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Stator coils transposed by 540[degrees] are widely used as one of the solutions to reduce the circulating current loss in the coil strands of turbine generators. However, the difference of the leakage fluxes in the two coil end parts, which is possibly caused by the coil end length deviation, the winding pitch, and the presence of the connection rings, may induce unbalanced voltage in the stator coil strands, which increase circulating current loss even in the transposition coils. This paper describes the mechanism and the analysis results of the circulating current increase in the coil strands due to the coil end flux difference. Then, some new schemes to reduce the circulating current loss are proposed and discussed. Index Terms--Circulating current loss, transposition, turbine generator, windings.

The numerical simulation of complex, nonlinear and coupled, electromagnetic and thermal dynamics involved in the quench phenomena of Magnesium Diboride (Mg[B.sub.2]) superconducting magnets requires a suitable modeling of the interaction among the different aspects. As a matter of fact, magnets wound using Mg[B.sub.2] tapes are characterized by material parameters and working temperatures leading to different behaviors with respect to either Low [T.sub.c] superconductors (LTS) and High [T.sub.c] (HTS) superconductors, and thus requiring special care in the modeling of quench diffusion phenomena. In this paper, a 3-D finite-element method (FEM) model able to cope with such phenomena is presented and model predictions are compared to experimental data. Index Terms--Coupled problems, Mg[B.sub.2], quench protections, superconducting magnets.

This paper presents a novel steady-state and transient performance analysis of the universal motors with appropriate turns ratio of lead coils to lag coils in an armature. Time-stepping finite-element analysis has been used to successfully predict the brush-to-bar voltage drop of the universal motor. The computed armature current and speed have been validated by tests in a 500-W universal motor. The turns ratio of lead coils to lag coils minimizing the brush-to-bar voltage drop has been determined from the simulation results. Index Terms--Brush-to-bar voltage drop, finite-element analysis, steady-state and transient performance characteristics, turns ratio of lead coils to lag coils, universal motor.

The article discusses the design and importance of the second-generation (2G) High Temperature Superconducting (HTS) wires for coil applications. Results suggest the viability of 2G HTS wire in coil applications as the 2G solenoid coil with a 5cm inner diameter is able to achieve 1.5 T at 64 K.

The quench characteristics of a High Temperature Superconducting (HTS) coil during over-current condition are discussed. Results suggest the occurrence of a global quench in the coil due to the sharp increase of the voltage across the coil at the base line current.

Various advancements have been made in the development of [YBa.sub.2][Cu.sub.3][O.sub.x] (YBCO) second generation HTS conductor scale-up at superpower. These conductors are found to exhibit very high values of the critical current.

The inductance of a coil in a slotted, conducting shell is investigated. At frequencies for which the coil is very small relative to wavelength, an integral equation is formulated and numerically solved for the electric field induced in the slots. From knowledge of the slot electric field, the inductance of the coil in the slotted shell can be calculated. The dependence of inductance on the presence of the slotted shell is assessed quantitatively and explained on the basis of physical principles. The inductance of a one-turn loop inside a slotted shell is measured, and the data are found to be in excellent agreement with computations. As an unslotted shield closes on a coil, inductance is reduced noticeably, but if the shield possesses axial slots, the reduction is much less significant. Index Terms--Apertures, coils, equations, inductance, integral.

In the present paper, a sensitivity analysis scheme for designing the shape of cylindrical probe coils is presented. These coils are used for the induction of specified eddy current distributions inside cylindrical conducting specimens. This requirement is satisfied by designing the outer surface of the coil, while the excitation current density is assumed to be known and constant all over the cross-section of the coil. An appropriate error function, which is related to the desired and the estimated values of the magnetic vector potential, is minimized by applying the Newton's gradient based optimization method. The estimated values of the magnetic potential are computed by an integral formulation, which is derived from the diffusion equation. During each iteration of the minimization process, the gradient and the second order partial derivatives of the error function, with respect to the design variables, are evaluated analytically. In numerical results, the method is applied to the induction of a uniform eddy current distribution parallel to the axis of a conducting cylinder. Index Terms - Eddy current testing, design methodology, sensitivity analysis, Newton's method.

The maximum safe operating limits of the DIII-D tokamak are determined by the force produced in the ohmic heating coil and the toroidal field coil during a plasma pulse. This force is directly proportional to the product of the current in the coils. Historically, the current limits for each coil were set statically before each pulse without regard for the time varying nature of the currents. In order to allow the full time-dependent capability of the ohmic coil to be used, a system was developed for monitoring the product of the currents dynamically and making appropriate adjustments in real time. This paper discusses the purpose, implementation, and results of this work.

A simple scaling relation useful for quantitatively measuring the inductance of a coil on a ferromagnetic half-space is presented. This is composed of two parameters, namely an angular frequency and a constant. It was observed that the inductance change can be described by a simple scaled curve at a certain characteristic frequency. Approximation techniques can be used to derive an analytic form for the curve.

It has been previously demonstrated that an induction machine drive with contactorless pole changing can be achieved by reversing current directions of certain stator coil groups. This paper compares the power and torque capability of this drive with conventional four-pole and two-pole induction machine drives. Based on the technique of vector space decomposition, the machine coupled-circuit model is transformed to a reference frame model. As a result of this transformation, the coupled coil group variables can be replaced by equivalent decoupled four-pole and two-pole dq0 variables. This reference frame model facilitates the analysis and control of the machine drive, especially during transients, such as the pole-changing transition. Index Terms - Electronic pole changing, reference frame model, induction motor.

Physical experiments often require a short-term magnetic field with a specified uniformity to be created in a certain space. In this case, various electric energy storages are used for the pulse supply of magnet systems, for example, the bank of capacitors. The simplest configuration of such a magnet system is formed by two identical coils. This paper presents the methods and main results of two coils system optimization taking into account the field uniformity and other requirements when this system is supplied either by mains or by capacitor banks. Index Terms - Capacitive energy storage, coils, discharge magnetic efficiency, geometry efficiency, inductance, magnetic fields, resistive circuits.

This paper deals with two efficient approaches for determining the mutual inductance between thin circular coils and disk coils in air. The first approach gives new expressions for calculating the mutual inductance of treated configurations. These results are expressed over the complete elliptical integrals of the first and second kind, Heuman's Lambda function, and one term that must be solved numerically. Another approach is based on the filament method where conductors are approximated by the set of Maxwell's coils. The obtained expressions are expressed over the complete elliptical integrals of the first and second kind and permit also fast calculation of the mutual inductance for mentioned systems. These new expressions are accurate and simple for useful applications. All results obtained by the two approaches are in excellent agreement. Index Terms--Biot-Savart law, circular coils, disk coils, Maxwell's coils, mutual inductance.

The expected future limit on a magnet's residual flux density Br due to decreased size in disk drive form factor is presented. Because, historically, the energy products of magnets have been increasing while the flux carrying capacity of steels has remained the same, one may expect a limit on further increase in Br. For numerical illustration, the force exerted by the moving coil actuators in 2.5' and 1.8' disk drives is calculated as a function of Br. These calculations show that one may expect no limit on Br for any practical, future scenarios, but that the ratio of an increase in force for an increase in Br diminishes.

This paper discusses a new suspension and guidance configuration for a high-speed, electrodynamic suspension (EDS) maglev system. The configuration can also be used to develop an electromagnetic guideway directional switch. The performance of the system is predicted using the dynamic circuit model. General expressions of the magnetic forces based on the harmonic approximation are obtained. The principle of the electromagnetic guideway directional switch for the EDS maglev system is discussed.

The article explains the benefits of the application of a coil array for improving the accuracy of a wireless motion sensing system. The integrated coil component is shown to be extremely beneficial in enhancing the accuracy of the system.

Models are developed for the inductance of a helical coil and a helical coil inside a conducting shield. Values of inductance are found from analysis. The dependence of inductance on the presence of the shield is assessed quantitatively and explained on the basis of physical principles, and the significance of skin and proximity effects in the wire coil is outlined. The inductance of an isolated, one-turn loop and a one-turn loop inside a conducting tube are measured and are found to be in excellent agreement with computed data. When the conducting shield and coil are very close, the inductance of the coil is found to be greatly diminished suggesting that one must account for the presence of shields when characterizing inductors, which might be used for loading and tuning of antennas. A nearby conducting shield must be accounted for in inductance calculations if reasonable accuracy is expected. Index Terms--Antenna loads, inductance, shielded coils.

This paper presents the analysis of two-dimensional heat transfer in an annular finned tube assembly during the process of dehumidification. All possible fin surface conditions, namely, dry, fully wet, and partially wet, have been studied and fin efficiency under these conditions have been modeled. Computations have been carried out using a control volume-based finite-difference method and compared with past one-dimensional analytical studies and available experimental data. The parameters that influenced the heat transfer rate in the finned tube structure are ratio of fin and wall thermal conductivities, ratio of fin thickness to fin pitch, ratio of wall thickness to fin pitch, ratio of fin length to fin pitch, cold fluid Biot number, ambient Biot number, the relative humidity and dry bulb temperature of the incoming air, and the cold fluid temperature inside the coil. It was found that the heat transfer increased with increment in both dry bulb temperature and the relative humidity of the air. The fin efficiency changed rapidly with relative humidity under partially wet condition. The results suggest that coil performance can be very significantly altered by the condensation phenomenon on the fin surface and designs with dry fin data may not be adequate. The present results are expected to be very useful for the design of dehumidifier (cooling) coils for air conditioning applications.

The PLG (combined Propulsion, Levitation and Guidance) method was proposed for a more favorable Maglev ground coil system, combining the functions of propulsion, levitation, and guidance of the vehicle into one coil. Research and development is currently being conducted on this method. In this paper, the characteristics of a newly-structured system for the PLG method is examined. The discussed characteristics include propulsion, levitation-guidance, vehicle dynamics in the cases of problems with the superconducting magnets, and the magnetic field on board the vehicle. Index Terms--cost reduction, ground coils, Maglev, PLG method.