As an electrical engineer, I am well aware of the importance of transformer heat dissipation to its performance and reliability. During operation, transformers generate a large amount of heat due to energy loss. If the heat cannot be dissipated effectively, this heat will lead to deterioration of insulation materials, decrease in equipment efficiency, and even cause serious failures. The design of the cooling system directly determines whether the transformer can operate safely and efficiently in different environments and load conditions.
The cooling method of transformer includes natural air cooling, forced air cooling, oil-based cooling, and water-based cooling systems, tailored for different load and environmental conditions.
This article will combine my experience to comprehensively analyze all types of transformers cooling, the significance of the IEEE logo, and how to choose the cooling method that suits your application scenario.
Figure 1 transformer cooling
Basic concepts of transformer cooling
What are the main causes of heat generated by transformers？
Figure 1-1 transformer cooling
The heat generated by the transformer mainly comes from the following three aspects:
- Coil (winding) losses (copper losses): Resistive heat generated by the current passing through the winding. The higher the load, the more heat.
- Core losses (iron losses): Hysteresis and eddy current losses due to changes in magnetic flux.
- Additional losses: such as magnetic leakage, mechanical vibrations and stray losses. Transformers are rated using parameters like voltage, current, power (kVA or MVA), and frequency to define their operational capacity.
What is Cooling:The Core Objective of Transformer Cooling
Figure 1-2 transformer cooling class
The core objective of transformer cooling is to direct heat away from the interior (windings and core) and into the environment through external systems. The cooling system is usually divided into:
1. Internal cooling: Heat is conducted through the cooling medium (air, oil or special liquids).
2 .External cooling: External radiators or enclosures discharge heat to the environment. The transformer is cooled using fans or natural air circulation to manage heat effectively.
Types of Cooling in Transformer: Dry Type Transformer
Dry-type transformers are widely used for their safety, environmental friendliness and low maintenance cost. Dry type transformer types include ventilated, non-ventilated, and cast resin designs, suited for diverse applications.Their cooling methods are classified as follows according to IEEE standards:
Figure 2-1 Dry Type Transformer Diagram
Table of transformer cooling methods for dry-type transformers
| Cooling Class | IEEE Designation |
| Ventilated Self-Cooled | AA |
| Ventilated Forced-Air Cooled | AFA |
| Ventilated Self-Cooled/Forced-Air Cooled | AA FA |
| Non-Ventilated Self-Cooled | ANV |
| Sealed Self-Cooled | GA |
Transformer heat dissipation of dry-type transformers in detail
Figure 2-2 cooling methods
AA (Natural Ventilation Self-Cooling): Natural convection cooling, suitable for well-ventilated environments, commonly used in low load applications.
AFA (Forced Air Cooling): Adding a fan to force air flow to improve cooling efficiency, suitable for high load operation scenarios.
AA/FA (Hybrid Cooling): Combines self-cooling and forced air-cooling modes, switching between different load conditions for greater flexibility.
ANV (Non-Ventilated Self-Cooling): anv full form Designed without ventilation holes, utilizing surface radiation to dissipate heat, suitable for dusty or humid environments.
GA (Sealed Self-Cooling): Completely sealed design, preventing corrosive gas intrusion, suitable for extreme environments.
Oil-immersed Transformer: Oil cooled vs Liquid Cooled
oil cooled transformer are widely used type of transformers in industry by using oil as cooling and insulating medium. Depending on the cooling method, oil-immersed transformers can be divided into the following common categories:
Figure 3-1 Oil-immersed Transformer Diagram
Liquid cooled vs oil cooled: Table of transformer cooling methods for general oil-immersed transformers
| Cooling Class | IEEE Designation |
| Oil-immersed self-cooled | ONAN |
| Oil-immersed forced-air-cooled | ONAF |
| Oil-immersed forced-oil-cooled (non-directed flow) with forced-air cooler | OFAF |
| Oil-immersed forced-oil-cooled (directed flow) with forced-air cooler | ODAF |
| Oil-immersed self cooled with forced-water cooler | ONWF |
| Oil-immersed forced-oil-cooled (non-directed flow) with forced-water cooler | OFWF |
| Oil-immersed forced-oil-cooled (directed flow) with forced-water cooler | ODWF |
Oil-immersed transformer cooling explanations
Figure 3-2 liquid cooled vs oil cooled
Oil Natural Air Natural Cooling (ONAN).
onan meaning:onan cooling in transformer is the most basic cooling method, through the natural convection of oil and the natural flow of air heat dissipation, without additional equipment, suitable for small and medium-sized transformers and low load scenarios.
Cooling O typically refers to oil-based cooling systems in transformers, such as ONAN or OFAF, where oil circulates to dissipate heat efficiently.
Oil natural air forced cooling (ONAF).
On the basis of ONAN, a fan is added to force air flow and improve cooling efficiency. It is suitable for medium-sized transformers with high loads and can effectively control the temperature rise in a short period of time.
Oil Forced Air Forced Cooling (OFAF).
Forced oil circulation through an oil pump and forced air flow using a fan is ideal for high load or continuous operation transformers. This method ensures that heat is quickly transferred from the inside of the transformer to the outside.
Oil Natural Water Forced Cooling (ONWF).
A water cooling system is introduced on top of the natural oil circulation, whereby the heat is transferred via a heat exchanger to a forced flow of cooling water. Ideal for scenarios where additional cooling capacity is required, such as high temperatures or equipment-intensive environments.
Oil Forced Water Forced Cooling (OFWF).
Uses an oil pump to force the oil to circulate and dissipate the heat through a water cooling system, making it an efficient cooling solution for extreme environments and ultra-high load conditions.
Cooling with Non-flammable Liquids (KNAN/KNAF etc.).
The use of non-flammable liquids (e.g. synthetic esters) meaning:transformer oils, combined with natural or forced cooling, for special applications where environmental protection and fire prevention are important.
| Cooling Class | IEEE Designation |
| Less flammable liquid-immersed self-cooled | KNAN |
| Less flammable liquid-immersed forced-air-cooled | KNAF |
| Less flammable liquid-immersed forced-liquid-cooled (non-directed flow) with forced-air cooler | KFAF |
| Less flammable liquid-immersed forced-liquid-cooled (directed flow) with forced-air cooler | KDAF |
| Less flammable liquid-immersed self cooled with forced-water cooler | KNWF |
| Less flammable liquid-immersed forced-liquid-cooled (non-directed flow) with forced-water cooler | KFWF |
| Less flammable liquid-immersed forced-liquid-cooled (directed flow) with forced-water cooler | KDWF |
How Many Types of Transformer Cooling with Non-flammable Liquids Explanations
Figure 3-3 cooling class
ONAN and ONAF: Onan transformer full form Small and medium-sized transformers commonly used in power transmission and distribution systems.
OFAF and OFWF: Suitable for heavy-duty equipment and continuous operation systems in industry.
KNAN and KNAF: Non-flammable coolants are preferred in petrochemical plants or where fire protection is required.
ODAF and KDWF: For high-voltage transformers and critical equipment such as data centers that require efficient heat dissipation.
Method of identification of transformer cooling categories
Transformer nameplate is an important carrier of equipment information, which the cooling class (Cooling Class) marking can help users quickly understand the transformer’s cooling mode, easy to select and use. The following is a detailed explanation of the cooling class labeling:
Figure 4-1 cooling of transformer
The role of nameplate marking
Transformer nameplates usually indicate a cooling category designation, such as ONAN or OFAF. These designations are based on internationally harmonized standardized representations, which make it easy for the user to quickly determine the transformer’s cooling method and applicable conditions.
A transformer label provides essential information such as voltage rating, power capacity, frequency, cooling method, and connection type.
With the information on the nameplate, the user can quickly determine the type of cooling method (e.g. natural or forced) and the required operating conditions to better match the application environment.
Definition of internal vs. external cooling
Figure 4-2 Cool transformers
Internal Cooling:
oRefers to the process of dissipating heat around the coil and core. The cooling medium (e.g., oil or air) carries the heat generated internally to the heat sink or enclosure. Cool transformers use advanced cooling systems like radiators or fans to manage heat efficiently during operation.
oFor example, in an oil-immersed transformer, oil transfers heat from the inside to the unit of transformer enclosure through natural convection or pumping flow. A forced circulation cooling system uses pumps or fans to enhance the movement of cooling mediums like oil or air, improving heat dissipation in high-load transformers.
External cooling
o Refers to the discharge of heat from the exterior of the class-transformer case and heat sink. Heat dissipation is usually accomplished by air convection, fans, or water cooling systems.
o The efficiency of external cooling of transformer directly affects the overall thermal performance of the transformer.Class transformer signifies a transformer designed to meet specific classification standards or application needs.
Example of a cooling category
Figure 4-3 cooling style
The cooling identification on the nameplate is usually a concise four-digit alphabetic code, with each of the two digits indicating the mode of circulation and area of action of the cooling medium. Transformer abbreviation refers to shortened terms like ONAN, ONAF, or OFAF that describe cooling methods. Xfmr meaning refers to a common abbreviation of transformer for the word “transformer” in electrical engineering.
Example:
ONAN (Oil Natural Air Natural).
onan definition:onan transformer meaning, Indicates the natural cooling method of oil-immersed transformers, where heat is dissipated internally by natural convection of oil and externally by natural convection of air to discharge heat. It is suitable for small and medium-sized oil-immersed transformers and general environments. Define ONAN as Oil Natural Air Natural, a cooling style method using natural oil and air circulation.
OFAF (Oil Forced Air Forced).
Indicates the forced circulation cooling method, using the oil pump to force the oil circulation, and combined with the fan to force the air flow to dissipate heat. Suitable for high load operation or high temperature environment.Letter transformers often refer to transformer classes categorized by specific codes, like ONAN transformer or OFAF, indicating cooling methods.Transformers letters often indicate cooling methods or classifications, such as ONAN (Oil Natural Air Natural) or ONAF (Oil Natural Air Forced).
KNAN (Less Flammable Liquid Natural Air Natural).
knan transformer use non-flammable liquid as the cooling medium, natural convection heat dissipation, suitable for environmental protection and fire prevention requirements of higher places.
Practical Tips
Quick selection:
The cooling category identification on the nameplate helps the user to quickly determine whether the transformers classes is suitable for specific operating conditions, such as high temperatures, high humidity or load fluctuations.
Maintenance reference:
Based on the information on the nameplate, users can select the correct maintenance strategy. For example, for transformers in the forced cooling category (e.g. ONAF or OFAF), the operating status of the fan and the oil pump should be checked regularly.
Environmental adaptation:
Nameplate marking also helps the user to select the applicable transformer in different scenarios. For example, in scenarios where there are fire protection or environmental requirements, preference can be given to transformers in the KNAN or KNAF categories.
Key factors affecting transformer cooling efficiency
Transformer cooling efficiency directly determines the safety and reliability of equipment operation. The following are several key factors affecting transformer cooling efficiency, analyzed one by one from the perspective of electrical engineers:
Transformer Core design and materials
The core design of the transformer and the materials used are fundamental factors in cooling efficiency:
- Iron Core Materials: High-quality silicon steel reduces eddy current and hysteresis losses, minimizing heat generation. Advanced materials like nanocrystalline cores enhance efficiency and lower cooling demands.
- Winding Design: Compact layouts prevent hot spots and ensure even heat dissipation. Insulation materials with high thermal conductivity, like epoxy resin, boost heat transfer. The “fow meaning” fow full form in the context of classification of transformer relates to the “flow of winding” or energy transfer process. Every transformer rely on electromagnetic induction to manage the fow meaning, efficiently converting voltage levels while maintaining energy flow integrity. Understanding the fow meaning highlights the importance of winding arrangements in ensuring optimal performance and heat dissipation.
- Radiator Design: The size, arrangement, and shape of radiators determine heat dissipation efficiency. Optimized designs, such as advanced fin structures, improve cooling performance significantly.
Impact of load fluctuations on heating
- Constant Load: Ensures stable cooling and maintains temperature within design limits. Transformer short formis often written as “xfmr,” commonly used in electrical engineering.Abbreviation for transformer is typically written as “xfmr transformer” in technical documents and diagrams.
- Overload: Increases heat generation, risks overheating, and accelerates insulation aging, reducing equipment life.
- Load Variation: Frequent fluctuations cause thermal cycling, stressing the cooling system and reducing fan/pump efficiency and lifespan.
Solution:
Use intelligent cooling systems to adapt cooling intensity in real time.
Opt for forced cooling transformers (e.g., OFAF, OFAW) in high or variable load conditions.
Environmental conditions (temperature, humidity, and altitude)
Impact of Operating Environment on Cooling Efficiency
- Ambient Temperature: High temperatures reduce heat dissipation efficiency. Transformers in hot regions may need forced cooling (e.g., ONAF, OFWF).
- Humidity: High humidity can degrade cooling mediums and cause insulation issues. Sealed designs (e.g., GA) are ideal for such conditions.
- Altitude: Reduced air density at higher altitudes lowers cooling efficiency, requiring additional cooling equipment or design adjustments.
Recommendations:
- Optimize Design: Choose materials with high thermal conductivity and efficient designs to reduce heat buildup.
- Dynamic Monitoring: Use temperature sensors and intelligent systems to adapt cooling strategies in real time.
- Environmental Adaptation: Select cooling methods suited to the environment (e.g., high temperature, high humidity, or high altitude) and consider auxiliary measures.
Conclusion
Transformer cooling methods have a direct impact on the performance and life of the equipment. Choosing an efficient and suitable cooling solution ensures stable operation and prolongs service life. For customized services, please feel free to contact us and we will provide you with professional support.
FQA
What is a transformer tank?
The transformer tank plays a vital role in cooling and protecting internal components. It holds the cooling medium, such as oil or air, and facilitates heat transfer from the core and windings to the environment. Tanks with fin-shaped extensions enhance heat dissipation by increasing the surface area. In high-load transformers, tanks often integrate oil pumps or radiators for efficient cooling. Hermetically sealed tanks prevent moisture and contaminants from affecting the insulation, making them ideal for humid environments. High-quality materials ensure the tank withstands pressure variations while maintaining structural integrity. An optimized tank design significantly improves transformer cooling performance.
What services does Fluid Cooling Systems LLC offer for industrial cooling solutions?
Fluid Cooling Systems LLC specializes in designing and manufacturing advanced cooling solutions for industrial equipment, including transformers. Their systems use innovative technologies to enhance heat dissipation and ensure operational efficiency. By offering customized fluid cooling systems, they cater to industries requiring precise temperature management and reliable performance.
What are the common types of dry type transformer used in electrical systems?
The common all kinds of transformers used in electrical systems include isolation transformers, control transformers, autotransformers, and cast resin transformers.Fow definition refers to the concept of “flow,” often used in the context of energy or current movement in systems like transformers.
What does f mean on a heating pad？
The “F” on a heating pad typically indicates a malfunction or error, often related to the temperature sensor or internal wiring. Refer to the user manual for troubleshooting or reset instructions.
What is Transformers class sizes?
Transformers class sizes refer to standard categories based on power capacity, voltage levels, and application requirements. Transformers size classes refer to categories based on power capacity, such as small (kVA range), medium (MVA range), and large (utility-scale) transformers.
How do transformer cooling systems prevent overheating and improve efficiency?
Transformer cooling plays a vital role in maintaining efficiency and preventing transformer heating during operation. Cooler force systems, such as transformer cooling fans, enhance heat dissipation by increasing airflow around the unit. For liquid cooling, the liquid abbreviation commonly used is “O” for oil in designs like OFAF or ONAF. Cooler transformer designs often include advanced radiators or innovative cooling technologies. Transformers cool better when equipped with efficient cooling mechanisms, making names like cooler transformer and cool transformer names popular in modern industrial settings.
What are the uses and cooling methods for different transformer classifications?”
A class 2 transformer is used for low-voltage applications like powering doorbells or thermostats, while a class 3 transformer is designed for higher current outputs. An cooling system, such as natural air ventilation (ANV meaning), provides efficient passive heat dissipation for certain transformer types. For larger transformers, a transformer cooling fan or self cooling fan enhances heat management to prevent a heating transformer situation. Cooling methods for transformers are classified into systems like natural cooling, forced air cooled transformer, and oil-based cooling,water cooled surface is necessary to collect, depending on the transformer classification. Proper cooling extends the lifespan and efficiency of transformers in diverse applications.
What is a class 2 transformer used for?
A class 2 transformer is used for low-voltage, low-power applications such as powering doorbells, thermostats, and security systems, where safety and limited energy output are crucial.
Transformer all parts name/Transformers all parts list
| Core | Windings | Transformer tank | Conservator tank |
| Breather | Radiator or cooling fins | Bushings | Tap changer |
| Insulation materials | Cooling fans | Temperature gauges | Buchholz relay |
| Pressure relief device | Oil level indicator |
Transformer oil name list
| Mineral oil | Silicone oil | Synthetic ester | Natural ester (vegetable oil-based) |
| FR3 (natural ester-based biodegradable fluid) | Midel 7131 (synthetic ester) | Alpha-1 (inhibited mineral oil) | Shell Diala series (mineral oil variants) |
| Nytro series (specialized transformer oil) | Envirotemp (biodegradable transformer oil) |
Transformer ratings list/Transformer rating in kva list
| Category | Rating (kVA) |
| Small Transformers | 5 kVA |
| 10 kVA | |
| 25 kVA | |
| 50 kVA | |
| 100 kVA | |
| Medium Transformers | 250 kVA |
| 500 kVA | |
| 1,000 kVA (1 MVA) | |
| 2,500 kVA (2.5 MVA) | |
| 5,000 kVA (5 MVA) | |
| Large Transformers | 10,000 kVA (10 MVA) |
| 25,000 kVA (25 MVA) | |
| 50,000 kVA (50 MVA) | |
| 100,000 kVA (100 MVA) | |
| 500,000 kVA (500 MVA) |