Electricity: conductors and insulators – With fluids or vacuum – Conduits – cables and conductors
Reexamination Certificate
2002-10-29
2003-09-23
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Conduits, cables and conductors
C174S0210CA, C174S212000
Reexamination Certificate
active
06624352
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Appln No. 01811053.6 filed in Germany on Oct. 29, 2001; the entire content of which is hereby incorporated by reference.
TECHNICAL FIELD
The present invention relates to the field of electrical components and systems for electrical power transmission and distribution, and in particular to the field of gas-insulated switchgear assemblies.
PRIOR ART
The surface of an insulator body is a dielectric weak point of the insulator. Electrically conductive particles such as metal swarf, which are produced by way of example by erosion in disconnector circuits or by wear products from the conductor owing to thermal cycling and the movement resulting from it, have the tendency to adhere to the surface of the insulator, and to accumulate there, owing to the high dielectric constant of the insulator. Particles such as these lead to a considerably lower breakdown voltage, since the electric field around the particles is increased by the proximity of the insulator body.
WO 99/18582 discloses a gas-insulated or air insulated switchgear assembly of this generic type. In order to improve the breakdown strength, an inner conductor is provided with a dielectric layer and with transversely projecting barriers. The barriers are arranged on both sides of, and closely adjacent to, post insulators to which the inner conductor is fitted. They are used to prevent surface discharges, so-called streamers which occur on the dielectric insulation layer of the inner conductor, from reaching the post insulator and from flashing over via the post insulator to the grounded encapsulation or to an adjacent inner conductor. For this purpose, the barriers are designed with a geometry which tapers in the transverse direction, effectively in the form of a series of peaks without any overhanging parts, in order firstly to lengthen the path for the surface discharge, and secondly to achieve field control which is advantageous for the triple point at the contact point between the inner conductor and post insulator. This has the disadvantage that the lengthening of the path is often not sufficient to cause a surface discharge to break down. Furthermore, in this arrangement, surface discharges which originate on the post insulator, or move to it, cannot be stopped. Overall, the risk of dielectric flashovers resulting from surface discharges in the area of post insulators is still very high.
WO 00/62309 discloses a dielectric insulator for supporting a high voltage electrode on a holder, which is surrounded by a protective body, for example a porous foam, with a low dielectric constant. The protective body prevents metal swarf from being deposited directly on the insulator and, in particular, at the triple point.
DESCRIPTION OF THE INVENTION
The object of the present invention is to specify a post insulator for a gas-insulated switchgear assembly, a gas-insulated switchgear assembly, and a switchgear assembly module with a post insulator, which have an improved breakdown strength. According to the invention, this object is achieved by the features of the independent claims.
In a first aspect, the invention comprises a post insulator with a base body for supporting a high voltage component on a holder, with the post insulator being designed to bridge a high voltage potential difference between the component and the holder and having a surface, which extends essentially along a bridging direction, i.e. essentially along a potential gradient in the undisturbed operating state, of the base body, the surface of the post insulator having a cup-shaped indentation, which is concave and open toward the component or the holder, in an area between the component and the holder. The concave cup shape is used to divert surface discharges which originate from the component and propagate along the bridging direction in a direction opposite the bridging direction. The section which is in the opposite direction to the original propagation direction results in discharges being brought to rest and, possibly, being diverted laterally on the insulator surface. Overall, the invention effectively suppresses surface discharges along insulator surfaces on which there are particles and which are subject to a potential gradient. In consequence, systems, for example gas insulated switchgear assemblies (GIS), can be designed for higher E field strengths, greater particle contamination, and/or with more compact dimensions.
In one exemplary embodiment, the indentation has a macroscopic rearward section for self-blocking of surface discharges, for surface discharge paths between the component and the holder. This means that the reverse movement and possible diversion of surface discharges takes place over macroscopic dimensions, for example in the millimetric or centimetric range. In this case, the surface discharges are guided so that, on the rearward section, either their distance from the holder increases or their distance from the component decreases, if the indentation is concave and is open toward the component, or its distance from the holder decreases and its distance from the component increases, if the indentation is concave and is open toward the holder.
In a further exemplary embodiment, the surface discharge paths between the component and the holder can be diverted by means of the indentation from the bridging direction through an angle which is more than 90°, preferably 120° and particularly preferably 150° or especially 180°, and which lies essentially in a plane which is defined by a normal to the surface of the base body and by the bridging direction. The closer the diversion angle is to 180°, the more efficiently surface discharges can be stopped or diverted by self-blocking, thus avoiding flashovers to the holder.
The exemplary embodiments as claimed in claim 3 allow as many of the surface discharge paths as possible, and preferably all the surface discharge paths, between the component and the holder to be provided with rearward self-blocking sections by means of at least one indentation.
The exemplary embodiment as claimed in claim 4 has the advantage that the indentation is formed in a particularly suitable manner between the base body and the projection of the dielectric barrier. In particular, the barrier can be attached to the base body of a conventional post insulator.
The exemplary embodiment as claimed in claim 5 has the advantage that the barrier has a simple shape, and the barrier causes only minor E-field distortion on the surface of the post insulator.
The exemplary embodiment as claimed in claim 6 has the advantage that the post insulator with a barrier and indentation can be produced in a particularly simple manner by adhesive bonding or casting.
The exemplary embodiment as claimed in claim 7 has the advantage that the rounding of the barrier and of the indentation and their arrangement in a region of the insulator surface where the field is weak, and preferably where the field is at its weakest, reduces the E-field loads, and/or the physical dimensions of the switchgear assembly can be reduced further.
A second aspect of the invention relates to a gas insulated switchgear assembly or to a switchgear assembly module which has a post insulator according to the first aspect and according to the associated exemplary embodiments.
Further embodiments, advantages and applications of the invention can be found in the dependent claims as well as in the description which now follows, and in the figures.
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patent: 03222621 (199
Heitz Christoph
Piemontesi Marco
Salge Gerhard
ABB Research Ltd
Nino Adolfo
Reichard Dean A.
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