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Electrical discharge machining bearing currents that may occur within electric machines of variable-speed-drive motor systems have been recognized for a long time. One key influential factor, the machine's capacitive voltage divider “bearing-voltage-ratio” (BVR) strongly depends on the rotor-to-frame and the stator winding-to-rotor capacitances; these are, in turn, affected by the design of the machine's stator slot. This paper presents an approach to improve the accuracy with which these capacitances can be estimated. It is based on the well-known plate capacitance equation which is then corrected by normalization functions. The functions are defined by extensive parameter studies using electrostatic finite element method (FEM) simulations. The final expressions not only allow for the prediction of the stator-winding-to-rotor and rotor-to-frame capacitances, they are also readily applicable. Thereby, they facilitate, for example, the clear-cut study of the sensitivity of the BVR towards changes in the different stator slot parameters. [ABSTRACT FROM AUTHOR]

The degrading effect of laser cutting on steel sheet material, and thus on the material's magnetic characteristics, is much less understood than that of mechanical cutting. Furthermore, the degrading influence on the magnetic properties is still difficult to determine. This paper focuses on the modeling of the degrading influence of laser cutting on the magnetic properties of electrical steel sheets. As the degradation depth and the degradation profile are still difficult to define, a method is needed, which takes the effect of laser cutting into account, but without the need of knowing the degradation profile exactly. This paper shows that a method that does not require any information on the physical phenomena that are introduced by the cutting process and that has already been verified for mechanically cut samples can also be applied to laser-cut samples, although the deterioration mechanisms and the resulting degradation profile and depths differ. Magnetic characteristics are identified for two different material zones and subsequently inserted into a finite-element model, which accounts for arbitrary geometries. The simulation results for the influence of laser cutting on the magnetic characteristics of the stator lamination stacks are verified by measurements, including three different materials and frequencies. [ABSTRACT FROM AUTHOR]

This paper presents an analytical equation that relates the number of broken bars in the rotor of an induction machine to the vibrations of its stator. The relation is given in terms of both amplitudes and frequencies and is validated by numerical and experimental investigations. The amplitude of vibrations of some frequency components is shown to increase quadratically with the number of broken bars when the motor is operated at rated load. The frequency components of interest are in the range of two to four times the value of the supply frequency, which simplifies the implementation with relatively low-cost instrumentation. The main focus and innovation of this paper is on the derivation of the analytical equations and their verification with numerical analysis, and the comparison of both results to the experimental measurements. [ABSTRACT FROM PUBLISHER]

The cutting process has a substantial influence on the ferromagnetic material properties of electrical steel sheets. In this paper, the properties of the degraded and nondegraded zones result from data obtained by two Epstein frame measurements using sample strips of two different widths. The magnetic characteristics of the degraded and nondegraded material are inserted into a finite-element model, which accounts for arbitrary geometries. The simulation results for the influence of degradation on a stator lamination stack are verified by measurements at three different frequencies and two different materials. [ABSTRACT FROM AUTHOR]

Permanent magnet brushless dc (BLDC) machines are widely used due to various advantages such as high efficiency and high torque density, and therefore compactness as well as long expected lifetime. All of these benefits are of major interest when designing a drive for a small fan application of a few watts. This paper presents the design investigations of a small single-phase BLDC motor for such an application. Notably, it discusses different constraints which arise during the design process and which may be of special relevance due to the particular given power level and application. [ABSTRACT FROM PUBLISHER]

In comparison with three-phase induction machines, modern single-phase induction machines normally have skewed rotors, but show an elliptic magnetic field during start-up. In order to properly model the start-up of such a machine, this three-dimensional (3-D) characteristic has to be accounted for. This leads to the application of the 3-D finite-element method. This paper will introduce a new approach to model and analyze the start-up of such a single-phase machine, with the aim of higher computational efficiency. Furthermore, this paper will discuss how symmetries, both in the circumferential direction and along the motor shaft, can be exploited despite the skewing. This is achieved through transforming (rotating) the cutting plane, doubling the skewing angle, and increasing the rotor conductor conductivity. The analysis is carried out on a small two-pole 100-W machine used for household appliances. The theoretical results are compared with experimental results for six rotors; each with a different skewing angle. [ABSTRACT FROM AUTHOR]

Aiming to better understand and model the different loss mechanisms occurring within electric machines during operation, we present a method to consider the degradation of steel during manufacturing due to punching in finite-element modeling of electric machines. The approach introduces a certain number of boundary layers along the punched edges, with the relative permeability decreasing toward the edge. The method, its implementation, and two example applications are presented and supported with experimental results. [ABSTRACT FROM AUTHOR]

Wave-propagation effects in machine windings are commonly simulated on the basis of a transmission-line model (TLM) where the parameters are extracted from cross-sectional electroquasistatic and magnetoquasistatic finite-element (FE) models of a stator slot. In this paper, three improvements are proposed. First, an additional radially-axially oriented FE model deals with the complicated return path of the common-mode current through the laminated core and leads to an additional impedance to be inserted into the TLM. Secondly, an additional TLM section is constructed using parameters extracted from an axisymmetric FE model of the winding overhang. Thereby, the impedance mismatches caused by the end-winding overhangs along the wave propagation direction are incorporated in the model. Thirdly, the capacitive and inductive inter-wire couplings are taken into account. The simulation results indicate the need of all three additions. [ABSTRACT FROM PUBLISHER]

Finite element models of electrical machines allow insights in electrothermal stresses which endanger the insulation system of the machine. This paper presents a thermal finite element model of a 3.7 kW squirrel-cage induction machine. The model resolves the conductors and the surrounding insulation materials in the stator slots. A set of transient thermal scenarios is defined and measured in the machine laboratory. These data are used to assess the finite element model. [ABSTRACT FROM AUTHOR]