FIELD OF INVENTION:
The invention in general relates to a segregated GAS to Air insulated termination
of Bus PT module in GIS.
BACKGROUND OF THE INVENTION:
Potential transformer or voltage transformer gets used in electrical power system
for stepping down the system voltage to a safe value which can be fed to low
ratings meters and relays. Commercially available relays and meters used for
protection and metering, are designed for low voltage. This is a simplest form of
potential transformer definition.
Voltage transformer or potential transformer theory
A voltage transformer theory or potential transformer theory is just like a theory of
general purpose step down transformer. Primary of this transformer is connected
across the phase and ground. Just like the transformer used for stepping down
purpose, potential transformer i.e. PT has lower turns winding at its secondary.
The system voltage is applied across the terminals of primary winding of that
transformer, and then proportionate secondary voltage appears across the
secondary terminals of the PT. The secondary voltage of the PT is generally 110 V.
In an ideal potential transformer or voltage transformer, when rated burden gets
connected across the secondary; the ratio of primary and secondary voltages of
transformer is equal to the turns ratio and furthermore, the two terminal voltages
are in precise phase opposite to each other. But in actual transformer, there must
be an error in the voltage ratio as well as in the phase angle between primary and
secondary voltages. The errors in potential transformer or voltage transformer can
be best explained by phasor diagram, and this is the main part of potential
transformer theory.
In pressurized gas insulated high voltage switching installations with single or
polyphase metal encapsulation, a switchgear section comprises several adjacent
pressure tanks having gas tight partitions for accommodating the high-voltage
switchgear and other current carrying parts. The number of encapsulation tanks
is minimized by arranging the switchgear and current carrying parts belonging to
one bus bar of the section in a first pressure tank, the power circuit breakers,

work grounding switches, current transformers and section related current
carrying parts of the section are arranged in a second pressure tank and the
equipment and current carrying parts required on the terminal side of each
section are arranged in a third pressure tank.
Basic purpose of an instrument transformer is metering and protection (with the
help of protection relay). Bus PT has metering core and protection core for bus bar
protection which monitors the faults in all the buses with respect to that in a
particular substation only. It is used for under/over voltage protection and
measure for volt and synchronization time use for voltage matching. As high
voltage and currents are not measured directly. So instrument transformers are
used for this purpose. PTs step down voltages to a certain ratio. Thus, easy in
measurement of the voltages using electronic meters.
The SF6 gas used in switch-gears is used for insulation which reduces the phase
to phase and phase to earth clearance. The insulating gas used in MV GIS
switchgear, sulphur hexafluoride (SF6), is a highly potent greenhouse gas with a
global warming potential 23,900 times greater than CO2.
SF6 also has an atmospheric life of 3,200 years, so it will contribute to global
warming for a very long time.
The cutting-edge technology of epoxy insulation of live part is used as principle for
insulating the termination module.
Conventionally, each phase of the GIS has to be connected to chamber having
various pre-assembled components. This method of assembly takes long time and
may not be economical as the chamber has to be leak proof. Any leakage if found
will lead to additional rework of dis-assembly and rectification of components.
This requires significant time for assembly during manufacturing. In order to
reduce the time to arrange the assembly of enclosed chamber for cable
termination in GIS, a novel design/arrangement has been proposed. The proposed
novel design shall accommodate the chamber in a compact single go with minor
assembly points.

OBJECTS OF THE INVENTION:
It is therefore an object of the invention to reduce the assembly time of Bus PT
module in a GIS bay. It will be as simple as plug and play.
Further object of the invention to reduce SF6 gas usage in a GIS bay by
eliminating SF6 Gas filled PT enclosure.
Another object of the invention to reduce the downtime for replacement of Bus PT
Module of GIS.
SUMMARY OF THE INVENTION:
Earlier in Medium voltage Gas Insulated metal-clad Switchgears, the Bus PT
module is connected through a pressurized Chamber filled with SF6 gas and
terminated in air through Bushing and Cable Connex suitable for System Voltage
application. GIS (Gas Insulated Substation) bay consisting these modules shall go
through a variety of components required for assembly during the manufacturing
stage. It involves a lot of assembly, evacuation time, gas filling, different
configurations of modules, dismantling etc. in particular to compact GIS. The
assembly shall be generally carried on each phase of GIS module during
manufacturing and on complete GIS bay prior to dispatch to site. This
arrangement / module is pre-assembled and then mounted in the GIS Panel.
In BUS PT this termination is encapsulated in a Resin Filled Chamber comprising
of Size-2 termination on cable side and Fixed contact on Breaker side. The module
thus invented will withstand the system voltage without failure of Dielectric
strength. Thereafter providing complete sealing of SF6 gas Bus chamber from
bottom side.
The invention relates to Gas Insulated Switchgear BUS PT termination chamber
filled with Resin for PT termination in each phase.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be considered
for limiting of its scope, for the invention may admit to other equally effective
embodiments. The detailed description is described with reference to the

accompanying figures. Some embodiments of system or methods in accordance
with embodiments of the present subject matter are now described, by way of
example, and with reference to the accompanying figures, in which:
Figure 1 shows the conventional termination chamber of three phase GIS bay.
Figure 2 shows the new Compact Single phase PT termination chamber molded in
insulated material.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS:
A modified segregated GAS to Air insulated termination of Bus PT Module in GIS
that comprises collet tube with multilam joint, a BUS bar in which the modified
size 2 bushing is moulded to form a compact design.
Accordingly, a special interface unit has been designed to integrate the single
phase chamber of PT termination GIS. The connection for each phase is done with
a special fixture developed for this module.
SF6 being environmentally concerned gas as insulation, in resin moulded
insulated switch gear used as solid insulation with improved and engineered
materials which withstands the insulation level required for 36kv GIS.
The Solid Insulation provided here is for reducing the Phase to Earth clearance as
well as Phase to Phase clearances. It forms the solid mass having compact mass
with stabilized modular arrangement.
In the invention of Solid insulation of GIS PT termination as shown in Fig 2, the
bushing arrangement of Size-2 has been compacted in a moulded insulating item
in order to form a single mass. The whole insulated part is then enclosed with a
very thin layer of Aluminium (1) which is utilized in strengthening and earthing
the arrangement. The modular design thus formed is used as plug-in
arrangement for termination of PT cable. The state of art in this design is having a
single module for termination of PT Cable within the existing design.

ADVANTAGES:
1. Touch proof Plug-in fit arrangement
2. No IAC compliance required since no enclosed chamber is required.
3. Easily withdrawal and easily maintainable
4. No- leakage issues.
5. Reduction in overall size and weight of termination chamber
6. Environmentally friendly
7. Elimination of use of SF6 gas in termination chamber
8. Ease of Installation.

WE CLAIM:
1. A modified segregated GAS to air insulated termination of Bus PT module in
GIS that comprises collet tube with multilam joint, a BUS bar in which the
modified size 2 bushing is moulded to form a compact design.
2. A modified segregated GAS to air insulated termination as claimed in claim 1,
wherein the module is enclosed in a thin layer of Aluminium.
3. A modified PT termination module as substantially described and illustrated
herein with reference to the accompanying drawings.