When a transformer exhibits discharge abnormalities, the following causes may be involved:
1. Insulation Aging or Damage
Aging of Insulation Materials: Over time, the insulation materials in a transformer can deteriorate, leading to a decrease in dielectric strength, which can trigger discharge phenomena.
Moisture in Insulation: Insulation materials that absorb moisture will see a reduction in insulation performance. This is particularly critical in oil-immersed transformers, where moisture in the oil can severely impair insulation, leading to discharge abnormalities.
Mechanical Damage: During installation or transportation, the transformer's insulation structure may be subjected to mechanical impacts or damage, causing insulation failure and leading to discharge.
2. Winding Issues
Winding Short Circuits: If there is a short circuit between turns or layers of the winding, it can lead to an increase in local electric field intensity, causing partial discharge or more severe insulation breakdown.
Loose Windings: The windings may become loose due to vibration or thermal expansion and contraction during operation, resulting in uneven electric field distribution and localized discharge.
3. Core Grounding Issues
Poor Core Grounding: The transformer core usually requires grounding. If the core is poorly grounded or ungrounded, it may discharge under high electric fields.
Discharge in Core Clamps: If the core clamps or other metal attachments are inadequately insulated or loose, they can also discharge under high electric fields.
4. Deterioration of Oil Quality
Insulating Oil Deterioration: The insulating oil in a transformer can oxidize or become contaminated over time, reducing its dielectric strength and making it prone to corona discharge or breakdown discharge.
Bubbles in Oil: Bubbles in the insulating oil can lead to high local electric field intensity, causing corona discharge or partial discharge.
5. External Contamination
External Environmental Contamination: If the surfaces of external insulators or bushings are contaminated with dust, salt fog, moisture, etc., surface discharge is likely to occur under high humidity or high voltage conditions.
Corona Effect: Particularly in high-voltage transformers, if there are sharp points or uneven surfaces on terminals or other exposed conductors, corona discharge is likely to occur.
6. Design or Manufacturing Defects
Uneven Electric Field Distribution: If the transformer design does not adequately account for electric field distribution, areas with excessively high electric field intensity may develop, leading to discharge phenomena.
Manufacturing Defects: Defects such as material flaws or insufficient machining precision can lead to partial discharge, such as burrs on winding edges or sharp edges on core laminations.
7. Overvoltage or Electrical Stress
Lightning Strikes or Switching Overvoltage: Lightning strikes or switching overvoltage in the power system can cause partial discharge or insulation breakdown inside the transformer.
Prolonged Overload: Long-term overload operation can raise the internal temperature of the transformer, accelerating insulation material aging and increasing the risk of discharge.
8. Improper Installation and Maintenance
Problems During Installation: If installation procedures are not strictly followed, it may result in insulation damage or poor grounding, increasing the risk of discharge.
Untimely Maintenance: If potential insulation issues are not detected and addressed in a timely manner during transformer operation, such as through Dissolved Gas Analysis (DGA) not identifying problems early, discharge phenomena may gradually worsen.
Summary
Discharge abnormalities in transformers are a serious issue that can arise from various factors such as insulation aging, winding faults, core grounding issues, oil quality deterioration, external contamination, design or manufacturing defects, overvoltage, electrical stress, and improper installation or maintenance. Timely detection and resolution of these issues are critical to ensuring the safe and reliable operation of the transformer.
