Optimal Setting of Under Frequency Load Shedding Relays in Low Inertia Networks

Abstract

Under Frequency Load Shedding (UFLS) is one of the most important protection schemes against frequency instability. In this paper a multi-stage UFLS plan is developed. The main devices of this scheme are under frequency relays that are tuned offline. The amount of load shedding, frequency threshold and time delay for load shedding are optimized according to the system conditions. Hence, the setting of these relays with regard to the actual operation conditions seems to be a necessity. The focus of this paper is to utilize the UFLS plan in the primary control of the frequency response, which ranges from the beginning of the contingency until tens of seconds later. The dynamics of governors and load damping are also considered. The performance of the multi-stage UFLS plans under the high penetration of non-synchronous renewable generation resources is investigated. The proposed scheme is implemented in IEEE 39-Bus test system using GAMS software.