Assessment of Under-Frequency Load Shedding in Mongolia Considering Inertia Scenarios

The Mongolian power system (MPS) has been changing in recent years mainly by the integration of wind power and solar photovoltaic sources which until 2019 has been reached a 20% of the total generation sources. The interconnection with the Russian power system is crucial from the frequency control and stability point of view, especially during the winter, since it provides the necessary power to cover the local energy lack. The importance of this interconnection was evident during the disconnection of the two transmission lines that connect MPS to RPS producing the major frequency event on 29
^th
June 2018, disconnecting 112 MW by the action of the under-frequency load shedding (UFLS) and making more than 1.5 million without electricity that day. The objective of this paper is assessing the existing UFLS schemes installed in the MPS by using numerical time-domain simulations. The disconnection from the RPS is used to evaluate the suitability of the UFLS considering two scenarios: winter high-demand, high-inertia and summer low-demand, low-inertia. Results of this research paper have demonstrated that the actual UFLS scheme is not enough to avoid frequency collapse in real-life conditions during the summer low-demand, low-inertia scenario.