Power capacitor

Details Power capacitor Power capacitor

1999-03-30

2001-04-03

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S301300, C361S329000

Reexamination Certificate

active

06212058

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a power capacitor comprising a plurality of round, wound elements accommodated in a common housing.
2. Description of the Prior Art
The previously customary power capacitors of this kind have, as a rule, a housing of round, circular cross-section or rectangular cross-section. Power capacitors with circular, round housings have, among other things, the disadvantage that any arrangement in which a plurality of such capacitors are arranged alongside one another requires a relatively large amount of space. Moreover, the outer cooling surface of such capacitors is relatively small. Capacitors with housings with a rectangular or square cross-section can admittedly be better placed together in a row. However, it is a disadvantage of such capacitors that when using round coils, the housing volume is only poorly exploited. In the known capacitors it is frequently also necessary for electrical connections of different potential to cross one another, which is, as a rule, associated with a relatively high insulating cost and complexity for the associated wiring. Moreover, the construction of electrical delta circuits always leads, both with round coils arranged above one another alongside one another and also with concentric round coils, to dissimilar, asymmetric line lengths with crossing lines of high potential difference, which, among other things, gives rise to the disadvantage of non-symmetrical series resistances and inductivities, and also to the danger of insulation faults. In connection with star circuits With round windings accommodated above one another in cylindrical housings, a relatively high level of cost and complexity for insulation for the lines is generally necessary and much space is required in order to form the star point and to lead the phase lines upwardly to the common connection.
Moreover, with fully potted, round, wound embodiments in the cylindrical housing, the possibility of leading off the gas which arises into the connection space, without a dangerous excess pressure arising, hardly exists in the case of a fault, i.e. in particular, with a non-self healing breakdown with gas formation. Cylindrical, potted capacitors thus require special passages or permeable winding sleeves in order to facilitate the leading off of gas. These additionally required measures are, however, always associated with an increased space requirement, a higher thermal resistance and higher additional costs.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to provide a power capacitor of the initially named kind, in which the previously named disadvantages are overcome, which is as compact as possible, which is of simple construction and which can be manufactured with low technical manufacturing cost and complexity. Through a reduced constructional height and simplified internal wiring, both the best possible ideal exploitation of the housing volume and also a good ability to place the power capacitors in a row should be ensured.
This object is satisfied in accordance with the invention wherein at least one wound element group comprising three round, wound elements is accommodated in the housing, with the wound elements of the group being arranged in a star-like arrangement alongside one another with their axes parallel to one another, and in that the housing generally has the shape of a triangle with rounded corners having a radius of curvature, which corresponds at least substantially to the radius of the round, wound elements.
As a result of this design, a compact power capacitor results, which can be arranged in a row and which is of reduced constructional height, in which two previously contradictory requirements are satisfied while achieving improved arrangeability in a row and an increased exploitation of the volume. In comparison to the previously customary capacitors with round, circular housings, not only is the ability to place the capacitor in a row improved, but rather one also obtains a larger, external cooling surface. As a consequence of the ideal exploitation of the housing volume, a lower requirement for filler materials results. Moreover, an optionally desired overpressure switch-off security device in the form of a rupturable fuse can be realized more simply with side walls which bend outwardly more easily. Moreover, the assembly of three-phase capacitors in a delta or star circuit or in an open circuit is in particular simplified, since all the connection elements have the same length and shape, and can thus have symmetrical line resistances and inductivities, whereby the manufacturing costs are lowered in total. The wiring lines can be laid without problem into the creases formed between the round, wound elements, in particular with a delta circuit and an open circuit. With a star circuit, symmetrical and extremely short connections are also possible for the phases and the end face. The leads can be attached in a simple manner to the end faces of the windings, without connections of different potential crossing one another. The cost and complexity of the insulation of the wiring is correspondingly lower.
In an embodiment of the power capacitor of the invention preferred in practice, the three wound elements have the same diameter, so that the housing can in general adopt a cross-section in the shape of an equilateral triangle.
One or more wound element groups, each comprising three round wound elements can be accommodated in the housing. If a plurality of such wound element groups are provided, then these should be expediently arranged above one another.
The preferably impregnated housing can basically consist of a metal material or plastic material. In accordance with a preferred, practical embodiment, it consists of a flow-pressed aluminum. Such manufacture from an aluminum in the flow-press process offers, in conjunction with a sealed, welded housing or a housing with a turned-over edge, an ideal corrosion protection, especially for outside use.
It is of particular advantage if the power capacitor is provided with an overpressure switch-off safety device, which can, for example, be a rupturable fuse. In this arrangement, electrical connections provided at the cover side can be lead through the closed housing, which is partly provided with a filling, preferably a potting material, with the electrical connections extending within the housing through a pressure space left between the filling and the housing cover, and being interruptable on the occurrence of a predeterminable overpressure in the housing. If the housing is partly filled with an insulating, potting material permeable to pressure gas, and if the pressure space is provided between this potting material and the housing cover, then a reliable and rapidly responding overpressure switch-off device can already be realized if the housing has at least substantially flat side walls, which, on the liberation of pressure gas, can be bent outwardly and also provide connections to the pressure space. It is important in this respect that flat side walls can be more easily bent outwardly on pressure loading than is the case with curved side walls, so that connections which are open to the pressure space can be provided in the desired manner. In this respect it is simultaneously of advantage that in normal operation the potting material is connected to the housing over the entire peripheral surface, whereby an ideal thermal dissipation is ensured.
The electrical connections can, in particular, be fixed to the housing cover, so that they can be torn off from the outwardly arching housing cover on pressure loading of the pressure space, which takes place with outward bending of the side walls.
In an embodiment of the power capacitor of the invention, which is preferred in practice, the electrical connections are fixed at one end to the housing cover and at the other end to at least one support element, housing step and/or the like arranged in the pressure space and having a predeterminable spacing from the housing cover. In th

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