Improvement of the transient negative-sequence rating formula for large generators based on the negative-sequence current component

Abstract

Summary This paper proposes an improved transient negative‐sequence calculation formula for a large‐capacity nuclear power generator system under unbalanced network conditions. Because of the disadvantages of traditional transient negative‐sequence ratings, I2*2 t is concluded to be inadequate for rating the generator imbalance capability. In fact, many factors, such as the possible fault asymmetry, the duration of the fault and non‐periodic components, should also be considered when rating a generator. According to the inherent relation between rotor heating and generator imbalance capability, the non‐periodic component is added to the improved transient negative‐sequence formula. In this paper, an AP1000 nuclear turbo‐generator was examined as a model to systematically analyse the electromagnetic properties and generator transient negative‐sequence capability affected by different types of typical short circuits. A comprehensive comparison based on accident examples, experimental results and extensive simulations shows that the improved transient negative‐sequence formula not only significantly enhances the assessment accuracy of large‐capacity generator imbalance capability but also provides a theoretical reference for the related research of large‐capacity generator systems. Copyright © 2015 John Wiley & Sons, Ltd.