Slot skew is applied as a method to increase the armature winding voltage waveform quality of synchronous hydro generators. Skew that matches the region of one slot pitch can effectively damp stator slot harmonics. However, achieving this condition can be difficult I some manufacturing cases, especially for the machines with greater axial length. That is why other methods are commonly used to increase the voltage waveform quality of large hydro generators. One such method is based on the damper winding slot pitch choice which ensures reduction of stator slot harmonics from the main magnetic field. Appropriate placement of damper bars over the pole shoe does not represent a significant technological problem and is much simpler to manufacture in compare with the slot skew or the fractional armature winding methods. The downside of damper slot pitch adjustment method is the damper bar currents incensement in steady state condition of the generator, which increases damper winding losses and also the rotor temperature. In order to decrease damper winding current for long term operating and enable the generator pole shoe design with smaller cross section damper bars, a combination of damper slot pitch and partial slot skew can be utilized. This paper gives insight on consequences that can occur for voltage waveform if slot skew does not not fully match the stator slot pitch and the advantages of above mentioned combined method for the design optimization of salient pole synchronous generator.
"Salient Pole Synchronous Generator Optimization by Combined Application of Slot Skew and Damper Winding Pitch Methods," Progress In Electromagnetics Research M,
Vol. 73, 81-90, 2018. doi:10.2528/PIERM18070508
1. Pyrhonen, J., T. Jokinen, and V. Hrabovcova, Design of Rotating Electrical Machines, John Wiley & Sons, 2013. doi:10.1002/9781118701591
2. Ahsanullah, K., R. Dutta, and M. Rahman, "Analysis of low speed IPMMs with distributed and fractional slot concentrated windings for wind energy applications," IEEE Transactions on Magnetics, Vol. 53, No. 11, 1-10, 2017. doi:10.1109/TMAG.2017.2726117
3. Ma, X., Q. Lu, X. Huang, and Y. Ye, "Optimization and performance of linear pm-assisted reluctance synchronous machine for wave energy generation," 2017 20th International Conference on Electrical Machines and Systems (ICEMS), IEEE, 1-6, 2017.
4. Vaseghi, B., N. Takorabet, and F. Meibody-Tabar, "Transient nite element analysis of induction machines with stator winding turn fault," Progress In Electromagnetics Research, Vol. 95, 1-18, 2009. doi:10.2528/PIER09052004
5. Williamson, S., T. J. Flack, and A. F. Volschenk, "Representation of skew in time-stepped two-dimensional nite-element models of electrical machines," IEEE Transactions on Industry Applications, Vol. 31, No. 5, 1009-1015, 1995. doi:10.1109/28.464513
6. Wang, X., T. D. Strous, D. Lahaye, H. Polinder, and J. A. Ferreira, "Computationally efficient calculation of skew effects in brushless doubly-fed induction machines," IET Electric Power Applications, Vol. 11, No. 3, 303-311, 2017. doi:10.1049/iet-epa.2016.0354
7. Petrov, I., et al., "Unequal teeth widths for torque ripple reduction in permanent magnet synchronous machines with fractional-slot non-overlapping windings," IEEE Transactions on Magnetics, 2015.
8. Zhan, Y., A. M. Knight, and N. Stranges, "Multislice inter-bar model for large synchronous machines with skewed stator slots," IEEE Transactions on Magnetics, Vol. 45, No. 3, 1800-1803, 2009. doi:10.1109/TMAG.2009.2012827
9. Bomela, X. B. and M. J. Kamper, "Effect of stator chording and rotor skewing on performance of reluctance synchronous machine," IEEE Transactions on Industry Applications, Vol. 38, No. 1, 91-100, 2002. doi:10.1109/28.980362
10. Neubauer, M., H. Neudorfer, and M. Schrodl, "In uence of the rotor optimization of an interior permanent magnet synchronous generator on the short circuit behavior," 2016 XXII International Conference on Electrical Machines (ICEM), IEEE, 1828-1834, 2016. doi:10.1109/ICELMACH.2016.7732772
11. Karmaker, H. and A. M. Knight, "Investigation and simulation of elds in large salient-pole synchronous machines with skewed stator slots," IEEE Transactions on Energy Conversion, Vol. 20, No. 3, 604-610, 2005. doi:10.1109/TEC.2005.852955
12. Jagiela, M., E. Mendrela, and P. Gottipati, "Investigation on a choice of stator slot skew angle in brushless PM machines," Electrical Engineering, Vol. 95, No. 3, 209-219, 2013. doi:10.1007/s00202-012-0252-8
13. Knight, A. M., S. Troitskaia, N. Stranges, and A. Merkhouf, "Analysis of large synchronous machines with axial skew, part 1: ux density and open-circuit voltage harmonics," IET Electric Power Applications, Vol. 3, No. 5, 389-397, 2009. doi:10.1049/iet-epa.2008.0155
14. Koo, M.-M., J.-Y. Choi, K. Hong, and K. Lee, "Comparative analysis of eddy-current loss in permanent magnet synchronous machine considering PM shape and skew effect using 3-d FEA," IEEE Transactions on Magnetics, Vol. 51, No. 11, 1-4, 2015.
15. Nuzzo, S., M. Galea, C. Gerada, and N. Brown, "A fast method for modeling skew and its effects in salient-pole synchronous generators," IEEE Transactions on Industrial Electronics, Vol. 64, No. 10, 7679-7688, 2017. doi:10.1109/TIE.2017.2694378
16. Flankl, M., A. Tuysuz, and J. W. Kolar, "Cogging torque shape optimization of an integrated generator for electromechanical energy harvesting," IEEE Transactions on Industrial Electronics, Vol. 64, No. 12, 9806-9814, 2017. doi:10.1109/TIE.2017.2733441
17. Guo, H. and M. Zuo, "2d and 3d magnetic eld nite element analysis and contrast of permanent magnet synchronous generator," 2011 International Conference on Electrical Machines and Systems (ICEMS), IEEE, 1-4, 2011.
18. Roshanfekr, P., S. Lundmark, T. Thiringer, and M. Alatalo, "Torque ripple reduction methods for an interior permanent magnet synchronous generator," 2014 16th European Conference on Power Electronics and Applications (EPE'14-ECCE Europe), IEEE, 1-7, 2014.
19. Fan, Z.-N., L. Han, Y. Liao, L.-D. Xie, K. Wen, J. Wang, X.-C. Dong, and B. Yao, "Effect of damper winding and stator slot skewing structure on no-load voltage waveform distortion and damper bar heat in large tubular hydro generator," IEEE Access, Vol. 6, 22 281-22 291, 2018. doi:10.1109/ACCESS.2018.2827704
20. Maljkovic, Z., D. Zarko, and S. Stipetic, "Unsymmetrical load of a three-phase synchronous generator," Przeglad Elektrotechniczny, Vol. 2013, No. 2b, 68-71, 2013.
21. Hargreaves, P., B. Mecrow, and R. Hall, "Open circuit voltage distortion in salient pole synchronous generators with damper windings,", 2010.
22. Knight, A. M., S. Troitskaia, N. Stranges, and A. Merkhouf, "Analysis of large synchronous machines with axial skew, part 2: inter-bar resistance, skew and losses," IET Electric Power Applications, Vol. 3, No. 5, 398-406, 2009. doi:10.1049/iet-epa.2008.0156
23. Ferkova, Z., "Comparison between 2D and 3D modelling of induction machine using nite element method,", 2015.