Electric power systems with transmission lines play the vital role for ensuring uninterrupted power delivery from the generating stations to the load locations. Power Transmission lines outages are relatively high and are exposed to disruptive actions over everyday life. Switching/Lightning Overvoltages for power transmission lines should not cause damage of line insulation or cause unreliable operation of transmission lines. This paper describes investigations on 220 kV transmission line for lightning overvoltage suppression, controlling the switching overvoltages and the line insulation coordination. The selected 220 kV transmission is operated by the Egyptian utility around greater Cairo. The modeled system consists of overhead line, surge arresters and the towers modelling with footing earth resistance. The system has been simulated using (MATLAB/EMTP) software packages. The controllable metal oxide surge arresters are used to act as the main overvoltage protection devices over the power line transmission line towers. The controllable surge arresters are implemented as an effective device to initiate deep suppression of the overvoltages. The effects of the earthing footing resistor under the transmission line towers are investigated. The probability normal distribution of the overvoltages for the different conditions and operations of the line is demonstrated. Different switching times of each phase of the power transmission line are applied. As a result of using these arresters, the insulation coordination rules will be regulated to fulfil the reliability and durability of the power transmission lines. The overvoltages performance has probably been exceeded accordingly. Moreover, the tower earth footing resistance has vital role in the overall overvoltage protection system design. |
