Inquiry Email Whatsapp

Transformer Cooling Methods Overview

1. Oil-Immersed Self-Cooling (ONAN)

The working principle of oil-immersed self-cooling is to harness the natural convection of oil to transfer the heat generated by the transformer to the surface of the oil tank and the location of the cooling tubes. Subsequently, the heat is dissipated through the effects of air convection and air heat conduction. This cooling system does not require specially prepared cooling equipment.

Products up to 31,500 kVA and 35 kV or below

Products up to 50,000 kVA and 110 kV

2. Oil-Immersed Forced-Air Cooling (ONAF)

The working principle of oil-immersed forced-air cooling is based on the principles of oil-immersed self-cooling. In addition to the basic principles, some fans are installed on the surface of the oil tank or on cooling tubes. These fans facilitate the cooling process by blowing air and can increase the transformer's capacity and load-carrying capability by nearly 35%. During operation, transformers generate losses such as iron loss, copper loss, and other forms of heat, which exist inside the transformer in the form of heat. The cooling process for oil-immersed transformers is as follows: first, through thermal conduction, the heat generated inside the iron core and windings is transferred to the surface and then to the oil. Subsequently, through the natural convection of the oil, the generated heat is continuously transferred to the inner walls of the oil tank and the radiator oil tubes. Through thermal conduction, the heat is then transferred to the outer surface of the oil tank and the radiator. Finally, through the effects of air convection and thermal radiation, the heat is transferred to the surrounding air.

Products 35 kV to 110 kV; from 12,500 kVA to 63,000 kVA

Products 110kV, below 75000kVA

Products 220kV, below 40000kVA

3. Forced-Oil Circulation Forced-Air Cooling (OFAF)

Products from 50,000 to 90,000 kVA and 220 kV

4. Forced-Oil Circulation Forced-Water Cooling (OFWF)

Used in general hydroelectric power plants for step-up transformers of 220 kV and above and products of 60 MVA and above.

The working principle of forced-oil circulation cooling and forced-oil circulation water cooling is the same. If the main transformer adopts a forced oil circulation cooling method, its operation is based on the circulation of oil within the transformer. It uses oil pumps to circulate the oil within the cooling system. The oil cooler is specially designed for efficient heat dissipation, and electric fans help to cool the medium. By increasing the oil circulation speed threefold, this method can increase the transformer's capacity by approximately 30%. The cooling process for forced-oil circulation transformers involves using a submerged oil pump to send oil into the oil pipes between the iron core or winding. The oil, which flows at a certain speed, carries away the heat generated, while the heated oil from the upper part of the transformer is extracted using a submerged oil pump. After cooling in the cooler, the oil is returned to the bottom of the transformer's oil tank, creating forced oil circulation cooling.

5. Forced-Oil Directed Circulation Forced-Air Cooling (ODAF)

Products of 75,000 kVA and above, 110 kV

Products of 120,000 kVA and above, 220 kV

Products of 330 kV class and 500 kV class

6. Forced-Oil Directed Circulation Forced-Water Cooling (ODWF)

Products of 75,000 kVA and above, 110 kV

Products of 120,000 kVA and above, 220 kV

Products of 330 kV class and 500 kV class

Components of a Forced Oil and Forced Air Cooling Transformer Cooler

Traditional power transformers are equipped with manually controlled fans. Each transformer typically has six sets of air-cooled motors that require control. The operation of these fans depends on the use of thermal relays. The fan power supply circuit is controlled through contactors. Fans operate based on temperature measurements inside the transformer's oil and load conditions, and their operation is determined through logical judgments. These traditional control systems rely heavily on manual intervention. However, a significant drawback is that all fans start and stop simultaneously, resulting in high inrush currents during startup, potentially damaging components in the circuit. Moreover, when the temperature is in the range of 45 to 55 degrees Celsius, the usual practice is to run all fans at full capacity, leading to significant energy wastage and maintenance challenges. Traditional cooling control systems mainly use components such as relays, thermal relays, and various contact-type logic circuits. The control logic is complex, and in practical operation, frequent contact and separation of contactors may cause burning. Furthermore, these fans often lack essential protections, such as overload, phase loss, and under-voltage, which can reduce operational reliability and increase costs.

Roles of the Transformer's Oil Tank and Cooling System

The transformer's oil tank serves as its outer shell, housing the core, windings, and transformer oil. Additionally, it provides some heat dissipation.

The cooling system for the transformer functions by creating oil circulation when there is a temperature difference between the upper and lower layers of oil in the transformer. This circulation moves the oil through the heat exchanger, allowing the hot oil at the top to flow downward. This process effectively reduces the temperature of the transformer oil. To enhance cooling efficiency, air cooling, forced oil and air cooling, or forced oil and water cooling measures can be employed.

We use cookies to ensure that we give you the best experience on our website. If you continue to use this site, we assume that you accept such use.