Wet Transformers: The Risks of Water Ingress in Oil-Filled Transformers

As an electrical engineer or electrician, you know that transformers play a critical role in power distribution systems.

They step up or step down the voltage of electric power, making it possible to transmit electricity over long distances.

One type of transformer that is commonly used is the oil-filled transformer. These transformers are filled with insulating oil, which helps to cool the transformer and provide electrical insulation.

But what happens if oil transformer gets wet? In this article, I’ll explore the immediate and long-term effects of water ingress, the causes of water ingress, and preventive measures that can be taken to avoid it.

Immediate Effects of Water Ingress

The first thing that happens when water enters an oil-filled transformer is that the cooling system fails.

This is because water is a poor conductor of heat, and it displaces the oil that is responsible for cooling the transformer. As a result, the transformer can quickly overheat and fail.

The second immediate effect of water ingress is electrical insulation breakdown. Water is a conductor of electricity, and when it enters the transformer, it can cause the insulation to break down, leading to short circuits and other electrical faults.

The third immediate effect of water ingress is the corrosion of metal parts. When water comes into contact with metal parts, it can cause rust and other types of corrosion, leading to the deterioration of the transformer components.

Long-Term Effects of Water Ingress

The long-term effects of water ingress are even more serious than the immediate effects. One of the most significant long-term effects is the degradation of oil quality.

When water enters the transformer, it can cause the oil to become contaminated, leading to a reduction in its effectiveness as an insulator and coolant. Over time, this can lead to the failure of the transformer.

Another long-term effect of water ingress is an increased risk of fire and explosions. This is because the combination of water and electrical equipment can be highly combustible.

If water enters the transformer and comes into contact with an electrical fault, it can cause a fire or explosion.

Finally, water ingress can cause structural damage to the transformer components. When water enters the transformer, it can cause the metal components to swell or contract, leading to cracks and other types of damage.

Causes of Water Ingress in Oil Transformers

There are several natural and man-made causes of water ingress in oil transformers. Some of the most common natural causes include rainwater, floods, and humidity.

In areas with high humidity, moisture can accumulate inside the transformer, leading to water ingress.

Man-made causes of water ingress include human errors, equipment failure, and sabotage. Human errors such as improper installation or maintenance can cause water ingress.

Equipment failure such as leaks or faults can also cause water ingress. Finally, sabotage can be a deliberate act to cause water ingress and damage to the transformer.

Preventive Measures to Avoid Water Ingress

Preventive measures can be taken to avoid water ingress in oil transformers. These include design considerations, maintenance practices, and emergency response plans.

Design considerations include proper placement of transformers, adequate enclosure design, and waterproofing and sealing of transformer components.

By ensuring that transformers are properly placed and protected from water ingress, the risk of damage can be significantly reduced.

Maintenance practices such as regular inspections, prompt repairs of leaks and faults, and replacement of worn-out parts can also help to prevent water ingress. By keeping transformers in good working condition, the risk of water ingress can be minimized.

Emergency response plans are also critical in preventing water ingress. Contingency plans for flooding and quick response to water ingress incidents can help to minimize the damage caused by water ingress.

Safety protocols for handling damaged transformers can also help to prevent accidents and injuries.


Water ingress in oil-filled transformers can have severe immediate and long-term effects on the transformer components, including the breakdown of insulation, corrosion, and even explosions.

Preventive measures such as proper design considerations, maintenance practices, and emergency response plans can help to minimize the risk of water ingress and its damaging effects.

It is important for electrical engineers, electricians, and safety engineers to be aware of the causes and effects of water ingress and to take proactive measures to prevent it.

By doing so, they can ensure that power distribution systems remain safe, reliable, and efficient.

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