What are the methods to deal with a current transformer that has become severely damp?
Jul 08, 2026| I. Mild to Severe Moisture Insulation (Insulation Resistance 50~100MΩ, Dielectric Loss 1%~2%): On-site Drying Treatment
Suitable for dry-type and oil-paper insulated instrument transformers. No factory return required; on-site treatment is possible:
1. Hot Air Circulation Drying Method: Disassemble the instrument transformer junction box and base ventilation holes. Circulate dry hot air at 100~120℃ into the windings. Continue drying for 24~48 hours, measuring the insulation resistance every 6 hours. Stop drying after three consecutive stable insulation resistance measurements.
2. Short-Circuit Current Drying Method: Short-circuit the secondary winding. Apply a small current to the primary side for heating, controlling the winding temperature to not exceed 85℃. Continue drying until the insulation resistance stabilizes and meets the standard. Suitable for small and medium-sized instrument transformers with windings.
3. Vacuum Drying Method: Place the instrument transformer in a vacuum chamber, evacuate, and then introduce dry nitrogen gas at 100~110℃. Dry for 24~36 hours. This method deeply removes moisture and is more effective than ordinary hot air drying. Suitable for epoxy dry-type instrument transformers. After drying, insulation resistance, withstand voltage, and dielectric loss tests must be repeated. Only after all tests pass can the transformer be put back into operation.
II. Severe Moisture Accumulation in Oil-Immersed Transformers: Oil Treatment + Drying Integrated Treatment
Moisture in oil-immersed transformers can penetrate the insulating oil and insulating paper, requiring comprehensive treatment:
1. Oil Drainage and Vacuum Drying: Drain the old insulating oil, evacuate the transformer body, heat to 100-105℃ and maintain for 24 hours to extract moisture absorbed by the insulating paper.
2. Insulating Oil Regeneration Treatment: After filtering, vacuum dehydration and degassing the old oil, and testing for trace moisture and passing the breakdown voltage test, re-inject it into the transformer and let it stand for 24 hours to release the fumes.
3. Seal Replacement: Replace all aged sealing rings, re-seal the enclosure to prevent moisture re-entry, and only after all tests pass can the transformer be put back into operation. III. Severe Moisture Infestation (Insulation Resistance < 50MΩ, Dielectric Loss > 2%, Winding Mold): Categorized Treatment
1. New Products/Service Life < 10 Years: Return to factory for disassembly and repair. Rewind the windings, replace the insulation material, and perform a full set of factory tests after repair. If qualified, it can be reused. The cost is only 30%~50% of that of new products.
2. Old Equipment (Service Life > 15 Years): Replace directly with new products. The insulation of old equipment is already aged, and its performance is unstable after repair, posing a high risk of long-term operation. Replacement is more economical and safer.
3. Dry-type Epoxy Resin Current Transformers: If moisture has penetrated into the epoxy resin, causing cracking, whitening, and peeling, repair is difficult, and the insulation performance cannot be restored to the original level. Direct replacement is recommended.
IV. Emergency Temporary Treatment (Scenarios Where Power Supply Needs to Be Restored Immediately)
If the site does not have drying conditions, temporary treatment can be performed to restore power supply:
1. Use a heating rod to continuously heat the body to remove surface moisture and increase the insulation resistance to a qualified range.
2. Place a desiccant inside the junction box to absorb moisture and maintain insulation performance in the short term.
3. After temporary commissioning, a planned power outage must be scheduled for formal drying or replacement treatment. Prolonged operation with defects is not permitted.
Post-treatment Acceptance Requirements
Regardless of the treatment method used, the following conditions must be met after treatment: insulation resistance ≥ 1000MΩ, absorption ratio ≥ 1.3, dielectric loss ≤ 0.8% (oil-immersed), and no breakdown in the power frequency withstand voltage test before formal commissioning.
