Research On New Anti-CT Saturation Strategy Of Digital Busbar Protection

Busbar, one of the most important elements in electric Power System, is connected with all kinds of components in various and complicated ways, so its protection is different from that of others such as generator protection, transformer protection etc. Though the current differential protection principle that is the essential portion of busbar protection has been widely used in practice, its accuracy is invariably reduced by current transformer (CT) saturation, which can cause the misoperation of the busbar protection. Thus the performance of the digital busbar protection to anti-CT saturation is crucial to improve.The main research work is focused on the key problem of anti-CT saturation and contains the following aspects:Based on the analysis of CT saturation mechanics, the thesis has amply discussed the CT transient saturation model which has been implemented in MATLAB development environment. The waveforms, which are perceived through the process of simulation, of the second current and magnetizing current of CT transient saturation have been compared with the waveforms of those obtained from the fault recorder. Consequently, the characteristics of the waveform of those can be found out.Each part of the digital busbar differential protection scheme is discussed respectively. The performance of the ratio-restrained differential protection based upon current phasor is analyzed, the performance which is in the presence of throughout current under busbar internal fault or CT transfer error under busbar external fault.A new digital busbar differential protection scheme based on a TA saturation indicator is put forward, a TA saturation indicator which can showcase the characteristic of differential current waveform when CT has been saturated. By using the proposed TA saturation indicator, the restraint factor can be adaptively adjusted. The scheme is operated by using the model which is composed of the Simulink blocksets. Several simulation tests involving all kinds of fault situation are carried out through running the protection model in MATLAB development environment. The results indicate that the new scheme will not misfuction when CT transient saturation occurs during busbar external fault, and it will quickly issue a trip signal after the external fault has transferred to busbar internal fault.In the last chapter, not only is all of the research work accomplished in this thesis summarized, future improvement is pointed out as well.