WAMS-Based Underfrequency Load Shedding With Short-Term Frequency Prediction

TLDR

Wide‑area monitoring systems are increasingly adopted by transmission operators, and under‑frequency load shedding is a key area for improvement while keeping measurement requirements minimal. This study proposes a method to predict system frequency a few seconds in advance. The prediction enables load‑shedding decisions and accounts for inevitable inaccuracies. Simulation on a 110 kV Slovenian model demonstrates that the predictive UFLS outperforms traditional schemes in evoked conditions and load removal, though extreme frequency gradients limit its applicability, positioning it as a smart supplement to existing UFLS.

Abstract

The importance of the wide-area monitoring system is rapidly increasing and many transmission system operators have already made several steps toward implementing wide-area monitoring, protection, and control. Underfrequency load shedding (UFLS) is undoubtedly one of areas that can be significantly improved within such an upgrade. However, in order to pursue finding a concept for practical implementation, as little measurements as possible should be used for the purpose. In this paper, an approach for obtaining a few-seconds-in-advance frequency prediction is described. It enables making decisions about the amount of load to be shed and, at the same time, being aware that inaccuracies in the procedure are inevitable. An extensive testing of the approach was performed on the 110 kV part of the Slovenian power-system model and the predictive UFLS appears to be highly superior to traditional UFLS on evoked frequency conditions as well as the total amount of disconnected loads. Consideration of practical limitations, such as all major time delays, unveiled a limitation for using the procedure at extreme values of system-wide frequency gradients. Consequently, the proposed algorithm is to be considered a "smart" supplement to already operational traditional UFLS.