Bohumil Skala

Key construction aspects of resonant wireless low power transfer system

The paper discuses an important construction aspects of resonant wireless power transfer (WPT) system for small portable devices. It focuses mainly on key electrical parameters of the systems resonant linkage and its proper construction shape. All presented theoretical presumptions are consequently verified by detailed measurement.

Electromagnetic Coil Gun – Construction and Basic Simulation

A single-stage, sensorless, coil gun was designed to demonstrate the capability to accelerate a ferromagnetic projectile to high velocity. This paper summarizes all important steps during coil gun design, such as physical laws of the coil gun, preliminary calculations, the testing device and the final product. The electromagnetic FEA model of the capacitor-driven inductance coil gun was constructed to be able to optimize the coil’s dimensions. The driving circuit was implemented as a dynamic model for the simulation of current. The coil gun was not designed for really shooting applications, i.e. the projectile is accelerated to a relatively low speed.

Determination of the force caused by broken rotor bar and static eccentricity in an induction machine

The paper deals with the force acting in the air-gap of an induction machine within unusual operating states, e.g. static eccentricity and broken rotor bar. Force is determined via FEM model of real induction motor. The study focuses on two special faulty operating states. First, the motor is under static eccentricity only. Second, static eccentricity and broken rotor bar are present simultaneously in the machine. The comparison of both cases is discussed in the paper.

The torque ripple reduction at the drive with the switched reluctance motor

The torque ripple has an adverse impact on the life of the machine and other drive components (especially bearings, gearboxes, couplings, etc.) and also produces an unpleasant acoustic noise. The reduction of the torque ripple can be solved in several ways - to select different configurations of SRM (to increase the number of phases or use the machine with higher number of steps), a suitable choice of commutation angles (so that they mutually overlap) or minimize the torque ripple by torque regulator or by direct torque control. This paper summarizes the practical results.

Determination of critical thermal operation for small squirrel cage motor

The thermal design of small squirrel cage machines is a challenge in comparison with the permanent magnets machines of the same frame size. When designing the machine, the calculated temperatures in all parts should be lower than their critical temperatures. This paper aims to perform thermal analysis for different load types in order to achieve a safe thermal design of the motor. The machine under study in paper is induction motor. Basic dimensions of the stator and the frame are based on the permanent magnet motor. Thermal network method was used for thermal analysis of the machines. Practical measurements for comparison and validation of the existing results should be implemented in future. The paper offer useful practical information for a safe thermal design of induction motor. Paper demonstrates how can be new designed induction motor loads without thermal damaged. The practical significance of the paper is beneficial for the designers of induction motor (IM).

Evaluation of different approaches of mathematical modelling of thermal phenomena applied to induction motors

This paper summarizes electro-thermal coupled analysis modeling methods. Two models of influence of temperature-dependent materials on mathematical modelling are presented together with two modelling methods of heat transmission through the air gap. Mathematical models are compared with measurement accomplished on an induction machine available on the market.

Simulation and measurement of angular vibration of induction machine via Hilbert transformation

This paper describes the utilization of the Hilbert transformation for the angular vibration measurement of an induction machine. When we use a very common incremental rotary encoder as a speed sensor, it is necessary to process very high frequencies. In this case, the Hilbert transformation is useful. In this paper, the background of the Hilbert transformation, the angular vibration simulation and the verification measurement are described.

The effect of space harmonic components in the air gap magnetic flux density on torque characteristic of a squirrel-cage induction machine

The paper discusses the effects of harmonic content of the air gap magnetic flux density on torque characteristic of a squirrel-cage induction machine. It mainly focuses on behavior of the harmonic content during the operation and quick prediction of its torque performance using steady state analysis. The study combines harmonic finite element analysis with analytical approach.

Problems concerning the overloading of the wastewater pump drive

This paper deals with overloading of Induction motors. In the article is examined the causes and effects of overloading. Rated operating condition of the Induction motor is S4. The operational measurement of induction motor was made and results are presented. Measuring data was analyzed and verified by numerical calculations. This paper also summarizes the initial conditions, verification measurement and the final conclusion.

Energy balance of huge asynchronous machine during its run-up

To determine the temperature of the active parts (windings) of a real asynchronous machine under transient phenomena is a serious problem. Especially the temperature calculation of the bars of the squirrel cage rotor of the asynchronous machine may yield results which differ relatively largely from reality. In addition, if the precise measurement on the rotor bars is impossible due to absence of any sensors, the situation is unpleasant. This paper presents one possible method of how to take a rough estimate of the rotor bars temperature thanks to run-up measurement.