FIELD OF THE INVENTION
Present invention relates to transmission lines bus conductors and more
particularly to an improved structure for handling gas insulated transmission
lines at very high voltages.
BACKGROUND OF THE INVENTION
In electrical engineering, bus bars and bus ducts are used for power
transmission. The bus duct used to transmit power over long distances or to
connect high and extra high voltage equipment with switchyards are made up
of straight circular pipes with conductors running inside them. The design is
bulky and causes difficulty in handling at sight during installation.
The bars and ducts have wide application in connecting high voltage equipment
at electrical switchyards such as in Gas Insulated switchgear where bus duct is
filled with SF6 gas making the outer tube immune to high voltage.
Previously there was no concept of using a conical casing in bus duct. It
generally comprised of tubular hollow cylindrical outer sheath.
US patent US4415763A teaches a Gas-insulated transmission line having
improved outer enclosure. In this patent, straight enclosure has been used.
US patent US3610947A teaches an encapsulated gas insulated high voltage
line. In this patent, they have claimed to use a tubular jacket as an outer
sheath. Further, US Patent US3585270A teaches a cylindrical outer conductor.
However, these designs disclosed in prior arts are bulky and cause difficulty in
handling at sight during installation.

Therefore, there is a dire need to develop a compact design having light weight
to provide easy installation to overcome technical problem existing in the prior
art.
OBJECT OF THE INVENTION
It is therefore one of the objective of the present invention to overcome one
or more of the above problem existing in conventional gas insulated
transmission lines.
Another primary object of the present invention is to propose a compact design
of bus duct casing.
Yet another object is to provide an optimized design of bus duct that could
meet the latest technical and environmental aspects of SF6 gas usage.
Still another object is to provide an optimized design of bus duct that could
lead to cost saving of raw material.
Yet another object is to design a metal casing which could ensure solid Electro-
Mechanical encapsulation of the bus conductor for Switchgear application at
extra high voltage rating.
These and other object of the present invention will be apparent to those skilled
in the art after considering the detail description in conjunction with the
accompanying drawings in which a preferred form of the present invention has
been illustrated.

SUMMARY OF THE INVENTION
One or more drawbacks of conventional arts for providing a compact bus bars
and bus ducts to be used in gas insulated switch gear with easy installation
procedure are overcome, and additional advantages are provided through the
present invention as disclosed. Additional features and advantages are realized
through the technicalities of the present disclosure.
The present invention discloses a conical shaped gas insulated transmission
line comprising of a non-magnetic outer sheath (001) which is at ground
potential encapsulating a non-magnetic inner conductor (002) which is at high
voltage held horizontal and concentric to the outer casing by means of
insulating barriers (003) and their conductors. The constituent of gas used for
insulation include Nitrogen with a proportion of SF6(Sulfur Hexafluoride)
wherein the minimum allowable proportion being 10% SF6 and 90% Nitrogen.
However, the percentage of SF6 may vary from 10% to 100%. The outer
metallic casing has conical shape to achieve compactness by reducing overall
diameter of the long cylindrical casing.
Various objects, features, aspects and advantages of the present invention will
become apparent to those skilled in the art from the following detailed
description when taken in conjunction with the accompanying drawings in
which like parts are designated by like numerals.
It is to be understood that the aspects and embodiments of the disclosure
described above may be used in any combination with each other. Several of
the aspects and embodiments may be combined to form a further embodiment
of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features
described above, further aspects, embodiments, and features will become
apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrate a conical shaped gas insulated transmission line according to
the present invention.
Figure 2 illustrate the schematic diagram conical shaped gas insulated
transmission line held horizontally according to the present invention.
DETAIL DESCRIPTION OF THE INVENTION
The embodiments as described below are exemplary means to describe the
invention and may subject to various modifications in alternate form falling
within the scope of the invention.
Drawings as illustrated are for explaining details of the present disclosure in
pertinent way and could be easily understood by person ordinarily skilled in the
art.
Referring to one of the embodiments fig.1 is a conical shaped gas insulated
transmission line comprising of a non-magnetic outer sheath (001) which is at
ground potential encapsulating a non-magnetic inner conductor (002) which is
at high voltage held horizontal and concentric to the outer casing by means of
insulating barriers (003) and their conductors. The gas insulated transmission
lines wherein the gas used is Nitrogen with a proportion of SF6(Sulfur

Hexafluoride) wherein the minimum allowable proportion being 10% SF6 and
90% Nitrogen. However, the percentage of SF6 may vary from 10% to 100%.
The outer sheath or the outer casing is a metallic casing and conical in shape.
The purpose of the conical shape is to reduce the overall diameter of the long
cylindrical casing.
However, a minimum clearance is required to be maintained between the outer
casing (001) and the inner conductor (002). This can be done by modifying
design of the outer casing in order to achieve more compactness. The overall
outer diameter can be reduced by tapering it to form a conical shape. In the
present invention, the clearance is determined by dimensions of support
insulator. Further insulated gas without any support insulator, used in the
instant invention exhibit better dielectric strength compared to the
conventional ones. Hence, the present transmission line has been structured
in a way where insulator is kept in conical section thereby reducing the
diameter of non-conical section in which only SF6 or mixture of SF6+N2 gas
used to insulate central bus bar.
Referring to another embodiment fig. 2 is a schematic diagram of conical
shaped gas insulated transmission lines held horizontally.
Today material cost and compactness are essential parameters in competitive
world. In the present invention, the optimization of the physical parameters is
possible through the conical design of the bus duct which resulted in cost
saving in terms of material used, simultaneously achieving overall
compactness.

The conical design provides better strength and support to the inner conductor
which is being disposed with the outer casing.
The present invention is a design to achieve reduction in overall volume of the
casing in terms of gas used, thus substantially reducing the amount of SF6 gas
used to achieve the insulation.
Bus bars and bus ducts are used for power transmission with voltage ranging
from 72.5kV to 1200kV and rated current up to 8000 A. They can also be used
to connect high voltage equipment at electrical switchyards.
Therefore, the present invention has got wide application in power
transmission where very high voltages are handled. In Gas Insulated
Switchgear, bus duct mainly consists of two concentric tubes, outer casing
generally made up of Aluminium alloy or seamless stainless steel pipes. The
inner tube is a circular conductor made up of electrical grade of Aluminium
which runs inside the outer casing and are held concentric to outer pipe by
means of epoxy resin insulators. This bus duct system is filled with Sulphur
hexafluoride gas or mixture of Sulphur hexafluoride gas and nitrogen gas which
act as a dielectric medium which make the outer tube of this arrangement
immune to high voltage.

WE CLAIM:
1. A gas insulated transmission line comprising of:
- a non-magnetic outer sheath (001) which is at ground potential ;
- a non-magnetic inner conductor (002) which is at high voltage
encapsulated by said outer sheath, held horizontally and concentrically
to said outer casing by means of insulating barriers (003) and their
conductors,
. wherein said outer sheath (001) is a conical shaped metallic
casing with reduced overall diameter of the long cylindrical
casing;
. wherein at least one of SF6 or mixture of SF6+N2 gas used for
insulation of central bus bar; and
. wherein a minimum clearance, decided based on physical
dimensions of support insulator, is maintained between said
outer sheath (001) and said inner conductor (002).
2. The gas insulated transmission line as claimed in claim 1, wherein the outer
sheath (001) is made up of Aluminium alloy or seamless stainless steel
pipes.
3. The gas insulated transmission line as claimed in claim 1, wherein said inner
conductor (002) is made up of electrical grade of Aluminium which runs
inside the outer casing, and are held concentric to outer pipe by means of
epoxy resin insulators.

4. The gas insulated transmission line as claimed in claim 1, wherein the bus
bars and bus ducts are operable under voltage ranging from 72.5kV to
1200kV with rated current up to 8000 A.