Computational modeling of protection functions for studies involving power oscillation and loss of synchronism in electrical systems

Abstract

Power systems are subject to different types of disturbances, such as faults, line switching or loss of a large generator. The system is designed to adjust to these changing conditions within voltage and frequency limits. However, some system disturbances may cause loss of synchronism between a generator and the rest of the grid, or between interconnected power systems. During events of loss of synchronism, it is necessary to separate the generator or system areas operating asynchronously to prevent cascading power outages and equipment damage. On the other hand, severe power swings may seem as a fault, leading to undesired trips for conditions which may be stable. In this scenario, it is necessary to block relays that are sensitive to operate. This paper aims to present a modeling for the out-of-step tripping relay (78 OST) and out-of-step blocking relay (68 OSB) using the Matlab\Simulink software. The models were availed for a range of events such as loss of generators, faults and line openings, in order to evaluate the effectiveness of these relays in avoiding major impacts on the system.