Patent EA-001869-B1 (EA)
Title: Axial-cooling of transformers
Inventor: KYLANDER GUNNAR
IPC: H01F27/08
Filed: 1998-02-02
Abstract: 1. A power transformer (1) comprising a transformer core, characterized in that the core is wound with a cable and that the cable is a high-voltage cable (111) which is composed of a core having a plurality of strand parts (112), an inner semiconducting layer (113) surrounding the core, an insulating layer (114) surrounding the inner semiconducting layer (113), and an outer semiconducting layer (115) surrounding the insulating layer (114) and that the winding is provided with spacers (4, 12) arranged to separate each cable turn in radial direction in the winding in order to create axial cylindrical cooling ducts (3). 2. A power transformer as claimed in claim 1, characterized in that the spacers (4, 12) are arranged axially between each turn of the winding. 3. A power transformer as claimed in claim 2, characterized in that at least six spacers (4) are distributed uniformly around the legs (8) of the transformer core. 4. A power transformer as claimed in any of claims 1-3, characterized in that the transformer winding is provided with a fan cowl (9) sealing against one end of the outermost turn of the winding, to which a fan (10) is connected and arranged to either force gas, such as air, through or withdraw gas, such as air, air from all turns of the winding axially to the transformer core (8). 5. A power transformer as claimed in any of the claims 1 to 4, characterized in that the high-voltage cable (111) has a diameter within the interval of 20 - 250 mm and a conducting area within the interval of 40 - 3000 mm<2>. 6. A power transformer as claimed in any of claims 1-5, characterized in that the cable (111) is flexible and the layers abut one another. 7. A power transformer as claimed in any of claims 1-6, characterized in that said layers are of materials having such elasticity and such coefficient of thermal expansion that the changes in volume in the layers caused by temperature fluctuations during operation are absorbed by the elasticity of the material, the layers thus retaining their adhesion to each other upon the temperature fluctuations that occur during operation. 8. A power transformer as claimed in any of claims 1-7, characterized in that the material in said layers has high elasticity, preferably with a modulus of elasticity less than 500 MPa, preferably less than 200 MPa. 9. A power transformer as claimed in any of claims 1-8, characterized in that the coefficients of thermal expansion for the materials in said layers are substantially the same. 10. A power transformer as claimed in any of claims 1-9, characterized in that the adhesion between layers is of at least the same magnitude as in the weakest of the materials. 11. A power transformer as claimed in any of claims 1-10, characterized in that each of the semiconducting layers essentially constitutes one equipotential surface. 12. A method of air-cooling a cable-wound power transformer according to any of the previous claims, characterized in that at least one fan (10) forces or withdraws air along the surface of the legs (8) of the transformer core and axially between each turn of the winding. 13. A method as claimed in claim 12, characterized in that temperature sensors control the speed of the fan to produce a suitable air flow.