Why Do Electrical Transformers Fail?

Why Do Electrical Transformers Fail?

Why Do Electrical Transformers Fail?

Why do electrical transformers fail? Well electrical transformers play a crucial role in modern society by enabling efficient transmission and distribution of electricity. These essential devices serve as intermediaries between power stations and end-users, stepping up or down voltage levels as needed. However, despite their necessity, transformers are not immune to failures. In this blog post, we will explore the underlying reasons why electrical transformers fail, shedding light on the various factors that can lead to their untimely demise.

Let’s start off with some statistics, cool right? Yes, it is! It’s quite insightful to see. The first graph we will show is a pie graph from “edtengineers.com”. The pie graph shows why failures occurred for 112 transformer failures in Germany, Austria, Switzerland, and the Netherlands. The largest portion of failures at 25% is “other”. Unfortunately, the “other” category is unknown failures, but looking at the next two categories they are “aging” and design. Design failures typically happen near the beginning of service for a transformer, while aging is obviously happening later in their service life.


One of the many good things about this is that with UTB’s reconditioned electrical transformers we can nearly negate the design failure statistic. The units that we recondition have been tested in the field for years. The aging of the units is set back because of the oil service that is also included in the reconditioning process. If you’d like to learn more about the up sides of our electrical transformers, feel free to read our other post about The True Power of Reconditioned Electrical Transformers.

In the next graph we can see how much more service life you can get out of simple oil services. 

Number of Oil Services

The numbers are very interesting to see. The average service life is nearly doubled just because of servicing the oil. This is caused by the oil breaking down over time, this is why we change the oil in an engine of a car. The difference is that the oil in an engine is to serve as a lubricant versus in a transformer it is used for insulation and cooling. The lubrication factor of oil is decreased as the oil breaks down in a car. In an electrical transformer the oil breaks down and the cooling and insulation factors decrease.

1. Overheating

One of the primary culprits behind transformer failures is overheating. Transformers, by design, experience losses during the process of stepping up or down voltage. These losses, such as resistive and magnetic losses, generate heat. That’s why they have insulating oil. Like we talked about before, as the oil breaks down the cooling factor of the oil breaks down over time. The overheating of the transformer can be accelerated by higher temperature climates. Allowing the electrical transformer to get hotter and hotter until it is too much for them to handle.

2. Insulation Degradation

Insulation materials inside transformers, such as paper, pressboard, or liquid dielectrics, are essential for preventing electrical breakdown and ensuring safe operation. However, over time, these materials can deteriorate due to factors like moisture absorption, thermal stress, and chemical interactions. As insulation weakens, it loses its ability to withstand high voltages, increasing the risk of internal short circuits.

3. Electrical Overloading

Transformer overloading is a common problem that occurs when the transformer is subjected to electrical currents beyond its rated capacity. Prolonged overloading can cause excessive heating, leading to the issues mentioned earlier, such as insulation degradation and overheating. Overloading can be a result of increased electricity demand, improper load management, or system malfunctions.

4. Contamination and Moisture

Contaminants and moisture are silent enemies of electrical transformers. External contaminants, like dust, dirt, and pollutants, can infiltrate the transformer’s core and windings. They act as conductive paths for electricity, leading to electrical breakdown and eventual failure. Similarly, moisture can penetrate the transformer’s insulation, causing it to deteriorate rapidly.

5. Electrical Surges and Faults

Electrical surges and faults, caused by lightning strikes, switching operations, or faults in the power grid, can expose transformers to sudden, intense electrical stresses. These events can lead to insulation breakdown, winding damage, and other issues, ultimately leading to transformer failure.


In conclusion electrical transformers can last a very long time, but that can only happen if you take good care of the units. As we saw earlier the oil servicing can lead to a fantastic bump in the average service life. It is well worth taking care of these marvelous machines. With all the different ways a transformer can fail, it may also be a good idea to have backups in case of an emergency. This can prevent longer than needed black outs. UTB Transformers is dedicated to great customer service. Our transformers, whether they are new, used, reconditioned, or rewound are great options. Feel free to explore our website for more information on our products and services. If you are wanting a quote for a pad mounted transformer, pole mounted transformer, or any other sort of power equipment, please feel free to reach out to us. You can send us a request on our website, call in at 855-214-0975, or email us at [email protected].