A Comprehensive Analysis on Transient Electromagnetic Force Behavior of Stator Windings in Turbo-Generator

Abstract

This paper presents a comprehensive analysis on the transient electromagnetic force behavior of the stator windings in a QFSN-600-2YHG type turbo-generator. Different from other studies, this paper investigates not only the distribution regularities of the resultant force and the force density, but also the force harmonic characteristics, and the mechanical responses which will cause sensitive impact on the insulation wearing. The whole work is generally based on a proposed simplified model and the 3D finite element coupling calculation. The simplified model contains two parts. The first part is the theoretical model that employs the approximate solution of the image current to obtain the analytic formula of the electromagnetic force on the end windings conveniently. The second part is the FEA model that employs only the end windings and one-tenth of the stator core to save the calculating memory and, meanwhile, obtain the qualified electromagnetic force as well as the mechanical response. It is shown that the nose-top, the connection point between the line part and the end part, and the middle of the involute are the three most dangerous positions of the end winding to sustain serious insulation wearing. Moreover, the winding, which endures the maximum mechanical response, is neither always consistent with the one that has the largest resultant electromagnetic force nor directly in accordance with the winding that affords the most intensive electromagnetic force density. The findings in this paper will be beneficial for the insulation monitoring and the manufacturing improvement on the stator windings.

Effect of Static Rotor Eccentricity on End Winding Forces and Vibration Wearing

“…During the calculation, we establish the same physical model and external coupling circuit as Ref. [1]. The static rotor eccentricity is set along the X axis, and the eccentricity rate is 0.03.…”

“…The axial length of the stator core is 6300 mm which requests many computing resources in 3D calculation. To balance the calculation accuracy and the resource, one-tenth of the stator, namely, 630 mm, is set for the finite element analysis [1]. The stator core has 42 slots, with the detailed slot distribution illustrated in Figure 2…”

“…As the capacity increases, the stator windings in generators, especially in large turbogenerators, will afford larger electromagnetic forces. Such electromagnetic forces will cause the winding to vibrate [1] and endure stresses [2,3].…”

“…Ohtaguro et al studied the mechanical strain of the end windings in high-voltage rotating machines and employed the strain gauges for the validation test [15], finding that the strains of the stator end windings due to the electromagnetic forces will be larger as the machine starts. The authors have also carried out the 3D FEM calculation on the end winding forces as well as the mechanical response in 600 MW turbogenerators, getting that the nose part, the root, and the middle part are the most dangerous positions to be damaged [1].…”

“…Actually, more and more large generators have installed the opticalelectrical conversion type sensors such as the fiber optic accelerometers, to monitor the radial vibration of the end windings. Since the electromagnetic force on the end windings has the prominent 2nd harmonic, it is requested for large generators that the natural frequency of the end windings should be away from the 2nd harmonic frequency as much as possible [1]. To find out a more comprehensive result, Mori and Ishikawa clarified the relationship among the radial electromagnetic force, the natural frequencies, and the vibration velocities [18], while Yang and Chen presented the general expression of the frequency and the corresponding mode number of the radial force harmonics for a permanent magnet synchronous machine (PMSM) which had three-phase symmetrical double-layer windings [19].…”