FIELD OF THE INVENTION
The present invention relates to a double dash pot core clamping device for
pressing windings of higher rating power Transformers and a method of
working the device.
BACKGROUND OF THE INVENTION
Dashpot device is used for pressing the transformer windings during
application of stabilization force after vapor phase dry out process. It provides
stability to the winding assembly during operation of transformer and short
circuit condition.. During the process of pressing winding assembly, the
device has to withstand enormous reaction forces from the windings to keep
them stable during various tests and operating conditions. The device
comprises top end frames having dash pot and clamp plates tied together
using yoke bolts, end tie rods, cross beams and feet.
Enormous mass, severel reaction forces from winding and stringent electrical
clearances of the windings, handling and transportation jerks, transportable
dimensional limitations makes the Pressing of winding of transformer very
challenging especially in high rating power transformers.

With the increasing trend in ratings of power transformers, forces for
stabilization of the windings having increased manifold. To accommodate the
same and maintaining other design parameters, it became necessary to
review and innovate new pattern of dashpot arrangement which can
effectively function in afore said forces from the windings. According to prior
art, each limb of a transformer is pressed by four dashpots per winding
assembly.
Up till now in the power Transformers, single dash pot device (4 no each)
were used to compress the windings for stabilization purpose. The single
dash pot device has limitations (Maximum up to 160 Ton) in applying forces
for stabilizing the windings.
In order to meet the new stabilization requirement of the windings of high
power transformers, it became necessary to propose a new Pressing
mechanism for the Windings of transformers. Also limitation in space due to
increase in the diameter of the Windings, a single dash pot device (4 no each
limb) pattern for pressing of windings requires modifications and
improvement so that higher forces can be applied in the windings uniformly
in a well distributed manner.
Conventional power transformer has box type top end frames where the dash
pot guides are welded through which stabilization forces are applied on the
windings.

In this new invention, number of dash pots have been increased two times
which when hydraulically pressurized, apply uniform pressure on windings.
Thus the stabilization forces to be applied on windings are being governed by
double dash pot (8 no each) and higher stabilization forces (320 Ton) can be
applied in windings.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a double dash
pot core clamping device for higher rating power transformers, which
eliminates the limitations of the prior art.
Another object of the present invention is to propose a double dash pot core
clamping device for higher rating power transformers, which allows sustaining
of higher stabilization forces in the windings of high rating power
Transformers.
A further object of the present invention is to propose a double dash pot core
clamping device for higher rating power transformers which enhances
manufacturing capabilities and saves manufacturing time and manpower.

SUMMARY OF THE INVENTION
Accordingly, there is provided a double dash pot core clamping device for
higher rating power transforms comprising:
- a plurality of rectangular shaped beams fabricated to form an End
frame assembly, the beams being arranged parallely and connected by
a number of cross bars along the length;
- a plurality of tie rods rigidly supporting the end faces of the end frame
assembly;
- a plurality of dash pot guides provided at top end frames of said end
frame assembly;
- a bottom plate by means of a plurality of clamp plates connected to
said top end frames; and
- a numbers of bottom foot assembly holding the end frames and clamp
plate assembly wherein at least eight dash pots are provided for
pressing the windings by hydraulic press.

After assembling the windings on core legs it is necessary to compress the
same with designed forces from top to ensure desired performance of the
windings during operating and test conditions.
The forces to be applied being high and depend upon the Transformer
ratings. The adoption of appropriate force application mechanism on
windings is a real challenging task to designer. According to the invention,
eight dash pots are arranged on top of the windings and are pressed
through hydraulic jacks. Dash pots get displaced downward, thus windings
get compressed. Forces on windings are controlled by jack pressure.
Forces are transmitted through eight Dash pot point loads on the
windings.
This newly developed Double Dash pot arrangement has eliminated the
present force limitations of pressing of winding experienced by the
designers.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : shows a prior art top box type end frame having Single
Dashpot arrangement.
Figure 2 : show a typical prior art core clamping frames having single
Dashpot Arrangement.

Figure 3: shows a top box type end frame having double Dashpot
arrangement according to the invention.
Figure 4 : show core clamping frames having double Dashpot
Arrangement according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The core clamping device (1) comprises a plurality of top end frame (1)
placed parallely, having joined with a plurality of cross beams (3) at top.
Each Top End Frame is provided with a number of dashpots (2) placed on
the length of each Top End Frame (1). 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 (1) is affixed with a plurality of bottom horizontal and vertical
clamp plate (6) with complete assembly is supported by a numbers of
Bottom Foot Assembly (7).

Method of Working
One core winding (8) is placed on each limb in between two vertical clamp
plates (6) which are placed on the two opposite sides of the device. On
the top of core winding, insulated material is placed. One core winding is
placed in each core leg placed concentrically in between two clamp plates
(6) inside the device. After assembling the windings on the core legs, it is
compressed by hydraulic press from top to ensure desired performance of
the windings during operation. Above the said insulating materials on top
end frame (1) a number of dashpots (2) are welded. The winding is
pressed by the dash pots (2) through hydraulic pressure. CRGO laminated
sheets cover the whole system from one end to other extending under
two parallel Top End Frames (1). After complete assembly of the device
and the windings, the hydraulic pressure is imparted on the dash pots (2)
which generate a downward pressure on the top face of the windings
which in turn compress the core windings. Finally, the dash pots are
locked by a screw pin and fastening means are fixed up.

WE CLAIM:
1. A double dash pot core clamping device for pressing windings of high
rating power transformers, the top windings provided with an insulated
layer, the device comprising:
- a plurality of rectangular shaped beam structures placed 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 provided with four number dash pots placed
along the beam;
- the Top End Frames connected to a bottom plate by means of a
plurality of clamp plates and the assembly resting on a numbers of
bottom feets; and
- a selected number of dash pots are activated to hydraulically press the
top face insulated covered windings.
2. The device as claimed in claim 1, wherein each beams structure, clamp
plates and bottom feets are made of steel materials.

3 . A method of operating a double dash pot core clamping device as
claimed in claim 1, the method comprising the steps of :
- placing the windings on core legs disposed between the two
opposite sides clamp plates of the device;
- placing an insulating materials on the top face of the winding;
- placing laminated sheets under the Top End Frames and fixed with
fastening means; and
- pressing the windings by dash pots by a hydraulic means.

ABSTRACT

The present invention relates to a double dash pot core clamping device
for pressing windings of high rating power transformers the top windings
provided with an insulated layer, the device comprising a plurality of
rectangular shaped beam structures placed 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 provided with four number dash pots placed
along the beam; the Top End Frames connected to a bottom plate by
means of a plurality of clamp plates and the assembly resting on a
numbers of bottom feets; and a selected number of dash pots are
activated to hydraulically press the top face insulated covered windings.