Abstract. The improvement of transient stability of power system was one of the most challenging research areas in power engineer.The main aim of this paper was transient stability analysis and improvement of IEEE 9 bus system. These studies were computed using POWER WORLD SIMULATOR. The IEEE 9 bus system was modelled in power world simulator and load flow studies were performed to determine pre-fault conditions in the system using Newton-Raphson method. The transient stability analysis was carried out using Runga method during three-phase balanced fault. For the improvement transient stability, the general methods adopted were fast acting exciters, FACT devices and addition of parallel transmission line. These techniques play an important role in improving the transient stability, increasing transmission capacity and damping low frequency oscillations.

Along with the increasing demand on improving power quality i.e generally defined as any change in power (voltage, current, or frequency) that interferes with the normal operation of electrical equipment, the most popular technique that has been used is Active Power Filter (APF); This is because Passive filters performance is limited to a few harmonics and they can introduce resonance in the power system. Passive filters are larger component sizes and therefore Costs high. So APF can easily eliminate unwanted harmonics, improve power factor and overcome voltage sags and eliminate any harmonic frequencies. This paper will discuss and analyze the simulation result for a three-phase three wire shunt active power filter using MATLAB program. This simulation will implement a non-linear load, to compensate line current harmonics under balanced and unbalance loads. As a result of the simulation, it is found that an active power filter is the better way to reduce the total harmonic distortion (THD)