Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2001-02-07
2002-12-24
Chen, Bret (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S489000, C427S569000
Reexamination Certificate
active
06497923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing an electrical insulator. A hydrophobic plasma-polymer coating is applied to a molded part of the insulator.
The term “electrical insulator” is to be understood in this context to mean any electrically insulating component in an electric circuit or an electrical installation. Such an insulating component is, for example, a barrier layer used in a circuit, an insulating sheathing of a current-carrying conductor or a printed-circuit board for electronics. For the purposes of the present description, however, an electrical insulator is in particular also an insulator as used in power engineering for routing current-carrying lines or keeping them apart. In particular, an electrical insulator is also understood as meaning a high-voltage insulator, as used for routing overhead power lines or for keeping them apart. An insulating housing of a high-power semiconductor or of an electrical switching element, such as a thyristor or a thyratron for example, also represents an electrical insulator for the purposes of the present description.
Electrical insulators are produced from many different materials. However, plastic, glass and ceramic, in particular porcelain, are primarily used. The production of an electrical insulator from these materials generally takes place by molding a deformable raw composition and subsequently curing it. Depending on the material used, the curing in this case takes place by cooling, exposure to light or, in the case of ceramic, by firing. The molded insulator, which may also comprise a plurality of pieces of different material (known as a composite insulator), is referred to below as a molding. The production of such moldings of electrical insulators is general state of the art. For the production of a ceramic high-voltage insulator, reference may be had, by way of example, to the Siemens company publication “High-Voltage Ceramics for all Applications—by the Pioneer of Power Engineering!”, Order No. A 96001-U10-A444-X-7600, 1997.
If an electrical insulator is used over a prolonged period, it is subject to a greater or lesser degree of superficial soiling, depending on the location at which it is used, which can considerably impair the original insulating characteristics of the clean insulator. For example, superficial flashovers occur due to the soiling. Because a rough surface soils more quickly than a smooth one, a ceramic insulator is, for example, provided with a surface glaze, which improves the technical properties of the insulator. The application of dirt-repellent lacquers or coatings to reduce the long-term soiling of the surface is also customary for other electrical insulators.
The same problem of loss of the insulating property exists if the electrical insulator is used in damp surroundings or where there is high atmospheric humidity or it is exposed outdoors to damp effects of the weather such as fog or rain. Condensation or rain causes water to precipitate on the surface of the electrical insulator. When it evaporates, previously dissolved dirt particles adhere to the surface of the insulator. Therefore, superficial soiling is formed over time, causing the insulating characteristics of the clean insulator to deteriorate. Even a smooth surface does not prevent this soiling. The same problem occurs if the insulator is used in a salty environment, such as for example near the coast or close to industrial sites.
To prevent premature flashover along the moist or soiled surface of the insulator, high-voltage insulators must be provided with so-called shielding ribs, whereby the creepage distance over the surface between the parts that are insulated from one another is extended to a considerable extent. However, this complex measure requires high expenditure on material and leads to high production costs.
As a solution to the problem of superficial soiling, in particular also in damp surroundings, the Siemens company publication “SIMOTEC Verbundinsulatoren: Ihr Schlüssel zu einer neuen Generation von Schaltanlagen” [SIMOTEC composite insulators: your key to a new generation of switchgear] Order No. A96001-U10-A413, 1996, discloses a so-called composite insulator which has shielding ribs made of a silicone rubber. The hydrophobic surface of the silicone rubber counters the formation of a film of water and the adherence of layers of foreign material. Water precipitated on the surface of such an insulator forms beads together with the foreign matter dissolved in the water, without a film of dirt being formed in the process.
However, in spite of its hydrophobic surface property, in damp surroundings silicone rubber tends gradually to take in water. This leads to a temporary deterioration in the insulating characteristics when there is high ambient atmospheric humidity and, if high voltages are to be insulated, leads to the insulator being destroyed if flashovers occur. This is because the taking in of water means that the flashover no longer occurs along the surface but partially through the insulator itself. The same adverse effects also occur if dust and dirt particles are incorporated into the surface of the silicone rubber.
Another proposal for producing a hydrophobic coating on an electrical insulator is disclosed by the publication “Insulators Glaze Modified by Plasma Processes”, Tyman, Pospieszna, and Iuchniewicz; 9
th
International Symposium of High-voltage Engineering, Graz, Austria, Aug. 28 to Sep. 1, 1995. There, a hydrophobic, plasma-polymer coating is produced on the glaze of a ceramic by plasma-treatment processes. For this purpose, in a first working step, a noble-gas plasma is produced from argon in a closed vessel, in order to detach alkali ions, such as sodium or potassium, that are located in the glaze, from the surface by gas bombardment. After this surface treatment, hexamethyldisiloxane (HMDSO) is admitted into the vessel as the working gas and a plasma is in turn produced from this gas at a pressure of over 1.12 mbar (112 Pa). The removed alkali ions are replaced by chemically solidly bonded hydrophobic groups by a plasma-polymerization process. In this process, a plasma-polymer, hydrophobic coating is formed. The hydrophobia and adherence of the plasma-polymer coating is disadvantageously dependent on the type of glaze. For instance, it is found that a brown glaze, which has far fewer sodium ions than a white glaze, offers better preconditions for a plasma-polymerization process and displays favorable chemical compounds for the formation of the hydrophobic layer.
The prior art process accordingly produces a hydrophobic coating on the glaze of a ceramic insulator by plasma polymerization. The quality of the coating, however, is strongly dependent on the composition of the glaze. The process was carried out on very small pieces of ceramic in a Leyden jar. It is not suitable for the coating of large electrical insulators.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method of producing an electrical insulator which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and wherein a hydrophobic plasma-polymer coating is applied to a molded part of the insulator. The hydrophobic plasma-polymer coating is intended in this case to be applied with the same quality, independently of the material of the molded part or of the material of its surface. Furthermore, the production method is to be equally suitable for insulators of any desired size, i.e. for insulators of microelectronics up to high-voltage insulators of several meters in length. The applied plasma-polymer coating is to be durable and hard and also solidly bonded to the material of the molded part.
With the above and other objects in view there is provided, in accordance with the invention, a method of producing an electrical insulator, which comprises the following steps:
introducing a molded part of an insulator into a vacuum chamber of a plasma reactor and evacuating t
Baalmann Alfred
Hennemann Otto-Diedrich
Liebermann Johannes
Vissing Klaus
Chen Bret
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
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