Materials for Generator Retaining Rings: A State-of-the-ART Review

摘要

Retaining rings are among the highest stressed components of electrical generators, whose integrity is critical to the reliable and safe operation of the generators. Numerous instances of cracking of the rings, culminating in some cases in a catastrophic burst of the ring and extensive damage to the generator have been noted. A major cause of the failures is known to be the susceptibility of the currently used 18 Mn-5 Cr steel to environmentally induced cracking. Data available in the literature indicates that the currently used alloys are quite susceptible to stress corrosion cracking in a variety of environments and that they have reached their limit not only in terms of fracture toughness in adverse environments but also in terms of achievable yield strength levels. The availability of newer materials and/or design concepts may become a limiting factor in the reliability of current machines as well as in the ability to build larger machines requiring larger diameter retaining rings in the future. The present method of fabricating the retaining rings by cold expansion requires special equipment and expertise available only with a few foreign manufacturers and hence has an adverse impact on the price as well as the procurement schedule for the rings. This paper presents a broad overview of the principal materials considerations involved and of the data available on currently used materials. Recent developments aimed at the use of alternate materials will be described. (ERA citation 06:004752)