Assessment of Frequency and Rotor Angle Stability of Integrated Nepal Power System

Power system stability assessment is highly crucial to study the behavior of the grid under dynamic conditions and helps to operate it in a secure manner. This paper assesses the power system stability: frequency and angle stability for Integrated Nepal Power System (INPS). The INPS modeled in this study consists of 24 machines, 58 buses, and 77 sections of the transmission line. The network components, generators, excitation systems, governor systems, etc. are first modeled and different stability indices related to the frequency and rotor angle stability of the power system are calculated using DIGSILENT PowerFactory. The frequency nadir and the Rate of Change of Frequency (RoCoF) are two indices used for determining the frequency stability, and eigenvalue, damping ratio, critical clearing time, and transient stability indices are used for angle stability assessment in this paper. The simulation results show that Mistri Khola hydropower and Chilime hydropower are most critical with respect to frequency stability due to the lowest frequency nadir and high RoCoF respectively. Similarly, Kaligandaki-A hydropower station is the most critical with respect to the system damping. Furthermore, the performance of the Battery Energy Storage Systems has also been analyzed and are found to improve the system frequency nadir and reduce RoCoF.