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Measurements were conducted on the field- and frequency dependent alternating current (AC) susceptibility in melt-textured YBaCuO at 77 K and under different field conditions. AC induction RMS values were measured up to 13 mT, and direct current induction values were found to be 0, 20, 40, 75 and 100 mT. Results suggest that high temperature superconductors' AC susceptibility is dependent on frequency as well as on DC and AC induction.

A study was conducted on boundary-induced coupling currents in a 1.3m long Rutherford-type cable. A field change was locally applied to the cable to demonstrate the currents. A special set-up was also developed to analyze the characteristic time, length and amplitude of the coupling currents and the parameters that affects them. The set-up was successfully employed in scanning the field exhibited by the currents along the full-length of the cable.

A study was conducted on alternating current losses in ITER joints in a varying parallel magnetic field. Results demonstrate that joints may be designed with the same or greater temperature margin as conductors operating in the same parallel field. Design considerations for suppressing alternating current losses while avoiding increases in direct current resistance are presented.

Solutions are proposed for the diffusion equation for flat superconducting cable flux penetration. The solutions are for cables that are partially exposed to applied fields and for magnetic fields changing along the cable. The equation was used to determine the alternating current losses, time constants and the current distribution in the strands. Results prove the existence of super coupling currents in some accelerator magnet cables.

Concurrent optical and electrical measurements have been used to characterize the physical phenomena associated with the prebreakdown and flashover behavior of high-voltage alumina ceramic insulator samples having both conventional and unconventional conical geometries. The critical parameters are the threshold voltage for initiating flashover events, the stable interelectrode current-voltage relationship, the luminescence pattern, and the breakdown rate as a function of time. These measurements have revealed that a well-conditioned sample of unconventional conical geometry can have very low, i.e., approaching zero, breakdown rate. Physical explanations of the findings are based on the current understanding of flashover mechanisms and the prediction from simulations using a field plotting technique. Index Terms - Ceramics, conical insulators, flashover, high-voltage, vacuum.

Circuit design techniques for very low-voltage bias circuits are discussed. A Nagata current mirror is very suitable for battery operation because it provides current regulation. Also, it is very suitable for start-up circuitry. In this brief, an inverse Widlar current mirror is newly proposed as a nonlinear current mirror with a negative temperature coefficient (TC), a Nagata/inverse-Widlar current mirror is also proposed as a Nagata current mirror or an inverse-Widlar current mirror with an optionally programmed positive or negative TC, and a TC shifter with an offset voltage proportional to absolute temperature (PTAT) is also proposed. Furthermore, fundamental characteristics and temperature characteristics of the bias circuits discussed in this brief were verified with transistor-arrays and discrete components. Index Terms - Bipolar, inverse PTAT, inverse-Widlar current mirror, low-voltage bias circuits, mutual-biasing, Nagata current mirror, self-biasing, TC shifter.

A method of computing non-linear, transient electromagnetic fields with eddy currents, in which the magnetic vector potential is decomposed into two components is presented. The transient electromagnetic field is coupled with equations describing the external driving circuits with power electronic components. The non-linearity of magnetic materials is treated through a modified Newton's non-linear iterative scheme combined with a time-domain, piecewise elemental linearisation that enables the implementation of the decomposed magnetic vector potential method. A practical application of the method to a study of the transient characteristics of a tubular linear actuator is presented to show the effectiveness of the proposed method.

Two-dimensional processes and device simulations are effective for designing and characterizing high-voltage NMOS and PMOS devices compatible with low-voltage 5 V, 0.8 micro-m BiCMOS processes. The optimized high voltage PMOS and NMOS devices have small unit-cell pitches of 7.3 and 7.8 micro-m, respectively, and low specific on-resistance of 11.5 and 0.9 m-ohm.square cm. The devices exhibit breakdown voltages of plus or minus 29 V.

Harmonic resonance has been observed, measured and modeled on parallel 500-kV lines that are about one wavelength at 2100 Hz, the 35th harmonic. A seemingly small harmonic injection at one location on the system causes significant problems some distance away such as telephone interference.

The high requirement of rated power of an active power filter leads to high costs and limits the range of operation especially for high voltage applications. To overcome these problems a combined system of a passive filter, using only one LC filter tuned to the lowest typical line current harmonic, and a shunt active power filter, sharing the filter capacitor to be decoupled from the fundamental line voltage, is proposed. These features strongly decrease the rated power of the active filter which is controlled only to suppress the harmonics of higher order and to eliminate resonance effects between the line impedance and the passive filter.

Current transformer (CT) saturation may cause relays to malfunction. The conventional method to deal with the problem is overdimensioning of the core so that CTs can carry up to 20 times the rated current without exceeding 10 % ratio correction. However, this not only reduces the sensitivity of relays, but also increases the CT core size. This paper presents a technique of estimating the secondary current corresponding to the CT ratio under CT saturation. The proposed algorithm can improve the sensitivity of relays to low level internal faults, minimize the instability of relays for external faults, and might ultimately assist in reducing the dimension of the required CT core cross section.

The purpose of this paper is to provide the relay engineer with a basic understanding of the physical and electrical characteristics of high voltage ac cables, 115 kV and above, and how this applies to protective relaying. It will also discuss the application of various protective schemes with the advantages and disadvantages associated with those schemes.

The performances of XLPE and EPR as materials candidate for insulation of high voltage power cables are investigated. Data obtained from laboratory tests performed on cable models aged under single thermal and electrical stresses, as well as under the combination of the two stresses, are considered. The drawing of electrical, thermal and multi-stress life lines provides a synthetic and exhaustive description of the behavior of the tested materials, and allows the determination of endurance indices, useful for electrical, thermal and multi-stress characterization.

A basic criterion that determines the behavior of an active power filter is the method of calculating the reference current. There are many ways of generating this reference, but the methods are generally complex and hard to tune. This paper describes a simple and effective method for calculating the reference current, necessary to feed a shunt active power filter to compensate the power factor and harmonic currents generated by a nonlinear load. Simulations and experimental results are presented, showing that the proposed circuit may operate at frequencies ranging from 40 to 65 Hz without adjustment.

The stationary distribution of ballistic current carriers moving across a thin doped base is shown to be unstable if there is a negative effective mass component in the carrier dispersion law. Under such a condition, a regime with quasistationary current oscillations is established for a wide range of voltages across ballistic diode. The oscillation frequency and amplitude are functions of the base length, doping concentration and applied voltage. The current oscillation occurs in a short-circuit regime.

This paper introduces a fuzzy logic-based tuning of the controller parameters for the rectifier side current regulator and inverter side gamma controller in a high voltage direct current (HVDC) system. A typical point-to-point system has been taken with the detailed representation of converters, transmission links transformers, and filters. The current error and it's derivative and the gamma error and it's derivative are used as the principal signals to adjust the proportional and integral gains of the rectifier pole controller and the inverter gamma controller, respectively, for the optimum system performance under various normal and abnormal conditions. Finally, a comparative study has been performed with and without tuning, to prove the superiority of the proposed scheme.

In this paper polyphase transformer arrangements with reduced kVA capacities are presented for harmonic current reduction in high power diode rectifier-type utility interface systems. Based on the concept of an autotransformer, a 12-pulse rectifier system is realized with a resultant transformer kVA rating of 0.18[P.sub.o] (pu). In this arrangement the 5, 7, 17, 19, etc. harmonics are absent from the utility input line current. In the second scheme an 18-pulse rectifier is realized with the kVA rating of 0.16[P.sub.o] (pu) and the 5, 7, 11, 13, etc. harmonics are canceled in the utility line currents. Analytical design equations are presented to facilitate the design of system components. Simulation results verify the proposed concept, and experimental results are provided from a 208 V, 10 kVA 12-pulse rectifier system. The advantage of employing the proposed system for utility interface of rectifier/PWM-inverter motor drive systems is also explained.

A method is presented for computing near- and far-field patterns of an antenna from its near-field measurements taken over an arbitrary geometry. This method utilizes near-field data to determine an equivalent magnetic current source over a fictitious surface which encompasses the antenna. This magnetic current, once determined, can be used to ascertain the near and the far fields. This method demonstrates that once the values of the electromagnetic field are known over an arbitrary geometry, its values for any other region can be obtained. An electric field integral equation is developed to relate the near fields to the equivalent magnetic current. A moment method procedure is employed to solve the integral equation by transforming it into a matrix equation. A least squares solution via singular value decomposition is used to solve the matrix equation. Computations with both synthetic and experimental data, where the near field of several antenna configurations are measured over various geometric surfaces, illustrate the accuracy of this method.

A new numerical technique is presented for calculating the current distributions on wire antennas with a high degree of curvature. The geometry of the wire antenna is expressed by a parametric equation and the current is directly expanded into a series of quadratic B-spline basis functions of the parameter, so that the truncation error in modeling the curved wire structure is avoided. This algorithm is used to analyze a circular loop antenna, a conical equiangular spiral antenna, and a four-arm Archimedian spiral antenna to demonstrate its validity and practical value.

An edge element is applied to the analysis of the electric current distribution on a thin conducting plate. The normal component of the surface current density across the edge of the triangular element is chosen as unknown variable preserving the normal continuity. By using Galerkin's weighted residual method, the formulation of the analysis is done for the electric field on the thin conductor surface taking account of the eddy current and the displacement current. In addition, the proposed method is applied to simple computation models in order to verify the applicability of the method.

The use of adjustable-speed drives requires transformers capable of withstanding high levels of harmonic currents under normal operating conditions. Experience has been that overheating problems are much more common with dry-type transformers than with liquid-filled transformers. Transformer insulation life is determined by the hot spot temperature but confirmation of hot spot temperature rise is one performance characteristic which is ignored in industry standards. This is especially important for transformers rated for nonsinusoidal load currents. Hot spot allowances used in IEEE standards for ventilated dry-type transformers were developed in 1944 and recent data indicates that revisions are required. The design of transformers for nonsinusoidal load currents should include an analysis of the eddy loss distribution in the windings and calculation of the hot spot temperature rise. Calculations and thermal tests giving only average winding temperature rises are not sufficient. Thermal tests with nonsinusoidal currents and measurements of hot spot temperature rises are extremely difficult on large transformers. The combination of testing and analysis may be the only economically practical approach. Analysis indicates that the dry type transformer hot spot temperature is very sensitive to the eddy loss magnitude and distribution. The Underwriters Laboratories Inc. (UL) K-factor rated dry type transformer and the recommended practices given in ANSI/IEEE C57.110 are reviewed. When purchasing transformers subject to nonsinusoidal load currents, considerations should be given to the manufacturer's development program and capability to calculate the eddy loss distribution and hot spot temperatures.

In this paper, we propose an approach to quantifying the distortion caused by a single customer, when there are many customers in the network. We have described a method for isolating the contributions to waveform distortion from a customer side and the supply side. The voltage and current measurements at a single point are sufficient. This approach will be useful in arriving at equitable ways of settling customer complaints, sharing the cost of waveform distortion through rate structures, penalties, etc. The principle is illustrated using six example loads. The method proposed can be implemented in any power quality measurement device, which monitors the voltage as well as the current harmonics simultaneously. Key words: Harmonics, origin, direction, Load, power quality, measurement, high voltage.

When the mixed translinear loop is used in a voltage follower implementation, the value of its output resistance depends on its bias current. This property is used in the realization of a current controlled conveyor (CCCII), which has therefore its serial resistance on port X controlled by the bias current. The two basic implementations, that allow from a CCCII and without additive resistances to realize controlled voltage-current converters, are described. A current-controlled voltage-amplifier and a current-controlled current-amplifier are then analyzed. They are implemented from only two CCCII's and do not require any passive component. The principal implementations for current controlled first-order transfer functions, operating either in voltage-mode or in current-mode, are introduced. They require one or two of the preceding controlled conveyors and use capacitors only. SPICE simulation results, obtained using the parameters of the HF3CMOS process from SGS THOMSON, are given for the CCCII and for its main applications. They confirm the validity of the theoretical analyzes and also underline the high frequency potential of the current controlled implementations introduced. A second-order bandpass filter, operating in voltage-mode, is also described. It is obtained from two CCCII's and two capacitors only. Its centre frequency, which is adjustable by acting on the control currents of the conveyors, is equal to 11.3 MHz for [I.sub.0] = 20 [[micro]amperes] and to 16.6 MHz for [I.sub.0] = 30 [[micro]amperes]. This variation produces very small changes in both the quality factor and the gain (variations less than 7%). Comparisons between existing OTA circuits and the ones implemented from controlled conveyors, are also given. They underline the advantage which result from implementations using controlled conveyors.

The current switching by means of a gas-filled electron switch has been studied experimentally and theoretically. The switch showed complete controllability under deep volume charge compensation conditions. The switched current density was an order of magnitude higher than the current density of a similar vacuum switch.

The formation of intense current filaments, destroying the homogeneity of the active laser volume, limits the energy extraction from XeCl-lasers. Using time-resolved spectrally integrated pictures, the morphology and temporal development of such filaments are studied. The time scale of this process is found to be controlled by HCl depletion. With strong preionization ([n.sub.e] > [10.sup.9]/[cm.sup.3]) and a fast (10 ns) rising discharge voltage applied at the end of the preionizing X-ray pulse, the filaments originate from hotspots formed in the cathode layer. The shot by shot statistics of spot formation on freshly prepared cathodes reveal that hotspots are not caused by streamers developing in the high field region of strongly reduced electron density built up by electron diffusion during formation of the cathode sheath. Unexpectedly, a large number of weak diffuse filaments are found in spotless discharges (current density 300 A/[cm.sup.2]; duration 200 ns), in spite of the strong preionization.

Insertion of internal impurities is one of the factors for the degradation of neutron output in plasma focus devices. In this context, neutron emission measurements were carried out in a 2.2 kJ (7.2 [[micro]farad], 25 kV) Mather type squirrel cage plasma focus device with various combinations of electrode and insulator materials. The neutron yield was measured by silver activation detector. The results indicate that a central electrode of low erosion rate material produces maximum neutron yield with the highest anisotropy factor. A time integrated X-ray pinhole image shows that focus corresponding to the highest neutron yield material is the most compressed. The dielectric constant of the ceramic insulators has, at best, a very weak correlation with neutron output. The nonceramic insulators like perspex, nylon, or teflon neither produce focus nor neutron.

With the experiments presented in this paper, applications of a retarding field analyzer (RFA) for the measurement of the ion energy [E.sub.i] in a vacuum arc plasma are discussed. The examined plasma was produced by a sinusoidal half-wave vacuum arc current. The experiments were concentrated on evaluating the plasma parameters at the last three milliseconds before current zero. In a current range from 300 [A.sub.rms] to 10 k[A.sub.rms], the ion energy distributions and their peak values were evaluated. With the increase of the arc current, a decrease of the ion energy was found. By additional investigations of the angular distribution of the ion energies, a transition from a collision dominated interelectrode plasma to a freely expanding plasma was observed, depending on the arc current.

The main parameters and dimensions of cathode spots have been under discussion for years. To solve these current questions, a new system was specially designed. The image converting High Speed Framing Camera (HSFC) combines a micrometer lateral resolution with a nanosecond time resolution and a very high optical sensitivity. This camera was used to study the microscopic behavior of vacuum arc cathode spots in a pulsed high current arc discharge on copper. The direct observation of these spots with high resolution revealed that one single cathode spot, as normally observed by optical means, consists of a number of simultaneously existing microscopic subspots, each with a diameter of about 10 [[micro]meter] and a mean distance of 30-50 [[micro]meter] between them. The mean existence time of these subspots on copper was found to be about 3 [[micro]seconds], where the position of a subspot remains unchanged (with an upper limit of about 5 [[micro]meter]) during its existence time. The lower limit of the current density in the cathode spots was estimated to be on the order of [10.sup.10]-[10.sup.11] A/[m.sup.2]. An upper limit of the crater surface temperature was estimated by a comparison between the brightnesses of a cathode spot and of a black body radiation lamp to about 3000 K.

The paper deals with the power properties of three-phase circuits with unbalanced loads supplied from a three-wire line. It discusses various definitions of the apparent power in such circuits and shows that they cannot be interpreted in terms of any physical phenomena. The paper shows that the unbalanced power does not occur as an effect of the power oscillations and explains why this power does occur. The paper presents a decomposition of the supply current into the active, reactive, and unbalanced currents and shows that this decomposition can be considered as a fundamental for the comprehension of the power phenomena in such circuits and for the power factor evaluation. Key words: unbalanced systems, apparent power, unbalanced current.