Design Of Generator Negative Sequence Current Monitoring Instrument

With the development of industry and improvement of living, energy becomes more and more important. In power plants, steady work is very significant. Turbo generator should endure certain degree of continuous and transitory imbalance load. Continuous imbalance load is judged by negative sequence current I₂ according to IEC criterion. When negative sequence current increases to large degree, the rotor will be destroyed. Thus generator negative sequence current is an important parameter related to safe and stable running of generator. Generator manufacturers and power plants all pay great attention to monitoring generator negative sequence current.At present, negative sequence current monitoring instruments mainly depend on analog monitoring circuits in our country, but their intelligence is relatively low. At the same time, their precision can hardly be guaranteed. With the application of float DSP chip, negative sequence current intelligent monitoring instrument as SL-2 is realized through negative sequence current digital calculation method based on DSP theory. In the design, one signal denoising algorithm is realized with cross-correlation and digital filtering. Real-time capability and accuracy are greatly improved through using negative sequence current digital frequency field algorithm. Moreover, in SL-2, intelligent control is implemented through using ARM7 embedded micro processor. Depending on embedded operating systemμC/OS-II, multi-tasks can work efficiently with each other. Its user interface is friendly and facilitative. It adds network communication function based on C/S mechanism to set parameters and to send real-time data.The paper discusses significance of monitoring negative sequence current and state of present monitoring instruments. It describes negative sequence current intelligent monitoring instrument as SL-2. The first chapter introduces research background and outlook; The second chapter and the third chapter discuss technology of DSP and knowledge of embedded system design based on ARM7 micro processor; The fourth chapter provides hardware configuration of design; The fifth chapter puts forward digital calculation method of negative sequence current and design of software ; The sixth chapter analyses technology parameters and results of testing.SL-2 has been applied to power plants. After enough time for running, the effect of monitoring is satisfactory. Experiments show that, being interfered by strong electromagnetic noise, it can work reliably. The measurement error of monitoring data is less than 5‰. The precision and real-time capability of SL-2 can meet the requirement of monitoring.