Analysis of Bhutan Power Systems using PSS®E Software

Electricity demand in Bhutan has been increasing steadily ever since utility-scale power supply wasintroduced into the country in the 1960s and 1970s and Bhutan’s first large-scale hydropowerproject, 336 MW Chhukha Hydropower Plant was commissioned in the 1980s. In the past threeyears, the rise in the demand has accelerated due to rapid growth in the industrial development. Thishas led to increasing stress on the power system infrastructure. Further, the country’s grid issubjected to varying operating conditions brought about by seasonal variations in generation,peaking in summer, flexible operation and reaching its lowest level in winter. Additionally, the gridis connected to Indian systems via thirteen feeders at different voltage levels further increasing therisks of disturbances and influence from the larger Indian grid. Therefore, it is of paramountimportance to carry out the system analysis at regular intervals to study and assess the behavior ofthe power systems, based on which the timely corrective measures can be implemented to ensuregrid stability and efficiency. In this study, the existing power system model of Bhutan is developedin PSS®E software and simulation is carried out for summer and winter seasons. For summer, thedata sets of 28th July 2024 at 20:00 hours is used while for winter, the data sets of 14th February2024 at 15:00 hours is used corresponding to the highest generation and the lowest generationrespectively. The simulation results show the overloading of Mangdechhu to Yurmo line,overloading of transformers at Gedu substations, and under voltage issues in a few substations inboth the study periods. Therefore, to resolve the overloading issues, upgradation of transformers atGedu substation and connection of a new line from Mangdechhu to Yurmo is recommended. Further,to resolve under-voltage issue, shunt capacitor of 12 MVAR is recommended in Damji substation,which has been determined based on the QV analysis.