Hydrodynamics and heat transfer in cooling channels of oil-filled power transformers with multicoil windings

• The CFD model of the transformer with external cooling circuit has been developed.
• The model also includes all the cooling channels in the space between coils.
• The analysis of hydrodynamic processes has revealed self-organizing oil flow.
• The flow features have an influence on the thermal state of windings coils.
• Zones with the maximum temperature shift along height and toward the radial velocity.

The analysis of heat transfer and oil flow in power transformers at natural convection of cooling oil is carried out by numerical simulation of the fluid dynamic problem in axisymmetrical formulation (CFD-approach). The effects of self-organization structure of oil flowing in the form of the unidirectional flow in the groups of horizontal channels between winding coils have been revealed.The flow features have an influence on the thermal state of winding coils of the transformer with the natural cooling system. At such oil flowing, in different channels, the heat transfer coefficient varies within the limits of 50–100 W/(m2 K), and the radial component of velocity is changed over the range of 2.1·10−4–2.2·10−3 m/s. Thus the region with maximum temperature values is removed towards oil flowing along the coil radius.