Finite element modelling of turbine generator stator end windings for vibration analysis

Abstract

In this study, the authors present methods for accurately modelling the bindings and the stator bars of turbine generator stator end windings for vibration analyses. The bindings are modelled with beam elements and multipoint constraint equations to take account of the bending, twisting, and shearing rigidities of the bindings. To reproduce the spatial distribution of rigidity in a cross-section of the stator bar, the bar is modelled as a composite material comprising a conductor bar with equivalent elastic moduli and ground insulation. The accuracies of the developed binding and stator bar models are verified by comparing measured natural frequencies of binding test pieces and stator bar specimens with calculated values. The developed models and conventional models are applied to the natural frequency analyses of stator end windings, and then the effects of the modelling methods on the calculation accuracy are investigated. While the maximum calculation errors of the conventional models are more than 12%, the calculation results of the developed models agree with the measured values within an error of 7%. Accordingly, for accurately calculating the end winding natural frequencies, end winding finite element models need to take the binding rigidities into account and reproduce the rigidity distribution of the stator bar.

Analysis of rotor winding interturn short circuits affected by the initial dynamic eccentricity in large synchronous condensers

“…When an RWISC occurs in a condenser, the air gap magnetic flux density at the short-circuit slot decreases, the uneven distribution of the magnetic field in the air gap leads to an unbalanced electromagnetic force, and the rotor is subjected to a UMP, which causes abnormal vibrations in the unit [23,24]. Since the axial component of the air gap magnetic field is much smaller than the radial component, it can be neglected.…”

Synchronous Reluctance Machines for Automotive Cooling Fan Systems: Numerical and Experimental Study of Different Slot-Pole Combinations and Winding Types

“…For machines with larger diameters, more poles can be used, and the number of slots has to be chosen accordingly to maximize the saliency. Trade-offs have to be made when increasing the number of poles [17], as the main advantages (e.g., reduction of active The motor produces the torque based on solely the reluctance principle, therefore in order to increase its torque/power density, the so-called saliency ratio, which is the ratio between the quadrature inductances (ξ = L d /L q ) has to be maximized. This can be achieved by adequately designing the machine's magnetic circuit.…”

“…For machines with larger diameters, more poles can be used, and the number of slots has to be chosen accordingly to maximize the saliency. Trade-offs have to be made when increasing the number of poles [17], as the main advantages (e.g., reduction of active materials, higher torque density and efficiency) come with some drawbacks such as: higher flux leakage and commutation frequency as well as increased iron losses.…”

Simulation and experimental illustration of vibration at load rejection in a continuously overloaded large hydrogenerator

“…Both at normal and faulty operating conditions the end windings of turbine generators vibrate due to the generation of electromagnetic forces. At normal operation, these electromagnetic forces created by stator current cause vibration at twice the natural frequency, whereas under fault conditions the electromagnetic forces will be much larger than the normal operation tending to high vibration [5,6]. In order to evade the additional vibration, it is necessary to predict and evaluate the electromagnetic forces accumulating with natural frequencies of the machine [7][8][9][10].…”