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The Ultimate Guide to Oil Cooled Transformers

Oil-cooled transformers are primarily used in industrial applications where space and weight are critical. Consumers and users can generally apply oil cooled transformers in many different kinds of utilization. That includes power and electricity generation, industrial manufacturing processes, heating and ventilation, cooling, and lighting management systems.

An oil cooling transformer uses an insulating oil as a medium to get cooling done and as an dielectric insulating system to improve transformer performance and thermal stability.

With this guide, we will have an in-depth discussion with oil cooled distribution transformers. These include their purpose, benefits, design, and requirements.

What Is An Oil Cooled Distribution Transformer?

An oil cooled distribution transformer is a type of transformer that uses oil cooling to reduce the transformer’s operating temperature of the transformer core and winding.

In a conventional oil cooled distribution transformer generator, the core is often housed in a tank made of welded steel that is filled with liquid insulation. This transformer coolant oil absorbs the heat generated during transformer operation and then transfers that heat to the outer cooling surface or the radiators of the transformer.

A properly designed and built transformer oil cooling system not only improves heat dissipation but also increases the transformer insulation performance. This greatly influences the operational reliability of the transformer under varying loading conditions.

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The Fundamentals of Operation Behind an Oil-Cooled Distribution Transformer

These transformers are generally used in distribution channels or for transmission and distribution. As a result, they are commonly submerged in oil, which conditions the internal components. This cooling oil in transformer performs two major functions. One is the function of heat transfer from the core of the transformer to the other environment. Second is working as a dielectric agent and providing dielectric insulation to the internal critical transformer components.

During operation, the coils and cores of these devices are usually covered in oil to remain cool and constructed.

With regard to circulation, oil travels through the internal pipelines of the coil as well as the tubes that cover the core component and the coil itself. Moreover, oil travels via the tubes that cover the core component.

The oil is often cooled by the exterior of the oil tank when the rated value is lower.

However, when the rated value is larger, the oil is then cooled by a radiator that makes use of air-cooling technology.

Oil cooled distribution transformers or air-natural cooling transformers are generally deployed, but other alternatives are available, according mostly to required capacity, for values from 6 and 36 kilovolts.

This approach is frequently applied in order to extract heat from the transformer’s core and windings by channeling it into the oil storage reservoir.

The remaining two methods of heat dissipation into the atmosphere are radiation and convection.

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Where Are Oil-Cooled Transformers Used?

Oil-cooled transformers have a wide variety of industrial uses, including power plants, substations, solar and wind power plants, and transportation equipment.

They also cater to metal processing machinery, elevators, and computer numerical control machines.

An oil cooled power transformer is especially suitable for applications where there is a need for high capacity electrical systems. This is because of their superior cooling efficiency and overload capabilities. This is one of the reasons that these transformers are widely used in metal processing industries, elevators, CNC machinery and renewable energy distribution systems

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What Are The Cooling Methods For Oil Cooled Transformers?

Although there are alternatives, oil is primarily responsible for conditioning oil-cooled transformers.

1. Oil Natural Air Natural (ONAN)

The oil natural air natural cooling system is the most common transformer oil cooling system you will see in all types of small to medium size electrical transformers. In this method, oil present inside the tank takes heat from the core and transfers it to the surrounding air through a natural convection method.

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How Do Air Natural Cooling Transformer Work?

When the Electrical Transformer starts working, the Transformer core produces a lot of waste heat. So, the surrounding Electrical Transformer oil absorbs that heat and transfers that heat to the Transformer tank in which the Transformer oil is kept. The natural air surrounding the Electrical Transformer tank then starts to absorb that waste heat based on the method of natural convection.

2. Natural Oil Air Forced(ONAF)

3. Air Forced Oil Forced

In Electrical Transformers where the heat produced at the Transformer core is of such quantity that it cannot be removed using the natural convection method, the Oil Forced Air Forced cooling method is used to remove the waste heat from the Transformer. An electrical pump is provided at the inside of the Electrical Transformer that works to circulate the Electrical Transformer cooling oil. Circulating Electrical Transformer oil absorbs much more waste heat as compared to the natural convection method. Now that oil, when it moves through the heat exchanger over the fins of the transformer tank, transfers that heat to the fast-moving natural air that is forced over the same using a cooling fan.

4. Water Forced with Oil Forced

In indoor applications, or in all those sensitive applications where there is no natural air forced-air application available, the Oil Forced Water Forced system is used. It works much like the Oil Forced Air Forced system, with the only difference being that there is a special heat exchanger designed and installed with the Electrical Transformer. Transformer cooling oil first takes heat from the Transformer core and then moves into the heat exchanger; water circulating in the tubes of the exchanger removes all the waste heat of the oil.

How Does Oil Filled Water Cooling Transformer Operate?

A steady flow of water is essential for this technique as it serves to cool the heat exchangers.

At the same time, oil temperature increases over time as a result of heat produced by a pump.

Once the hot water has been then withdrawn from the system in general, it is regularly cooled in a specialized cooler.

These cooling systems are useful for large oil filled water cooling transformers with a capacity of 100 MVA or higher.

Ultimate Guide To Oil-Filled Transformer

Why Does Oil Cooled Transformer Manufacturer Use Oil Inside A Transformer?

Oil is also a crucial component for transformers. Because of this, manufacturers ensure that their transformers function properly only when loaded with the appropriate oil.

The transformer oil helps in

Cooling the winding and core section of transformer
Suppressing electrical arcs within the transformer
Improving dielectric insulation of the transformer
Reducing the operating temperature of the transformer
Extending the useful life of the transformer

Without using the proper transformer oil cooling, excessive heat inside the transformer can damage the insulation system and reduce the transformer reliability.

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What Are The Advantages and Disadvantages Of Using Oil-Cooled Transformers?

Let’s talk about the pros and cons of using this oil in a transformer.

Transformer Oil Benefits

Cooling oil for transformers is cheap, efficient, and has high insulating and thermal conductivity characteristics.
It’s effective in isolating high voltages from transformers and dissipating heat from high capacities.
Oil cooled power transformers can have ratings of 100MVA or higher since oil and a radiator are frequently used as heat dissipation mechanisms. A dry-type transformer cannot achieve the rating.
When compared to a transformer with a higher rating, it produces significantly less noise while in operation.
Improved energy efficiency as a baseline.
Has a lower operational loss.
Increased potential for lifespan.
The core coil assembly is recyclable.

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Transformer Oil Disadvantages

Regular exposure of cooling oil to flame creates the possibility of explosions or fires.
An oil cooled transformer is prone to leakage and can age gracefully.
When oil leaks at the operating site, it threatens both the integrity of the machinery and the quality of the surrounding environment.
When submerged in oil, a transformer’s sealing performance suffers, yet it ages well.
It’s a major problem when oil leaks at the operating site, endangering both the integrity of the machinery and the surrounding ecosystem.
Comparatively larger and heavier than dry-type converters
The added weight necessitates a more robust base and a dedicated oil pit.
The price of oil cooled transformer is higher.
Because of the increased potential for fire, a dedicated nitrogen or water-based fire suppression system is typically built. It draws more budget.
A greater amount of upkeep is necessary compared to the dry variety

Because of the fact that Transformer coolant oil is a combustible fluid the large installations after required are dedicated for production systems and other oil contaminate arrangements. this can significantly increase the overall cost of the project and also can heavenly influence the running cost and maintenance cost of the project

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What Are The Oil Cooled Transformer Design Requirements?

One of the most important parts of any electrical system is the power transformer. Several transformer layouts are feasible due to the availability of efficient cooling and electrical insulation.

Oil-Cooled Transformer Design, Built and Construction

Oil cooled Transformer are specifically designed and built to support the oil cooling Transformer system. They are mainly consist of

Magnetic core
Windings
Bushings
Radiators
Conservator tank
Breather
Cooling system

The transformer oil cooling system is one of the most critical part of the transformer design because it directly affect the efficiency, insulation life and operation temperature of the transformer.

Necessary Oil To Use

These are some of the most standard oil that oil cooled transformers are using:

Mineral oil, is one of two main types of petroleum products:

Naphtha Oil: Sewage, an oxidative byproduct, absorbs more easily in naphtha oil than in liquid paraffin.
Paraffin Oil: While paraffin oil oxidizes at a lesser speed than naphtha oil, the accompanying filth eventually settles to the bottom of the tank, limiting adequate conditioning of the transformer.

Synthetic Oil: These oils are often manufactured in a lab and include Silicon Oil.

Because of their high level of fire resistance, they are only used in high-risk settings.
Low heat conductivity and high moisture absorption. This oil is more expensive than mineral oil.

Vegetable Oil: This oil is extracted from plants.

Not only can it be regenerated, but it can also be 100% degraded, which is more environmentally friendly and ecological, and helps to extend the service life of the transformer.

The Transformer oil cooling system is one of the most critical Electrical Transformer parts. because it directly affects the efficiency of insulation life and operating temperature of the Electrical Transformer. Daelim can provide the above three oils. Daelim can provide vegetable oil with UL certification, and there are two brands of FR3 and RAPO for you to choose from.

Rating Of Oil-Cooled Transformer

For transformer values under 30 MVA, natural oil, and air technologies have always been generally implemented.
As you can see, the cooling capability of oil-natural and air-forced systems can usually be combined to a maximum of 61 MVA.
The continuous rating for distribution transformers must be either 100kVA, 250kVA, 400kVA, or 630kVA.

The rated power of an oil cooled transformer is always determined by multiplying the line side winding’s rated voltage by its rated current. The higher capacity oil cooled Transformer mainly uses oil natural Air Force, oil Force Air Force or oil Force Air Force cooling system depending on the load requirements and heat dissipation demand of the Electrical Transformer.

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Conclusion

Oil-cooled transformers remain one of the most reliable and widely used electrical transformers in the electrical transformer industry. With advanced transformer oil cooling systems, improved insulation materials, and an efficient radiator design, the modern oil-cooled power transformer solution provides wide and excellent efficiency, reliability, and operational lifespan for utility and industrial applications. For all types of queries related to the oil-cooled transformer, contact Daelim Transformer.