Importance of periodic inspection of power transformers

Why periodic inspection of transformers is important


The transformer is a static device, thus it requires less attention but with proper periodic inspection & diagnostics, it would be possible to avoid the unwanted breakdown. A transformer is the heart of the power network, the maximum availability of it and also to meet the full lifetime of a transformer is a matter to think of.

The top 5 factors that affect the transformers performers are as follows

  1. Winding failure: Windings are an important part of a transformer. In distribution side transformers there are commonly two windings. One of the primary side and the second on the secondary side. High voltage/low current flows in the primary side winding and through electromagnetic induction voltage is stepped down and current stepped up in the secondary side winding. These windings withstand dielectric, thermal and mechanical stress during this process. The faults that occur in the winding are due to these stresses. This causes the breaking of the windings or the burn-out. The winding fault PN number is usually between 6 to 30.
  2. Bushing Failure: Bushes are insulating devices that insulate a high voltage electrical conductor to pass through an earth conductor. In transformers, it provides a current path through the tank wall. Inside the transformer, paper insulators are used which are surrounded by oil that provides further insulation. Bushing failure usually occurs over time. Bushes failure PN number is between 24 to 48.
  3. Core failure: The transformers have laminated steel cores in the middle surrounded by the transformer windings. The function of the core is to concentrate the magnetic flux. Fault in the core directly affect the transformer windings, causing faults in them. The cores of the transformers are laminated to reduce eddy-current. The lamination of the core can become defected by poor maintenance, old oil or corrosion. The breakdown of the smallest part of the lamination results in an increase of thermal heat due to eddy-current
  4. Tank Failures: The function of the tank in the transformer is to be a container for the oil used in it. The oil in the tank is used for insulation and cooling. The tank can also be used as a support for other equipment of the transformer. The PN number for the failure is 18. The fault in the tank occurs due to environmental stress, corrosion, high humidity and sun radiation resulting in leakage or cracks in the tank walls
  5. Cooling system failure: Cooling system reduces the heat produced in transformers due to copper and iron losses. The cooling system contains cooling fans, oil pumps, and water-cooled heat exchangers. The failure in the cooling system causes the heat to build up in the transformer which effects different parts of the transformer and also causes more gas pressure to be built inside which may cause the transformer to blow. The PN is between 26 to 48.

Measures taken to prevent transformers failure

  1. Gauge readings (once in a month): Gauge readings, ambient temperature, and kvA load should be measured and recorded. Any abnormal reading suggests that further diagnostic testing or inspection should be done. If pressure/vacuum gauge and/or fluid level gauge readings suggest a possible tank leak, perform a pressure test according to instructions. Tank leaks must be repaired immediately to prevent serious damage to the transformer and danger to life.
  2. Cooling fans (annually): Check the cooling fans (if any) by setting the fan “auto/manual” control switch to the “manual” position. The fans should rotate at full speed within approximately five seconds. The fans should rotate smoothly with minimal vibration.
  3. Control wiring (annually): Control wiring should be checked to ensure that wire insulation is in good condition. The control cabinet and associated conduit should be inspected to ensure that weather seals are intact. Control power supply voltage should be checked.
  4. Paint finish (annually): Inspect the paint finish for damage or weathering that exposes the primer coat or bare metal. Repair any paint damage that might be found.
  5. Bushing and surge arrester insulators (annually): Bushing and surge arrester insulators should be clean. If the surfaces are excessively dirty, they should be cleaned while the transformer is not energized.


In this article, you have studied the factors that affect transformers and measures to avoid transformer failure. If you are looking for installing a power transformer, Apollo can help you with it. Feel free to get in touch with us at




Pooja R

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