Evaluation of Volts/Hertz and over-excitation limiters acting under unbalanced load conditions

Currently, a worldwide tendency of decentralization of electric energy production (called Distributed Generation) is observed, where small generators - sometimes composed by synchronous machines - are connected mainly to distribution grids. Due to the intrinsic characteristic of load imbalance between phases in these systems, there are a series of questions about operation of these generators and its respective control loops. Some of these questions are related to the imbalance impact over the actuation of limiters in the excitation systems of these generators. In this context, this paper presents an analysis of the actuation of the Volts/Hertz and over-excitation limiters, when the synchronous generator is submitted to extreme situations under unbalanced load conditions. Additionally, the effect of different terminal voltage transducer representations over the actuation of these limiters was evaluated. The obtained results demonstrate that the unbalance condition, associated with an inappropriate specification of the voltage transducer, may have a significant impact on the actuation of these limiters.