Large mill power outages caused by potential transformer ferroresonance

Investigative procedures relating to a subtle 30 Hz ferroresonant instability of high-voltage potential transformers, which has caused several costly power outages to a large paper mill are reported. Included are unusual field oscillograms of this instability. Corrective measures were developed which have been implemented. An alternate recommended approach is to be incorporated in a similar high-voltage supply to a new mill to eliminate this instability as a possible jeopardy to selective ground-relay protection.<
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