Research On Coupling Mechanism Of Switching Field Transient In Substation

With the transmission operation voltage increasing the microprocessor based protection and control equipments are susceptible to be interfered. Therefore for predicting and making measures to protect them from interference it is important in theoretical and practical application to research on characteristics of EMI, susceptibility of electrical equipments to EMI. Supported by the Scientist funds for Outstanding Young Scientists of China (grant No. 50325723), the characteristics of switch field transient, susceptibility of microprocessor relay and computer to switch transient field, and electromagnetic coupling mechanism to lines are researched. The main innovative achievements are as follows:1 It is the first measurement of switching transients in China. Electric field transients are measured in five 500kV pilot substations and magnetic field transients are measured in three pilot 500kV substations. After analyzing the data of switching transient the characteristics of switching transients in time and frequency domain are obtained. It establishes the foundation for validation of models for calculating the switching transients and for research on susceptibility of electrical equipments to switching transients.2 It is the first experiment to research the susceptibility of microprocessor based relay to intense EMP in China. Based on the data of switching transients and considering the need in other fields the bounded EMP simulator was designed. The susceptibility of microprocessor-based relay to switching transients was studied by experiments based on the EMP simulator. The results show that with regard to switching transients the shielding measure with two layers of metal enclosures is conservative, and the coupling path was analyzed for fault of equipment. This thesis also studies the susceptibility of personal computers to EMP and the shielding effectiveness of metal enclosure with an aperture.3 Based on the EMP simulator coupling voltage and current responses are measured at terminals of overhead lines and shielded cables. The results show that coupling currents at terminals of internal lines of shielded cable are different with different ground configurations of the shield, and the current at the source end is not sensitive to shield ground as that at the load end of the shielded cable. The sequence of peak to peak currents at terminals of internal line from most to least is: shield grounding at source end and floating at load end, two terminals of shield floating, two terminals of shield grounding, shield floating at source end and grounding at load.4 A method of nodal admittance equations is presented for analyzing coupling voltage at terminals of coupling multiconductor transmission lines, and the formulas of voltage in frequency domain are derived when line is excited by uniform plane wave, and these formulas are validated by comparison simulation results with the reference. Based on this method crosstalk responses between two line with common ground is studied, The results show that simulation is agreement well with the experiments when considering the inductance effect in terminals. The formulas of current response at terminals are also derived when the line is excited by electromagnetic field in the volume of the EMP simulator, and the current simulation results is agreement with that by experiments.