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Thesis (Ph. D.)--Northwestern University, 1926. / Cover title: The slow acting relay; an investigation of Eddy current and magnetism during release ... Engineering bulletin 304. Bibliography: p. 39.

Thesis (Ph. D.)--Northwestern University, 1926. / Cover title: The slow acting relay; an investigation of Eddy current and magnetism during release ... Engineering bulletin 304. Bibliography: p. 39.

[No abstract available] / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

No description available.

No description available.

No description available.

The thesis is mainly concerned with experimental studies of the heating effects of eddy currents. Sinusoidal and non-sinusoidal eddy current heating losses in non-magnetic conducting discs and spheres, subjected to a uniform field, are studied both theoretically and experimentally. The theory uses two different methods to calculate the power dissipation in the objects, and it employs Fourler series for the non-sinusoidal case. Some approximations for the losses at low frequency have been derived. The experimental study has three main sections. The first deals with the generation of uniform field for inducing eddy currents. Square Helmholtz coils have been designed, constructed and calibrated for this purpose. The second part is concerned with the measurement of the heat generated by eddy currents. A differential thermometer, using two matched therrnistors in a Blumlein bridge circuit, has been designed, built and calibrated. Operating close to balance, with a phase sensitive detector, the thermometer detects differences of 10-5 degrees C. In the third part, the experiment arranged for the eddy current heating measurements is described. The measured and the calculated results are compared, and the agreement was found to be about 2%. In foil wound inductors excited by alternating current, eddy currents together with proximity effect cause a redistribution of the current density across the width of the inductors. The current flow is increased along the edges of the foil and decreased along the centre portion. A thermal demonstration of this phenomenon, which is known as width effect, is described and studied by using the differential thermometer.

The travelling magnetic wave of a linear induction motor induces eddy currents in a secondary circuit (usually a sheet consisting at least partly of a non-magnetic metal, often aluminium), which cause the unrestrained member to move linearly in the direction of the travelling wave. A linear motor can also transport ferromagnetic powder, although this travels in the opposite direction to the travelling magnetic field. The motion is therefore due to a mechanism other than the eddy currents flowing in the sheet secondary. Expressions for the forces acting on an iron particle due to a travelling magnetic field are derived in the thesis. Preliminary experiments support the assumptions made in the derivations of the force expressions and lead to the formation of an hypothesis. This is shown to be capable of predicting both linear and rotational particle speeds and, with greater accuracy, the distance travelled and the rotation experienced by the particles. Experiments conducted on tubular and transverse flux motors have enabled different linear motors to be identified as suitable for a number of powder transportation applications. The results obtained show also the importance of large flux density values, the tangential to normal flux density ratio and large pole-pitch winding arrangements, with the latter lending support to the original hypothesis. The results of a finite element investigation of the tubular motor did not closely agree with the results from the experimental motor although similar trends were evident. Flux density values within particles were found to be considerably greater than those outside, as assumed in the hypothesis.