Analysis of options to limit occurrence and duration of under frequency load shedding in small, renewable dominant power systems:

Abstract

The power system Sri Lanka is an islanded power system of a relatively small size. Other than the coal power plants, combined cycle plants and gas turbines, a significant portion of electricity requirement is supplied by large hydro, mini hydro and other non-conventional renewable energy power plants. Accordingly, the power system of Sri Lanka can be identified as a low-inertia power system. CEB, the power transmission operator of Sri Lanka, adheres to N-1 reliability in the transmission network. They are not expected to keep N-1 reliability in generation according to the current practice. It means that the internationally practiced power system reliability levels do not exist in the power system Sri Lanka. Even before Non-Conventional Renewable Energy (NCRE) additions, the power system was largely dependent on under-frequency load shedding (UFLS) after large generator disconnection. Introducing NCRE to the power system has worsened the situation further. The aim of the study was to identify the behavior of the power system of Sri Lanka during and after generation disconnection and study possible methods to improve the power system performance after generation disconnection event. The impact of battery energy storage systems on frequency response was studied for the power system of Sri Lanka. A cost analysis on battery energy storage system was performed. Increase in costs was also calculated if an internationally practiced level of spinning reserve is maintained in the power system Sri Lanka. Suggestions to improve the performance of the system are included in the thesis, based on the findings of the research.