FIELD OF THE INVENTION
The present invention relates to a heatpipe radiator and in particular a transformer
oil cooling device based on heat pipes, which are compact occupying lesser space
and reliable in operation with minimum maintenance in comparison to the bulky
radiator units conventionally used in the power transformers.
BACKGROUND OF THE INVENTION
According to the prior art, the transformer oil is cooled in radiator units disposed
on the transformer wherein the top and bottom headers are connected to multiple
flute fin elements as show in figure 1. The transformer oil enters the radiator from
the top header, passes through the flutes of the radiator elements, gets cooled by
transfer of heat by conduction and convection to the surrounding air. Normally
there are three modes of operation namely 1) ONAN (Oil Natural and Air Natural)
2) ONAF (Oil natural and Air Forced) and 3) OFAF (Oil Forced and Air Forced) for
cooling the transformer. Under the natural circulation mode (ONAN) the driving
force is due to the thermosiphon effect created by the density difference between
the columns on the transfer side and radiator side. The available head is

low and depends on the height of the columns and the difference of the height of
the radiator is low and depends on the height of the columns and the difference of
the height of the radiator and the transformer. To improve the circulation rate, the
pressure loss due to flow is kept low by providing large cross sectional flow areas
and hence the oil flow is normally laminar. Thus the sizes of the prior art radiators
are bulky. Further, the flow of oil from the radiator elements is not uniform due to
low thermosiphonic heads, particularly the performance of the farthest element is
low, which causes the average heat transfer coefficients to be low. Hence, there is
a need to develop compact, cost effective and efficient radiator for cooling the
transformer oil.
The non-patent literature entitled Technology of application of heat pipes to oil
filled transformers' authored by Mr Hirakawa Koichi of M/s Matsushita Industrial
Equipment Co Ltd, Japan, teaches a basic structure, performance of heat pipes
and designs requirements of heat pipe cooling system as applied to oil filled
transformers. The author has applied a heat pipe cooling system for a 300 kVA oil
filled transformer, and concluded that the heat pipe cooling system could achieve
40% saving in space, reduce the quantity of oil, simplify the manufacturing
process and reduce the cost of the container. According to this prior art, a low
boiling and high-pressure working fluid (R134a) is used in the heat pipes for
cooling the transformer oil. The pressure of the working fluid at 90 deg C is about
31 bar, which necessitates the use of thick walled heat pipes for reducing the heat

transfer rates. The heat pipes are directly immersed into the transformer tank
because of it accessibility for maintenance, which however, makes the
isolation/replacement of the defective heat pipe difficult.
WO/2007/104190 dated 20/09/07 entitled 'Transformer using separating heat pipe
for radiating heat", by Mr ZENG and Mr SUN of China as shown in figure 2
discloses a transformer (1) using a separating type heat pipe for radiating heat,
and includes a transformer member, a separating type heat pipe and heat
exchanger (2). An oil box (4) of the transformer (1) is connected with a heat
source box (5) of the heat exchanger (2). The transformer oil (6) is the heat
source of the heat exchanger (2), and a heat gatherer (7) of the heat exchanger
(2) is the heat absorber of the separating type heat pipe, and wherein the heat
absorbing medium of the heat gathered is the working liquid of the heat pipe. The
heat absorbing medium of the heat gatherer (7) absorbs the heat from the
transformer oil (6) and produces steam, and the steam (8) is transmitted to the
heat radiator (2) via a steam transmitting pipe and condensed in liquid after
radiating the heat. The liquid condensate returns to the heat absorber (7) via
liquid returning pipe under the gravitational force and then a circular process of
heat absorbing, heat radiating, evaporation, condensation, steam transmitting and
liquid returning is repeated to realize the purpose of transmitting the heat of the
transformer to the heat radiator (2).

The prior art of Figure 2 discloses a loop typed heat pipe wherein the evaporating
medium (water) absorbs heat from the oil (6) from the conducting walls of the
heat source box (5) and forms steam, condenses in the heat exchanger (2) and
returns to the evaporating chamber (9). According to the configuration disclosed in
prior art, its is difficult to provide adequate heat transfer area for the power
transformers with few hundred kW of heat dissipation rates. Furthermore the
configuration is not modular for ease of fabrication, transport, erection,
commissioning and maintenance.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved Heat pipe
Radiator Device for cooling transformer oil, which eliminates the disadvantages of
prior art.
Another object of the invention is to propose an improved Heat pipe Radiator
Device for cooling transformer oil, which is compact and reduces the installation
space on the transformer block.
A further object of the invention is to propose an improved Heat pipe Radiator
Device for cooling transformer oil, which is efficient and reduces maintenance
efforts.

SUMMARY OF THE INVENTION
Accordingly, there is provided a heat pipe radiator comprising a radiator tank, a
plurality of copper heat pipes, several aluminum cooling fins, and a cooling fan
attached to the unit.
The improved heat pipe radiator device is modular in design, which is externally
attached to the transformer block and facilitates easy maintenance.
The radiator tank is a double walled cylindrical tank made of metal sheet. The
transformer oil from the transformer tank flows through a space between of the
two shells of the radiator tank. The radiator tank is provided with a first nozzle at
the top, through which the transformer oil enters, and gets cooled while passing
down over the heat pipes and then returns to the transformer tank through a
second nozzle provided at the bottom of the radiator tank.
The immersed heat pipes transport bulk quantities of heat from the oil to the
atmospheric air through the cooling fins by the latent heat of vaporization of the
working fluid. Thus, the transformer oil is not required to flow through the narrow
flute passages as in the case of the conventional radiators. Due to the innovative
configuration, the performance of the heat pipe radiator device is high under
different conditions. For example, in Oil Natural and Air Natural (ONAN), Oil
Natural and Air Forced (ONAF, Oil Forced and Air Forced (OFAF) conditions, the
heat pipe radiator is efficient under different modes of operation such as natural
and forced circulation of oil and air through the radiator.

According to the invention, fabricated copper heat pipes are immersed in the
transformer oil contained in the space between the two walls of the radiator tank.
About 80% of the total length of the heat pipes is immersed in the oil of the
radiator tank and the remaining portion, which constitutes a condenser part, is
projected out of the tank.
Aluminium fins are attached to the condenser part of the heat pipes above the
radiator tank for extracting heat from the transformer oil and dissipating to the
surrounding air.
A cooling fan is provided on the radiator tank for sucking air through the cooling
fins to collect the heat and release into the atmosphere.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the side and front view of a prior art Radiator used in power
transformers.
Figure 2 shows a loop-type heat pipe radiator device of prior art.
Figure 3 shows the elevation and plan view of the improved heat pipe radiator
device mounted on a transformer block for cooling the transformer oil.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
In figure 3, a preferred embodiment of the present invention is illustrated.
The heat pipe radiator device consists of a double walled cylindrical tank (1) made
of metal sheet. The transformer oil flows through an annular space between the
two shells of the radiator tank (1). The radiator tank (1) is provided with a nozzle
(7) at the top of the tank through which the transformer oil enters, gets cooled
while passing down over the fabricated heat pipes (2) and then returns to a
transformer tank (9) through a second nozzle (8) provided at the bottom of the
tank (1). The annular space between the two tanks is closed with a bottom flange
(5) at the bottom, whereas a top flange (6) with threaded nipples is welded at the
top of the radiator tank (1).
A plurality of fabricated copper heat pipes (2) are immersed in the transformer oil
contained in a space between two walls of the radiator tank (1). About 80% length
of the heat pipes (2) are immersed in the oil of the radiator tank (1) and the
remaining portion, which constitutes a condenser part of the heat pipes (2) is
projected outside the tank (1).

A plurality of aluminium cooling fins (3) are fixed to the condenser part of the
heat pipes (2) above the radiator tank (1) for extracting heat from the transformer
oil and dissipating to the surrounding air.
A cooling fan (4) is provided on the radiator tank (1) for sucking air through the
cooling fins (3) to collect the heat and release the heat into the atmosphere.
ADVANTAGES OF THE INVENTION
1. The heat pipe radiator device reduces the volume/space required for
installation of transformer oil cooling system.
2. The weight of the heat pipe radiator device is reduced by over 50% in
comparison to the conventional radiator.
3. The total quantity of transformer oil required for the transformer when
operated with heat pipe radiator devices of the invention is reduced by about
30% in comparison to conventional radiators.
4. The reliability of the heat pipe radiator is improved as the welding length of the
heat pipe radiator tank is about 1/10 of the conventional radiator.

WE CLAIM:
1. An improved Heat pipe radiator device for cooling transformer oil, comprising:
a radiator tank; a plurality of copper heat pipes; a plurality of aluminium
cooling fins, and a cooling fan; wherein:
the radiator tank is formed as a double walled cylindrical tank made of metal
sheets with a space between the tank walls to allow the transformer oil to flow
through the space, the radiator tank being provided with a first nozzle at the
top for ingress of transformer oil so as to get cooled during passage, a second
nozzle at the bottom returning the transformer oil to the oil tank of the
transformer;
the plurality of copper heat pipes filled with water, which acts as working fluid,
are immersed in the transformer oil contained in the space between the two
walls of the radiator tank, a first part of the plurality of tubes is immersed in
the oil of the radiator tank and a second part acting as a condenser portion
projects out of the tank;
the plurality of aluminium fins are attached to the condenser part of the heat
pipes above the radiator tank for extracting the heat from the transformer oil
and dissipating the heat to the surrounding air;

the cooling fan is provided on the radiator tank above the cooling fins assembly
for sucking air through the cooling fins so as to collect the heat and release
into the atmosphere.
2. The device as claimed in claim 1 wherein 20% of the total length of the
tube bundle is projected out of the tank.
3. The device as claimed in claim 1 or 2, wherein the tube bundle is enabled to
collect and transmit bulk of the heat from the transformer oil by latent heat of
evaporation of the working fluid in the heat pipes and release to the
atmosphere through the cooling fins.
4. The device as claimed in claim 1, wherein the device is modular in design
so as to be attachable to the transformer block for cooling the transformer oil,
and wherein a plurality of the device can be attached to the transformer block
depending on the heating load.
4. The device as claimed in claim 1, wherein the heat pipes are individually
inserted into the radiator tank with the cooling fins fixed on to it.

ABSTRACT

The present invention relates to an improved Heat pipe Radiator device for
cooling transformer oil, comprising, a radiator tank; a plurality of copper heat
pipes; a plurality of aluminium cooling fins, and a cooling fan; wherein, the
radiator tank is formed as a double walled cylindrical tank made of metal sheets
with a space between the tank walls to allow the transformer oil to flow through
the space, the radiator tank being provided with a first nozzle at the top for
ingress of transformer oil so as to get cooled during passage through a second
nozzle at the bottom, the second nozzle returning the transformer oil to the oil
tank of the transformer; the plurality of copper heat pipes filled with water which
acts as working fluid are immersed in the transformer oil contained in the space
between the two walls of the radiator tank, a first part of the plurality of tubes is
immersed in the oil of the radiator tank and a second part acting as a condenser
portion projected out of the tank; the plurality of aluminium fins are attached to
the condenser part of the heat pipes above the radiator tank for extracting the
heat from the transformer oil and rejecting the heat to the surrounding air; the
cooling fan is provided on the radiator tank above the cooling fins assembly for
sucking air through the cooling fins so as to collect the heat and release into the
atmosphere.