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FIELD OF THE INVENTION:
The present invention relates to a variable blast interrupter for gas
circuit breaker.
More specifically the present invention relates to variable blast
interrupter of a puffer type gas insulated circuit breaker with moving
piston and metallic blast cylinder used for interrupting high electric
current.
BACKGROUND OF THE INVENTION WITH DIFFICULTIES OF
PRIOR ART:
In the existing practice of encountering rapid increase in levels of
short circuit currents accounting with extra high voltage transmission
system, puffer type gas insulated circuit breakers are employed in
which gas is stored at an predetermined high pressure inside an
enclosure and the said gas is further-compressed to a higher

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pressure inside a compression chamber, generally termed as a puffer
or blast cylinder.
A relative motion between the blast cylinder and a piston effects
compression during the opening operation of the circuit breaker. All
these breaker deploy one or more nozzle through which a high
pressure blast of insulating gas is blown over high temperature arc
plasma that is struck between a pair of contacts. The arc is
surrounded by the envelope of high-pressure gas and is ultimately
quenched.
Prior art Indian Application No: 1022/DEL/2001 has taught of
developing a puffer type gas blast circuit breaker with movable piston
and metallic blast cylinder in this field of development wherein
moving piston compresses gas within a fixed metallic blast cylinder
distingushing from prior state of art at the time wherein a moving
cylinder was compressing the gas against a fixed pistion.

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In the said prior patent application 1022/DEL/2001, in the interrupter
of the puffer type gas circuit breaker the blast cylinder pressures
change with magnitude of current, gas blast pressure being low at
lesser currents, interruption process is delayed.
Inside such an interrupter, no control mechanism is available to
effect variations of exhaust gas conductance with changes in current.
Lack of such a control results in insufficient blast cylinder pressure
build-up during current interruption.
Voltage recovery across the interrupter contacts is delayed with such
interrupters.
Deficient thermal dielectric recovery at high currents results due to
insufficient blast cylinder pressure.
The proposed invention is aimed to solve the above difficulties of the
prior art.

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DESCRIPTION OF THE INVENTION
One object of the invention is introduction of a pressure regulating
device for controlling blast cylinder pressures.
Another object of the invention is to improve the rate of differential
pressure build-up inside the blast cylinder.
A yet another object of the invention is to ensure early availability of
required blast pressure inside the blast cylinder.
A still another object of the invention is reduction in arcing time due
to high differential pressure build up and effective early arc blow out
action.
A still further object of the invention is to provide auto change-over
system from uni-directional exhaust gas flow at low currents to bi-
directional gas flow at high currents.

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The proposed invention will be better understood from the following
description with reference to the accompanying drawings in which
Figure 1 represent a puffer interrupter with moving piston and
metallic blast cylinder of the prior art.
Figure 2 represent variable blast interrupter with moving piston and
metallic blast cylinder.
In figure 1 the various parts with reference numeral are 1. Insulating
chamber 2. Fixed contact system 3. Movable contact system 4. Fixed
contact terminal 5. Contact terminal 6. Fixed contact support 7.
Normal current contact 8. Fixed arcing contact 9. High voltage shield
10. Movable contact support 11. Metallic blast cylinder 12. Movable
piston 13. Insulating nozzle 14. Movable arcing contact 15. Link to
mechanism 16. Movable contact tube,
A- Isolating gap, B- Volume compressed.

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In figure 2 the various integral parts shown with reference numerals
are
1. Insulating chamber 2. Fixed contact system 3. Movable contact
system 4. Fixed contact terminal 5. Contact terminal 6. Fixed
contact support 7. Normal current contact 8. Fixed arcing contact
9. High voltage shield 10. Movable contact support 11. Metallic
blast cylinder 12. Movable piston 13. Insulating nozzle 14. Movable
arcing contact 15. Link to mechanism 16. Movable contact tube
17. Gas entry port 18. Spring baded device 19. Spring support 20.
Fixture for spring support. 21. Control spring 22. Variable passage
for gas exit 23. Gas exit route,
A- Isolating gap, B- Gas volume compressed.
The invention, as represented in Fig.2 relates to a spring baded
device (18) built inside the gas exhaust path to regulate blast
cylinder pressure, which is developed during the opening operation of
the interrupter or by compression of the gas in volume B. Through

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this invention, self adjustment of exhaust gas conductance varying
with magnitudes of interrupted current Is made feasible. This brings
about an ability to effectively control blast cylinder pressure (blow out
pressure) build-up through change of parameters of the spring
loaded device. Effecting conservation and optimal utilization of blast
cylinder gas during the current interruption process is thus effected.
Self-triggered transition "unidirectional" to "bi-directional" exhaust
gas flow based on the magnitude of current is made possible by
incorporation of this device. The said device assists in obtaining
improved thermal recovery characteristics during the current
interruption process. As a further advantage the device offers
possibility of variation (22) of the gas discharge angle.

The invention relates to an improved blast interrupter of a puffer-type gas insulated circuit breaker, comprising a piston (13) movable in a metallic blast cylinder (12) for interrupting a high electric current. A spring-loaded device (19) is interposed on a gas-exhaust path (23) to regulate the pressure of the blast cylinder corresponding to the magnitude of the interrupted current.