As we live in smart grid revolution, the conventional power systems turn into a fast pace toward smart grids, this transition creates new and significant challenges on the electrical network security level; In addition to the important features of the smart grids, cyber security transpire to be a serious issue due to connecting all the loads, generation units, renewable resources, substations and switches via communication network. Cyber-physical attacks are classified as the major threatening of smart grids security, this attacks may lead to a many severe repercussions in the smart grid such as large blackout and destruction of infrastructures. Switching attack is one of the most serious cyber-physical attacks on smart grids because it is direct, fast, and effective in destabilizing the grids. We start the thesis by introducing a state-of-the-art on cyber attacks from the power layer point of view i.e. the cyber attacks that affect the smart grid stability and what are the power system based solutions have been done so far to prevent or reduce the cyber attacks severity .As we focus on cyber switching attack and the method of preventing it, firstly a study on the attack principles and effects is introduced, we construct the attack on a single machine connected to an infinite bus through a transmission line. The attack on the target generator implemented by modeling the system using swing equation on Matlab platform, then we verified the result by implementing the same attack on Simulink Platform. Finally we present a novel solution to mitigate such type of attacks by using Thyristor-Controlled Braking Resistor (TCBR).The suggested solution is able to recapture the machine stability directly after the attack
