MXPA99003146A - A self-healing capacitor - Google Patents

Abstract

A self-healing power capacitor (1) comprising at least one capacitor unit (9-1, 9-2, 9-3), each capacitor unit (9) comprising at least one winding (2), said windings (2) of each capacitor unit (9) being provided with a first and a second connection electrode (10, 11), said windings (2) being surrounded by an encapsulation material (4) and housed in a first casing (3), said capacitor (1) having at least one protection element (6) for each capacitor winding (2), said protection element (6) comprising a membrane (16) provided for activating, upon a pressure exerted on said membrane (16) by a gas produced by a short-circuit within sais windings (2), a current interruption element (19), said protection element (6) being mounted in a second casing (13) which is mounted inside said first casing (3), said second casing (13) having one side formed by said membrane (16) and which is separated by a narrow gap (12) from an end-face of said windings (2).

Description

SELF-REGENERATING CAPACITOR DESCRIPTIVE MEMORY The present invention relates to a self-regenerating energy capacitor comprising at least one capacitor unit, each capacitor unit comprising at least one winding made with at least two films of insulating material on which a metallic coating has been deposited, each winding of each capacitor unit provided with a first and second connection electrodes, said windings being surrounded by an encapsulation material and housed in a first housing, said capacitor having at least one protection element for each winding of the capacitor, said element being of protection mounted on a second housing which is formed by a membrane, said protection element being provided for activating, after a pressure is exerted on said membrane by a gas produced by a short circuit inside said winding, an interrupting element of current connected in series with one of said electro two, said protection element being separated from one end face of said winding. A self-healing energy capacitor as such is known from GB-A-2 204 996. The energy capacitor is for example used in electrical networks to compensate reactive energy (eos f corrected) or as parts of filters to absorb harmonic currents and therefore decrease the distortion of harmonic voltage on the networks. Known energy capacitors are made by first evaporating a metal material on a film and then winding the metallized film. A first and second electrodes are applied at the ends of the metallized film, to provide suitable electrical connectors. The windings are surrounded by encapsulation material or filler material, such as resin, oil or a gel. The windings and their encapsulation material are housed in the first housing. When the metallized film of a self-healing capacitor breaks, the short circuit is automatically removed by the following procedure. Since a short circuit is established, the current through the point of failure will increase rapidly. This high current will create a high current density in the thin electrode evaporated around the point of failure. The current will quickly be so high that the evaporated electrode will transform into gaseous plasma and move away from the film around the point of failure. Without the electrode around the point of failure, the insulation will be restored. The capacitor has self-regenerated and can continue to operate normally. The self-regeneration procedure is very short (microseconds), and the isolation area created around the point of failure is very small (a few square millimeters). Since the area of a capacitor winding is typically tens of square meters the relative loss in capacitance resulting from a self-regeneration operation is very small. Many thousands of self-regeneration operations can occur without a noticeable effect on the capacitor or its performance. As the dielectric system ages, a situation will develop where the thermal and dielectric load of the system becomes too high for the mechanism to work. At this point an avalanche of self-regenerations will arise and create a short circuit of the capacitor element. However, self-healing capacitors do not always create a short circuit with a low voltage drop, ie a low short circuit impedance. The short circuit impedance can vary between low values and totally high values. To adequately protect the self-healing energy capacitors against such short circuits, protective elements are incorporated into the energy capacitor housing. With the known capacitor, the protection element is formed by an overpressure switch. The principle of such an overpressure switch is that the gases, produced by a short circuit within the capacitor windings will accumulate in the space between the windings and the second housing and cause the overpressure to build up. This overpressure causes the membrane of the protection element to buckle, which is applied to the windings. In the known capacitor the membrane includes a wire that is connected in series with one of the electrodes. The overpressure created by the gas causes the membrane to buckle. This buckling causes the wire to break and therefore the current flow in the winding is interrupted. A drawback of known self-regenerating energy capacitors is that the second housing which houses the protection element is fixed to the upper end wall of the first housing. This means that the protection element is not physically separated from the end walls of the first housing. Therefore, deformation or damage to the first housing can cause damage to the protection element. In addition, incorrect mounting of the second housing on the upper end wall of the first housing could lead to malfunctioning of the protective element. In addition, a leak in the upper wall of the first housing could lead to malfunctioning of the protection element. An object of the present invention is to construct a self-healing energy capacitor wherein the protection element is mounted in a less vulnerable manner. For this purpose, a self-healing energy capacitor is characterized in that said second housing is housed within the first housing, separate from the upper and / or lower walls belonging to said first housing, said second housing being housed in said encapsulation material and having the less a separate wall of said windings by a narrow space. Since the second housing is housed separately from the side walls of the first housing, the protection element and the windings form separate elements that are mounted together in the first housing, which no longer needs to be provided with an upper end wall. The encapsulation of the protection element and the encapsulation of the windings allows them to be mounted in the first housing in an easy and reliable way. Since the protection element is independent of the side walls, it is less vulnerable to damage to the first housing. Since the windings and the protection element are both encapsulated but separated from one another by a narrow space, the gas can accumulate only in the narrow space. The dimension of the space and the fact that the protection element is housed in the encapsulation material, will cause the gas to remain in the space and in this way exert sufficient pressure on the membrane, thereby providing a reliable operation of the element. protection. A first preferred embodiment of a self-healing energy capacitor according to the invention is characterized in that said current interrupting element comprises a fuse and said protection element comprises a switch, provided for switching by said membrane, said switch being connected in parallel with the first and second electrodes. In this mode the membrane acts as a switch, which short-circuits the first and second electrodes. Since the fuse is connected in series with one of the electrodes, a short circuit of the electrodes will melt the fuse and in doing so, disconnect the capacitor unit. A second preferred embodiment of a self-healing energy capacitor according to the invention is characterized in that said current interrupting element comprises a fuse wire connected in series with one of the electrodes and placed in front of a cutting element, which is part of said protection element, said cutting element being provided to be moved by the membrane towards said wire to properly cut said wire, when said pressure is exerted on said membrane. With this mode, the movement of the membrane, caused by a gas pressure applied thereto, will cause the cutting element to be moved towards the fuse wire. Once the cutting element reaches the wire, it will cut the latter by disconnecting the capacitor unit. The travel distance of the cutting element is calibrated in such a way as to allow a reliable protection element. Preferably said membrane is a bi-stable membrane. A bi-stable membrane has the advantage that it provides either a connection or a disconnection of the capacitor unit, which helps to contribute to reliable operation of the protection element. This invention will be described in more detail by means of the appended drawings which show some examples of a self-healing energy capacitor in accordance with the present invention.

In the drawings: Figures 1 and 3 respectively show a cross section through first and second preferred embodiments respectively of a self-healing energy capacitor in accordance with the present invention; Figures 2 and 4 respectively illustrate schematically a capacitor unit, provided with its protection element, as it is performed in the first and second modes respectively; Figure 5 shows a detailed view of the upper side of a self-healing capacitor according to the first embodiment of the present invention. In the drawings the same reference has been assigned to the same analogous element. Figure 1 shows a first preferred embodiment of a self-healing energy capacitor in accordance with the present invention. In the illustrated example, capacitor 1 comprises three capacitor units 9-1, 9-2 and 9-3. The three capacitor units are interrupted according to a delta or triangle configuration for a three-phase current, where each side of the triangle comprises a capacitor unit. The number of capacitor units mounted in a first housing 3 is not however restricted to three, and more or less capacitor units can be mounted in the same first housing, depending on the phases that make up the current circuit in which the capacitor will be mounted. Each capacitor unit comprises at least one winding 2, made of at least 2 films of insulating material on which a metal coating has been applied. It should be noted that several windings can be coaxially wound, however for the present description it will be considered as a single winding. The capacitor unit is for example made by first evaporating a metal deposit on a polypropylene film, which is subsequently wound on cylindrical or oval windings. The windings are sprinkled with metal on the end faces to achieve an electrical connection to a first 10 and second 11 evaporated electrodes. The first electrode 10 and second electrode 11 respectively of each capacitor unit is connected to a first conductor 5 and a second conductor 8 respectively, to which a source of electric power is connectable. The windings 2 of each capacitor unit are surrounded by an encapsulation material 4, which fills the space between the inner side of the first housing 3 and the windings 2. The encapsulation material is formed of resin, for example polyurethane. A protection element 6 is mounted above the windings 2 of each capacitor unit. The location of the protection element above the windings is again a practical choice and the protection element can also be located below the windings 2. The protection element must be mounted in such a way that a gas produced by an evil Capacitor operation can move between the layers of the film and reach the protection element. The protection element 6 is separated from the upper end face of the windings by a narrow space 12 of for example 0.5 -2 mm. The protection element is mounted in a second housing 13 which in turn is further mounted inside the first housing 3. The conductors 5 and 8 are adhered to a second housing 13. The second housing is further encapsulated by the encapsulation material 4 It should be noted that the encapsulation material, due to the high viscosity of the resin used, practically does not flow within the narrow space between the windings and the second housing. If even a little resin flowed into the narrow space, this would not affect the operation of the protection element, since the small dimension of the space would ensure that only very little resin penetrated the space. The second housing comprising the protection element, is mounted separately from the winding 2 of the capacitor, and the upper and / or lower walls forming the first housing 3. The second housing is also preferably separate from the first housing. Since the second housing is encapsulated by the encapsulating material, the protection element is also protected by the encapsulating material. The fact that the second housing is separated from the walls of the first housing, as shown in Figure 1 and 3, means that damage to, or leakage from, the first housing will not influence or endanger the element of the first housing. protection, as it is embedded in the resin. As can be seen in figures 1 and 3, the first housing does not necessarily need to have an upper wall since the windings and the second housing are both encapsulated. In a similar way the encapsulation material is responsible for the protection of the capacitor and forms the cover of the energy capacitor. The operation of the protection element 6 will now be described in more detail by means of FIG. 2, which schematically illustrates a first embodiment of a capacitor unit in accordance with the present invention. The protection element 6 is connected in parallel on the windings 2 of the capacitor, and comprises a switch, which has 2 contact elements 15. A fuse 7 is connected in series with one of the electrodes of the capacitor unit and acts as a current interruption element, as will be described later. The protection element 6 further comprises a membrane 16 with a contact plate 17. The contact plate 17, which is part of the switch, is provided to close the latter. The second housing is mounted in such a way that the membrane 16, which forms one side of the second housing, is in contact with the space 12. As already described above in the preamble of the present application, the present capacitor is a capacitor of self-healing energy. The protection element serves to disconnect the capacitor when a short circuit or an electrical fault occurs, which can not be suppressed by the self-healing properties of the capacitor unit. When an electrical failure as such occurs, a gas will be produced within the windings 2. The gas will travel through the windings and will reach the narrow space 12 between the outer face of the windings and the second housing 13. The gas will accumulate on a pressure within the narrow space 12. As the membrane 16 is facing the narrow space, said overpressure is applied on the membrane. The pressure thus applied on the membrane will cause the membrane 16 to move towards the contact elements of the switch. When the applied pressure is sufficiently high, the contact plate 17 will reach the contact elements 15 of the switch, causing the latter to close. The current applied to the electrode 8 will now flow through the switch to the fuse 7, causing the latter to melt creating a high short-circuit current, directly between the winding electrodes. Once the fuse has been blown, the capacitor unit is disconnected from the electrical source, since the link between the second electrode 11 and the power source is broken. The membrane 16 is preferably a bi-stable membrane, which closes the switch from an open initial position to a closed position. The bi-stable membrane is more reliable, since the function of the membrane is to operate the contact plate 17 of the switch 15. Since the protection element 6 is mounted in the second housing 13, which is housed in the material of encapsulation, and since the second housing is separated from the windings 2 by the narrow space 12, the protection element forms a separate component of the capacitor winding. Therefore, it is not influenced by the external environment, nor the elaboration of the winding is influenced by the protection element. The latter being a separate component, which is separately tested during the development of the capacitor. Through the location of the protection element, in the direct vicinity of the windings, the sensitivity of the element is increased and the response speed is improved. Figures 3 and 4 show a second preferred embodiment of a self-regenerating energy capacitor in accordance with the present invention. The second embodiment differs from the first, in the construction of the protection element 6. In the second embodiment, the current interruption element is integrated within the housing 13. The current interruption element is formed by a conductor 19 which is mechanically susceptible to being broken, which is connected in series with one of the electrodes of the capacitor unit. A cutting element 18 is mounted on the membrane 16. Preferably the cutting element 18 is formed by a piece of glass, which has the advantage of being particularly suitable for cutting purposes and which is a poor electrical conductor. The mechanically breakable conductor 19 is placed in front of the cutting element 18.

When a pressure is exerted on the membrane 16, the cutting element will move towards the cable of the fuse 19. Once the pressure has reached a predetermined value, the cutting element will have reached the cable of the fuse, and cuts the latter by disconnecting in this way the windings of the capacitor of the power source. The travel distance of the cutting element 13 as well as of the contact plate 17 in the first mode are adjusted in such a way that the disconnection of the capacitor unit will take place once the pressure on the membrane has reached a limit value , indicative of an electrical fault within the winding, which can not be autoregenerated by the capacitor. Figure 5 shows a top view of the first embodiment of a self-healing energy capacitor in accordance with the present invention, and in particular the manner in which the electrical contacts are incorporated. In Figure 5 the encapsulation material is not visible to make the electrical contacts adequately visible. In their final configuration these contacts are coupled in the encapsulation material, so that only the terminals 30 extend towards the encapsulation material. Two of the second conductors 8-1 and 8-2 are connected each time to a first plate 21-1, 21-2 which contacts one end of the fuse 7-2 and 7-3 respectively. The other end of the fuse 7 being connected to a second plate 22, to which the first conductors 5 are connected each time. The second plates 24 are also connected each time to one of the switches 15. The other switch 15 is connected to third plates (not shown), which are connected each time to the first plates 21. A fourth plate 20, connected to the fuse 7-1, is additionally connected to terminal 30-3. Perforations 25 are provided to properly position the second housing within the first housing 3. The first, second, third and fourth plates are all fixed on the second housing 13, wherein the protection element is housed. The second housing is preferably made of a plastic material, which is a good electrical insulator and aids in easier processing.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A self-regenerating energy capacitor comprising at least one capacitor unit, each capacitor unit comprising at least one winding, made of at least two films of insulating material on which a metal coating has been applied, said windings being of each capacitor unit provided with a first and second connection electrode, said windings being surrounded by an encapsulation material and housed in a first housing, said capacitor tending at least one protection element for each capacitor winding, said protection element being mounted in a second housing, of which one side is formed by a membrane, said protection element being provided to activate, under a pressure exerted on said membrane by a gas produced by a short circuit of said windings, a current interruption element connected in series with one of said electrodes, said element being separate protection of an end face of said windings, further characterized in that said second housing is housed inside said first housing, separate from the upper and / or lower walls belonging to said first housing, said second housing being housed in said encapsulation material and having at least one wall separated from said windings by a narrow space.

2. A self-regenerating energy capacitor according to claim 1, further characterized in that said current interruption element comprises a fuse, and said protection element comprises a switch, provided to be interrupted by said membrane, said switch being connected in parallel with said first and second electrodes.

3. A self-regenerating energy capacitor according to claim 1, further characterized in that said current interrupting element comprises a fuse wire, connected in series with one of said electrodes and placed in front of a cutting element, which is part of said protection element, said cutting element being provided to be moved by said membrane toward said cable, to properly cut said cable, when said pressure is exerted on said membrane.

4. A self-regenerating energy capacitor according to one of claims 1 to 3, further characterized in that said membrane is a bi-stable membrane.

5. A self-regenerating energy capacitor according to one of claims 1 to 4, further characterized in that said protection element is made of a plastic material characterized in that a metallic conductor is housed.

6. - A self-healing energy capacitor according to any of said claims 1 to 5, further characterized in that at least 3 capacitor units are housed in said first housing.

7. A self-regenerating energy capacitor according to claim 3, further characterized in that said cutting element is formed by a piece of glass.