FIELD OF INVENTION
The present invention relates to a method of immersion of HTSC coil assembly in liquid
nitrogen inside the double wall container for HTSC transformers.
BACKGROUND OF THE INVENTION AND PRIOR ART
HTSC transformer has a core made of conventional material. Windings are made of
superconducting material immersed in liquid nitrogen at 77K.
Superconductors developed earlier period called Low Temperature Super Conductors
(LTSC) requires liquid helium at 4.2 K for cooling. Liquid helium is expensive gas and
difficult to handle. With this reason it could not find wider acceptance for
commercialization.
With the development of high temperature super conductors in the market (HTSC),
many leading manufacturers of electrical equipments have shown a renewed interest in
application of HTSC superconductors for motors/generators, fault current limiters etc.
As it requires liquid nitrogen for cooling, which is available abundantly and easy to
handle compared to liquid helium.

High temperature superconducting transformers are one of the future areas for
application of high temperature superconductors for commercialization.
High temperature super conducting transformer is small in size, weight and volume and
more efficient. They are commercially viable for higher rating where high voltage in
variably used for bulk transmission of power.
High temperature superconductors are made of ceramic material and are available in
tape form having typical size of 4.0 mm x 0.3 mm. It does not have strength on its
own; it requires a mechanical support when formed in a coil form. Coils have to be
invariably immersed in liquid nitrogen in order to get superconducting properties.
Coils are assembled outside the container and core with the help of fixture and inserted
inside the GFRP containers.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method of immersion of
HTSC coil assembly in liquid nitrogen inside the double wall container for HTSC
transformer which eliminates the existing state of arts.
Another object of the present invention is to propose a method of immersion of HTSC
coil assembly in liquid nitrogen inside the double wall container for HTSC transformer
which helps in cooling of the transformer.
A further object of the present invention is to propose a method of immersion of HTSC
coil assembly in liquid nitrogen inside the double wall container for HTSC transformer
which also helps counter weight balancing of coil assembly due to upward buoyancy of
liquid nitrogen.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows a line diagram of the coils assembly resting on the floor of the container.
Fig.2 - shows a line diagram of coils assembly hanging from the cover of the container.
Fig.3 - shows a line diagram of coil assembly hanging from the cover and immerse in
liquid nitrogen.
Fig.4 - shows a schematic diagram of the coil assembly immersed in liquid nitrogen in a
double walled container.
SUMMARY OF THE INVENTION
The present invention relates to a method of immersion of HTSC coils assembly in liquid
nitrogen inside the double wall container for HTSC Transformer comprises one coil

assembly having tightened with a plurality of bakelite rods and nuts with the cover of
GFRP container keeping two terminals of coils outside through cover and liquid nitrogen
is poured into the inner container of GFRP container and coils assembly are suspended
from the top open end of the inner container and cover is placed in right position and
tightened with fastener with the collar surface of GFRP container.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Present invention relates to a new method of immersion of HTSC coils assembly inside
the double wall vacuum insulated GFRP container.
The top cover of GFRP container which is used to seal the container is connected to
HV/LV windings. Winding connections are also taken out from the top cover.
If windings are placed at the bottom of container the total weight of winding and its
associated components (Wc) will be borne by the bottom surface of inner container.
This total weight will be supported at the resting surface (AB) as shown in Fig.l and it
may not be distributed evenly. In contrast, if the coil is suspended from the top, the
entire coil weight is borne by top cover (CD) in Fig.2. But the process requires that coils
are immersed in liquid nitrogen. This provides an inbuilt advantage of reducing the
weight coming on top plate. The apparent loss of coils weight due to liquid nitrogen
buoyancy (Wn) is exerted upward from the bottom surface of the coil. Thereby part of
the coil weight is supported by buoyancy of liquid nitrogen and to that extent the
weight exerted on the top plate is relieved. As shown in Fig. 3, the coils are surrounded
by liquid nitrogen, the circulation is even better than that available in Fig. I i.e. bottom
support.
The method of supporting the HTSC coils of a transformer is shown in Fig.4. The HTSC
coils (5) are suspended with 6 nos. of Bakelite rods (4) from the top cover (1). The
double-wall GFRP container (7) (torroidal shape with through hole at the center)
surrounds one limb of transformer. The outer container of double-wall GFRP container
(7) is at room temperature. The HTSC coil assembly is tightened to the top plate (1)
with the help of Bakelite nut (6) outside the container. Liquid nitrogen is poured into
the inner container to a certain level wherein the suspended coils remain below the
level of liquid nitrogen. Next the coils are suspended in liquid nitrogen and cover is
placed in position of GFRP container (7) and tightened with some fasteners with the
collar surface (2) of the GFRP container (7). The apparent loss of coils weight due to
buoyancy of liquid nitrogen is exerted uniformly on the bottom surface (3) of inner
container. Rest of the weight of coils is borne by container cover, thereby sharing the
coils weight.
WE CLAIM
1. A method of immersion of HTSC coils assembly in liquid nitrogen inside the
double wall container for HTSC Transformer comprises:
- one coil assembly having tightened with a plurality of bakelite rods (4)
and nuts (6) with the cover of GFRP container (7) keeping two terminals
of coils outside through cover;
- liquid nitrogen is poured into the inner container of GFRP container (7);
- coils assembly are suspended from the top open end of the inner
container and cover (1) is placed in right position and tightened with
fastener with the collar surface (2) of GFRP container;
characterized in that the upward buoyancy force of liquid nitrogen counter
balance a part of the weight of coils assembly which relieves downward
carrying weight by the cover of GFRP container (7).
2. The method as claimed in claim 1 wherein the coils are assembled outside the
container.
3. The method as claimed in claim 1 wherein liquid nitrogen is poured into the inner
container of GFRP container (7).

4. The method as claimed in claim 1 wherein the superconductors are highly
protected from damage.

The present invention relates to a method of immersion of HTSC coils assembly in liquid
nitrogen inside the double wall container for HTSC Transformer comprises one coil
assembly having tightened with a plurality of bakelite rods (4) and nuts (6) with the
cover of GFRP container (7) keeping two terminals of coils outside through cover and
liquid nitrogen is poured into the inner container of GFRP container (7) and coils
assembly are suspended from the top open end of the inner container and cover (1) is
placed in right position and tightened with fastener with the collar surface (2) of GFRP
container characterized in that the upward buoyancy force of liquid nitrogen counter
balance a part of the weight of coils assembly which relieves downward carrying weight
by the cover of GFRP container (7).