Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1995-08-25
1997-01-14
DeBoer, Todd
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361130, H02H 904
Patent
active
055946143
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a cylindrical surge arrester with a porcelain housing having safety shields surrounding the housing and at one end at least one blow-out aperture that is directed parallel to the cylinder axis of the surge arrester at the surface of the porcelain housing.
Such a surge attester is known, for example, from German patent DE-OS 2, 655,557. The surge arrester described therein has a porcelain housing with surrounding safety shields, all of which have the same outside diameter. In the event of a high short-circuit current, hot gas is blown over the safety shields and the surface of the surge arrester parallel to its axis from a blow-out aperture. The hot gas is blown out at a high pressure, and the flow of gas can break away the porcelain from the safety shields.
German patent DE-A 3,417,648 discloses a surge arrester that has a porcelain housing surrounded with safety shields. In this device the safety shield closest to the blow-out aperture has a smaller diameter than the safety shield that follows it.
SUMMARY OF THE INVENTION
The present invention provides a surge arrester that reduces the danger of damage to the safety shields.
According to the present invention by the fact that the diameter of the safety shields closest to the blow-out aperture increases with the distance from the blow-out aperture in at least two steps from one safety shield to the next.
In most cases the core of the porcelain housing is cylindrical.
Due to the fact that the first safety shields have a smaller diameter than the other safety shields, the first safety shields do not present a large obstacle for the quenching gas flow, and therefore the mechanical load at this point is greatly reduced. The term "diameter" refers to the distance by which a safety shield projects beyond the core of the porcelain housing. Some of the gas stream is deflected by the first safety shield in such a way that the succeeding safety shields are not stressed by the gas. At a greater distance from the blow-out aperture the gas stream has expanded and is also cooler, so there is no risk that the gas will damage the other safety shields.
It is advantageous for the safety shields to be arranged in a barrel shape in the longitudinal cross section of the surge arrester. This creates an especially favorable guidance of the gas discharged.
The other safety shields may be designed, for example, as safety shields with a larger diameter alternating with safety shields having a smaller diameter along the longitudinal axis of the surge arrester.
If the surge arrester has two blow-out apertures, one at each of its opposite ends, it is expedient for the safety shield closest to each blow-out aperture to have a smaller diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the following figure and described in greater detail below.
FIG. 1 shows a surge arrester according to this invention in a partially sectional view.
DETAILED DESCRIPTION
Surge arrester 1 has a cylindrical barrel shape. For example, it may have one or more columns of metal oxide discharge resistors on the inside. Housing 2 of the surge arrester is a porcelain housing with surrounding safety shields 3. In the central area along the longitudinal axis of the housing, safety shields 3 with a larger diameter alternate with safety shields 4 having a smaller diameter.
Surge arrester 1 has blow-out apertures 5, 9 at its ends, so in the event of a high short-circuit current, if an appropriate safety device such as a rupture disk is activated, hot gas flows out of these blow-out apertures at a high pressure in the direction of arrows 6, 10.
To protect safety shields 3, 4 from the effects of the gas, two safety shields 7, 8 having smaller diameters than safety shields 3, 4 are placed in front of them. Safety shield 7 which is closest to blow-out aperture 5 has the smallest diameter. In this way, the gas flow denoted by arrow 6 is deflected, and the load on safety shields 3, 4 is thereby reduced. The same set-up with safety sh
REFERENCES:
patent: 3715626 (1973-02-01), Olsen
DeBoer Todd
Siemens Aktiengesellschaft
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