FIELD OF THE INVENTION
The present invention relates to a three phase compact disconnector switch with
all three phases located in a single enclosure to prevent secondary breakdowns
in gas insulated switchgear equipment.
BACKGROUND OF THE INVENTION
Disconnector switch (DS) is primarily used to isolate high voltage sections of
switchgear equipment. When a (DS) is closed, the capacitive charging current
flow through the contacts of the disconnector in proportion to the line voltage
and the line length in conventional disconnector switches, its suffers with re-
strikes, leading to arc breakouts during switching operations.
The gas insulated disconnect switch consists of a metallic chamber filled with SF6
gas wherein a movable contact is provided to isolate/disconnect the parts of Gas
insulated high voltage sections. The movable contact and a drive system are
connected by an insulating element to have isolation for the drive system from
high voltage when the device is in closed condition. A three phase gas insulated
disconnect switch consists of three numbers of such disconnection paths for
three phases of gas insulated electric system where in the SF6 gas at specified
gas density provides the voltage isolation between the phases as well as
between the individual phases and the grounded metallic enclosure. The
reliability of the disconnector switch depends on design of the moving contact,

its housing and shielding arrangement. Very fast transient over-voltages (VFTOs)
are common to such disconnector switch operation and are result of rapid
dielectric breakdown under severe electrostatic stresses experienced by the
insulating media (SF6) for relatively slow operating speeds of the disconnector
switch, Sometimes these breakdowns lead to secondary breakdowns such as arc
breakouts.
Disconnector switches are employed in electrical systems to interrupt / make
capacitive currents in principle . When the capacitive current is interrupted, a
spark is formed, which shunts the potentials on the two electrodes. When this
spark extinguish, a few seconds later, results in different potentials on the source
side and the load side of the disconnector. When the contacts of a disconnector
switch separate, several restrikes (spark/discharge) take place, causing transition
of E-field distribution from axial to radial direction (towards other phases or
towards grounded enclosure). This process tends to influence the axial
discharges, deflecting it towards the grounded metallic enclosure. This recurrent
phenomenon at times leads to secondary breakdowns (arc breakout) to the
grounded enclosure or to the other phases of the disconnector switch. The
VFTOs magnitude at / near the disconnector switch contacts during its operation
may also lead to voltage multiplication as high as three times, depending on the
observation point and the substation configuration. Intense VFTOs may result to
the voltage close to basic insulation levels (BIL) leading to frequent VFTOs lead
breakouts in high voltage gas insulated systems.

Conventional disconnector switches are primarily constituted by a fixed contact, a
moving contact and an inter-electrode gap. A metallic grounded enclosure is
used to contain SF6 gas insulation at specified density. The system is designed
for minimum average electrostatic fields, without considering the impact of axial
and radial electrostatic fields. The switching (transition) of electrostatic fields
during presence of a spark/discharge due to re-strikes is also seldom considered.
The conventional disconnector switch in above situation suffers the following
deficiencies:
• Field non-uniformity between/surrounding the contacts during discharges.
• Long discharge lengths/inter-electrode gap.
• Secondary breakdown from contact system to grounded enclosure or to
the other phases of disconnector switch.
• Longer pre-arcing and arcing times.
• Participation of fixed contact shields in arcing phenomena.
• Optimal location of three phases of disconnector switches in single
enclosure.
In conventional disconnector switches, the pre-arcing and arcing times are very
high as fixed contact shields are arranged away from fixed contacts (ref : EP 0
344 744 A2). According to this patent, even though uniform electric field is
achieved between contacts, there is a possibility of long arcing / pre-arcing
time during bus charging current duties. One more difficulty in this type of
design is that the fixed contact shield participates in arcing and profile of shield
gets modified over a period of time and hence results in degradation of
performance. In some of the conventional three phase disconnector switches,
all three phases are placed one after the another, which is not economical as it

occupies lot of volume (refer US 4 821 140). In such designs there is a
possibility of secondary breakdowns between phases if we try to optimize the
design. Further, all three phases arcing / discharges takes place side by side
and result to breakdowns during switching duties. In some of the existing
designs there is a possibility of secondary breakdown from the arcing channel
during movement of contact as there is no control on electric field around
moving contact system (refer US 4 413 166). Such designs have difficulty
against bus charging current duty.
The aim of the present invention is to achieve a secondary breakdown-free and
a reliable gas insulated disconnector switch by transferring current with very
low power losses. The present design aimed to provide shortest pre-arcing and
arcing times and to improve life of disconnector switches. The contact shields
are proposed in such a way that they are free from arcing phenomena.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a three phase compact
disconnector switch with all three phases located in a single enclosure to
prevent secondary breakdowns in gas insulated switchgear equipment which
includes a single common drive for isolation of high voltage sections of all the
three phases.
Another object of the invention is to propose a three phase compact
disconnector switch with all three phases located in a single enclosure to
prevent secondary breakdowns in gas insulated switchgear equipment which

includes a spherical connector with self-contained shield and stopper
arrangement.
A further object of the invention is to propose a three phase compact
disconnector switch with all three phases located in a single enclosure to
prevent secondary breakdowns in gas insulated switchgear equipment in which
the moving contact assembly is accommodated in the spherical connector.
A still further object of the invention is to propose a three phase compact
disconnector switch with all three phases located in a single enclosure to
prevent secondary breakdowns in gas insulated switchgear equipment in which
a profiled movable plate with guiding arrangement to operate against gas
pressure.
SUMMARY OF THE INVENTION
Accordingly, there is provided a three phase compact disconnector switch with
all three phases located in a single enclosure to prevent secondary breakdowns
in gas insulated switchgear equipment comprising a spherical connector
extending electrical connections in multiple directions; a fixed contact covered
by a fixed contact shield held on an insulator via an adapter; a moving arcing
contact surrounded by a moving contact shield, the moving arcing contact
accommodated within the spherical connector; a grounded metallic enclosure
with SF6 gas connected to the switch system by an insulated operating rod and
necessary linkages, wherein a distance (D) is maintained to separate the fixed
contact shield and the moving contact shield, the distance being selected based
on the system voltage and density of SF6 gas; wherein the spherical ,

connector is provided with one each current collector device with plurality of
shields cooling means in the form of gas flow vents, current transfer connector,
wherein said support insulator is terminated with a terminal cum shield, and
wherein a stopper cum shield is integrated to said spherical adapter and
ensures uniform electric field across the insulated operating rod.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention is described with the help of Figures 1 to 7, where :
Figure 1 : Conventional disconnector switches.
Figure 2 : Moving Contact system of Disconnector switch.
Figure 3 : Spherical connector with self contained shields
Figure 4 : Spherical connector with current collector arrangement
Figure 5: Three phase Moving contact assembly with insulated operating rods.
Figure 6: Guide Arrangement of Moving plate
Figure 7 : Invented Three phase compact Disconnector Switch.

DETAILED DESCRIPTION OF THE INVENTION
The fixed contact [01] of the disconnector switch (DS) is made of a high
conductivity material with low erosion refractory material tip held on a support
insulator [02] with suitable adapter [03]. The fixed contact [01] is covered by a
fixed contact shield [04] with designed axial and annular space to control the
axial field between the fixed and moving contacts. The moving arcing contact
[05] is surrounded by a moving contact shield [06], when DS is in fully open
condition. The moving arcing contact [05] is located in housing called as
Spherical adapter [07]. The DS operation is achieved by using an insulated
operating rod [08]. The entire contact system is insulated from the grounded
metallic enclosure [09] with designed SF6 gas density. The moving contact shield
[06] is separated from the fixed contact shield [04] by a distance 'D' proportional
to the system voltage and the SF6 gas density. Figure 2 shows the contact
system of disconnector switch.
A spherical shaped universal connector [07] according to the invention comply
with all connection requirement of metal clad gas insulated substation
equipment. Invented spherical connector [07] is a unique component to cater
for the multiple requirements of compact switchgear equipment. The objective of
the connector is to transfer current from one module of the switchgear / power
equipment to another module. It is also to commensurate electric stress relieved
connection in different orientations like "L", "T" or 0°-90° of any orientation.

The spherical connector provides low resistance path with controlled electrical
stress around its geometry i.e. self contained shield (refer Figure 3). The
invented connector also acts as a housing for a moving arcing contact [05], a
current collector [10] and plurality of shields [22] against unwanted openings of
the connector. The profile of the spherical connector [7] allows an optimal design
of the contact system. Figure 4 shows the spherical connector [07] with current
collector [10] arrangement. The third objective of the invented spherical
connector [07] is to ensure that it acts as a guide to an insulated operating rod
[08] used for operating the disconnector switch. The profile of the spherical
connector [07] makes it possible to provide a cost-effective system for compact
switchgear equipment. The fourth objective of the invented spherical connector
[07] is to enable the connector to act as a current transfer connector [12], i.e.
transfers current from the movable arcing contact [05] to a module connected to
the switching element through the current collector [10]. The current collector
[10] also acts as a stopper for the disconnector switch during its closing
operation. The spherical connector [07] is self contained and is an electrically
stress relieved component. The spherical connector [07] is provided with a
cooling means in the form of gas flow vents. This arrangement helps in
maintaining uniform temperature distribution for the switchgear equipment. The
support insulator [02] is terminated with a terminal cum shield [13]. A stopper
cum shield [14] is integrated to a spherical adapter [07] which has a provision of
stopper arrangement to avoid over run of the disconnector switch during opening
operation. This profile of stopper cum shield [14] ensures uniform electrical field
across the insulated operating rod [08].

The invention provides a three phase gas insulated disconnector switch which in
each phase consists of a spherical connector [07] for extending electrical
connections in multiple directions. The moving contact [05] is plugged into the
fixed contact [01] when the disconnector switch is in close condition. The current
collector [10] is used to extend dynamic current transfer during the travel of
moving contact. The current collector [10] extends the dynamic current transfer
of discharge/arcing current of HV sections from the fixed contact [01] to the
movable arcing contact [05] and to the spherical connector [07] when the
movable contact is about to make contact with the fixed contact (during pre-
arcing time). The moving arcing contact [05] is isolated from the operating link
[15], through the insulated operating rod [08]. The drive system provides the
energy required for the operation of the movable contact system consisting of
the moving arcing contact [05], the insulated operating rod [08], an operating
link [15], a coupling element [16], a lever arrangement [17]. For three phase
operation of the disconnector switch, three numbers of movable arcing contact
[05] with electrical isolation through three numbers of insulated operating rod
[08] are attached to a single movable plate [18], which on another side attached
to the drive system through the operating link [15] and the coupling element
[16]. All three fixed contacts [01] and moving arcing contacts [05] are integrated
to respective shields to protect the high voltage system from secondary
breakdown. The individual phases of three phase system are oriented in an
equilateral triangle manner by placing each phase at one of the three vertices of
triangle. This equilateral triangle configuration enables the uniform electric field
distribution between phases as well as between individual phases to ground.

Apart from this, triangular arrangement of the movable contact system also
enables uniform distribution of drive energy among the three phases. Figure 5
shows three phase moving contact assembly with insulated operating rods.
A movable plate [18] similar to a triangular profile with three vertices of triangle
is connected to three insulated operating rods [08] on one side. The other side
of the movable plate [18] is connected to the single operating link [16] at the
centre of the plate. The movable plate [18] consists of a guide arrangement
[19] for smooth operation and is guided by a metallic tube cum shield [20]
located in a drive housing [21]. The metallic tube cum shield [20] has a shield
arrangement to provide uniform electric field across the insulated operating rod
[08]. The movable plate [18] is designed in such a way that it has suitable
operating area to avoid unwanted pressure build-up in the drive housing [21]
during opening / closing operation which otherwise affect operating speed
characteristics. Figure 6 shows the guide arrangement of the moving plate. The
three phase contact system has. been arranged in an equivalent triangle
configuration in a spherical grounded enclosure [22]. The spherical grounded
enclosure [22] is profiled in such a way that the electrostatic field around the
contact system is highly uniform and result into a secondary breakdown free
three phase disconnector switch. Axial E-field must be uniform between the
contact shields, when DS is in fully open condition. Axial E-field must also be
uniform between the moving contact shield [06] and the fixed contact shield [04]
during DS is in operation. During contact movement, axial E-field should be
highest between fixed contact shield [04] and the moving contact [05] around
the central axis. The moving contact [05] is designed in such a way that the field
shall be highest at the central axis rather than on the surface of the tip.

During a discharge between the contacts, the radial E-field from the moving
contact tip / discharge towards the grounded metallic enclosure [22] and other
phases contact system increased significantly and may lead to secondary
breakdowns. These breakdowns are difficult to handle at higher system voltages
as highest electric field levels at the tip of discharge are extremely high if they
are not controlled. These electric field levels could be controlled to certain extent
with suitable profiles of the fixed contact shield [04] and the moving contact
shields [06], The profile of the fixed contact shield [04] and the moving contact
shield [06] are designed in such a way that the E-field around the contact system
is highly uniform. The radial electric field is made further uniform by profiling
grounding enclosure. The spherical grounded enclosure [22] is of spherical type
and around contact system more insulation distance is made available and helps
in avoiding secondary breakdowns. Figure 7 shows the three phase compact
disconnector switch.

WE CLAIM :
1. A three phase compact disconnector switch with all three phases
located in a single enclosure to prevent secondary breakdowns in gas
insulated switchgear equipment comprising a spherical connector (07)
extending electrical connections in multiple directions; a fixed contact (01)
covered by a fixed contact shield (04) held on an insulator (02) via an
adapter (03); a moving arcing contact (05) surrounded by a moving
contact shield (06), the moving arcing contact accommodated within the
spherical connector (07); a grounded metallic enclosure (09) with SF6 gas
connected to the switch system by an insulated operating rod (08),
wherein a distance (D) is maintained to separate the fixed contact shield
(04) and the moving contact shield (06), the distance being selected
based on the system voltage and density of SF6 gas; wherein the spherical
connector (07) is provided with one each current collector device (10)
with plurality of shields (11) cooling means in the form of gas flow vents,
current transfer connector (12), wherein said support insulator (02) is
terminated with a terminal cum shield (13), and wherein a stopper cum
shield (14) is integrated to said spherical adapter (03) and ensures
uniform electric field across the insulated operating rod (08).
2. The disconnector switch (DS) as claimed in claim 1, wherein the
insulated operating rod (08) is attached to a movable plate (18) at one
end, and connected at other end to an operating link (15) and a
coupling element (16).

3. The (DS) as claimed in claim 1 or 2, wherein the moving arc contact
(05), the insulated operating rod (08), the operating link (15), the
coupling element (16) including a lever means (17) constitutes a movable
contact system.
4. The (DS) as claimed in claim 2, wherein the movable plate (18) comprising
a guide arrangement (19) consisting of a metallic tube shield (20) located
in a drive housing (21).

ABSTRACT

The invention relates to a three phase compact disconnector switch with all three
phases located in a single enclosure to prevent secondary breakdowns in gas
insulated switchgear equipment comprising a spherical connector extending
electrical connections in multiple directions; a fixed contact covered by a fixed
contact shield held on an insulator via an adapter; a moving arcing contact
surrounded by a moving contact shield, the moving arcing contact accommodated
within the spherical connector; a grounded metallic enclosure with SF6 gas
connected to the switch system by an insulated operating rod wherein a distance
(D) is maintained to separate the fixed contact shield and the moving contact
shield, the distance being selected based on the system voltage and density of SF6
gas; wherein the spherical connector is provided with one each current collector
device with plurality of shields, cooling means in the form of gas flow vents,
current transfer connector, wherein said support insulator is terminated with a
terminal cum shield, and wherein a stopper cum shield is integrated to said
spherical adapter and ensures uniform electric field across the insulated operating
rod.