When Do I Need A Fan For Transformer?

September 20th, 2024

Transformers play a crucial role in electrical power distribution, converting voltages to appropriate levels for different applications. However, as transformers operate, they generate heat due to the energy losses occurring primarily in the form of I²R losses (resistive losses) and core losses. Effective cooling is essential to ensure that transformers operate reliably and efficiently. In certain scenarios, adding a fan to the transformer’s cooling system becomes necessary to manage heat dissipation and maintain the transformer’s performance.

Scenarios Requiring a Fan for Transformers

1. High Power Ratings:

Transformers with high power ratings (typically above 5 MVA) tend to generate more heat. The natural convection cooling might not suffice to dissipate the excessive heat generated during operation. In such cases, forced air cooling (using fans) is necessary to enhance the cooling capacity and maintain the transformer’s temperature within safe limits.

2. Compact Designs with Limited Cooling Surface:

As the demand for more compact transformer designs increases, the available surface area for natural cooling decreases. This limited surface area reduces the effectiveness of natural air cooling, making it essential to integrate fans into the design. Fans help to increase the airflow around the transformer, thereby improving heat dissipation and preventing overheating.

3. Environments with Elevated Temperatures:

In locations with high ambient temperatures, transformers are more prone to overheating. Elevated environmental temperatures reduce the temperature gradient between the transformer and the surrounding air, which diminishes the natural cooling effect. To counteract this, fans are employed to force more air over the transformer, enhancing cooling and ensuring the transformer remains within its operational temperature range.

Power Transformers Over 3 MVA

For power transformers with capacities over 3 MVA, the need for enhanced cooling becomes even more critical. These transformers are often used in industrial and utility applications, where they must handle large amounts of power continuously. The high electrical loads generate significant heat, which if not properly managed, can lead to serious issues such as insulation breakdown, reduced transformer life, and even catastrophic failures.

1. Enhanced Cooling Requirements:

For transformers with capacities above 3 MVA, natural cooling methods are usually insufficient. Fans become an integral part of the cooling system, often in conjunction with radiators, to provide the necessary cooling. These fans are typically controlled by temperature sensors that activate them when the transformer’s temperature reaches a certain threshold, ensuring efficient heat management.

2. Load Fluctuations and Peak Demands:

Power transformers over 3 MVA are often subject to fluctuating loads and peak demands, especially in industrial settings or during seasonal variations in power usage. During these periods, the transformer can become heavily loaded, generating excess heat. Fans help in managing these peaks by increasing the cooling capacity, allowing the transformer to operate safely even under high-stress conditions.

3. Prolonging Transformer Lifespan:

By effectively managing the heat generated in transformers over 3 MVA, fans contribute significantly to extending the transformer’s lifespan. Overheating is one of the leading causes of transformer degradation, leading to issues such as insulation failure and core damage. Proper cooling ensures that the transformer operates within its designed temperature limits, reducing wear and tear on internal components and thereby prolonging its operational life.

Increasing Transformer Capacity with Fans: ONAN/ONAF Transformers

Transformers equipped with ONAN (Oil Natural Air Natural) cooling systems rely on natural convection to cool both the oil and the air surrounding the transformer. However, this cooling method can be limited when the transformer is subject to heavy loads or in high-temperature environments. By adding fans, the cooling system can be upgraded to an ONAF (Oil Natural Air Forced) system, significantly improving the transformer’s performance.

1. Capacity Boost of Up to 1/3:

One of the key benefits of adding fans to an ONAN transformer is the potential to increase its rated capacity by up to 1/3. This is particularly advantageous in situations where load demands exceed the transformer’s original design specifications. By switching from ONAN to ONAF, the forced air cooling provided by the fans enhances heat dissipation, allowing the transformer to handle higher loads without overheating.

2. How It Works:

In an ONAN transformer, the oil circulates naturally, absorbing heat from the windings and dissipating it through the transformer’s radiators. When fans are added, the system transitions to ONAF, where the forced air generated by the fans increases the efficiency of heat transfer from the radiators to the surrounding environment. This enhanced cooling capability effectively increases the transformer’s load-bearing capacity, as it can now operate at higher temperatures without the risk of damage.

3. Operational Flexibility:

The ability to switch between ONAN and ONAF modes provides operational flexibility. Under normal conditions, the transformer can run in ONAN mode, conserving energy by relying on natural cooling. When higher loads are expected, the fans can be activated, enabling ONAF mode to accommodate the increased demand. This dual-mode operation ensures that the transformer can efficiently handle varying load conditions while maintaining optimal performance.

Ensuring Reliable Performance

The incorporation of fans in transformer cooling systems is essential for maintaining reliable performance, especially in scenarios involving high power ratings, compact designs, and elevated ambient temperatures. For power transformers with capacities over 3 MVA, fans are crucial for managing the high heat loads generated during operation. Additionally, for ONAN/ONAF transformers, the ability to increase the rated capacity by up to 1/3 with the addition of fans provides significant operational advantages, ensuring that transformers can meet increased demand while maintaining safe operating conditions. By effectively dissipating heat, fans help in prolonging the transformer’s lifespan, preventing insulation damage, and ensuring consistent performance under diverse operating conditions.