Real-Time Digital Simulation for Coordination Analysis of V/Hz AVR Limiter With Overexcitation, Overvoltage, and Underfrequency Protections of Synchronous Generators

Abstract

Synchronous generators have automatic voltage regulators with limiters that are used to prevent high or low flux in the generator by controlling the Volts/Hertz ratio. Within the operating range of this limiter, it is not necessary to activate the protection functions associated with voltage and frequency. For that, it is necessary to coordinate these limiters with such protection functions. So, this article increases the scope of (Coelho <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2018) and (Coelho <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2019) by including the coordination studies between Volts/Hertz limiter with overexcitation, overvoltage, and underfrequency protections of synchronous generators. A hardware-in-the-loop simulation is implemented in laboratory to test and evaluate this coordination, and the best settings for it are proposed. An actual power system was modeled in a real-time digital simulator. A great quantity of tests was applied to a synchronous machine (including all its electrical protections and controls) by separately applying frequency steps and voltage steps. The hardware-in-the-loop simulator was prepared to observe an actual digital relay's dynamic responses to these steps. A Volts/Hz limiter, associated with the generator under analysis, is added to the RTDS library. In addition, by analyzing the abovementioned protections and their interaction with the Volts/Hertz limiter of the synchronous machine's excitation system, it is demonstrated that the protections and the limiter should always be jointly investigated.