Electrical Operating Conditions Research Articles

Photocatalysis enhancement by electric field: TiO 2 thin film for degradation of dye X-3B

According to the theory of photocatalysis, the efficiency of photocatalysis decreases mostly due to the recombination of photo-generated electron–hole pairs. An electric field across a photocatalyst can promote the separation of photo-generated electrons and holes and prevent them from recombination so as to enhance the efficiency of photocatalysis. And the synergetic decomposition efficiency of photocatalysis and an electric field is greater than that of the simple combine of their single efficiency. The performance of photocatalysis enhanced by electric field (PEEF) and operating conditions such as the direction of the electric field, the voltages between the two electrodes, the material of the electrodes, which may affect the efficiency of PEEF, were investigated in this paper. The results indicate that the system of PEEF abides the established theory of photocatalysis.

Quantification of scanning capacitance microscopy measurements for 2D dopant profiling

Several Scanning Probe Microscopy (SPM) techniques are currently under development for 2D dopant profiling; among these the Scanning Capacitance Microscopy (SCM). The signal-to-noise ratio in SCM measurements is a critical issue, due to the small tip-to-semiconductor differential capacitance (typically in the attoFarad range). Many factors may have a negative influence on the reproducibility of SCM data and must be kept under control: sample-related problems, tip-related problems, and problems related to the electrical operating conditions. Furthermore, the conversion of the SCM experimental data into a quantitative 2D map of the local dopant concentration requires a huge effort in terms of reverse simulation. In this paper, the current procedures for preparing SCM samples are briefly reviewed. Then, the sample preparation and the experimental dC/dV curve of a calibrated staircase structure are presented. Finally, the experimental SCM data (the dC/dV and the conversion curves) are compared with the theoretical data simulated with a device simulator.

A new approach to electric motor acoustic noise standards and test procedures

Current acoustic noise standards for induction machines originated when electric motor operating conditions were far less complex than those of today. The use of adjustable speed drives, incorporating electronic inverters, has led to dramatically changed motor noise characteristics. This paper presents a systematic approach to broadening the existing standards, to make them more useful in the true operating environment.

Electrically driven polarization-insensitive liquid crystal narrow-bandpass intensity modulator

The proposed intensity modulator consists of two in-tandem Fabry-Pérot (FP) filters with perpendicular orientation of the optical axis of homogeneously oriented liquid crystal (LC) layers. The device utilizes the electro-optic effect of refractive-index modulation in a uniaxial nematic layer. Since the refractive index in the LC is different in two orthogonal directions, the transmission spectrum of the FP filter exhibits two sets of peaks corresponding to ordinary and extraordinary rays, respectively. Application of an external electric field tilts the optical axis towards the propagation direction and therefore changes only the extraordinary refractive index, reducing its effective value. In order to modulate the ordinary beam emerging from the first FP, a second filter with the orientation of the optical axis perpendicular to that of the first filter has been used. This construction for monochromatic light is equivalent to electrically tunable crossed polarizers, enabling intensity modulation to take place. Electric operating conditions and optical efficiencies are given.

A simplified thermal analysis approach for power transistor rating in PWM-controlled DC/AC converters

A simplified dynamic thermal analysis approach is proposed for the estimation of the peak junction temperature in power IGBT transistors operating in pulse-width modulation (PWM) controlled DC/AC converters. This approach can be used for the rating of electron devices or heatsink systems in power circuit design, as it provides a direct analytical link, in terms of electrical and thermal device parameters and converter operating conditions between the case and the peak junction temperatures. In this way, by imposing a given upper limit on the junction temperature, indirect constraints on device size or load current or heatsink efficiency can easily be obtained. The approach is based on mild, pessimistic approximations on both the spectrum of dissipated power and on the dynamic thermal behavior of the device. The validity of such approximations has been verified by comparison with the results of accurate numerical simulations carried out by using measurement-based loss models. Possible ways of using this approach in a converter rating context are outlined in the paper, by considering different design scenarios.

Electrically stimulated agglomeration at an earthed surface

With the aid of a microscope and a video camera, settling particles have been observed when passing a classical point-plate arrangement and, because of the deflection in the electrical field, impacting on the wall. As the cinematographic studies show, the particles arriving form agglomerate chains orientated along the electrical field lines and increasing to a critical length, dependent on the electrical operation conditions. In the video tapes, it is clearly seen that agglomerate chains of critical length are pulled off by the electrical forces. The observed agglomeration phenomenon is governed decisively by the particle material itself, in particular particle resistivity. Graphite and limestone particles, and glass spheres in the size range around 30 μm have been investigated. In order to illustrate this electrically stimulated agglomeration the whole process has been video taped. These mainly phenomenological investigations reveal the physical background of a successful electro-mechanical two-stage system for the separation of diesel soot particles.

Numerische feldberechnung in elektrofiltern im hinblick auf elektrisch ähnliche betriebszustände

Earlier investigations of electrostatic precipitators yielded a method to keep grade efficiency independent of absolute precipitator size. A transfer of measuring results from small to larger plants requires a change of precipitator size true to scale. In addition, precipitators have to be operated at a constant dimensionless voltage defined by U/( E 0 r SE) in order to provide equivalent electrical operating conditions, i.e. identical spatial distribution of the relative electrical fields. This could be confirmed by analytical field calculations assuming a uniform space charge distribution. Moreover, this paper presents a numerical simulation method allowing calculation of both the electrical field distribution and the ionic space charge distribution. The method solves alternatingly Poisson's equation by a finite element technique and the equation of continuity. The results show the principal effect of the ionic space charge. This calculation procedure is applied on three geometrically similar precipitators of different size. The field gradients and space charge densities were calculated for precipitator operation at constant current density, constant (pseudouniform) field strength and constant dimensionless voltage. The results show that only a constant dimensionless voltage leads to identical electrical field distributions.

Particle Dynamics in an Electrohydrodynamic Flow Field investigated with a two‐component laser‐doppler velocimeter

AbstractA laser‐Doppler instrument has been used to measure the migration velocity of NaCl particles in an electrohydrodynamic flow field of an electrical precipitator. The measured average migration velocity of 1.40‐μm particles (number distribution median with a geometric standard devitation of 1.46) is approximately five to six times higher than the calculated steady‐state velocity for a 1.40‐μm particle, provided there is a saturation charge of at least 90f%. Further, the particle velocities in the main flow direction are also influenced by the electrical operation conditions. Both observations demonstrate the important role of the state of the electrohydrodynamic flow field (superposition of moving gas ions and neutral gas molecules) on the particle transport, characterized by the dimensionless electrohydrodynamic number NEHD. A comparison between six different electrohydrodynamic states revealed that NEHD ≈︁ 1 is a critical value for the mutual interactions between the gas ions and the neutral gas phase. Whereas for NEHD values > 1 the stochastic particle motion is chiefly determined by the nonsteady‐state character of the negative corona, for NEHD values < 1 the particle velocity fluctuations are governed by the turbulence level of the neutral fluid. These finding might be helpful in adjusting the operating conditions in electrical precipitators for and optimized particle separation.

A new protection system against high voltage vacuum breakdowns

A passive, electrical fast-switch-off/on system for protecting electrodes subject to fortuitous high voltage vacuum breakdown has been developed. This system is based on the principle of oscillatory discharges in an RLC network coupled with the use of a diode. When a breakdown occurs, the current is automatically and rapidly switched off, preventing the damaging of electrodes and power supply by the electrical arc. The interruption lasts as long as required to stop the short-circuit metal vapor arc: a couple of milliseconds are generally sufficient. Then the current is automatically restored, allowing a rapid recovery of the normal electrical operating conditions. Besides the economical advantages of this circuit, one should note that its operating characteristics are very useful for electrode conditioning. The study of this protection circuit has been made for protecting some elements of the neutral beam injectors in the Tore Supra Tokamak experiment, but its field of application should be quite large.

High-voltage auxiliary switchgear for power stations

Air-break switchgear has been used extensively for many years to control station auxiliaries. Vacuum and SF/sub 6/ techniques, already well established in the distribution field, are now being applied for the higher ratings and more onerous duties of switchgear in large fossil-fired and nuclear power stations. The author discusses power plant auxiliary systems and the environmental, mechanical and electrical operating conditions of the switchgear. The author then describes in detail the criteria affecting the choice of appropriate switchgear for auxiliaries. The choice of operating mechanisms and special requirements for nuclear power stations are also discussed.

NASA/General Electric Broad-Specification Fuels Combustion Technology Program: Phase I

Programme destine a developper la technologie requise pour utiliser les combustibles avec des proprietes elargies par les turbines a gaz d'aviation. La premiere phase de ce programme consiste en une evaluation experimentale de trois concepts differents de chambre de combustion

Optimization of mechanical and electric operating conditions of magnetically anisotropic force transducers

Optimization of mechanical and electric operating conditions of magnetically anisotropic force transducers

A Microwave Slab Line Cavity for the Excitation of Electrodeless Discharge Tubes

A new form of microwave cavity, operating at 2.45 GHz, is described for use with electrodeless discharge tubes. The size and electrical operating conditions of the cavity may be changed readily. The second spectrum of helium, neon and argon has been strongly excited, using a sealed low pressure electrodeless discharge tube, in the new cavity.

Nematic Liquid Crystal Digital Light Deflector

We report the principle of a new type of digital light deflector utilizing the electrooptic effect of index modulation in nematic liquid crystals and the results of the optical tests that were performed on this device. Optical efficiencies and contrasts, electrical operating conditions, and subsequent turnon times are given. A further experiment concerning the deflection of a colored image in incoherent white light is described, which shows that this device seems to be the more interesting for a lot of applications, especially portable ones.

Model for corona modes in point-to-plane device with coated electrodes

A corona device with point-to-plane electrode geometry is used to simulate electrical operating conditions in industrial electrostatic precipitators. The particular aspect investigated is the effect of electrode coating by precipitated particulates of high resistivity, and as simulated by layers of porous insulating materials. The typical measured d.c.characteristics and square-wave response of the device are presented and discussed. The corona modes are identified from measurements, and the device performance is represented by a lumped-element circuit model based on a spatial systematisation of corona phenomena into four regions described as the primary-ionisation, accumulation, transport, and secondary-ionisation regions. The lumped parameters of the circuit model are used for a semiquantitative formulation of criteria for typical corona modes and corresponding electrical characteristics. Further, the circuit model is implemented in the design of a simple solid-state analogue, which can simulate the negative-corona characteristics of the device under different operating conditions.

Use of tests at elevated temperatures to accelerate the life of an m.o.s. integrated circuit

Assurances of a long service life will often be demanded of m.o.s. integrated circuits used in telecommunication equipment. An attempt has accordingly been made to identify failure risks and devise life-prediction procedures by accelerated testing, ambient temperature being the primary stress variable. The test vehicle, manufactured on a volume production line, had a simple circuit configuration permitting direct access to its constituent transistors and allowing each of them to be operated under different electrical conditions. The parameters monitored included threshold voltages, both of the transistors and of a spurious device, gain factors, transistor resistances (in the conduction mode), leakage currents and protective-diode breakdown voltage. The most significant response was obtained from the transistor threshold voltages, which change substantially but in a manner consistent both with the electrical operating conditions and with known physical theories of charge instability in the m.o.s. system. It is suggested that at least the drift of transistor threshold voltage is amenable to a life-prediction procedure, and it is shown how the results could be exploited for procurement-specification purposes.

Zone Electrophoresis: A Study of the Mutual Effects of Polymeric and Electrical Parameters

A correlation is made between serum protein electrophoresis behavior on various cellulosic media and the electrical parameters eliciting the observed behavior. In a standard electrophoresis procedure for human serum employing 1-by 6-inch strips of a cellulose acetate support medium, a tris-barbital buffer having an ionic strength of 0.05 for the combined molarity of its ionizable salts is employed at a constant 250 volts over a period of 45 minutes at ambient temperature (about 26°C). The natures of several polymer support media are correlated with buffer strengths, current densities, and separation times. Variances in electrical operating factors, such as resistivity and heat production, are compared to standard results obtained on a control cellulose acetate membrane. The effects of polymeric structural differences are defined in terms of the adjustments in the standard electrical operating conditions that are necessary to yield control-quality electrophoretic separation. Protein separation characteristics are discussed in terms of the theory involved, the results obtained, and the clinical significances of the findings.