Electrical device having heat generating components with improved heat removal using turbulent flow

An electric device (1) comprises a portion generating heat and a portion for dissipating said generated heat by heat exchange with a fluid, wherein said heat dissipating portion comprises means for generating a turbulent flow in the fluid.

BACKGROUND

Technical Field

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

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.

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

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.

This and other objects are achieved by an electric device in accordance with claim1.

Dependent claims define possible advantageous embodiments of the invention.

DETAILED DESCRIPTION

With reference to the annexed Figures, an electric device in general is indicated with reference1. 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.

The electric device1in 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 SF6(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, SF6(Sulfur hexafluoride), whereas secondary fluids can include air or water.

With reference for example to a transformer (FIG.1), it includes a core2and one or more windings3mounted to the core2, 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 tank4filled 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 core2and any metallic clamping structure thereof, the windings3, conductors connecting parts thereof, tank walls.

In this exemplary arrangement, the heat dissipating portions can for example include: internal cooling ducts5of the core2, the core outer surfaces6, windings internal cooling ducts7, windings outer surfaces8, insulated conductors9, internal or external tank walls10, fins15.

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).

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.

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

In accordance with a possible embodiment, the means for generating the turbulent flow comprise denticles11positioned so to be in contact with the fluid (FIG.2). Thus, the denticles can be added to the heat dissipating portions (e.g., internal cooling ducts5of the core2, the core outer surfaces6, windings internal cooling ducts7, windings outer surfaces8, insulated conductors9, internal or external tank walls10, fins15).

In accordance with a possible embodiment, the denticles11comprise ribs12positioned so to be in contact with the fluid. The ribs12comprise elongated bodies developing longitudinally on the heat dissipating portion surface13(e.g., on the surface of the internal cooling ducts5of the core2, on the surface of the core outer surfaces6, on the surface of windings internal cooling ducts7, on the surface of windings outer surfaces8, on the surface of insulated conductors9, on the surface of internal or external tank walls10, and/or on the surface of fins15). The main longitudinal dimension of the ribs is in particular parallel to the heat dissipating portion surface13, whilst ribs12height protrude transversally from the heat dissipating portion surface13. According to a possible embodiment, the means for generating the turbulent flow comprise a plurality of said ribs12, preferably oriented parallel one to each other. Still more preferably, the ribs12are 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 ribs12are grouped in a plurality of groups, wherein each group comprises a plurality of parallel ribs12. Advantageously, in each group the ribs12are dimensioned differently, such that their ends define two opposite sinusoidal waves14.

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 inFIG.3. The transformer inFIG.3comprises tank walls having corrugations15extending thereon externally. The corrugations15can be formed by a plate which is bended so to assume, in transversal section, a shape alternating peaks16and valleys17. Each corrugation15extends preferably parallel to the next one developing transversally to the heat dissipating portion surface, in this case transversally from the respective tank wall10. It is to be noted that in this embodiment corrugations15also 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.

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 (see, e.g.,FIG.10), still more preferably greater than 1 mm (see, e.g.,FIG.11). Advantageously, the roughness does not exceed 6 mm (see, e.g.,FIG.12).

According to a possible embodiment, the above described fins15in turn can have a high roughness with the values disclosed above.

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.

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.

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

InFIG.4a sectional view of core2according to an exemplary embodiment is shown. According to this embodiment, the core2comprises a plurality of lamination blocks18arranged between two opposite clamp plates24. Here the lamination blocks peripheries approximates a substantially circular shape where windings can be wounded. Inside the core, cooling ducts19are formed. The cooling ducts19may be the same cooling ducts as internal cooling ducts5. In particular, some lamination blocks18are spaced and the cooling ducts19are positioned or formed in the spaces20therebetween. The cooling ducts19extend longitudinally inside the core and a cooling fluid, such as oil, flows inside them. Inside the cooling ducts19, 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.

InFIGS.5-6cooling ducts19within windings3are shown in two possible embodiments. The winding turns are separated by insulating walls21. In a first embodiment (FIG.5), layer windings3are provided and cooling ducts19develop axially in or between the insulating walls21, which can be provided with the means for generating turbulent flow. In a second embodiment (FIG.6), foil windings26are provided and cooling ducts19extend longitudinally along the insulating walls21. The cooling ducts19can be formed for example between adjacent spacing ribs25formed in the insulating walls21. The cooling ducts19in both embodiments are provided with means for generating turbulent flow in the fluid flowing in the cooling ducts19. 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.

InFIGS.7-9conductors22are shown. In the embodiment shown inFIG.7, the means for generating the turbulent flow is a net23made of wire that is applied on the heat dissipating portion or wrapped around the heat dissipating portion such as being wrapped around the conductor22, forming the means for generating the turbulent flow. In the embodiment shown inFIG.8, the net23is wrapped on a continuously transposed cable, whilst in the embodiment inFIG.9, the means for generating the turbulent flow is a netting tape27that is wrapped on a continuously transposed cable. The netting tape27can carry a net, or be configured as a net itself, for example it can comprise a plurality of holes28. In all the above described cases, the net and the netting tape are configured to increase the surface roughness and therefore realize means for generating a turbulent flow.

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.