Christian Kreischer

Modal analysis of operational end winding vibrations

This paper presents the validation of a method for a modal transformation of operational end winding vibrations, which can be monitored by fibre-optic accelerometers. The validation is done by the analysis of the vibrational behaviour of a mechanical finite element model which is excited by electromagnetic forces and deformations of the stator core. The study focuses on the connection end because of the higher complexity of this end winding compared to the non-connection end. After the validation different strategies for the placement of the fibre-optic accelerometers are discussed. The modal observation of operational end winding vibrations is found to be a useful method to represent and analyse the vibrational behaviour.

Detection of broken bars and rings in induction machines

Determining the number of broken bars due to the failure or the number of ring segments of the rotor cage of induction motor is an important problem during the operation of such machine. The Unscented Kalman Filter (UKF), used to achieve this goal, provides precise information on numbers of broken bars and ring segments. To generate such information, the filter requires measurements of the stator currents and currents of additional single-winding coils located at the stator teeth and loaded with large resistances (~1 kΩ). The measurement of the rotational speed of the rotor and the related angle of the machine shaft rotation is also needed. The method of determining the numbers of broken bars and ring segments of the rotor and the method of detecting only the broken bars of the rotor cage were tested. The presented method can be used for the protection of large and expensive induction drives.

Analysis of transformer short circuit characteristics based on 3-D Finite Element Method

Based on a 3-D Finite Element Model built up in FLUX 3-D, this paper shows simulation results of a single phase transformer to study the behavior of its reactance during short circuits with respect to saturation effects. In the first step measurements on a real transformer were done to determine its equivalent circuit parameters and to verify the Finite Element Model. In the second step the influence of core saturation on the impedance was studied. From the result of this study it can be concluded that the saturation has a big impact on the maximum short circuit current and has to be taken into account for detailed network studies.

Analysis of the Distribution of Air Flow Rate Through Stator End Winding of Turbo Generator

This paper presents a combined method of FEM and 1-D fluid network theory to model the distribution of the air flow rate in the stator end winding of an air cooled turbine generator. The model of the end winding can be integrated into a 1-D fluid network of the whole cooling system. Thus, the result of simulation can be directly used for further studies of the cooling system.

Study of the dynamic stability for small power plants

This paper focuses on the changing requirements for small power units connected to the grid and the task of stability studies to ensure the adherence of this requirements. Belong the coupled simulation of grid faults to determine the critical fault clearing time of a machine the main influences on the ability of a machine on keeping connected to the grid during a fault with deep voltage transients are discussed. This influences are especially important to know, if a synchronous generator does not fulfill the stability requirements and has to be optimized.

OPTIMIZED STEAM TURBINE GOVERNOR CONTROLLING SINGLE OR MULTIPLE GRID FAULTS

This paper uses simulation results to figure out how SIEMENS handles a single grid fault of a three–phase short circuit close to the power plant and a multiple grid fault of a load rejection due to a three–phase short circuit close to the power plant.The correct response of the steam turbine governor to the single and the multiple grid fault can increase power plant availability, prevent steam turbine trips and reduce overspeed. Therefore the power supply to the electrical grid can still be maintained, and in case of a de-stabilized electrical grid a black-out could be prevented.If the steam turbine trips caused by the single or the multiple grid fault the steam turbine runs down and has to be restarted. This could take several hours as worst case. During this time the power plant is not available to support and stabilize the electrical grid.If the steam turbine governor is able to handle the single grid fault, the power plant is still connected to the grid. This will not further stress the de-stabilized electrical grid.If the steam turbine governor is able to handle the multiple grid fault, the house load of the power plant will still be provided by the steam turbine. The operator could re-synchronize the power plant with the de-stabilized electrical grid as fast as possible.In both cases for the single and the multiple grid fault the power plant remains available by the optimized steam turbine governor.Copyright

Neuronale Netze in der Schwingungsdiagnostik

Neuronale Netze besitzen im Allgemeinen ein sehr groses Anwendungsspektrum, sie kommen sowohl bei der Modellierung von technischen, als auch von sozialen Systemen vor. Die Betrachtungsebene ist dabei vom jeweiligen Anwendungsfall abhangig. Je nach Aufgabe, muss eine Anpassung der Netzstruktur vorgenommen werden.