Zdeňka Benešová

Overvoltages in photovoltaic systems induced by lightning strikes

The high number of photovoltaic systems raises questions regarding their operational security even under extremely weather conditions like thunderstorms. Therefore a simplified model of a photovoltaic system, consisting of typical arrangement of solar-panels, was investigated. The influence of lightning strike was simulated by different lightning current shapes and striking points into the solar-panels. It was found, that besides the construction size and shape of the lightning current the striking point has a main influence on the value of induced overvoltages, occurring on the connection point of the solar-panels. The simulation results were confirmed by measurement with an impulse current. The results demonstrate the dangerousness of lightning currents with very fast rise time e.g. subsequent impulse as well as the reducing of induced overvoltages by an appropriate earthing connection. This has to be considered at the design of the lightning protection system.

Comparison of Joule's losses on transposed and non-transposed transmission line

The paper deals with the calculation of Joules losses on overhead transmission lines. The presented method allows taking into consideration the influence of a current asymmetry caused by various conductors layout and their inductive and capacitive couplings. The losses evaluation has been carried out with respect to the total transmitted energy, data given by year and day load diagrams were used. The various properties of a load including its asymmetry connected to the transmission line could be involved. The proposed method enables to determine operating costs respecting all important factors, to accomplish an economic analysis for an assessment the whole service life costs and to compare economic advantages of a transposed or non-transposed transmission lines.

Surge Waves Propagation on Transmission Lines Induced by Lightning Stroke

The paper deals with surge phenomena on homogeneous and non-homogeneous transmission lines. The case of surge phenomena caused by the lightning stroke is considered. The lightning is modeled as the current wave injected by the source placed at any internal point of the line. The propagation of the surge wave induced by the lightning affecting the overhead line and transmitting to the cable is evaluated. Problem is solved numerically in the time domain. The efficiency and correctness of the proposed method is shown on some illustrative examples. According to the suggested algorithms is calculated the distribution of induced current and voltage along the whole transmission line namely near to the place of the connection both lines. The manner of the lines-connection can be modeled due to various two-ports

Analysis of the transients on the multi-circuit overhead transmission line

Abstract In this paper a method for a transient analysis on the multi-circuit overhead transmission line with different voltage levels (EHV and HV) is presented. The influence of inductive and capacitive couplings between the parallel circuits placed on the same tower is studied. The transmission line model consists of mutual coupled two-port cascades which can be described by a system of ordinary differential equations (ODE). This system has been solved numerically in MATLAB, the obtained results provide the time distribution of currents and voltages in all conductors along the transmission line. The presented algorithm allows solving various types of transients which can occur during switching off- and on-operations, shortcircuits etc.