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This article introduces a unique three-phase induction machine with a large air gap and a copper-coated iron cylinder. The motor is built in an X-ray tube for medical applications where key performance indicators are the start-up time, generated rotor, and total energy during the run-up. The common equivalent circuit for induction motors is utilized to systematically analyze the effect of the rotor protrusion length variation on these key performance indicators by means of three-dimensional (3D)-FEA. However, due to the large air gap and dominating winding head standard evaluation tools, such as the no-load and locked-rotor tests do not provide accurate circuit parameters. Thus, a combined no-load and locked-rotor test evaluation is introduced. Furthermore, to avoid the time and computational effort of time-stepping 3D-FEA, time harmonic and static 3D-FEA is introduced. To validate these simplified 3D-FEA simulations, results are compared with the selected time-stepping 3D-FEA results. Experimental results verify the 3D-FEA results. After establishing a routine to identify accurate equivalent circuit parameters by means of 3D-FEA, the parameters for three different stator lengths each combined with six different rotor lengths are identified. V/f-controlled run-up simulations are then conducted to generate the results. Results quantify the tradeoff between start-up time, generated rotor, and total energy depending on the rotor protrusion, e.g., the start-up time is indirectly proportional to the rotor protrusion and directly proportional to the rotor frequency (the relative frequency between stator field and rotor speed). The effect of the rotor temperature, which can reach up to $\sim 390^\circ \,$ C, on the results is included. [ABSTRACT FROM AUTHOR]

This article investigates the additional opportunities and aspects in the design process of large hydro power wound-field salient-pole synchronous machines provided by full-size converter (FSC) operation. As a matter of fact, thus far, power converters for hydro power plants have been mainly selected to meet the demands of conventionally designed machines and retrofit applications. The new optimization possibilities in the motor-generator design given by the FSC operation have not yet found much attention in the literature. This article shows how FSC operated hydro power synchronous machines can be designed to have smaller volumes, lower material cost, and higher efficiencies than their conventional counterparts. A cost evaluation of various generator designs including costs for materials as well as costs for power loss during operation is performed. Furthermore, the power loss evaluation cost factors are varied to show their impact on the choice of the machine parameters for an optimum generator design. For the presented evaluation, the partial load operation of large pumped storage power plants in turbine and pumping modes is analyzed, as is the effect of the free choice of the design frequency, the power factor, as well as the synchronous reactance. Finally, a suggestion for the generator design for FSC operation is presented. [ABSTRACT FROM AUTHOR]

Cogging torque reduction measures are hardly applied to low-cost sub-fractional hp brushless direct current (BLDC) motors, because the additional fabrication operations involved typically increase both the manufacturing complexity and cost significantly. By proposing an innovative punching layout, this paper shows how to minimize the high cogging torque of the mass-produced single-phase outer-rotor BLDC claw-pole motor—opposed to conventional cogging torque reduction—with no increase to the manufacturing cost. Systematically, a way is presented in which the selected introduction of auxiliary slots can double the cogging torque fundamental frequency, making stator claw skewing much more effective in reducing the cogging torque; both measures can be included at the stage of punching the steel sheets and subsequent deep-drawing thereof, at no additional cost. A detailed analysis of the effects of the cogging torque reduction measures on the most important motor performance parameters is conducted. The findings show that, with the exception of a three percentage point reduction in the efficiency, the proposed design can reduce the peak-to-peak cogging torque by 70% in both the simulations and experiments. The reduction in the cogging torque translates into a reduction in the output torque ripple of 17%, ensuring smoother operation especially at low speeds. [ABSTRACT FROM AUTHOR]

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]

As for mass-produced sub-fractional horsepower drives, non-optimal motor behavior (e.g., high cogging torque, output torque ripple, and noise) is often accepted when cost can be reduced, provided reliability is not compromised. This paper proposes an innovative claw-pole motor design for a low-cost single-phase brushless direct current fan drive, improving motor behavior with no increase to the manufacturing cost: 1) reducing cogging torque by proposing unconventional claw-pole skewing and 2) ensuring self-starting capability by implementing air-gap asymmetry. Both measures help reduce the total output torque ripple. The goal is to reduce fan drive noise, especially at low-speed operation, where cogging torque is often the dominating noise source. The design of stator claw skewing and air-gap asymmetry is presented; their effects on motor quantities are studied via simulations and experiments. With the exception of a small reduction of about 1.8% in the back electromotive force fundamental, skewing the stator claws by 30 $^{\circ }$ can reduce the cogging torque by 23% in the simulations and by 28% in the experiments. [ABSTRACT FROM AUTHOR]

Advancing the turn-off angle of the phase current of brushless direct current (BLDC) motors is a common control practice to improve the operating behavior and energy conversion efficiency of such drives by, e.g., reduction of current peaks, copper losses, and breaking torques. This paper investigates a refined switching strategy for a single-phase BLDC motor with bifilar winding to increase the energy conversion efficiency of the system. In addition to advancing the phase current turn-off angle, the turn-on angle is delayed to improve the drive's performance and increase the efficiency even further. This efficiency increase of up to 20.6% is verified experimentally for a speed range from 3000 to 8000 rpm, translating into a reduction of copper losses of up to 37.4% or a decrease of current peaks by 27.4%. The focus is on sub-fractional horsepower single-phase BLDC motors with bifilar winding which, concerning this matter, have not drawn much attention in the literature yet. The findings show that the improved switching strategy can reduce current peaks, breaking torques, copper losses, and therefore increase efficiency over the speed range of interest for fan applications. [ABSTRACT FROM AUTHOR]

Single switch open-circuit faults in three-phase ac drives lead to undesired effects and potentially to a total failure of the drive. This paper proposes a postfault operation strategy for such faults with a focus on the limitation of losses after the reconfiguration and thereby an extension of the possible range of operation. Furthermore, a method for the reduction of alternating torque components during the postfault operation of a squirrel cage induction machine drive is proposed. The performance of the postfault operation strategy and the alternating torque reduction method are shown both via simulations and experiments. [ABSTRACT FROM PUBLISHER]

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]

This paper discusses the design process of permanent-magnet-free ac machine-based actuators working in elevated-temperature environments for high-dynamic applications. Both demands given by the application with respect to maximum volume, torque-over-speed performance, and the thermal limits of the insulation materials, which limit the maximal loss that may occur, have to be considered. Starting from the geometry, semianalytic modeling approaches are used within an optimization algorithm to obtain a machine design suitable for this application. [ABSTRACT FROM AUTHOR]

The degrading influence of different cutting techniques on the magnetic behavior of electrical steel sheets has been well recognized. However, more research is needed to understand how the influences of different cutting techniques compare, notably with respect to laser versus mechanical cutting and for different materials. This paper addresses the influences of CO2 laser cutting, FKL laser cutting, and mechanical cutting on the magnetization characteristics and specific losses of electrical steel sheets determined by Epstein frame measurements on rectangular samples and by the measurements of stator lamination stacks. Experimental results based on three different materials commonly used with electric machines and investigated at different frequencies are provided. [ABSTRACT FROM PUBLISHER]