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We investigated spin-polarized current switching of elongated Pac-man (EPM) elements in a Pac-man shaped spin valve (Co/Cu/Py). The aspect ratio, pulse duration, and effect of antiferromagnetic (AFM) layer were simulated to obtain coherent switching. Pulse duration was varied on the picosecond (ps) scale and showed that ultra-fast switching could be achieved. A critical aspect ratio of 4.2 was found, where a minimum current density was observed. For antiparallel to parallel (AP-P) switching, a vortex formed during the switching process for aspect ratios less than 7. Aspect ratios of 7 or higher did not form a vortex and showed similar current densities to parallel to antiparallel (P-AP) switching as a result. It was found that the AFM layer prevented the formation of a vortex at the critical aspect ratio of 4.2 and effectively changed the switching mechanism. This allowed coherent switching with current densities for AP-P and P-AP to be only 7% from each other at the aspect ratio of 4.2. Index Terms--Current, MRAM, Pac-man, simulation.

The electric wind produced by corona discharge of a high-voltage electrode in air is employed for destabilizing a horizontal water film. In wire-to-plane geometry, the phenomenon is characterised by current versus voltage curves and visual observations of the onset of free-surface oscillations. The effect of the following parameters is examined for both positive and negative coronas: distance between the wire and the film (S), film thickness (h), wire diameter ([phi]) and composition, applied voltage (HV), and relative humidity (RH). The free-surface destabilisation is retarded by increasing d and [phi] and is insensitive to h in the tested range. The onset of corona discharge is predicted by Peek's law and compared with the experimentally observed threshold. In negative corona discharge, the current values are higher and the film is destabilised at lower HV than in positive polarity. Humidity tends to decrease the corona current at a given HV. Correlations are proposed for the current-voltage curves, in terms of the mean electric field in the inter-electrode gap and of RH, satisfactorily agreeing with the experimental data. Both positive and negative corona currents turn out to be stable for days of operation. The power loss by corona discharge is in any case lower than 12 W. Wave induction on the liquid-gas interface can effectively enhance heat and mass exchange between the two phases. Index Terms--Corona discharge, ionic wind, thin liquid films, free-surface waves, wire-to-plane geometry, current-voltage characteristics, humidity effects.

The reliability of Power/Ground networks is becoming significantly important in modern integrated circuits, while decap insertion is a main approach to enhance the power grid safety. In this brief, we propose a fast and efficient decap allocation algorithm, and adequately consider the leakage effect of decap. This approach borrows the idea of random walks to perform circuit partitioning and does subsequent decap insertion based on locality property of partitioned area, which avoids solving a large nonlinear programming problem in traditional decap optimization process. The optimization flow also integrates a refined leakage current model for decaps which makes it more practical. Experimental results show that our proposed method can achieve approximate 15X speed up over the optimal budget method within the acceptable error tolerance. Also this algorithm only causes a few penalty area to compensate the leakage effect. Index Terms--Leakage, optimization, power/ground (P/G) network, random walks.

The power-line infrastructure has been identified as an efficient system suitable for broadband power-line communication (BPLC) to connect and control various end users. However, the network is affected by stochastic attenuations due to the number of interconnected branches, their line lengths, associated terminal loads, etc. There is yet another parameter that could influence the above stated attenuations or distortions depending on the way the signals are allowed to return to the transmitting end. In this paper, we investigate whether a finitely conducting ground return could be used for BPLC and to investigate its performance over the conventional methods where one of the adjacent power-line conductors is used as signal return. This study could be helpful to those who are proposing the use of ground as a return conductor in BPLC systems. It will be shown that the use of ground return for the BPLC system is effective or better only when the ground conductivity is high (>50 mS/m). When ground conditions are poorer, attenuations increase with frequency, making them unsuitable for BPLC. There are situations where poor ground conditions can still be used but only the transmission-fine lengths are shorter. The analysis presented here is based on transmission-line solutions both under lossless (without ground return) and lossy (with ground return) conditions and are applied to typical low-voltage and medium-voltage channels. Comparisons are also made based on the power spectral densities and channel capacities. Index Terms--Branched network, broadband power line, channel capacity, frequency response, ground impedance, low-voltage (LV) channel, medium-voltage (MV) channel, multi-path, power-line channel, transfer function.

The article presents a SPICE-like approach for solving the detailed current and voltage distributions in vertical-cavity surface-emitting lasers (VCSELs). The mode changes are a result of hole burning due to anisotropy of the resistivity of the p-distributed Bragg reflector (p-DBR) mirror.

A three-dimensional finite-element tool was developed to compute time-harmonic electromagnetic fields and impedance of substation grounding systems. The formulation employs edge-based finite elements for the magnetic vector potential A and nodal shape functions for the electric scalar potential V. The method has been applied in several configurations presented in the literature. The results are compared with both analytical and experimental data reported by other authors, with overall good agreement. Index Terms--Finite elements, grounding, impedance.

In this paper, we present how the finite-element method can be utilized to analyze the influence of an additional substance in the trenches surrounding the grounding grid's conductors on the grounding grid's performance. For this purpose, we modified the preliminarily existent FIELD_GS program code in such a way that the additional substance in the immediate vicinity along the grounding grid's conductors can be simulated. Different soil structures and various volumes of the additional substance in the soil have been analyzed to prove the suitability of surrounding the grounding grid's conductors in trenches with the additional substance. Index Terms--Electromagnetic fields, finite-element method (FEM), grounding electrodes, numerical analysis.

Based on finite-element method (FEM) of 1-D conductor element coupled with 3-D soil element, we take into account the frequency dependent characteristic of the discretized elements to analyze the grounding performance of the substation grounding grids. Compared with A-V formulation of 3-D FEM, the proposed method can greatly save the CPU time, and the frequency can be considered during FEM modeling. In comparison with the method of moment (MoM) and the measured results, the presented method is proved to be correct and effective. Furthermore, we can calculate the H-field generated by the substation grounding grids with both currents in the underground conductors and leakage currents flowing in the soil. The results show slight difference between FEM and MoM, which can be explained by the fact that the leakage currents in the soil are not taken into account for MoM. Index Terms--Finite-element method (FEM), frequency domain method, method of moment (MoM), substation grounding grids.

Spacer cable provides compact distribution of three-phase power. However, the close proximity of the phases to each other and the neutral carrier wire results in very high fields under lightning conditions. The concept of spacer cable is based on the assumption that the neutral carrier wire is grounded at each pole with an earth resistance no greater than 25 [OMEGA]. In many areas, this assumption is far from met. In this paper, we compute lightning-induced overvoltages for long lengths of spacer cable including the effect of every lightning arrester, transformer, etc., on the line and using measured ground resistances, for a range of lightning currents and rise times. Index Terms--Grounding, lightning, spacer cable.

Recent focus has been placed on improving the reliability and safety of new equipment. This paper describes a few cost-effective upgrades and retrofits for existing electrical systems, which can improve maintenance effectiveness, reduce process downtime, limit physical exposure to hazards, and improve personnel safety. A typical power system, which comprises a high-voltage substation, medium-voltage switchgear, and low-voltage switchgear, has many attributes that are prone to failure and misoperation. These common features in existing systems can be unsafe since failures and misoperations typically result in increased exposure to hazards. A few select cost-effective upgrades or modifications that increase reliability and safety are presented in the general categories of protection, control, operation, and diagnostics. Index Terms--Circuit-breaker diagnostics, control power, high-resistance grounding, protective relays, reliability, retrofits, safety, switchgear, upgrades.

This paper presents a novel converter configuration, based solely on conventional thyristors and aimed for the use with high voltage dc (HVDC) transmission. The converter utilizes resonant turn off and forced commutation with auxiliary thyristors to aid commutation in the converter switches. The PSCAD/EMTDC simulation confirms that the HVDC inverter is capable of operating with a wide range of firing angles, including operation with reactive power export. Further simulation proves that the system is immune to commutation failure even in the case of most severe close single-phase faults. The harmonic generation is comparable to the conventional converter and also the thyristor voltage stress is not significantly increased. The auxiliary thyristors do increase costs, but this is offset by the elimination of reactive power support and the improvements in performance. Index Terms--Commutated circuits, HVDC converters, HVDC transmission, reactive power.

This paper concerns the determination of the electric current requirements for an anti-icing technique based on the Joule effect. The minimum current intensity needed for preventing ice accretion depends on several conductor parameters, including external diameter, electrical resistance, as well as surface geometry (number and diameter of external strands). It depends also on meteorological conditions, such as air temperature, wind velocity, and liquid water content. The study comprises the elaboration of a mathematical model and the laboratory experiments for validation. This research work is mainly concerned with power-line conductor and atmospheric parameters. Therefore, four different types of single A1/S1 power-line conductors are investigated. The analytical model was validated with the experiments performed in the wind tunnel of CIGELE Icing Research Pavilion at the University of Quebec, Chicoutimi. In order to complete the mathematical model, it is necessary to assess the overall heat transfer coefficient (HTC) for stranded conductors. The HTC measurements are presented for conductors with different surface geometries. Index Terms--Atmospheric parameters, heat-transfer coefficient, ice prevention, Joule effect, stranded conductors, wind tunnel.

This paper is intended to present a comprehensive and objective approach to the behavior of grounding electrodes when subjected to lightning currents. Index Terms--Grounding, lightning currents, transient grounding behavior.

This paper presents an improved design method for a novel transformer inrush current reduction scheme. The scheme energizes each phase of a transformer in sequence and uses a neutral resistor to limit the inrush current. Although experimental and simulation results have demonstrated the effectiveness of the scheme, the problem of how to select the neutral resistor for optimal performance has not been fully solved. In this paper, an analytical method that is based on nonlinear circuit transient analysis is developed to solve this problem. The method models transformer nonlinearity using two linear circuits and derives a set of analytical equations for the waveform of the inrush current. In addition to establishing a set of formulas for optimal resistor determination, the results also reveal useful information regarding the inrush behavior of a transformer and the characteristics of the sequential energization scheme. This paper also proposed a method, the use of surge arrester, to solve the main limitation of the sequential phase energization scheme--the rise of neutral voltage. Performance of the improved scheme is presented. Index Terms--Inrush current, power quality, transformer.

Excitation thresholds for long nerve or muscle fibers with two point sources parallel to the fiber axis depend on the dipole length. The aim of this study was to find the optimal interelectrode distance for the minimum stimulation current. For a specific electrode-fiber distance (z_el) dipole length is constrained by the energy efficacy of the electrodes requiring small interelectrode distances, and by rather low stimulation currents requiring large dipole distances. Far-field values for optimal dipole distance (~ 1.4 * z_el) can be explained by the superposition of the positive parts of the activating functions for the monopolar elements of the dipole. A current redistribution effect in a target fiber close to the electrodes shifts the dipole length for threshold stimulation from the theoretical optimal activating function approach value towards greater dipole distances. Spike initiations in straight fibers and retinal ganglion cell axons are investigated. Index Terms--Activating function, dipole length, microelectrode, threshold current.

Shaped charges are a warhead technology often applied to rocket propelled grenades and represent a dangerous threat for armored vehicles in combat as well as in peace-keeping operations. Their armor piercing performance rests upon an explosively induced collapse of a metallic liner to a stretching jet with very high particle velocities. A copper jet produced by a shaped charge can be distorted by high electric currents injected into the jet by means of spaced electrode plates connected to a high voltage capacitor. In tests carried out at Fraunhofer EMI, a shaped charge with a well characterized jet was used for the experiments in order to examine the current flow through the jet and its effect on the jet evolution. The measured current flow is related to the jet dynamics and the distortion pattern observed by multiple flash X-ray images. As expected, the current flow starts when the jet tip reaches the back electrode plate. No significant change of the current flow is observed at the characteristic jet break-up time. The current flow continues after the tail of the copper jet has left the electrodes and resembles a damped sinusoidal. A distortion of the jet is observed where the jet particles are not aligned along the jet axis. Instead the particles are stretched orthogonally to the jet axis with increased separation along the jet axis. The tip part of the jet is hardly affected. The jet distortion is analyzed with respect to jet dynamics and current flow which allows formulating criteria for the design of electric armor systems. The current injection effective for jet distortion is limited to a time slot of a magnitude of 60 [micro]s for the 44-mm caliber-shaped charge used in the experiments. To a first approximation, the current flow can be modeled by an electric arc. An electric circuit model can describe the current flow behavior with respect to the electric impedance and allows designing an electrical circuit adequate for the time slot. By the analogy of a wire explosion the necessary current magnitude for an effective jet disruption with respect to the interaction time slot can be estimated to begin at 300 kA. For the tip portion of the shaped charge jet, the time of effective current injection is very short. When the current starts to set in, the jet tip is already passing the back electrode plate. For this reason, an effective distortion of the jet tip represents a challenge that has to be mastered. Index Terms--Electric armor, electromagnetic armor, shaped charge jet disruption.

Railguns involve both static and sliding electrical contacts, which must transmit the large transient electrical currents necessary to impart high forces onto a projectile for acceleration to hypervelocity. Static electrical contacts between metals initially take place through small asperities, or 'a-spots', distributed over the contact area. The voltage developed across the interface is directly related to the contact temperature and force, the number of a-spots, the thermophysical and mechanical properties of the contacting materials, the current history, and any interfacial materials that may be present. To physically simulate some of the conditions attained within a railgun, a pulsed current static electrical contact experimental facility has been developed at the Naval Research Laboratory. This facility employs a 500-kN capacity servohydraulic load frame equipped with an electrically insulated load train to establish a contact force on interfaces between metals through which a pulsed current is transmitted. The time dependent evolutions of the voltage drops across the interfaces, as detected by probes pushed into the contacting materials, are recorded during a 40-kA peak current pulse having a 300-[micro]s rise time with peak current densities on the order of 50 kA/[cm.sup.2]. The interface stack is assembled from a 12-mm outside diameter annular disk of metal with a 6.3-mm hole which is compressed between two hollow pedestals of a second metal. The evolution of the voltage drop across an interface during a pulse will be described as a function of initial contact pressures, current density, and polarity for dissimilar (AI/Cu) metal contacts. Thermal effects on the surfaces, including localized melting of the interlace materials, were also investigated. Index Terms--Dissimilar metals, electrical contacts, pulsed current, railgun.

Single Event Transient (SET) current is one of the most interesting issues for understanding and predicting Single Event Effects (SEEs) in real space environments. Since space radiation consists of high energy heavy ions, estimation of the energy dependence of SET currents is required. In order to estimate this effect, we have developed the Transient Ion Beam Induced Current (TIBIC) system combined with collimated high energy ion beams accelerated by AVF Cyclotron. We have demonstrated the function of TIBIC developed here. Using the newly developed TIBIC system and the Technology Computer Aided Design (TCAD) simulator, the influence of ion energy on SET currents is estimated. Index Terms--Collimated beam, single event transient (SET) current, transient ion beam induced current (TIBIC).

Increasing the number of antennas for wireless communications, while concealing them within their environment, is an area of great importance as demand for wireless devices increases. One method to achieve this goal is to use the existing conducting objects in an environment as antennas. This requires altering the natural current distribution on conducting objects such that optimal radiation properties can be obtained. In this paper, a composite dielectric bead element is introduced for this purpose on electrically large wire structures. The operation of the bead element is described using transmission line theory, and a wire model of the element is given. Using the wire model, the loading for several electrically large wire structures is designed such that they resonate and radiate similarly to a half-wavelength dipole. Index Terms--Current control, cylindrical antennas, dielectric loaded antennas, linear antennas, loaded antennas, monopole antennas, wire antennas.

Realistic and accurate numerical simulations of electrostimulation of tissues and full-body biomodels have been developed and implemented. Typically, whole-body systems are very complex and consist of a multitude of tissues, organs, and subcomponents with diverse properties. From an electrical standpoint, these can be characterized in terms of separate conductivities and permittivities. Accuracy demands good spatial resolution; thus, the overall tissue/animal models need to be discretized into a fine-grained mesh. This can lead to a large number of grid points (especially for a three-dimensional entity) and can place prohibitive requirements of memory storage and execution times on computing machines. Here, the authors include a simple yet fast and efficient numerical implementation. It is based on LU decomposition for execution on a cluster of computers running in parallel with distributed storage of the data in a sparse format. In this paper, the details of electrical tissue representation, the fast algorithm, the relevant biomodels, and specific applications to whole-animal studies of electrostimulation are discussed. Index Terms--Distributed currents, LU decomposition, parallel computing, tissue modeling, whole body.

This paper analyzes four basic ground methods for personal protection during maintained distribution transformers considering reverse energy from end users. The test in this paper considers that no loads are connected at both the primary and secondary of the distribution transformer. The results are summarized to determine the effective grounding method of protecting distribution line workers on de-energized lines during accidental-line energization from the end users. The secondary voltage at the transformer was recorded with various configurations of temporary grounds, and the primary voltage is then computed by using the transformer turn ratio. As a result, the case of installing no temporary ground is considered lethal. Moreover, the cases of installing temporary ground with a short circuit at either the primary or secondary of the transformer are considered to be the effective means of protecting distribution line workers. Index Terms--Electric shocks, overhead distribution lines, temporary grounding conductor.

In order to measure the grounding impedance of a grounding system more precisely and easily, two key problems of the measurement system: the location of the voltage electrode and the elimination of the noise and interference must be conquered. The new theoretical analysis and measurement system of the grounding impedance based on short-current lead wire and a swept frequency ac source is proposed. The compensating position of the voltage electrode to obtain the real grounding impedance is evaluated by analyzing the soil structure, the grounding system under test, and the position of the current electrode. This new system measures the ground impedance at several frequencies other than power frequency, then interpolates them to acquire the ground impedance at the power frequency. The mutual inductance between the potential and current wires is analyzed and eliminated. The industrial computer-based grounding impedance measurement system is developed and the analysis software is programmed. A field test was performed and compared with the traditional method in the substation and the novel system worked well. Index Terms--Grounding impedance, quasi-synchronous sampling algorithm, substation, swept frequency ac source.

A Fredholm integral equation of the first kind has been developed for analyzing the performance of the toroidal high-voltage direct current (HVDC) grounding system buried in the horizontal multilayer soil. The method of moment is used to solve the equations. The formulation of potential in the earth due to a circular current is proposed in closed form by means of conception of the complex resistivity and depth, which leads to the saving of the computational time greatly. The numerical results show the good agreements with those in other papers and the measured data. Index Terms--Galerkin's moment method, grounding electrodes, high-voltage direct current (HVDC), multilayer soil.

In a high-temperature superconducting (HTS) transformer leakage magnetic field, especially its radial component, decreases the critical current and increases the ac losses in the tapes. Because of zero resistance of HTS tapes a slight unbalance among the branch inductances of the windings may result in heavy circulating current, however, an accurate calculation of it must depend on the magnetic field analysis. Thus, a numerical analysis of the leakage magnetic field is especially necessary for an HTS transformer design. In this paper the leakage magnetic field of several transformer geometries is studied by finite element method, and based on it, the circulating current distribution is calculated. Some suggestions for improving the leakage field and circulating current distribution are presented to make HTS transformers more efficient. Index Terms--Circulating current, finite element method (FEM), HTS transformer, leakage magnetic field.

The grounding systems are simply handled as lumped resistances with constant values in traditional lightning transient analysis of substation. A complete transmission line model is proposed to consider the actual transient process of power network and the grounding grid of the substation and the grounding devices of transmission towers. A loss transmission line model with time-variable parameters is proposed to calculate the transient characteristics of grounding systems under lightning current in which the soil ionization phenomena around the ground conductors are considered. The analyzed results by the proposed model have large differences with those obtained by the traditional simplified method. The transient characteristics of grounding systems have strong influence on the lightning transient process of substation. Index Terms--Grounding system, lightning, soil ionization, substation, transient performance, transmission line model.

When dc current is injected into the earth through the grounding electrodes of a high-voltage direct current (HVDC) system, transformers in ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a numerical method coupling the method of moments (MOM) to circuit equations is presented to calculate the dc current distribution in ac power system caused by an HVDC system. The MoM is used to calculate the electric fields in complex earth structure caused by all the grounding systems including the dc grounding electrodes, the ac substation grounding systems and the long metal pipe lines. The circuit equations are coupled to the moment method to take account of the effects of the transmission lines. By using the method, the dc current distribution in an ac power system caused by an HVDC system is analyzed. Some useful conclusions are drawn from the analyzed results. Index Terms--Current distribution, grounding electrodes, high-voltage direct current (HVDC) transmission, method of moments (MOM).

The design of grounding system often relies on the performance simulations. The evaluation of the current distribution of grounding system for many frequencies by using the method of moments (MoM) may take a long time since the impedance matrix must be recomputed at each new frequency. A multiobject adaptive spatial sampling approach is presented to construct the fitted model of the electric field intensity generated by a horizontal electric dipole. The [Z] matrix spatial interpolation technology with MoM is described to reduce the computational time needed for the transient characteristics analysis of a horizontal grounding system. The accuracy and computational time of the [Z] matrix interpolation method are compared with those of the direct MoM. The numerical examples show that the [Z] matrix spatial interpolation method can reduce the computation requirement effectively. Index Terms--Adaptive sampling, fitting model, grounding grid, interpolation, method of moment (MoM).

A novel experimental technique is presented to identify the energy of traps responsible for the stress-induced leakage current (SILC) in Flash memories, based on a standard gate-stress analysis with a drain bias used to accelerate channel restrictions. From the study of the rolloff in SILC characteristics, evidence for the existence of high-energies above the silicon dioxide, located at energies above the silicon conduction band minimum is provided.

A low defect at Si surface was formed by a high-temperature annealing in hydrogen atmosphere. This was used to study the effects of the defects at high-k dielectric/Si interface on the electrical characteristic of metal-oxide semiconductor.

An interpretation of the physical mechanisms involved in the generation of laser beam-induced current (LBIC) in semiconductor p-n junction diodes is presented. LBIC is a nondestructive semiconductor characterization technique that is especially useful for examining individual photoiodides within large two-dimensional arrays of devices.

A nonuniform transmission line approach is adopted in this paper for modeling the transient behavior of different types of grounding systems under lightning strikes in time domain by solving Telegrapher's equations based on finite-difference time-domain (FDTD) technique. Electromagnetic couplings between different parts of the grounding wires are included using effective per-unit length parameters (l, c, and g), which are space and time dependent. The present model can predict both the effective length and the transient voltage of grounding electrodes accurately, while, an uniform transmission line approach with electrode length dependent per-unit length parameters [19]-[22] fails to predict the same. Unlike the circuit theory approach [1]-[4], the present model is capable of predicting accurately the surge propagation delay in the large grounding system. The simulation results for buried horizontal wires and grounding grids based on the present model are in good agreement with that of the circuit and electromagnetic field approaches [3], [9]. From an engineering point of view, the model presented in this paper is sufficiently accurate, time efficient, and easy to apply. Index Terms--Grounding, lightning, transient analysis, transmission line and finite-difference time-domain (FDTD) methods.

It is shown that, in the analysis of fractional polarization thermally stimulated depolarisation current, the values obtained for the activation energy W and the pre-exponential factor [[tau].sub.0] depend on which one is assumed constant. The elemental peak position and shape change significantly for simulations where we assume that the activation energy is variable and the pre-exponential factor is constant, or vice-versa. A mathematical expression for the current is proposed in the case where W and [[tau].sub.0] are both variable. The uncertainties affecting the relaxation parameters produce a broadening of the theoretical peak. The minimum uncertainties in the relaxation parameters are estimated. For a current peak at temperature [T.sub.m], a calculated distribution of W with width [approximately equal to] k[T.sub.m], or a calculated distribution of [[tau].sub.0] with width [approximately equal to] [[tau].sub.0], is physically meaningless. Index Terms--Thermally stimulated current, relaxation parameters, relaxation times, minimum uncertainty interval, activation energy, polarization, depolarization.

A new approach for electrical characterization of forward AC behavior of real semiconductor diodes is discussed.

A low-stress I-V measurement system for characterizing the insulator in metal-insulator-metal (MIM) tunneling cathodes is described and discussed.

A novel CMOS low-voltage positive current conveyor of second generation is described in this paper. This solution allows almost rail-to-rail input and output operation and a high driving capability, thanks to the adoption of a class AB current output stage. A prototype was fabricated in a 0.35-[micro]m technology and experimentally tested. Using a 1.5-V supply, the circuit exhibited an input resistance of lower than 100 [ohm] at terminal X and a better than [+ or -] 0.9 mA current drive capability, which was about 45 times the quiescent current in the output branch. Good frequency performance was also obtained. Index Terms--CMOS, current conveyor, low voltage.

This paper presents a study of prebreakdown phenomena (usually called streamers) occurring at high voltage in liquid nitrogen. A special cryostat has been constructed to allow dielectric measurements in liquid nitrogen up to 200 kV, and 0.5 MPa hydrostatic pressure. Streamers are detected and studied with various techniques: high speed visualization, streak camera, and recording of transient currents and emitted light. The propagation of positive and negative streamers is investigated at gap distances up to 80 mm. Streamers are then compared to similar phenomena observed in mineral oil. In liquid nitrogen, streamers are different compared to mineral oil. A transition from slow to fast positive streamers (velocity about 10 km/s) is observed at a threshold voltage below the breakdown voltage. The hydrostatic pressure has almost no influence on this phenomenon. Some experiments carried out with a solid barrier perpendicular to the gap axis are also presented. The practical consequences for the design of HV insulation in superconducting systems are then discussed.

Cryogenic liquids show a noteworthy impact on the concept of improved future power equipment with superconductors. Superconducting materials eliminate any Joule heating but are based onto very low operating temperatures. A high overall current density in the equipment may be presupposed. Cooling however must be guaranteed by cryogenic liquids, i.e. liquid helium or liquid nitrogen, respectively. The cooling liquids are interesting basic insulating fluids with a reasonable dielectric performance in the medium high voltage domain. Most exciting is the chemical inertness. Hazards such as fire risk in case of severe faults can be ruled out, thus reducing insurance cost drastically. Thermal aging of the liquids can also be disregarded because no chemical reaction must be taken into account during service, even in case of temporary overload operation. Dielectric aging due to partial discharges may be of little concern because the liquids can be fully reprocessed easily by vaporizing and recondensing in a closed cooling circuit; no memory effects may degrade the liquid at all. On the other hand, overload operation may yield a large amount of thermal bubbles which can affect the dielectric strength seriously. Finally, the liquids are produced from gases which are found in the open atmosphere. There is no danger of any poisonous reaction in case of uncontrolled leakage, and the disposal of insulation systems at the end of operational life is straightforward without the need of costly processing.

This paper presents the results of a project aimed at the development of reliable corona-suppression systems for high voltage rotating machines. These systems are based on both conducting and semi-conducting dry and B-stage tapes as well as paints of different resistivity. Three groups of anti-corona systems were developed; namely, paint (on the slot portion)--paint (on the slot exit) system, paint (on the slot portion)--tape (on the slot exit) system, and tape (on the slot portion)--tape (on the slot exit) system. Sample results of standard evaluation and acceptance tests are presented. The accelerated life-aging test was run on test coil samples at the National Electric Coil HV testing facility. A numerical 2-dimensional finite difference model for the electric potential and field analysis along the end-turn zone was developed and the model results are used as guidelines through the design process of the grading system. Laboratory test results on randomly selected sample coils were confirmed by an independent testing facility. The proposed corona-suppression systems were applied on thousands of production coils.

A novel zero-voltage and zero-current switching PWM dc-dc converter with low conduction losses is presented in this paper. A new interleaved two-switch forward soft-switching converter topology is developed to minimize circulating current with no additional auxiliary circuits. This converter has many advantages such as less components, better efficiency, high power density and cost effective for high power applications. The principle of operation is illustrated together with steady-state analysis. Moreover, the effectiveness of the proposed converter topology is verified by implementing a 500 W-100 kHz breadboard using IGBTs. Index Terms--Circulating current, conduction losses, dc-dc converter, tapped inductor, zero-current, zero-voltage.

By dramatically decreasing the storage time, the emitter turn-off thyristor (ETO) has a very good match in storage time. Storage time dispersion of less than [+ or -]100 ns is normal for ETOs and can be further reduced through adjustment of the emitter switch gate resistance. Thus, the capacitance required for dynamic voltage balancing in the ETO series connection is significantly reduced. Uniform current sharing for parallel-connected ETOs is also guaranteed at the device level through the open-base p-n-p turn-off mechanism. The current-balancing inductance can be essentially removed. Theoretical analysis and experimental results of 53-mm ETOs are presented. Index Terms--Emitter turn-off, emitter turn-off thyristor, gate turn-off thyristor, integrated gate-commutated thyristor, MOS turn-off thyristor, thyristor, unity gain turn-off.

Interaction of the third harmonic magnetic field with the third harmonic current in a five-phase synchronous reluctance motor (SynRM) can produce additional torque. However, it is still not clear about the SynRM power factor and its impact on the associated power converter because of the third harmonic components. Using time-stepping finite-element method, a mathematical model of the SynRM, which allows any desired harmonic component in computation, is presented. Performance of the five-phase SynRM with two rotor structures has been computed. The study finds that contribution of the third harmonic current to the output torque depends on the rotor structures. It is also shown that the required terminal voltage to regulate the desired current waveform is substantially increased, a result not reported before. Index Terms--Finite-element methods, synchronous reluctance motor, third harmonic, time stepping.