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

摘要

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