Review of PES Failures and Lessons Learned from the Tunisian Blackout of August 2014

This paper presents a review of the blackout that impaired the Tunisian power system on august 31, 2014. This event is particular in its time frame of the cascaded failures leading to generalized power disruption. First, the paper reviews the operational profile of the system: topological layout, generation topology, power demand profile, grid interconnection assets. Many stability issues are addressed: angular stability, fault critical clearing time, frequency recovery, and PSS performances. Corrective controllers performances are assessed: load shedding scheme for variable primary operating reserve quantities, in off-peak and peak loading conditions. Then, the chronological sequence of the blackout events are detailed and supported by real operator recording. Hidden failure of system protection apparatus and excitation system performances were particularly determinant factors, added to the operational constraints profile of the system. The simulations revealed fall reserve requirements, system isolation risks, corrective controller limitations. A set of countermeasures is proposed to the utility in order to prevent its reoccurrence and reinforce the power supply reliability.