Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2002-07-29
2004-08-03
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S521000
Reexamination Certificate
active
06771487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to power electronics components. In particular, the present invention is directed to power electronics components having an electrically active region and a housing.
2. Brief Discussion of the Related Art
In power electronics components such as power capacitors, phase modules for low-voltage reactive current compensation, or similar components, reliable heat elimination is of great significance. In other words, such components should have a low thermal resistance.
These components may be either dry, gas-impregnated or filled with oil or resin. Gas-impregnated components have a poorer thermal resistance than components filled with oil or resin. Compared to the latter however, gas-impregnated components are preferred in view of environmental pollution. Oil and resin filled components, as is well known, produce environmental problems that particularly occur when they are disposed of or when a fire takes place.
Power capacitors in particular can have either what are referred to as “Wet formats”, wherein an oil impregnation or a semi-impregnation is used, or “dry formats”, wherein a gas impregnation or a casting with materials such as epoxy resin, polyurethane resin or castor oil with a polyurethane curing agent is used. These materials can thereby have different viscosities whose range extends from hard to gelatinous.
All of these different versions are generally widespread and are marked by their own advantages and disadvantages in terms of production and operation of the power capacitors. For example, in addition to environmental problems, oil-impregnated components also have a higher fire risk.
In the decision as to whether “wet formats” or “dry formats” are to be used, consideration should be given to their properties with respect to flammability, creation of smoke and to toxicity. Specific casting compounds raise considerable problems in this respect.
In general, dry, gas-impregnated power capacitors are somewhat inferior to the “wet formats” in terms of thermal resistance, but raise fewer problems in view of environmental pollution. Thus, “dry formats” with gas impregnation are superior to wet formats during operation, and at the end of their service life, as well as in the event of a fire.
Another advantage of the “dry formats” rests in their substantially lower weight, compared to the “wet formats”.
However, components having higher power handling capabilities, such as phase shifter capacitors suitable for low-voltage reactive current compensation in the range of approximately 25 kVAr through 50 kVAr, are currently in development. Thus, there is a tendency toward using higher currents in intermediate circuit capacitors and circuit capacitors used with IGBT (Insulated Gate Bipolar Transistor) frequency converters, wherein better thermal resistance is advantageous for components operating at higher power.
Given these considerations, moisture absorption in the case of the various formats must also be taken into account. In some applications, one must count on a finite moisture diffusion into the component housing, given cast versions, so that an adequate adsorption of moisture should be done for dependable operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to create a power electronics component that will not cause environmental pollution when disposed of, has excellent thermal resistance, is capable of adsorbing moisture, and has a low weight.
This objective is achieved in a power electronics component, such as a power capacitor having an electrically active region, a winding, a housing, and a gap between the housing wall and the electrically active region, by filing the gap with a mineral bulk granular material.
According to the present invention, the mineral bulk granular material serves as an insulator, and fills the gap between a winding envelope and an inside housing wall in the power capacitor. On the basis of a suitable pre-treatment, the mineral bulk granular material can easily be placed in a position that it is capable of efficiently adsorbing moisture. Substances that have this property are often referred to as “molecular sieve”. For example, synthetically produced zeolite with a crystalline lattice structure are such molecular sieves.
The granular material, as was already pointed out, is placed in the gap between the winding envelope and the inside housing wall. The granular material can be adequately compacted therein by shaking.
The molecular sieve property can be potentially foregone when the power electronics component is utilized in a dry environment. In this case, suitable materials with granulation can be selected for the granular material without having to pay attention to moisture adsorption.
Experiments carried out by the inventor on large phase shifter capacitors have shown that desirable thermal conduction properties were achieved without great financial outlay using a granular material as an insulator in the gap between the winding envelope and the inside housing wall, so that heat generated in the active region of the phase shifter capacitors, i.e. in the winding, can be effectively eliminated toward the outside. A granular material with a standard implementation has an apparent density of approximately 0.7 kg/dm, and is considerably lighter than oil or casting compound.
Thermal conduction of the granular material can be influenced with the apparent density. When a lower apparent density material is used the thermal conduction is lower than when a higher apparent density material is used.
The financial outlay for the granular material is extremely low and lies clearly below that for oil or for casting compound. In addition, the granular material can be concentrated in those regions in the component that are critical for the heat elimination, which is fundamentally not true of oil impregnation or casting compound.
Measurements for a 25 kVAr cylindrically encased phase shifter capacitor of the MKKAC (Metallized Plastic Capacitor, Alternating Current) type show that what is referred to as the “hot spot” temperature, i.e. hottest location in the capacitor, given a reactive power of 50 kVAr, can be lowered by 7° K. with a fill of granular material in the gap between the winding envelope and the inside housing wall, compared to a gas-impregnated version. Comparative tests of power capacitors with gas impregnation, oil impregnation, casting resin impregnation, and granular material in the gap between the winding envelope and the inside housing wall clearly yield the best result for a power capacitor having granular material in the gap.
The considerable reduction in thermal resistance encourages development of power capacitors having higher power handling capabilities.
The good adsorption properties of the granular molecular sieve material also have a positive influence on the service life of a power capacitor with a dry format. Also, demands made during manufacturing and testing can be considerably reduced, which leads to a cost reduction in manufacture. Moisture adsorption of the granular molecular sieve material also enable design concepts with partial plastic covering in the terminal region of large rectangular capacitors. Plastic coverings or casting compounds always exhibit pronounced moisture diffusion, so that the material data known therefrom can be used to define a quantity of granular material, such that the granular material absorbs any moisture that diffuses into the component over its entire service life.
Preferably, the power electronics component of the present invention is a power capacitor. However, it can also be some other component, such as an inductance or a power semiconductor component, whereby good heat elimination is needed.
The granular material does not raise any environmental problems since its basic mineral material is also thermally stable in case of fire and thus does not exhibit a toxic effect or cause a greenhouse environmental problem. Further, a reduced amount of granular material is needed if the moisture ab
Dinkins Anthony
EPCOS AG
Schiff & Hardin LLP
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