FIELD OF THE INVENTION:
The present invention relates to system and method for controlling over heating
of Low Voltage (LV) side bushing mounting turrets, pads & tank cover due to
stray loss in higher rating power Transformers.
BACKGROUND OF THE INVENTION:
A bushing is an insulated device that allows an electrical conductor to pass
safely through an (usually) earthed conducting barrier such as the wall of a
transformer and mounted in steel structure housing called turret. During flow
of current through bushing, stray loss produced due to eddy current which can
result in over heating of structural component and affect the life of
transformer.
In the low power rating transformer, turrets, pads and part of tank cover are
made of structure steel having magnetic property and bushings are placed on
single rectangular turret. Due to low intensity of eddy current, stray loss is
limited and overheating phenomenon of structure components not happened.
As the transformer power rating increases, the current on the low voltage side
increase. This leads to increase in the eddy current in the structures that
surrounds the bushings (e.g. turrets, pads, and tank cover).
Size of large rating transformer is also limited due to transport constraint.
Hence, the magnitude of stray field area on the structure parts increases much
faster with growing rating of transformers.
With the increasing trend in ratings of power transformers, currents on low
voltage side have increased manifold. To accommodate the same and
maintaining other design parameters, it became necessary to review and
innovate new design of turret and tank cover arrangement which can effectively
function in afore said high current from the windings and subsequently
eliminate over heating due to stray loss. According to prior art, all the bushings
of low voltage side are mounted on single rectangular turret of magnetic
structural steel and also tank cover and pad are made from magnetic

structural steel. Electrical Clearances between bushing and turret are kept as
per prevailing practice.
In order to meet the high current requirement from the windings of large rating
power transformers, it became necessary to propose a new system and method
for controlling over heating of Low Voltage side structure components (e.g.
turret, pads and tank cover).
OBJECTS OF THE INVENTION:
It is therefore an object of the invention to propose a new system and method
for turrets and tank cover for higher rating power transformers, which
eliminates the limitations of the prior art.
Another object of the invention is to propose a new system and method for
turrets and tank cover for higher rating power transformers, which allows
sustaining of high currents generated in the windings of high rating power
transformers.
Another object of the invention is to propose a new system and method for
turrets and tank cover for higher rating power transformers which defined
clearances between bushing and turret.
A further object of the invention is to propose a new system and method for
turrets and tank cover for higher rating power transformers which enhances
manufacturing capabilities and increase reliability of the transformer.
SUMMARY OF THE INVENTION:
Accordingly, to alleviate the drawbacks of the prior art, a number of turrets has
been increased to accommodate individual bushings and shaped changed from
rectangular to circular or oval. Material of turret, pads and associated tank
cover area changed to non- magnetic stainless steel. Moreover, clearances
between bushing and turret are redefined. With this, overheating of structural
components are eliminated completely.

A system is provided for turrets, pads and tank cover for higher rating power
transformers comprising: a numbers of circular or oval shaped turrets to house
low voltage side bushings; non-magnetic stainless steel material for turret
housing; Non-magnetic stainless steel material for tank cover and pads;
clearances between bushing and turret is redefined; after assembling the
transformer with core and winding on bottom tank, top tank cover is fitted.
Turrets are mounted on the pads provided on tank cover. Material of turrets,
pads and part of tank cover is non-magnetic stainless steel.
Computation of stray losses is difficult manually because transformers are
asymmetrical and of three dimensional structures. Hence FEM analysis is
required to simulate complex electromagnetic structure of transformer for
control of stray loss and elimination of hot spot.
FEM analysis is a tedious process for each and every transformer. Hence, the
proposed system and method is useful to address over heating problem of
turrets, pads and tank cover for higher rating power transformers.
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 a rectangular common turret made of magnetic structural steel
in accordance to the prior art.
Figure 2 shows a typical transformer fitted with rectangular common turret in
accordance to the prior art.

Figure 3 shows circular or oval individual turret arrangement according to the
invention.
Figure 4 shows transformer fitted with circular or oval individual turret
arrangement according to the invention.
Figure 5 shows current density distribution in the turret in accordance to the
invention.
Figure 6 shows temperature distribution in the turret in accordance to the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:-
The top tank cover (05) and its pads (07) for circular shaped turrets (03) are
made of non-magnetic stainless steel. The turrets (03) are placed on Pads (07)
welded on tank (06) and rim bolts are tightened to get leak- proof joint,
LV Bushings (01) are fitted in circular shaped turrets (3) with designed
clearances and connections are done through inspection cover (04). Bus duct
assembly are fitted on flange (02) at site.
Method of Working
LV turret heating takes place due to effect of large current carrying conductors
passes through the turret and connect LV bushings mounted on the turret to
LV coil of transformer.
The large current carrying LV busbar produces surrounding flux and this
generate good amount of circulating currents in adjacent magnetic steel plates
of LV Turret. This induced circulating currents cause heat generation and
overheating of LV turret body. In the rectangle shaped LV turret, the circulating
current is concentrated on corners of rectangle which leads to dangerous
overheating.
In new circular corner shaped LV turret, the circulating current is uniformly
distributed as shown in Figure 5, hence no current concentration in the turret.

Also, the LV Turret body is made of non-magnetic stainless steel plate grade-
316, which decreases the flux linkage with it. The clearance between LV
current carrying conductors and surrounding LV turret body also increases.
Above new design methodology substantially reduced the temperature of LV
turret body and observed temperature is in normal range of 80°C as shown in
figure 6.

WE CLAIM:
1. An apparatus for controlling over heating of Low Voltage (LV) side bushing
mounting turrets, pads & tank cover due to stray loss of higher rating power
transformers, the apparatus comprising:
- plurality of circular shaped turrets (3) to house low voltage side
bushings;
- non-magnetic stainless steel material for turret housing;

- non-magnetic stainless steel material for tank cover and pads;
- wherein the clearances between bushing and turret are provided;
- wherein the circular turret (3) uniformly distributes the circulating
current, thereby avoiding overheating of the turret-body.
2. An apparatus as claimed in claim 1, wherein as illustrated in the
accompanying drawings.