Dynamic Unbalanced Pull from Field Winding Turn Short Circuits in Hydropower Generators

Wallin, Mattias; Lundin, Urban

doi:10.1080/15325008.2013.835360

Cited by 13 publications

(8 citation statements)

References 9 publications

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“…Wan et al [50] studied the influence of the short circuit on the force acting on the rotor and pointed out that the inter-turn short circuit in generator rotor caused thermal imbalance and magnetic imbalance. Wallin et al [51] studied the UMF and flux density distribution resulting from winding inter turn-short circuits. Through experimental and numerical simulations, it was found that an additional unbalanced electromagnetism was generated.…”

Section: Electromagnetic Sourcesmentioning

confidence: 99%

Review of Electromagnetic Vibration in Electrical Machines

Han

Chu

2018

Energies

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Electrical machines are important devices that convert electric energy into mechanical work and are widely used in industry and people's life. Undesired vibrations are harmful to their safe operation. Reviews from the viewpoint of fault diagnosis have been conducted, while summaries from the perspective of dynamics is rare. This review provides systematic research outlines of this field, which can help a majority of scholars grasp the ongoing progress and conduct further investigations. This review mainly generalizes publications in the past decades about the dynamics and vibration of electrical machines. First the sources of electromagnetic vibration in electrical machines are presented, which include mechanical and electromagnetic factors. Different types of air gap eccentricity are introduced and modeled. The analytical methods and numerical methods for calculating the electromagnetic force are summarized and explained in detail. The exact subdomain analysis, magnetic equivalent circuit, Maxwell stress tensor, winding function approach, conformal mapping method, virtual work principle and finite element analysis are presented. The effects of magnetic saturation, slot and pole combination and load are discussed. Then typical characteristics of electromagnetic vibration are illustrated. Finally, the experimental studies are summarized and the authors give their thoughts about the research trends.Energies 2018, 11, 1779 2 of 33 vibration mechanism can be helpful for the design of electrical machines. Therefore, the study of the electromagnetic vibration of electrical machines has practical significance.Electromagnetic vibrations are usually generated by the distorted air-gap field of an eccentric rotor in electrical machines. The uneven air-gap is directly related to the eccentricity, which is common in rotating electrical machines. Eccentricity can be caused by several reasons, such as relative misalignment of the rotor and stator in the fixing stage, misalignment of the load axis and rotor shaft, elliptical stator inner cross section, wrong placement or rubbing of ball bearings, mechanical resonance, and unbalanced loads [1,2]. Eccentricities can be further subdivided into two categories: circumferential unequal air gaps and axial unequal air gaps. The former can be grouped into static eccentricity and dynamic eccentricity. In the case of static eccentricity, the rotor rotates around its own geometric axis, which is not the geometric axis of the stator. In the case of dynamic eccentricity, the rotor is not concentric and rotates around the geometric axis of the stator. In reality, both static eccentricity and dynamic eccentricity tend to coexist. An inherent static eccentricity exists, even in newly manufactured machines, due to the build-up of tolerances during the manufacturing and assembly procedure, as has been reported in [3]. Unequal air gaps cause unbalanced magnetic forces (UMFs) [4] on the rotor, which lead to mechanical stress on some part of the shaft and bearing. After prolonged operation, these fac...

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Section: Electromagnetic Sourcesmentioning

confidence: 99%

Review of Electromagnetic Vibration in Electrical Machines

Han

Chu

2018

Energies

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“…It is found that the induced voltage in rotor can be used to predict the location and the number of short circuit turns [4]. Meanwhile, researchers have also studied the characteristics of the excitation currents [5,6], the copper losses [5], and the unbalanced magnetic pull (UMP) for the ISCF monitoring [7][8][9]. Generally, at present, the application of search coils, which is mainly based on the magnetic field density (MFD) variation, is still adopted as a primary approach to monitor and diagnose this fault [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Analysis and Simulation on the Effect of Rotor Interturn Short Circuit on Magnetic Flux Density of Turbo–Generator

Tang

et al. 2016

Journal of Electrical Engineering

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The intent of this paper is to investigate the effect of the interturn short circuit fault (ISCF) in rotor on the magnetic flux density (MFD) of turbo-generator. Different from other studies, this work not only pays attention to the influence of the faulty degrees on the general magnetic field, but also investigates the effect of the short circuit positions on the harmonic components of MFD. The theoretical analysis and the digital simulation through the FEM software Ansoft are performed for a QSFN-600-2YHG turbo-generator. Several significant formulas and conclusions drawn from the analysis and the simulation results are obtained to indicate the relation between the harmonic amplitude of the MFD and the faulty degree (via nm , the number of the short circuit turns), and the relation between the MFD harmonic amplitude and the faulty position (via αr , the angle of the two slots in which the interturn short circuit occurs). Also, the developing tendency of the general magnetic field intensity, the distribution of the magnetic flux lines, and the peak-to-peak value of MFD are presented.

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“…The fault, however, might develop; more turns can be short-circuited and the situation may also lead to rotor earth faults that are more serious. In the case of major inter-turn faults, the asymmetry of the airgap field could cause considerable unbalanced magnetic pull (UMP) and vibration problems [3].…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic Analysis and Electrical Signature-Based Detection of Rotor Inter-Turn Faults in Salient-Pole Synchronous Machine

2018

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In this paper, rotor inter-turn faults in salient-pole synchronous machines are investigated using finite-element (FE) analysis. The machine under study is a 22 MVA 8-pole hydropower generator with fractional-slot windings. Simulated faulty cases include 1, 2, 5, 10, and 20 short-circuited turns (out of 58 turns) in one rotor pole. In the electromagnetic analysis, the effect of faults on airgap flux density and radial forces is studied. Furthermore, the paper investigates on-line detection of inter-turn faults using spectral analysis of stator voltage or current is studied. The amplitude of fault-related harmonics is investigated at various fault severities, as well as at no-load and full-load operations. The paper also discusses the effects of damper bars, influence of parallel circuits in the stator windings, and influence of the pole pair number. In addition, a comparison between fault-related harmonics in the case of dynamic eccentricity and rotor inter-turn faults is presented.

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Dynamic Unbalanced Pull from Field Winding Turn Short Circuits in Hydropower Generators

Cited by 13 publications

References 9 publications

Review of Electromagnetic Vibration in Electrical Machines

Review of Electromagnetic Vibration in Electrical Machines

Analysis and Simulation on the Effect of Rotor Interturn Short Circuit on Magnetic Flux Density of Turbo–Generator

Electromagnetic Analysis and Electrical Signature-Based Detection of Rotor Inter-Turn Faults in Salient-Pole Synchronous Machine

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