Identification of Critical Issues in Angle, Voltage, and Frequency Stability of the Nepal Power System

After end of decades of loadshedding, the power system of Nepal is moving towards the scenario of self-sufficiency. The Government of Nepal has formulated a policy to add 20 GW of hydropower in the next ten years, making a ten-fold increase compared to the current capacity. Therefore, there is a high need for the assessment of the power system stability of the current Nepal grid to mitigate any potential issues that can occur due to the addition of this huge generation. This paper conducts a comprehensive assessment of the power system stability namely voltage (static), angle (transient and small signal), and frequency stability. The proposed assessment methodology consists of three stages: the first stage constitutes the selection and modeling of the components (generator, load, line, excitation system, governor, renewable energy resources) of the power system of Nepal. The second stage then uses the stability assessment tools: time domain simulations for frequency and transient stability, modal (eigenvalue) analysis for small signal stability and voltage stability, and sensitivity analysis for identification of critical areas prone to instability. The result shows that the current grid of Nepal has a low margin of the small signal stability. The critical clearing time of the system is approximately 0.51s. The result also show that there are five potential voltage instability areas in Nepal but is robust in terms of the frequency stability. Additionally, the integration of photovoltaic generation to the Nepal grid has also been studied in this paper. The study shows that the margin of the low frequency oscillatory stability decreases with the penetration of photovoltaic generation of the power grid of Nepal.