Research On Switching Transient Field And Coupling Mechanism Of It To Secondary Cable In Substations

With the grid is developing for UHV/compactness and microelectronic technology is used in secondary equipment, transient electromagnetic environment is becoming more and more complex, and electromagnetic compatibility problem of secondary equipment is more and more severe in substations. It is provided with important theoretical meaning and applied value to investigate switching transient field and the mechanism of it coupling to secondary cable. In this paper, on the base of finite-difference time-domain (FDTD) Method, time-domain simulating method of switching transient field is investigated, transient electromagnetic environment in the soil and in the cable tunnel is analyzed, the design of the transmission line of bounded-wave electromagnetic pulse simulator, coupling mechanism of near-field to finite-length wire and cable, and computing method of transient electromagnetic field coupling to shielding cable are investigated. The main achievements are as follows:1. Time-time model of simulating switching transient field is founded, according to the theory of spark discharge, time-dependant resistance and inductance expression of arc discharging channels are put forward while the insulating switch is operated. The range of time-dependant resistance is achieved by fitting the measured datum of switching transient field in typical substations. Using the founded model, the factors of influencing switching transient field are studied, which can be used to investigate switching transient field in EHV/UHV substations.2. Aiming at the distribution of transient electromagnetic field in the cable tunnel, uneven mesh FDTD Method is put forward. The switching transient field is systematically analyzed in the soil and in the cable tunnel in substation, and distribution rule is achieved. The factors of cover board which influence the distribution of switching transient field in the cable tunnel are analyzed, which supply the qualification of designing the cable tunnel and laying secondary cable.3. Aiming at simulating technology of EMP in substations, the influencing parameters of transmitting mode of electromagnetic wave in the workroom of bounded-wave EMP simulator are investigated, including the width and length of the transmission line of bounded-wave EMP simulator,the dielectric constant and conductance of the soil, the results indicate the width of transmission line is primary parameter, which can be used to help design the transmission line of bounded-wave EMP simulator. 4. Time-domain method of near-field coupling to finite length thin wire is put forward, the FDTD discrete equations of electromagnetic fields on the surface of the mesh which intersect the different thin wires are deduced, the merit of the time-domain method is that near-field and thin wire are regarded as one whole to be directly computed in the time-domain. In this paper, near-field method and far-field method for investigating the field-to-wire coupling are compared. Using the time-domain method, coupling mechanism of field-to-wire is investigated, and mutual interference of different loop is also investigated.5. Domain decomposition FDTD algorithm is firstly put forward which be used to investigate transient electromagnetic field coupling to shield cable, on the base of integral expression of Faraday law, FDTD discrete equation of magnetic component in triangle mesh is deduced. Elementary investigation indicates that fast transient electromagnetic field is difficult to penetrate the shield of the cable; aperture is primary possible pass of transient electromagnetic field coupling to the core of the cable.