How to Handle Transformer Insulation Damage?

Regular Maintenance Cycle for Transformers

Transformer maintenance is classified into major overhaul and minor maintenance based on the nature of the work. For oil-immersed transformers, major overhaul refers to maintenance requiring oil drainage and core lifting (or tank cover lifting), while minor maintenance refers to external inspections, oil replenishment, or oil treatment without oil drainage or core lifting.

1. Major Overhaul Cycle for In-Service Transformers

In accordance with DL/T 573-2010 Guide for Maintenance of Power Transformers, the major overhaul cycle for in-service transformers is stipulated as follows:

(1) The major overhaul interval for transformers shall generally be 10 years or more. However, core lifting maintenance may be performed ahead of schedule if transformer failure occurs during operation or anomalies are detected during preventive tests.

(2) The major overhaul schedule may be adjusted (either advanced or extended) based on the transformer's structural characteristics, manufacturing quality, exposure to through-fault short-circuit currents, daily load profiles, and historical electrical test and oil analysis results. For fully sealed transformers, major overhaul is typically performed only in cases of severe oil leakage or confirmed internal faults.

(3) Major overhaul of the on-load tap-changer shall be carried out upon reaching the manufacturer's specified number of operations, or when defects are identified.

2. Minor Maintenance Cycle for Transformers

Minor maintenance shall be performed every 1 to 3 years. For transformers installed in heavily contaminated environments, the frequency of minor maintenance may be increased.

Handling Transformer Insulation Damage

In-service transformers shall be regularly inspected for oil leakage at all sealing points. The transformer tank shall be kept free of water accumulation to prevent moisture and air ingress that may impair insulation performance.

The oil seal of the transformer breather shall be maintained at the proper oil level and kept clear. The desiccant shall remain dry to ensure effective moisture adsorption.

The explosion-proof diaphragm and pressure relief valve shall be periodically inspected to ensure integrity, preventing direct exposure to atmosphere, which may increase moisture content in the oil and degrade insulation properties.

When replenishing transformer oil, the oil quality in the conservator shall be confirmed as compliant to avoid oil degradation. Refilling oil from the bottom of the tank is prohibited to prevent air and foreign particles (particularly metallic debris) from entering the transformer interior.