Earticle

Based on investigation on basis of physical process of the motor running under different negative sequence, calculation simulation model for steam turbine generator field was established on a 1266 MW half speed steam turbine generator for nuclear power generation, and according to time-step finite element electromagnetic theory, the 2-d finite element mathematical model is established. According to the numerical method, the magnetic field distributions inside the motor at the rated running state, with 1%IN, 2%IN, 3%IN, 4%IN and 5%IN negative sequence current were calculated. Based on the comparison and analysis of the magnetic fields inside the motor, influence of the negative sequence component proportion on the magnetic field distribution was investigated. The results could provide the reference for the design of operation and protection scheme of the generator.

The current in frequency domain can not be analyzed at the same time because of the limitations of the Fourier transform algorithm. Hence, the wavelet transform method is used to analyze the short circuit transient current and calculate the negative-sequence component in this paper. Then, the non-periodic component and periodic component fundamental wave of the transient current are obtained, and the high harmonic components and decreased periodic component are removed. The non-periodic component is seriously considered in the transient negative-sequence component calculation. The calculation results indicate that the transient negative-sequence component contains two parts, the equivalent negative-sequence component of non-periodic component and the negative-sequence component of negative-sequence current. The world's first AP1000 third generation 1250 MVA nuclear half-speed (4-pole) turbo-generator is adopted as the calculation model. The transient parameters of the large generator are calculated on the principle of transformed current waveform in the internal short circuit fault condition. Furthermore, the transient negative-sequence component of the large-capacity generator is also calculated and the negative-sequence ability is deeply discussed in this work, which provides a theoretical basis for the large generators’ protection and design.