The Study Of Power System Line Tripping Criterion And Its Simulation

The correct state of the system is the premise of a stability control device to determine the correct action, non-fault tripping criterion based on the electrical quantities is important part in the stability control system. The technical difficulties of non-fault tripping criterion is how to distinguish between power swing and non-fault tripping, how to ensure the correct criterion when system oscillation. The main contents of this article are as follows,1. Study the algorithm of electromagnetic transient simulation software PSCAD / EMTDC, summarize the calculation of electromagnetic transient model of several lines, as well as their scope of application, study the simulation of frequency-dependent transmission line model in detail.2. Propose that frequency-dependent (phase) model should be used to the study and simulation of line tripping criteria, so that not only enables accurate and reliable simulation results, and the structure of the simulation system is suitable for a variety of complex electromagnetic transient process. The introduction of frequency-dependent (phase) model resolved non-uniform line models on the study of line tripping criteria, improved the reliability of simulation results.3. Propose non-fault tripping criterions based on local electrical quantities, this criterion fully considers the various working conditions of power system, takes advantage of electrical characteristics at the tripping time. Compare with the traditional criterion, this criterion has been improved in the following aspects: the introduction of three-phase sampling measurement algorithm of RMS values, use the change rate of RMS to distinguish between the line tripping and power swing; propose that measurement impedance should bu used to identify the line contralateral tripping, to solve that the traditional criterion is difficult to operate because the larger reactive current when the long line tripping at the opposite site; propose double-action areas to identify the change rate of measurement impedance, use the time of moving through the double-action areas to distinguish between line tripping and system oscillation, as well as identify non-fault tripping under system oscillation.4. Build three-machine nine-bus simulation system in PSCAD / EMTDC, in which frequency-dependent (phase) model is chosen.With a large number of simulation, get waveform data of line triping, power swing and system oscillation.5. Compile program of non-fault tripping criterion, run the program used the simulation data and the wave data recorded in stability control equipment, the running results show that whatever the system circumstances, the criterion can identify non-fault tripping, does not occur maloperation or refuse action. The criterion can be applied to the actual.