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

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. It steps high voltage/low current flows in the primary side winding 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 for these stresses. This causes the breaking of the windings or the burn-out. The winding fault PN number is usually between 6 to 30.

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, it uses paper insulators surrounded by oil that provides further insulation. In addition, bushing failure usually occurs over time. Bushes failure PN number is between 24 to 48.

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. It laminates the cores of the transformers 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 because of eddy-current

Tank Failures:

The function of the tank in the transformer is to be a container for the oil used in it. It uses the oil in the tank for insulation and cooling. We can also use the tank as a support for other equipment of the transformer. The PN number for the failure is 18. The fault in the tank occurs because of environmental stress, corrosion, high humidity and sun radiation resulting in leakage or cracks in the tank walls

Cooling system failure:

Cooling system reduces the heat produced in transformers because of 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 affects different parts of the transformer and also causes it to build more gas pressure inside which may cause the transformer to blow. The PN is between 26 to 48.

Measures taken to prevent transformers failure

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.

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.

Control wiring (annually):

we should check Control wiring to ensure that wire insulation is in good condition and inspect the control cabinet & associated conduit to ensure that weather seals are intact. We should check control power supply voltage.

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.

Bushing and surge arrester insulators (annually):

Bushing and surge arrester insulators should be clean. If the surfaces are excessively dirty, we should clean them as it does not energize the transformer.


In conclusion, this article helps you to study 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. Get in touch with Apollo power system.




Pooja R

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