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We understand that 35kV Oil Immersed Power Transformers, through long-term development and practical experience, have achieved mature and stable technology, performance, and structure, finding widespread application in power grid systems. These products feature a more advanced design and significant improvements in materials, structure, and technology.
For the manufacturing of core components, we prioritize the use of copper foil for low-voltage windings, while high-voltage windings adopt a multi-layer cylindrical structure. Axial oil passages are incorporated as needed, which not only ensures ampere-turn balance between high and low voltage windings but also endows the coils with high mechanical strength and strong short-circuit resistance. The design of axial oil passages also significantly enhances heat dissipation, effectively reducing the hot spot temperature of the windings. The iron core is made from selected cold-rolled silicon steel sheets with high permeability, formed using a full oblique joint stacking process, and the core limbs feature a multi-stage circular section, with the same cross-section as the core yoke. The windings utilize corrugated oil channels, are not dipped in paint, are tightly bound, and are concentric coils.
To ensure the reliability of our products during transportation and operation, we implement fastening measures for both the iron core and windings, utilizing self-locking anti-loosening nuts as fasteners. This allows the transformer to withstand bumps during transit, ensuring that it can be directly put into operation upon arrival at the site without requiring core inspection, thus supporting reliable operation. In our manufacturing process, we employ vapor phase drying and vacuum oiling processes, ensuring thorough insulation drying and minimal air bubbles in the oil. A capsule is installed within the oil conservator, completely isolating the transformer oil from the air. This effectively prevents oil degradation and moisture ingress, significantly extending the transformer's maintenance cycle and greatly reducing maintenance costs.
These optimizations result in our 35kV oil-immersed transformers demonstrating consistent performance in terms of low loss, low noise, and operational reliability, with competitive performance compared to similar products.
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View MoreWhat Type of Oil Is Used in Transformers?
The most commonly used oil in transformers is mineral oil, specifically formulated for electrical insulation and cooling. Mineral-based transformer oil is favored for its excellent dielectric strength, thermal conductivity, and chemical stability.
However, other types of oils are also used depending on the application and environmental considerations:
Silicone-based oils: These offer better fire resistance and are used in indoor or fire-prone environments.
Synthetic esters and natural esters (vegetable-based oils): These are biodegradable alternatives with high fire points, making them more environmentally friendly and safer in some applications.
High-temperature hydrocarbon fluids: Used in specialized transformers where higher thermal stability is required.
The selection of transformer oil depends on various factors such as voltage rating, cooling method, environmental safety requirements, and fire hazard assessments.
How Often Should Transformer Oil Be Replaced?
Transformer oil does not require frequent replacement under normal operating conditions, but it must be regularly tested and maintained. The frequency of oil replacement depends on factors such as the age of the transformer, its load profile, operating environment, and the results of periodic oil analysis.
General Guidelines:Routine Testing: Transformer oil should be tested annually or semi-annually for key parameters such as dielectric strength, moisture content, acidity, and dissolved gas content.
Replacement Intervals: If test results show significant degradation—such as low dielectric strength, high moisture, or presence of contaminants—oil filtering, regeneration, or full replacement may be necessary. For well-maintained transformers, oil can last 15 to 20 years or more without replacement.
Factors That Influence Replacement Frequency:
Moisture ingress due to poor seals or humid environments.
Thermal stress from heavy load cycles.
Oxidation over time, especially in older units without oil preservation systems.
Contamination from sludge, dissolved gases, or metallic particles.
Rather than relying on a fixed schedule, transformer oil replacement should be condition-based, guided by diagnostic testing. Preventive maintenance like oil filtering and degassing can also significantly extend the life of the oil and transformer itself.
How Is Oil Added to a Transformer?
Adding oil to a transformer is a precise process that must be done carefully to ensure electrical and operational safety. This procedure is typically carried out during installation, maintenance, or after oil has been filtered or replaced. Here are the key steps involved:
1. Preparation and Safety
Before adding oil, it's essential to:
De-energize the transformer and isolate it from the power supply.
Ground the equipment to prevent static electricity buildup.
Inspect the transformer for any damage or contamination.
Ensure that the transformer is in a clean, dry, and dust-free environment.
2. Filtering the Oil
Transformer oil must be clean and free from moisture and contaminants before filling. Usually, vacuum filtration or centrifuging is used to purify the oil. This step is crucial to maintain the dielectric strength and insulation properties of the oil.
3. Filling Process
Oil is added slowly through the filter inlet valve at the base of the transformer or as specified by the manufacturer.
A vacuum may be applied during or before the filling process to eliminate air pockets and prevent moisture absorption.
The oil level is carefully monitored using oil level gauges or sight glasses to avoid overfilling or spillage.
4. Deaeration and Final Checks
Once filled:
The transformer is often subjected to vacuum treatment again to remove dissolved gases and trapped air.
All fittings and seals are checked for leaks.
Insulation resistance tests and dielectric strength tests may be performed before the transformer is put back into service.
Important Tips:
Always use compatible oil as recommended by the transformer manufacturer.
Only qualified personnel should perform oil filling due to the risk of fire, contamination, and electrical hazards.
How Is Moisture Removed from Transformer Oil?
Moisture is one of the most harmful contaminants in transformer oil. Even small amounts can significantly reduce the oil’s dielectric strength, accelerating insulation degradation and increasing the risk of failure. Therefore, removing moisture is a critical part of transformer maintenance.
Common Methods for Moisture Removal:
1.Vacuum Dehydration
This is the most effective and widely used method. The oil is heated under vacuum conditions, allowing moisture to evaporate at lower temperatures. The process not only removes water but also eliminates dissolved gases and some impurities. It is often done using a transformer oil purification machine.
2.Oil Filtration Units
These mobile or stationary systems combine filtration and vacuum dehydration. They are used on-site and can process oil directly from the transformer without the need for disassembly or oil draining.
3.Adsorption Using Desiccants
Materials like silica gel or molecular sieves are used to absorb moisture from the oil. This method is less effective for large volumes but can be suitable for smaller transformers or during storage and transport.
4.Hot Oil Circulation
In this method, heated oil is circulated through the transformer. The heat helps release moisture from the solid insulation and the oil itself, which can then be removed via vacuum or absorption techniques.
5.Dry Air/Nitrogen Purging
Dry air or nitrogen is introduced into the transformer tank to replace moist air and help dry internal components. This is typically used during maintenance when the transformer is de-energized.
Use a conservator with a breather system filled with silica gel to absorb atmospheric moisture.
Perform regular oil testing to monitor moisture content and take action before it becomes a problem.
Is Transformer Oil Flammable?
Yes, transformer oil is flammable, particularly mineral-based transformer oil, which is the most commonly used type. It has a relatively high flash point—typically around 140°C to 160°C (284°F to 320°F)—but it can still catch fire if exposed to an ignition source under certain conditions.
Fire Risk Considerations
While transformer oil is essential for insulation and cooling, its flammability poses a potential hazard, especially in the event of electrical faults, leaks, or overheating. If a transformer fails catastrophically, the hot oil can ignite, potentially leading to explosions or fires. This is why fire safety measures—such as fire barriers, containment pits, and automatic fire suppression systems—are often installed around oil-filled transformers.
Alternatives for Fire-Sensitive Areas
To mitigate fire risks, fire-retardant oils like silicone oil or ester-based fluids are used in locations where safety is critical—such as indoor substations, high-rise buildings, and densely populated areas. These fluids have higher flash points and lower flammability compared to mineral oils.
Regulatory Standards
Most countries follow strict fire safety codes and standards (such as IEC, IEEE, or NFPA) that specify acceptable fire characteristics for transformer oil and installation practices to reduce risks.
Is Transformer Oil Harmful to Humans or the Environment?
Transformer oil can pose health and environmental risks, depending on its composition and how it is handled.
Health Risks
Most modern transformer oils—particularly mineral oil and synthetic esters—are considered to have low acute toxicity. However, prolonged skin contact, inhalation of vapors, or accidental ingestion can lead to health issues, including skin irritation, respiratory problems, or nausea. Workers handling transformer oil should always use personal protective equipment (PPE) such as gloves, goggles, and protective clothing to avoid direct exposure.
Historically, some older transformers used polychlorinated biphenyls (PCBs) as insulating fluids. PCBs have since been banned in many countries due to their toxic and carcinogenic properties. Any remaining transformers containing PCBs must be handled and disposed of under strict regulatory controls.
Environmental Risks
If transformer oil leaks or spills, it can contaminate soil, groundwater, and surface water. Mineral oil is non-biodegradable, and even small leaks over time can cause significant environmental damage. Esters, especially natural ones, are more environmentally friendly because they are biodegradable and less toxic.
For these reasons, environmental regulations require that transformers be equipped with oil containment systems (such as bunds or spill trays) and that any leaks or spills be reported and cleaned up immediately.
Safe Handling Practices
To minimize harm to both humans and the environment, transformer oil must be:
Stored in sealed, labeled containers away from heat and ignition sources.
Handled in well-ventilated areas or with appropriate exhaust systems.
Disposed of according to local environmental regulations and hazardous waste protocols.
Proper training, routine inspections, and compliance with safety standards are essential in ensuring transformer oil is used and managed responsibly.
What Happens When a Transformer Leaks Oil During Operation?
1. Drop in Oil Level
As the oil leaks out, the level inside the tank drops. Since transformer oil is responsible for cooling and insulating the internal components, a reduced oil level can cause localized overheating, especially around the windings and core.
2. Increased Operating Temperature
With less oil circulating or in contact with heat-generating parts, the transformer cannot effectively dissipate heat. This leads to rising temperatures, which may trigger protective relays or cause thermal degradation of insulation over time.
3. Reduced Dielectric Strength
Transformer oil prevents electrical arcs by maintaining high dielectric strength. When oil leaks, air and moisture can enter the system, reducing dielectric strength and increasing the risk of partial discharges, arcing, or even internal flashovers.
4. Moisture Contamination
Oil leaks often create negative pressure inside the tank, allowing moisture and oxygen to be drawn in. Moisture is especially harmful, as it drastically lowers the insulating quality of both oil and solid insulation (like paper), accelerating aging and increasing the chance of electrical failure.
5. Formation of Gas and Sludge
As temperature rises and oxygen enters the system, the oil may begin to oxidize, forming sludge and gases. These byproducts can clog cooling ducts, reduce oil circulation, and trigger gas accumulation in the Buchholz relay—an early warning of internal faults.
Our Oil Immersed Power Transformer offers exceptional reliability and efficient performance, making it ideal for a wide range of electrical applications. Specifically designed for high voltage requirements, the 35kV Oil Immersed Power Transformer provides superior insulation and cooling capabilities, ensuring long-lasting operation and enhanced safety. Its robust construction and advanced oil-immersed technology help minimize maintenance needs while maximizing power transfer efficiency.
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