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COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 42 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 25 June 2019

Christian Kreischer

Problems caused by end winding vibrations in power plant generators have become increasingly evident in recent years and reveal a need for monitoring and diagnostic systems. An…

93

Abstract

Purpose

Problems caused by end winding vibrations in power plant generators have become increasingly evident in recent years and reveal a need for monitoring and diagnostic systems. An increasing number of operational outages are caused by failures of the winding insulation or the conductor itself due to end winding vibrations. Meanwhile, it is clear that the condition of the end winding must be continuously monitored during operation to detect ineffective end winding support in time and to plan the repair.

Design/methodology/approach

In this paper, the complex and nonlinear excitation mechanisms in large machines are presented and modern methods for vibration monitoring are described. Through a consistent use of vibration monitoring in the end winding area as well as the vibration diagnosis done by experts, damage mechanisms can be detected at an early stage, repair measures can be planned and serious damage owing to a weakened main insulation can be avoided.

Findings

By combining modal analysis and trend monitoring in relation to the learned vibration behaviour, the end winding condition can be assessed in a differentiated manner and changes in the end winding structure can be detected early.

Originality/value

Finally, an assessment for a two-pole, air-cooled turbo generator is proposed.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 38 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 26 January 2023

Moritz Benninger, Marcus Liebschner and Christian Kreischer

Monitoring and diagnosis of fault cases for squirrel cage induction motors can be implemented using the multiple coupled circuit model. However, the identification of the…

68

Abstract

Purpose

Monitoring and diagnosis of fault cases for squirrel cage induction motors can be implemented using the multiple coupled circuit model. However, the identification of the associated model parameters for a specific machine is problematic. Up to now, the main options are measurement and test procedures or the use of finite element method analyses. However, these approaches are very costly and not suitable for use in an industrial application. The purpose of this paper is a practical parameter identification based on optimization methods and a comparison of different algorithms for this task.

Design/methodology/approach

Population-based metaheuristics are used to determine the parameters for the multiple coupled circuit model. For this purpose, a search space for the required parameters is defined without an elaborate analytical approach. Subsequently, a genetic algorithm, the differential evolution algorithm and particle swarm optimization are tested and compared. The algorithms use the weighted mean squared error (MSE) between the real measured data of stator currents as well as speed and the simulation results of the model as a fitness function.

Findings

The results of the parameter identification show that the applied methodology generally works and all three optimization algorithms fulfill the task. The differential evolution algorithm performs best, with a weighted MSE of 2.62, the lowest error after 1,000 simulations. In addition, this algorithm achieves the lowest overall error of all algorithms after only 740 simulations. The determined parameters do not completely match the parameters of the real machine, but still result in a very good reproduction of the dynamic behavior of the induction motor with squirrel cage.

Originality/value

The value of the presented method lies in the application of condition-based maintenance of electric drives in the industry, which is performed based on the multiple coupled circuit model. With a parameterized model, various healthy as well as faulty states can be calculated and thus, in the future, monitoring and diagnosis of faults of the respective motor can be performed. Essential for this, however, are the parameters adapted to the respective machine. With the described method, an automated parameter identification can be realized without great effort as a basis for an intelligent and condition-oriented maintenance.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 42 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 6 January 2023

Johannes Liebrich and Christian Kreischer

Superconductors offer several advantages compared with conventional conductors. However, it is not clear at this stage whether these types of conductors provide the same…

38

Abstract

Purpose

Superconductors offer several advantages compared with conventional conductors. However, it is not clear at this stage whether these types of conductors provide the same durability. For this reason, tape conductors under mechanical forces need to be studied in detail. The purpose of this paper is to investigate the relationship between critical temperature and axial mechanical stress of GdBaCuO tape conductors.

Design/methodology/approach

The paper investigates the influence of axial mechanical stresses on the critical temperature of superconductors. For these investigations, a multi-physical test rig was developed, which makes it possible to perform these types of investigations. With the presented measurement methodology, the influence of mechanical stresses on the tape conductor can be determined.

Findings

The investigations show a correlation between the critical temperature and the acting mechanical stresses. The analytically presented approach to describe the transition temperature is valid for the investigated samples. In addition, it is determined that the effects are not reversible, and therefore, permanent damage to the tape conductor is observed.

Originality/value

The presented investigations make it possible to create more accurate models of GdBaCuO tape conductors. This enables to extend the superconducting state space, which so far depends on three critical quantities, by the quantity of the axial stress.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 42 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 27 January 2022

Matthias Kowalski, Martin Hanke and Christian Kreischer

Resolving eddy currents in three dimensions with finite elements, especially in geometrically complex structures, is very time consuming. Notable additional efforts will be…

73

Abstract

Purpose

Resolving eddy currents in three dimensions with finite elements, especially in geometrically complex structures, is very time consuming. Notable additional efforts will be required, if these eddy currents are influenced by magnetic fields arising from larger parts or range over widespread regions. The purpose of this article is to present a new sub-modelling simulation technique, based on the finite-element approach. This method offers remarkable advantages for solving this type of problems.

Design/methodology/approach

A novel sub-modeling technique is developed for the finite-element method addressing this problem by dividing the process into two steps: firstly, a simulation of a “source”-model is carried out providing magnetic field distributions within the entire domain neglecting local eddy current effects and without modeling it in full detailed geometry. A subsequent “sub”-model comprises only the region of interest in higher resolution and is solved while being constrained with boundary conditions derived from the previous source-model. An implementation in ANSYS Mechanical is carried out with the objective to validate finite-element simulation against measurement results.

Findings

The proposed simulation technique performs robustly and time efficiently. Applying this method to an end-region of a turbogenerator allows comparisons with test data of this region for validation purposes. The comparison between measured and simulated radial flux densities shows good correspondence.

Originality/value

This work is novel in many aspects: a new technique for three-dimensional (3D) finite-element method using edge-elements is introduced. To the best of the authors’ knowledge, for the first time, these 3D sub-models are compared against measurement results of an electric machine with net currents. Leveraged from this work, detailed analyses of eddy current phenomena under influences of external magnetic fields can be investigated in higher detail within shorter calculation times.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 41 no. 2
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 11 January 2023

Florian Zellmer, Markus Löffler, Markus Schneider and Christian Kreischer

The purpose of this paper is to investigate a novel approach toward electromagnetic launch.

64

Abstract

Purpose

The purpose of this paper is to investigate a novel approach toward electromagnetic launch.

Design/methodology/approach

The field of linear electromagnetic acceleration aims at accelerating macroscopic masses (up to several kg) to speeds in excess of 2 km/s. This can be achieved using accelerators of the railgun type. The innovation of this work lies in the use of multiphase current instead of the classically used quasi-direct current (DC). The approach taken is to work out in a first step the potential performance of such a configuration, for example, by showing that a constant propulsive force can be realized. Next, the necessary changes for the system setup were carefully analyzed. Both the accelerator and the power supply have to be considerably modified with regard to the classical approach.

Findings

Thorough analysis of the electromagnetic behavior of the launcher including nonlinear effects lead to an innovative system design which is considered to be the main finding of the work presented here. Moreover, a prototype was build. The preliminary experimental results obtained are in very good agreement with corresponding simulations validating the underlying modeling approach.

Research limitations/implications

For the purpose of this paper, power levels of only 450 kVA are considered. However, this research can be used to design more powerful devices in the future.

Originality/value

While DC powered railguns are modeled very well in a variety of papers, the use of multiphase alternating current is not very well discussed yet. It could be of value for launch scenarios, for which very high speeds are required such as the launch of micro satellites to space.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 42 no. 6
Type: Research Article
ISSN: 0332-1649

Keywords

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