As a critical component in power systems, the operational safety and efficiency of transformers are closely tied to the heat dissipation performance of their oil tanks. With the continuous growth in transformer capacity and increasingly complex working environments, the design of oil tank heat dissipation structures has become more significant than ever. Among the various designs, the plate radiator and the corrugated box wall are the two most widely adopted cooling structures. This article provides a systematic comparison of these two structures in terms of design principles, manufacturing processes, and application performance to support engineering design and product selection.
Structure and design concept
The plate radiator oil tank uses heat sinks to increase the heat transfer area of the transformer. It has a beautiful appearance and is a new type of transformer oil tank structure. This type of oil tank first welds the heat sink to the round tube (oil collecting pipe), and then welds the round tube to the wall of the transformer oil tank to ensure that the oil in the internal cavity of the heat sink is connected to the oil in the transformer oil tank, which can be applied to transformers with a larger capacity range.
As the capacity of the transformer increases, it is difficult to meet the heat dissipation requirements by simply welding the heat sink to the tank wall through a round tube. In this case, multiple heat sinks can be welded together to form a so-called plate radiator, and multiple groups of such radiators can be connected to the tank wall through connecting flanges.
Manufacturing process and specifications
The heat sink is generally pressed from thin steel plates. Each single piece has the same size, and every two single pieces are combined into a heat sink. The sheet width is generally 310mm, 460mm, and 530mm. The sheet spacing is 45mm. The upper and lower oil collecting pipes mostly use Ø80 welded steel pipes, and the center distance ranges from 1600 to 3200mm (every 200mm interval) standard size to adapt to different oil tank heights. Each group of radiators can be composed of different numbers of heat sinks according to the requirements of heat dissipation capacity.
A long notch that matches the shape of the end of the heat sink is opened on the oil collecting pipe, and a special automatic welding machine is used to weld the heat sink and the oil collecting pipe from the outside. Then weld the welded oil collecting pipe with heat sink to the tank wall like the elbow of the tubular oil tank (or weld the connecting flange).
Note: The tubular transformer oil tank is named after the elbows connected up and down, welded on the flat wall of the transformer oil tank. It is a traditional structure commonly used in small and medium-sized transformers. It has gradually been replaced by corrugated wall oil tanks.
Accessories and Functional Features
The upper oil collecting pipe of the detachable plate radiator is welded with an exhaust plug and a lifting lug, and the lower oil collecting pipe is welded with an oil drain plug. When the transformer needs to be cooled by air blowing, a support plate for fixing the air blowing device is also welded on the lower oil collecting pipe.
When the transformer capacity reaches 800kVA and above, it is recommended to install a pressure relief device and install a gas relay on the pipeline from the oil tank to the oil storage cabinet. Some manufacturers also use larger heat sinks on smaller capacity transformers. On the one hand, its function is to meet the requirements of heat dissipation; on the other hand, it uses a larger heat sink group to compensate for the expansion and contraction of transformer oil caused by temperature changes.
Application characteristics and advantages
The plate radiator system allows the installation of forced-air cooling fans at the bottom or sides, enabling it to serve transformers up to 240 MVA. In order to reduce the vibration of the plate-type radiator, reduce noise and prevent oil leakage, the plate-type radiators of the same transformer should be connected with each other by steel plates.
Since the plate-type radiator is formed by thin steel plates, it is much lighter than the tube-type radiator at the same heat dissipation capacity; on the other hand, from the manufacturing point of view, if a suitable special welding unit and forming unit are used to form a mechanized flow operation, the plate-type radiator is more superior than the tube-type radiator and more in line with the aesthetics of most people. Another advantage compared with general coolers is that it can still operate at around 60% load in the event of a failure of the blowing device, and is widely used in low-noise urban distribution transformers in urban power grids.
Corrugated transformer oil tank
Application Scope and Basic Structure
Corrugated oil tanks are mainly used for small and medium-sized transformers, and their cross-sections are mostly rectangular or elliptical. The bushing is generally installed on the oil tank cover (the low-voltage bushing can also be installed on the side of the tank wall, but this will sacrifice part of the corrugated heat dissipation area).
Material and corrugation design
The main material of the corrugated oil tank is generally made of high-quality carbon structural steel, such as Q235B. The thickness of the steel plate is determined according to the capacity and voltage level of the transformer, usually between 2.5mm and 6mm. The corrugated sheet material is generally cold-rolled steel sheet with a thickness of 0.5mm to 1.5mm, and its material should have good formability and corrosion resistance.
The inner side of the corrugated oil tank is filled with oil, which is connected to the oil inside the tank, which actually increases the heat dissipation area of the tank, thereby greatly improving the cooling performance of the transformer. The shape, size and arrangement of the corrugated sheet should be optimized according to the heat dissipation requirements of the transformer and the overall structure of the tank. The wave height of the corrugated sheet is generally between 30mm and 100mm, and the wave distance is between 50mm and 150mm.
Heat Dissipation and Expansion Compensation
Corrugated tanks provide natural convection cooling and eliminate the need for an external oil conservator by absorbing oil expansion through the flexible corrugations. The system must maintain a uniform surface temperature and keep maximum oil temperature rise below 55K (ONAN) or 65K (ONAF). The elastic deformation range of the corrugated sheets must meet oil volume changes between 25°C and 95°C without compromising the tank’s structural integrity or sealing performance.
Manufacturing process
The corrugation thickness W and the corrugation pitch P are both standard sizes, which are combined with the corrugation width B to form several standard size series. Based on this premise, it is continuously pressed with special equipment, and a gap without corrugation can be left to prepare for bending or rounding at this place to form the required box wall cross-sectional shape, or two or four pieces can be butt-jointed to form a box wall. After the box wall is formed, it is butt-welded with the pre-prepared box bottom and box edge to form a complete oil tank.
When the corrugation height is large, in order to prevent the corrugated box wall from deforming too much when the internal oil expands, several bosses are pressed out while the corrugation is pressed, and then the bosses are spot welded with a special spot welding machine.
The corrugation thickness W and the corrugation pitch P are both standard sizes, which are combined with the corrugation width B to form several standard size series. Based on this premise, it is continuously pressed with special equipment, and a gap without corrugation can be left to prepare for bending or rounding at this place to form the required box wall cross-sectional shape, or two or four pieces can be butt-jointed to form a box wall. After the box wall is formed, it is butt-welded with the pre-prepared box bottom and box edge to form a complete oil tank.
When the corrugation height is large, in order to prevent the corrugated box wall from deforming too much when the internal oil expands, several bosses are pressed out while the corrugation is pressed, and then the bosses are spot welded with a special spot welding machine.
Structural strength and accessories
To ensure the strength of the oil tank, a short, flat wall is still present at the box edge or bottom part, connected to the corrugation. The thickness of this short wall is usually thicker than the steel plate for pressing the corrugation, so that the lugs or other accessories can be welded on it.
For transformers with larger capacity, whether it is a tubular or corrugated oil tank, the lifting lug structure shown in the Figure is usually used.
When the corrugation width B is large and the length is long (the oil tank is high), the corrugations should be connected along the edge (periphery) of the corrugation with flat steel to increase its overall rigidity so that it will not generate large vibration and noise during transportation and transformer operation.
