FIELD OF THE INVENTION
Present invention is related to the field of Circuit Breaker primarily used for
interrupting normal/ faulty/capacitive/inductive currents of high voltage power
transmission and distribution system. More particularly, it is related to a two
5 stage blast interrupter used in high voltage gas circuit breaker for efficient gas
flow rate at interruption.
BACKGROUND OF THE INVENTION
When fault current is interrupted by a circuit breaker, an arc is struck between
the arcing contacts. The energy content of the arc depends on the current
10 magnitude, length of the arc and similar other parameters. As the temperature
of the arc is quite high it decomposes the insulating medium (gas) and
materials exposed to arc. Byproducts of the chemical reaction at elevated
temperature also accumulate in the vicinity destabilize insulation and shall be
removed for sustaining the dielectric properties of the inter-electrode gap for
15 subsequent interruptions.
In conventional interrupters one of the two contacts is fixed, during
interruption the moving contact is driven by operating mechanism and an arc
is struck on contact separation (Fig.1 (a)). At current-zero the arc is
20 extinguished naturally exposing the developed inter-electrode gap to system
and transient recovery voltages. The gap reignites or the arc is re-struck should
the gap fail to withstand these voltages. For mechanical constraints limited
inter-electrode gaps only can be generated in conventional interrupters,
promoting use of multiple breaks for EHV (Extra High Voltage) circuit breakers.
25 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 require voltage equalizing devices like grading capacitors etc.,
affecting circuit breaker reliability and cost.
3
Additionally, the conventional interrupters use static field profiling electrodes
resulting in varying filed intensities as the contact separate. More clearly, when
shields are fixed the electrostatic field and voltage withstand capabilities of the
5 inter-electrode gap are limited. To overcome this constraint and to achieve
desired interrupter performance excess quantity of gas and higher differential
pressures are employed by designers.
Two-stage blast interrupter is a hybrid of self-blast and puffer interrupters. In
10 this interrupter, a fraction of energy dissipated by the arc, during high current
phase, is stored as potential energy in the gas. A gas flow created by the stored
energy, close to current-zero (CZ), sweeps the arc out of inter-electrode gap
facilitating interruption. The cool gas from compression volume is introduced
in the thermal volume as well as the inter-electrode gap for recovery of the
15 gap dielectric strength. The renewed medium helps to withstand against the
applied transient recovery voltage (TRV) and complete the interruption
successfully. One of the prior art US419967A1 discloses Puffer circuit breaker for regulating
the pressure of an arc-extinguishing gas between separating contacts. The gas
20 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 gas and the gas flow rate in
interrupters are considered to be functions of compression volume (in case of
puffer interrupters (Fig. 1(a)) and expansion volume (in self-blast (Fig. 1(b)))
25 neglecting the coupling pockets and channels. In thermally assisted gas
interrupters, i.e., combination of self-blast and puffer circuit breaker (refer Fig.
1(c)), the gas availability and flow for interruption are improved. However, in
most available devices as puffer and expansion volumes are open, mixing of
high temperature gas and the cold compression volume gas is inevitable. The
4
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 that is obtained is at a relatively higher
5 temperature (due to mixing) and results in correspondingly poor insulation
capabilities of the gas, as disclosed in a prior art, WO2016005435A1. Thus for
the cited reasons, available interrupters rarely utilize full capability of the
interrupting medium.
10 Referring to another Prior Art US 20080257866A1, which relates to the circuit
breakers for high or medium voltages, for which the drive energy is reduced
by virtue of double-acting motion of the contacts. A multiple break system is
operated by same drive which requires higher energy drive for its operation.
In general, to limit the voltage appearing across the contacts during
15 interruption, multiple breaks are preferred. Such high energy requirement
makes it difficult to operate with low energy mechanism.
The optimization of two-stage blast interrupter is difficult because this type of
circuit breaker (CB) has two gas chambers, one of which generates high
pressure by using heat of the arc and other chamber generates high pressure
20 by mechanical compression.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to solve the aforementioned
and other drawbacks existing in the prior arts.
25 It is primary object of the invention to introduce a protection volume for limiting
very high pressure at the end of strokes particularly for higher current faults.
Yet another object is to improve the gas interrupter performance in terms of
interrupting capacity, dielectric recovery of the gas and reliability.
5
Still another object of the invention is to design a non-returnable valves with
fast response time and operational under differential pressure.
These and other objects of the present invention will be apparent to those
skilled in the art after a consideration of the detailed description taken in
5 conjunction with the accompanying drawings in which a preferred form of the
present invention is illustrated.
SUMMARY OF THE INVENTION
The present invention is therefore intended to solve one or more of the above
problems by providing a method for two stage blast interrupter for limiting very
10 high pressures at the end of strokes particularly for higher current faults. Present device is constituted by four strategically coupled volumes. This aim of
the arrangement is to achieve efficient gas flow rate at interruption.
The aim of the present invention is to modify and synchronize the gas delivery
process, utilizing additional pockets and considering responses of all flow
15 elements in the flow circuit. The invention is further based on selective
availability of cold gas in two stages and by proper isolation of cold and hot
zones using gating devices.
The method comprising steps of introducing a protection volume in series to a
compression volume for limiting very high pressures at the end of higher fault
20 current strokes, for non-evacuation of said compression volume under high
pressures or at the end of the opening operation or during current interruption;
Constituting four strategically coupled volumes of gas to ensure efficient gas
flow rate during current interruption, wherein said volumes of gas are operable
when Pc > Pi where Pc and Pi are compression volume pressure and
25 intermediate volume pressure resp.
The proposed two stage Blast interrupter mainly comprises of a non-returnable
valve – I, non- returnable valve – II, wherein non-returnable Valve-I working
6
between compression volume and intermediate volume, and non- returnable
valve- II working between compression volume and a main volume.
The preferred embodiment of the present invention having other features and
advantages which are disclosed in the appended dependent claims.
5 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The illustrated embodiments of the subject matter will be best understood by
reference to the drawings, wherein like parts are designated by like numerals
throughout. The following description is intended only by way of example, and
simply illustrates certain selected embodiments of apparatus that are
10 consistent with the subject matter as claimed herein.
Figure 1 illustrates Conventional interrupters.
Figure 2 illustrates moving contact Assembly with conventional nonreturnable valve design. Figure 3 illustrates a Non-returnable valve between compression and
15 intermediate volumes. Figure 4 illustrates Assembly of the Non-returnable valve-I between
compression and intermediate volumes. Figure 5 illustrates Non-returnable valve-II between compression and main
volume. 20 Figure 6 illustrates complete Assembly of the two stage Blast interrupter in
single embodiment.
DETAIL DESCRIPTION OF THE INVENTION
While the embodiments of the disclosure are subject to various modifications
and alternative forms, specific embodiment thereof have been shown by way
25 of example in the figures and will be described below. It should be understood,
7
however, that it is not intended to limit the disclosure to the particular forms
disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternative falling within the scope of the disclosure.
Referring to the embodiments, fig. 2 illustrates the First movable contact
5 Assembly having a Socket (01), made up of high conductivity and low erosion
material, held by a Socket Support (02). The socket support is covered by an
insulating shroud (03) made up of low erosion insulating material. A nozzle
(05) is fixed to a dynamic current carrying (CC) contact (04) and to a socket
contact assembly. The socket (01), the insulating shroud (03) and the current
10 carrying contact (04) are together termed as the Socket Contact Assembly. According to the figure, the device constituted of four strategically coupled
volumes of gas to ensure efficient gas flow rate at a current interruption. The
first volume is the Compression Volume (06), second is the Expansion Volume
(07), third is Intermediate Volume (08) and the fourth is the Protection Volume
15 (09).
The compression volume (06) or the compression cylinder having a piston- cylinder arrangement which allows storage of cold gas and its compression
during interruption by movement of a piston (16) conventionally coupled to the
operating mechanism drive. A volume of fresh gas is collected and retained in
20 this volume during closing operation. The expansion volume (07) having the
available gas directly exposed to an arc (01A) during arcing. For the
intermediate volume (08) of the gas, where stored gas is compressed by
expansion volume [07] gas and where gas pressure rises during arcing period
due to both compressions by expansion volume gas and by mixing.
25 The fourth volume being an additional volume in series to compression volume
is called as Protection volume (09). At the end of stroke during opening
operation this volume helps to avoid in creating excessive gas pressures and
will not load the mechanism. At the end of opening operation, the compression
8
volume gets close to zero, so the pressure becomes very high (inversely
proportional to volume) and the mechanism is effected in terms of speed. In
other words, this concept of introducing protection volume (09) in series to
compression volume (06) is for limiting very high pressures at the end of stroke
5 particularly for higher fault currents. This helps in non-evacuation of
compression volume (06) under high pressures or at the end of the opening
operation or during current interruption. This also provides a back-up volume
to the compression volume (06) for limiting extremely high pressures during
higher arcing periods. The extremely high pressure as created in a two stage
10 blast interruption is eliminated here through the back-up volume. This
protection volume (09) shall be optimized so that interruption during no-load/
light load conditions is not affected. In the present disclosure, a socket support
(02) and protection volume (09) are same.
When the interrupting current is small, the arc diameter is smaller than nozzle
15 throat diameter. In this situation, gas in the compression chamber (06) flows
through intermediate volume (08) to the nozzle and cools the arc for
interruption and mixes in the main volume (10). When the interrupting current
becomes large enough, the arc blocks the nozzle throat. Arc diameter increases
with increasing current magnitude. The interrupting current having range of
20 few kA to about 100 kA. When the nozzle clogging occurs, the gas pressure in
the nozzle (05) region increases rapidly and becomes higher than pressure in
intermediate volume (08). Due to this reverse pressure distribution, gas
pressure in intermediate volume (08) increases and this gas is blasted to arc
when current decreases from its peak and comes to a level where nozzle
25 clogging is released. During pre-arcing period, the pressure-rise in the compression volume (06)
takes place due to movement of piston. The compression volume (06) reduces
with time.
9
Referring to figure 3 is a non-returnable Valve – I (11) between said
compression volume and intermediate volume in such a way that the gas can
flow from the compression volume to the intermediate volume, when Pc>Pi, through a pre-defined opening area, wherein Pc is compression volume (06)
5 pressure and Pi is intermediate volume (08) pressure. During this period, the
gas in the compression chamber (06) gets pressurized. During pre-arcing
period, the intermediate volume (08) pressure follows compression chamber
[06] pressure as the chambers are connected. During arcing period, the gas
flows from the expansion volume (07) to a main chamber (10). Area of opening
10 through which gas flows from said expansion to main chamber (10) depends
on the time varying arc diameter and annular area available for gas passage.
Beyond particular point of time, the movement of nozzle (05) and moving
contact in downward direction allow the gas to flow from expansion volume
(07) to the main chamber (10). During arcing period, the pressure-rise in the
15 expansion volume (07) and intermediate volumes (08) are different due to
variation in gas volume and the exposed arc energy.
The non-returnable Valve-I (11) operates when compression volume pressure
is more than intermediate volume (08) pressure (Pc > Pi). The performance of
this valve depends on parameters like response time, pressure difference
20 between compression volume (06) and intermediate volume (08), area of
opening during valve operation etc. In conventional non-returnable valves,
there is a possibility of high pressure gas leakage during non-functional time.
The non-returnable valve -I (11) further consists of spring (12) loaded flying
plate (13) that will be moved in required direction when there is a positive
25 pressure difference between compression volume (06) and intermediate
volume (08). If there is positive pressure difference, then plate will try to move
away from compression volume (06) and compress the spring against guide
plate (14). The guide plate (14) has multiple grooves to locate and held
10
springs/dampers in position. The flying plate (13) also has protrusions to hold
springs in position.
Spring loaded flying plate (13) is under pre-compression load when
5 compression volume pressure is less than or equal to intermediate volume (08)
pressure (Pc <= Pi). The pre-compression load is decided by the weight of
flying plate (13) and helps to come back the flying plate (13) to its original
position with fast response. With this pre-compression the flying plate (13) is
closed against compression volume so that there is no gas leakage during its
10 non-operational time. The flying plate (13) is moved during the positive gas
pressure difference between compression volume (06) and intermediate
volume [08]. The distance to which it moves or the distance to which spring
gets compressed from pre-compression position depends on pressure
difference and gas discharge rate through opening area between compression
15 volume (06) and intermediate volume (08). During operation of nonreturnable Valve-I (11), the springs (12) will be compressed against fixed guide
plate (14) which is located at a predefined distance from spring loaded flying
plate (13). This distance is more than allowed spring compression limit. In the
absence of flying plate (13), there is an opening area between compression
20 volume and intermediate volume. This opening area is decided by gas flow rate
demanded by nozzle (05) and outlets (15A,15B). Referring to the Fig. 4, the weightless flying plate (13) is kept on this Interface- I (09A) opening area to block the gas flow under normal conditions. The guide
25 plate (14) is supported from this interface through flying plate (13). The flying
plate (13) can freely move through a supports (16) of guide plate (14). The
supports are locked at a Locking (16A) at guide plate to ensure permanent
location to the guide plate (14) during service. The guide plate further protects
the flying plate (13) from high pressure hot gas which is generated in
11
intermediate volume (08). The number of springs (12), diameter of springs
(12) and weight of flying plate (13) (as in fig. 3) decide the response time of
the Non-returnable valve–I [11] operation.
5 Referring to figure 5, is a Non- returnable valve- II (17) between compression
volume and main volume. It comprises of piston cum current collector (17)
supported by a puffer base (18). The structure basically consists of a flap plate
(20) loaded by springs (21) which are further compressed against a guide plate
(22) supported on said piston (17). The guide plate is further tightened over a
10 supports (23) made of hard metal and locked at the top (24).
The compression volume (06) is pressurized by the said piston collector (17).
Once breaker is in open condition, gas available inside the compression volume
(06) is minimum. Accordingly, there is a need for compression volume (06) to
be filled up with rated gas pressure for next opening operation. Since this gas
15 filling is not possible with non-returnable Valve-I (11), a separate provision is
made to fill up this gas on the piston (17). This is achieved by creating a nonreturnable valve between a main chamber (10) and said compression volume
(06). The valve remains non-functional when breaker is under opening
operation. Once low pressure is created inside the compression volume (06), 20 gas will be flushed through the non-returnable valve-II (19). The flap plate (20)
is lifted/moved against this guide plate (22) during closing operation of breaker
as compression volume sucks the gas through the openings provided on the
piston.
Referring to figure 6, a non-returnable valve-II (19) is seated on an interface- 25 II (25) between the compression volume (06) and the main volume (10). The
piston (17) is also used as current collector and transmits current to the
compression cylinder (06) during making and breaking of breaker. The piston
is static type and the compression volume (06), intermediate volume (08),
nozzle (05), protection volume (09) and expansion volume (07) are dynamic
12
with respect to time during making or breaking of breaker. The springs (21)
used in non-returnable valve II (19) are different from the non-returnable valve –I (11) as valve II is used for sucking gas from rated gas pressure to negative
pressure. This valve II has to operate for entire duration of closing operation.
5 During opening operation, non-returnable valve-II (19) is not functional.
However, the guide plate (22) is under continuously increasing pressure and
its role is not only to keep flap plate (20) in required position but also to
safeguard from transient pressure rise of gas generated inside compression
volume (06). This is more critically to be protected at the end of opening
10 operation.
Similarly, the non-returnable Valve-I (11) has to operate for intermittent
duration of opening operation. During closing operation, non-returnable Valve- I (11) is not functional. However, the guiding plate (14) is under continuously
increasing pressure and its role is not only to keep flying plate (13) in required
15 position but also to safeguard from transient pressure rise of high temperature
gas generated inside intermediate volume (08). This is more critical during
opening operation.
20
25
13
WE CLAIM:
1. A method for current interruption by High voltage gas circuit breaker, the
method comprising steps of: - constituting four strategically coupled volumes of gas to ensure efficient gas
flow rate during current interruption, wherein said volumes of gas are
operable when
Pc > Pi, wherein Pc and Pi are compression volume pressure (06) and
intermediate volume pressure (08) resp; - introducing a protection volume (09) in series to compression volume (06)
for limiting very high pressures at the end of higher fault current strokes, for
non-evacuation of said compression volume (06) under high pressures or at
the end of the opening operation or during current interruption.
2. The method as claimed in claim 1, wherein said strategically coupled
volumes of gas being compression volume (06), expansion volume (07),
intermediate volume (08) and expansion volume/protection volume (09).
3. The method as claimed in claim 1, wherein operable condition Pc > Pi is
operated by a non-returnable valve- I (11) between said compression
volume and intermediate volume for flow of gas from the compressed
volume to the intermediate volume.
4. The method as claimed in claim 1, wherein operable condition Pc <= Pi
defined as pre-compression load and decided by weight of a spring loaded
flying plate (13), wherein said flying plate is closed against the compression
volume for no gas leakage during non-operation of the blast interrupter.
14
5. A two stage blast interrupter for high voltage gas circuit breaker comprises
of: non-returnable valve – I (11), non- returnable valve – II (19), wherein
non-returnable Valve-I (11) working between compression volume (06) and
intermediate volume (08), and non- returnable valve- II (19) working
between compression volume (06) and a main volume (10).
6. The device as claimed in claim 5, wherein said valve – I (11) operating based
on differential pressure and operating for intermittent duration of opening
operation with higher pressure difference and higher gas flow rates.
7. The device as claimed in claim 5 and 6, wherein a guide plate (14) to protect
the flying plate (13) from any transient rise in gas pressure or from
generated high temperature gas inside intermediate volume.
8. The device as claimed in claim 7, wherein said guide plate (14) having
multiple grooves to locate and held springs/dampers in position and said
flying plate (13) having protrusions to hold springs in position.
9. The device as claimed in claim 7 and 8, wherein said flying plate (13) to
freely move through a support (16) of said guide plate (14).
10. The device as claimed in claim 9, wherein said support are locked at a lock
(16A) at the guide plate to ensure permanent location to said guide plate
during operation.
11. The device as claimed in claim 5, wherein non- returnable valve – II (19)
comprising of a flap plate (20) loaded by a springs (21) which are further
compressed against a guide plate (22) supported on the piston (17).
15
12. The device as claimed in claim 5, wherein a guide plate (22) to protect a
flap plate (20) from any transient pressure rise generated inside the
compression volume.
13. The device as claimed in claim 12, wherein said guide plate tightened on a
support (23) and locked from top (24).
14. The device as claimed in claim 5, wherein said non-returnable valves (11,
19) active during opening (current interruption) and closing operations.