Air-Oil Cooler for Large Capacity Power Transformer

Air-Oil Cooler for Large Capacity Power Transformer

Large capacity power transformers require highly efficient cooling equipment, and air-oil coolers are one of the commonly used cooling devices.

The hot oil in the transformer transfers heat to the cooling tubes when flowing through the finned tubes. The heat on the surface of the finned tubes is taken away by the air flow above it under the forced action of the fan, so as to keep the transformer operating at a proper temperature.

Structural Composition

Heat Exchanger: Usually, aluminum plate-fin heat exchangers are used. The heat exchanger is a cross-flow type. The oil flow path is generally more than one meter long, and the air flow path is generally 0.2-0.3 meters long. The fins on the air side are generally 10-15mm high and 0.1-0.2mm thick, and are flat; the fins on the oil side are generally 2-3mm high and 0.2-0.3mm thick, and are serrated.

Submersible Oil Pump: It is composed of a casing and a pump body. The casing is welded with steel plates, and a non-metallic sealing bushing is inlaid at the sealing place of the oil inlet impeller chamber to prevent leakage. The pump body is composed of a special three-phase asynchronous motor and a centrifugal single-stage impeller directly installed at the motor shaft extension end, with a head of generally less than 10 meters and a flow rate of about 120 cubic meters per hour.

Fan: It is composed of an axial-flow single-stage impeller and an outdoor three-phase asynchronous motor. The impeller adopts forward-swept twisted blades to reduce noise.

Control Box: In order to prevent the thermal relay from malfunctioning due to the high ambient temperature, a tube is welded in the control box to communicate with the air duct to force air to flow in the control box. Relays for the fan and oil circuit are installed in the control box.

Advantages

High Heat Dissipation Efficiency: The heat transfer efficiency is high due to the good thermal conductivity of aluminum materials and the large heat exchange area of the plate-fin structure.

Compact Structure: The heat exchange area per unit volume is twice that of the fin-tube type, so the volume is greatly reduced, which is convenient for installation and saves space.

Low Power Consumption: Due to the large heat exchange area, the air volume and oil flow can be reduced, resulting in a decrease in the power consumption of the fan and oil pump, and the unit capacity power consumption can be greatly reduced.

Good Corrosion Resistance: The anti-rust aluminum material has good corrosion resistance, which is equivalent to that of copper materials and better than that of galvanized steel plates.

Application Scenarios

It is mainly applicable to large-capacity power transformers, such as main transformers in substations and industrial large transformers, usually those above 110kV and with a capacity above 10MVA. For example, in power systems, transformers with a capacity of 60MVA and above basically use forced-oil circulation air-cooled transformers.