Exploring Rate of Change of Frequency (RoCoF) Events in the Nordic Synchronous Area from 2015 to 2023

Abstract

As the world moves towards a sustainable and emission-free future, the power grid emerges as a key participant in providing electrical energy. With the demand for electrical energy rising, the power grid is challenged with larger loads. These higher loads, combined with more penetration of the lower inertia power sources, wind and solar, challenge the stability of the grid. A part of the power-grid stability is its frequency, which should be kept stable at all times. This thesis explores whether there has been an increase in the Rate of Change of Frequency (RoCoF) events in the Nordic Synchronous Area (NSA) from 2015 to 2023. Where the NSA consists of the power grids of Norway, Sweden, Finland, and a part of Denmark.

The aim is to identify whether there has been an increase in the frequency or severity of RoCoF events, which are critical indicators of grid stability. To perform this, the analysis utilises a comprehensive dataset of power-grid frequency measurements provided by Fingrid, the Finnish transmission system operator. To ensure accuracy and reliability in the findings, the data undergoes extensive processing, including cleaning and smoothing. Smoothing techniques are applied to filter out noise and prepare the data for precise RoCoF calculations. This preparation is crucial for accurately detecting and analysing RoCoF events, setting the stage for a robust analysis.

From the RoCoF analysis, results show that the total number of events is not increasing. However, it is revealed that there is a remarkable increase in the severity of RoCoF events. Specifically, the number of RoCoF events in the range 100–160 mHzs−1 averaged about four events annually in the period 2015–2021. This number has increased drastically for the years 2022 and 2023, which had 17 and 12 events. This increasing trend is also found in the ranges above 100–160 mHzs-1. Where the analysis finds an annual increase in RoCoF events from 2020 to 2023.

In summary, this thesis demonstrates that RoCoF events within the NSA have shifted and become more severe from 2015 to 2023. The findings are crucial for Transmission System Operators in the NSA, highlighting the need for enhanced monitoring techniques and the development of advanced grid management.