FIELD OF INVENTION
The present invention relates to a two stage blast process for improving current
interruption capabilities of high voltage, high pressure gas circuit breakers.
BACKGROUND OF INVENTION
A Circuit Breaker (CB) is primarily used to make or break normal or fault currents
of high voltage Installations. When the CB is in closed condition it allows
conduction of electrical charge (current) through a closed electrical system
(circuit) depending on the system characteristics and conditions.
When current is interrupted by a circuit breaker, such as a common puffer circuit
breaker, arc is struck between the arcing contacts and is quenched by a puff or
blast generated within a cylinder known as puffer cylinder. The energy content of
the arc depends on the current magnitude, length of the arc and similar other
parameters. In conventional puffer breakers, the gas flow rate is dependent on
the differential pressure between the puffer cylinder and the volume outside the
cylinder. Further, it is independent of the fault current level. In self-blast
interrupters, the arc energy is utilized to heat the surrounding gas and to
generate gas flow for substantial interruption duration. Even though sufficient
coolant gas is available in the interrupter, a poor design of gas pockets and flow
channels may lead to non-availability of arc quenching medium at the right
instant of interruption, which may promote substantial gap conduction and
ultimate failure to interrupt.

The interruption capability of a gas circuit breaker depends mainly on arc cooling
rate (insulation recovery rate) leading to close to interruption (near current zero
for alternating current interrupters).
In conventional puffer breakers, the gas flow rate is almost independent of the
fault current level. In self blast circuit breakers, the gas quantity and flow rates
for lower currents are insignificant due to limited arc energy. The flow of coolant
and the gas flow rate in interrupters are considered to be functions of
compression volume (in case of puffer interrupters) and expansion volume (in
case of self-blast) design neglecting the coupling pockets and channels. In
thermally assisted gas interrupters, i.e., combination of self blast and puffer
circuit breaker (refer Fig. 1), the gas availability and flow for interruption are
improved. However, in most available devices, as the puffer and expansion
volumes are open, mixing of high temperature gas and the cold compression
volume gas is inevitable. The mixing process elevates average temperature and
pressure in the vicinity resulting in slowing down of the compression process (for
limited operating energies). The consequential reduction in gas delivery affects
recovery and interruption. Further, the gas flow obtained is at a relatively higher
temperature (due to mixing) and results in corresponding poor insulation
capabilities of the gas.
Thus for the cited reasons, available interrupters rarely utilize full capability of
the interrupting medium.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process to improve current
interruption capabilities of high-voltage, high-power gas interrupters.
Another object of the invention is to propose a process to improve current
interruption capabilities of high-voltage, high-power gas interrupters which
adapts a two-stage release of arc quenching coolant gas in a controlled and
synchronized manner.
A still another object of the invention is to propose a process to improve current
interruption capabilities of high-voltage, high-power gas interrupters which
reduces coolant requirement per unit arc energy.
Yet another object of the invention is to propose a process to improve current
interruption capabilities of high-voltage, high-power gas interrupters which
enhances utilization efficiency of the interrupting medium.
A further object of the invention is to propose a process to improve current
interruption capabilities of high-voltage, high-power gas interrupters, whicn
improves the current interruption capability of the interrupter.
A still further object of the invention is to propose a process to improve current
interruption capabilities of high voltage, high-power gas interrupter, which
modifies and synchronize the gas delivery process.

Yet further object of the invention is to propose a process to improve current
interruption capabilities of high voltage, high-power gas interrupter, which
utilizes additional pockets and takes into account the response of all the flow
elements in the flow-circuit.
Another object of the invention is to propose a process to improve current
interruption capabilities of high voltage, high-power gas interrupter, which is
based on selective availability of cold gas in two stages and isolation of cold and
hot zones adapting gating devices.
SUMMARY OF THE INVENTION
Accordingly there is provided a process to improve current interruption capability
of high-voltage, high-power gas interrupters which utilizes the arc energy during
peak arcing and achieves desired dielectric recovery by delivering cold gas with
higher dielectric properties at interruption. An intermediate volume and a gating
device are introduced for isolating hot gases from the cold gas. The invention
also eliminates high pressure rise in compression / expansion volume of
conventional interrupters during arcing phase. The gas vents and geometries are
tuned for effective / efficient discharge of hot arc products according to the
invention.
BRIEF DESCRIPTION OF THE ACOMPANYING DRAWINGS
The invention is described with the help of Figures 1 to 4, where:

Fig. 1 shows the conventional SF6 interrupters like puffer, self-blast and
thermally assisted interrupter.
Fig. 2 Identifies different gas zones / pockets / volumes proposed in the
invention like, the Expansion, Intermediate and Compression.
Fig. 3 Shows a gating device between compression and intermediate volumes
according to the invention.
Fig. 4 shows the proposed Two-stage blast interrupter arrangement according to
the invention.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly, there is provided a device which constitutes a two-stage blast
interrupter, and operated on the basis of three strategically coupled volumes.
The device is capable to achieve efficient mass flow rate at interruption. The first
volume is the compression volume (01) where a piston-cylinder arrangement
allows storage of cold gas and its compression during interruption by movement
of the piston conventionally coupled to the operating mechanism/drive. Fresh
gas is collected and retained in this volume (01) during closing operation. The
second is an expansion volume (02), where the available gas is directly exposed
to arc during contact separation /arcing. The third is an intermediate volume
(03), where stored gas is compressed by expansion volume gas and where gas
pressure rises during arcing period due to compression by the expansion volume
gas and mixing (refer Fig. 2) thereof.

During the opening operation of the device, reduction in compression volume
(01), is utilized to increase pressure (Pc) of the contained gas. The pressure (Pi)
of the intermediate volume (03) at this stage is elevated by the reaction from the
gas at the expansion volume (02) which expands and compresses the
intermediate volume (03) gas due to absorbed arc energy. The invention
provides a conditional gating device, a non-returnable flap valve (04), between
the compression volume (01) and the intermediate volume (03). The valve (04)
allows gas flow from the compression volume (01). to the intermediate volume
(03) only when Pc is greater than Pi. The gating device (4) is positioned between
the intermediate and compression volumes (03, 01) (refer Fig. 3). The response
time of the flap (4) is selected corresponding to specific rating of the interrupter
/ application. During non-arcing/ low energy arcs, the intermediate chamber
pressure follows compression .chamber pressure as the condition is satisfied and
the valve (4) permits gas flow to the intermediate volume (03).
The concept and advantage of an intermediate volume (03) is introduced in the
(two-blast) interrupter of the invention to facilitate isolation of cold compression
volume gas from high temperature gasses present in the expansion volume (02).
Two-fold advantages are drawn by the invention; first, the intermediate volume
(03) is added to the expansion volume (02) improving favorably the arc energy
distribution and second, the interrupter is operated in arc-assisted mode during
the arcing phase.
In the first stage of operation of the invented two-stage blast interrupter,
pressure differential between the intermediate volume pressure and the base
pressure (main volume (05)) is utilized to push the majority of arc and the arc
products out of inter-electrode space. The process is largely controlled by arc

current and the characteristics of the intermediate volume (03). In the second
stage, cold gas blast from the compression volume (01) supplements the first-
stage blast until the pressure Pc and Pi equalize and activate the gating device.
Timely availability of cold gas from the compression volume (01) in the inter- -
electrode space improves its dielectric strength and provides desired insulation .
recovery rate for intended interruption. Fig. 4 shows the invented two-stage
blast interrupter.
The present invention is unique in the sense that the interrupting medium
available to the interrupter, especially the cold gas contained in the compression
is selectively used. The process enables release of compressed gas only during
requirement of higher dielectric recovery. It saves important cold gas resource
from use during initial cleaning of the inter-electrode space. For cyclic and pulsed
arcing the gating device (4) responds favorably and conserves the cold gas for ^
better utilization later. The operation / ON time of the gating device increases
with the increase of arcing period as the gas pressure in compression volume
increases.

WE CLAIM
1. A two stage blast process for improving current interruption capabilities of
high voltage, high pressure gas circuit breakers comprising the steps of:
- introducing a compression volume (1) in which storage of cold gas and its
compression during the interruption takes place;
- introducing an expansion volume (2) where the available gas being directly
exposed to the arc during the contract separation;
- identifying and introducing an intermediate volume (3) and a strategic coupling
with the compressed volume (1) such that a stored gas being compressed by
the expansion volume gas (2) to allow gas pressure rising during the arcing
stage;
- providing a gating device (4) between the compression volume (1) and the
intermediate volume (3) such that mixing of the hot gas to the cold gas is
eliminated in the compressed volume (1);
- building-up an effective and controlled high-pressure during the arcing phase in
the components of the interrupter; and
- applying logic for controlling and operating the gas flow rate.
- characterized in that the introduction of an intermediate volume (03) facilities
the isolation of cold compressive volume gas (01) from the high temperature
gases present in the expansion volume (02) wherein the gating device (4)
equipped with non-returnable flap valve positioned between the compression

volume (01) and intermediate volume (03) allows gas from higher compression
volume (01) pressure to the lower intermediate volume (03) pressure to enable
the release of arc quenching coolant gas by enhancing higher dielectric recovery.
2. The process as claimed in claim 1, wherein the logic to be applied comprises
allowing gas flow from the compression volume (1) to the intermediate volume
(3) when PoPi, wherein Pc = pressure of the contained gas in the compression
volume, and Pi = pressure of the intermediate volume.
3. The process as claimed in claim 1, wherein the pressure differential between
the intermediate volume (3) pressure and the main volume (5) pressure is
utilized at the first stage to push the arc and the arc products out of the inter-
electrode space.
4. The process as claimed in claim 1 or 3, wherein the cold gas blast from the
compression volume (1) supplements in the second stage the first stage blast
until the pressure Pc & Pi equalize to actuate the gating device.
5. The process as claimed in claim 1, wherein the gating device (4) is a non-
return flap value.
6. The process as claimed in claim 1 or 5, wherein the response time of the flap
(4) is selected corresponding to the application and rating of the interrupter.
7. The process as claimed in claim 1, wherein the interrupter is enabled to
operate in arc-assited mode during the arcing phase.

8. The process as claimed in any of the preceding claims, wherein the
compressed gas (1) is allowed to be released only during the requirement to
higher dielectric recovery, and wherein the cold gas (1) resource is reserved for
use during initial cleaning of the inter-electrode space.

ABSTRACT

A TWO STAGE BLAST PROCESS FOR IMPROVING CURRENT INTERRUPTION
CAPABILITIES OF HIGH VOLTAGE, HIGH PRESSURE GAS CIRCUIT BREAKERS
The invention relates to a two stage blast process for improving current
interruption capabilities of high voltage, high pressure gas circuit breakers. The
first volume is compression volume (1) where a piston cylinder arrangement
allows storage of cold gas. The second volume is expansion volume (2) where
the available gas is directly exposed to arc during contact separation/ arcing. The
third is an intermediate volume (03) where stored gas is compressed by
expansion volume gas and where gas pressure rises during arcing period due to
compression by the expansion volume gas and mixing. A gating device (4),
consists of non-return flap valve. The process ensures selective use of cold gas
contained in the compression volume to the interrupter. The process also
ensures release of compressed gas only during requirement of higher dielectric
recovery.