The impact of recloser transients on Fierza HPP generators

Power system networks are subject to various forms of transients. Various studies have shown that 70-90 % of the faults occurred in overhead lines are transient. Therefore the overhead lines beside relay protection are equipped with recloser, in order to identify the transient faults. When a fault occurs in the network, turbine-generators experience a step change in torque. The fault clearing produces a second step change usually in the opposite direction. This second shock can reinforce oscillations. Unsuccessful reclosing events coupled with low damping for shaft oscillations would provide more opportunities for further amplification. During the rehabilitation work of Fierza HPP, damages have been reported at the shaft of turbine-generator. This experience has aroused our interest in transient shaft torque oscillations leading to a more detailed analysis of the effects of short circuit and line switching transients was performed. In this paper are presented and discussed the representative results of the transient analyses during simulation of reclosers´ operation. Simulations are performed using ATP software.