of three cells. With appropriate optical coatings on the silicon surface and optimized cell dimensions, it should be possible to generate a few milliwatts per cm 2. The structures may have applications in electronic circuits for glass fibres or can be used to power small CMOS circuits.

Starting process in an induction heating system with a naturally commutated cycloconverter link circuit

A naturally commutated cycloconverter can be used between an induction heating load and the mains supply to effect the necessary transfer of power. For commutation of converter thyristors, it is necessary that the tank voltage should exist throughout. However, at the start of the system the tank voltage is zero. The process of transient build-up of the tank voltage is discussed. Two cases are studied : one with a constant quasi-square wave feed current corresponding to a three-phase supply, and the other with a sinusoidal mains current corresponding to a single phase system. The results are digitally simulated and compared with the approximate mathematical expressions. Tank Q requirements are discussed for reliable natural starting of the induction heating system.

Electron transport self-shift display using an AC plasma panel

Using an electron transport mechanism, a self-shift display has been successfully implemented on an ac plasma panel providing higher resolution, higher shifting speed, and wider operating margins than previously obtained. The mechanism consists of a unidirectional and efficient transport of a large portion of electrons (generated during the display site discharge) to a neighboring OFF transfer site by a low transverse voltage. The process results in a large wall voltage build-up at the transfer site to switch its state from OFF to ON. The implemented electron transport self-shift display consists of a 7 × 128 site array of an Owens-Illinois 60 lines per inch panel where the 128 columns are driven by a four-phase driver. A resolution of one display site for every two electrodes and a shifting speed better than 600 characters per second have been successfully demonstrated. The ranges of the shifting voltages V D and V T are better than 15 V over a 10-V sustain range. The shifting operation also was successfully demonstrated on an 83 lines per inch panel with good operating margins.

A constant-current stimulator

This device produces constant-current pulses for brain stimulation. Voltage build-up on the tissue (tissue-polarization) is prevented by a discharge circuit that is operative during the pulse interval. Control pulses must be supplied from an external source.

Semiautomatic measurements of thin-film breakdown voltages

A semiautomatic setup is described which provides the destruction-free measurement of breakdown voltages of thin-film structures for applications like process control and quality prediction. The method of measuring the breakdown voltage consists in feeding a constant current to the thin-film device and analyzing the voltage buildup across the device. This method has been described in a recent paper. The setup provides the successive analysis of breakdown behavior of a given matrix of wafer dots by means of a positioning table, an electropneumatic prober, and a microprocessor-controlled measurement unit via handshake commands. The results are given in a histogram form.

Gamma ray induced charge buildup in insulators

Irradiation of an insulator by gamma rays can produce voltage and charge buildups near thin layers of foreign material within the insulator. Measurements have been made of the current produced as a function of atomic number and thickness of the perturbing layer. Current was also measured as a function of separation from the perturbation, as was voltage buildup within the insulator close to the perturbation.