BACKGROUND Technical field

[001] The present invention relates to heat removal in electric devices, such as liquid immersed and dry-type transformers, and parts thereof, motors, fans, or the like.

Description of the Related Art

[002] In the transformers field, the transformer includes parts where heat is generated, such as the core and the windings. Heat is transferred from such parts to a fluid surrounding them and then eventually dissipated in the environment through a suitable cooling system. In general, the heat removal influences the dimensions of the cooling system and consequently the overall costs of the transformer.

[003] Similar considerations apply in different electric devices such as motors or fans, wherein heat is removed by the air flowing around heat dissipating portions thereof, such as fins, radiators or the like.

BRIEF SUMMARY OF THE INVENTION

[004] The object of the present invention is to provide an electric device, such as a transformer, a motor, a fan, or the like, configured for optimizing the heat removal, so to reduce the overall dimensions and costs of the device.

[005] This and other objects are achieved by an electric device in accordance with claim 1.

[006] Dependent claims define possible advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [007] Further characteristics and advantages of the electric device according to the invention will be more apparent from the following description of preferred embodiments given as a way of an example with reference to the enclosed drawings in which:

[008] Figure 1 shows a perspective, partially sectional, view of a transformer according to an embodiment of the invention; [009] Figure 2 shows a schematic view of means for generating a turbulent flow according to a possible embodiment of the invention;

[0010] Figure 3 shows a perspective, partially sectional, view of a transformer according to a further possible embodiment of the invention;

[0011] Figure 4 shows a schematic sectional view of a transformer core according to a possible embodiment of the invention;

[0012] Figure 5 shows a sectional view of a detail of a transformer winding according to a possible embodiment of the invention;

[0013] Figure 6 shows a partial perspective view of a detail of a transformer winding according to a further possible embodiment of the invention;

[0014] Figure 7 shows a perspective view of a conductor strand according to a possible embodiment of the invention;

[0015] Figure 8 shows a side view of a continuously transposed cable according to a possible embodiment of the invention;

[0016] Figure 9 shows a perspective view of a continuously transposed cable according to another possible embodiment of the invention.

DETAILED DESCRIPTION [0017] With reference to the annexed Figures, an electric device in general is indicated with reference 1. The electric device within the meaning of the present invention can include for example transformers, motors, fans, and parts thereof, such as conductors, a core, windings, a tank, radiators.

[0018] The electric device 1 in general comprises at least one portion generating heat and at least one portion for dissipating the heat generated by said heat generating portion. The heat is mainly generated due to electric phenomena, such as Joule effect, Eddy currents, hysteresis, or the like. In order to remove heat, the heat dissipating portion is in a heat exchange relationship, for example in contact, with a fluid. The fluid in general can include a liquid, such as oil, an ester or silicone, or a gas such as SF ₆ (Sulfur hexafluoride), or air. For example, in case of dry-type transformers, heat is removed by environmental air in contact with the transformer active part, which generates heat. It is however to be noted that sometimes heat is removed through a primary fluid and a secondary fluid. In particular, the heat generating portion can be in a heat exchange relationship with a primary fluid, which in turn is in a heat exchange relationship with the heat dissipating portion which is in a heat exchange relationship with a secondary fluid. For example, in mineral oil filled transformers, the oil flows around the active part, which generates heat. Heat is conveyed from the mineral oil to the cooling system, such as radiators, heat exchangers and the like. Then heat is conveyed from the cooling system to the environmental fluid, such as air or water. In general, therefore, primary fluids can include oil, ester, silicone, air, SF ₆ (Sulfur hexafluoride), whereas secondary fluids can include air or water.

[0019] With reference for example to a transformer (Figure 1), it includes a core 2 and one or more windings 3 mounted to the core 2, wherein each winding comprises at least a low voltage winding and at least a high voltage winding. Depending on the type of transformer, the windings can include cast coils, foil windings, layer windings, helical windings, disc windings, or foil-disc windings. The transformer can be placed in a tank 4 filled with oil if it is of the oil immersed type, or any other suitable fluid, as described above. In a transformer, the heat generating portions can for example include: the core 2 and any metallic clamping structure thereof, the windings 3, conductors connecting parts thereof, tank walls.

[0020] In this exemplary arrangement, the heat dissipating portions can for example include: internal cooling ducts 5 of the core 2, the core outer surfaces 6, windings internal cooling ducts 7, windings outer surfaces 8, insulated conductors 9, internal or external tank walls 10, fins 15.

[0021] It is to be noted that in a transformer the above heat dissipating portions can be in heat exchange relationship with air (for example the fins) or with oil (for example the internal tank walls).

[0022] According to the invention, the above cited heat dissipating portions comprise means for generating a turbulent flow in the fluid in contact with the heat dissipating portion itself. Indeed, usually the fluid in contact with the heat dissipating portions is laminar. If on the contrary the flow pattern is turbulent, the heat exchange with the fluid can be increased. As a consequence, for example it is possible to reduce the dimensions of heat exchanging surfaces.

[0023] The means for generating the turbulent flow can be configured in several manners.

[0024] In accordance with a possible embodiment, the means for generating the turbulent flow comprise denticles 11 positioned so to be in contact with the fluid (Figure 2).

[0025] In accordance with a possible embodiment, the denticles comprise ribs 12 positioned so to be in contact with the fluid. The ribs 12 comprise elongated bodies developing longitudinally on the heat dissipating portion surface 13. The main longitudinal dimension of the ribs is in particular parallel to the heat dissipating portion surface 3, whilst ribs 12 height protrude transversally from the heat dissipating portion surface 13. According to a possible embodiment, the means for generating the turbulent flow comprise a plurality of said ribs 12, preferably oriented parallel one to each other. Still more preferably, the ribs 12 are oriented such that their longitudinal direction is transversal to the fluid main flow direction, if the latter is known (for example in case of a forced flow around the heat dissipating portions). According to a possible embodiment, the ribs 12 are grouped in a plurality of groups, wherein each group 13 comprises a plurality of parallel ribs 12. Advantageously, in each group 13 the ribs 12 are dimensioned differently, such that their ends define two opposite sinusoidal waves 14.

[0026] In accordance with another embodiment, the means for generating the turbulent flow comprise corrugations on a surface of the heat dissipating portions, destined to be in contact with the fluid. To this regard, see for example the exemplary embodiment shown in Figure 3. The transformer in Figure 3 comprises tank walls having corrugations 15 extending thereon externally. The corrugations 15 can be formed by a plate which is bended so to assume, in transversal section, a shape alternating peaks 16 and valleys 17. Each corrugation 15 extends preferably parallel to the next one developing transversally to the heat dissipating portion surface, in this case transversally from the respective tank wall 10. It is to be noted that in this embodiment corrugations 15 also form fins. The same fins arrangement can be provided in a radiator of an electric machine of different type, such as an electric motor or a fan.

[0027] It is also to be noted that, according to further possible embodiments, corrugations can be more generally intended also with the meaning of high roughness surfaces. In other words, the heat dissipating portions in general can have high roughness surfaces forming the means for generating the turbulent flow, which can be obtained in several manners, for example by tooling the surface in a suitable manner, by printing the surface, or by spot painting a proper insulating material on the surface of the heat dissipating portion. Preferably, the high roughness surfaces have a roughness greater than 0,2 mm, still more preferably greater than 1 mm. Advantageously, the roughness does not exceed 6 mm.

[0028] According to a possible embodiment, the above described fins 15 in turn can have a high roughness with the values disclosed above.

[0029] In accordance with a further possible embodiment, the means for generating the turbulent flow comprise a net made of wire to be applied on the surface of the heat dissipating portion or to be wrapped around the heat dissipating portion. The net can be arranged in a netting tape.

[0030] It is to be noted that the above cited means for generating the turbulent flow can be positioned on conductive surfaces (such as fins, tank walls), on insulating surfaces (for example paper for insulating conductors), as well as in the cooling ducts.

[0031] In the following some further exemplary embodiments of electrical devices according to the invention will be described.

[0032] In figure 4 a sectional view of core 2 according to an exemplary embodiment is shown. According to this embodiment, the core 2 comprises a plurality of lamination blocks 18 arranged between two opposite clamp plates 24. Here the lamination blocks peripheries approximates a substantially circular shape where windings can be wounded. Inside the core, cooling ducts 19 are formed. In particular, some lamination blocks 18 are spaced and the cooling ducts 19 are positioned or formed in the spaces 20 therebetween. The cooling ducts 19 extend longitudinally inside the core and a cooling fluid, such as oil, flows inside them. Inside the cooling ducts 19, means for generating a turbulent flow in the cooling fluid, such as denticles or ribs of the types described above, or high roughness surfaces as discussed above, or of the types which will be described below, are provided. Furthermore, such means for generating a turbulent flow in the air or in the oil can be provided in the core outer surfaces.

[0033] In figures 5-6 cooling ducts 19 within windings 3 are shown in two possible embodiments. The winding turns are separated by insulating walls 21. In a first embodiment (figure 5), layer windings 3 are provided and cooling ducts 19 develop axially in or between the insulating walls 21, which can be provided with the means for generating turbulent flow. In a second embodiment (Figure 6), foil windings 26 are provided and cooling ducts 19 extend longitudinally along the insulating walls 21. The cooling ducts 19 can be formed for example between adjacent spacing ribs 25 formed in the insulating walls 21. The cooling ducts 19 in both embodiments are provided with means for generating turbulent flow in the fluid flowing in the cooling ducts 19. Additionally, means for generating a turbulent flow can be provided on the windings outer surfaces, for example in cast coils. This also improves the dielectric performance, in particular a higher creep strength is obtained.

[0034] In figures 7-9 conductors 22are shown. In the embodiment shown in figure 7, a net made of wire 23 is wrapped around the conductor 22, forming the means for generating the turbulent flow. In the embodiment shown in figure 8, the net 23 is wrapped on a continuously transposed cable, whilst in the embodiment in figure 9, a netting tape 27 is wrapped on a continuously transposed cable. The netting tape 27 can carry a net, or be configured as a net itself, for example it can comprise a plurality of holes 28. In all the above described cases, the net and the netting tape are configured so to increase the surface roughness and therefore realize means for generating a turbulent flow.

[0035] To the above-mentioned embodiments of electric device according to the invention, the skilled person, in order to meet specific current needs, can make several additions, modifications, or substitutions of elements with other operatively equivalent elements, without however departing from the scope of the appended claims.