WO2011039417A1

WO2011039417A1 - Method for cooling a coil, coil cooling system and liquid cooled coil

Info

Publication number: WO2011039417A1
Application number: PCT/FI2010/050752
Authority: WO
Inventors: Aleksi Naatula; Matti SEPPÄ; Pertti Arvonen
Original assignee: Trafotek Oy
Priority date: 2009-09-30
Filing date: 2010-09-30
Publication date: 2011-04-07
Also published as: FI20095996A0; CN202905379U; KR20120004367U; BR212012007336Y1; EE01184U1; BR212012007336U2; DE212010000159U1; ES1077591Y; DK201200055U3; AT13475U1; CZ24201U1; ES1077591U; DK201200055U1

Abstract

In the method cooling elements (102) are arranged in connection with a coil (100) and cooling liquid is led to flow through the cooling elements. The cooling elements are arranged in connection with the coil so that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil. The cooling system comprises at least three cooling elements, which are placed on the perimeter of the coil, so that the distance between adjacent cooling elements is essentially equal. The cooling elements can be placed outside the coil against the outer surface (122) of the coil, inside the coil against the inner surface (120) of the coil or inside the coil between superposed conductor wire or foil layers of the coil. The flow route of the cooling liquid comprises a cooling channel formed inside a cooling element, a first flow tube (112a) for leading the cooling liquid into the cooling channel and a second flow tube (112b) for leading the cooling liquid out of the cooling channel. The face surface (124, 126) of the cooling elements settling against the inner or outer surface of the coil can be curved. The coil to be cooled can be the coil of a choke or a transformer.

Description

Method for cooling a coil, coil cooling system and liquid cooled coil

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for cooling a coil, in which method cooling elements are arranged in connection with the coil and cooling liquid is led to flow along a flow route through the cooling elements. The invention further relates to a cooling system with liquid circulation for cooling a coil and a liquid cooled coil.

BACKGROUND OF THE INVENTION

Inductive components, such as transformers and chokes, have an insulated coil, along which electric current runs. In the centre of the coil there may be ah iron core or the coil can have an air core. The resistance of the coil causes heating of the coil. A very high amount of heat is generated especially in high-current inductive components. In order to keep the coil in an optimal operational temperature range specified for it, the coil needs to be cooled during use. Various cooling systems with liquid circulation have been developed for cooling transformers and chokes. A liquid cooled choke is known from patent publication Fl 118397 B, which choke comprises a core of the choke and a coil around the core. The core of the choke is divided into at least two parts, which are adapted to a cooling profile, through which one or more travel routes of the cooling liquid pass.

A method and a system for cooling a transformer are known from patent publication US 6157282. A coil is formed in the method, through which coil one or more channels in the longitudinal direction of the coil lead. The ends of the channel are connected with a tube to form a closed flow route for cooling liquid. The flow route can have a heat exchanger for cooling the cooling liquid. In this solution the cooling channel is formed inside the coil, which makes the structure of the inductive component complicated and its configuration difficult. Additionally the cooling surface area of the cooling channel is small, wherefore the cooling effect remains low. Patent publication EP 068055 A1 shows a transformer, where some of the conductor turns of the coil are hollow. The coil is cooled by circulating cooling liquid along the hollow conductor. In this solution voltage is induced in the cooling liquid, wherefore an electrically conductive liquid cannot be used as the cooling liquid. An electrically non-conductive liquid must thus be used in the cooling system or the apparatus must be equipped with a separate voltage remover for the cooling liquid. Both alternatives clearly raise the costs of the cooling system.

OBJECTS OF THE INVENTION An object of the invention is to provide a new method for cooling a coil, a coil cooling system and a liquid cooled coil, with which disadvantages and flaws relating to the prior art can be significantly reduced.

The objects of the invention are obtained with a method, a cooling system and a coil, which are characterized in what is presented in the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims.

DESCRIPTION OF THE INVENTION

The invention relates to a method for cooling a coil, such as a coil of a choke or a transformer. In the method at least three cooling elements are arranged in con- nection with the coil and cooling liquid is led to flow along a flow route through the cooling elements. The flow route comprises at least one cooling channel formed inside a cooling element, which cooling channel has a first opening for the inflow of cooling liquid and a second opening for the outflow of cooling liquid. The heat generated in the coil is thus by conducting transferred first into the cooling element and onwards into the cooling liquid flowing through the cooling element. In the method the cooling elements are arranged in connection with the coil so that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil. Significant voltage is thus not generated in the cooling liquid, even though an electrically conductive liquid, such as tap water, were to be used as the cooling liquid.

Three or more cooling elements are used in the method according to the invention, in order for the coil to be cooled evenly in its various parts. The cooling elements are advantageously placed on the perimeter of the coil, so that the distance between adjacent cooling elements is essentially equal.

In an advantageous embodiment of the method according to the invention at least some of the cooling elements are placed outside the coil against the outer surface of the coil. In an advantageous embodiment of the method according to the invention at least some of the cooling elements are placed inside the coil against the inner surface of the coil.

In an advantageous embodiment of the method according to the invention at least some of the cooling elements are placed inside the coil between the superposed conductor wire or foil layers of the coil.

A cooling system with liquid circulation according to the invention for cooling a coil comprises at least three cooling elements to be arranged in connection with the coil and a flow route for cooling liquid for circulating cooling liquid through the cooling elements. The flow route comprises at least one cooling channel formed inside a cooling element, which cooling channel has a first opening for the inflow of cooling liquid and a second opening for the outflow of cooling liquid. The cooling elements of the cooling system can be placed in connection with the coil to be cooled, so that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil.

In an advantageous embodiment of the cooling system according to the invention the first opening of the cooling channel is in the first end surface of the cooling element and the second opening of the cooling channel is in the second end surface of the cooling element. The cooling channel is advantageously a straight hole leading from the first end surface of the cooling element to the second end surface of the cooling element.

In an advantageous embodiment of the cooling system according to the invention the cooling element comprises at least two cooling channels. The cooling channels of the cooling element are advantageously essentially parallel.

In an embodiment of the cooling system according to the invention the first opening and the second opening of the cooling channel are in the same end surface.

In an advantageous embodiment of the cooling system according to the invention the flow route of the cooling liquid comprises a first flow tube for leading cooling liquid into the cooling channel, a second flow tube for leading cooling liquid out of the cooling channel and a bypass manifold, wherein the flow tubes are connected.

In an advantageous embodiment of the cooling system according to the invention the cooling element has at least one curved first face surface, which first face surface can be settled against the inner surface of the coil. The radius of curvature of the first face surface of the cooling element is typically 25-500 mm, advantageously 50-250 mm and especially advantageously 150-200 mm. The width of the cooling element is typically 30-200 mm. When the radius of curvature of the first face surface is selected so that it is essentially equal to the radius of curvature of the inner surface of the coil, the heat is efficiently transferred from the coil into the cooling element.

An advantageous embodiment of the cooling system according to the invention has at least one curved second face surface, which second face surface can be settled against the outer surface of the coil. The radius of curvature of the second face surface of the cooling element is typically 25-500 mm, advantageously 50- 250 mm and especially advantageously 150-200 mm.

Both of the face surfaces of the cooling element can be curved. The radii of curvature of the first and the second face surfaces can be equally large or of a different size. This embodiment of the cooling element is suited for placement inside the coil between superposed coil wire or foil layers.

A liquid cooled coil according to the invention comprises at least three cooling elements with liquid circulation and a flow route for cooling liquid for circulating the cooling liquid through the cooling elements. The flow route comprises at least one cooling channel formed inside a cooling element, which cooling channel has a first opening for the inflow of cooling liquid and a second opening for the outflow of cooling liquid. The flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil. The liquid cooled coil is advantageously the coil of a choke or a transformer.

It is an advantage of the invention that the cooling of the coil can by means of it be handled efficiently over the entire area of the coil.

It is a further advantage of the invention that no voltage is induced in the cooling liquid in it. An electrically conductive liquid, such as tap water, can thus in the invention be used as the cooling liquid.

It is an advantage of the cooling system according to the invention that it is structurally simple, small in size and small in mass. The small size and mass make possible the use of the cooling system in several different use situations.

It is a further advantage of the cooling system according to the invention that it can be placed entirely outside the structure of the coil. The cooling system does thus not require any structural changes in the coil itself. BRIEF DESCRIPTION OF THE DRAWING

In the following, the invention will be described in detail. In the description, reference is made to the appended drawing, in which

Figure 1a shows as an example a cooling system according to the invention seen diagonally from above,

Figure 1 b shows the cooling system of Figure 1a seen from above, in the direction of the longitudinal axis of the coil,

Figure 1c shows an individual cooling element of the cooling system of Figure 1a seen diagonally from above, Figure 2a shows as an example an advantageous embodiment of the cooling system according to the invention seen from above, in the direction of the longitudinal axis of the coil,

Figure 2b shows as an example a second advantageous embodiment of the cooling system according to the invention seen from above, in the direction of the longitudinal axis of the coil,

Figure 3a shows as an example an advantageous embodiment of a cooling element of the cooling system according to the invention seen diagonally from the front,

Figure 3b shows as an example a second advantageous embodiment of a cooling element of the cooling system according to the invention seen diagonally from the front,

Figures 4a-4d show some advantageous embodiments of the cooling elements of the cooling system placed in connection with a coil and

Figure 5 shows as an example a cooling element of the cooling system accor- ding to the invention seen diagonally from above.

DETAILED DESCRIPTION OF THE DRAWING

Figure 1a shows as an example a cooling system according to the invention seen diagonally from above and Figure 1 b shows it from above. The coil 100 to be cooled is constructed from one or more coil wire or foil layers, between which there are necessary insulations. The coil wire or foil layers form a tube-like structure, which has an inner surface 120 and an outer surface 122. In the centre of the coil there is an open cylindrical space, where there can be a ferritic coil core. The structure of the coil is commonly known prior art, hence it will not be described further here. There are four elongated cooling elements 102 around the coil. The cooling elements are arranged symmetrically around the coil, so that their longitudinal axis is essentially parallel to the longitudinal axis of the coil. In Figure 1 the cooling elements are parts, the cross-section of which is rectangular, i.e. they have two opposite face surfaces, a first face surface 124 and a second face surface 126, and two opposite edge surfaces (Figure 1 b). The cooling elements are placed so in connection with the coil that the first face surface 124 of the cooling element is settled against the outer surface 122 of the coil. The heat generated in the coil can thus by means of conducting transfer from the coil to the cooling element. A cooling channel 104 runs inside a cooling element, which cooling channel functions as the flow route of the cooling liquid (Figure 1 c).

Each cooling element is connected with two flow tubes 112a, 112b to a bypass manifold 110 belonging to the cooling system. The bypass manifold has an inlet connection 114, along which the cooling cooling liquid is led into the bypass manifold, and an outlet connection 116, through which the heated cooling liquid coming from the cooling elements is led out of the bypass manifold. The heated cooling liquid is cooled back to a suitable temperature in a heat exchanger, which can be attached to the cooling system, whereafter the cooling liquid is returned to the bypass manifold. The heat exchanger does not belong to the scope of this invention, hence it is not described in more detail here. Figure 1c shows an individual cooling element of a cooling system seen diagonally from above. The cooling channel 104 passes inside the cooling element in a U- shaped route starting from the first end surface 118 and ending in the first end surface. Inside the cooling element the cooling channel comes close to the second end surface. In the first end surface 118 of the cooling element, which end surface points upwards in Figure 1c, there are openings 106a, 106b of the cooling channel, wherein the second ends of the flow tubes are connected. The cross- sectional shape of the cooling channel is selected so that its flow resistance for the cooling liquid is as small as possible. The cooling elements are manufactured from some material which conducts heat well, such as aluminium. The heat conducted from the coil to the cooling element is thus easily transferred from the cooling element onwards into the cooling liquid flowing in the cooling channel. The cooling element shown in Figure 1 has one cooling channel, both of the openings of which open into the same end surface. One cooling element can also have several cooling channels, such as two, three or four cooling channels, and the openings of the cooling channels can open also in opposite end surfaces of the cooling element. At its simplest, the cooling channel can thus be a straight hole leading from the first end surface of the cooling element to the second end surface of the cooling element. The first flow tube thus connects to the first opening of the cooling channel in the first end surface and the second flow tube connects to the second opening of the cooling channel in the second end surface of the cooling channel.

Cooling liquid is led through the inlet connection 114 to the bypass manifold 110 and from the bypass manifold onwards along the first flow tubes 112a through the first opening 106a into each cooling element. Inside the cooling element heat is transferred by conducting from the cooling element to the cooling liquid. The cooling liquid exits the cooling element through the second opening 106b into the second flow tube 112b and onwards into the bypass manifold. Any suitable cooling liquid, such as tap water or a water-glycol mixture, can be used as the cooling liquid in the system. In the invention the flow tubes and cooling elements are placed around the coil, so that the flow route of the cooling liquid does not form a closed loop around any of the individual conductor wires of the coil 100. Significant voltage is thus not induced in the cooling liquid circulating in the cooling system, even though an electrically conductive liquid, such as tap water, were to be used as the cooling liquid.

Figure 2a shows as an example an advantageous embodiment of the cooling system according to the invention seen from above, in the direction of the longitudinal axis of the coil 100. In this advantageous embodiment of the invention the cooling elements 102 are placed inside the coil, so that the second face surface 126 of the cooling element settles against the inner surface 120 of the coil. The inside of the coil in this presentation means the space formed in the centre of the coil, delimited by the wire or foil layers of the coil. In this embodiment there are three cooling elements, and they are placed at even intervals against the inner surface of the coil. The first ends of the flow tubes 112a, 112b are connected to the bypass manifold 110 and the second ends to the openings of the cooling channels in the first end surface of the cooling elements. The cooling liquid thus flows into the cooling elements on the inside of the coil through the opening in the first end of the coil and exits from the inside through the same opening. The cooling liquid is not led to circulate around any individual conductor wire of the coil.

Figure 2b shows as an example a second advantageous embodiment of the cooling system according to the invention seen from above, in the direction of the longitudinal axis of the coil. In this embodiment the cooling elements 102 are in connection with the manufacturing of the coil 100 placed inside the coil between the superposed coil wire or foil layers. Also in this embodiment the flow tubes exiting the bypass manifold are connected to the cooling elements so that the flow route of the cooling liquid does not circulate around any of the individual conductor wires of the coil (the flow tubes and the bypass manifold are not shown in the figure).

The cooling systems shown in Figures 1a, 1 b, 1c, 2a and 2b have three or four cooling elements. The number of the cooling elements is however not limited to these numbers, but there can also be another number of them. What is essential in the invention is that there are so many cooling elements that a sufficient cooling effect is achieved with the system. The suitable number of cooling elements thus depends on the cooling needs of the coil, which in turn depends among others on the number of wire turns of the coil and the amount of electrical current passing in the coil. The system can thus include three, four, five, six, seven or eight cooling elements. It has through testing been discovered that at least three cooling elements have to be arranged in connection with the coil in order to achieve a sufficiently effective and evenly distributed cooling.

Figure 3a shows as an example an advantageous embodiment of an individual cooling element of the cooling system. In this embodiment the first face surface 124 of the cooling element is curved and the second face surface 126 is even. The first face surface has a radius of curvature R1. This advantageous embodiment of the cooling element is especially well suited for use in cooling systems, where the cooling elements are placed inside the coil, so that the first face surface 124 of the cooling element settles against the inner surface 120 of the coil. When the radius of curvature of the first face surface is selected so that it is essentially equal to the radius of curvature r1 of the inner surface of the coil, the heat is efficiently transferred from the coil into the cooling element.

Figure 3b shows as an example a second advantageous embodiment of an individual cooling element 102 of the cooling system. In this embodiment both the first face surface 124 and the second face surface 126 of the cooling element are curved. The first face surface has a radius of curvature R1 and the second face surface has a radius of curvature R2. The radii of curvature R1 and R2 can be equally large or of a different size. This advantageous embodiment of the cooling element is especially well suited for use in cooling systems, where the cooling elements are placed outside the coil, so that the second face surface of the cooling element settles against the outer surface of the coil. When the radius of curvature R2 of the second face surface is selected so that it is essentially equal to the radius of curvature r2 of the outer surface of the coil, the heat is efficiently transferred from the coil into the cooling element. The cooling element shown in Figure 3b is further suited for placement inside the coil between superposed coil wire or foil layers.

Figures 4a-4c show certain embodiments of the cooling elements shown in Figures 3a and 3b placed in connection with different coils 100. In the figures the coils are shown as seen from the end, in the direction of the longitudinal axis of the coil. In Figure 4a there is a coil 100 with a circular cross-section, the radius of the inner surface of which is r1. Three cooling elements 102, the first face surface 124 of which is curved, have been placed against the inner surface 120 of the coil. The radius of curvature R1 of the face surface is essentially equal to the radius of curvature r1 of the inner surface. In Figure 4b there is a coil 100 with an oval cross-section. The coil has a wall section s, the radius of curvature of which is r1. A cooling element 102 has been placed against this wall section of the coil, the radius of curvature R1 of the first face surface of which cooling element is essentially equal to the radius of curvature r1 of the wall section s1. In Figure 4c there is a coil 100 with a circular cross-section, the radius of curvature of the outer surface 122 of which is r2. Four cooling elements 102 have been placed against the outer surface 122 of the coil, the radius of curvature R2 of the second face surface of which cooling elements is essentially equal to the radius of curvature r2 of the outer surface of the coil. Figure 4d shows a coil, where four cooling elements 102 have in connection with the manufacturing of the coil been installed inside the coil 100 between superposed wire or foil layers of the coil. Both face surfaces of the cooling elements are curved. Figure 5 shows an individual cooling element of a cooling system according to an embodiment of the invention seen diagonally from above. The cooling channel 104 passes inside the cooling element 102 starting from the first end surface 118 and ending in the second end surface 119. In the first end surface 118 of the cooling element there is a first opening 106a of the cooling channel, through which the cooling liquid flows into the cooling channel. In the second end surface of the cooling element there is a second opening 106b, through which the cooling liquid exits the cooling channel.

Some advantageous embodiments of the method, the cooling system and the coil according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea can be applied in numerous ways within the scope of the claims.

Claims

1. A method for cooling a coil (100), in which method at least three cooling elements (102) are arranged in connection with the coil and cooling liquid is led to flow along a flow route (110, 112a, 112b, 104) through the cooling elements, which flow route comprises at least one cooling channel (104) formed inside a cooling element, which cooling channel has a first opening (106a) for the inflow of cooling liquid and a second opening (106b) for the outflow of cooling liquid, characterized in that the cooling elements are arranged in connection with the coil so that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil.

2. The method according to claim 1 , characterized in that at least some of the cooling elements (102) are placed outside the coil against the outer surface (122) of the coil.

3. The method according to claim 1 or 2, characterized in that at least some of the cooling elements (102) are placed inside the coil against the inner surface

(120) of the coil.

4. The method according to any of the claims 1-3, characterized in that at least some of the cooling elements (102) are placed inside the coil (100) between the superposed conductor wire or foil layers of the coil.

5. The method according to any of the claims 1-3, characterized in that the cooling elements (102) are placed on the perimeter of the coil (100), so that the distance between adjacent cooling elements is essentially equal.

6. The method according to any of the claims 1-5, characterized in that an electrically conductive liquid, such as tap water, is used as the cooling liquid.

7. The method according to any of the claims 1-6, characterized in that the method is used to cool one or more coils (100) of a choke or a transformer.

8. A cooling system with liquid circulation for cooling a coil (100), which cooling system comprises at least three cooling elements (102) to be arranged in connection with the coil and a flow route (110, 112a, 112b, 104) for cooling liquid for circulating cooling liquid through the cooling elements, which flow route comprises at least one cooling channel (104) formed inside a cooling element, which cooling channel has a first opening (106a) for the inflow of cooling liquid and a second opening (106b) for the outflow of cooling liquid, characterized in that the cooling elements can be placed so in connection with the coil to be cooled that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil.

9. The cooling system according to claim 8, characterized in that the first opening (106a) of the cooling channel (104) is in the first end surface (118) of the cooling element (102) and the second opening (106b) of the cooling channel is in the second end surface (119) of the cooling element.

10. The cooling system according to claim 9, characterized in that the cooling channel (104) is a straight hole leading from the first end surface (118) of the cooling element (102) to the second end surface (119) of the cooling element.

11. The cooling system according to any of the claims 8-10, characterized in that the cooling element (102) comprises at least two cooling channels (104).

12. The cooling system according to claim 11 , characterized in that the cooling channels (104) of the cooling element (102) are essentially parallel.

13. The cooling system according to claim 8, characterized in that the first opening (106a) and the second opening (106b) of the cooling channel (104) are in the same end surface.

14. The cooling system according to any of the claim 8-13, characterized in that said flow route for cooling liquid comprises a first flow tube (112a) for leading the cooling liquid into the cooling channel (104) and a second flow tube (112b) for leading the cooling liquid out of the cooling channel and a bypass manifold (110), wherein the flow tubes are connected.

15. The cooling system according to any of the claims 8-14, characterized in that the cooling element has at least one curved first face surface (124), which first face surface can be settled against the inner surface of the coil (100).

16. The cooling system according to any of the claims 8-15, characterized in that the cooling element has at least one curved second face surface (126), which second face surface can be settled against the outer surface of the coil (100).

17. A liquid cooled coil (100), which comprises at least three cooling elements (102) with liquid circulation and a flow route (110, 112a, 112b, 104) for cooling liquid for circulating cooling liquid through the cooling elements, which flow route comprises at least one cooling channel (104) formed inside a cooling element, which cooling channel has a first opening (106a) for the inflow of cooling liquid and a second opening (106b) for the outflow of cooling liquid, characterized in that the flow route of the cooling liquid does not form a uniform loop around the coil or around an individual conductor wire of the coil.

18. The liquid cooled coil (100) according to claim 17, characterized in that the coil has an inner surface (120) and at least some of said cooling elements (102) are placed inside the coil against the inner surface of the coil.

19. The liquid cooled coil (100) according to claim 17 or 18, characterized in that the coil has an outer surface (122) and at least some of the cooling elements

(102) are placed outside the coil against the outer surface of the coil.

20. The liquid cooled coil (100) according to any of the claims 17-19, characterized in that at least some of the cooling elements (102) are placed inside the coil between the superposed conductor wire or foil layers of the coil.

21. The liquid cooled coil according to any of the claims 17-20, characterized in that it is the coil of a choke or a transformer.