An experimental investigation into the behaviour of stray fluxes and currents in and around the core frames of turbogenerators
An experimental investigation into the behaviour of stray fluxes and currents in and around the core frames of turbogenerators
The aim of this research was to provide information to designers of turbogenerators to enable them to assess the effects of making various electrical connections to the core frame. In particular they will be interested in the effects on the efficiency of the machine and on the risk of serious damage to the stator core. These experiments were made using a small physical model to represent a turbogenerator. This model was designed and built specifically for this investigation. The reasons for building a new model and the design of this model are described. Measurements of stray fluxes are presented showing both the effects of changing the working voltage or current in the model windings and the effects of connecting various conducting strips to the frame. Although it is damage to the stator core and losses in the frame and the core which are of greatest interest, these cannot easily be measured. Instead attention is focused on stray fluxes - it being argued that many of the less well understood losses can be directly associated with one type of stray flux, and that most damage can be associated with heating or with eddy currents driven by stray fluxes. Qualitative predictions are made of the effects on stray fluxes and the associated losses that would result from the presence or absence of the following electrical connections to the frame: axial conducting strips between the core and the frame, shorting straps connecting these axial strips together, and the electrical connection of the core to the frame. In addition to the above options which formed the original subject of this investigation, a number of other changes are discussed which might produce a reduction in core end saturation and losses. Of particular interest is the effect of reversing the pitch direction of the stator winding. It is often assumed that this makes no difference to the magnitudes of the flux densities or to the losses within the machine. However, it is shown that there is a difference and a preferred pitch direction for a synchronous generator is identified. In addition to making qualitative predictions based on our arrangements and/or a theoretical understanding of the behaviour of stray flux, proposals are made for simplified numerical models of the frame which might be interfaced to the powerful numerical models which are now available for core end design.
University of Southampton
1992
Goddard, Kevin Frank
(1992)
An experimental investigation into the behaviour of stray fluxes and currents in and around the core frames of turbogenerators.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The aim of this research was to provide information to designers of turbogenerators to enable them to assess the effects of making various electrical connections to the core frame. In particular they will be interested in the effects on the efficiency of the machine and on the risk of serious damage to the stator core. These experiments were made using a small physical model to represent a turbogenerator. This model was designed and built specifically for this investigation. The reasons for building a new model and the design of this model are described. Measurements of stray fluxes are presented showing both the effects of changing the working voltage or current in the model windings and the effects of connecting various conducting strips to the frame. Although it is damage to the stator core and losses in the frame and the core which are of greatest interest, these cannot easily be measured. Instead attention is focused on stray fluxes - it being argued that many of the less well understood losses can be directly associated with one type of stray flux, and that most damage can be associated with heating or with eddy currents driven by stray fluxes. Qualitative predictions are made of the effects on stray fluxes and the associated losses that would result from the presence or absence of the following electrical connections to the frame: axial conducting strips between the core and the frame, shorting straps connecting these axial strips together, and the electrical connection of the core to the frame. In addition to the above options which formed the original subject of this investigation, a number of other changes are discussed which might produce a reduction in core end saturation and losses. Of particular interest is the effect of reversing the pitch direction of the stator winding. It is often assumed that this makes no difference to the magnitudes of the flux densities or to the losses within the machine. However, it is shown that there is a difference and a preferred pitch direction for a synchronous generator is identified. In addition to making qualitative predictions based on our arrangements and/or a theoretical understanding of the behaviour of stray flux, proposals are made for simplified numerical models of the frame which might be interfaced to the powerful numerical models which are now available for core end design.
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Published date: 1992
Identifiers
Local EPrints ID: 461645
URI: http://eprints.soton.ac.uk/id/eprint/461645
PURE UUID: 79eb4fdf-5600-4288-a7b5-d56e8c34dcd4
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Date deposited: 04 Jul 2022 18:51
Last modified: 04 Jul 2022 18:51
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Author:
Kevin Frank Goddard
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