Evaluation of Weakening Effect of Stator Parallel Branch Circuit on Main Field Asymmetry

doi:10.11930/j.issn.1004-9649.202404088

Abstract

Abstract:

The short circuit between turns of the rotor winding is a weak characteristic electrical fault of the turbine generator, which makes the fault detection difficult. This paper investigates the weakening effect of the circulating magnetic field inside the parallel branch of the stator winding of a turbine generator on the asymmetric magnetic field generated by the rotor winding turn-to-turn short-circuit, derives the expression of the excitation magnetic field under the fault condition, obtains the expression of the circulating current of the parallel branch of the stator winding and the expression of the magnetic field generated by the circulating current, and finds out the offsetting effect of the circulating field on the original asymmetric magnetic field. A 300MW steam turbine generator is used as an example to carry out finite element simulation, which proves the weakening effect of the parallel branch structure of the stator winding on the short-circuit fault characteristics of the rotor winding, and the research conclusion is helpful to analyze the external appearance and causes of the short-circuit fault characteristics between turns of the rotor winding, and also provides theoretical support for the feature extraction in the fault diagnosis stage.

Key words: turbine generator, rotor winding inter-turn short circuit, diagnosis, parallel branch loop method, asymmetric magnetic field

CHEN Bingbing, WU Yucai, JI Xuan, ZHU Xinkai. Evaluation of Weakening Effect of Stator Parallel Branch Circuit on Main Field Asymmetry[J]. Electric Power, 2025, 58(5): 189-198.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202404088

https://www.electricpower.com.cn/EN/Y2025/V58/I5/189

Figures/Tables 15

Fig.1 Short-circuit turn potential distribution

Fig.2 Rotor magnetic potential distribution in the short-circuit condition of the rotor winding of a turbine generator

Fig.3 Trajectory of conductor a

Fig.4 Long distance coil model and its electromotive force vector

Fig.5 The electric potential vector of a set of coils

Fig.6 Stator one-phase winding structure

Fig.7 Coil magnetic potential

Fig.8 Magnetic potential contrast

Fig.9 2 D model of generator

Table 1 Basic parameters of QFSN-300-2-20 B turbine generator

项目	数值	项目	数值
额定功率/MW	300	额定功率因数	0.85
额定电压/kV	20	同步电抗标幺值	1.85477
额定电流/kA	10.19	定子绕组电阻/Ω	0.001658
相数	3	磁极数	2
额定励磁电流/A	2075	转速/(r·min^–1)	3000
接法	YY

Fig.10 Magnetic density contrast at different observation points

Table 2 Magnetic density contrast at different observation points 单位：T

观测点	波峰		波谷		不对称度		削弱程度
观测点	环流	无环流	环流	无环流	环流	无环流	削弱程度
1	0.990	0.986	–0.994	–0.998	0.004	0.012	0.008
2	0.929	0.925	–0.933	–0.937	0.004	0.012	0.008
3	0.919	0.915	–0.923	–0.927	0.004	0.012	0.008

Fig.11 Magnetic density contrast under different degrees of short circuit

Table 3 Magnetic density contrast under different degrees of short circuit 单位：T

短路匝数	波峰		波谷		不对称度		削弱程度
短路匝数	环流	无环流	环流	无环流	环流	无环流	削弱程度
2	0.990	0.986	–0.994	–0.998	0.004	0.012	0.008
4	0.980	0.976	–0.989	–0.995	0.009	0.019	0.010
6	0.976	0.968	–0.985	–0.992	0.009	0.024	0.015

Fig.12 Harmonic analysis of magnetic density at point 1

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