Field Of Invention:-
The invention relates to per break capability of Circuit Breaker(CB) used to
interrupt currents of high voltage power transmission and distribution systems
during make and break operation of Circuit Breaker, in general and to an
improvement of interrupting capabilities of gas Circuit Breaker with movable
shield in particular.
Background And Prior Art:
When fault current is interrupted by a circuit breaker, arc is struck between the
arcing contacts. The energy content of the arc depends on the current
magnitude, length of the arc and similar other parameters. As the temperatures
of the arc are quite high it decomposes the insulating medium and materials
exposed to arc. Byproducts of the chemical reaction at elevated temperature also
accumulate in the vicinity and shall be removed for sustaining the dielectric
properties of the inter-electrode gap on interruption. In conventional
interrupters, the high voltage shields are mostly in static condition and may not
serve their purpose in all situations encountered during interruption process.
More clearly, when shields are fixed the electrostatic

field and withstandable voltage between the contacts is limited. To achieve
desired interrupter performance excess quantity of gas and higher differential
pressures are used in conventional gas interrupters as on date.
In general, the electrostatic field between movable and fixed contacts is non-
uniform for various reason and design of the CB. During recovery the gas
between the contacts is ionized/hot with poor voltage withstand ability. In most
of the interrupters, the arced gas after leaving the nozzles may spill out into the
contact system due to improper channeling and this may lead to thermal
failures. Beyond particular instant of time during current interruption, minimum
arcing time is decided not only on the effectiveness with which arcing gas is
being removed but also on the uniformity of the electrostatic field between
arcing contacts. The static shields provided around the contacts do not provide
uniform field between contacts beyond certain distance of travel. To overcome
this problem, creepage length of nozzle is increased by different ways.
Nevertheless performance of the system is limited and none of the interrupters is
utilized to full capabilities.
For successful interruption under high impressed voltage (recovery), the design
requirement are primarily; optimal dielectric properties of the gas and lower
electrostatic stresses in inter-electrode gap (by reduction in high electrostatic
field locations and higher clearances between the live contacts of an interrupter).

Objective Of The Invention:-
The main objective of invention is to improve the gas interrupter performance
both in terms of capacity and recovery and also per break capability of CBs. by;
• Reducing post-arc field intensity by addition of a dynamic HV electrode on
fixed end of the circuit breaker.
• Specifying specific shape to this electrode, promoting uniform electrostatic
field in the gas-gap.
• Specifying optimal inter-electrode gap for chosen interrupting capability
and the voltage class of the circuit breaker.
• Efficiently guiding the gas exhaust during current interruption preventing
leakage of hot ionized gas to voltage sensitive location.
• A common drive for dynamic HV electrode and moving contact assembly
of gas circuit breaker.
Description Of Inventions:-
A circuit Breaker (CB) is primarily used to interrupt
normal/fault/capacitive/inductive currents of high voltage power transmission
and distribution systems. When the CB is in closed condition it allows conduction
of normal electrical charge (current) through a closed electrical system (circuit).

The magnitude of current is governed by the system characteristics and state.
Short circuits, causing abnormal flow of current, are sensed by current sensors
and prevented by isolating the source and the load by circuit breakers.
Up to 245kV single-break circuit breaker designs are common, beyond this rating
two or more breaks are used in series to form a circuit breaker. The multiple
breaks demand higher operating energy, voltage equalizing devices etc and
make the circuit breaker unreliable.
Brief Description Of The Accompanying Drawings:-
The invention is described with the help of Figures 1 to 4, where:
Figure 1: Shows the conventional interrupter of prior art.
Figure 2: Shows Movable contact Assembly.
Figure 2(a): Shows the first movable Assembly.
Figure 3: Shows Concept of Movable shield approach.
Figure 4: Shows Invented interrupter with Movable shield approach in Closed
condition.
Figure 4(a): Shows the fixed current carrying contact assembly.

Detailed Description of the Invention:
The invention will now be described with help of the accompanying drawings
which depict exemplary embodiments of the invention. However, there can be
several other embodiments, all of which are deemed covered by the description.
In the present invention, the first movable contact (01) made of a high
conductivity material with low erosion refractory material tip is held on a contact
support (02). The first movable contact is covered by a movable contact shield
(03) made from low erosion refractory material. The movable current carrying
(CC) contact (04) in movable contact assembly as shown in Figure. 2, is fixed to
nozzle (05). The first movable contact (01), movable contact shield (03) and
movable current carrying contact (04) are in total called as the first movable
contact assembly (A).
Fig. 2(a) shows the first movable contact assembly (A). The second movable/
fixed contact (06) is surrounded by a movable shield (07), when CB is in fully
open condition. The second movable contact is located inside the movable shield
and the arrangement is again inside the fixed current carrying (CC) contact
assembly. As shown in figure 4(a), the fixed current carrying contact assembly
(B) comprising fixed current carrying contact (08) and fixed CC contact shield
(09). In open condition of circuit breaker, the movable shield (07) projects out
from the fixed CC contact shield (04) and the gas gap between movable shield
and first movable CC contact (04) decide withstandable voltage. The entire

contact system is insulated from the grounded metallic enclosure with designed
SF6 (Sulpher hexafluoride) gas density. The first movable CC contact is separated
from the fixed CC contact shield by a distance proportional to the system voltage
and the SF6 gas density. The entire contact system can be even contained in an
insulating housing to contain arced hot gas during CB operation. Electrostatic
field must be uniform between the following components:
1. First movable contact shield (03) and second movable/fixed contact (06).
2. Movable shield (07) and first movable CC contact (04).
3. Fixed CC contact shield (09) and first movable CC contact (04).
In the invention, movable shield (07) is introduced between first movable contact
assembly and fixed current carrying contact shield (09). Movable shield improves
uniformly electrostatic field between moving contact system and fixed CC contact
assembly. First movable contact assembly is coupled to movable shield through
nozzle (05) by means of a guide plate (10) which has profile depending on the
following:
1. Distance to which movable shield has to be moved.
2. Instant of presence of movable shield between CC shield and first
movable CC contact.
The nozzle is connected to guide plate through suitable coupler which in turn
controls the movement of movable shield (07). The movable shield is clamped to
guide plate by means of guide rods (11). Fig. 3 shows the concept of movable

shield approach. During opening operation, movable shield moves in downward
direction at a particular instant of its operation depending on minimum arcing
time and the instant at which second movable/fixed contact crosses the movable
shield (07). More clearly, at current zero, the withstanable voltage between
contacts is improved in the presence of movable shield (07). Profile of guide
plate (10) is made in such a way that the moving shield presence between the
contacts can be adjusted to get optimum benefit as required. The first movable
contact assembly (A), movable shield (07) and the coupling system are arranged
in such a way that during current interruption the arced hot gas vented through
the guide nozzle and mixed with main volume gas. This is more effective in
present invention and helps to overcome the problem of leaking out of hot gas
across the gas gap of the contact system. Fig. 4 shows the invented interrupter
in closed condition.

We Claim:-
1) Gas circuit breaker as the movable shield for improvement of interrupting
capabilities, consisting:-
- the first movable contact assembly (A) comprising movable contact (01) held
on contact support (02), movable contact shield (03) covering the first movable
contact (01) and movable current carrying (CC) contact (04);
- the movable current carrying(CC) contact (04) in movable contact Assembly
(A), is fixed to nozzle (05);
- the second movable/fixed contact (06), which is surrounded by movable shield
(07);

- the fixed current carrying contact assembly comprising fixed current carrying
contact (08) and fixed CC(current Carrying) contact shield(09);
- a movable shield (07);
-a guide plate (10); and
-a plurality of guide rods (11);
Characterized in that introduction of the movable shield (07) between contact
assembly and fixed current carrying contact shield (09) improves the gas
interrupter performance in the gas circuit breaker (CB) both in terms of capacity
and recovery.

2. The gas circuit breaker as claimed in claim 1, wherein the first movable
contact (01) is made of a high conductivity material with low erosion material tip.
3. The gas circuit breaker as claimed in claim 1, wherein movable contact shield
(03) is made from low erosion refractory material.
4. The gas circuit breaker as claimed in claim 1, wherein the second
movable/fixed contact (06) is surrounded by a movable shield (07), when the
circuit breaker (CB) is fully open condition.
5. The gas circuit breaker as claimed in claim 1, wherein said open condition of
CB creates in between movable shield (07) and the first movable current carrying
contact (04), a gas gap which decides withstand voltage.
6. The gas circuit breaker as claimed in claim 1, wherein said movable shield
(07) improves uniformity of electrostatic field between moving contact system
and fixed CC contact assembly (B).
7. The electrostatic field as claimed in claim 1, is kept uniform between the
following components: (a) first movable contact shield (03) and second movable

/fixed contact (06), (b) movable shield (07) and first movable CC contact (04),
(c) first CC contact shield (09) and first movable CC contact (04).
8. The arced hot gas as claimed in claim 1, is contained in an insulating housing,
wherein the entire contact system is even accommodated.
9. The gas circuit breaker as claimed in claim 1, wherein the first movable CC
contact (04) is separated from the fixed current carrying contact shield (09) by a
distance proportional to the system voltage and SF6(Sulphur hexa fluoride) gas
density.
10. The gas circuit breaker as claimed in claim 1, wherein the nozzle (05) is
connected to guide plate (10) through a coupler which controls the movement of
the movable shield (07) and clamped to guide plate by means of guide rods(ll).
ll.The gas circuit breaker as claimed in claim 1, wherein the movable shield (07)
moves downward direction at a particular current zero instant of its opening
operation, depending on minimum arcing time and the instant at which second
movable/fixed contact (06) crosses the movable shield (07).

12. The gas circuit breaker as claimed in claim 1, wherein the first movable
contact assembly(A) is connected to movable shield (07) through nozzle (05) by
means of a guide plate (10) which has profile depending on, distance to which
movable shield (07) will move and instant of presence of movable shield (07)
between current carrying contact shield (09) and first movable CC contact (04).
13. The gas circuit breaker as claimed in claim 1, wherein the guided plate (10)
is made in such a way that the moving shield (07) presence between the
contacts can be adjusted to get optimum benefit as required.
14. The gas circuit breaker as claimed in claim 1, wherein the guided nozzle (05)
vents out arced hot gas to mix with the main volume of gas during current
interruption instead of leaking out of the gas across the hot gas gap of the
contact system.
15. The gas circuit breaker as claimed in claim 1, wherein said venting out of
arced hot gas through guided nozzle (05) is done by adjusting the first movable
contact assembly (A) movable shield (07) and the coupling system.

Gas circuit breaker as the movable shield for improvement of interrupting
capabilities, consisting:-
- the first movable contact assembly (A) comprising movable contact (01) held on
contact support (02), movable contact shield (03) covering the first movable
contact (01) and movable current carrying (CC) contact (04);
- the movable current carrying(CC) contact (04) in movable contact Assembly
(A), is fixed to nozzle (05);
- the second movable/fixed contact (06), which is surrounded by movable shield
(07);
- the fixed current carrying contact assembly comprising fixed current carrying
contact (08) and fixed CC(current Carrying) contact shield(09);
- a movable shield (07);
-a guide plate (10); and
-a plurality of guide rods (11).
Introduction of the movable shield (07) between contact assembly and fixed
current carrying contact shield (09) improves the gas interrupter performance in
the gas circuit breaker (CB) both in terms of capacity and recovery.