A theoretical and practical approach for underexcitation protection and control studies of large hydrogenerators in a real-time environment

Protection devices and excitation systems are essential components for the protection and control of synchronous generators. The installation and settings of these devices are performed during commissioning and require experience since a failure can cause damage to the generator and the corresponding grid. A test bed implemented in a real-time digital simulator is presented in this paper as an alternative for the training and learning process that involves the knowledge of an effective coordination between such protection and control systems. A complete generation system is implemented in a real-time digital simulator, including an excitation system model with its limiters. These limiters are coordinated with the protection functions implemented in a physical relay. The contributions of this work are: the demonstration of the importance of this type of study (i.e., real time simulations results through hardware-in-the-loop tests); the consolidation of the impedance (R-X) and admittance (G-B) planes as the more accurate ones to analyze the coordination between the ANSI 40 function and the underexcitation limiter; and the presentation of a study focused on large hydrogenerators (including novel settings for the 40 protection). This research also paves the way for improvements on similar studies focusing on turbogenerators.