Core faults in large generators

A core fault is a failure in the laminated core of a large electrical machine. Such faults are relatively rare but when they occur, the value of the machine and its importance mean that the investigation of the failure assumes a high priority. On many occasions the details of such failures assume major commercial significance, therefore failure investigations have, of necessity, to be handled in a confidential manner, touching as they do on the design, manufacture, operation and insurance of large electrical plant. There has therefore been no published literature on core faults. However, the scientific principles of the mechanisms at work have been studied in considerable detail and papers published on those principles in the international literature. This paper brings together that literature and those scientific principles, giving details of the underlying design, constructional and operational factors which affect these faults. New evidence is presented of the underlying factors which allow core faults to initiate and grow. The paper will allow engineers to analyse such faults, draw rational conclusions on the causes for each occasion and devise suitable repair/rebuild strategies applicable to that situation.