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Title:
WOUND CAPACITOR ENCAPSULATED IN HOUSING
Document Type and Number:
WIPO Patent Application WO/2019/141388
Kind Code:
A1
Abstract:
The present invention concerns a capacitor comprising a winding element (1), a housing (7) in which the winding element (1) is arranged, a first insulating material (11) which encapsulates the winding element (1), and a second insulating material (12) which forms a layer covering the first insulating material (11).

Inventors:
ALBENDIZ, Azahara (Centauro 8, Bajo D, Malaga, 29190, ES)
MOYANO, Alejandra (Av Miguel Fernandez de Alcuza, 1 B 3-2, Torremolinos, 29620, ES)
KULKARNI, Gayatri (Plot. No. 11, Near MIDC Pipeline Road, Nashik 7, 422007, IN)
BANDARUPALLI, Charan (Atmakuru, Mangalagiri Guntur,D. No 3-158/1, Andhra Pradesh 3, 522503, IN)
PANNALA, Kamalesh Kartik (Korlamapeta, Rajahmundry E.G.Dt., Andhra Pradesh,Door No.: 21-13-23, Behind Nagadevi theater, Rajahmundry 4, 533104, IN)
LI, Tim (Baijiao Nanlu Num 26 building #1, Zhuhai, 5, 519125, CN)
LI, Luis (Doumen, baiteng 2 streetHuxingshuian 11-30, Zhuhai 0, 519100, CN)
Application Number:
EP2018/071667
Publication Date:
July 25, 2019
Filing Date:
August 09, 2018
Export Citation:
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Assignee:
TDK ELECTRONICS AG (Rosenheimer Str. 141 e, München, 81671, DE)
International Classes:
H01G4/32; H01G4/224; H01G4/236; H01G2/10
Foreign References:
JP2877364B21999-03-31
JPS5911615A1984-01-21
JPS6189618A1986-05-07
US3806766A1974-04-23
DE7813772U11979-10-18
DE3130837A11983-02-24
US5196651A1993-03-23
Other References:
None
Attorney, Agent or Firm:
EPPING HERMANN FISCHER PATENTANWALTSGESELLSCHAFT MBH (Schloßschmidstr. 5, München, 80639, DE)
Download PDF:
Claims:
Claims (We claim)

1. Capacitor comprising

a winding element (1),

a housing (7) in which the winding element (1) is arranged,

a first insulating material (11) which encapsulates the winding element (1), and

a second insulating material (12) which forms a layer covering the first insulating material (11) .

2. Capacitor according to claim 1,

wherein the first insulating material (11) is more flexible than the second insulating material (12) .

3. Capacitor according to one of the preceding claims,

wherein the first insulating material (11) comprises polymer chains, and

wherein the second insulating material (12) comprises polymer chains, wherein an average length of the polymer chains of the second insulating material (12) is shorter than an average length of the polymer chains of the first insulating material (11).

4. Capacitor according to one of the preceding claims,

wherein the second insulating material (12) has a lower flammability than the first insulating material (11).

5. Capacitor according to one of the preceding claims,

wherein the first insulating material (11) has a higher adherence than the second insulating material (12) .

6. Capacitor according to one of the preceding claims, wherein the second insulating material (12) has a higher cross-linking rate than the first insulating material (11) ·

7. Capacitor according to one of the preceding claims,

wherein the first insulating material (11) comprises a polyurethane,

and

wherein the second insulating material (12) comprises a polyurethane or an epoxy resin.

8. Capacitor according to one of the preceding claims,

further comprising a wire (6) forming an electrically conducting terminal which is electrically contacted to the winding element (1),

wherein the wire (6) comprises at least one kink (8, 9) .

9. Capacitor according to the preceding claim,

wherein the at least one kink (8) is arranged such that it abuts an end face (2, 3) of the winding element (1) and an inner surface of the housing (7) .

10. Capacitor according to one of claims 8 or 9,

wherein the wire (6) comprises at least a second kink (9) .

11. Capacitor according to the preceding claim,

wherein the second kink (9) is arranged such that the parts of the wire (6) which are free of the first kink (8) and the second kink (9) do not contact the inner surface of the housing (7) .

12. Capacitor according one of claims 8 to 11, wherein projections (22a, 22b) are arranged at an inner surface of the housing (7) which form a guide for the wire ( 6) .

13. Capacitor according one of the preceding claims,

wherein a rib (20, 21) is arranged at an inner surface of the housing (7),

wherein the rib (20, 21) abuts the winding element (1), wherein the rib (20, 21) is adapted and arranged such that the rib ensures that the winding element (1) is surrounded by the first insulating material (11) in a minimum thickness.

14. Capacitor according one of the preceding claims,

wherein a material of the housing (7) comprises a polypropylene, a polybutylene terephthalate, a poly(p- phenylene sulfide) , a polycarbonate or a polyphenylene oxide

and/or

wherein the material of the housing (7) is reinforced with glass fibres.

15. Capacitor according one of the preceding claims,

wherein the capacitor is designed to withstand

temperatures of 85°C under a relative humidity of 85%.

Description:
Description

WOUND CAPACITOR ENCAPSULATED IN HOUSING

The present invention concerns a capacitor.

A self-healing metallized film capacitor which may be used for various applications typically consists of a winding element housed in a plastic or metal housing impregnated with insulating material. The metallized film capacitor is typically designed to work in ambient environment of -40°C to a maximum of 125°C. Under the effects of an application environment, the ambient working conditions and an applied electric field, the metallized film capacitor suffers from various capacitance loss mechanisms. The capacitance loss mechanisms are typically due to self-healings resulting in a loss of metallized electrode area and electrode oxidation.

Eventually, the metallized film capacitor fails due to a high capacitance drift. The failure should normally occur after the expected end of life of the capacitor. Drift in the capacitance is typically associated with an increase in the loss factor.

Present day applications demand key components to withstand higher amount of electrical as well as environmental

stresses. Capacitors are required to operate at higher ambient temperatures in the presence of high relative humidity conditions while achieving higher lifetime and reliability for the products.

Capacitance loss mechanisms are accelerated under harsh environmental working condition. In particular, the presence of humidity lead to corrosion on the metallized film. The capacitance loss phenomenon affect either an active electrode surface or an electrode edge. In electrochemical corrosion, the series resistance of the capacitor increases over a period of time causing a further increase in loss factor due to de-metallization of the metallized electrode leading to an increase in local hotspot temperatures. Higher ambient temperatures further accelerate this failure mechanism.

There is a growing demand for the capacitors capable to withstand high temperatures of 85°C or more, under high relative humidity of 85% or more. As discussed above, under these stringent ambient working conditions, the capacitance loss mechanisms are accelerated. Thus, this situation calls for new design considerations to be adopted in the metallized film capacitor.

Therefore, it is an object of the present invention to provide an improved capacitor which is less likely to suffer from capacitance loss mechanisms under harsh environment conditions .

This object is solved by a capacitor according to claim 1. Preferred embodiments are subject of the dependent claims.

A capacitor is provided which comprises a winding element, a housing in which the winding element is arranged, a first insulating material which encapsulates the winding element, and a second insulating material which forms a layer covering the first insulating material.

The capacitance loss mechanisms have been analyzed and it has been found that subjecting a capacitor to high thermal stresses may intensify the following capacitance loss

mechanisms: Cracks may be generated on the housing surface. Nano-pores and micro-scopic cracks may develop in the

insulating material, which may allow humidity to enter into the insulating material. There may be non-adhesion between the insulating material and the housing surface and non adhesion between insulating material and electrical

conducting terminals or leads. Further, the insulating material may be de-laminated from electrical conducting terminals or leads.

By providing a capacitor having two insulating materials, it is possible to optimize the first insulating material in such a manner that the above discussed capacitance loss mechanisms which may be intensified under high thermal stress can be prevented or at least significantly reduced. In particular, the first insulating material can be optimized to prevent at least one of the generation of cracks on the housing surface, the development of nano-pores and micro-scopic cracks in insulating material, the non-adhesion between the insulating material and the housing surface, the non-adhesion between insulating material and electrical conducting terminals or leads and the de-lamination between the insulating material and electrical conducting terminals or leads. Thermal

stresses may result, for example, from natural temperature changes in an environment or from heat being applied to the capacitor during a soldering process. The capacitor may be used in an environment having a high humidity, for example a relative humidity of 85% or more.

Apart from preventing these capacitance loss mechanisms, an insulating material has to fulfil other requirements in a capacitor, too. The second insulating material can be provided to fulfil these requirements, for example providing a low flammability. As these requirements may be fulfilled by the second insulating material, the first insulating material can be chosen without restrictions from the other

requirements. For example, there may not be a need that the first insulating material has a low flammability, if the low flammability of the capacitor can be guaranteed by the second insulating material.

The first insulating material may be a different material than the second insulating material. The first insulating material may form a fist layer and the second insulating material may form a second layer. The layers may not mix with each other. The second insulating material may have a lower density than the first insulating material. Thus, the second layer may float on the first layer.

The first insulating material may completely cover the winding element. In particular, the outer surface of the winding element may be completely covered by the first insulating material. Further, an opening extending through the winding element may be completely filled with the first insulating material. The second insulating material may not be in direct contact to the winding element.

The first insulating material may not provide any direct path for water vapor to the winding element. Accordingly, in the first insulating material, no cracks or voids may be formed and the first insulating material does may not suffer from a lack of adherence between interfaces. Otherwise, water vapor could quickly damage the winding element. The second

insulating material may be a barrier against water vapor diffusion . The first insulating material may be more flexible than the second insulating material.

The flexibility of an unbranched chain polymer may

characterized by its persistence length. The persistence length is a basic mechanical property quantifying the

stiffness of a polymer. For example, for pieces of a polymer that are shorter than their respective persistence length, the molecule behaves rather like a flexible elastic rod or beam, while for pieces of a polymer that are much longer than the persistence length, the properties can only be described statistically, like a three-dimensional random walk.

As the first insulating material may be very flexible, it may show a high adhesion. Therefore, the first insulating

material adheres to the winding element, to wires and to an inner surface of the housing in such a way that a de

lamination or non-adhesion does not occur between the first insulating material and these elements, even under high thermal stresses and/or high humidity. Thus, no channels or voids may be generated in the first insulating material which could be penetrated easily by humidity. Accordingly, due to its high flexibility, the first insulating material may protect the winding element against the above-discussed capacitance loss mechanisms.

As the second insulating material may not be in direct contact to the winding element, it may not have to have a high flexibility. Voids and channels in the second insulating material do not present a problem as humidity cannot access the winding element through these voids or channels. The first insulating material may comprises polymer chains, and the second insulating material comprises polymer chains. An average length of the polymer chains of the second

insulating material may be shorter than an average length of the polymer chains of the first insulating material. A shorter average length may result in a lower flexibility.

The second insulating material may have a lower flammability than the first insulating material. Further, the second insulating material may float on the first insulating

material and, thereby, it may form a sealing on the first insulating material preventing oxygen from contacting the first insulating material. Due to the low flammability of the second insulating material and due to the sealing of the first insulating material, an ignition of the first

insulating material may be prevented. Thus, very low

requirements can be posed to the flammability of the first insulating material. In particular, a highly flammable material may be used as a first insulating material. Flexible materials often have a high flammability.

The first insulating material may have a higher adherence than the second insulating material. The adherence of a material may describe the tendency of particles of this material to cling to dissimilar particles or surfaces. The higher adherence of the first insulating material may result from the first insulating material having a high free surface energy and a similar polar character than the surface to be bonded.. The polar character refers to the polarity of the material. Polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polarity underlies a number of physical properties including surface tension. As the first material may have a high adhesion, it may be connected to the winding element, the inner surface of the housing and to wires without forming any voids or channels even under thermal stress and/or high humidity. Thereby, the first insulating material may prevent the loss of capacitance of the winding element due to humidity affecting the winding element .

The second insulating material may have a higher cross- linking rate than the first insulating material. A cross-link is a bond that links one polymer chain to another. The cross- linking rate indicates a number of bonds between the polymer chains of the respective material. The first insulating material having a lower cross-linking rate than the second insulating material may further contribute to the first insulating material being more flexible than the second insulating material.

The first insulating material may comprise a polyurethane. In particular, the first insulating material may consist of a polyurethane. The second insulating material may comprise a polyurethane or an epoxy resin. In particular, the second insulating material may consist of a polyurethane or an epoxy resin. The polyurethane of the second insulating material may be different from the polyurethane of the first insulating material .

The capacitor may further comprise a wire forming an

electrically conducting terminal which is electrically contacted to the winding element, wherein the wire comprises at least one kink. The kink may help to center the winding element in the housing such that the winding element does not abut an inner surface of the housing. The kink may, thereby, ensure that the winding element is encapsulated in a layer of the first insulating material wherein the thickness of this layer corresponds to a width of a protrusion formed by the kink.

The at least one kink may be arranged such that it abuts an end face of the winding element and an inner surface of the housing. Thereby, the kink may ensure that the end face of the winding element is spaced apart from the inner surface of the housing at least by a width of the kink.

The wire may comprise at least a second kink. The second kink may be arranged such that the parts of the wire which are free of the first kink and the second kink do not contact the inner surface of the housing. Thus, the second kink may ensure that humidity cannot enter into the capacitor along a path formed by an abutment of the wire and the inner surface of the housing. The second kink may be covered with the first insulating material and the second insulating material.

Further, projections may be arranged at an inner surface of the housing which form a guide for the wire. The projections may help to fix the wire at its position even when the capacitor is subjected to high thermal stresses.

A rib may be arranged at an inner surface of the housing, wherein the rib abuts the winding element, wherein the rib is adapted and arranged such that the rib ensures that the winding element is surrounded by the first insulating

material in a minimum thickness. A material of the housing may comprise any polymer material which provides an electrical insulation, a high resistance to moisture ingress and withstands high temperatures and thermal stresses. For example, the material of the housing may comprise a polypropylene, a polybutylene terephthalate, a poly (p-phenylene sulfide) (PPS) , a polycarbonate or a

polyphenylene oxide (PPO) . The material of the housing may be reinforced with glass fibres.

The capacitor may be designed to withstand temperatures of 85°C under a relative humidity of 85%.

The capacitor may be a metallized film capacitor.

In the following, the invention and preferred embodiments are described with respect to the Figures.

Figure 1 shows a winding element of a capacitor.

Figure 2 shows a capacitor comprising the winding element.

Figure 3 shows a top view on the capacitor shown in Figure 2.

Each of Figures 4, 5 and 6 shows a cross-sectional view of the capacitor.

Figure 7 shows a more detailed view of a part of Figure 5.

Figure 8 shows a perspective view a wire which forms an electrically conducting terminal.

Figure 9 shows a schematic view of a part of the wire. Figures 10 shows perspective view of a housing of the

capacitor .

Figure 11 shows a partial view of one compartment of the housing .

Figure 12 shows a cross-sectional view of the compartment.

Figures 13 and 14 show cross-sectional views of a third embodiment of the capacitor.

Figure 1 shows a winding element 1 of a capacitor, in

particular of a metallized film capacitor. The winding element 1 has a cylindrical shape, in particular a right circular cylinder.

The winding element 1 is formed by a dielectric film which is metallized on its surface. A dielectric material of the film is a material in which electrostatic fields can persist for a long time. The dielectric material may include polypropylene (PP) , polyethylene terephthalate (PET) or polyethylene naphthalate. The winding element forms a parallel plate capacitor wherein the metallization is separated by the dielectric material.

The winding element 1 has two end faces 2, 3 opposite to each other. One end face 2 corresponds to a bottom face of the cylinder which is formed by the winding element 1 and the other end face 3 corresponds to a top face of the cylinder. The winding element 1 has an opening 4 which extends through the winding element 1 from one end face 2 to the other end face 3. The opening 4 is arranged along a symmetry axis of the cylinder. Each of the end faces 2, 3 is covered with a metallic contact layer, the so-called schoopage 5. The schoopage 5 allows to electrically contact the metallization of the dielectric film.

The schoopage 5 on each end face 2, 3 is contacted by a wire 6 which forms an electrically conducting terminal. In

particular, Figure 1 shows four wires 6, each wire 6 forming an electrically conducting terminal. A voltage can be applied to the winding element 1 via the wires 6. Each wire 6 is fixed to one of the end faces 2, 3 of the winding element 1, e.g. by soldering. In particular, two wires 6 are fixed to the bottom face and two wires 6 are fixed to the top face.

The wires 6 are fixed to the end faces 2, 3 in positions that are symmetric to each other. This arrangement of the fixing points of the wires 6 to the end faces 2, 3 helps to centre the winding element 1 inside a housing 7 of the capacitor. In an alternative embodiment, only exactly one wire 6 may be fixed to each end face 2, 3 of the winding element 1.

Each of the wires 6 has two kinks 8, 9, which will be

discussed in more detail later.

Figure 2 shows a capacitor comprising the winding element 1 in a perspective view. The capacitor further comprises the above-mentioned housing 7. The housing 7 forms a box having a bottom wall 7a and four side walls 7b, 7c, 7d, 7e. The housing 7 forms a cavity in which the winding element 1 is placed. The cavity is boarded by the bottom wall 7a and the side walls 7b, 7c, 7d, 7e. In particular, two of the side walls 7b, 7c are parallel to the end faces 2, 3 of the winding element. These two side walls 7b, 7c are each directly adjacent to one end face 2, 3 and spaced apart from the respective end face 2, 3 by a minimum distance. The other two side walls 7d, 7e are perpendicular to the end faces 2,

3.

The housing 7 further comprises a lid 10, which is not shown in Figure 2. In an alternative embodiment, the housing 7 does not comprise a lid 10. The lid 10 can be placed such that it closes the cavity formed by the housing 7. Accordingly, the lid 10 can be arranged opposite to the bottom wall 7a. The lid 10 has one opening for each of the wires 6 which form the electrically conducting terminals. Each wire 6 can protrude out of the cavity formed in the housing 7 through the

corresponding opening in the lid 10. Thereby, the wires 6 allow electrically contacting the winding element 1 to a circuit outside the housing 7.

The housing 7 is designed such that it will provide a high resistance to moisture ingress and withstand high

temperatures. In particular, the material of the housing 7 is chosen to provide high resistance to humidity and to thermal stress. The material of the housing 7 may be one of

polypropylene (PP) , polybutylene terephthalate (PBT) , p- phenylene sulphide (PPS) or nylon. The material of the housing 7 may be reinforced with glass fibres. Further, a thickness of the bottom wall 7a, the side walls 7b, 7c, 7d,

7e and the lid 10 is chosen to provide high resistance to humidity and to thermal stress.

The housing 7 is filled with two insulating materials 11, 12, as will be discussed in more detail later. In Figure 2, only a second insulating material 12 is visible. Figure 3 shows a top view on the capacitor shown in Figure 2. In Figure 3, sections AA, BB and CC are marked. Each of

Figures 4, 5 and 6 shows a cross-sectional view of the capacitor shown in Figure 3. The cross-sectional view shown in Figure 4 is taken along the section AA. The cross- sectional view of Figure 5 is taken along the section CC . The cross-sectional view of Figure 6 is taken along the section BB.

The capacitor comprises a first insulating material 11 and the second insulating material 12. Each of the first and the second insulating material 11, 12 forms a separate layers.

The layers do not mix with each other. A volume occupied by the first insulating material 11 is larger than a volume occupied by the second insulating material 12.

The first insulating material 11 completely encapsulates the winding element 1. The opening 4 extending from one end face 2 of the winding element 1 to the other end face 3 of the winding element 1 is completely filled with the first

insulating material 11. A height H of the cavity inside the housing 7 may be defined as the distance from the lowest point of an inner surface of the bottom wall 7a to the lid 10. The layer formed by the first insulating material 11 has a thickness which corresponds to at least 90% of the height H of the cavity, preferably to at least 95% of the height H of the cavity.

The second insulating material 12 is arranged on the first insulating material 11. In particular, in a direction from the bottom wall 7a of the housing 7 to the lid 10, the second insulating material 12 is arranged on top of the first insulating material 11. Each of the two insulating material 11, 12 is optimized for a different purpose. In particular, the first insulating material 11 is optimized to prevent or at least reduce capacitance loss mechanisms which over the lifetime of the capacitor result in a drift in the capacitance of the winding element 1. The second insulating material 12 is optimized to fulfil other tasks of an insulating material in a metallized film capacitor, in particular to provide a low flammability.

In a common capacitor having only one insulating material, different and sometimes contradicting requirements are demanded from the insulating material. As the capacitor has two insulating materials, it is possible to fulfil some requirements by the first insulating material 11 and some requirements by the second insulating material 12, thereby preventing problems from contradicting requirements.

The first insulating material 11 is a polyurethane. The first insulating material 11 is more flexible than the second insulating material 12. Each of the insulating materials 11, 12 comprises polymer chains. The polymer chains of the first insulating material 11 are longer than the polymer chains of the second insulating material 12.

The first insulating material 11 has similar polar character than housing 7.. Thereby, it is ensured that the first insulating material 11 shows a good adhesion to an inner surface of the housing 7, to the wires 6 and to the winding element 1. Thus, no voids or channels are formed in the first insulating material 11 or between the first insulating material 11 and one of the inner surface of the housing 7, to the wires 6 and to the winding element 1. Otherwise, there would be a significant risk that humidity from outside of the housing 7 accesses the winding element 1 via the voids or channels and, thereby, would result over a rather short time in a loss of capacitance of the winding element 1 and, eventually, in a failure of the capacitor.

Moreover, the first insulating material 11 is optimized to prevent cracks on the inner surface of the housing 7 due to its low expansion and contraction with temperature changes. The first insulating material 11 is optimized to prevent the development of nano-pores and microscopic cracks in the first insulating material 11 as the first insulating material 11 is very flexible. Thus, the first insulating material 11 is optimized to prevent or at least reduce capacitance loss mechanisms which may occur at high thermal stresses and/or high humidity.

The second insulating material 12 may be a polyurethane or an epoxy resin. The second insulating material 12 is more rigid than the first insulating material 11. The second insulating material 12 may be exposed to an external environment as it is formed on the top of a cavity defined by the housing 7.

The second insulating material 12 shows a low flammability.

In particular, the second insulating material 12 has a lower flammability than the first insulating material 11. The second insulating material 12 is optimized to have a low flammability and thereby to fulfil requirements regarding the flammability of the capacitor. As these requirements are fulfilled by the second insulating material 12, the first insulating material 11 can be optimized for preventing performance losses due to thermal stress and high humidity. Figure 7 shows a more detailed view of a part of Figure 5 which is marked in Figure 5 by line X. Figure 8 shows a perspective view of one of the wires 6 which forms an

electrically conducting terminal. Figure 9 shows a schematic view of a part of the wire 6.

The wire 6 comprises a first kink 8 and a second kink 9. Both kinks 8, 9 are arranged such that they are inside the housing 7 when the wire 6 is fixed to the end face 2, 3 of the winding element 1.

The wire 6 mostly forms a straight line. Each of the kinks 8, 9 defines a deviation from the straight line. Both kinks 8, 9 point in the same direction, i.e. away from the winding element 1 and towards the inner surface of the housing 7. The first kink 8 is arranged such that it abuts an inner surface of the housing 7 and the end face 2, 3 of the winding element

1. The first kink 8 forms a protrusion which protrudes by a distance D towards the inner surface of the housing 7.

Thereby, the first kink 8 ensures that a layer of the first insulating material 11 having a thickness of D is arranged between the inner surface of the housing 7 and the end face

2, 3 of the winding element 1. Accordingly, the first kink 8 prevents that the end face 2, 3 of the winding element 1 directly contacts the inner surface of the housing 7. The end face 2, 3 of the winding element 1 is covered by the

schoopage 5 which is very sensitive to humidity. As the first kink 8 prevents a direct contact of the schoopage 5 and the housing 7, humidity is prevented from travelling directly from the inner surface of the housing 7 to the schoopage 5.

The second kink 9 is arranged on the wire 6 at such a height that it is above the winding element 1 and below the second insulating material 12 in the direction from the bottom wall 7a to the lid 10. Accordingly, the second kink 9 is covered by the first insulating material 11. The second kink 9 ensures that the remainder of the wire 6 is spaced away from the inner surface of the housing 7 by a distance which is defined by a length L of a protrusion of the second kink 9. Accordingly, this space is filled with the first insulating material 11. The second kink 9 ensures that no air channel is created between the wires 6 and the inner surface of the housing 7 because the wires 6 and the inner surface of the housing 7 are separated by a minimum thickness of insulating material 11, 12..

In the following, the design of the wire 6 is described in more detail with respect to Figures 1, 8 and 9. Only one wire 6 is described in the following. However, each of the wires 6 is designed in the same manner. In the shown embodiment, the capacitor comprises four wires 6. However, the capacitor may also comprise another number of wires, for example two wires or six wires .

The wire 6 comprises a first straight section 13, a first kink 8, a second straight section 14, a second kink 9 and a third straight section 15. In the each of the straight sections 13, 14, 15, the wire 6 is completely straight, i.e. free from turns.

The first straight section 13 of the wire 6 is fixed to the schoopage 5 on the end face 2, 3 of the winding element 1.

The first straight section 13 does not extend beyond the end face 2, 3 of the winding element 1. The first straight section 13 merges over in the first kink 8. The first kink 8 is adjacent to the first straight section 13. The first kink 8 is formed by a first bend 16 of the wire 6, a second bend 17 of the wire 6 and a third bend 18 of the wire 6. The first bend 16 is in a direction away from the winding element 1 and towards the inner surface of the housing 7. The second bend 17 of the wire 6 is directly adjacent to the first bend 16. The second bend 17 is directed towards the winding element 1. The second bend 17 is arranged at a position furthest away from the winding element 1. The third bend 18 is directly adjacent to the second bend 17 and is formed such that the first kink 8 merges over to the second straight section 14. The first kink 8 is formed such that the distance D from the second straight section 14 to the inner surface of the housing 7 is identical to the distance from the first straight section 14 to the inner surface .

The second straight section 14 is dimensioned such that it extends beyond the end face 2, 3 of the winding element 1.

The second straight section 14 is completely arranged inside the layer of the first insulating material 11. The second straight section 14 merges over into the second kink 9.

The second kink 9 is completely arranged inside the layer of the first insulating material 11. The second kink 9 is formed by three bends similar to the first kink 8. The first and the second bend are formed identical. The third bend of the second kink 9 is formed at a different position. Thus, the distance L from the third straight section 15 to the inner surface of the housing 7 is smaller than the distance D from the second straight section 14 to the inner surface. The second kink 9 merges over into the third straight section 15. The third straight section 15 extends through the layer of the second insulating material 12 and protrudes out of the housing 7.

Figures 10 shows a perspective view of the housing 7 of the capacitor according to a second embodiment. The housing 7 comprises multiple compartments 19, each compartment 19 being configured to receive one winding element 1. Figure 10 shows the housing 7 upside down. It can be seen in Figure 10 that the bottom of each compartment 19 is curved.

Figure 11 shows a partial view of one of the compartments 19 wherein parts of the housing 7 are not. The compartment 19 is free of a lid. In an alternative embodiment, the compartment 19 may additionally comprise a lid 10.

Figure 12 shows a cross-sectional view of the compartment 19 shown in Figure 11.

Ribs 20, 21 are arranged on the inner surface of the housing

7.

The bottom wall 7a of the housing is shaped as a halfpipe.

The halfpipe has the radius R. Two ribs 20 are arranged at the bottom wall 7a of the housing 7. At the position of the ribs 20, the bottom wall 7a has a reduced radius r which is smaller than the radius R. When the winding element 1 rests on the ribs 20, the winding element 1 is spaced away from the remainder of the bottom wall 7a by at least a minimum

distance which corresponds to the difference between the radius R and the radius r. Further, ribs 21 are arranged at the inner surfaces of the side walls 7d, 7e of the housing 7 which are perpendicular to the end faces 2, 3 of the winding element 1. In particular, three ribs 21 are arranged on the inner surface of one of the side walls 7d, 7e that are perpendicular to the end faces 2,

3 and three ribs 21 are also arranged on the inner surface of the opposite side wall 7d, 7e.

The ribs 21 on the side walls 7d, 7e abut the winding element 1 and, thereby, ensure that the winding element 1 is centred inside the housing 7. The ribs 21 further ensure that the winding element 1 is spaced apart from the inner surface of the housing 7 and does not directly contact the inner

surface. Thus, it is prevented that humidity can access the winding element 1 directly from the housing.

Moreover, on the inner surface of the side faces 7b, 7c which are arranged adjacent to the end faces 2, 3 of the winding element 1, two rails 22 are defined by projections of the inner surface. These rails 22 form guiding elements for the wires 6 which are used as electrically conducting terminals. The rails 22 help to keep the wires 6 in their respective position even when thermal stress is applied to the

capacitor. Each rail 22 is formed by two projections 22a, 22b which are arranged to sandwich the corresponding wire

inbetween .

Figures 13 and 14 show cross-sectional views of a third embodiment of the capacitor. The housing 7 of the capacitor comprises a flat bottom wall 7a. Two ribs 20 are arranged at the bottom wall 7a. Each of the two ribs 20 protrudes into the inside of the housing 7. The winding element 1 rests on the ribs 20. Thus, the winding element 1 is spaced away from the remainder of the bottom wall 7a by at least a minimum distance which corresponds to a height of the ribs 20.

Figures 13 and 14 show a housing 7 which consists of only one compartment. In an alternative embodiment, the housing 7 may comprise multiple compartments wherein each compartment has a flat bottom wall 7a.

The housing 7 may additionally comprise ribs 21 arranged at the inner surfaces of the side walls 7d, 7e of the housing 7 similar to the second embodiment. The housing 7 may

additionally comprise two rails 22 defined by projections of the inner surface similar to the second embodiment. These rails 22 may form guiding elements for the wires 6 which are used as electrically conducting terminals.

Reference numerals

1 winding element

2 end face

3 end face

4 opening

5 schoopage

6 wire

7 housing

7a bottom wall

7b side wall (parallel to end face)

7c side wall (parallel to end face)

7d side wall

7e side wall

8 first kink

9 second kink

10 lid

11 first insulating material

12 second insulating material

13 first straight section

14 second straight section

15 third straight section

16 first bend

17 second bend

18 third bend

19 compartment

20 rib

21 rib

22 rail

22a projection

22b projection

H height of cavity D protrusion of first kink L protrusion of second kink

R radius of the bottom wall r radius of the ribs