Evaluation of under-excitation limiter actuation under unbalanced load conditions

The increase of distributed generation in a worldwide level, combined with its characteristic of operating under load imbalance between phases, motivated the study of various aspects of its operation, such as the analysis of possible low-frequency oscillations and the generation penetration level that meets the minimum energy quality criteria. Among the features that deserve a careful scrutiny, there is the investigation of the distributed synchronous generator dynamics under severe operating conditions, including the relevant dynamic associated to its control loops. In this context, this paper presents an analysis of the actuation of the under-excitation limiter, when operating in synchronous generators subject to load imbalance between phases. In addition, the effect of different representations of the generator terminal voltage transducer (which is used as a feedback signal to the excitation system and its associated elements) on the actuation of the under-excitation limiter was evaluated. The obtained results show that significant levels of imbalance, associated with certain terminal voltage transducer representations, may have an adverse impact on the actuation of the under-excitation limiter.