FIELD OF INVENTION
The present invention relates to an improved arrangement of directed oil flow
(DOF) for efficient cooling of transformer.
BACKGROUND OF INVENTION
Transformer is an equipment that helps in stepping up or stepping down of
voltages in the transmission line. The major components of transformer are:
1. Core made up of CRGO steel.
2. Concentric windings made of copper.
With increase in ratings, the copper loss and iron loss become important criteria
for designing of transformer. As these losses are ultimately converted into heat,
the oil inside the transformer gets heated. This heat results into temperature rise
of the oil and may lead to decomposition of oil and aging of insulations leading
to deterioration of dielectric strength. The cumulative effect may lead to failure

of transformer. The solution is to transfer heat through some media or circuits
and get it cooled within the prescribed limits.
In old scheme, the oil is forced into winding through the curvature made in
bottom tank known as directed oil flow (DOF) hole (1), as shown in the figure 1.
This hole size may vary as per required quantity of oil to be forced into the
winding. As such the core and end frame assembly (2) becomes the integral part
of bottom tank (3). The coil assembly is kept on tank flange.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose an improved arrangement of
directed oil flow (DOF) for efficient cooling of transformer which is capable of
transferring heat from the heated oil in the transformer to a cooled oil.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.l - Shows the arrangement of transferring oil to the winding through
Direct oil flow (DOF) hole in bottom tank.

Fig.2 - Shows the oil being forced into winding by a pipe assembly
carrying the cooled oil and attached to the endframe flange on one
side and to the tank on the other side.
Fig.3 - Shows an arrangement of the pipe structure to the endframe.
Fig. 4 - Shows the pipe with its Flange and endframe flange
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in fig.2, in the present invention, DOF (5) is part of the core and
endframe assembly (2). In this scheme, the oil is forced into winding by a fixture
known as pipe assembly (4) that carries the cooled oil from the tank into
winding.
In this arrangement, the pipes are detachable. So assembling of end frame and
its isolation test can be carried out independently. The size of the pipe is 200 NB
and its flange is attached to the end frame flange (2) on one side and to the
tank wall (6) on the other side. One important aspect of the pipe is it does not

extend directly to the tank wall rather a gap of 30 mm is kept between the pipe
extending from tank and the pipe coming from end frame assembly. Later on
these are assembled by aligning the two pipes and then kept in straight position
by wrapping sealing cover made of cork gasket followed by P'BD sheet and then
tightening with heat shrinkable tape. In this way the direction of flow of oil is
kept straight and there is no leakage from gap.
The advantages of the present invention over the prior art are as follows:
1. The active part assembly of transformer does not have to wait for bottom
tank. As such the active part is made independent saving considerable
waiting time.
2. The possibility of iron particle during shot blasts available in bottom tank
is avoided by not having it as part of the tank structure. It helps in making
the transformer life healthier and longer.
3. Since there is no jack arrangement to engage the locking pin of clamp
plate, where the chance of failure in isolation is often observed, the
success rate of isolation test is enhanced.
4. The cold oil is flown inside the winding through the simple pipe structure
(4) which is detachable.

5. The detachable pipe structure (4) is the part of end frame (2). The
advantage is that it can be cleaned independently for any type of dust,
iron shots or impurities present.
6. It helps in increasing the overall productivity of the transformer product.
7. It is the simplest and the most effective way of cooling winding assembly
of transformer.
8. The chances of presences of impurities, dust or shot blast reduced
considerably.
9. The chances of passing the isolation test increases by 50%.

WE CLIAM
1. An improved arrangement of directed oil flow (DOF) for efficient cooling of
transformer comprising:
disposing directed oil flow holes (5) as part of core and end frame
assembly (2);
fixing a detachable pipe assembly fixture (4) to a end frame (2)
with its flange (7) being attached to the end frame flange (8) on one side
and to the tank wall (6) on the other side;
allowing a gap between the pipe extending from tank and the pipe
coming from end frame assembly;
assembling and aligning the pipe assembly in a straight position by
wrapping sealing cover;
tightening the assembly with heat shrinkable tape while the
direction of flow of oil is kept straight without any leakage from gap when
the pipe assembly carries the cooled oil from the tank into winding.
2. An arrangement as claimed in claim 1, wherein the size of the pipe is 200
NB.

3. An arrangement as claimed in claim 1, wherein a gap of 30mm is kept
between the pipe extending from tank and the pipe coming from end
frame assembly.
4. An arrangement as claimed in claim 1, wherein the wrapped sealing cover
is made of cork gasket followed by P'BD sheet.

ABSTRACT

The invention relates to an improved arrangement of directed oil flow (DOF) for
efficient cooling of transformer. The arrangement comprises of disposing
directed oil flow holes as a part of core and end frame assembly and fixing a
detachable pipe assembly fixture (4) to a end frame (2) with its flange (7) being
attached to the end frame flange (8) on one side and to the tank wall (6) on the
other side. A gap is allowed to exist between the pipe extending from the tank
and the pipe coming from end flange assembly. The pipe assembly (4) is
assembled and aligned in a straight position by wrapping sealing cover and the
assembly is tightened with heat shrinkable tape. The direction of flow of oil is
kept straight without any leakage from gap when the pipe assembly carries the
cooled oil from the tank into winding.