Why do Transformers fail?


Yes, you heard, right. Transformers if left periodically unchecked fails. They need minimum maintenance but do require maintenance to perform year after year successfully. Everything needs maintenance, and so does the transformers. The failures could be because of human failures or could be because of electrical or mechanical reasons.But what are transformers and why they interest us?

What are transformers?

Transformers are the static devices used to step up or step down the voltage across the galvanically isolated primary windings and the secondary windings utilizing the principle of magnetic induction. Electricity is the core of modern life, whether it’s residential, commercial or industrial, and the transformers are the core of the electrical system. So, they are as crucial to as is our life to us. We cannot think of a proper civilization without them.

What is the average life of the transformers?

The transformers are designed to work for 24 hours non-stop, effectively and efficiently up to 40 years but how long they work entirely depends upon how their use. They are static devices, so need very less maintenance but do need maintenance. They are also subjected to failures and mishappenings if not used properly or maintained timely. In the worst case, they can explode too.

What makes the transformer fail?

The transformer’s electrical windings and the magnetic core encounters different forces while in working, depending upon the several factors from the overloading of the transformers to the environment they are operated in. Few of these forces could be-

  1. Expansion or contraction of the windings and the core because of the thermal cycling process.
  2. Local heating of the windings as well as the core, including the enclosure because of the local heating.
  3. Damaging, erratic, and impact forces generated because of the fault current or extreme overloading of the transformer.
  4. Overloading of the transformer could also lead to the excessive heating of inadequate cooling to deteriorate the entire system beyond repair.
  5. Short circuit or continuous sparking at the contacts or somewhere inside in the transformer could lead to Fire in the transformer, which may end up in a huge explosion also.

What Fails in Transformer?

There are many components in the transformer that could result in the transformer’s failure. Let’s take them one by one.

  1. Windings – The windings may fail because of their insulation deterioration. The insulation of the windings may deteriorate because of numerous things such as moisture, overheating, voltage surges, vibrations or mechanical stress arising through faults or some other physical accidents. Once the windings got punctured because of the insulation failure or something else the short circuit of the windings is must without escape.
  2. Load Tap Changers – The tap changers regulate the output voltage of the transformers by changing the turns ratio of the transformers, which is changed by altering the number of turns in one winding. The tap changers are of two types. They could be either on-load tap changer or a de-energized tap changer.These load tap changers could malfunction because of their mechanical switching mechanism leading to erratic results of these LTCs resulting in accidents during operations. The high resistance contacts could be another culprit as they result in sparking at the windings or overheating of the windings. The contamination of insulating oils is another cause leading to failure of transformers.
  3. Bushings – The bushing of the transformers connects the windings to the feeding lines and insulate the supplying lines from the transformer’s main tank. They are generally made up of porcelain.The bushings of the transformers may get cracked by time or general aging. The contaminations and internal moisture also lead to their erratic operations and misbehaviours. The breakdown process of the bushes cannot be detected instantly, and sudden failures of the bushes, as well as the transformers itself, cannot be denied.
  4. Core – The core of the transformers could be subjected to core insulation failure or core overheating because of shorted laminations. The open ground straps could also lead to core problems, which may fail the transformers.
  5. Miscellaneous issues – The various other reasons failing the transformers could be oil contamination, oil leakage, defects in other accessories, harsh operating conditions, insulation deterioration, current transformer’s (CT) failures, etc.
  6. The insulation deterioration increases the propensity of a short circuit in the magnetic flow that produces a constant short circuit current there, which generates excessive heat that could lead to significant failures.

Are all failures slow and planned?

No, all failures are not slow and planned. Dielectric interruptions, abnormal tensions, lightning, short circuits leading to excessive current, physical damages, earthquakes, fires, floods and other natural disasters are few of the failures which are sudden, unplanned and momentary, that can happen any time without reason or control, and could jeopardize the transformer and the entire electrical system any time. Failures could be discovered earlier but not the above ones.

What to do to prevent failure?

Timely maintenance, proper operation, and use of the transformer could prevent the transformer failure and can make it work for years efficiently and effectively. Early diagnosis of faults and in-time action would prevent the failure to a great extent along with downsizing the damages and the losses to minuscule. A careful and detailed analysis of the cause that results in problems pave a long way in enhancing the performance and the life of the transformer.

How to detect failures in the transformers?

The failures could be detected either mechanically or electrically. Some devices are physically attached to the transformers detect the faults mechanically –

  1. Buchholz relay
  2. Pressure rise relay
  3. Pressure relief device

Similarly, some devices are indirectly connected to the various parts of the system to find out the failures electrically-

  1. Differential relay
  2. Overcurrent relay
  3. Ground current relay

But how much maintenance does a transformer need?

The maintenance of transformer broadly depends upon the rating of the transformer, the place where installed in the system, ie, whether it is installed up-stream or down-stream. The other things what matters are, the environment and the general working conditions the transformer is subjected to operate. All the above factors collectively decide the schedule of the maintenance.

Proper procedures should be laid for the regular inspections and routine maintenance of the transformers. Detailed diagnosis, in-depth analysis, regular maintenance, and a scheduled review prevents the transformers failure to a great extent.


The transformers do fail like other equipment and gadgets. Better information about the performance and failures of the transformer leads to longer life of the transformers. Early discoveries of the faults are the second major contributor in overcoming the transformer failures. If the transformers are used as per the manufacturer’s instructions and guidelines, their life can be extended exorbitantly, even beyond the expected and the anticipated life. Transformers being static have very less probability and limited ways to get failed. If properly installed with all precautions and timely maintenance is done as per the planned schedule, you could use them from generations to generations, leave aside years to years.

We, Servostar servo Voltage Stabilizers are an established renowned manufacturer based out of India and are catering to entire pan India in power equipment like Servo Stabilizers and all type of transformers including isolation transformers for domestic households and other industries. We have a proven track record of supplying quality transformers and voltage stabilizers to various industries, commercial setups, residences, and the utility. We do provide consultancies services and customized transformers too.