Electromagnetic transport and confinement of liquid metals

Applications in which electromagnetic forces are used to stir, transport, dispense, and/or confine liquid metal are described. Applications include the electromagnetic trough, the electromagnetic mould, pedestal melting, thin strip casting, and levitation casting. Fundamentals relating to the production of electromagnetic forces are reviewed, a number of important applications are discussed, essential design limitations are identified, and the question of modeling for design purposes is considered. It is shown that with present technology, electromagnetic confinement methods cannot be expected to support ferrostatic heads in excess of 10-25 cm. This limit imposes a constraint on the development of new applications, such as the extension of the electromagnetic mold to steel casting and the use of electromagnetic confinement in the strip-casting process     

Eddy-current power loss in toroidal cores with rectangular crosssection

In this paper, we investigate eddy-current power loss in toroidal cores with a rectangular cross section. An analytical method is used in which the field variables are expressed in terms of products of Bessel functions and trigonometric functions. A closed-form expression is derived for the power loss. The influence of various parameters such as skin depth and core dimensions over a wide range is discussed. Simplified expressions for the power loss at special cases such as very small and very large skin depths are provided. A comparison with measured values is presented     

Minimizing the three-phase unbalance in an electric arc furnace

A method is proposed to reduce impedance imbalance in the electrode arms of an arc furnace. Conducting plates or tubes are used to shield the magnetic fields around busbars in order to minimize the mutual inductance. The volume integral equation method is used to calculate bus impedances, current distribution, and eddy current losses. The numerical results indicate a significant improvement in system balance even during bus movement. Two types of shields are investigated. Shielding the center phase by using a large tube reduces the unbalance at the coplanar bus positions, but it has little effect when one bus is offset. Shielding by two conducting plates standing between buses yields good balance and constant reactance for all bus positions. The power loss in the shields is only a small percentage of the bus loss, the shields can be replaced by parallel conducting bars bounded at ends. By combining the new method with a smaller center bus diameter, better results have been achieved     

Using the ALPHA form in practice to assess antenatal psychosocial health. Antenatal Psychosocial Health Assessment

BACKGROUND: The assessment of the psychosocial health of pregnant women and their families, although recommended, is not carried out by most practitioners. One reason is the lack of a practical and evidence-based tool. In response, a multidisciplinary group created the Antenatal Psychosocial Health Assessment (ALPHA) form. This article describes the development of this tool and experience with it in an initial field trial. METHODS: A systematic literature review revealed 15 antenatal psychosocial risk factors associated with poor postpartum family outcomes of woman abuse, child abuse, postpartum depression, marital/couple dysfunction and increased physical illness. The ALPHA form, incorporating these risk factors, was developed and refined through several focus groups. It was then used by 5 obstetricians, 10 family physicians, 7 midwives and 4 antenatal clinic nurses in various urban, rural and culturally diverse locations across Ontario. After 3 months, these health care providers met in focus groups to discuss their experiences. A sample of pregnant women assessed using the ALPHA form were interviewed about their experience as well. Results were analysed according to qualitative methods. RESULTS: The final version of the ALPHA form grouped the 15 risk factors into 4 categories--family factors, maternal factors, substance abuse and family violence--with suggested questions for each area of enquiry. The health care providers uniformly reported that the form helped them to uncover new and often surprising information, even when the women were well known to them. Incorporating the form into practice was usually accomplished after a period of familiarization. Most of the providers said the form was useful and would continue to use it if it became part of standard care. The pregnant women in the sample said they valued the enquiry and felt comfortable with the process, unless there were large cultural barriers. INTERPRETATION: The ALPHA form appears to be an important tool in assessing psychosocial health in pregnancy and to be readily integrated into practice. More study is required to quantify the number of risks identified and resources used, to determine the form's reliability and validity and, ultimately, to assess the effect of its use on postpartum outcomes.     

Estimation of core losses when the flux waveform contains the fundamental plus a single odd harmonic component

This paper examines the behaviour of the core losses in thin laminations when the flux density waveform is highly distorted at peak flux densities of up to 2.0 T. It is shown that the presence of harmonics can increase the loss significantly over the value that exists when the flux density waveform is purely sinusoidal. A simple method that corrects the eddy current component of core loss for the effects of flux harmonics is used to estimate the total loss due to a distorted waveform. Provided the waveform does not contain harmonics greater than the 5th, it is shown that such a method of estimation yields acceptable results for the distortion levels encountered in practice.     

Determination of Harmonics of Converter Current and/or Voltage Waveforms (New Method for Fourier Coefficient Calculations), Part II: Fourier Coefficients of Nonhomogeneous Functions

The method used in Part I for the determination of Fourier coefficients of homogeneous functions is generalized here for nonhomogeneous functions. A number of examples from the field of power converter and inverter circuits are presented. Such special cases as harmonics of oscillations at the moments of valve's ignitions and extinctions are analyzed here.     

A Method of Examining in Detail Electric Arc Furnace Performance

A method of data acquisition and analysis is described that has been developed to assess in detail the performance of electric arc furnaces. The method has been implemented on a small single user minicomputer (a PDP 11/40) and on a large mainframe (an IBM 3033). The method was specifically developed in order to determine reliable statistical parameters that can be used to characterize arc furnace performance. The method is outlined, and its use is illustrated using data recorded on magnetic tape at the new Iron and Steel Company of Trinidad and Tobago (ISCOTT) plant. Results are presented that illustrate the operation of the ISCOTT furnace for scrap and pellet feed.     

Real-Time Measurement of Electric Arc-Furnace Disturbances and Parameter Variations

The general nature of electrical-supply network disturbances caused by arc-furnace operation is reviewed, including the guidelines adopted in several countries concerning disturbance-level estimation for single-and multifurnace installations. The meters available for the measurement of voltage flicker, including the international standard meter proposed by the International Union of Electroheat (UIE) are briefly described. The basic statistical properties of arc-furnace disturbances and parameter variations, treated as random variables, are discussed. Measured data are used to examine the probability distributions for variations in furnace voltage and current. Particular attention is given to methods of reliably measuring the disturbance and parameter-variation levels in real time on-line. Strategies are developed, and a microprocessor-based data-acquisition system, developed for this purpose, is described.     

Analysis of a filter circuit for nonlinear loads

A capacitor is connected in parallel with a saturated core coil assembly (a nonlinear load) to reduce the magnetizing current. A linear reactor is connected in series with supply to reduce the distortion in supply current. This typical reactor capacitor filter system has been analyzed by an iterative procedure based on harmonic equivalent circuits. The analysis presented here predicts the harmonic resonance points of the circuit with good accuracy. The technique is applicable, in general, to any nonlinear load.     

An Improved Method of Calculating the Power Generated in an Inductively Heated Load

Normally, coil and load end effects are neglected when calculating the power generated in an inductively heated load. Empirical correction factors are used to account for the effects of leakage flux. In this paper, the coil and load are approximated by a short current sheet and an infinitely long conductor. The resulting load power distribution is determined analytically for a cylindrical geometry. A correction factor that can be incorporated directly in the classical expression for load power is then derived in closed form. This factor describes the axial distribution of power in the load and inherently includes the effects of leakage flux. Numerical values are given in normalized form for a wide range of coil-load configurations. The accuracy of the method is illustrated by comparing predicted and experimental values of load power. The improvement relative to the classical methods is discussed.