High-voltage, blast-actuated power switch having a collapsible contact

A high-voltage, blast-actuated power switch is disclosed which includes a sealed switch casing having a pair of electrical switch contacts, at least one of which can be collapsed by the pressure generated by a blasting cap. The switch casing is filled with a high dielectric strength medium having a low compressibility. When a short circuit or overload condition occurs, the blasting cap is ignited thereby generating a pressure wave. The pressure wave is transmitted through the medium and is practically instantaneously applied to the region of contact between the electric switch contacts. The electric switch contacts are deformed by the pressure wave and separate from each other. The switch contacts preferably include predetermined bending or breaking points to facilitate bending or breaking. The switch includes a screen which delays the gaseous materials emitted from the blasting cap from reaching the region between the separated electrical switch contacts. The screen is located between the blasting cap and the region of contact between the electrical switch contacts.

BACKGROUND OF THE INVENTION 
In power transmission and distribution systems, rapid current rises can 
occur, such as those occurring during short-circuit conditions. In order 
to protect the high-voltage power lines against dynamic and thermal 
stresses which accompany the rapid current rises, the line must be 
electrically opened or cut-off before the short-circuit current has 
reached its first peak value if the line is carrying alternating current, 
or before the line has reached its final value if the line is carrying 
direct current. The cut-off time required, which depends upon the 
frequency of the alternating current and on the inductance, capacitance 
and resistance of the power line, should not exceed a few milliseconds. 
Such rapid cut-off times, however, cannot be obtained with mechanically or 
magnetically actuated switches in medium-voltage and high-voltage power 
networks. Therefore, switches have been developed which are actuated by 
blasting. 
One conventional type of blast-actuated switch includes a torsion-rod 
spring having a contact projecting radially outward from its free end. The 
switch further includes a pull-rod which cooperates with a lever to place 
the torsion-rod spring under tension, and to press the elements fastened 
to the contact onto the main conductor line. The pull-rod has a recess 
into which a blasting cap is inserted. Upon the occurrence of a short 
circuit, the blasting cap is exploded, thereby causing the pull-rod to be 
torn apart. The lever is released and the contact elements are lifted away 
from the main conductor line as the torsion-rod spring contracts. 
Another conventional type of blast-actuated switch includes a casing having 
a conductor arranged therein. The conductor includes a recess which 
accommodates a blasting cap. When the blasting cap is exploded, the 
conductor is directly torn apart. 
Such conventional blast-actuated switches, however, have certain 
disadvantages. In the first mentioned type, the blasting cap is located 
outside of the region of the electric contacts and therefore does not 
influence the contacts directly. The separation of the contacts is 
accomplished exclusively by the spring force of the torsion-rod spring. 
Consequently, a significant time delay is experienced before the contacts 
are actually separated. 
The second mentioned type of switch provides for a much shorter time delay 
than that of the first type. However, in the second type of switch, the 
gaseous materials emitted from the blasting cap as the cap explodes 
tearing apart the conductor, substantially lower the breakdown voltage 
across the ends of the blasted conductor, thereby substantially lowering 
the dielectric strength of the switch. 
It is therefore an object of the present invention to provide a 
high-voltage, blast-actuated power switch in which the contacts are 
separated without auxiliary mechanical means, and in which the gaseous 
materials generated by the explosion of the blasting cap essentially does 
not penetrate the area between the separated contacts. 
SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, the 
high-voltage power switch includes a casing which is filled with a medium 
of low compressibility. The exploding blasting cap produces a pressure 
wave which is practically instantaneously transferred through the medium 
from the blasting cap to the electrical switch contacts. At least one of 
the two switch contacts is designed such that it will collapse when 
subjected to the pressure wave. 
The present invention permits the pressure wave generated by the blasting 
cap to be transferred to the point of contact between the electrical 
switch contacts directly, and not through auxiliary mechanical devices. 
This arrangement, therefore, results in switch actuating speeds not 
feasible with conventional high-voltage, blast-actuated switches. 
The medium transferring the pressure wave from the blasting cap to the 
electrical switch contacts will itself actively prevent the gaseous 
materials emitted from the blasting cap from reaching the region between 
the contacts during the critical time as the contacts separate from each 
other. Thus, breakdown voltage is not reduced by the gaseous material as 
in conventional blast-actuated switches. 
A preferred embodiment of the present invention includes a screen which is 
arranged between the blasting cap and the region of contact between the 
electrical switch contacts. The screen prevents the gaseous materials 
emitted from the blasting cap from spreading in a straight line in the 
direction of the region of separation of the electric switch contacts. 
According to the present invention, the medium which fills the switch 
casing has a low compressibility and a high dielectric strength. According 
to a preferred embodiment of the present invention, the medium is 
transformer oil. According to another preferred embodiment of the present 
invention, the medium is sulfur hexafluoride (SF.sub.6).

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a high-voltage, blast-actuated power switch 10 
includes two external connections 11,12 which are mechanically connected 
to each other by a tube 13 made from an insulating material. The tube 13 
is sealed to each of the external connections 11,12 so as to form a 
gas-tight and fluid-tight switch casing 14. The switch 10 is rotationally 
symmetric about an axis 8. 
The switch 10 includes a first switch contact 16 which is soldered to the 
surface of the external connection 11 inside the switch casing 14. The 
first contact 16 has a curved base place 17 which is directly soldered 
onto the external contact 11; a corrugated tube 18 which is soldered onto 
the base plate 17; and a contact plate 21 which is soldered onto the 
corrugated tube 18. 
The base plate 17 includes a corrugation 22 which is substantially 
coaxially situated about the axis 8. The corrugation 22 facilitates the 
resilient deflection of the center part of the base plate. The base plate 
also includes an aperture 58 which provides communication between a 
chamber 49 enclosed by the corrugated tube 18 and a bore 55 through the 
external connection 11. 
The corrugated tube 18 is terminated at one end by the base plate 17, and 
is terminated at the other end by the contact plate 21. The corrugated 
tube 18 contains two punctures 23,24 which form predetermined bending 
points at which the mechanical strength of the corrugated tube is 
relatively low. The contact plate 21 contains a conical recess 26 at its 
center which forms a predetermined breaking point at which the mechanical 
strength of the contact plate is relatively low. 
A second switch contact 36 is welded to a cup-shaped screen 27 which is in 
turn welded to the external connection 12 inside the casing. The screen 27 
includes a rim which is directly welded to the external connection 12. The 
screen includes cylindrical sidewalls which have a plurality of large 
openings. Only some of the openings, specifically openings 28, 29, 30, 31 
and 32, are illustrated in the figure. 
A rim 34 of the second switch contact 36 is welded to an outer surface of 
the screen 27. The rim 34 is flanged outwardly. The switch contact 36 
includes a cup-shaped part 37 having an aperture 60 substantially 
coaxially located about the axis 8. The second switch contact also 
includes a conical part 38 which forms a transition between the cup-shaped 
part 37 and the rim 34. A contact plate 41 is soldered onto the cup-shaped 
part 37. 
The second switch contact 36 includes notches 42,43 coaxially disposed 
about the axis 8. The notches are located at the region of transition 
between the conical part 38 and the rim 34, and between the conical part 
38 and the cup-shaped part 37. The notches 42,43 are predetermined bending 
points which increase the ability of the switch contact 36 to deform in 
the axially direction. The contact plate 41 contains a conical recess 26 
at its center which forms a predetermined breaking point which lowers the 
mechanical strength of the contact plate 41. 
The distance between the contact plate 21 and the surface of the external 
connection 11, and the distance between the contact plate 41 and the 
external connection 12 are dimensioned such that the contact plates 21, 41 
are forced against each other after the switch is assembled with such a 
pressure that the contact resistance between the contact plates 21, 41 
will be relatively small but yet the switch contacts 16, 36 are especially 
the predetermined breaking and bending points are not damaged. The contact 
plates 21, 41 may be soldered together so as to produce a practically 
resistance-free connection between the switch contacts 16, 36. 
A blasting cap 44 is located within the region delimited by the external 
connection 12 and the cup-shaped screen 27. The blasting cap includes a 
pair of conductors 46 which permit the blasting cap to be electrically 
ignited. The conductors 46 are lead through the external connection 12 to 
the outside of the switch casing. 
The entire switch casing 14 is filled with transformer oil which is 
practically incompressible and which has a high dielectric strength. A 
cylinder 47 with a relatively easily movable piston 48 is included in the 
external connection 11. The cylinder 47 is in communication with the 
transformer oil contained within the switch casing 14. The piston 48 moves 
within the cylinder 47 to compensate for any expansion or contraction of 
the transformer oil caused by temperature changes. 
In the event the high-voltage power network becomes overloaded, the 
blasting cap 44 is ignited. The blasting cap generates a pressure wave 
which is transmitted through the transformer oil. The two switch contacts 
16, 36 are subjected on all sides to the pressure wave transmitted through 
the transformer oil. The switch contacts will collapse, and the contact 
plates 21, 41 will be torn apart within approximately 10 microseconds. 
Since the transformer oil penetrates the region between the switch 
contacts, the transformer oil will normally prevent any arcing or will 
quench an arc within a very short time after the arc ignites. 
Unavoidably, gases are generated by the blasting cap as the blasting cap 
explodes. The gases are deflected by the screen 27 toward the surrounding 
tube 13, and will reach the region between the separated contact plates 
only sometime after the plates have already separated and the potential 
originally applied to the external connections 11,12 has been removed by 
some additional less rapidly switching device. Additionally, the 
transformer oil itself will permit the pressure wave to be rapidly 
transmitted from the blasting cap to the contact plates 21, 41, but will 
prevent the gases from rapidly reaching the contact plates. 
The pressure wave generated by exploding the blasting cap travels through 
the transformer oil relatively quickly because the transformer oil is a 
relatively incompressible medium. As the pressure wave travels from the 
blasting cap toward the external connection 11, the second switch contact 
36 is deformed in the axially direction bending at the notches 42, 43. The 
pressure wave causes the conical recess 26 contained in the contact plate 
41 to break forming an opening through which the medium can flow from the 
switch casing 14 into a chamber 51 enclosed by the second switch contact 
36. 
The pressure wave also causes the conical recess 26 contained in the 
contact plate 21 to break forming an opening through which the medium can 
flow into the chamber 49 of the first switch contact 16. The advancing 
pressure wave further causes the corrugated tube 18 to bend at punctures 
23, 24. 
The pressure generated by the explosion is quickly reduced as the switch 
contacts collapse and the relatively incompressible medium flows from the 
switch casing 14 into chambers 49, 51 through the openings 26. Therefore, 
the tube 13 of the casing is subjected to a pressure load for only a brief 
period of time. 
A switch according to the present invention need not be rotationally 
symmetric. The switch casing may be spherical, cubical or rectangular. 
Additionally, transformer oil need not be used as the relatively 
incompressible mediun. Other relatively incompressible mediums having high 
dielectric strength can be used, such as sulfur hexafluoride (SF.sub.6) 
which has been liquefied under pressure. 
A switch according to the present invention can also be operated by means 
of a quenching device which is connected in parallel with the switch and 
which contains a fusible element. Such arrangements are known to those 
skilled in the art. Additionally, devices for determining the existence of 
over-currents or short-circuits within the main conductor in order to 
generate the ignition voltage for the blasting cap are also well known in 
the art. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing specification. The 
invention which is intended to be protected herein, however, is not to be 
construed as limited to the particular forms disclosed, since these are to 
be regarded as illustrative rather than restrictive. Moreover, variations 
and changes may be made by those skilled in the art without departing from 
the spirit of the present invention.