Circuit breaker fitted with a device for indicating a short circuit

A circuit breaker or cut out provided with a short-circuit indicating device and comprising, for each pole, separable contacts disposed inside a breaking chamber in which an electric arc develops when the contacts become separated. The said short-circuit indicating device is actuated by the gas pressure waves generated by the electric arc in the breaking chambers.

The invention relates to circuit breakers of the type having their contacts 
in the air, i.e. not immersed in any special circuit breaking fluid such 
as oil or SF.sub.6 gas. The invention relates more particularly to the 
means of providing a device to indicate that such an air-type circuit 
breaker has broken a short-circuit current. 
BACKGROUND 
Circuit breakers and cut-outs are already known which have what is known as 
a short-circuit indicator. This is the case particularly with cut-outs 
having magneto-thermal trips provided with a device indicating the 
magnetic or thermal mode of operation of the trip. Such a device is 
described for example in French Pat. No. 1 401 630. 
For the user it is indeed of interest to know whether the tripping of the 
circuit breaker is a result of magnetic or thermal operation. But in many 
cases indication of the magnetic functioning of the trip will be 
inadequate as a means of judging whether there is an actual short-circuit 
or simply an abnormally high over-current. Furthermore, the structural 
elements of such an indicator are directly linked with those of the trip, 
which considerably limits the possibilities of construction. 
The progress at which the present invention aims resides in providing 
circuit breakers with a short-circuit indicator, the functioning of which 
is linked not to the tripping of the protective devices but to the power 
developed in the breaking chambers of the apparatus and more precisely the 
wave of gas pressure which results therefrom. 
Air-type circuit breakers intended to break short-circuited currents 
generally comprise a fixed contact and a moving contact per pole disposed 
inside a relatively closed breaking chamber. In the event of over-voltage, 
under the action of protective trips or the direct effect of 
electro-dynamic stresses generated by the current, the contacts open and 
an electric breaking arc appears, the voltage of which depends upon the 
structural characteristics of the breaking chamber and the current 
intensity. The higher the current intensity, the greater will be the power 
of the electric breaking arc. The effect of the power of the arc gives 
rise to a gas pressure wave in the breaking chamber resulting from the 
sudden rise in temperature and possibly from the emission of gases through 
the walls of the breaking chamber. The amplitude of this pressure wave is 
linked to the power of the breaking arc and thus to the intensity of the 
current actually broken by the apparatus. For low levels of current, the 
pressure will be small and in contrast for high currents such as those 
which may result from a short-circuit the pressure may attain levels 
sufficient to actuate a pressure-sensitive indicating device. 
BRIEF SUMMARY OF THE INVENTION 
The present invention provides an air-type circuit breaker provided with a 
device for indicating the existence of a short-circuit and comprising, for 
each circuit-breaking pole, separable contacts disposed inside a breaking 
chamber in which an electric arc develops upon separation of the contacts, 
wherein the said short-circuit indicating device is actuated by the gas 
pressure wave created by an electric arc in the breaking chambers. 
Preferably, the short-circuit indicating device comprises a movable member 
subject both to a stress developed by the gas pressure wave and to an 
opposing stress, the said movable member passing from a first "no 
pressure" position to a second "pressurized" position when the stress 
developed by the gas pressure wave is greater than the opposing stress.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a three-pole low voltage air-type circuit breaker which is 
provided with a short-circuit indicator in accordance with the invention. 
The circuit breaker 1 comprises a moulded casing 2 closed by a cover 3 
through which passes an operating lever 4. Inside the casing 2 are mounted 
the various components of the circuit breaker, comprising in particular an 
operating mechanism for opening and closing the contacts, a three- pole 
excess current trip with separable contacts 5 disposed inside a breaking 
chamber 6 for each pole. Fixed on the circuit breaker casing 2 is a 
short-circuit indicator 7 operated by the gas pressure generated in either 
of the breaking chambers 6 when a short-circuited current is broken. 
The short-circuit indicator 7 comprises a casing 8 closed by a cover 9, the 
whole assembly being mounted on the circuit breaker casing and closing off 
the breaking chambers 6. The casing 8 comprises two housing chambers 10 
and 11 separated by a partition 12 in which there is a slot 13. A movable 
flap 14 is applied to the bottom of the housing 10 by a spring clip 15 
compressed between the flap 14 and the cover 9. The flap 14 occludes 
apertures 16 provided in the bottom of the casing 8 opposite each of the 
breakage chambers 6. 
A visual indicator 17 subject to the thrust of a spring 18 is mounted to 
slide in the housing 11. The front face of the indicator 17 carries 
reference markings visible through a window 19 in the cover 9. The lateral 
face of the indicator 17 includes a slot 40 of sawtooth shape, each of the 
teeth corresponding to a reference marking on the front face. The end 20 
of the spring 15 is engaged through the slot 13 in the partition 12 in the 
sawtooth slot 40 of the indicator 17. 
The manner in which the device operates will now be explained, the fact 
being taken into account that initially the end 20 of the spring 15 is 
engaged in the sawtooth slot in the indicator 17 opposite the reference 
marking 0 which appears in the window 19 of the cover 9. 
Installed in an electric power distributing circuit, the circuit-breaker 
will operate automatically in the event of the current intensity exceeding 
the operating threshold of the excess current trip. The contacts 5 open 
and an electric arc appears in the breaking chambers 6. The gas pressure 
generated in the breaking chambers 6 is applied to the flap 14 through 
windows 16. If this pressure is sufficient to overcome the opposing stress 
applied to the flap 14 by the spring 15, that is to say if the current 
intensity is very high, corresponding to a short-circuit, the flap 14 
rises and the end 20 of the spring 15 passes over the first sawtooth of 
the indicator 17 which advances by one notch, propelled by the spring 18. 
After the current has been broken by the circuit breaker, the pressure 
returns to its normal level, the flap 14 and the end 20 of the spring 15 
return to their initial position while the reference marking 1 of the 
indicator 17 appears in the window 19 of the cover 9. The user is thus 
warned that the circuit breaker has broken a short-circuited current and 
he will be able to check the condition of the installation before putting 
it into operation again. If a fresh short-circuit should occur, the device 
will operate again in the same way and the reference marking 2 of the 
indicator 17 will then appear in the window 19 of the cover 9. In the same 
way, the reference marking 3 will appear in the event of the circuit 
breaker breaking a short-circuited current a third time. The user is then 
warned that the circuit breaker may need to be replaced or be overhauled 
or serviced in accordance with the manufacturer's instructions. Of course, 
the force of the spring 15 and the disposition and dimensions of the 
apertures 16 will be determined by the manufacturer according to the 
specifications of the circuit breaker on which the indicating device has 
to be installed, so that the indicating device operates only with effect 
from a specific level of current which is matched to the rated current and 
circuit breaking capacity of the apparatus. 
In the present description, the flap 14 and the spring 15 are common for 
all three breaking chambers of the apparatus, but it is quite obvious that 
it is equally well possible to use one flap and one return spring for each 
of the breaking chambers, the movement of any of the flaps operating a 
common indicating device. 
Many alternative forms of embodiment are obviously possible with a 
combination of various types of movable elements which become displaced 
under the effect of pressure with different models of indicating devices 
operated by such displacement. 
Thus, FIGS. 2a, 2b, and 3a, 3b show simple forms of embodiment which are 
particularly suitable for closed circuit breakers in moulded casings in 
which the pressure wave generated in the breaking chambers is propagated 
through the entire casing. In these embodiments the movable member, moving 
under the effect of the pressure, likewise serves as an indicating device, 
moving from a first stable "no pressure" position to a second stable 
position after passage of the pressure wave and it is necessary to reset 
the indicating device after each short-circuit. 
In FIGS. 2a and 2b, the device is constituted by an indicator piston 21 
fitted with a sealing washer 22 consisting for example of an elastomer, 
sliding in a cylinder 23. Under the effect of the pressure inside the 
casing, the indicating piston 21 moves from the position shown in FIG. 2a 
to the position shown in FIG. 2b. The stress opposing the force exerted by 
the pressure inside the casing is provided by the friction of the sealing 
washer 22 against the cylinder 23, friction which can be adjusted by 
tightening or slackening a screw 24. This same frictional force prevents 
the return of the piston 22 from the position in FIG. 2b to the position 
in FIG. 2a unless the user has pressed the indicator piston 21 to return 
it to its initial position. 
In FIGS. 3a and 3b, the indicating device is constituted by a bistable 
capsule 31 of generally hemispherical form fixed in front of an aperture 
32 in the cover of the apparatus. Under the effect of the internal 
pressure resulting from breaking of a short-circuit current, the capsule 
31 changes from the position shown in FIG. 3a to the position shown in 
FIG. 3b. The stress opposing the force exerted by the pressure inside the 
casing is provided by internal tension in the material of which the 
capsule consists and may be suitably obtained by judicious choice of the 
thickness and elasticity of the material from which the capsule is made. 
Similarly, the internal tension in the material of the capsule prevents 
return from the position shown in FIG. 3b to the position shown in FIG. 3a 
until the user has pressed on the capsule 31 to restore it to its original 
position. 
Although FIGS. 2a, 2b and 3a, 3b do not demonstrate the fact, it is 
possible to associate with the indicators 21 or 31 a totalising device 
which is operated step by step at each displacement of the piston 21 or 
the capsule 31 in one direction. Such a totalising counter may in per se 
known manner consist for example of a ratchet wheel, a rack with a catch 
or any similar device. 
Thus, the user is not only warned every time a short-circuited current is 
broken but he is in a position to know how many short-circuits the circuit 
breaker has already handled. 
Of course, without departing from the scope of the invention, it is 
possible to provide further alternative indicating devices other than 
those described hereinabove which are given purely by way of example. In 
particular the indicating device could be combined other devices actuated 
by it and fulfilling other associated functions such as the prevention of 
reclosure of the circuit breaker or the causing of contacts to close to 
produce a remote signal either at each short-circuit or after a given 
number of short-circuits.