7 most common transformer faults and issues

7 most common transformer faults and issues
7 most common transformer faults and issues

A transformer is a device that step up or step down electrical voltages. Transformers are an important factor of 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 its time to share my experience with you.

Different types of Transformer faults

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

Overheating fault

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

  1. Cooling fans are not working properly. Check fans and oil pumps if found.
  2. 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 temperature affect the TR temperature. If so, increase cooling stations.
  5. Low oil level, Oil main purpose is cooling the transformer, check the level and increase the oil. But check for any leakage.

 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 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 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 winding short circuit faults.

  How to discover this fault?

One of the following signs are 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)

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 of 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 of the leakage is:

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

So making periodic visual inspection is important to discover any leakage early.

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 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 produce 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 open circuit fault?

  • In this case an arc sound inside the transformer.
  • Measuring current of each phase will indicate that the open circuit phase current is not equal to the other two phases.
  • performing resistance test 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 inspection and cleaning the bushings will reduce this fault.
  • Also check lightning protection system.

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