Transient Analysis And Control Of Medium&Low Voltage Electrical Equipment With Smart Switch

According to requirement of flexible control to smart grid, Firstly, a detailed analysis about very short transition process after the induction motor, transformer, reactor and capacitor loads are turned on is performed in the dissertation. On this basis, the objective of this research is to devise smart switch controlling the very short transition process in order to suppress inrush current and overvoltage. And lastly, the controlled transition process is successfully applied in a new power communication field (power frequency communication). The work and research results are as follows:(1) It is first presented that smart switch controlled via the embedded computer consists of vacuum breaker and thyristor valve in parallel connection. The load current is charged with vacuum breaker in operation status and the thyristor valve is working short time during switching loads in order to stress inrush current and overvoltage. It has advantage of compact, low cost and high reliability. The work in project includes thyristor valve design, thyristor electronic board, high frequency power delivery system and control protection system.(2) The mathematics model of transition process during switching electrical equipments is established. From switching capacitor with medium-voltage smart switch, the current transfer transition process between vacuum breaker contact tripping and producing arc voltage and the load current transferred from vacuum breaker to thyristor valve is studied and the conditions of realizing current transfer successfully are obtained. The research includes the mathematics model of piecewise linear voltage-current characteristic curve of arc, the mathematics and physical model of current transfer and analytical solutions of capacitor current and voltage of thyristor valve. Accordingly the optimal trigger time of thyristor valve and theoretical foundation for thyristor valve design are established.(3) The objective of this study is to devise analytical analysis solution of control parameter with smart switch about transition process analysis and control on induction motor and transformer with capacitor load, inductive load and no load reclosed to power. Based on the non symmetry to symmetry mathematical model, analytical solution of residual voltage and the function relationship between the control parameter and induction motor parameter is discovered via mathematical analytical method. Consequently it is realized that three phase windings are conducted in one power cycle rapidly for suppressing inrush current.(4) For smart switch technique applied on power frequency communication field for remote monitoring of motor, hardware and software design which solve some key technical problems are proposed. Firstly, aberration signals through the transformer are made with smart switch controlled via MCU. Secondly, aberration signals is distinguished from background via differential filter technique and information in aberration signals of code is realized via demodulation cross-correlation. Thirdly, a new demodulation strategy is designed, in which the leading information is modulated based on pseudo-random code, thus the adaptive synchronous monitoring can be performed by overcoming the influence of phase differences of voltages at sending and receiving ends of the signal. Lastly, the continually varying amplitude and phase of fundamental current within the stroke of electric machine are calculated by complex wavelet method to provide information of the operation and fault for pumping units.