FIELD OF INVENTION:
The present invention relates to a modified core clamping device for large
rating power Transformers and a method of working the device.
BACKGROUND OF THE INVENTION:
Core clamping frame of Transformer has various functions to play
simultaneously. Besides providing sufficient rigidity to transformer core, it also
retains to their position core laminations under pressurized condition and forms a
solid frame for facilitating flux flow. It also has to withstand enormous reaction
forces from windings to keep them stable during various tests and operating
conditions. This arrangement usually contains a Top End Frame and clamp plates
clamped together using tie rods, cross beams, feet etc. Enormous mass, severe
reaction forces from windings, stringent electrical clearances, handling and
transportation jerks, transportable dimensional limitations make the design of core
clamping frame of transformer very challenging especially in case of high rating
power transformers.
With the increase trend on ratings of power transformers, forces for
stabilization of windings are increased manifold. To accommodate same and
maintaining other design parameters, it became necessary to review and innovate
new core clamping device which can effectively function in afore said limitations and
also mechanically robust enough to withstand high reaction forces from windings.
Up till now in the power Transformers dash pots (2) shown in Fig-1 were
used to compress the windings for stabilization purposes. The dash pots have
limitations in applying forces for stabilizing windings. With the increased rating and
reduced losses in power Transformers the stabilization forces increased enormously

beyond dash pots capacities. In order to meet this requirement and overcoming
above limitations, it became necessary to derive a new design mechanism for core
frames of transformers. Also due to limitation in space for increasing top ring
thickness, overall economy and increased mass of copper per leg, pattern of load
transmission in windings through ring was required to be relooked so as without
increasing the thickness higher forces can be transmitted in windings uniformly in
well distributed manner. Conventional power transformer has box type top end
frames where dash pot guides are welded through which stabilization forces are
applied on windings. The wider Box End Frame creating restrictions of space for top
lead to take out from windings hence embarrassing designers to always change lead
taking out position from middle of windings. Assembling of all the dashpots and
application of pressure simultaneously is highly time consuming and need more man
power to complete the task.
In this new invention existing dash pots have been totally eliminated and
replaced with number of parallel high strength hose pipes which when pressurized
apply uniform force in windings. Thus the stabilization forces to be applied on
windings are being governed by length and pressure value in hoses i.e. higher
stabilization forces can be applied in windings with increasing length and pressure in
hoses.
Thus with the help of this newly developed core clamping device it is possible
to meet the requirement of higher stabilization forces in winding without increasing
any dimensions of transformer. Also with the reduced width of top end frame we are
able to get more space and electrical clearances. This new device can be used in all
Transformers irrespective of ratings.

OBJECTS OF THE INVENTION:
It is therefore, an object of the present invention to propose a modified core
clamping device for larger rating power transformers which eliminates the
disadvantages of the present state of arts.
Another object of present invention is to propose a modified core clamping
device for larger rating power transformers which eases the manufacturing
activities.
A further object of the present invention is to propose a modified core
clamping device for larger rating power transformers which saves manufacturing
time and manpower.
A yet further object of the present invention is to propose a modified core
clamping device for larger rating power transformers which reduces the stay losses.
SUMMARY OF THE INVENTION:
The present invention is provided with a modified core clamping devices for
large rating power transforms comprises a plurality of rectangular shaped beam
structures disposed parallely, connected by a number of cross bars along the length
and the end faces are fixed up by tie rods; and each Top End Frame is provided
with a plurality of stay bars disposed outside of the beam and stray bars are placed
on both the sides of the clamp plate; and the Top End Frames are connected to a
bottom plate by means of a plurality of clamp plates and the total assembly rest on
a numbers of bottom feets; characterized in that a number of hose pipes are placed
in between the top face of insulated covered core winding and the bottom surface of
yoke and stay arms to compress the core windings when the hose pipes are
energized, filling the gap with insulating materials on the top of each core winding
to prevent spring back of the winding.

BRIEF DESCRIPTION OF THE ACCOMPANYING
FIGURE/SKETCHES:
Figure 1— shows a photo view of a box type end frame with dash pots used for
coil pressing as per prior art.
Figure 2— shows a schematic view of a box type end frame with staying arm as
per new invention.'
Figure 3— shows an isometric schematic view of core clamping device as per new
Invention.
Figure 4— shows a schematic plan view of core clamping device
as per new invention.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION.
The core clamping device (1) comprises a plurality of top end frame (2)
disposed parallely, having joined with a plurality of cross beams (3) at top. Each Top
End Frame is provided with a numbers of staying arm (4) disposed on the outerside
of each Top End Frame (2). Each Top End Frame is a fabricated steel parts like a
beam having inside hollow throughout the length and a rectangular shaped cross
section at the end. Each Top End Frame (2) is affixed with a bottom plate (5) by a
plurality of clamp plates (6) and the bottom plate (5) with complete assembly is
supported by a numbers of Bottom feet (7). Now the total structure looks like
inverted ladder.

METHOD OF WORKING:
One core winding (8) is placed from the top of the device in between two
clamp plates (6) disposed on the two opposite sides of the device. On the top of
core winding some insulated material is placed. One core winding is placed in each
core leg disposed concentrically in between two clamp plates (6) inside the device.
After assembling windings on core legs it is necessary to compress the same
by some pressurised means from top to ensure desired performance of windings
during operation and test conditions. The forces to be applied are enormous and
depends upon the transformer ratings.
Top face of each core winding is covered with an insulating material. Above
the insulating materials, a number of parallel hose pipes are laid in flat condition in
between top face of windings and bttom surface of yoke and Stay Arm. One CRGO
laminated sheets are covered e whole system from one end to other, under the
two parallel Top End Frames (2).
After complete assembly, the hydraulic pressure is imparted in the hose pipe
which will inflate the pipe and generating a downward pressure on the top face of
the windings which in turn compressed the core windings. A gap is created in
between the top face of the winding and the bottom surface of the yoke which is
being filled up with solid insulated material to prevent the spring back reaction of
the core winding. Finally all fastening means are fixed up and release the hydraulic
pressure from the hose pipes and withdrawn those pipes from the device.

WE CLAIM:
1. A modified core clamping devices for large rating power transforms
comprises:-
— a plurality of rectangular shaped beam structures disposed parallely,
connected by a number of cross bars along the length and the end faces are
fixed up by tie rods;
— each Top End Frame is provided with a plurality of stay bars disposed
outside of the beam and stay bars are placed on both the sides of the clamp
plate;
— the Top End Frames are connected to a bottom plate by means of a plurality
of clamp plates and the total assembly rest on a numbers of bottom feets;
Characterized in that a number of hose pipes are placed in between the top
face of insulated covered core winding and the bottom surface of yoke and
stay arms to compress the core windings when the hose pipes are energized,
filling the gap with insulating materials on the top of each core winding to
prevent spring back of the winding.

2. The device as claimed in claim 1 wherein each beam structure, clamp plates
and bottom feets are made of steel materials.
3. The method of working of the device comprises

— placing the core windings on the core leg disposed between the two opposite
sides clamp plates of the device;
— placing an insulating materials on the top face of the core winding;
— placing a plurality of hose pipes on the top face of the insulating covered core
winding and the bottom face of yoke and stay arms;
— placing laminated sheets under the Top End Frames and fixed with fastening
means;

— energizing the hose pipe by hydraulic means;
— filling the gap with insulating material in between top face of core winding and
the bottom surface of yoke to prevent spring back of core winding;
Characterised in that the core windings are compressed while the hose pipes are
energized by a hydraulic means and inflates the pipes which exerts a downward
pressure on the top face of core winding and also exerts a upward thrust and the
upward trust is counterbalanced by the strength of yoke and stay arms, resulting
downward pressure compresses the core windings without any damage of the
device.
4. The modified device for core claiming device of large rating power
transformer as substantially described and illustrated herewith an
accompanying drawing.

A modified core clamping devices for large rating power transforms comprises
a plurality of rectangular shaped beam structures disposed parallely,
connected by a number of cross bars along the length and the end faces are fixed
up by tie rods; and each Top End Frame is provided with a plurality of stay bars
disposed outside of the beam and stray bars are placed on both the sides of the
clamp plate; and the Top End Frames are connected to a bottom plate by means of
a plurality of clamp plates and the total assembly rest on a numbers of bottom
feets; characterized in that a number of hose pipes are placed in between the top
face of insulated covered core winding and the bottom surface of yoke and stay
arms to compress the core windings when the hose pipes are energized, filling the
gap with insulating materials on the top of each core winding to prevent spring back
of the winding.