Metodologia para detecção de perda de excitação, curto-circuito e oscilações de potência em geradores síncronos

Abstract

Synchronous Generators are known to be machines capable of supplying electrical power at a constant frequency. The term synchronous refers to the synchronism between the mechanical speed of rotation of the generator and the electrical frequency produced. This synchronism feature makes synchronous generators widely used in the vast majority of electricity generating plants. However, failures in the excitation system of synchronous generators can lead the machine to abnormal operating conditions. When the failure of the excitation system causes loss of excitation, the synchronous generator becomes subject to effects that can lead to permanent damage. These effects include reducing the terminal voltage, increasing the current in the stator, absorbing reactive power, reducing the active power generated and increasing the speed. Thus, due to these problems, protection methods were developed, aiming to identify and mitigate the impacts caused by the loss of excitation. Methods like those of Mason (1949) and Berdy (1975), based on the mho type distance relay, although old, are still used today. However, selectivity may be compromised in cases of stable power swings. Thus, in recent years, protection methods have been developed which, in some cases, seek to adapt and improve the conventional methods developed by Mason and Berdy, or to propose new logics of protection against loss of excitation. In this context, this work presents a new technique to detect loss of excitation events in synchronous generators, which is capable to detect short-circuits or power swings events at the generator terminals, differentiating them from the loss of excitation. The proposed technique was robust and did not act improperly in situations of power swings and short circuits. In addition, the events of loss of excitation in most cases were detected faster than the classical methods.