FIELD OF THE INVENTION
The present invention relates to a three phase compact earthing switch with all
three phases located in a single enclosure to directly discharge the trapped
charges in high voltage sections of gas insulated switchgear equipment. More
particularly, the invention relates to a three phase common enclosure type gas
insulated switchgear, particularly to a three phase common enclosure type gas
insulated earthing switch module.
BACKGROUND OF THE INVENTION
It is known that earthing switch modules are normally provided in a gas
insulated switchgear (GIS) m as well as in an air insulated switchgear (AIS), to
discharge remnant DC charge on long lines/cables. Under normal working
conditions, the earthing switch remains in open condition. During maintenance
and shut down period, the live parts/section of a power-generation substation
are grounded through the earthing switches to ensure safety of the maintenance
personnel. The earthing switches within GIS are also used as the return path
during calibration/accuracy assessment of a current transformer. Two types of
earthing switches are recommended for GIS to cover both the requirements.

First type is a low speed maintenance earthing switch and second type is a high
speed fault-proof earthing switch. The fault-proof earthing switch, connected at
the entrance of a substation, experiences fault current at system voltage “make”
operation. The earthing switch also interrupts and makes electro-magnetically
and electro-statically induced currents.
The gas insulated earthing switch consists of a metallic chamber filled with SF6
gas wherein a movable contact is provided to connect the components of high
voltage section of Gas insulated switch to ground. A three phase gas insulated
earthing switch consists of three numbers of contact system for three phases of
gas insulated electric system, wherein 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. All three phases of the
moving contacts are connected to common ground through a current collector.
An insulating spacer is provided between the metallic enclosure and ground
terminal to make the metallic enclosure potential free during the discharge of
trapped charges to ground. The reliability of an earthing switch depends on
design of the moving contact, its housing and shielding arrangement. Very fast

transient over-voltages (VFTOs) are common to such earthing switch operation
which results from rapid dielectric breakdown under severe electrostatic stresses
experienced by the insulating media (SF6) for relatively marginal operating
speeds of the earthing switch (less than circuit breaker). However these voltages
are less than the transients generated during circuit breaker and disconnector
switch operation.
Gas-insulated bus bars / conductors are enclosed in a metal encapsulation that is
filled with an insulating gas, e.g., SF6 or N2 or mixture of these gases or mixture
with any other compatible gas. With reference to Patent No. RU2523429, the
three phases are arranged in a row and enclosure dimensions increase
significantly with system voltage. In conventional arrangements, the bus of one
phase of a three-pole bus bar is made with bends and curves around the bends
of adjacent phases. Hence electrostatic field levels are quite high. Figure 1(a)
shows the conventional bus bar arrangements. Following are some of the
drawbacks with these arrangements.
1. If the three phase arrangement is in a row, the dimensions of enclosure
are quite high. Compactness of equipment is limited.

2. If the three phase of earth switches are in a row, there is a resultant
magnetic field on the grounded enclosure and may result to eddy currents
for some type of enclosure materials.
3. In the conventional right angled arrangement, current transfer takes place
through complex machined terminals, bends etc.
4. In the conventional right angled arrangement, uniform electrostatic field
levels between the phases are quite difficult to achieve because of HT
crossings across three phase conductors.
In some of the conventional earthing switches referred in EP 1 068 624 B1, US
7122758 B2 and US 20060283842 A1, the earthing switch fixed contact is in the
form of a pin-like contact piece which is mounted on a contact support and the
fixed contact assembly consists of movable contact tube, housing for fixing
contact assembly and require special shields in case of ultra high voltage
applications. The movable arcing contact and insulated current collector are
orthogonal to each other (refer Figure 1(b) and 1 (c)). The current transfer
arrangement requires loss-less contact connections to ensure for all high speed
and current applications. Hence, the present patent aims to improve the above
design features.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure
which includes a single common drive for grounding of high voltage sections of
all the three phases.
Another object of the invention is to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure
which includes a single common drive for grounding of high voltage sections of
all the three phases, in which an insulating spacer is provided to make the
metallic enclosure potential free.
A still another object of the invention is to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure
which includes a single common drive for grounding of high voltage sections of
all the three phases in which a hollow arcing contact is provided for efficient
making operation.

Yet another object of the invention is to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure
which includes a single common drive for grounding of high voltage sections of
all the three phases, wherein a profiled movable insulated plate with openings is
provided to operate against gas pressure to achieve high speed making
operation.
A further object of the invention is to propose a three phase compact gas-
insulated earthing switch with all three phases located in a metallic enclosure
where the fixed arcing contact is surrounded by high voltage shield for uniform
electric field distribution including withstanding against arcing.
A still further object of the invention is to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure,
where the fixed arcing contact is surrounded by high voltage shield tip made up
of high conductive and low erosion refractory material to work against arcing.
Another object of the invention is to propose a three phase compact gas
insulated earthing switch with all three phases located in a metallic enclosure
where the fixed arcing contact assembly is simplified by incorporating innovative
spherical connector.

A further object of the invention is to propose a three phase compact gas
insulated earthing switch, which reduces complexity of manufacturing of the
compact earthing switch assembly.
A still further object of the invention is to propose a three phase compact gas
insulated earthing switch, which reduces complexity of manufacturing of the
compact earthing switch assembly, which reduces assembly time of the compact
earthing switch assembly.
SUMMARY OF THE INVENTION
The present invention provides a reliable three phase compact earthing switch
with all three phases in single enclosure. The operation of the earthing switch is
simplified by proposing a unique spherical connector for the housing of the fixed
contact system and strategically locating three phases in the compact earthing
switch. The contact shields are arranged in such a way that they work against
arcing phenomena. The current transfer contact is insulated from the grounded
enclosure to ensure on-line measurements as and when required during service.

The present invention is enabled to achieve a high speed / marginal speed gas
insulated earthing switch to discharge the trapped charges of HV sections to
ground. The contact shields are provided in such a way that they are free from
arcing phenomena. The current transfer contact is insulated from grounded
enclosure to ensure on-line measurements as and when required during service.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention is described with the help of Figures 1 to 7, where:
Figure 1: Conventional Earthing switches.
Figure 2: Contact system of earthing shields.
Figure 3: Spherical connector with self contained shields.
Figure 4: Spherical connector with fixed arcing contact arrangement.

Figure 5: Three phase Moving contact assembly with insulator cum guide.
Figure 6: Guide Arrangement of insulated Moving plate.
Figure 7: Invented Three phase compact earthing Switch.
DETAIL DESCRIPTION OF THE INVENTION
The fixed contact [01] of the earthing switch (ES) is made of a high conductivity
material with low erosion refractory material tip held on a support insulator [02]
or spherical connector [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 FC shield [04] tip [04a] in particular
is made up of high conductive and low erosion refractory material to work
against arcing and short circuit currents. The moving arcing contact [05] is
surrounded by a moving contact shield [06], when ES is in fully open condition.

The moving arcing contact [05] is located in housing called as drive housing
[07]. The ES operation is achieved by using an insulated operating element
assembly [08, 09]. In other words, operating element [08] is isolated from the
moving arching contact [05] using a guide cum insulator [09]. The entire contact
system is insulated from the grounded metallic [06] 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 earthing switch.
A spherical shaped universal connector [03] has been designed to meet all
connection requirement of metal clad gas insulated substation equipment.
Invented spherical connector [03] is a unique component designed to cater
multiple requirements in 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 0o-90o of any orientation.
The spherical connector provides low resistance path with controlled electrical
stress around its geometry i.e., self contained shields or spherical connector
shield [03A] (refer Figure 3). The invented connector also acts as housing for
fixed arcing contact [01]. The patented spherical connector [03] profile helps in

optimal design of the contact system. Figure 4 shows the spherical connector
[03] with fixed arching contact [01] arrangement. The profile of spherical
connector [03] helps in designing cost-effective system for compact switchgear
equipment. The invented spherical connector [03] is to act as a current transfer
connector, i.e. transfers current from movable arcing contact [05] to the body of
spherical connector through fixed arcing contact [01]. The connector is self
contained and is an electrically stress relieved component. The spherical
connector [03] is also facilitated with high level cooling by means of suitable gas
flow vents. This arrangement helps in maintaining uniform temperature
distribution for the switchgear equipment. The support insulators [02] are used
to support spherical connector [03] assembly. The support insulator [02] which is
at open end gets terminated with a terminal cum shield [11].
The invention relates to a three phase gas insulated earthing switch in each
phase consists of a spherical connector [03] for extending electrical connections
in multiple directions. The moving contact [05] is plugged into fixed contact [01]
when the earthing switch is in close condition. A current collector [12] is used to
extend dynamic current transfer during the travel of movable contact. The
current collector [12] extends the dynamic current transfer of discharge/arcing

current of HV sections from fixed contact [01] to movable arcing contact [05] to
current transfer flange [13] when the movable contact [05] is about to make
contact with fixed contact (during pre-arcing time). The current transfer flange
[13] is insulated from grounded enclosure by using special insulators [14]. This
insulated current transfer flange [13] is connected to grounding grid through
grounding connectors separately. The advantage with this type of connection is
calibration of current transformers connected on either side of earthing switches
can be performed during service without opening GIS. One more advantage with
this model is that high fault current need not pass through grounded enclosures.
The moving arching contact [05] is isolated from the operating link [15], through
an insulator cum guide [09] and metallic operating element [08]. The drive
system provides the energy required for the operation of movable contact
system consists of moving arcing contact [05], insulator cum guide [09], metallic
operating rod [08], operating link [15], coupling element [16], lever arrangement
[17]. For three phase operation of the earthing switch, three numbers of
movable arcing contacts [05] are attached to a single movable insulator cum
guide [09], which in turn attached to the drive system through a single operating
link [15] and 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 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.
The insulator cum guide [09] cross section is similar to a triangular profile with
three vertices of triangle and connected to three arcing contacts [05] one side.
Other side of this insulator cum guide [09] is connected to a single operating link
[15] at the centre of the plate. The insulator cum guide [09] consists of guide
arrangement for smooth operation and is guided by metallic tube [18] located in
drive hosing [07]. Figure 5 shows three phases moving contact assembly with
insulator cum guide [09]. The metallic tube [18] has a provision of shield
arrangement to provide uniform electric field across contact system. The
insulator cum guide [09] is designed in such a way that it has suitable opening
area to avoid unwanted pressure build-up in drive housing [-7] during opening /
closing operation which otherwise affect operating speed characteristics. Figure

6 shows the insulator cum guide. The three phase contact system has been
arranged in an equivalent triangle configuration in a spherical grounded
enclosure [10]. The spherical grounded enclosure [10] is profiled in such a way
that the electrostatic field around the contact system is highly uniform. Axial
E-field is also made it uniform between moving contact shield [06] and fixed
contact shield [04] during ES is in operation. Figure 7 shows the inventive three
phase compact earthing switch. The earthing switch contact is electrically
insulated from the GIS housing and can be short-circuited with the GIS housing
via a flexible / pre-defined current transfer joint.

WE CLAIM :
1. A three phase compact gas insulated earthing switch, comprising:
- a fixed arcing contact;
- a fixed contact shield;
- a moving contact;
- a moving contact shield;
- a grounded spherical enclosure;
- an insulator cum guide; and
- an insulated current transfer flange,
wherein the fixed contact is covered by the fixed contact (FC) shield with
designed axial and annular space to control the axial field between the fixed
and moving contacts, wherein at least one each spherical connector is
provided for each phase to house the fixed contact with shield and act as a
fixed contact assembly for operation of the earthing switch, wherein the
spherical connector with self contained shields achieves uniform electric field
between the contact systems and limits radial E-field during operation of
earthing switch, wherein the spherical connectors of three individual phases
of the earthing switch are oriented at the vertices of an equilateral triangle
configuration to avoid breakdown between the phases.

2 The switch as claimed in claim 1, wherein the insulated current transfer
flange acts as a stopper for the earthing switch during its closing
operation.
3. The switch as claimed in claim 1, wherein the tip of the FC shield is made
up of high conductive and low-erosion refractory material to delimit arcing
and short - circuit currents.