Loss-of-Excitation Protection and Underexcitation Controls Correlation for Synchronous Generators in a Real-Time Digital Simulator

This paper presents the results of a study that analyzes the relationship between the excitation system of a synchronous machine and the settings of the loss-of-excitation (LOE) relay applied to protect this machine. A complete generation system taking into account all the physical components was modeled in a real-time digital simulator, including a new excitation system model (ST7B). By considering a method to protect the generator against partial and total LOE, the settings of the LOE protection were made taking into account the technical data of the synchronous machine. A hardware-in-the-loop simulation using a numeric relay was implemented in a laboratory. Thus, several tests were performed in order to evaluate the coordination between the protective relay and the limits of the modeled excitation system during underexcited operation.