Non-uniform Air Gap Research Articles

Inductances of electrical machine winding with a nonuniform air-gap

In this paper the inductances of electrical machine windings for arbitrary shape of the air-gap are the subject of interest. Introducing sinusoidally distributed (harmonic) windings as a hypothetical equivalent to the actual windings, a general formula for the inductances has been obtained. The expression can be used for determining the mutual inductance of two arbitrary phase windings, coils or particular turns, and also for their self inductances. All types of air-gap geometry are divided into four categories described by appropriate permeance functions. The procedure necessary for applying the formula is presented.

Dielectric breakdown in nonuniform field air gaps

The sparkover characteristics of rod-rod and rod-plane gaps in air under DC voltages are reviewed. The linear characteristics of both configurations are associated with the prominence of streamer discharges during the prebreakdown phase. The limits of linearity are shown to be a function of humidity, gap spacing and electrode profile, all of which determine the predischarge mode. It is shown that the rod-plane gap offers a wider range of linearity than the rod-rod gap and that it can have a valid role as a DC voltage measurement tool.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A complete model characterization of brushless DC motors

The authors address the modeling problem associated with brushless DC motors (BLDCMs) with nonuniform air gaps that operate in a range where magnetic saturation may exist. The mathematical model includes the effects of reluctance variations as well as magnetic saturation to guarantee proper modeling of the system. An experimental procedure is developed and implemented in a laboratory environment to identify the electromagnetic characteristics of a BLDCM in the presence of magnetic saturation. It is demonstrated that the modeling problem associated with the class of BLDCMs can be formulated in terms of mathematically modeling a set of multidimensional surfaces corresponding to the electromagnetic torque function and the flux linkages associated with the motor phase windings. The accuracy of the mathematical model constructed by the developed method is checked against experimental measurements. >

Practical Aspects in the Application of Conductive Barriers to Field Controlled Air Gaps

The principles of an optimization technique to improve the dielectric strength of nonuniform air gaps, by mitigating the field intensity of the most stressed point(s) in the gap, is presented in this paper. The approach consists of modifying the gap geometry and, if required, of adding a minimum number of conductive barriers of proper shapes. The technique is applied to some practical and relatively complex geometries, namely an air insulated wall bushing and the top electrode of a high voltage transformer. Experimental verifications are performed for the former configuration. Application of the optimization scheme to outdoor geometries is also discussed.

THE CHARACTERISTIC PERFORMANCE OF INDUCTION MOTORS WITH ECCENTRICITY

ABSTRACT A new method to predict the flux density distribution in an induction machine with nonuniform air gap is described. The method employs an approximate electromagnetic model suitable for efficient computer calculations. Effects of slotting, winding arrangement, saturation, and slot combinations are considered in the model. From the nonuniform distribution of magnetic flux density, the variation of unbalanced magnetic pull, average output torque, and cogging torque with eccentricity Is calculated. Comparison between computed and measured results shows good agreement which proves the validity of this technique to be employed for any type of induction machine of known design data.

Atmospheric Influences on the Switching Impulse Performance of I-Meter Gaps

This paper deals with the effects of atmospheric conditions on the flashover characteristics ics of non-uniform symmetrical field air gaps. Special emphasis is placed on the investigation of these effects with regards to the use of open air, protective gaps on high voltage power systems.

Miniature sheet-rotor induction motors for extremely high speeds

Electronically fed 2-phase motors capable of operating at speeds up to 150 000 rev/min are considered. Theoretical comparison is given between sheet-rotor and squirrel-cage induction motors having rotors of approximately 1 cm diameter. A design approach is presented for sheet-rotor machines, based on the fundamental rotating field, which relates performance to winding temperatures. Experimental results from a naturally cooled and a force-cooled motor are given. The validity of standard equivalent circuits is discussed and the effect of nonuniform airgap permeance presented.

General Rotating mmf Theory of Squirrel Cage Induction Machines with Nonuniform Air Gap and Several Nonsinusoidally Distributed Windings

General Rotating mmf Theory of Squirrel Cage Induction Machines with Nonuniform Air Gap and Several Nonsinusoidally Distributed Windings

Equivalent Circuit Model for a Shaded-Pole Induction Motor: II. One Shading Coil with a Stepped Air Gap

The rotating coupled circuit equations for an induction motor with a nonuniform air gap and two stator windings at an arbitrary displacement angle are transformed to formulate d-q, forward-backward, and equivalent circuit models. The air gap is assumed to be a constant plus a second harmonic variation. Shaded-pole performance is simulated by setting the auxiliary winding voltage to zero and adding the effect of mmf and permeance harmonics. Comparisons between test data and model predictions show reasonably good correlation. The major difference between modeling the reluctance variation and using an average constantair gap is seen in the value of starting torque. For the motor simulated, modeling the variable air gap more than triples the calculated starting torque

Growth of a positive leader in long nonuniform air gaps

The leader stage of the discharge in a long rod-plane air gap was investigated. Based on the assumption that optimum conditions for the advancement of the leader are obtained when the field prevailing around the leader tip maintains a constant optimum value, mathematical expressions are developed relating the gradient along the leader with quantities directly measurable during breakdown tests.

A comment on the methods of calculation of corona onset voltage

Two methods of calculating corona onset voltage (cov) in nonuniform air gaps are studied. The variation of number of electrons (or positive ions) in primary and secondary electron avalanches for short (⩽20 cm) as well as long (2–10 m) positive point-to-plane air gaps is obtained. Several conclusions regarding critical charge carrier numbers are drawn from this study.

Homopolar Generator Effect of Sudden Short Circuit

The effect of a sudden short circuit on a homopolar generator is analyzed and the transient time constant is deduced. The effect of nonuniform air gap flux is considered. It is shown that the time constant of a machine with a very small air gap and thick cylinder is quite large, while the time constant of a thin cylinder machine with a larger air gap is small.

The Effect of a Nonuniform Air Gap on the Reentrant Excitation of Hypersonic Waves

The Effect of a Nonuniform Air Gap on the Reentrant Excitation of Hypersonic Waves

Inductance coefficients of rotating machines expressed in terms of winding space harmonic

The paper develops expressions for the self- and mutual-inductance coefficients of machine windings for the general case of nonsinusoidal winding distributions and nonuniform air gap. These expressions involve the harmonics of the winding distribution and the air-gap permeability. For some sample cases, numerical values are given and the departures from the ideal sinusoidal case assessed. The coefficients evaluated in the paper are those which form the starting point of the generalised mathematical theory of machines. The results are of significance in showing how, and to what extent, departures from the ideal machine modify the coefficients and introduce new terms not amenable to the usual mathematical treatment.

Effects of negative ion space charge formation on nonuniform air gaps

A modified a-c streamer theory is set forth on the basis of established d-c theory, taking into account the various effects of negative ion space charge formation. The theory is found to be useful in describing electrical breakdown phenomena in nonuniform gaps that are excited with a-c potentials

Voltage harmonics of salient-pole generators under balanced 3-phase loads - II

In part I of this article [AIEE Transactions, pt. Ill-B (Power Apparatus and Systems), vol. 78, 1959 (Feb. 1960 section), pp. 1573-80] there were presented design formulas and curves for the calculation of hannonic content in the output voltage of salient-pole ac generators with both uniform and nonuniform air gaps, under balanced, 3-phase loading. This part of the paper presents the derivation of these curves and experimental verification of the formulas, as well as a convenient calculation sheet for analytical determination of the harmonics.

Calculation of No-Load Wave Shape of Salient-Pole A-C Generators [includes discussion

This paper presents equations for the evaluation of harmonic content of the no-load output voltage of salient-pole a-c generators with both uniform and non-uniform air gaps. Results are presented in curve form for harmonics up to and including the 11th, making possible rapid determination of such harmonics.