Common Failure of Hermetically Sealed Transformers and Repair Methods

The most common failure in hermetically sealed transformers is insulation breakdown, which can be caused by moisture ingress, thermal cycling, and electrical stress. This issue can lead to short circuits, overheating, and ultimately transformer failure. Understanding these causes and the repair process is crucial for maintaining the reliability and safety of these devices.

Causes of Insulation Breakdown

Hermetically sealed transformers, despite providing excellent protection against atmospheric contaminants, can still be affected by several factors that lead to insulation breakdown:

Moisture Ingress

Even hermetically sealed transformers can experience moisture accumulation due to temperature fluctuations. This can disrupt the electrical insulation, leading to a breakdown.

Thermal Cycling

Repetitive heating and cooling cycles can put significant stress on the insulation materials, causing them to degrade over time.

Electrical Stress

High voltage spikes can exceed the breakdown voltage of the insulation, leading to degradation and eventual failure.

Repairing Insulation Breakdown

Repairing a hermetically sealed transformer is a complex process and often requires professional intervention. Here are the general steps involved in the repair process:

Assessment

Perform a thorough inspection to determine the extent of the damage. Use insulation resistance testing (e.g., megohmmeter) to assess insulation integrity.

Decommissioning

Disconnect the transformer from the power supply and remove it from service to ensure safety.

Opening the Transformer

Carefully open the hermetic seal, which may involve cutting or unscrewing the casing. Take precautions to protect any sensitive internal components.

Replacing Insulation

Remove damaged insulation materials. Replace with new insulation that meets the original specifications. Ensure that the new insulation is properly dried and free of contaminants.

Reassembly and Sealing

Reassemble the transformer components. Re-establish the hermetic seal using appropriate sealing methods (e.g., welding, gaskets).

Testing

Conduct thorough testing, including insulation resistance tests and functional tests, to ensure the transformer operates correctly.

Reinstallation

Reinstall the transformer and monitor its performance closely after returning it to service.

Preventive Measures

To reduce the likelihood of future failures, consider the following preventive measures:

Regularly inspect and maintain the transformer. Monitor temperature and humidity levels in the installation environment. Implement surge protection and voltage regulation to minimize electrical stress.

Given the technical complexity and safety risks involved, it is often advisable to consult with or hire professional repair services for hermetically sealed transformers.