FIELD OF THE INVENTION
The present invention relates to an insulating nozzle to improve interrupting
performance of higher voltage circuit breakers.
BACKGROUND OF THE INVENTION
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 flow 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.
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
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 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 (figure 1(a)). At current-zero the arc is 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 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 require voltage equalizing devices like
grading capacitors etc. affecting circuit breaker reliability and cost.
In general, to limit the voltage appearing across the contacts during interruption,
multiple breaks are preferred. The multiple break system is operated by same
drive which requires higher energy drive for its operation. To overcome this
problem, a dual motion contact system has been identified as an alternative
solution (fig. 1(b)). However, in all these systems, the second movable contact
i.e. other than primary moving contact takes sufficient portion of energy from the
operating mechanism. In some of the conventional breakers, such system have
relatively high energy requirements and are difficult to operate with low energy
mechanisms (ref: US 20080257866A1).
The electrostatic field, between movable and fixed contacts, is non-uniform for
various reasons like electrode profile and relative position of contacts. The field
intensification adversely affects voltage withstanding capabilities of the gas gap.
The availability of hot and conducting gas further complicates the situation
preventing successful interruption. In most of the interrupters the arced gas after
leaving the nozzle 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 by the
effectiveness with which arcing gas is being removed across inter-electrode gas

gap and uniformity of the electrostatic field between arcing contacts. 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. The dielectric strength of inter-electrode gap not only
depends on the effective removal or arced gas but also on the density of fresh
gas which occupies the arced gas. In conventional interrupters, once gas
released from throat to divergence zone, there is a possibility of mach number
more than one due to sudden expansion of gas (ref: US Patent No.5739495).
Because of increased Mach number, gas pressure near throat region falls
abruptly and sometimes negative (refer fig.2). This in turn create low gas density
region which become critical for withstanding transient recovery voltages during
current interruption.
For successful interruption, the primary design requirements are : sufficient
inter-electrode gap; optimal dielectric properties of the gas and field uniformity,
in inter-electrode gap. To address some of these requirements, a movable shield
approach is disclosed herein. Interrupting capability of a breaker is also further
improved by means of a relative motion of contact system with a charging and
toggling mechanical system for pin (second movable contact) vide patent
application no. 1391/kol/2009. Currently, an improved insulating nozzle is
proposed to enhance interrupting performance of the breaker. The insulating
nozzle addresses higher TRV challenges of single break system around current
zero.
OB3ECTS OF THE INVENTION
It is therefore an object of the invention is to propose an insulating nozzle to
improve interrupting performance of higher voltage circuit breakers.

Another object of the invention is to propose an insulating nozzle to improve
interrupting performance of higher voltage circuit breakers, which reduces
breaks per pole for the circuit breakers of higher voltage class.
A still another object of the invention is to propose an insulating nozzle to
improve interrupting performance of higher voltage circuit breakers, which is
enabled to protect the inter-electrode gap (main current carrying contacts) from
hot/conducting gas contamination.
Yet another object of the invention is to propose an insulating nozzle to improve
interrupting performance of higher voltage circuit breakers, in which the moving
contact is integrated to the nozzle in a self-locked manner.
A further object of the invention is to propose an insulating nozzle to improve
interrupting performance of higher voltage circuit breakers, which is configured
to allow the inter-electrode gap to be free from low density zone during current
interruption.
A still further object of the invention is to propose, an insulating nozzle to
improve interrupting performance of higher voltage circuit breakers, which
includes different divergence zones including a convergence zone.
Yet further object of the invention is to propose, an insulating nozzle to improve
interrupting performance of higher voltage circuit breakers, which acts as a flow
link between self blast volume and inter electrode gap for pressurized gas
transportation.

SUMMARY OF THE INVENTION
Accordingly, there is provided an insulating nozzle to improve interrupting
performance of higher voltage circuit breakers, the high voltage circuit breaker
comprising : a socket contact assembly comprising a socket, an insulating
shroud, and a dynamic current carrying contact; a socket support covered by the
insulating shroud of the socket contact assembly; a dynamic field electrode
surrounding a pin acting as a second movable contact, the pin is constructed
such that the pin upon entering inside the nozzle accelerates the arcing energy
till the pin exits a throat region; a stationary current carrying contact assembly
internally accommodating the assembly of the pin and dynamic field electrode,
the static current contact assembly comprises a static current carrying contact
shield and a static current carrying contact; the dynamic field electrode in the
open condition of the interrupter projecting out from the static current carrying
contact shield to allow the gas gap between the dynamic field electrode and the
dynamic current carrying contact determine the withstandable voltage; the
interrupter operating under three coupled volumes, the first volume being a
compression volume, the second volume being an expansion volume, and the
third volume being an intermediate volume which in combination provides an
efficient gas flow rate at the time of interruption; the nozzle comprising :- a first
terminal integrated to the socket contact assembly; a second terminal coupled to
the pin through a mechanical coupling and energy storage device; a converging
zone connecting the intermediate volume and the throat region and having a
converging angle, and an extendable length, the length being dependent on
profile of said insulating shroud including the fault current to be interrupted; a
straight zone or throat region convergingly connecting a first diverging zone, the
occupied length

of the zone depending on speed of the moving contact system and the diameter
of the zone corresponding to the fault current to be interrupted; the first
diverging zone having an angle of divergence about 40 to 60°, and an occupied
length corresponding to the diameters of the throat, fixed contact and fixed
movable contact; a second diverging zone having a divergence angle about 2 to
5° and an extendable length corresponding to speed of the moving contact, dual
motion contact means and arcing time of the circuit breaker; and a third
diverging zone having a divergence angle more than 40°, and an occupiable
distance depending on the difference between time to establish isolation
between the arcing contacts and maximum arcing time, wherein the electrostatic
field across main current carrying contacts and arcing contacts is maintained
uniform, wherein communication of hot/ionized gas from the arcing contacts to
the gas gap formed between the socket contact assembly and static current
carrying contact assembly is prevented, wherein the gas gap between the socket
and the insulating shroud and between the insulating shroud and the insulating
shroud and the nozzle allows discharge of sufficient gas flow from the
intermediate volume including maintenance of uniform electrostatic field across
insulator shroud and the nozzle. The insulating nozzle transfers energy required
to drive a second movable contact/pin from main drive, and achieves the
required contact separation at faster rate without consuming energy from the
main drive. According to the invention, the inner surface of the nozzle is
constructed such that there will be no low density zone at the convergence,
straight and divergence zones during current zero to ensure withstandability of
the breaker for TRV. The nozzle eliminates communication of hot/ionized gas
from arcing contacts to the gas gap between main/current carrying contacts. The
nozzle ensures uniform electrostatic field across contact system i.e., both arcing
and current carrying contacts.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS :
The invention is described with the help of figures 1 to 5, where:
Figure 1 Conventional interrupters
Figure 2 Conventional insulated nozzle
Figure 3 Socket contact Assembly
Figure 4 Integration of Nozzle to socket contact assembly
Figure 5 Insulated nozzle according to the invention
Figure 6 Improved interrupter with integrated nozzle and relative/dual
motion contact system according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
In the present invention, a socket [01], made of a high conductivity and low
erosion material is held on a socket support [02]. The socket is covered by an
insulating shroud [03] made from insulating material. This material can
withstand higher arcing temperatures. A nozzle [05] is fixed to a dynamic current
carrying (DCC) contact [04] and to the socket contact assembly (01,03,04). The
socket [01], insulating shroud [03] and the dynamic current carrying contact [04]
are termed as the socket contact assembly. Figure 3 shows the socket contact
assembly.
In the interrupter fully open condition, a pin [06] or a second movable contact is
surrounded by a dynamic field electrode [07]. The pin [06] dimension is selected
in such a way that when it moves inside the nozzle [05], the arcing energy
allows the pin to accelerate till the pin [06] comes out of a throat region. The pin
[06] is located inside the dynamic field electrode [07] and the arrangement is
disposed inside a stationary current carrying (scc) contact [08] assembly. The pin

is dimensioned such that it promotes uniform electrostatic field between the two
arcing contacts. The static current carrying contact assembly comprising the
static current carrying (SCC) contact [08] and a static current carrying contact
shield [09]. In interrupter open condition, the dynamic field electrode [07]
projects out from the static current carrying contact shield [09] and the gas gap
between the dynamic field electrode [07] and the dynamic current carrying
contact [04] decides the withstand voltage. The distance to which the dynamic
field electrode [07] project out from the static current carrying contact shield
[09] depend on voltage to which inter-electrode gap has to withstand at current
zero. This has to be adjusted as per speed characteristics of the contact system.
The device of the invention includes three strategically coupled volumes to
achieve an efficient gas flow rate at the time of interruption. The first volume is a
compression volume [10], where a piston-cylinder arrangement allows storage of
cold gas and its compression during interruption by movement of a piston
conventionally coupled to the operating mechanism/drive. Fresh gas is collected
and retained in this volume (10) during closing operation. The second is an
expansion volume [11], where the available gas is directly exposed to arc during
contact separation/arcing. The third is an intermediate volume [12], where
stored gas is compressed by the expansion volume gas and where gas pressure
rises during arcing period due to both compression by the expansion volume gas
and by mixing.
Conventionally, the second movable contact system is engaged to the main drive
using insulating rods which may affect the electrostatic field across the inter-
electrode gap. In order to improve the electrostatic field across the inter-
electrode gap, an insulating nozzle has been designed in such a way that the
second movable contact/pin [06] is engaged to the main drive through the

nozzle. The proposed nozzle [05] provides good mechanical strength against
electro-mechanical forces. Proposed nozzle [05] has two terminals. First terminal
is integrated to the primary moving contact assembly/socket contact assembly
(01,03,04). Alternatively, the nozzle [05] is connected to the socket contact
assembly (01,03,04) in self locked manner which helps to work against
mechanical forces. Figure 4 shows the nozzle integrated to the socket contact
assembly. The second terminal of the nozzle is coupled to the pin through a
mechanical arrangement and an energy storage device. The second terminal of
the nozzle is at a fixed potential rather than at floating potential as in the some
of the conventional systems. The nozzle [05] design is optimized by considering
mechanical, thermal, electrical and flow parameters. The nozzle [05] shall
withstand mechanical forces offered by drive and pressure rise during arcing
phenomena. The design shall be suitable for uniform electrostatic field across
nozzle surface and effective mass (pressurized gas) transportation. Total profile
of the proposed nozzle [05] has been divided into five zones:
These zones are defined as Converging zone CZ1 [13], straight zone or throat
region SZ1 [14], First diverging zone DZ1[15], Second diverging zone DZ2 [16]
and Third diverging zone DZ3 [17].
Each zone has its significance in the gas flow and decides the performance of the
circuit breaker during current interruption.
CZ1 [13] is a converging zone which connects the intermediate volume [12] and
the throat region (SZi). The converging angle decides the gas pressure/density
at the tip of moving arcing contact. The distance to which it occupies depend on
the profile of the insulating shroud (03) and fault current to be interrupted.

SZ1 [14] is a straight zone or throat zone and convergingly connects diverging
portion of the nozzle. The distance to which it occupies depends primarily on
speed of the moving contact system. The diameter of the throat depends on
fault current to be interrupted. The dimensions of zone decide minimum,
medium and maximum arcing times, gas flow rate during current interruption
and in particular current zero, gas density across inter-electrode gap etc. If the
throat zone is less than required input pressure from thermal volume may not be
sufficient to develop necessary density for the gas across the contact system.
The diverging angle of the diverging zones (DZ1, DZ2 and DZ3) is different from
each other. The angle of divergence of DZ1 [15] is about 40 to 60 degrees. The
distance to which this zone occupies depend on the diameter of throat/fixed
contact/fixed movable contact. This profile decides the density of gas in the SZ1
zone [14] and DZ1 zone [15] during current zero period. In other words, DZ1
profile decides withstandability of the breaker for transient recovery voltage at
current zero. If the profile allows sudden expansion, there is a possibility of Mach
number more than 1 (one) and negative pressure prevails in the SZ1 zone [14]
and in the divergence zone. High Mach number in this zone results to low gas
density area and reduces the dielectric strength of the gas across inter-electrode
system (across arcing contacts/inner surface of nozzle).
The divergence angle of DZ2 zone [16] is about 2 to 5 degrees. The distance to
which this zone occupies depends on speed of the moving contact/fixed contact
(dual motion) and arcing times of the breaker. More clearly, the distance to
which this zone occupies depend on nozzle length required to meet conditions
like the following :

1. Mach number should be much less than one across inter-electrode gap for
all arcing times i.e., minimum, medium and maximum. Gas density across
inter-electrode gap decides the withstandability of the breaker for TRVs.
2. Gas flow rate across arcing channel shall be sufficient enough to quench
the arc around current zero. If the angle of the DZ2 zone [16] is less,
contact system has to travel more distance to get sufficient gas flow and
may increase arcing time.
The divergence angle of DZ3 [17] zone is about 40 degrees or more. The
distance to which it occupies depends on the difference between time to
establish isolation between arcing contacts (Moving contact and movable
fixed contact) and maximum arcing time. This zone helps to guide arced
gas to vent out effectively without spilling out into the region of current
carrying contact system.
The profile of nozzle [05] proposed in the application has been optimized
by considering the following aspects also:
1. Uniform electrostatic field across main current carrying contacts (the
socket contact assembly and static current carrying contact assembly) and
arcing contacts (pin[06] and socket [01]).
2. There is no communication of hot/ionized gas from arcing contacts to the
gas gap between socket contact system and static current carrying
contact assembly. Hence withstandable voltage or field uniformity
between main current carrying parts will not get disturbed during fault
current interruption. In other words, spilling of ionized gas from nozzle

[05] vent into gas gap across main current carrying contacts is totally
removed.
3. The profile of nozzle [05] is such that the push from arcing energy to the
pin [06] along with the energy stored in the pin [06] helps in achieving
required arcing contact separation at higher speed than offered by drive
alone.
4. The gas gap between the socket [01] and insulating shroud [03] and
between the insulating shroud [03] and nozzle [05] shall be such that

(a) there remaining sufficient gas flow from the intermediate volume [12]
and
(b) the electrostatic field across insulator surfaces (insulating shroud [03]
and nozzle [05] shall be uniform.

WE CLAIM :
1. An insulating nozzle to improve interrupting performance of higher voltage
circuit breakers, the high voltage circuit breaker comprising :
- a socket contact assembly comprising a socket, an insulating shroud, and
a dynamic current carrying contact;
- a socket support covered by the insulating shroud of the socket contact
assembly;
- a dynamic field electrode surrounding a pin acting as a second movable
contact, the pin is constructed such that the pin upon entering inside the
nozzle accelerates the arcing energy till the pin exits a throat region;
- a stationary current carrying contact assembly internally accommodating
the assembly of the pin and dynamic field electrode, the static current
contact assembly comprises a static current carrying contact shield and a
static current carrying contact;
- the dynamic field electrode in the open condition of the interrupter
projecting out from the static current carrying contact shield to allow the
gas gap between the dynamic field electrode and the dynamic current
carrying contact determine the withstandable voltage;
- the interrupter operating under three coupled volumes, the first volume
being a compression volume, the second volume being an expansion
volume, and the third volume being an intermediate volume which in
combination provides an efficient gas flow rate at the time of interruption;
the nozzle comprising :-
- a first terminal integrated to the socket contact assembly;

- a second terminal coupled to the pin through a mechanical coupling and
energy storage device;
- a converging zone connecting the intermediate volume and the throat
region and having a converging angle, and an extendable length, the
length being dependent on profile of said insulating shroud including the
fault current to be interrupted;
- a straight zone or throat region convergingly connecting a first diverging
zone, the occupied length of the zone depending on speed of the moving
contact system and the diameter of the zone corresponding to the fault
current to be interrupted;
- the first diverging zone having an angle of divergence about 40 to 60°,
and an occupied length corresponding to the diameters of the throat,
fixed contact and fixed movable contact;
- a second diverging zone having a divergence angle about 2 to 5° and an
extendable length corresponding to speed of the moving contact, dual
motion contact means and arcing time of the circuit breaker; and
- a third diverging zone having a divergence angle more than 40°, and an
occupiable distance depending on the difference between time to
establish isolation between the arcing contacts and maximum arcing time,

wherein the electrostatic field across main current carrying contacts and arcing
contacts is maintained uniform, wherein communication of hot/ionized gas from
the arcing contacts to the gas gap formed between the socket contact assembly
and static current carrying contact assembly is prevented, wherein the gas gap
between the socket and the insulating shroud and between the insulating shroud
and the insulating shroud and the nozzle allows discharge of sufficient gas flow
from the intermediate volume including maintenance of uniform electrostatic
field across insulator shroud and the nozzle.

ABSTRACT

The invention relates to an insulating nozzle to improve interrupting performance
of higher voltage circuit breakers, the high voltage circuit breaker comprising : a
socket contact assembly comprising a socket, an insulating shroud, and a
dynamic current carrying contact; a socket support covered by the insulating
shroud of the socket contact assembly; a dynamic field electrode surrounding a
pin acting as a second movable contact, the pin is constructed such that the pin
upon entering inside the nozzle accelerates the arcing energy till the pin exits a
throat region; a stationary current carrying contact assembly internally
accommodating the assembly of the pin and dynamic field electrode, the static
current contact assembly comprises a static current carrying contact shield and a
static current carrying contact; the dynamic field electrode in the open condition
of the interrupter projecting out from the static current carrying contact shield to
allow the gas gap between the dynamic field electrode and the dynamic current
carrying contact determine the withstandable voltage; the interrupter operating
under three coupled volumes, the first volume being a compression volume, the
second volume being an expansion volume, and the third volume being an
intermediate volume which in combination provides an efficient gas flow rate at
the time of interruption; the nozzle comprising :- a first terminal integrated to
the socket contact assembly; a second terminal coupled to the pin through a
mechanical coupling and energy storage device; a converging zone connecting
the intermediate volume and the throat region and having a converging angle,

and an extendable length, the length being dependent on profile of said
insulating shroud including the fault current to be interrupted; a straight zone or
throat region convergingly connecting a first diverging zone, the occupied length
of the zone depending on speed of the moving contact system and the diameter
of the zone corresponding to the fault current to be interrupted; the first
diverging zone having an angle of divergence about 40 to 60°, and an occupied
length corresponding to the diameters of the throat, fixed contact and fixed
movable contact; a second diverging zone having a divergence angle about 2 to
5° and an extendable length corresponding to speed of the moving contact, dual
motion contact means and arcing time of the circuit breaker; and a third
diverging zone having a divergence angle more than 40°, and an occupiable
distance depending on the difference between time to establish isolation
between the arcing contacts and maximum arcing time, wherein the electrostatic
field across main current carrying contacts and arcing contacts is maintained
uniform, wherein communication of hot/ionized gas from the arcing contacts to
the gas gap formed between the socket contact assembly and static current
carrying contact assembly is prevented, wherein the gas gap between the socket
and the insulating shroud and between the insulating shroud and the insulating
shroud and the nozzle allows discharge of sufficient gas flow from the
intermediate volume including maintenance of uniform electrostatic field across
insulator shroud and the nozzle.