volume | PIER Journals

Abstract

In order to analyze the influence of three-phase asymmetrical operation of a generator on its stable operation, firstly, taking a 24-MW bulb turbine generator as an example, the 2-D transient electromagnetic field model is established. Through the comparison analysis of the experimental results and simulation data, the correctness of the model is verified. Secondly, the values of air gap flux density, torque and loss in different conditions are obtained by using the finite element method. The effects of asymmetric three-phase current on air gap flux density, torque and loss are determined. Thirdly, the corresponding relationships between the three-phase current unbalance degree and torque ripple, eddy current loss are established, and the variations of torque ripple and eddy current loss are given when the three-phase current unbalance degree is changed. The result shows that the asymmetry three-phase current makes the torque ripple and eddy current loss increase dramatically, which seriously threaten the safe and stable operation of the generator. Finally, the further study on the torque ripple and eddy current loss of the generator under different current distributions and the same three-phase unbalance degree identifies that the content of negative sequence current is a key factor to affect the torque ripple and eddy current loss.

1. Pei, X. J., W. Zhou, and Y. Kang, "Analysis and calculation of DC-link current and voltage ripples for three-phase inverter with unbalanced load," IEEE Trans. Power Electron., Vol. 30, No. 10, 5401-5412, Oct. 2015.
doi:10.1109/TPEL.2014.2375353

2. Sezgin, E., M. Göl, and Ö. Salor, "State-estimation-based determination of harmonic current contributions of iron and steel plants supplied from PCC," IEEE Trans. Ind. Appl., Vol. 52, No. 3, 2654-2663, Dec. 2016.
doi:10.1109/TIA.2016.2521598

3. Vijayan, V. and S. Ashok, "High-performance bi-directional Z-source inverter for locomotive drive application," IET Electr. Syst. Transp., Vol. 5, No. 4, 166-174, Dec. 2015.
doi:10.1049/iet-est.2014.0053

4. Mwasilu, F., J. J. Justo, K. S. Ro, and J. W. Jung, "Improvement of dynamic performance of doubly fed induction generator-based wind turbine power system under an unbalanced grid voltage condition," IET Renew Power Gener., Vol. 6, No. 6, 424-434, Nov. 2012.
doi:10.1049/iet-rpg.2012.0110

5. Yan, R. and T. K. Saha, "Investigation of voltage imbalance due to distribution network unbalanced line configurations and load levels," IEEE Trans. Power Del., Vol. 28, No. 2, 1829-1838, May 2013.
doi:10.1109/TPWRS.2012.2225849

6. Woolley, N. C. and J. V. Milanovic, "Statistical estimation of the source and level of voltage unbalance in distribution networks," IEEE Trans. Power Del., Vol. 27, No. 3, 1450-1460, Jul. 2012.
doi:10.1109/TPWRD.2012.2195230

7. Esfahani, M. T. and B. Vahidi, "A new stochastic model of electric arc furnace based on hidden markov model: A study of its effects on the power system," IEEE Trans. Power Del., Vol. 27, No. 4, 1893-1901, Oct. 2012.
doi:10.1109/TPWRD.2012.2206408

8. Song, H. B. and Z. G. Li, "Alteration of cognate curve and its influences on bulb tubular turbines," Journal of Gansu Sciences, Vol. 22, No. 4, 145-149, Dec. 2010 (in Chinese).

9. Song, H. B., W. L. Li, and F. Y. Yang, "Placement angle effect of axical and radial stent on ventilation structure in bulb tubular turbine," Journal of Jiangsu University (Natural Science Edition), Vol. 34, No. 3, 281-286, May 2013 (in Chinese).

10. Moradian, M. and J. Soltani, "An isolated three-phase induction generator system with dual stator winding sets under unbalanced load condition," IEEE Trans. Energy Convers., Vol. 31, No. 2, 531-539, Jun. 2016.
doi:10.1109/TEC.2015.2508958

11. Peña, R., R. Cárdenas, E. Escobar, J. Clare, and P. Wheeler, "Control system for unbalanced operation of stand-alone doubly fed induction generators," IEEE Trans. Energy Convers., Vol. 22, No. 2, 544-545, Jun. 2007.
doi:10.1109/TEC.2007.895393

12. Singh, S. B., A. K. Singh, and P. Thakur, "Accurate performance assessment of IM with approximate current unbalance factor for NEMA definition," Int. Conf. Harmonic and Quality of Power, 674-678, 2014.

13. Yu, Q., X. S. Wang, and Y. H. Cheng, "Determination of air-gap flux density characteristics of switched reluctance machines with conductor layout and slotting effect," IEEE Trans. Magn., Vol. 52, No. 8, 8107307, Aug. 2016.
doi:10.1109/TMAG.2016.2553649

14. Barcaro, M. and N. Bianchi, "Air-gap flux density distortion and iron losses in anisotropic synchronous motors," IEEE Trans. Magn., Vol. 46, No. 1, 121-126, Jan. 2010.
doi:10.1109/TMAG.2009.2030675

15. Wallin, M., J. Bladh, and U. Lundin, "Damper winding influence on unbalanced magnetic pull in salient pole generators with rotor eccentricity," IEEE Trans. Magn., Vol. 49, No. 9, 5158-5165, Sep. 2013.
doi:10.1109/TMAG.2013.2259633

16. Kurihara, K., "Effects of damper bars on steady-state and transient performance of interior permanent-magnet synchronous generators," IEEE Trans. Ind. Appl., Vol. 49, No. 1, 42-49, Jan.-Feb. 2013.
doi:10.1109/TIA.2012.2229371

17. Wang, L. K., F. Y. Huo, W. L. Li, Y. H. Zhang, Q. Li, Y. Li, and C. W. Guan, "Influence of metal screen materials on 3-D electromagnetic field and eddy current loss in the end region of turbogenerator," IEEE Trans. Magn., Vol. 49, No. 2, 939-945, Feb. 2013.
doi:10.1109/TMAG.2012.2212026

Dr. Hongbo Qiu

Mr. Xiaobin Fan

Dr. Jianqin Feng

Dr. Cunxiang Yang