Proteção seletiva contra faltas à terra no estator de múltiplos geradores conectados em paralelo

Abstract

Generator stator earth fault protection is one of the main topics evaluated during protection studies. Several methods against this type of fault have been developed over the years, however, none of the traditional methods is able to guarantee the selectivity of the protection system in scenarios that consider the operation of multiple generators in parallel, grounded by high impedance. From the literature review, it was identified the proposition of a new method capable of overcoming this problem caused by the parallelism of the machines. However, despite the high potential, this methodology was evaluated only through offline simulations. Therefore, this dissertation proposes a test platform through a real-time digital simulation environment in the RTDS (Real-Time Digital Simulator) and evaluates the new selective method of protection against earth faults in an electrical system composed of two synchronous generators connected in parallel. This work also contributed to the development of an electrical circuit capable of emulating the generation of different levels of third harmonic voltage, both at the terminals and at the neutral of each machine. In this context, nine operating scenarios were modeled from the main system and the simulation of phase-to-ground short circuits along the entire length of the stator winding of the synchronous machine was performed. The simulations contemplated the integration of commercial protection relays through the technique called hardware-in-the-loop in RTDS. In addition, for the correct application of the evaluated methodology, a communication system between the equipment was developed. The results obtained allow us to conclude that the scope and effectiveness of the evaluated method is conditioned to the harmonic level present in each of the generators that share the same bus.