Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1981-11-17
1983-10-04
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
H01T 504
Patent
active
044082495
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates in general to surge arresters, and in particular to surge arresters enclosed in an electrically conductive, grounded enclosure and having a columnar active portion formed by a stack of disc-shaped arrester elements, and screening and controlling elements to produce a linear potential-distribution along the active portion of the arrester.
BACKGROUND OF THE INVENTION
An arrester having the aforementioned configuration is disclosed, for example, in the article "Reliability and Application of Metal Oxide Surge Arrestors for Power Systems," by S. Tominaga et al, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-98, No. 3 (1979), in particular beginning with page 809. In the Tominaga et al arrester, a linear potential-distribution along its active portion and a good dielectric strength are achieved by means of an electrically conducting shield which is connected to an element conducting the high voltage and extends along the arrester elements, as well as by means of screening rings. Considerable costs are associated with the construction of arresters of this type. Furthermore, the shape and dimensions of the screening and controlling bodies can be determined only with the aid of relatively complicated measurements and computation procedures. High manufacturing costs must accordingly be expected, especially in cases involving the building of arresters in small series.
SUMMARY OF THE INVENTION
The object of the invention is to produce an arrester of the type initially mentioned, in which a linear potential-distribution along its active portion and an optimum dielectric strength are achieved by simple means, and which, furthermore, can be manufactured in an economical manner, even when small series are involved.
This object is achieved in accordance with the present invention by a surge arrester in which the screening and controlling bodies comprise electrically conducting coatings disposed in a body composed of insulating material. The coatings are offset with respect to each other, are parallel to the column-axis of the active portion, and surround the active portion substantially concentrically. Further, the coating which is located at the shortest distance from the active portion is disposed opposite that part of the active portion which is at high potential and the coating which is located at the largest distance from the active portion is disposed opposite that part of the active portion which is at ground potential. In addition, the insulating body is externally configured, at least partially, as a truncated cone, and internally defines channels, extending along the active portion, through which the insulating gas circulates to carry away any heat which may occur at the active portion. Further, the distances between adjacent coatings advantageously are identical and the lengths of adjacent coatings decrease with increasing distance from the part of the active portion which is at high potential.
In the case of the arrester according to the invention, the numerical design of the coatings which act as controlling and screening bodies can be accomplished very precisely at a low cost. A high degree of linearization of the potential-distribution along the active portion of the arrester is achieved, by simple means, as a result of the finely gradated arrangement of the coatings. This means that the dimensions of the arrester can be minimized and electric field patterns are not needed for determining the potential-distribution.
In accordance with the invention, a degree of linearization is achieved with as few as 10 coatings, which is sufficient for the majority of arresters, whereas an arrester having 50-150 coatings is distinguished by a virtually linear degradation of the potential. By disposing the coating which is located at the shortest distance from the active portion of the arrester opposite that portion of the arrester which is at the high potential, the surge arrester according to the invention exhibits particularly low stray capacitances in the
REFERENCES:
patent: 1935820 (1933-11-01), Scott et al.
patent: 2219910 (1940-10-01), Webb et al.
patent: 2939976 (1960-06-01), Manni
BBC Brown Boveri & Company Ltd.
Moose Jr. Harry E.
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