Research On Heat Transfer Enhancement In The Axial Airway Of Casting Epoxy Resin Dry-type Transformer

In the construction of national economy,oil immersed transformer is still used largely in our country.While in the EU countries,the transformer of “oil free” is promoted vigorously,encouraging the use of dry type transformer as far as possible instead of oil immersed transformer.Dry type transformer has the advantages of small size,fire prevention,explosion protection,can penetrate into the load center.Therefore,the largely application of dry type transformer is the trend in our country.The thermal performance hinders the development of dry type transformer,resulting its capacity can not be too large.The mainly heat dissipation of dry type transformer is natural convection,which can have a long-term continuous operation,when over load is needed,it relies on forced wind cooling.In order to improve the heat dissipation capacity of dry type transformer,first,it should be in a well ventilated environment,making full use of wind pressure in the external environment to strengthen the ventilation effect of the transformer room.Second,the self structure must be considered of,by using some methods of heat transfer enhancement to improve heat dissipation of dry type transformer.In this paper,the numerical simulation method is used to study the different schemes to enhance the heat transfer capability of the dry type transformer under the condition of natural convection and forced wind cooling.The scheme is as follows:1.The airway braces of dry type transformer are designed and optimized,in terms of reducing the volume and covering area of braces and increasing turbulence,four kinds of brace structure are designed.2.The insulation cylinder structure between high and low voltage winding is designed and optimized,by increasing in height of insulation cylinder and using “chimney effect”,the natural convection heat dissipation capability is improved.3.Also using “chimney effect”,ventilation board is added at the top of the low voltage winding and air flux is aspirated more.Deflector is added at the bottom of the low voltage winding to reduce the inlet resistance,and more air is deflected into the airway.Meanwhile,structure and position optimization of both are studied.4.With vortex generator in the insulation cylinder and brace to strengthen the natural convection and forced wind cooling heat transfer.The optimum size of vortex generator is also studied.Each program has a specific model and implementation and numerical simulation analysis is conducted by commercial software Fluent.It is found that the above schemes can effectively reduce the average temperature rise and hot spot temperature rise of dry type transformer,which can improve the working life of the transformer.