7 most common transformer faults and issues

A transformer is a device that steps up or steps down electrical voltages. Transformers are an important factor in electrical systems. It is clear that faults are common everywhere. In this article, we will discuss different types of transformer faults.

As an electrical engineer, I made many electrical maintenance jobs for electrical transformers. Now it’s time to share my experience with you.

Different types of Transformer faults

Transformer faults include earth, Interturnes, tank, Phase 2 phase, and open circuit faults.

Overheating fault

One of the common issues that you can face with transformers is that the temperature gets high. This issue has some causes which you should check step by step to overcome it.

  1. The cooling fans are not working properly. Check fans and oil pumps if found.
  2. The radiator is not clean. Check it and remove any dirt, dust, or plastic bags.
  3. Overcurrent, check the current of the TR and reduce loads if necessary to be suited to the rated current of the tr.
  4. Hot day, The surrounding atmosphere’s temperature affects the TR temperature. If so, increase cooling stations.
  5. Low oil level, Oil’s main purpose is cooling the transformer, checking the level, and increasing the oil. But check for any leakage.

I have a detailed article about Transformer temperature rise, read it for more information.

 Earth Faults

Earth faults occur due to the earthing of transformer windings to the ground. In this case, the current depends upon the value of earthing impedance.

Earth fault also occurs when the winding turns come between the neutral and fault point.

There are different conditions during the earth fault conditions. In the first case, the current flows into and out of windings.

While in the second case, the ampere-turns balance is maintained between windings.

 Interturnes faults

This type of transformer fault is caused due to the winding turns flashover by line surges. When a number of turns in the same winding short circuit. A decrease in the terminal current occurs. This type of fault is also referred to as a winding short circuit fault.

  How to discover this fault?

One of the following signs is expected in this fault.

  • Over-current in the primary side.
  • Overheated transformer.
  • Buchholz relay operation.


The common causes are:

  •  Lightning strike.
  • Overloading the TR.
  • Low oil level.
  • Transformer aging.
  • Low winding insulation.

Tank Faults (oil level)

damaged transformer tank
mechanical damage of transformer tank

This type of fault is related to the oil in the transformer. When the oil reduces in tanks, it causes winding insulation reduction. Tank fault causes an abnormal temperature rise in the transformer.

This oil loss usually happens due to leakage, While the leakage can be checked visually on the tank body.

   The most common reason for the leakage is:

  1. Loss of tightening of tank body screws.
  2. Corrosion at the tank body.
  3. mechanical damage due to a strong hit to the tank body.

So making periodic visual inspection is important to discover any leakage early. For more in formation about oil leak read my article about transformer oil here.

Phase to phase Faults

These are common-to-earth faults. It occurs due to the phase disturbance of the transformer. However, these types of Faults are rare to occur.

 How to discover it?

In this case, the protection devices will work to isolate the transformer, and the oil will flow out of the tank body.

     Causes of a short circuit fault

  • Low oil level.
  • Bad oil because of water containment.
  • Aged transformer.
  • High voltage due to electric surge or lightning.

Open Circuit faults:

In this type of fault, abnormal heat is produced inside the transformer. As a result, the transformer heats up.

If the fault continues it is necessary to disconnect the transformer from the system to avoid any inconvenience.

       How to discover an open circuit fault?

  • In this case an arcing sound inside the transformer.
  • Measuring the current of each phase will indicate that the open circuit phase current is not equal to the other two phases.
  • performing resistance tests for all three phases by low DC voltage. The resistance of the faulty phase will be greater than the others.

Bushings flashover

This fault happens due to polluted bushings body, or due to lightning strikes.

  • Making regular visual inspections and cleaning the bushings will reduce this fault.
  • Also, check the lightning protection system.

We hire a hot washing company to wash all transformer bushings and OHTL insulators. They use water to do this job.

For more information about OHTL Maintenance read my article here.

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