In this work, stability aspect of the power system, undergoing three-phase symmetrical fault, has been considered. When a fault occurs, the load angle increases and it may lead to loss of synchronism depending upon the severity of fault. Normally the fault affects two main aspects of power system: transient stability and terminal voltage (voltage regulation). For proper operation of power system it is required to control the system under abnormal condition. The linear and nonlinear control applications to power system undergoing fault are discussed. Stability of a power system mostly depends upon the magnitude and location of the disturbance and to a lesser extent on the initial state or operating condition of the system. The objective here is to design controller to restore the system to pre-fault operating conditions in finite time.