Multi-physics modelling of a grid connected diesel engine driven synchronous generator set for the analysis of transient low voltage ride through performance

Tweedy, Oliver (2021) Multi-physics modelling of a grid connected diesel engine driven synchronous generator set for the analysis of transient low voltage ride through performance. PhD thesis, University of Nottingham.

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Understanding the electromechanical behaviour of synchronous generators during severe low voltage fault conditions is vital to measure the potential performance impact and damage that may occur as a result to both connected equipment and the generator set. The work outlined in this paper addresses the process of developing a multi-physics model of a grid connected synchronous generator utilising 2D transient electromagnetic modelling with co-simulation of a 1D torsional beam element model. A 3D finite element model of a synchronous generator rotor is created and analysed using the ANSYS modal solver to obtain the orthotropic elastic properties of the laminated generator rotor core using a parametric modal analysis technique. The first 8 modes are obtained with a mean error of 1.3%, proving the accuracy of the method as the first contribution to knowledge.

The dynamically validated rotor model is used to obtain the torsional stiffness values for an equivalent 1D torsional model which is coupled to a 2D transient magnetic model of the generator (ANSYS Maxwell and Simplorer), completing the multi-physics generator set model. Three phase short circuit simulation results are compared with experimental test results to validate the model for use in low voltage ride through simulations.

The relationship between the relative angular position of the rotor and stator fields and the peak electromagnetic torque transient is obtained. In the case of an unprotected generator, a peak torque of 16.5 pu is observed with a relative angular shift of 360o. Five distinct peak torques were discovered over the 360o range that was simulated, occurring in steps of 90o owing to the four-pole configuration of the rotor. The discovery of this relationship provides the second contribution to knowledge in this research.

Finally, three modifications are made to the generator set model subjected to the worst-case transient, an increase in rotor inertia, inclusion of controlled series braking resistors and a clutch to reduce the angular displacement of the flexible coupling between the two machines. The peak electromagnetic torque is reduced by 0.88 kNm (32.2%) and 4.17 kNm (73.8%) respectively. Ultimately, the peak stress in the generator shaft keyway is reduced by 77.4%. The relative impact of the modifications on low voltage fault ride through performance represents the third contribution to knowledge.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Garvey, Seamus
Galea, Michael
Keywords: Synchronous generators, low voltage ride through, multi-physics, modal analysis, diesel engine, short circuit, fault, stress, rotor, damage, laminated, transient torque
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 65308
Depositing User: Tweedy, Oliver
Date Deposited: 04 Aug 2021 04:41
Last Modified: 04 Aug 2021 04:41

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