Toomas Vaimann

Magnetic properties of reduced Dy NdFeB permanent magnets and their usage in electrical machines

This paper describes the magnetic properties of different permanent magnet materials and their industrial usage as crucial components of permanent magnet electric machines. As the prices of rare earth materials, especially neodymium-iron-boron (NdFeB), has been rising rapidly during the last few years and has been quite unstable during the past decade, the search of new cheaper and yet durable alloys has started. One of the possibilities of cutting the price of NdFeB alloys is the decreasing of the dysprosium (Dy) content of such material. Possibilities of using these new materials in electrical machines as well as potential risks are analyzed in the paper. An overview of the development of low Dy magnets is presented. Necessity of further investigations is pointed out.

Comprehensive computations of the response of faulty cage induction machines

This paper presents the results from extensive computations of the vibrations as well as other relevant quantities of a cage induction machine under different fault conditions, i.e. broken bar, static, and dynamic eccentricity, stator windings turn short-circuit and short-circuit in the core of the stator. The 2D finite element method is adopted for both mechanical and electromagnetic analysis, where the circuit equations of the windings are also included. The computation results are compared with measurements made on a test bench. The comparison of the computation results from healthy and faulty machines shows that the combination of vibrations with either current or phase voltages leads to a better segregation between the different faults. It shows also that the low frequency components are usually enough to monitor. This result is of significance when designing the diagnosis and monitoring system of induction machines.

Residential load harmonics in distribution grid

Purpose of the present paper is to provide the results of the study performed in order to assess current distortion of domestic loads and corresponding voltage distortion in the residential distribution networks. For the study harmonic current amplitudes and phase angles of different home appliances were measured and afterwards the corresponding models were composed in DIgSILENT Power Factory. The focus of the study was to analyse the characteristics of the residential distribution network with different amounts of real nonlinear loads. The results of the study showed an extensive harmonic distortion in residential load current and considerable voltage distortion at the substations busbar. The results presented in this paper are especially important when dispersed generation (DG) and electrical vehicles (EV) are going to be connected in bulk into the distribution networks.

Analysis of the eccentricity in a low-speed slotless permanent-magnet wind generator

This paper presents the analytical analysis of different eccentricities in the rotor of a novel slotless wind power generator. The analytical expressions for the air gap eccentricity have been derived and the effects of these eccentricities on the air gap flux density, the resultant unbalanced magnetic pull and the induced emf are investigated. The analysis shows a strong pull in the case of static eccentricity, which is not seen when the case of elliptic eccentricity for example. The analysis shows also that the induced emf per coil can vary very much but due to the series connection of the coil per phase emf is uniform but has higher rms value than in the case of healthy machine. The analytical equations are verified for the case of healthy machine on a constructed laboratory prototype.

Computation of stator vibration of an induction motor using nodal magnetic forces

In the case of rotating electrical machines, the magnetic forces acting on the stator teeth are the principal electromagnetic cause of vibrations. Based on this fact, this paper presents a method to compute the vibrations of an induction motor with the aid of magnetic nodal forces. An accurate computation of local or nodal forces is essential in problems pertaining to vibration and noise analysis of electrical machines. Virtual work method is utilized here to compute the nodal forces as the local derivative of magnetic energy from the Finite Element (FE) solution of the magnetic field problem. The magnetic problem is then coupled to an elasticity solver to calculate the displacement due to these forces. The nodal force method is implemented in an open source finite element software Elmer and the entire magneto-mechanical computation is carried out in the same open source tool. The calculated results are then compared to vibration measurements of the motor.

Direct Liquid Cooling in Low-Power Electrical Machines: Proof-of-Concept

This paper evaluates the feasibility of a direct liquid cooling approach in the thermal management of an axial flux permanent-magnet machine. To demonstrate the cooling method, a test motor was fitted with helical tooth coil windings formed from a hybrid conductor comprising a stainless steel coolant conduit tightly wrapped with a stranded Litz wire. The motor is a 100-kW permanent-magnet, axial-flux, double-stator, single-rotor machine. The proof of concept integrated the motor with a closed liquid coolant loop, appropriate instrumentation, and a data acquisition system. The general performance of the motor was examined at various power levels using polyalphaolefin oil as the cooling fluid. The results show the proposed cooling method to be feasible, and furthermore, to provide significant improvements to the machine thermal management.

Exterior-rotor permanent magnet synchronous machine with toroidal windings for unmanned aerial vehicles

This paper represents the study of the multimode permanent magnet synchronous machine constructed for a small-sized unmanned aircraft. An overview of commonly used electrical machine types for unmanned aircrafts is also given within this paper. The main objective of the research was to create an electrical machine that could be used in addition to the combustion engine as a motor-generator. Based on the specifics of the area and the goal of the research the most suitable and optimal solution of the machine topology is considered. The paper gives an overview of the design of the permanent magnet electrical machine and its mechanical and electrical parameters. The test bench for experimental study of the prototype permanent magnet machine was also designed and built. Using the test bench the no-load test was carried out and corresponding characteristics were charted in a generator mode of the machine.

Analysis of a slow-speed slotless permanent magnet synchronous generator

Department of Electrical Engineering at Tallinn University of Technology has been involved in the development of novel electrical machines for wind applications. This paper presents the analysis of the electrical parameters of a novel slow-speed slotless permanent magnet synchronous generator. Firstly, some of the design parameters are calculated and a simplified analytical mathematical model of the generator is constructed to calculate the output variables under different operational conditions. Secondly, some FEM calculations are carried out to check the validity of the analytical model. Thirdly, test results are analyzed and compared to the calculated values. Finally, the analytical model is evaluated and final output parameters of the generator are determined.

Lifecycle-based design and optimization of electrical motor-drives - Challenges and possibilities

This paper describes the procedure of lifecycle-based design and optimization of electrical motor-drives as well as related methodologies to be developed. As the electric motor-drives are the most electrical energy consuming apparatuses, thorough and in depth optimization of the drives during their design process is essential to support energy efficient and environmental friendly development in electrical engineering and industry processes. Lifecycle-based optimization would grant a possibility to evaluate a wider range of variables that affect the environment and energy consummation of the drives. An overview of existing optimization techniques and related literature is presented. Necessity of new methodologies is pointed out.

Sensorless Detection of Induction Motor Rotor Faults Using the Clarke Vector Approach

Sensorless Detection of Induction Motor Rotor Faults Using the Clarke Vector Approach Due to their rugged build, simplicity and cost effective performance, induction motors are used in a vast number of industries, where they play a significant role in responsible operations, where faults and downtimes are either not desirable or even unthinkable. As different faults can affect the performance of the induction motors, among them broken rotor bars, it is important to have a certain condition monitoring or diagnostic system that is guarding the state of the motor. This paper deals with induction motor broken rotor bars detection, using Clarke vector approach.