Oil-immersed transformers have a simple system called a transformer breather!
This system lets the transformer oil expansion process happen during load peaks. Let’s discuss transformer breather in this article.
Table of Contents
What is a Transformer Breather?
A “Transformer Breather” refers to a component used in electrical transformers to manage changes in the volume of oil or insulating liquid inside the transformer tank due to temperature variations.
Transformers are essential in the electrical distribution and power transmission systems to step up or step down voltage levels. They consist of a core and coils immersed in insulating oil or liquid to dissipate heat generated during operation.
The insulating oil within the transformer tank can expand and contract with temperature changes, which can lead to the creation of a vacuum or pressure inside the tank.
To prevent excessive pressure buildup or the entry of air and moisture into the transformer, a transformer breather is used.
A transformer breather typically consists of a cylindrical container filled with a moisture-absorbing desiccant material, such as silica gel. This container is connected to the transformer tank through a pipe.
When the transformer oil contracts due to lower temperatures, the air is drawn into the transformer tank through the breather, passing through the desiccant material, which removes moisture from the incoming air. Conversely, when the oil expands as temperatures rise, excess air inside the tank is expelled through the breather.
By regulating the exchange of air with the outside environment and removing moisture, a transformer breather helps maintain the integrity of the insulating oil and prevents the formation of moisture-related problems, such as dielectric breakdown or the formation of sludge and corrosive compounds within the transformer.
What is the transformer breathing Process?
The transformer breathing process, also known as the “breather operation” in electrical transformers, is a crucial mechanism for managing changes in the volume of insulating oil or liquid inside the transformer tank due to temperature variations.
This process helps maintain the integrity of the transformer’s insulation system and prevents the entry of moisture and air, which can degrade the transformer’s performance and longevity.
Here’s a step-by-step explanation of the transformer breathing process:
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Temperature Change: Transformers experience temperature variations during normal operation. When the transformer’s temperature rises, the insulating oil inside the tank expands, and when the temperature drops, the oil contracts.
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Breather Installation: A transformer breather is installed on the transformer tank. The breather typically consists of a cylindrical container filled with a moisture-absorbing desiccant material, such as silica gel. The breather is connected to the transformer tank through a pipe.
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Expansion and Contraction: As the oil inside the transformer tank expands due to higher temperatures, it creates excess pressure inside the tank. Conversely, as the oil contracts due to lower temperatures, it creates a vacuum inside the tank.
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Air Exchange: When the transformer experiences an increase in temperature and pressure inside the tank, the breather allows ambient air to be drawn into the transformer through the desiccant material. This incoming air passes through the desiccant, removing moisture and other impurities. The desiccant acts as a drying agent, preventing moisture from entering the transformer.
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Pressure Release: When the transformer’s temperature drops, causing the oil to contract and create a vacuum inside the tank, the breather allows excess air from inside the tank to be expelled. This prevents the tank from collapsing due to the vacuum and ensures that the internal pressure remains within safe limits.
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Moisture Control: The desiccant material in the breather continues to absorb moisture from the incoming air, ensuring that the insulating oil remains dry and free from contaminants. This helps maintain the dielectric properties of the oil and prevents moisture-related issues.
A small amount of transformer oil is used in a small cab in the breather. Let’s find out why.
Why is Transformer Oil Used in Breather?
A simple, but effective protection method, for both transformer oil and silica gel, is using an oil cap, or transformer breather oil cup, at the bottom of a breather, and serves two purposes.
- Firstly, it absorbs the dust particles that are present in the air during the breathing process.
- Secondly, it acts as a barrier between silica gel and air when there is no breathing in or out.
Do All Transformers Have Breathers?
Not all transformers require breather and conservator tanks.
Breathers are essential for transformers where the breathing in and out could cause oil to escape.
Dry-type transformers don’t use oil, so they don’t require breathers. Similarly, hermetically sealed transformers don’t have breathers because they are completely sealed, with no connection to the outside atmosphere.
For heat dissipation, corrugated fins are used in place of breathers. These fins provide enough flexibility to accommodate oil expansion without the need for external air exchange.
Similarly, Current Transformers (CT) and Potential Transformers (PT) which are dry type transformers, there is no need of breathers as temperature inside the transformers remains within the limit, and require no oil.
This leads us to another type of transformer oil protection system called hermetically sealed transformers. Let’s know more about it!
Why does Hermetically Sealed Transformers require no breather?
Hermetically sealed transformers have no contact with the outside environment. These transformers are designed without any conservator tank, breather, or silica gel.
Hermetically sealed transformers require no breather because, their sealing is done in such perfection that, the oil expansion is allowed within the transformer body.
The absence of the transformer breather makes the use of these transformers very common in environments where rain or snow percentage is quite high, also environments with high levels of gases in the air, and placing a transformer with a breather outside could cause destructive for transformer’s life.
Is Silica Gel Effective in Transformer Breather?
A silica gel breather is a way to allow the oil expansion and at the same time to prevent moisture from entering the transformer.
Breather and Silica Gel protect the oil from moisture during transformer breathing.
Silica gel plays the main role in protecting transformer oil from moisture. It has a great ability to absorb moisture from air and pass it on to the dry air only into the transformer tank. So, it is effective and does its role perfectly.
Silica gel in the transformer breather changes its color if it adsorbs moisture and water, so we are indicated to replace it.
Silica Gel Colors:
White silica gel: this is a non-indicating silica gel, which means no color change will happen if it adsorbs water.
Blue silica gel: This type of silica gel has cobalt chloride which changes its color to to be pink after adsorbing water. When it becomes pink this means it reached its adsorption maximized capacity.
Orange silica gel: This is another color indicating type which is suitable to be used in silica gel breather of transformers.
How Is Moisture Controlled in a Transformer Breather?
A breather on power transformers controls moisture by using a desiccant material that absorbs moisture from the air entering the transformer tank.
Here’s how the moisture control process works:
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Desiccant Material: The breather contains a desiccant material, commonly silica gel, which has a high affinity for moisture. Silica gel is a porous substance that can absorb and hold a significant amount of water vapor.
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Air Exchange: As the temperature changes, causing the oil volume within the transformer tank to expand and contract, the breather allows for the exchange of air between the transformer tank and the external environment. When the transformer oil heats up and expands, it increases the pressure inside the tank. To balance this pressure, the breather draws in external air.
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Moisture Absorption: When the external air enters the breather, it passes through the desiccant material. The desiccant absorbs moisture from the incoming air, effectively drying the air before it enters the transformer tank. The silica gel traps any moisture in the air, preventing it from entering the transformer and contaminating the insulating oil. Read my article Moisture and transformer oil- a deadly combination!
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Protection Against Moisture: The desiccant material continues to absorb moisture from the incoming air over time. This ongoing moisture absorption helps maintain the dryness of the air inside the transformer tank. Dry air is essential for preserving the dielectric properties of the insulating oil and preventing the formation of sludge, corrosion, and other moisture-related issues.
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Indicator System: Transformer breathers often include an indicator system to monitor the condition of the desiccant material. The indicator changes color or provides a visual signal when the desiccant becomes saturated with moisture. When the indicator shows that the desiccant is saturated, it’s time to replace or regenerate it to ensure effective moisture control.
By using a desiccant-filled breather, power transformers can effectively control moisture levels inside the transformer tank, ensuring the integrity and performance of the insulating oil and preventing moisture-related problems that can lead to transformer failure.
I have written a detailed article about transformer moisture causes and solutions.
When Should I Replace Transformer Silica Gel?
Silica gel plays a vital role in protecting transformers by absorbing moisture from the air entering the conservator. To ensure optimal performance, it’s recommended to replace the silica gel when it reaches 1/3 of its saturation level. Waiting until full saturation increases the risk of moisture transferring into the transformer, which can compromise its insulation and performance.
Here’s how the process works:
- Silica gel absorbs moisture gradually, starting at the bottom of the breather and moving upward until the gel becomes fully saturated.
- The time it takes to reach saturation varies between transformers, but the principle remains the same.
To monitor saturation levels, silica gel changes color:
- Orange silica gel turns transparent when saturated.
- Purple silica gel turns pink when it’s time for replacement.
Regularly checking and replacing silica gel ensures the transformer remains dry and operational, preventing moisture-related damage.
If the silica gel is absorbed by the oil, especially after a fault like the one in the photo, you should replace it. In this case, silica gel becomes bad.
The photo is of one 500KVA transformer in my workplace, it had a short circuit and the oil came out of the transformer through the silica gel breather. The silica gel became bad.
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