Concerning The Simulation Of The Connection Of The No-Load Transmission Lines In High Voltage Networks

This paper describes a Matlab program designed to compute the switching over voltages which appear when no-load high voltage lines are energized. The mathematical models of the high voltage distribution lines are presented also. The Matlab program is applied for the case of the high voltage distribution lines from the 220kV network of the ST Craiova, for which the characteristic parameters are known. INTRODUCTION The values of the switching over voltages appearing when the no-load lines are energized depend on the parameters of the electrical diagram or the equivalent circuit diagram at initial instant. The complexity of the mathematical model depends on the number of characteristics of the switching process and also on the type of electrical diagram used (mono or three phase one). The values of the computed over voltages are very important for the high or very high voltages networks, having the neutral point directly earthed. In this case a mono phase diagram can be used because the processes are analogous to the others phases. Considering the line model with concentrated parameters, the line can be represented by the T or Π quadripole, the resistances being neglected in comparison with the reactance values, as is shown in the Figures 1a and 1b. Figure 1: Equivalent Diagram: a) T Quadripole; b) Π Quadripole Corresponding to the steady state operation at 50Hz, the value of the concentrated parameters can be computed by means the impedances having the following expressions: ⋅ for T quadripol : 2 c Z l L tg λ β   =   ω   ,