Gas circuit breaker having independent main and arcing circuits

A puffer-type gas-blast circuit-breaker comprises an interrupting unit mounted in a housing filled with an insulating gas of high dielectric strength such as sulfur hexafluoride. The interrupting unit includes a main circuit having a pair of stationary and movable main contacts, and an arcing circuit having a pair of stationary and movable arcing contacts. An operating mechanism comprises a control rod coupled to the movable contacts so as to open the main contacts before the separation of the arcing contacts. A pair of input and output terminals extend out of the housing, and a shunt conductor is arranged in the arcing circuit between operating rod and the lower terminal. The longitudinally extending main and arcing circuits are connected in parallel to the terminals and form two independent current paths which are cross-wise spaced inside the housing. A partition wall divides the inner space of the housing into two superposed compartments, one of them including the main contacts, and the other the arcing zone.

The invention relates to a circuit breaker with an arc-extinguishing device 
mounted in a housing filled with an insulating gas of high dielectric 
strength such as sulfur hexafluoride, and including: 
a main circuit having stationary and movable main contacts, 
an arcing circuit comprising stationary and movable arcing contacts forming 
an auxiliary circuit bypassing said main circuit, 
an operating mechanism coupled to said movable contacts so as to open said 
main contacts before the separation of said arcing contacts, 
said main and arcing contacts being surrounded by said same insulating gas, 
a pair of input and output terminals extending through the wall of said 
housing. 
The main contacts of a usual circuit breaker surround coaxially the arcing 
contacts. A slidable member carries the movable main and arcing contacts 
which are electrically connected to one terminal by a sliding contact. The 
mass of the movable structure is very important and the main current flows 
always through the sliding contact. The operating mechanism requires a 
high operating force and the electrical circuit needs important sections 
for the current flow. Another disadvantage of the aforesaid prior 
construction is that an interaction between the main and arcing breakings 
is possible. 
An object of the present invention is to construct a gas circuit-breaker in 
such a way that the mass of the movable structure is low. 
Another object is to provide a circuit-breaker in which a small fraction of 
main current flows through the relative movement connecting member. 
Still another object is to avoid any arc retriking between the main 
contacts. 
In accordance with the present invention, there is provided a gas 
circuit-breaker in which said main and arcing circuits are connected in 
parallel to the input and output terminals so as to form two independent 
current paths inside said housing. Most of the current flows through the 
main circuit in the closed position of circuit-breaker, and the current is 
transferred to the arcing circuit at the separation of the main contacts. 
The arcing circuit comprises a relative movement connecting member 
arranged between the movable arcing contact and the corresponding terminal 
so that the value of main current in said member is very low. The main 
circuit extends along the shortest path arranged between the terminals 
inside the housing, and is cross-wise spaced from the longitudinally 
extending arcing circuit. The opening stroke of the pivoting main contact 
is independent of that of the arcing contacts.

Referring now to FIGS. 1 and 2, there is shown a pole of a puffer-type 
gas-blast circuit breaker located within a housing 10 filled with an 
insulating gas of high dielectric strength such as sulfur hexafluoride. A 
top cover 12 closes the housing 10 of molded insulating material which 
includes a main circuit 14 through which flows the main current, and an 
auxiliary arcing circuit 16 which shunts the main circuit. Circuit-breaker 
opening is effected by an operating mechanism 18 which actuates the 
movable structure for the successive opening of the main and arcing 
circuits 14, 16. Two terminals 20, 22 for the current supply are formed by 
longitudinally spaced bushings extending out of the housing 10. 
Main circuit 14 comprises a movable main contact 24 having a plurality of 
pairs of conductive fingers 26a, 26b, 26c, 26d, pivotally mounted upon a 
stationary pin 28 secured to a first conductor 30 connected to the lower 
terminal 22. Elastic means, such as a compression spring 32 is associated 
to each pair for biasing the corresponding fingers against each other so 
as to form a clamp cooperating in the closed position of main circuit 14 
with an extension 34, 36 of a stationary main contact 38. A second 
conductor 40 connects the stationary main contact 38 to the upper terminal 
20. The electrodynamic attraction developed between the fingers of each 
pair, reinforces the clamping of fingers 26a, 26b; 26c, 26d upon the 
corresponding extension 34, 36. 
The auxiliary circuit 16 is connected in parallel to the main circuit 14 
inside the housing 10, and includes a pair of aligned arcing contacts 42, 
44. The stationary arcing contact 42 is electrically connected to the 
upper terminal 20, and the movable arcing contact 44 is actuated by a 
vertically extending conductive rod 46 suitably coupled to a driving crank 
48. The external operating mechanism drives the crank 48 by means of a 
rotative transmission shaft 50 located in a tight bearing 52 arranged in 
the wall of housing 10. A flexible shunt conductor 54 of the arcing 
circuit 16 connects electrically conductive rod 46 to the lower terminal 
22. 
A longitudinally extending inner partition wall 56 divides the inner space 
of the housing 10 into two superposed compartments 60, 62. The lower 
compartment 60 includes the main contacts 24, 38, and the upper 
compartment 62 comprises the arcing zone 64 arranged between the separated 
arcing contacts 42, 44. The physical separation between arcing zone 64 and 
the interrupting zone of the main contacts avoids any arc restriking near 
said interrupting zone due to hot arcing gases. 
Terminals 20, 22 form two shunting knots of the two parallel connected main 
and arcing circuits 14, 16, and the fault current flows exclusively in the 
shunt conductor 54. The two parallel extending main and arcing circuits 
14, 16 are cross-wise spaced inside the housing 10 so as to form a loop of 
low reactance in which main circuit 14 has the shortest length. 
The gas-blast puffer device of a conventional design is lodged in the upper 
compartment 62 and comprises a movable piston 68 mechanically coupled to 
driving rod 46. Piston 68 carries a blast nozzle 70 that closely surrounds 
arcing contacts 42, 44 in the closed position, and is slidably mounted 
within a stationary cylinder 72 so as to define a puffer chamber 74 in 
which occurs compression of the insulating gas when contact rod 46 is 
driven downwardly during the circuit-interrupting operation. An electric 
arc is then drawn between the separated arcing contacts 42, 44 and a blast 
of compressed gas flows upwardly through apertures 76 of piston 68 in the 
nozzle 70 to produce an arc-extinguishing effect. 
The operating mechanism comprises a transmission linkage 78 which 
mechanically connects rod 46 of arcing contact 44 to the movable main 
contact 24 so as to convert the rectilinear movement of rod 46 into a 
pivoting movement of contact 24 during circuit interrupting operation. One 
end of transmission linkage 78 is actuated by a driving pin 82 secured 
upon rod 46, and the opposite end cooperates with fingers 26 of the 
movable main contact 24. 
In the closed position of circuit breaker, most of the main current flows 
in the main circuit 14 which has a substantially lower electrical 
impedance than that of arcing circuit 16. The current flows from upper 
terminal 20 through conductor 40, stationary main contact 38, movable main 
contact 24 (shown in dotted lines in FIG. 1), conductor 30 and lower 
terminal 22. Current through shunt conductor 54 is very low. 
At the appearing of a fault current, circuit breaker opening is effected by 
a downward translation of operating rod 46, indicated by arrow F. During 
the initial stroke of opening operation, transmission linkage 78 rotates 
clockwise thus interrupting current flow through main contacts 38, 24. All 
the current that had been flowing via main circuit 14 is then transferred 
to the derived arcing circuit 16. Current flows now from upper terminal 20 
through stationary arcing contact 42, movable arcing contact 44, 
conductive rod 46, shunt conductor 54, conductor 30 and lower terminal 22. 
Upon further movement of rod 46 occurs separation of arcing contacts 42, 
44 and a blast of pressurized arc-extinguishing gas flowing from puffer 
chamber 74 upwardly into the arcing zone to extinguish the arc. Partition 
wall 56 separates arcing zone 64 from main contacts 38, 24 and prevents 
any arc restriking between said main contacts. 
When the circuit breaker is closed, arcing contacts 42, 44 may be closed in 
first or after closing of main contacts 24, 38. 
The invention has been described in reference to a puffer-type gas-blast 
circuit breaker, but it is also appropriate to other circuit-breakers 
having magnetic arc-extinguishing devices or combined magnetic and 
gas-blast arc-extinguishing devices. 
It should be noted that the invention is not restricted to the form of 
construction shown and many variations in detail may be made; the movable 
main contact 24 may be a bridging conductive member radially actuated in 
translation by the operating mechanism during axial movement of rod 46.