Low-frequency transients and impedance in the power mains considering line loading

Protection against the transients originated by the connection or disconnection of loads in the power mains is of fundamental importance for the electric energy quality. The knowledge of the parameters of the disturbances and of the characteristics of the mains lines is essential for the mitigation of the unwanted phenomena and for the design of protection measures. This paper offers a lumped-constant analysis of the influence of the network loads on the transient waveshapes, and on the impedance seen when looking into the mains. The complex problem involving two loads and two line sections is reduced to a simplified model permitting analytical treatment with the consequent possibility of prediction and of extraction of the important features. The simplifying assumptions are (1) the line losses are low, and (2) the distance between the loads involved in the transient is short with respect to the total line length. The approximation limits are pointed out and the experimental validation demonstrates excellent agreement. Only the more significant case involving capacitive loading of the line is worked out in detail. Other cases of interest also involving resistive-inductive loading have been treated and are delineated in summary.