Istvan Vajda

Modeling the high frequency behavior of the Rogowski-coil passive L/r integrator current transducer with analytical and finite element method

The Rogowski current transducers are widely used because they have several advantages over iron-cored devices: no saturation at high current, higher operating frequency and less error in wider measurement range. The main components of these current transducers are the measuring coil and integrator. Latter can be passive or active. The main advantage of passive integrator is the wider bandwidth. The simplest is the L/r integration method, where the coil itself makes the operation of integration. In this case the knowledge of the resistance and the inductance of the coil not enough to make a proper equivalent circuit model, because the upper limit of the frequency characteristic depends on the distributed capacitance of the winding. The paper of Tamus (2002) has showed a new analytical model, which takes the distributed capacitance of the windings into consideration. The knowledge of distributed capacitances enables to calculate the upper frequency bandwidth limit and can help to determine the phase error decrease at normal frequencies. This analytical model is based on the classical lumped parameter winding model in the work of Karsai et al. (1987), which originally designed for large power transformers and assumes continuous voltage distribution along the windings. In this paper, the authors present a finite element method for calculation of distributed capacitances of winding, where the discrete behavior of the turns is taken into consideration to make a novelty for the estimation of the upper frequency limit, which cannot be determined correctly from the analytical calculation.

Design Optimization with Geometric Programming for Core Type Large Power Transformers

Abstract A good transformer design satisfies certain functions and requirements. We can satisfy these requirements by various designs. The aim of the manufacturers is to find the most economic choice within the limitations imposed by the constraint functions, which are the combination of the design parameters resulting in the lowest cost unit. One of the earliest application of the Geometric Programming [GP] is the optimization of power transformers. The GP formalism has two main advantages. First the formalism guarantees that the obtained solution is the global minimum. Second the new solution methods can solve even large-scale GPs extremely efficiently and reliably. The design optimization program seeks a minimum capitalized cost solution by optimally setting the transformers geometrical and electrical parameters. The transformers capitalized cost chosen for object function, because it takes into consideration the manufacturing and the operational costs. This paper considers the optimization for three winding, three phase, core-form power transformers. This paper presents the implemented transformer cost optimization model and the optimization results.

Core-form transformer design optimization with branch and bound search and geometric programming

The optimization of power transformers is one of the earliest applications of geometric programming. This approach works well with shell-form transformers, and the constructed models can be solved accurately with the new interior point method based solvers. However, a less well-known fact is that this kind of modeling becomes problematic in the case of core-form transformers. This paper shows a new metaheuristic solution to circumvent the main obstacle which is the calculation of short-circuit impedance.

E-assessment using image processing in ∞Exams

This paper features a software system called ∞Exarns (InfinityExams) which supports (primarily in higher education) paper-based examination and makes it easier, more comfortable and speeds up the whole process while keeping every single positive attribute of it but also reducing the number of negative aspects. The approach significantly differs from the ones used in the previous 10+ years which were implemented in such a way that they could not reproduce and replace the traditional paper-based examination model. The heart of the article relies on the most important element of the software which is the image processing flow.

Optimal Design of Electrical Machines: State of the Art Survey

Scientific optimization has become a popular term in the modern design of electrical machines. Due to the current completive and dynamic market, and the increasing importance of energy efficiency and energy conservation, the design optimization of electrical machines has become an essential strategy for research and development. Yet the multi-disciplinary, multiobjective, high-dimensional, nonlinear, and coupled nature of the electrical machines’ design optimization poses a great challenge to the research communities. Nevertheless, the recent advanced algorithms for multiobjective optimization and multiple-criteria decision analysis have been empowering designers to push the existing boundaries of electrical machines design in dealing with the complexity for the novel concepts and innovative designs. This paper presents a state of the art survey on the advancements of the novel optimization tools and applications, and further demonstrates the progress of the academic research in this realm.

A hybrid method for cogging torque calculation for mass produced permanent magnet machines

Permanent magnet brushless machines are widely used in high performance applications like the field of automotive industry or robotics. In most cases these applications need high torque density and smooth torque. There are many fast analytic calculation methods for cogging torque but they cope only with machines having no mechanical misalignments. A hybrid calculation method is presented in the paper which can be used to calculate cogging torque, and is also applicable to analyse the effect for usual manufacturing misalignments like air gap eccentricity.

Analysing the characteristics of specific torque in HTS quasi-diamagnetic motor by variation of rotor blade geometry

We presented a new concept for a superconducting electrical rotating machine in 2013 in which we have utilized the quasi-diamagnetic behavior of Type II high-temperature superconducting (HTS) materials in order to create repulsion force between the excited stator pole(s) and HTS rotor blade(s). We have investigated a new arrangement of this improved quasi-diamagnetic machine (QDM) with different rotor blade geometries by means of finite-element method simulations and analytical calculations. In this paper, we present the results of this investigation and identify the leading parameters to get the maximum torque.

Magnet leakage flux of axial flux PM synchronous machines for EV

This paper presents the study of an axial flux permanent magnet synchronous machine specially designed for electric vehicle (EV) applications. Based on the analysis of the physical machine a 3D simulation model is created. The goal of the simulations is to investigate the influence of certain input design parameters on the machines PM leakage flux. The paper shows how much, and under what conditions specific parameters affect the resulting PM leakage flux.

Comparison of different PMSM rotor configurations

There are quite much rotor configurations available for pmsm applications. All of them has advantages and disadvantages. This article copes with five usual rotor configurations simulated by FEA software using the same stator and winding system.

Co-Simulation of an Inverter Fed Permanent Magnet Synchronous Machine

Abstract Co-simulation is a method which makes it possible to study the electric machine and its drive at once, as one system. By taking into account the actual inverter voltage waveforms in a finite element model instead of using only the fundamental, we are able to study the electrical machines behavior in more realistic scenario. The recent increase in the use of variable speed drives justifies the research on such simulation techniques. In this paper we present the co-simulation of an inverter fed permanent magnet synchronous machine. The modelling method employs an analytical variable speed drive model and a finite element electrical machine model. By linking the analytical variable speed drive model together with a finite element model the complex simulation model enables the investigation of the electrical machine during actual operation. The methods are coupled via the results. This means that output of the finite element model serves as an input to the analytical model, and the output of the analytical model provides the input of the finite element model for a different simulation, thus enabling the finite element simulation of an inverter fed machine. The resulting speed and torque characteristics from the analytical model and the finite element model show a good agreement. The experiences with the co-simulation technique encourage further research and effort to improve the method.