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7 Common Causes of Transformer Faults and How to Prevent Them

Causes of Faults in Transformers

Transformers are critical components in electrical power systems, and their failure can lead to significant operational disruptions. Various factors contribute to transformer faults, which can be classified based on their origin and impact. Here are some of the most common causes of transformer faults:

 

1. Winding to Core Faults (Insulation Failure)

One of the most common transformer faults occurs due to weakening of insulation between the winding and core. Over time, insulation deteriorates due to aging, overheating, or moisture, leading to short circuits.

Key Points:

  • Phase to phase faults inside transformers are rare.
  • Faults may occur at terminals, which are within the transformer protection zone.

2. On Load Tap Changer (OLTC) Faults

Power transformers are often equipped with an On Load Tap Changer (OLTC) to regulate voltage levels. This component is prone to mechanical failures, contact wear, or improper operation, leading to transformer faults.

Key Points:

  • OLTC gear failure can cause arcing and voltage fluctuations.
  • Regular maintenance is required to ensure proper OLTC functioning.

3. Oil Leakage in Oil Immersed Transformers

Large transformers are oil immersed for cooling and insulation. However, oil leakage can occur due to damaged gaskets, loose connections, or cracks in the transformer body.

Key Points:

  • Oil leakage leads to reduced insulation and increases the risk of internal faults.
  • Continuous oil loss can result in transformer overheating and eventual failure.

4. Inrush Current During Switching

When a transformer is switched on without load, it experiences a high inrush current that contains harmonic distortions. This inrush current can be several times higher than the rated current, causing stress on the windings and protection relays.

Key Points:

  • Inrush current can damage insulation over time.
  • Transformer differential protection relays should be set to differentiate inrush currents from internal faults.

5. Inter Turn Faults (Hot Spots in Windings)

A transformer may develop inter turn faults, where short circuits occur between turns of the same winding. This leads to localized overheating or hot spots, which further degrade insulation and increase the risk of complete failure.

Key Points:

  • Overheating at specific locations weakens insulation over time.
  • Preventive maintenance and thermal monitoring help detect early stage faults.

6. Over Fluxing Due to Voltage and Frequency Imbalance

Transformers experience over fluxing when the ratio of voltage to frequency (V/f) exceeds the designed limit. This occurs due to:

  • Under frequency operation at rated voltage.
  • Overvoltage conditions at rated frequency.

Over fluxing leads to excessive core heating, increasing the risk of damage.

Key Points:

  • Over fluxing results in excessive noise and vibration in the core.
  • Transformers should be protected by flux relays to detect over excitation conditions.

7. Sustained Overload Conditions

Continuous overloading of a transformer beyond its rated capacity leads to excessive heating, insulation degradation, and reduced lifespan.

Key Points:

  • Overloaded transformers can overheat and trip due to thermal protection.
  • Proper load management and cooling system maintenance are essential.

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