What are the fault classifications of transformers?

Faults in oil-immersed power transformers are generally divided into two main categories: internal faults and external faults. Internal faults primarily occur within the transformer's oil tank, including phase-to-phase short circuits between winding groups, turn-to-turn short circuits between winding turns, and grounding faults caused by winding or lead wires touching the outer casing. External faults mainly occur on the external insulation bushings and lead wires of the transformer's oil tank, involving flashovers or fractures of insulation bushings leading to grounding short circuits through the outer casing and phase-to-phase faults between lead wires, which may lead to internal faults or deformation of windings.

Internal faults of transformers can be broadly categorized into two types based on their nature: thermal faults and electrical faults. Thermal faults typically involve localized overheating and temperature rise within the transformer. Depending on the severity, thermal faults can be classified as mild overheating (generally below 150°C), low-temperature overheating (150–300°C), moderate-temperature overheating (300–700°C), and high-temperature overheating (generally above 700°C). Electrical faults usually refer to the degradation or deterioration of insulation performance within the transformer under the influence of high electric field intensity. Based on different energy density levels of discharges, electrical faults can be further classified into partial discharge, spark discharge, and high-energy arc discharge.

Due to the broad scope of transformer faults, they can be classified from different perspectives. Circuit-wise, faults may include circuit faults, magnetic circuit faults, and oil circuit faults. Structurally, faults may involve winding faults, core faults, oil-related faults, and accessory faults. Additionally, considering common fault-prone areas, classifications may include insulation faults, core faults, tap changer faults, and others. Among them, the most severe and frequent is the transformer's output short circuit fault. Other types of faults include transformer leakage faults, oil flow electrification faults, protection misoperation faults, etc. These different types of faults may reflect thermal faults, electrical faults, or a combination of both, while transformer leakage faults may not exhibit typical thermal or electrical fault characteristics under normal circumstances.

LuShan, est. 1975,  is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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