Puffer-type gas blast switch

In a puffer-type gas blast switch including a gas compression device composed of two components defining, respectively, a piston and a cylinder, one of the components being stationary and the other one of the components being movable for compressing a quenching gas in the chamber during switch opening, a nozzle mounted for directing the compressed quenching gas from the chamber against a switching arc, a first power contact fixed to the movable component of the gas compression device and movable between a switch closing position and a switch opening position, a second power contact arranged to be conductively connected to the first power contact when the latter is in its switch closing position and movable with the latter during at least the initial portion of its movement from the switch closing position, and spring means urging the second contact in a direction to break its connection with the first contact, the second contact is directly and releasably connected to the first contact when the first contact is in its switch closing position, and the switch further includes an abutment member for limiting the path of movement of the second contact with the first contact during movement of the first contact to its switch opening position.

BACKGROUND OF THE INVENTION 
The present invention relates to a puffer-type gas blast switch as defined 
in the preamble of claim 1. 
Puffer-type gas blast switches with insulating nozzles have relatively long 
arc periods because at the time the contact is severed there is present a 
comparatively low gas pressure which is not yet sufficient to quench 
strong arc currents. A sufficiently high pressure builds up only after the 
switch has passed through a larger stroke. In such switches there 
essentially exist the following drawbacks: the arc is drawn out, it burns 
a long time, and quenching gas is wasted at a time when there is as yet no 
chance of quenching. The energy consumption in the switching path becomes 
high as a result of these influences and either limits the circuit 
breaking capability of such switches or necessitates comparatively large 
quenching chambers so as to avoid undue pressure increases. 
Puffer-type switches are known in which the contact piece which is actuated 
by the switch drive as well as the counter contact piece are movable. In 
such switches the counter contact piece is controlled by the movement of a 
piston. However, such switches are costly and complicated and can 
therefore not be used in an atmosphere containing SF.sub.6 dissociation 
products, as disclosed in German Offenlegungsschrift No. 2,100,808. 
German Offenlegungsschrift No. 2,708,546, and corresponding U.S. 
application Ser. No. 881,719, filed Feb. 27th, 1978, now U.S, Pat. No. 
4,211,904, issued July 8th, 1980, also discloses a puffer-type gas blast 
circuit breaker in which a switching contact disposed in an insulating 
nozzle is mounted to be axially displaceable in a guide actuated by a pull 
rod. In the on-state, the switching contact disposed in the insulating 
nozzle is latched in a stationary counter contact. For breaking the 
circuit, the guide, the insulating nozzle and cylinder connected with 
these parts are moved in the OFF direction. Due to the latching, the 
contact disposed in the insulating sleeve is pulled out of the guide 
whereby an annular projection of the switching contact abuts against the 
upper edge of the guide. At this moment, the switching contacts are pulled 
apart and the contact that has been pulled out of the guide is accelerated 
by the compression spring to spring back into the guide, or the insulating 
nozzle, respectively. 
Although with such a gas blast switch the arc period can be shortened and 
blasting of the arc before reaching the quenching distance can be 
prevented, a correspondingly large stroke is required to attain a 
sufficiently high pressure in the cylinder, causing the contact to be 
pulled out by a corresponding amount. This makes it impossible to maintain 
the optimum quenching distance. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the drawbacks present 
in such prior art switches. 
This and other objects are accomplished, according to the present 
invention, in a puffer-type gas blast switch including a gas compression 
device composed of two components defining, respectively, a piston and a 
cylinder, one of the components being stationary and the other one of the 
components being movable for compressing a quenching gas in the chamber 
during switch opening, a nozzle mounted for directing the compressed 
quenching gas from the chamber against a switching arc, a first power 
contact fixed to the movable component of the gas compression device and 
movable between a switch closing position and a switch opening position, a 
second power contact arranged to be conductively connected to the first 
power contact when the latter is in its switch closing position and 
movable with the latter during at least the initial portion of its 
movement from the switch closing position, and spring means urging the 
second contact in a direction to break its connection with the first 
contact, by constructing the second contact to be directly and releasably 
connected to the first contact when the first contact is in its switch 
closing position, and further providing the switch with abutment means for 
limiting the path of movement of the second contact with the first contact 
during movement of the first contact to its switch opening position. 
This solution provides a puffer-type switch offering the following features 
and advantages: 
1. quenching can take place in an optimum range; 
2. short arcs and short arcing periods; 
3. low quenching gas losses at a time when there is no chance for 
quenching; 
4. particularly simple design of the switch. 
Various embodiments of the invention provide, inter alia, the following 
further advantages: 
5. particularly small minimum arcing periods since the second contact is 
moved back at approximately the same speed with which it hits the 
abutment; this permits the use of very high breaking speeds so that it 
becomes possible to use only few switching paths, e.g. two switching paths 
for 525 kV even at an operating frequency of 60 Hz. without interfering 
the re-ignition freedom of the switch; 
6. even high short-circuit currents can be switched to advantage; 
7. the contact disposed in the insulating nozzle, which is under the 
greatest stress, can be made very stable; 
8. the advantages of the gas blast switch can be utilized in connection 
with a resistance switching path; 
9. the lagging masses of the second contact are reduced; 
10. there is little thermal influence on the latching since the conical 
undercut of the contact piece is sheltered from the plasma stream; 
11. substantial changes in the latching forces due to partial burning away 
of the conical contact faces is prevented; 
12. force locking oblique latching faces arranged at a certain angle are 
avoided, or replaced, by force locking latching faces which are arranged 
at a right angle to the axis of movement. The unlatching process is thus 
no longer produced in dependence on the forces acting on the latching but 
independently of position by means of a separate spreading device which 
during a switch-off movement temporarily impinges on its own abutment 
shortly before the impingement of the second contact piece and spreads the 
first contact piece via a previously unstressed oblique face to unlatch 
it. The position and width of this oblique face are necessarily 
dimensioned in such a manner that the first contact piece has already been 
spread before the second contact piece is braked by the abutment. Due to 
the form-locking connection on the one hand and the position dependent 
unlatching on the other hand, the motion sequence realized is essentially 
independent of the wear of the components. Changes in the contact 
conditions due to wear of the contact faces of the latching system are 
excluded during the unlatching process, when the edges of the latch are 
subjected to high specific areal pressures. Moreover these parts 
simultaneously transmit, for a brief time, the full current of the 
switching path; 
13. Burning away of regions of the contact area required for latching is 
prevented; and 
14. it is assured that the arc does not attack the conical face so that the 
arc remains better suited for the latching function although the contact 
carries a plasma stream.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The gas blast switch shown in FIG. 1 is essentially composed of the 
following parts pertaining to its contact system: a gas compression 
chamber 2 defined by a stationary piston 2a and a movable cylinder 2b; a 
nozzle 4 made of an electrically insulating and heat resistant material 
attached to the cylinder 2b; a movable power contact piece 6 provided in 
the insulating nozzle and movable therewith; a movable power contact piece 
8 disposed to be axially displaceable on a slide-tube 17 mounted in the 
upper portion 10 of the switch. The contact piece 8 forms a counter 
contact for piece 6. The switch further includes an abutment member 12 and 
a compression spring 14. 
The contact piece 6 disposed in the insulating nozzle 4 is provided at its 
front end with a conical undercut 7 which can be seen more clearly in FIG. 
2. Correspondingly the front end of the counter contact piece 8 is 
provided with a conical protrusion 9 which latches with the undercut 
portion 7. 
The counter contact piece 8 is arranged to be axially displaceable in a 
cylindrical recess 16 in the upper portion 10 and includes an upper flange 
18 against which the upper end of compression spring 14 rests. 
The abutment 12 is disposed in a mount 20 carried by portion 10 and 
delimiting the lower end of recess 16. This abutment 12 may be made 
resilient so that the counter contact piece 8 will be driven away from 
contact piece 6 at approximately the same speed as it impacts on abutment 
12. This makes it possible to realize very minimal arc periods. 
However, the abutment 12 may also be made to produce a mechanical damping 
action on piece 8 which is of particular advantage if high currents have 
to be switched. 
FIG. 2 shows the contact pieces 6 and 8 in the latched state. In order to 
permit unlatching of the contact pieces, longitudinal slots (not shown) 
are advantageously provided in the counter contact piece 8 so as to permit 
lateral deformation of piece 8. However, as shown in FIG. 2, the contact 
piece 6 disposed in the insulating nozzle may be provided with slots, 
either in addition or alternatively to piece 8. 
Starting with the switched-on position of the switch, in which the contact 
pieces are latched as shown in FIG. 2, contact 8 is in the position shown 
in FIG. 1, and nozzle 4 fits around piece 8 the switch-off process takes 
place as follows. A switching rod 30 actuated by a drive (not shown) moves 
the contact piece 6 as well as the cylinder 2b connected therewith and the 
insulating nozzle 4 downwardly so that quenching gas disposed in chamber 2 
is compressed. In the initial phase, the nozzle opening is closed by the 
contact piece 8. During the downward movement, the contact pieces 6 and 8 
initially remain latched together, i.e. the counter contact piece 8 
follows the movable contact piece 6, thus compressing the spring 14. 
Unlatching occurs when the countercontact piece 8 impacts on the abutment 
12, whereupon the contact pieces 6 and 8 are pulled apart and the 
countercontact piece 8 then jumps back, under the action of spring 14, 
into the end position shown in FIG. 1. This unblocks the nozzle opening 5 
and the blasting of gas onto the arc begins. 
FIGS. 3 are schematic illustrations of the design of a switch including a 
switch-on resistor 28.*) During switch-on, starting from the off position 
shown in FIG. 3a, approximately 8 to 10 ms before the main switching path 
is closed the resistance switching path 26 is closed as shown in FIG. 3b, 
and remains closed after completion of the switch-on of the main path, as 
shown in FIG. 3c. During switch-off both contact pieces move in the OFF 
direction. Because the main contact initially carries along the movable 
contact, the resistance switching path 26 opens first, as shown in FIG. 
3d, after which the fully open state depicted in FIG. 3e is reached. 
Therefore, this arrangement does not require a complicated sliding or 
spring lock. 
FNT *) The form of this switch is described in connection with FIG. 7. 
A corresponding arrangement is shown in FIG. 7. The gas blast switch shown 
in FIG. 7 corresponds partly the switch shown in FIG. 1. The corresponding 
parts have equal numbers. The gas blast switch of FIG. 7 has an additional 
switch or connector 26 for switching a conductive path containing a 
switch-on resistor 28. 
The switch 26 is essentially composed of a movable contact piece 50 and a 
counter contact piece 51. The movable contact piece 50 is a tube which is 
arranged axially displaceable in a cylindriacal part 52 and which is 
engageable with the counter contact piece, which is conductive connected 
with the resistor 28. The switch 26 with the resistor 28 and the gas blast 
swich are connected parallel as it is shown in FIGS. 3a-3e. The movable 
contact pieces 6 and 50 of the switches are actuated by an actuation rod 
54 and hinged levers 56, 57, 58. The operation of the switch shown in FIG. 
7 is described in connection with FIG. 3. 
In the embodiment shown in FIG. 4, the insulating nozzle 4 is enclosed by a 
metallic shield 34 which serves to shield the contact piece disposed in 
the insulating nozzle against flashovers from contact piece 8. 
The contact system shown in FIGS. 5, 6 and 8 includes, as does the system 
shown in FIGS. 1 to 4, a first contact piece 6 which is firmly connected 
with the movable part of a piston/cylinder unit (not shown here) of a 
compression device for the quenching gas, and a counter contact piece 8 
which during switch-off is initially kept in engagement with the first 
contact piece 6 and moves therewith until unlatching, piece 8 then 
returning to its starting position under spring pressure. The counter 
contact piece 8 is again directly and releasably connected with the first 
contact piece 6 and the following movement of contact piece 8 is again 
limited by abutment 12. 
A positive, form-locking connection is provided between the two contact 
pieces 6 and 8, in that the two pieces are provided with mating contact 
faces 35 which lie at a right angle to the axis of movement so that pieces 
6 and 8 are interlocked to establish a force transmitting connection 
therebetween. 
For unlatching the contact pieces 6 and 8, a spreading device 36 is 
provided which is connected with the counter contact piece 8 and comes up 
against an abutment 37 shortly before the counter contact piece 8 reaches 
its abutment position, thus initiating unlatching of the two contact 
pieces 6 and 8. 
FIG. 8 shows these contact pieces when they are unlatched, i.e. when the 
switch is open. 
The spreading device 36 includes, as shown in FIGS. 5 and 8, a conical 
camming surface 36' over which the end of contact piece 6 travels during 
braking of the spreading device when the spreading device impinges on its 
abutment 37, thus spreading all of its contact fingers 6' in radial 
direction. The radial height and axial position of surface 36' are here 
selected such that they correspond to the unlatching stroke of the 
unlatching device. Thus, during a switch-off movement the unlatching 
stroke is performed before the counter contact piece 8 impinges on its 
abutment 12. 
In an advantageous manner, as shown in FIG. 6, the spreading device 36 
includes two or more fingers 36a, b, c, which fit into corresponding 
recesses between portions 8', of the substantially tubular counter contact 
piece 8 and which are connected with a ring 40 or sections of a ring, 
which during the switch-off movement comes up against abutment 37 which 
limits the stroke of the spreading device. Preferably, piece 6 is provided 
with a number of fingers 6' equal to the number of fingers 36a, b, etc., 
with each of the latter fingers engaging a respective finger 6'. 
As a protection for the gaps between the spreading device 36 and the 
counter contact piece 8 against soiling from combustion particles or as a 
protection for the parts themselves against the wear to be expected from 
the arc during switch-off, a protective tube 38 of fire-proof material is 
disposed in the interior of the arrangement and is connected with the 
counter contact piece 8. 
In practical devices according to the invention, the spreading device 36 
can be made of a hard resilient metal such as steel or titanium, or may be 
made entirely of a suitable plastic. When device 36 is made of metal, the 
slide faces thereof which act on contact 6 can be covered or coated with a 
low friction plastic, such as Teflon. The portions (FIG. 2) 6a, 8a of 
contacts 6 and 8 which contact one another can be made of a suitable 
fireproof material. The contact 6, or the portions thereof in the region 
where connection is effected with contact 8, can be made of copper or a 
suitable copper alloy e. g. chromium-copper. The parts 8b of the contact 8 
which do not conduct current are made of titanium. 
A suitable resilient abutment 12 is a cup spring; a suitable material for 
the movement damping body is polyurethan. The inclination angle of the 
conically tapered surfaces is in the range of 15.degree.-20.degree. 
relative to a line perpendicular to the longitudinal axe of the switch 
pieces. When the surfaces have different inclinations, the inclination 
angle of the contact piece 8 is in the range 13.degree.-18.degree.. 
Suitable plastic materials for the spreading device are Teflon or Delrin. 
The fireproof materials for the contacts and the protective tube can be 
copper-tungsten-alloy or graphite. The metallic shield 34 material can be 
copper. 
It is to be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.