EP1247284A1

EP1247284A1 - A capacitive element and electric devices comprising such an element

Info

Publication number: EP1247284A1
Application number: EP01942468A
Authority: EP
Inventors: Anders Aberg; Stefan Valdemarsson
Original assignee: Asea Brown Boveri AB; ABB AB
Current assignee: ABB AB
Priority date: 2000-01-14
Filing date: 2001-01-12
Publication date: 2002-10-09
Also published as: JP2003520425A; CA2397461A1; WO2001052287A1; AU2001228968A1; CN1418367A

Abstract

A capacitive object comprising an elongated layered structure (10, 11, 14, 15, 55, 56, 20, 60, 61, 36, 62), which includes one or several sets of two electrode forming layers (5, 6, 13, 17) of electrically conductive material, which two layers are mutually separated by at least one layer (3, 4, 16) of an electrically insulating material. The capacitive object is designed as a cable-shaped conductor, the elongated layered structure being surrounded by a protective sheath (22). The invention also relates to a capacitor and other electric devices comprising such a capacitive object and the use of such electric devices in a high voltage network.

Description

A capacitive element and electric devices comprising such an element

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a capacitive object according to the preamble of claim 1 and a method for production thereof. The invention also relates to a capacitor and a bank of capaci- tors. Furthermore, the invention relates to an electric device having capacitive as well as inductive properties, and a filter for filtering harmonics in a high voltage network. The invention also relates to the use of a capacitor and the electric device.

The capacitor and the bank of the capacitors according to the invention are particularly intended for use in connection with a network for transmission and distribution of electric power, and in particular for high voltage applications but also for low voltage and medium voltage applications. High voltage here refers to voltages being higher than 1 kV, preferably higher than 10 kV.

When producing capacitors, it is previously known to let a capacitor comprise a capacitive object comprising two dielectric films, each of which in its turn being provided with an electrically conductive layer on one of its sides. The electrically conductive layers have interruptions extending in their longitudinal as well as in their latitudinal direction. The electrically conductive layers will consequently have a plurality of rectangular, electrically conductive elements, each of which being electrically insulated from adjacent electrically conductive elements. Furthermore, the electrically conductive layers are arranged in such a way in rela- tion to each other that an electrically conductive element in one of the electrically conductive layers overlaps two electrically conductive elements in the longitudinal direction of the dielectric film and two electrically conductive elements in the latitudinal di- rection of the dielectric film in the other electrically conductive layer. In this way, a network of capacitor elements is formed, which capacitive elements are mutually connected in series and in parallel. The advantage of such an arrangement of a network of capacitor elements, in comparison with a capacitor which only has two continuous, electrically conductive layers separated by a dielectric film, is that a breakthrough in the dielectric film only results in that a single capacitor element will be put out of operation. The area of the electrically conductive layers being disconnected due to the breakthrough is thereby limited to the size of the electrically conductive element of the capacitor element. The size of the area of the electrically conductive layers being disconnected due to the breakthrough will thereby be very small in comparison with the case for a capacitor having continuous electrically conductive layers.

Conventional capacitors comprising two dielectric films provided with layers of electrically conductive elements on one of the sides of the respective film, are arranged rolled up so as to form a roll built up in layers. In the radial direction of the roll, every second layer is therefor of electrically conductive elements and every second layer of dielectric film.

A dielectric film is provided with a layer of electrically conductive elements by being covered, normally by steaming, with a thin layer of metal, such as aluminium or zinc. Said dielectricum preferably consists of polypropylene.

In a capacitor arranged in the form of a roll and having two rolled up dielectric films, each of which being provided with said layer of electrically conductive elements, the layers of electrically conductive elements will form several turns in the roll. The turns increase in circumference with increasing radius. The electrically conductive elements in the two layers will therefor be displaced to a different extent in relation to each other in the circumference direction. This implies, in its turn, that the capacitor elements formed by the electrically conductive elements will have different capacitances. A capacitor roll formed in this way and being put under voltage will therefor have a non-uniform voltage distribution over the capacitor elements.

The above mentioned capacitors are today used in connection with networks for transmission and distribution of electric power. Many electric components, such as for instance transformers and electric motors, consume reactive power. The generators in the power stations can deliver such reactive power, but since the reactive power burdens lines and cables, it is advantageous to generate the reactive power as close as possible to the load.

Capacitors have a phase angle close to 90° and therefor generate reactive power. By connecting capacitors close to the com- ponents that consume reactive power, the desired reactive power can be generated there. Lines and cables can thereby be fully used for transmission of active power. The consumption of reactive power of the load can vary, and it is desirable to always generate an amount of reactive power corresponding to the con- sumption. For this purpose, several capacitors are connected in series and/or in parallel in a so-called bank of capacitors. A required number of capacitors can be connected so as to correspond to the consumed reactive power. To compensate for consumed power by using capacitors in the above mentioned way is called power correcting. A bank of capacitors in the form of a so-called shunt bank is for this purpose arranged closed to the components that consume reactive power. Such a shunt bank consists of several capacitor units connected together. The separate capacitor unit comprises, in its turn, several capaci- tors. The construction of such a conventional capacitor unit is explained below. A shunt bank normally comprises a number of chains of several series connected capacitor units. The number of chains is determined by the number of phases, which normally is three. The first one of the capacitor units in a chain is connected to a line for transmission of power to the consuming component. The line for transmission of electric power is arranged at a distance from the ground, which distance depends on the voltage of the line. The capacitor units are connected in series from the first capacitor unit, which is connected to the line, and downwards. A second capacitor arranged at an end of the chain of series connected capacitor units opposite the first capacitor unit is connected to ground. The number of capacitor units and the construction of these is determined in such a way that the voltage over the series connected capacitor units corresponds to the voltage in the line. Several capacitor units are se- ries connected and arranged on platforms on different levels in altitude at a stand. A number of pin insulators are furthermore arranged between adjacent platforms. Consequently, such a bank of capacitor comprises several different components and requires a relatively large amount of material. Furthermore, a relatively robust construction is required for the stand to endure external influence in the form of wind, earthquake etc. It is therefor laborious to build such a bank of capacitors. This problem is particularly noticeable when the bank of capacitor consists of a large number of capacitor units. Furthermore, the bank of capacitors occupies a relatively large area of land.

Long lines for alternating voltage are inductive and consume reactive power. Banks of capacitors for so-called series compensation are therefor arranged at mutual distances along such a line, for generation of the required reactive power. Several capacitor units are connected in series for compensating the inductive voltage drop. In a bank of capacitors for series compensation, the series connection of the capacitor units normally, in contrast to a shunt back, only takes up a part of the voltage in the line. The chains of series connected capacitor units included in the capacitor bank for series compensation are furthermore arranged in series with the line to be compensated.

A conventional bank of capacitors comprises several capacitor units. Such a capacitor unit, in its turn, comprises several capacitors in the form of capacitor rolls. The capacitor rolls are flat and piled near each other so as to form a pile of for instance 1 m. A very large number of dielectric films with intermediate metal layers will be arranged in parallel in the vertical direction of the pile. When a voltage applied over the pile increases, the pile will be somewhat compressed in vertical direction due to Coulomb-forces, which act between the metal layers. When the voltage is lowered, the pile will expand somewhat in the vertical direction for the same reason. The pile has a certain mechanic resonance frequency, or natural frequency, which is relatively low. A strong noise will arise if the frequencies of the current are close to the mechanic resonance frequency of the pile. Such a frequency is constituted by the network frequency, which is defined by the fundamental tone of the current and normally is 50 Hz. Noise can also be caused by overtones of the current.

When producing a capacitor unit, several capacitor rolls, fuses and discharge resistors are arranged in a container, which thereafter is being filled with impregnating liquid. Means are being arranged for connection of the capacitor unit to further capacitor units. Several capacitor units formed in this way are subsequently connected so as to form part of a bank of capacitors. The assembly of a capacitor unit takes place step by step, i.e. component after component is being assembled, which is time consuming and economically disadvantageous.

As mentioned above, the present invention also relates to an electric device having capacitive as well as inductive properties. The electric device is particularly intended for use in high volt- age applications, but can also be used for low and medium voltage applications. High voltage here refers to voltages being higher than 1 kV, preferably higher than 10 kV. The electric device is particularly intended for use in connection with a network for transmission and distribution of electric power and then in particular as a filter for the purpose of filtering harmonics.

Henceforth, the inventional electric device having capacitive as well as inductive properties will be explained when constituting a filter for filtering harmonics in a network for high voltage. This field of application is only discussed in exemplifying purpose and not in any way in a limiting purpose.

Different apparatus arranged in industrial plants, such as static frequency changers and soft starters, comprise thyristors and influence or distort the voltage curve in one way or another. This type of apparatus give an effective use of electric energy, but they generate disturbances in the form of harmonics on the network. All electric apparatus intended for use in alternating current networks are dimensioned for a voltage having a curve shape in the form of a clean and smooth sine curve. In a net- work having apparatus which generate harmonics, it is however more common that the voltage has a distorted curve shape, where the sine shape is distorted. This distortion is an aggregation of harmonics. Harmonics are disturbances consisting of voltage and current having a higher frequency than the funda- mental frequency, the fundamental tone, of the network. The harmonics have frequencies which are multiples of the frequency of the fundamental tone. Harmonics are not desired and can for instance disturb telecommunication as well as computer and electronic controls.

According to previous technique, a harmonic filter in power applications consists of a capacitor connected in series with a coil, a reactor, where the included components are dimensioned so as to create a series resonant circuit for a given frequency. By means of such a filter, a harmonic can be filtered away. A so- called tuning frequency for the filter is determined for the filter by means of the formula (1 ) below, where ω_n is the tuning frequency, C is the capacitance of the capacitor and L is the inductance of the coil. The capacitance of the capacitor depends on the need of reactive power.

ω. = 1

In order to achieve a filter, a capacitor is arranged in series with a coil, the capacitor and the coil are produced separately and are connected to each other via a conduit. The connection of the capacitor and the coil can either be done before they are transported to the place where the filter is intended to be arranged, or be performed at this place.

A conventional capacitor comprises, as mentioned above, a layered structure formed of two layers of electrically conductive material rolled up around an axle, which layers are mutually separated by electrically insulating material. The capacitor is also provided with means for voltage connection at the ends of the roll. Each of these means is electrically connected to one of the electrically conductive layers.

A conventional coil comprises an electric conductor arranged in several loops, for instance in spiral-shape. When the coil is traversed by an electric current, a magnetic field is generated, which is directed through the coil in the longitudinal direction of the coil.

SUMMARY OF THE INVENTION

A first object of the invention is to develop the capacitive object indicated in the preamble of the subsequent claim 1 further, in such a way that it, while maintaining the basic functional features of such a capacitive object, obtains a construction that creates the prerequisite of a capacitor production being more rational than the one used according to known technique.

The first object of the invention is achieved in that the capacitive object is formed in the way defined in the characterising part of claim 1 . Since the capacitive object is formed as a cable-shaped conductor having a protective sheath surrounding the elongated layered structure, very long capacitive objects can be produced in a manner that is simple from a production technical point of view, and these capacitive objects can for the production of the capacitors be used in the lengthes obtained by the method of production or a separately produced capacitive object can be cut in several parts, which are one by one used for the formation of capacitors.

In an advantageous embodiment, the inventional capacitive ob- ject can be produced in very large lengthes. In case the capacitive object is designed with such a flexibility that it is wind- able into roll-shape, the capacitive object can in connection with the production or at any desired moment thereafter be brought into the shape of a roll for favourable storage and transport. At subsequent capacitor production by means of the capacitive object, required lengthes of the capacitive object are unrolled from this roll and the capacitive object is cut into parts having required lengthes.

The invention entails that one single capacitor produced from such a capacitive object to a long and narrow configuration can replace arrangements, normally used according to previous technique, comprising several capacitors connected together so as to form a capacitor unit. This entails many constructional advantages. Due to the long and narrow configuration, the total thickness of the network of the capacitor elements formed by the layers in the layered structure, will be smaller for a specific capacitance. When used in a bank of capacitors, a considerably lower sound level will arise as compared to the sound level arising when using conventional capacitor units. According to a preferred embodiment of the invention, each of the electrode forming layers of electrically conductive material comprises several electrically conductive, electrode forming elements, and the electrically conductive elements in at least one of these layers are arranged so as to be displaced in the longitudinal direction of the capacitive object in relation to the electrically conductive elements in an adjacent layer. In this way, the electrically conductive elements in two adjacent layers will become capacitively coupled to each other and the layered structure defines an electric alternating current conductor. The layered structure will form a network of capacitor elements connected in series or in parallel. A relatively small breakthrough in the structure would only result in that one single, or possibly a few numbers of capacitor elements being put out of operation.

According to a preferred embodiment of the invention, the layered structure comprised in the capacitive object is formed by one or several band-shaped or plate-shaped elongated mem- bers, each such separate band-shaped or plate-shaped elongated member comprising at least one of the layers in one of said sets and extending with at least one component of its longitudinal extension in the longitudinal direction of the layered structure so as to give the layered structure, and thereby the capacitive object, a longitudinal extension which essentially exceeds the width of said band-shaped or plate-shaped elongated member. By different arrangements of the elongated members, the capacitive object can be given different properties.

According to an embodiment of the invention, it is suggested that present layers of electrically conductive material extend essentially flatly between the ends of the layered structure. Such a capacitive object can easily be produced by arranging several of said elongated members against each other between the ends of the capacitive object.

According to a further embodiment of the invention, the capacitive object comprises plate-shaped support members, which are arranged on opposite flat-sides of the layered structure. The plate-shaped support members can furthermore have a waveshape extending in the longitudinal direction of the layered structure, so that the layered structure will be in a wave-shaped state corresponding to the wave-shape of the plate-shaped sup- port members. In this way, a capacitor produced from the capacitive object can be bent with a reduced risk of the formation of air pockets in the network between the electrically conductive elements. The presence of such air pockets would increase the risk of partial discharge, so called clow. A capacitor built up in this way is particularly suited for winding onto a roll, for instance for transport.

According to a further embodiment of the invention, the capacitive object comprises at least one pressure member, which is arranged at least partially around the plate-shaped support mem- bers so as to apply a pressure on the plate-shaped support members in a direction towards each other. In this way, the size of and/or the presence of possible air inclusions around the electrically conductive elements can be reduced.

According to a further embodiment of the invention, said elon- gated member/members is/are arranged in a spiral-shaped path along the longitudinal direction of the capacitive object. In a capacitor formed by this capacitive object, a magnetic flux will hereby be generated in the longitudinal direction of the capacitor inside said path. In addition to its capacitance, the capacitor will therefore also obtain an inductance. The capacitor will consequently be tuned to a specific frequency. By adapting the inductance to the capacitance, a pure resistive connection can at this frequency be achieved between two points in an electric network by means of the capacitor. Owing to the spiral-shape of the band-shaped or plate-shaped member, the elongated, capacitive object has inductive properties also when arranged along an essentially straight line.

According to a further embodiment of the invention, said elon- gated members are arranged around a core of a material having a high resistance to deformation. In this way, said elongated members can be wound relatively hard around the core during the production of the capacitive object. This reduces the presence of air inclusions in the layered structure and can give the capacitive object a relatively high stiffness.

A further object of the invention is to achieve an electric device having capacitive as well as inductive properties, which can be produced in a rational and cost effective way.

The second purpose of the invention is achieved in that the electric device is formed as defined in the characterising part of claim 32 and claim 33, respectively. This implies that the assemblage of a capacitive object and an inductive object required according to previous technique is eliminated.

According to a first variant of the inventional device, defined in claim 32, the capacitive object included in the device comprises one or several band-shaped or plate-shaped elongated members arranged in a spiral-shaped path along the longitudinal direction of the capacitive object. In an electric device formed of such a capacitive object, a magnetic flux will thus be generated in the longitudinal direction of the capacitive object inside said path. In addition to its capacitance, the electric device will therefore also obtain an inductance. Owing to the spiral-shape of said band- shaped or plate-shaped members, the capacitive object and thereby the electric device will have inductive properties even when it is arranged along an essentially straight line.

According to a second variant of the inventional device, defined in claim 33, a section of the capacitive object is wound in coil- shape to obtain inductive properties. Said section of the capaci- tive object here defines a coil. It is well known that a coil has good inductive properties. In this way, several functional advantages are achieved. For instance, the capacitive object can be produced in a first operation and by winding into a suitable coil-shape be given desired inductive properties and tuned to a desired frequency in a second operation.

According to an embodiment of the invention, the electric device comprises at least one electric resistor, which is magnetically connected to a magnetic flux generated when the capacitive object is connected to a voltage source. In this way, a damping of higher frequency components in a network is made possible in case the electric device is used as a filter.

The invention also relates to a method for producing a capacitive object according to claim 27, a capacitor according to claim 28, a bank of capacitors according to claim 30 and 31 , respectively, and a filter according to claim 41 .

Furthermore, the invention relates to the use of the inventional capacitor and the inventional electric device according to claim 29 and claim 40, respectively.

Preferred embodiments of the invention in addition to the ones mentioned above, appear from the dependent claims and the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the enclosed drawings, a more detailed description of preferred embodiments of the invention brought forward as examples will follow hereinbelow.

Fig 1 illustrates in a sectional view and in a view from above, two band-shaped or plate-shaped elongated members included in a capacitive object according to the invention.

illustrates in a sectional view a layered structure com- prising elongated members according to fig 1 .

illustrates schematically a circuit diagram over capacitor elements of the layered structure according to fig 2.

illustrates a layered structure according to a further example, in a sectional view.

illustrates schematically a circuit diagram over capacitor elements of the layered structure according to fig 4.

illustrates in a schematic perspective view an example of a band-shaped or plate-shaped member intended to form part a capacitive object according to the invention.

illustrates a further example of a band-shaped or plate- shaped elongated member, in a view from above.

illustrates a further example of a band-shaped or plate- shaped elongated member, in a schematic view from above.

illustrates a layered structure according to a further example, in a longitudinal cross-sectional view.

illustrates a layered structure according to a further ex- ample, in a longitudinal cross-sectional view. illustrates schematically a circuit diagram over capacitor elements of the layered structure according to fig 1 1 .

illustrates a layered structure according to a further example, in a perspective view.

illustrates an embodiment of the inventional capacitive object in a schematic perspective view.

illustrates a further embodiment of the inventional capacitive object in a schematic perspective view.

illustrates a further embodiment of the inventional ca- pacitive object in a schematic perspective view.

illustrates a circuit diagram for the embodiment according to fig 21 , according to a first variant.

illustrates a circuit diagram for the embodiment according to fig 21 , according to a second variant. illustrates a further embodiment of the inventional capacitive object in a schematic perspective view.

illustrates schematically a method for producing the inventional capacitive object.

illustrates an example of a bank of capacitors built up of inventional capacitors.

illustrates a further example of a bank of capacitors built up of inventional capacitors.

illustrates an electric device in the form of a filter ac- cording to a first embodiment. The filter is formed from a capacitive object according to fig 15 or 16 and is illustrated in a perspective view.

illustrates the filter according to fig 28 in a schematic, partly cut sectional view.

illustrates a circuit diagram over the section of the capacitive object that according to fig 28 forms a coil- shape.

illustrates a variant of the filter according to fig 28, which here also comprises a resistor.

illustrates an arrangement for filtering harmonics com- prising three filters having capacitive objects according to fig 20.

illustrates several resistors arranged around the capacitive object for damping of higher frequency compo- nents. Fig 34 illustrates a circuit diagram corresponding to fig 33.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The inventional capacitive object comprises an elongated layered structure, which in its turn comprises at least one layer of several electrically conductive elements and at least one adjacent layer of electrically insulating material. The layered struc- ture of the capacitive object has an elongated shape and band- shaped or plate-shaped elongated members forming the layered structure extend with at least one component of their longitudinal extension along the longitudinal direction of the layered structure. Preferably, said electrically conductive elements of the band-shaped or plate-shaped elongated members are arranged in several layers, two adjacent layers of electrically conductive elements being separated by a layer of electrically insulating material. Fig 1 -13 illustrates different examples of the elongated band-shaped or plate-shaped member and layered structures formed thereof.

In the following, the elongated band-shaped or plate-shaped members, which can have either a stiff or a flexible constitution, will be denominated "band members". However, it is emphasised that the elongated band-shaped or plate-shaped members suitably are designed to be flexible so as to give the capacitive object flexibility in order to, thereby, facilitate storage, transport and the general handling thereof. Preferably, the capacitive object is then designed with such a flexibility that it is windable into roll-shape.

Fig 1 shows a view from above and a view from the side of two band members 1 , 1 a according to a first example. They are both provided with an electrically insulating layer 3 and 4, respec- tively, and a layer 5 and 6, respectively, of several electrically conductive elements arranged on this electrically insulating layer. The electrically conductive elements in the respective layer 5, 6 are arranged after each other in a row in the longitudinal direction of the band member. The electrically conductive elements are furthermore electrically insulated from each other, and the layer of electrically conductive elements is therefor discontinuous. The electrically conductive elements can for instance through usual methods be applied on an electrically insulating layer via steaming. The electrically insulating layer can for instance consist of polypropene and the electrically conduc- tive elements of aluminium.

The two band members 1 , 1 a are in fig 1 arranged with a mutual displacement in the longitudinal direction of the band members of half a partition (L/2). A partition (L) here refers to the length of an electrically conductive element in said longitudinal direction and the distance between two electrically conductive elements in said longitudinal direction. By applying the two band members lying on each other with said mutual displacement, the electrically conductive elements of a first of the band members will overlap two electrically conductive elements of a second of the band members in said longitudinal direction. A layered structure 10 illustrated in fig 2 is then obtained. An electrically conductive element 7 will be capacitively coupled to two electrically conductive elements 8, 9 in the adjacent layer. Essentially half the upper surface, namely the left half in fig 2, of the electrically conductive element 7 forms a capacitor element together with essentially half the lower surface of the electrically conductive element 8. In a corresponding way, the right half of the upper surface of the electrically conductive element 7 and essentially half the lower surface of the electrically conductive element 9 form a further capacitor element. The two capacitor elements are furthermore connected in series by the electrically conductive element 7. The layered structure 10 will consequently form a network of capacitor elements. The layered structure 10 comprises several series connected capacitor elements in its longitudinal direction. The two layers of electrically conductive elements are arranged essentially in parallel. All the capacitor elements will furthermore have essentially the same capacitance, since they have essentially the same geometry. Variations of the capacitance can however occur, for instance due to the fact that the electrically insulating layer, also denominated dielectric, can have partial defects. In fig 3, the network of the series connected capacitor elements according to fig 2 is illustrated.

By arranging several band members 1 , 1 a against each other with displacement in longitudinal direction between two adjacent band members, a layered structure 1 1 having the configuration illustrated in fig 4 can be obtained. The electrically conductive elements then form a 2-dimensional network of capacitor ele- ments connected in series and in parallel, which is illustrated in fig 5. The voltage is then intended to by applied at the ends of the layered structure. A breakthrough would only result in a single capacitor element being put out of operation.

It is emphasised that it is also within the scope of the invention to design each of the electrode forming layers as one continuous, elongated capacitor element.

Fig 6 illustrates, in a schematic perspective view, an example of a band member 1 intended to form part of a capacitive object according to the invention. The band member 1 here includes several sets of two electrode forming layers 5, 6 of electrically conductive material mutually separated by a layer 3 of an electrically insulating material. Each of the electrode forming layers 5, 6 of electrically conductive material comprises several electrically conductive, electrode forming elements 7-9. The electrically conductive elements 7 in one of these layers are arranged with a mutual displacement in the longitudinal direction of the band member 1 of half a partition. In this way, each of the elec- trically conductive elements of a said first layers 5 overlaps two electrically conductive elements 8, 9 in a second of said layers 6 in said longitudinal direction. In the example illustrated in fig 6, the electrically conductive elements 7-9 extend all the way up to the longitudinal lateral surface of the band member.

In fig 7 a band member 1 according to a further example is illustrated in a view from above. The band member 1 comprises a layer 13 of several electrically conductive elements. They are arranged in rows in the longitudinal direction of the band member and in columns in the lateral direction of the band member. By arranging two such band members on each other, in the same way as in fig 2, with said mutual displacement in longitudinal direction, the layered structure 14 according to fig 8 is obtained. A number of parallel loops of series connected capacitor elements are formed in the layered structure. The num- ber of loops corresponds to the number of electrically conductive elements in the latitudinal direction of the layered structure. In fig 9 two band members 1 are furthermore arranged displaced in relation to each other laterally. In this way, a layered structure 15 having a 2-dimensional network of capacitor elements connected in series and in parallel is obtained. By applying further band members 1 on each other, while two adjacent band members being mutually displaced according to fig 9, a layered structure with a 3-dimensional network of capacitor elements connected in series and in parallel is obtained.

Fig 10 illustrates a layered structure 55 in a longitudinal cross- sectional view. The layered structure 55 is provided with a high- resistance element in the form of a layer 18 between an electrically insulating layer 16 and a layer 17 of electrically conductive elements. The layer 18 of high-resistance material is arranged to connect the electrically conductive elements in each of the electrode forming layers. The high-resistance layer 18 can for instance be a SiO_x-layer. The conductivity of the SiO_x-layer can be controlled by choice of the oxygen content x The high-resistance layer 18 has such a low conducting capacity that it essentially does not influence the capacitive function of the capacitive object formed by the layered structure, when a voltage is applied to this. The high-resistance layer secures, however, that the capacitor elements can be discharged after the voltage having been removed, and consequently forms a discharge resistor. The discharge takes place in that the high- resistance layer forms a galvanic connection between the electrically conductive elements in two adjacent capacitor elements. The high-resistance layer can furthermore achieve a field equalisation and thereby a reduction of the large local field strengthens that can arise at the edges of the electrically conductive elements. This reduces the risk of glow. According to previous technique, impregnating liquid is used in order to counteract glow. By using high-resistance layers, the need of impregnating liquid is eliminated or at least reduced. This entails lower costs for the production of a capacitor.

The possibility to use a capacitor built up of said layered struc- ture in DC-applications is furthermore improved owing to the high-resistance layer, since this has the ability to equalise the capacitive potential difference between the capacitor elements.

Fig 1 1 illustrates a layered structure 56 in a cross-sectional view. The layered structure 56 constitutes a variant of the layered structure illustrated in fig 10. Instead of a continuous high- resistance layer 18, the high-resistance layer 19 is in fig 1 1 intermittent and has only sections 19 which overlap the distance between two adjacent electrically conductive elements in a layer of electrically conductive elements. The sections 19 create a galvanic connection between the conductive elements. With these sections, essentially the same function is achieved as with the continuous, low conductive layer 18. In fig 12 a circuit diagram of the capacitor element and discharge resistors arranged over these in accordance with the examples illustrated in fig 10 and 1 1 , is schematically illustrated.

Fig 13 illustrates a layered structure 20 in a schematic perspective view. The layered structure 20 is provided with several well insulating barrier layers 21 . The barrier layers 21 insulate sections on different sides of the same from each other. In this way, a breakdown in one of these sections is efficiently prevented from being propagated to a section separated from the same by said barrier layer. Each of these sections constitutes a network of capacitor elements. For instance, each of these sections consists of a band member 1 1 . The barrier layers extend essentially in parallel with said layers of electrically conductive elements in the longitudinal direction of the band member. The well insulating barrier layer has a larger thickness than the respective electrically insulating layer and/or consists of a material having a higher electrically insulating capacity than the same.

Fig 14 illustrates an embodiment of the inventional capacitive object. The capacitive object has a sheath 22, which is intended to protect the layered structure from mechanical loads in the form of impacts etc. Preferably, the sheath 22 also has electrically insulating properties. Such a sheath can for instance consist of polymeric material. Fig 15 and 16 illustrate further embodiments of the capacitive object. The material 23 located between the layered structure 20 and the sheath 22 preferably has insulating properties. The sheath can for instance consist of an extruded polymeric layer.

The capacitive object according to the invention, has, as appears from the embodiments illustrated in fig 14-16, cable-shape and functions as a conductor. The conductor is in this case capacitive and, consequently, also generates reactive power. Con- ventional conductors of large lengthes are inductive. The inventional conductor can with advantage be used in a bank of capacitors for series compensation of conventional conductors instead of the capacitor units used today.

The length of the inventional capacitor, which is intended to be applied in for instance a so-called shunt bank, is dimensioned with regard to the voltage level at which the capacitor is intended to be used. The allowed voltage over the capacitor for a specific geometry of the conductive elements increases with an increasing length of the capacitor, due to an increased number of series connected capacitor elements in the longitudinal direction of the capacitor.

The reactive power generated by a capacitor increases with an increased number of capacitor elements connected in parallel and/or an increasing capacitor element surface of the capacitor. The reactive power of a bank of capacitors built up of inventional capacitors is increased by the same reason by an increase of the number of capacitors connected in parallel.

In the embodiments of the capacitive object illustrated in fig 14- 16 the layered structure 20 is arranged with a first end at a first end of the capacitive object and with a second and at the second end of the capacitive object. Furthermore, the layered structure extends in such a way between the ends of the ca- pacitive object that the layers of electrically conductive elements are located in planes which are in parallel with the longitudinal direction of the capacitive object. In other words, the perpendiculars to the layers have essentially the same direction all along the length of the capacitive object.

The thinner a layer of conductive material between the electrically conductive elements in the respective capacitor element, the smaller field amplification is obtained at the edges of the capacitor elements. A smaller field amplification entails a smaller risk of glow. In order to counteract the occurrence of glow, the electrically conductive material around the respective electrically conductive element should furthermore be arranged to be tight around the electrically conductive element. In case of existing air inclusions in the vicinity of the capacitor elements, there is a larger risk of glow. In order to counteract the occur- rence of glow, the capacitive object is provided with plate- shaped support members on opposite sides of the layered structure. These are essentially in parallel with the layers of electrically conductive elements. The plate-shaped support members are intended to, when applied against the layered structure, exert a pressure against this so as to reduce the presence of air inclusions around the electrically conductive elements.

According to a further embodiment of the capacitive object, see fig 17, the plate-shaped support members 24 have a waveshape in the longitudinal direction of the capacitive object. The layered structure 20, which is located between the support members, is arranged in a wave-shaped state, which corresponds to the wave-shape of the plate-shaped support mem- bers. The wave-shaped support members are arranged essentially in parallel with the layers of electrically conductive elements of the layered structure. Members 25 are arranged in order to achieve a pressure influence on the plate-shaped support members 24 in a direction towards each other. The pressure member 25 can for instance consist of a band having a high tensile strength.

When the capacitive object according to fig 14-16 is bent, the layers arranged inwards, towards the centre of the bending, will be subjected to a compressive stress and the layers arranged on the outside of the bent section will be subjected to tensile stress. Due to the compressive stress, there is a risk of folding of the layers located on the inside of the bent section. Such a folding could cause air pockets. Due to the fact that air does not insulate as good as conventional insulating materials, the risk of partial discharges increases. It can for instance be desired to bend the elongated capacitive object or a capacitor formed thereof during transport. It would for instance be desired to be able to wind the capacitive object/the capacitor into a roll in accordance with conventional technique for cables. This problem is solved by arranging the capacitive object with the plate- shaped members in wave-shape. When such a capacitive object is bent, the sections subjected to compressive stress will shorten their wavelength without any risk of local foldings.

It is realised that the plate-shaped support members should have a relatively high stiffness in order to be able to achieve a sufficient compression of the layered structure. The plate- shaped support members can furthermore have a rounded cross-sectional shape in order to facilitate the elimination of possible air inclusions of the layered structure when the support members are being applied. The convex surface of the support members is directed towards the layered structure and by winding said band of a material having a high tensile strength relatively hard around the support members, these will obtain an es- sentially flat state, while possible air inclusions are being pressed out of the layered structure.

Fig 18 illustrates a schematic perspective view of a further embodiment of a capacitive object according to the invention. This embodiment of the capacitive object reduces, in the same way as the previous embodiment, the risk of the occurrence of foldings in the layers in the layered structure 20 subjected to compressive stress. The layered structure is here twisted in its longitudinal direction.

Fig 19 illustrates a further embodiment of an inventional capacitive object in a schematic perspective view. A first band member 26 is arranged in a spiral-shaped path around an axle 27 and forms a first stratum around the axle. A second band member 28 is arranged in a spiral-shaped path and forms a second stratum radially outside the first stratum. The two band members 26, 28 are arranged so as to extend in different directions in the circumference direction of the capacitive object. Furthermore, a protective sheath 22 is also schematically illustrated. The arrows 29, 57 shown in fig 19 illustrate that the current runs in the longitudinal direction of the respective band member. By applying the band members around an axle, preferably having a high resistance to deformation, these band members can be wound relatively hard around the axle during the production of the capacitive object. In this way, the risk of air inclusions around the electrically conductive elements is counteracted. Electrically insulating material in said electrically insulating layers will be arranged tightly against and at least partly around the respective electrically conductive element. The core is preferably also flexible in order to make a bending of the capacitive object possible. Such a bending of the capacitive object or a capacitor produced thereof can be desired for instance for transport of the same.

Furthermore, a not shown stratum having good insulating prop- erties, for instance in the form of a mica band, is preferably arranged between these stratums of band members. Such a mica band consists of a ceramic material, has a high resistance to penetration of arcs and is high temperature durable. By the presence of such a stratum having good insulating properties, a breakthrough in a band member is prevented from propagating into an adjacent band member.

Fig 20 illustrates a further embodiment of the inventional capacitive object. In contrast to the embodiment in fig 19, the band members 30, 31 extend in the same direction in the two stratums. This entails that the current is intended to be conducted in the same direction in the circumference direction of the capacitive object, see arrows 32 , 33, whereby the band members form a kind of coil. In addition to its capacitance, the capacitive ob- ject thereby also obtains an essential inductance. The capacitive object is consequently tuned to a specific frequency. By adapt- ing the inductance to the capacitance, a purely resistive connection can thereby be achieved between two points in a network at a specific frequency. It is realised that the capacitive object can obtain inductive properties also when it comprises one single band member 30 arranged in a spiral-shaped path around an axle 27 and forming a single stratum around the axle. It is also realised that the capacitive object can obtain inductive properties also when it comprises more than two band members arranged in a spiral-shaped path around an axle 27 and forming more than two stratums around the axle, the band members extending in the same direction in the different stratums.

The band member 26, 28 and 30, 31 illustrated in fig 19 and 20 form layered structures 60 and 61 , respectively.

Fig 21 illustrates a further embodiment of the inventional capacitive object. An elongated band 34 is wound around a structure 36 of band members, for instance according to the embodiment in fig 19 and 20. The elongated band 34 of semiconductor material extends between the two ends of the capacitive object and constitutes a discharge resistor. Furthermore, a band 35 of electrically insulating material having a width larger than the width of the band of semiconductor material is arranged on the inside of this band. Such an arrangement makes it possible to dimension the discharge resistance by regulation of the length of the semiconductor band. This is performed by an overlap winding of the insulating band with the semiconductor band arranged along the same. It is realised that the resistance increases with an increasing length of the semiconductor band.

Fig 20 illustrates a schematic circuit diagram over the embodiment in fig 21 , the discharge resistor 34 being supposed to be comprised in a capacitive object of the type shown in fig 20.

Fig 24 illustrates a further embodiment of the inventional capacitive object. It is here shown that the capacitive object can be provided with a grounded sheath surface in the same way as conventional cables. A capacitor provided with a grounded sheath surface can thereby be arranged buried below ground. This is advantageous in particular since a band of capacitors built up of such capacitors can be arranged below ground. Such an arrangement saves space above ground and eliminates the need of stands for carrying the capacitors according to previous technique. The capacitor is according to fig 22 provided with, from the inside and outwards in the radial direction of the ca- pacitor: a structure 36 of band members, discharge resistor 34, insulating stratum 37, insulating shield 38, conductive shield, for instance of copper, 39 and a mechanical protective stratum 40.

Capacitors produced from the above described, inventional ca- pacitive objects can with advantage be used for the formation of banks of capacitors. An inventional capacitor can replace a so- called capacitor unit according to prior art. Such a capacitor unit was discussed by way of introduction and comprises several capacitors in the form of rolls. The capacitor rolls are arranged flattened and piled adjacent to each other in such a capacitor unit. The height of the layers arranged on each other in the radial direction of the inventional capacitor is essentially smaller than the height of a pile of flattened capacitor rolls according to previous technique. This results in that the mechanic resonance frequency of the inventional capacitor is essentially lower than the network frequency and within a frequency range above the harmonics being most severe as regards resonance amplification. This results in a low sound level.

The electrically conductive elements are preferably plate- shaped, and rectangular. The electrically conductive elements in two adjacent layers overlap each other with half a partition according to the above described examples of layered structures. Such a relation is preferred, but it is not necessary for the func- tioning of the capacitor. The electrically conductive elements should however be at least somewhat displaced in relation to each other in at least two adjacent layers in the longitudinal direction of the layered structure. According to the above described examples of layered structures, the electrically conductive elements have the same shape and size. This is to be pre- ferred in order for the capacitor elements to have the same capacitance, but not necessary for the capacitor to function. By the capacitor elements having essentially the same capacitance, a uniform voltage distribution in the network of the capacitor elements is obtained. In a capacitor according to fig 14-18, the electrically conductive elements in two respective adjacent layers can be arranged such that the capacitor elements have essentially the same capacitance due to the fact that the longitudinal direction of the layered structure essentially coincides with the longitudinal direction of the capacitor. This is also possible, even though not as prominent, with the embodiments in fig 19- 22 and 24. It can in these cases be achieved for instance in that the respective layered structure only comprises a low number of layers of electrically conductive elements. The conductive elements in two adjacent layers should in that case overlap each other with half a partition. When the band member is wound around the axle, and external layer of electrically insulating material is intended to be more stretched in the longitudinal direction of the band member than a layer located inside this layer. This stretch makes it possible for the electrically conduc- tive elements to be arranged with said desired mutual overlap. The layers of electrically conductive elements extend over essentially the entire length of the layered structure.

The inventional capacitor can be used for direct current as well as alternating current.

In fig 25 a method for producing a capacitive object according to the invention is schematically illustrated. Several supplies 41 are arranged, each of which has a roll of a wound dielectric film. The dielectric film is provided with a layer of several electrically conductive elements arranged at mutual distances. Possibly, a high-resistance layer is also arranged between the dielectric film and the layer of electrically conductive elements. Furthermore, one or several of the supplies 41 can also comprise a roll with a dielectric film without any layer of electrically conductive ele- ments. Such a dielectric film is intended to form a barrier layer in the layered structure. Bands of said dielectric film and said layers of electrically conductive elements are gradually unwind from the rolls, redirected and fed to a first station 42. In the station 42, the bands are put together and form a layered structure 62 according to any of the above described examples. The layered structure is gradually produced in a feeding direction.

Band members can according to the method be arranged so as to form a capacitive object according to any of the above de- scribed embodiments. When a capacitive object is intended to be produced with band members having a longitudinal direction essentially corresponding to the longitudinal direction of the capacitive object, the capacitive object is preferably produced in a feeding direction essentially corresponding to the feeding di- rection of the band members. The band members can for instance be guided along an essentially straight lined path and put together into a layered structure. Two supplies comprise plate- shaped support members 24. The plate-shaped support members are fed forward and arranged on two opposite sides of the layered structure. In the first station 42, a band of semiconductor material is wound around the layered structure, and possibly also around the support members 24, for the achievement of said discharge resistor. In a second station 43, a protective sheath is applied around the band. Thereby, a capacitive object in the form of an elongated cable has been achieved. The capacitive object can thereafter be cut into desired lengthes depending on the need or the available space. The process of cutting is in the figure indicated with the reference 58. A thus formed capacitive object can be said to have a capacitance per unit of length. After cutting into desired length, means 59 for connection to a voltage can thereafter be arranged at the re- spective end of a cut capacitive object for the production of the actual capacitor.

When producing a capacitive object having band members in a spiral-shaped path, the band members are preferably produced in a first step and wound onto a roll. The roll is arranged on a rotatable part in a production device. The band member is thereafter unwound from the roll and applied around an axle during rotation of the rotatable part. Thereby, the spiral-shaped layered structure is formed. Thereafter, the thus formed capacitive object can be provided with a protective sheath, for instance of polymeric material. It is of course within the scope of the inventional claims to wind several band members around said axle.

According to an alternative, the supplies can include rolls with only dielectric film. In such a case, layers of electrically conductive elements are applied on the dielectric film after the film has been unwound from the roll.

With the above mentioned method, the capacitive object is consequently gradually produced in a feeding direction. Preferably, the production is carried out continuously.

According to an alternative method for producing a capacitive object, a dielectric film is unwound from a dielectric film roll, and a layer of electrically conductive elements are applied on the film. The layer of electrically conductive elements comprises several rows, for instance eight rows, of electrically conductive elements, which rows run in the longitudinal direction of the dielectric film. The electrically conductive elements are preferably arranged displaced in relation to each other with half a partition in adjacent rows. Thereafter, the dielectric film is cut in said longitudinal direction, the cuts being achieved between said rows of electrically conductive elements. In that way, several, for instance eight, strips of dielectric film having electrically conductive elements arranged after each other are obtained. These strips are thereafter arranged lying against each other in such a way that the respective layer of electrically conductive elements are arranged separated from an adjacent layer of electrically conductive elements by a dielectric film. Thereby, this method does not require any equipment for guiding the strips in the longitudinal direction of the rows in order to achieve the desired overlap. For instance, the respective strip is angled 90°, whereupon the strips are brought together to form the lay- ered structure. Consequently, the strips can in a simple manner be brought together to form a layered structure comprising a network of capacitor elements. This layered structure can thereafter be fed forward in its longitudinal direction so as to form the capacitive object.

Furthermore, it is within the scope of the inventional claims that several layered structures are joined along the longitudinal direction of the capacitive object.

When it is desired to produce a capacitive object having a predetermined length, it is according to an alternative production method possible to arrange band members to and fro between for instance two axles. The positions of these axles thereby form the ends of the capacitive object.

In case the capacitive object comprises only one band member, which in its turn only comprises one layer of several electrically conductive elements and only one adjacent layer of electrically insulating material, the band member is arranged so as to ex- tend to and fro between the ends of the capacitive object.

In fig 26 a bank of capacitors 44 for series compensation is illustrated. The bank of capacitors is built up of several inventional capacitors. The series compensation device comprises three sets of capacitors 45, 46, 47. Each of the sets is intended for one of the three phases of the network. The sets of capacitors are arranged hanging in the air between two stands 48, 49.

In fig 27 a bank of capacitors 50 in the form of a so-called shunt bank is illustrated. The bank of capacitors is built up of several inventional capacitors. The bank of capacitors 50 comprises three sets of capacitors 51 , 52, 53: each set being intended for one of the three phases of the network. The capacitors are arranged hanging from a stand 54.

The respective inventional capacitor of the sets of capacitors in fig 26 and 27 should be compared with a capacitor unit according to prior art. The construction of such a capacitor unit has been described above. In the light of the description above, it is realised that the inventional capacitor has an essentially simplified construction. Furthermore, an essentially simplified production, transport and assemblage is made possible. The banks of capacitors according to fig 26 and 27 furthermore, in relation to conventional banks of capacitors, require an essentially smaller space as regards ground surface.

Fig 28 illustrates a first embodiment of an electric device 70 having capacitive as well as inductive properties, which device here is intended to constitute a filter. A section of a capacitive object 71 of the type illustrated in fig 15 or 16 is here wound in a spiral-shaped path. Owing to the capacitive object 71 being arranged to conduct current in its longitudinal direction, an inductive element 72 in the form of a coil is formed. The filter 70 also comprises a core 73 of magnetically well conductive material. The capacitive object 71 is partly wound around two legs 74 of the core 73.

In fig 29 a schematic, partly cut sectional view of the filter 70 in fig 28 is illustrated. The core has an air gap 75 between said legs 74. The air gap 75 is intended to receive a magnetic energy generated when the capacitive object is connected to a voltage source. In the electric device 70 in fig 28, the capacitive object 71 consequently forms an inductive element in form of a coil. The two properties are however integrated into one single component. This is schematically illustrated in a circuit diagram in fig 30.

Fig 31 illustrates a variant of the electric device illustrated in fig 28 and 29. An electric resistor 76 is magnetically connected to a magnetic flux generated when the capacitive object 71 is con- nected to a voltage source. The resistor 76 is here connected to the iron core 73 via an electric line wire arranged around the core. When the current is conducted in a spiral-shaped path, a magnetic flux is generated in the core inside the turns of the capacitive object 71 . This flux gives rise to a current through the line wire, which current will flow through the resistor 76. The resistor 76 thereby functions as a damping resistor.

The electric device according to the invention, which has capacitive as well as inductive properties, can of course comprise other types of capacitive objects in the form of cable-shaped conductors than the ones illustrated in fig 28-31 . The capacitive object 71 can for instance advantageously be of the type illustrated in fig 17, in which case the capacitive object is wound in such a way that the perpendiculars to the layers in the layered structure are essentially perpendicular to a geometric centre line of the coil. Owing to the wave-shape of the layered structure, the effect of a compressive stress in the layers arranged inwards, towards the centre line, is mitigated, which reduces the risk of folding of these layers. Such a folding could cause air pockets, which in their turn could cause glow.

The capacitive object 71 included in the inventional electric device can also advantageously be of the type illustrated in fig 18, in which case the occurrence of foldings in the sections of the layers of the layered structure being subjected to compressive stress is reduced during winding of the capacitive object into coil-shape in the same way as in the previous example.

The capacitive object included in the inventional electric device can also advantageously be of the type illustrated in fig 20, in which case the capacitive object does not have to be wound into coil-shape to obtain inductive properties, since a capacitive object of this type has inductive properties also in a rectilinear state. An electric device comprising a capacitive object of this type is tuned to a specific frequency. By adapting the inductance to the capacitance, a purely resistive connection can thereby be achieved between two points in a network at a specific frequency.

Fig 32 illustrates an arrangement for filtering harmonics. A rectifier 77 is arranged to rectify alternating current from an alternating voltage source 78 into direct current. Three filters 79 are connected in parallel with the rectifier 77 for the purpose of filtering one harmonic each. The filters 79 suitably comprise ca- pacitive objects of the type illustrated in fig 20.

Fig 33 illustrates several electric resistors 80 in the form of electric resistor wires. Each of the electric resistor wires 80 extends around a layered structure, and in the case shown in fig 33 around the capacitive object 81 . Means 82 are also arranged for maintaining the distance between each of the resistor wires 80 and internally located, heat sensitive parts of the capacitive object. The distance means 82 are preferably formed of a high temperature durable material and arranged in such a way that a low heat transfer is obtained between the resistor wires and the internally located, heat sensitive parts of the capacitive object. For instance, they comprise a ceramic material. In the case illustrated in fig 33, the distance means are designed in such a way that air-cooling is achieved in the space between each of the resistor wires and the capacitive object 81 . It is of course also within the scope of the inventional claims that the resistors 80 are arranged inside the sheath of the capacitive object 81 . The resistors 80 will consequently be magnetically connected to a magnetic flux generated by a current through the capacitive object. This is schematically illustrated in fig 34. The invention is of course not in any way limited to the preferred embodiments described above, on the contrary, a number of possibilities to modifications thereof should be obvious to a man skilled in the art, without departing from the basic idea of the invention as defined in the appended claims.

Claims

1 . A capacitive object comprising an elongated layered structure (10, 1 1 , 14, 15, 55, 56, 20, 60, 61 , 36, 62), which includes one or several sets of two electrode forming layers (5, 6, 13, 17) of electrically conductive material, which two layers are mutually separated by at least one layer (3, 4, 16) of an electrically insulating material, characterized in that the capacitive object is designed as a cable-shaped conductor, the elongated layered structure being surrounded by a protective sheath (22).

2. A capacitive object according to claim 1 , characterized in that the sheath (22) has insulating properties.

3. A capacitive object according to any of the preceding claims, characterized in that the capacitive object is designed to be flexible.

4. A capacitive object according to claim 3, characterized in that the capacitive object is designed with such flexibility that it is windable into roll-shape.

5. A capacitive object according to any of the preceding claims, characterized in that the layered structure (20) comprises at least one barrier layer (21 ) having an electrically insulating capacity which is higher than the electrically insulating ca- pacity of said layer (3, 4, 16) of electrically insulating material, which barrier layer (21 ) is arranged between two adjacent electrode forming layers in order to insulate the part of the layered structure located on one side of the barrier layer from the part of the layered structure located on the other side of the barrier layer. A capacitive object according to any of the preceding claims, characterized in that the electrode forming layers (5,

6, 13, 17) of electrically conductive material each comprises several electrically conductive, electrode forming objects (7, 8, 9), and that the electrically conductive objects (7, 8, 9) in at least one of these layers are arranged so as to be displaced in the longitudinal direction of the capacitive object in relation to the electrically conductive objects in an adjacent layer.

7. A capacitive object according to claim 6, characterized in that the electrically conductive objects (7, 8, 9) in at least one of said layers (5, 6, 13, 17) of electrically conductive objects are arranged in at least a partly overlapping relation in the longitudinal direction of the capacitive object in relation to the electrically conductive objects in an adjacent layer.

8. A capacitive object according to claim 6 or 7, characterized in that each of the electrically conductive objects (7, 8, 9) in the respective layer (5, 6, 13, 17) is arranged essentially electrically insulated from adjacent electrically conductive objects in the same layer.

9. A capacitive object according to any of claims 6-8, characterized in that the layered structure (55, 56) comprises at least one high-resistance object (18, 19), which is arranged to connect the electrically conductive objects in one of said layers of electrically conductive objects.

10. A capacitive object according to claim 9, characterized in that said high-resistance object (18) is a layer of high-resistance material.

1 1 . A capacitive object according to any of the preceding claims, characterized in that the layered structure is provided with a layer (34) of semiconductor material forming a discharge resistor.

12. A capacitive object according to claim 1 1 , characterized in that the layer (34) of semiconductor material is formed by a band which is wound around the layered structure.

13. A capacitive object according to claim 1 1 or 12, characterized in that an insulating means (35) is arranged between the layer (34) of semiconductor material and the layered structure.

14. A capacitive object according to claim 13 in combination with claim 12, characterized in that the insulating means (35) is a band of electrically insulating material having a width larger than the width of the band of semiconductor material.

15. A capacitive object according to any of the preceding claims, characterized in that the layers of electrically conductive material extend essentially flatly between the ends of the capacitive object.

16. A capacitive object according to any of the preceding claims, characterized in that it comprises plate-shaped support members (24) which are arranged on opposite flat-sides of the layered structure.

17. A capacitive object according claim 16, characterized in that it comprises at least one pressure member (25), pref- erably in the form of a band of a material having a high tensile strength, which is arranged at least partly around the plate-shaped support members (24) so as to apply a pressure on the plate-shaped support members in a direction towards each other.

18. A capacitive object according to claim 16 or 17, characterized in that said plate-shaped support member (24) have a wave-shape extending in the longitudinal direction of the layered structure so as to put the layered structure (20) in a wave-shaped state corresponding to the wave-shape of the plate-shaped support members.

19. A capacitive object according to any of the preceding claims, characterized in that the layered structure (20) is twisted in the longitudinal direction of the capacitive object.

20. A capacitive object according to any of the preceding claims, characterized in that the layered structure is formed by one or several band-shaped or plate-shaped elongated members (1 , 1 a, 26, 28, 30, 31 ), each such separate band-shaped or plate-shaped elongated member comprising at least one of the layers in one of said sets and extending with at least one component of its longitudinal extension in the longitudinal direction of the layered structure so as to give the layered structure, and thereby the capacitive object, a longitudinal extension which essentially exceeds the width of said band- shaped or plate-shaped elongated member.

21 . A capacitive object according to claim 20, characterized in that said elongated member/members (26, 28, 30, 31 ) is/are arranged in a spiral-shaped path along the longitudinal direction of the capacitive object.

22. A capacitive object according to claim 21 , characterized in that said elongated member/members (26, 28, 30, 31 ) is/are arranged around a core (27) of a material having a high resistance to deformation.

23. A capacitive object according to any of claims 20-22, char- acterized in that the layered structure comprises an assembly of two or more stratums of elongated members.

24. A capacitive object according to claim 23, characterized in that the elongated members (26, 28) are arranged in a spiral-shaped path along the longitudinal direction of the ca- pacitive object in the respective stratum, the elongated members (26, 28) in two adjacent stratums extending in different directions as seen in a circumference direction of the capacitive object.

25. A capacitive object according to claim 23, characterized in that the elongated members (30, 31 ) are arranged in a spiral-shaped path along the longitudinal direction of the capacitive object in the respective stratum, the elongated members (30, 31 ) in two adjacent stratums extending in the same direction as seen in a circumference direction of the capacitive object.

26. A capacitive object according to claim 24 or 25, characterized in that a layer having good insulating properties is ar- ranged between two of said stratums of spiral-shaped elongated members so as to prevent a breakdown in a band member from propagating to an adjacent band member.

27. A method for producing a capacitive object according to claim 1 , characterized in that the layered structure (10, 1 1 ,

20, 55, 56) is formed by applying a layer of electrically conductive objects on a layer of electrically insulating material, which layer of electrically conductive objects comprises several rows of electrically conductive objects, which rows extend essentially in parallel with each other, the electrically conductive objects being displaced in relation to each other in adjacent rows in the longitudinal direction of the rows, that the layer of electrically insulating material is subsequently cut between said rows so that several strips of elec- trically insulating material are formed, each of which comprises at least one row of electrically conductive objects (5, 6), and that the strips subsequently, while maintaining said displacement, are applied on each other so that the row of electrically conductive objects of the respective strip is arranged in parallel with the row of electrically conductive objects of an adjacent strip and separated from the same by said electrically insulating material, whereupon the thus formed layered structure is provided with a protective sheath (22.)

28. A capacitor, characterized in that it comprises a capacitive object according to any of claims 1 -26, the capacitive object being provided with means for voltage connection at its respective end.

29. Use of a capacitor according to claim 28 in a high voltage network.

30. Bank of capacitors for generation of reactive power, characterized in that the bank of capacitors comprises capacitors according to claim 28.

31 . A bank of capacitors for series compensation of long alternating current lines, characterized in that the bank of capacitors comprises a capacitor according to claim 28.

32. An electric device having capacitive as well as inductive properties, characterized in that it comprises a capacitive object according to any of claims 21 , 22 or 25, the capacitive object being provided with means for voltage connection at its respective end.

33. An electric device having capacitive as well as inductive properties, characterized in that it comprises a capacitive object according to any of claims 1 -26, the capacitive object being provided with means for voltage connection at its re- spective end and a section of the capacitive object being wound in coil-shape so as to form an inductive object (72).

34. An electric device according to claim 33, characterized in that said section of the capacitive object is wound in a spiral.

35. An electric device according to claim 33 or 34, characterized in that the electric device comprises a core of magnetic material, and that said section of the capacitive object is wound around a part (74) of the core.

36. An electric device according to any of claims 32-35, characterized in that the electric device comprises at least one electric resistor (76, 80), which is magnetically connected to a magnetic flux generated when the capacitive object is connected to a voltage source.

37. An electric device according to claim 36 in combination with claim 35, characterized in that the electric resistor (76) is connected to the core (73) via an electric line wire arranged around the core.

38. An electric device according to claim 36, characterized in that several electric resistors (80) are arranged at a mutual distance in the longitudinal direction of the capacitive object, each of which resistors extending around the layered structure.

39. An electric device according to claim 38, characterized in that means (82) are arranged for maintaining the distance between each of the electric resistors (80) and internally located, heat sensitive parts of the capacitive object.

40. The use of an electric device according to any of claims 32- 39 in a high voltage network. A filter for filtering harmonics in a high voltage network, characterized in that it comprises an electric device according to any of claims 32-39.