Transformer Loss Shows Need for Review

Executive summary

A large transformer failed under full load conditions. The arcing and violent fault of the high voltage windings caused a bulging of the tank. Oil escaped and started a fire that was controlled by the deluge system. Internal damage to the transformer was extensive and it took two weeks to replace the unit. Fortunately, the insured had a spare on-site. The replacement cost was significant, but relatively minor compared to the multi-million dollar business interruption loss.

The full article

Transformer Loss Shows Need for Review

The cause of the fault was overheating several days before. The plant had completed a major overhaul. During startup, the transformer was severely overheated because it was taken to full load with cooling fans and cooling pumps out of service. The lack of circulation and cooling severely damaged the transformer's insulation. Ten days later, under full load, the violent failure occurred. A review of the incident reveals an unlikely chain of events during the startup, including a failure to energize the fans and pumps, a failure of the DC control power and faulty logic in the control software.


Some recommendations that may help avoid similar losses:

  1. Assign a transformer-competent person to the plant, who is responsible for monitoring, testing and repairs of all station transformers.
  2. Review unit startup procedures and training. Modify if necessary. Use lock-out /tag-outs when transformer maintenance is performed.
  3. If startup procedures are excessive, consider adding personnel from other plants to provide temporary support.
  4. Failure of the main transformer's auxiliary power supply should activate an alarm. Individual alarms on the transformer should default to "abnormal" instead of "normal" condition.
Disclaimer statement:

All recommendations are general guidelines and are not intended to be exhaustive or complete, nor are they designed to replace information or instructions from the manufacturer of your equipment. Contact your equipment service representative or manufacturer with specific questions.

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