What failure modes are possible in a transformer? How to identify and fix these failures?

Transformers are critical components in power systems, and various failure modes can affect their operation. Timely identification and resolution of these failure modes are essential to prevent costly downtime and ensure system reliability. Below are some common transformer failure modes, along with methods to identify and address them:

• Insulation Failure
  Identification: Insulation failure leads to decreased insulation resistance, which can be detected through insulation resistance testing (megger testing).
  Repair: Replace or repair damaged insulation materials as necessary, including bushings, leads, or entire windings. Investigate the root cause of insulation failure, which may be due to overheating, moisture ingress, or contamination.

• Overheating
  Identification: Overheating may result from overloading, inadequate cooling, or loose connections. High temperatures can be detected using temperature sensors and infrared thermography.
  Repair: Reduce load within the transformer’s rated capacity, ensure proper cooling, and tighten loose connections. Consider redesigning the cooling system if necessary.

• Core Saturation
  Identification: Core saturation occurs when the magnetic core reaches its limit, causing output waveform distortion. This can be observed through harmonic distortion in current and voltage waveforms.
  Repair: Install harmonic filters to mitigate core saturation. Evaluate whether a different core material or design is needed to prevent saturation.

• Winding and Core Damage
  Identification: Visual inspection may reveal physical damage such as cracks, warping, or deformation in windings or the core.
  Repair: Repair or replace damaged components. Minor winding damage may be repaired locally, while severe damage may require rewinding or core replacement.

• Oil Contamination and Degradation
  Identification: Oil analysis, including Dissolved Gas Analysis (DGA), can detect contaminants and gases generated during incipient faults. Darkened or foaming oil may also indicate problems.
  Repair: Replace contaminated oil and address the root cause of contamination. Consider upgrading to environmentally friendly and less flammable insulating fluids if applicable.

• Bushings and Gasket Leaks
  Identification: Oil leaks can be visually observed, especially around bushings and gaskets.
  Repair: Repair or replace damaged bushings and gaskets. Tighten connections and ensure proper sealing.

• Short Circuits
  Identification: Short circuits cause overcurrent and may produce distinctive sounds. Protective relays should trip due to the short circuit.
  Repair: Investigate the cause of the short circuit, repair damaged components, and replace any affected winding sections.

• Tap Changer Problems
  Identification: Tap changer failures may cause voltage regulation issues or arcing in No-Load Tap Changers (NLTC). Monitoring voltage variations helps identify tap changer problems.
  Repair: Clean, lubricate, and maintain the tap changer. If significant issues persist, consider repairing or replacing it.

• Moisture Ingress
  Identification: Moisture ingress can be detected through moisture content analysis. Visual inspection may also reveal signs of moisture damage, such as rust or corrosion.
  Repair: Address the source of moisture ingress, repair or replace damaged components, and maintain proper sealing.

Regular preventive maintenance is crucial, including visual inspections, oil sampling, and insulation resistance testing, to detect potential issues early. Additionally, consider employing condition monitoring techniques such as online monitoring and partial discharge testing to continuously assess transformer health. Timely maintenance and repairs help extend transformer lifespan and prevent costly failures.