Electrical circuit breaker with self-extinguishing expansion and insulating gas

An inside of tubular contacts of a self-extinguishing expansion SF.sub.6 -gas circuit breaker including guiding ribs arranged to oppose any vortex-effect swirling gas flow between a first extinguishing chamber and a second expansion chamber. The presence of these ribs improves the dielectric withstand of the circuit breaker, and prevents any arc restriking inside the contacts.

BACKGROUND OF THE INVENTION 
The invention relates to a self-extinguishing expansion electrical circuit 
breaker having a sealed enclosure filled with a high dielectric strength 
insulating gas, and housing one or more pole-units, each pole-unit 
comprising: 
a first extinguishing chamber designed to store insulating gas heated by an 
arc; 
a pair of contacts with relative axial translation movement comprising 
separable arcing contacts bounding a breaking gap in the first chamber; 
a tubular gas outflow duct, arranged inside at least one of the contacts to 
make the first extinguishing chamber communicate with the remaining volume 
of the enclosure forming the second gas expansion chamber. 
A circuit breaker of this kind is described in the European patent document 
EP-A-298,809 the corresponding U.S. Patent is U.S. Pat. No. 4,900,882. 
Tests have shown that the gas outflow via the ducts of the tubular contacts 
to the second expansion chamber can generate an ordered gas outflow, with 
spiral movement along the axis. The resulting Vortex effect then causes a 
variation of the gas density with the formation of a central zone of low 
density located in the vicinity of the axis of each tubular contact. This 
results in a decrease of the dielectric withstand, with risks of arc 
restriking inside the arcing contacts. 
The object of the invention consists in improving the dielectric withstand 
of a circuit breaker with self-extinguishing expansion of the insulating 
gas. 
SUMMARY OF THE INVENTION 
The circuit breaker according to the invention is characterized by the fact 
that the outflow duct is equipped with guiding means arranged to oppose in 
the duct any swirling gas flow, notably of the Vortex type. 
The gas flow guiding means can be formed by ribs or bosses arranged around 
the internal periphery of the tubular contacts. 
The ribs can be radial or inclined in the opposite direction to the gas 
rotation movement. 
The presence of these ribs or bosses channels the gas flow to generate a 
laminar or turbulent regime, defined in terms of the value of the 
Reynolds' number, and with a direction which is overall parallel to the 
axis. 
A coil or permanent magnet can advantageously be incorporated in the 
extinguishing chamber to set the arc in rotation, enabling the arc to be 
extinguished faster.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, the invention is described with respect to a medium or high 
voltage circuit breaker or switch described in the European patent 
document EP-A-298,809, but it is clear that it is applicable to any other 
type of self-extinguishing expansion circuit breaker. 
The pole-unit comprises an enclosure 10 confined by a cylindrical casing 
12, sealed at its ends by two base-plates 14, 16. The enclosure 10 is 
filled with a high dielectric strength gas, notably sulphur hexafluoride 
at atmospheric pressure or overpressure. The cylindrical casing 12 can be 
made of insulating material and the base-plates 14, 16 of conducting 
material constituting current input terminal pads. An operating rod 18, 
arranged in the axis of the enclosure 10, passes tightly through the 
base-plate 16 and is extended inside the enclosure 10 by a tubular movable 
contact 20. The tubular movable contact 20 bears at its end a movable 
arcing contact 22, cooperating with a stationary arcing contact 23 
supported by the contact 24 fixed to the opposite base-plate 14. An 
extinguishing chamber 26, formed by a cylindrical surface 28 and two 
base-plates 30, 32, surround the contacts 22, 24 coaxially. The 
cylindrical surface 28 and the base-plate 30 are metallic and electrically 
connected to the stationary contact part 24. The opposite base-plate 32, 
through which the movable contact 20 passes, is made of insulating 
material ensuring electrical insulation between the movable contact 20 and 
the cylindrical surface 28. 
Inside the extinguishing chamber 26 there is located a coil 34 fitted 
against the metal base-plate 30. The coil 34 is capped by an electrode 36 
constituting an arc migration track arranged facing the movable arcing 
contact 22. The coil 34 is electrically connected both to the electrode 36 
and to the base-plate 30 in such a way as to be inserted in series between 
the movable arcing contact 22 and the stationary contact part 24 in the 
closed position of the circuit breaker. 
In the open position of the circuit breaker represented in the left-hand 
part of FIG. 1, the extinguishing chamber 26 communicates with the 
enclosure 10, which constitutes an expansion chamber, on the one hand by 
the tubular duct 41 of the movable contact 20 whose base has communicating 
orifices 38 between the tubular inside of the contact 20 and the enclosure 
10, and on the other hand by the tubular-shaped stationary contact part 
24, which is extended through the coil 34 by a central duct 40 and which 
communicates at its base by orifices 42 with the enclosure 10. The 
stationary arcing contact 23 is represented schematically on the internal 
annular edge of the electrode 36. In the closed position of the circuit 
breaker, represented in the right-hand half-view of FIG. 1, the movable 
arcing contact 22 is abutting on the electrode 36 sealing off the two 
outflow ducts constituted by the contacts 20, 24. 
The movable arcing contact 22 is a semi-stationary telescopic contact 
biased by a spring 44 to the extension position. A sliding contact 46, 
supported by the base-plate 16 of the enclosure 10, cooperates with the 
movable contact 20 to ensure the electrical connection of this movable 
contact 20 and of the current input terminal pad formed by this base-plate 
16. 
The cylindrical surface 28 of the extinguishing chamber 26 is extended 
protruding beyond the insulating base-plate 32 by a flange 48 arranged as 
a stationary main contact. The stationary main contact 48 cooperates with 
a movable main contact 50 formed by a tulip-finger contact borne by a 
support 52 securedly united to the movable contact 20. The tulip-shaped 
contact fingers cooperate with the internal surface of the flange 48 in 
such a way as to respect the size of the extinguishing chamber 26, but it 
is clear that a reverse arrangement so as to encompass the flange 48 
externally can be used when the dimensions of the main contacts are 
secondary. 
Operation of a switch of this kind is well-known to those specialized in 
the art, and it is sufficient to recall that opening of the circuit 
breaker is controlled by downwards sliding in FIG. 1 of the operating rod 
18 which drives the tulip-shaped main contact 50 downwards to a separation 
position of the stationary main contact 48. During the first phase of the 
circuit breaker opening movement, the telescopically-mounted movable 
arcing contact 22 remains in abutment on the electrode 36 due to the 
action of the spring 44. As soon as the main contacts 48, 50 separate, the 
current is switched to the parallel circuit formed by the movable arcing 
contact 22 and the coil 34. Opening of the main contacts 48, 50 takes 
place without an arc forming, and as soon as the current is switched to 
the parallel circuit, the coil 34 generates a magnetic field which 
contributes to extinguishing the arc formed when the arcing contacts 22, 
36 separate in the course of the continued opening movement of the circuit 
breaker. The arc drawn in the extinguishing chamber 26 causes a heat rise 
and a pressure increase of the gas contained in this chamber, this gas 
escaping via the tubular contacts 20, 24 to the expansion chamber 
constituted by the enclosure 10. This results in a gas outflow which 
causes the arc to be blown out. 
In the example described above, the coil 34 is switched into circuit as 
soon as the main contacts 48, 50 open, but it is clear that this switching 
into circuit can be achieved in a different way, notably by switching of 
the arc onto the electrode 36. The coil 34 can also be replaced by a 
permanent magnet and the gas outflow can take place via one of the 
contacts only. 
According to the invention, at least one of the outflow ducts 40, 41 
arranged in the stationary 24 and movable 20 tubular contacts comprises 
guiding means 56, 58 (see FIG. 1) of the gas flow escaping to the 
expansion chamber of the enclosure 10 during the arc extinguishing phase. 
In FIG. 2, the guiding means 56 and 58 are formed by radial ribs securedly 
united to the cylindrical internal wall of the hollow arcing contacts 22, 
23. 
FIG. 3 shows the guiding means 56 with four ribs 60 arranged at right 
angles along the cylindrical periphery of the support tube of the arcing 
contact 23. The four ribs 60 do not extend up to the center, so as to 
delimit a continuous central channel 62 at the inlet to the duct 40. 
In FIG. 4, a single diametrical separating rib 60 subdivides the inside of 
the hollow contact 23 into two adjacent channels 64, 66. 
In FIG. 5, two diametrical ribs 60 are arranged in a cross to define four 
distinct channels 68, 70, 72, 74 at the inlet to the duct 40. 
The ribs 60 and other guiding means 58 are identical to those described 
previously. 
In the alternative embodiment in FIG. 6, the guiding means 56 comprises an 
alternating succession of grooves 78 and protuberances 80, arranged 
circumferentially along the internal tube of the arcing contact 23. 
The function of these ribs 60 or protuberances 80 consists in channelling 
the gas axially in the ducts 40, 41 to prevent any swirling gas flow, 
notably of the Vortex type. 
This results in a laminar or turbulent flow depending on the value of the 
Reynolds' number, which depends on the dimensioning and structure of the 
chamber 26 and arcing contacts 23, 22. The absence of ordered spiral 
movement of the outflow gas in the contacts (23, 22; 24, 20) contributes 
to regulating the density of SF.sub.6 to improve the dielectric withstand 
and prevent any arc restriking inside the contacts. 
In the alternative embodiments illustrated in FIGS. 2 to 6, the ribs 60 or 
protuberances 80 are made of conducting material. 
The longitudinal position of the ribs 60 can be modified in terms of the 
ratings and breaking characteristics. 
According to an alternative embodiment (not represented), the ribs 60 or 
protuberances 80 can be made of insulating material, and be of any shape, 
and notably be inclined in the opposite direction to the rotation movement 
of the gas. 
The invention also applies to a self-extinguishing expansion circuit 
breaker without magnetic arc rotation means.