High voltage sulfur hexafluoride circuit-breaker capable of operating at low outside temperatures

A high voltage sulfur hexafluoride circuit-breaker capable of operating at low outside temperatures and comprising at least one current-interrupting chamber comprising a sealed insulating enclosure containing a fixed contact inside a blast nozzle and a set of moving contacts associated with an operating member, the circuit-breaker including the improvement of means for maintaining a quantity of liquefied gas in the vicinity of the contact separation zone while the circuit-breaker is in the closed position.

The present invention relates to a high voltage sulfur hexafluoride 
SF.sub.6 circuit breaker capable of being used at very low outside 
temperature. 
BACKGROUND OF THE INVENTION 
The interrupting power of an SF.sub.6 circuit-breaker depends to a great 
extent on the pressure inside the circuit-breaking chamber since pressure 
has a direct effect on the mass flowrate of the SF.sub.6 gas used for 
extinguishing the arc. As temperature falls, so does the pressure of the 
gas and the mass flowrate is greatly reduced, which can lead to arcs 
re-striking while the circuit-breaker is interrupting an electric current. 
U.S. Pat. No. 4,273,978 describes an SF.sub.6 circuit-breaker in which a 
piston urges liquid SF.sub.6 into the contact zone when the 
circuit-breaker is opened. This arrangement increases the mass flowrate of 
SF.sub.6 at the moment of extinction, but it requires very high operating 
energy. An aim of the invention is to obtain a high mass flowrate of 
SF.sub.6 when interrupting a current, without requiring the operating 
energy for opening the circuit-breaker to be increased. 
SUMMARY OF THE INVENTION 
To this end, the present invention provides for liquefied sulfur 
hexafluoride to be directed to a zone adjacent to the contacts so that in 
the presence of an electric arc at the moment when the circuit-breaker 
opens, the liquid is vaporized, thereby increasing the mass flowrate of 
vapor through the blast nozzle. 
More precisely, the present invention provides a high voltage sulfur 
hexafluoride circuit-breaker capable of operating at low outside 
temperatures and comprising at least one current-interrupting chamber 
comprising a sealed insulating enclosure containing a fixed contact inside 
a blast nozzle and a set of moving contacts associated with an operating 
member, the circuit-breaker including the improvement of means for 
maintaining a quantity of liquefied gas in the vicinity of the contact 
separation zone while the circuit-breaker is in the closed position.

DESCRIPTION OF PREFERRED EMBODIMENT 
The circuit-breaker chamber comprises: 
(a) An insulating envelope 1 having good pressure performance, and closed 
at each end in sealed manner by respective metal end plates 2 and 3 having 
respective current connection fittings 2A and 2A. 
(b) A set of fixed contacts comprising a tubular metal support 4 having an 
insulating nozzle 5 fixed thereto together with two-tab contact fingers 6A 
and 6B. The fingers 6A are made of tungsten and serve as arcing contacts 
whereas the fingers 6B are made of silver-plated copper and serve as 
permanent contacts. In a variant, fingers could be used having single 
tungsten silver tabs and serving both as arcing contacts and as permanent 
contacts. 
(c) A set of moving contacts including an electrode 14 which may be hollow 
or solid, a ring of fingers 25 made of copper tungsten alloy, and a system 
of insulating rods 15 for fixing the electrode 14 to a moving piston 16. 
The electrode 14 is fixed to a metal cylinder 17 which slides via sliding 
electric contacts 18 in another metal cylinder 19 which is fixed to end 
plate 3. The main moving contacts 25 and the insulating fingers 15 are 
fixed on a support 17A which is fixed in turn to the cylinder 17. The 
cylinder 17 is connected, outside the envelope, to operating means (not 
shown). 
A metal deflector 7 surrounds the contact fingers, thereby providing better 
die electric performance. The nozzle delimits an inside volume 20 which is 
partially filled with liquefied gas when the circuit-breaker is in the 
closed position, as described below. 
The annular chamber piston 16 is capable of moving in an annular 9 which is 
delimited by a portion of the tubular support 4, a coaxial tube 4A, and 
two end pieces 4B and 4C. The end piece 4C has channels 24 passing 
therethrough for putting the volume 20 into communication with the volume 
9. The end piece 4B has sealed passages therethrough for passing the 
piston rods 15A. 
A duct 11 connects the volume 9 to a tank 12 located above the 
circuit-breaking chamber. This tank is put into communication with the 
inside of the chamber by a duct 12A. The pressure to which the chamber is 
filled with SF.sub.6 is chosen so that at low outside temperatures (for 
example less than 0.degree. C.), the tank 12 contains a considerable 
quantity of liquefied gas. The duct 11 opens out into the volume 9 level 
with the piston so that the liquid remains above the piston so long as the 
circuit-breaker is in the closed position. 
A transfer duct 26 serves to transfer liquid SF.sub.6 from the volume 13 to 
the volume 20 of the insulating nozzle during a closure maneuver in a 
manner explained below. 
A cone 21 whose profile corresponds to that of the diverging portion of the 
nozzle 5 is threaded over the electrode 14. The cone is used to close the 
nozzle when the circuit-breaker is in the closed position. 
A spring 22 is disposed between the cone 21 and the support 17A. 
The tube 4A is extended by a metal portion 10 for allowing current to pass 
from the end plate 2 to the end plate 3 via the portion 10, the tubes 4 
and 4A, the contacts 6B and 25, the support 17A, the tube 17, and the 
contacts 18. 
The circuit breaker operates as follows: 
(a) Opening operation 
The apparatus is in its closed position (see FIG. 1). Liquid SF.sub.6 is 
contained in the volume 20. The manner in which this liquid reaches this 
volume is explained below. 
The operating member acts on the cylinder 17 by pulling it downwardly until 
the electrode 14 arrives to the throat of the nozzle 5. The spring 22 
serves to ensure that the cone 21 keeps the nozzle closed. 
An electric arc 27 is struck between the electrode 14 and the arcing 
contacts 6A (see FIG. 2) immersed in the liquid SF.sub.6, thereby 
vaporizing the SF.sub.6. This high density of SF.sub.6 is kept close to 
the arc by the action of gas coming from the volume 9 and blasted by the 
piston 16 through the orifices 24. 
The gas escapes via the throat of the nozzle towards the volume 23 
delimited by the tube 4. The volume 23 advantageously has a nozzle-forming 
necked portion 23A. 
The moving electrode continues its stroke until the circuit-breaker is 
fully open (see FIG. 3), thus moving the cone 21 away from the nozzle. At 
the moment that zero current passes, the mass flowrate through the nozzle 
23 and the throat of the blast nozzle is very high because of the high 
upstream pressure, thereby interrupting the arc. 
The duct 11 is then unblocked and the volume 13 is filled with liquid 
SF.sub.6 under the effect of gravity. The liquefied gas is thus stored in 
a storage zone constituted by the volume 13 until the circuit-breaker is 
re-closed. 
(b) Closure operation 
The operating member acts on the cylinder 17 and thrusts it upwardly. 
The piston 16 then expels the liquid from the volume 13 into the volume 20 
via the duct 26 (see FIG. 4). A portion of the liquid runs away until the 
cone 21 closes the divergent portion of the gap between the nozzle 3 and 
the electrode 14. 
By suitably selecting the volumes and the strokes involved, a sufficient 
quantity of liquid can be put into the volume 20. 
Once closed, the apparatus is again ready for an opening operation. 
The invention is not limited to the embodiment described. In particular, 
the tank 12 above the chamber may be replaced by a tank placed below the 
circuit-breaker and fitted with a pump.