Title of Invention	SEALED OIL FILLED TRANSFORMER
Abstract	A sealed oil filled transformer (A) comprises: main transformer tank (01), conservator (06), rollers (03) and HV/LV bushings (04), Buchholz relay (07), additional stiffness (02), pressure relief valve/vent (08) and magnetic oil level gange (09). The empty portion of the conservator (06) is filled with dry air or nitrogen after filling the transformer with oil and then sealed to achieve a trouble-free and maintenance free long service life.

Title of Invention

SEALED OIL FILLED TRANSFORMER

Abstract

A sealed oil filled transformer (A) comprises: main transformer tank (01), conservator (06), rollers (03) and HV/LV bushings (04), Buchholz relay (07), additional stiffness (02), pressure relief valve/vent (08) and magnetic oil level gange (09). The empty portion of the conservator (06) is filled with dry air or nitrogen after filling the transformer with oil and then sealed to achieve a trouble-free and maintenance free long service life.

Full Text	Field Of The Inyeotign: The present invention relates to sealed oil filled transformers and a method of making the same. These transformers are used for conversion of electric energy from one level to another for various purpose, and are of sealed construction to eliminate ingress of atmospheric moisture. Background Qt The Inventign:- For distribution and transmission of electricity from generating station to various utilities transformer is a Vital device. The transformers are generally oil filled and the oil in the transformers acts as a cooling and dielectric agent to cater to the requirement of the transformer for working at high voltages. For good service life it is required to continuously maintain the oil quality so that it carries out both the required functions effectively throughout the long service life of the transformer. The dielectric capacity of the transformer oil is dependent on the moisture content of the oil. Presence of even minute traces of moisture, above a certain level, lowers the oil dielectric property drastically even so much so that if moisture content is higher, even in parts per millions, it becomes a reason for failure of the transformer. Hence, to ensure good dielectric property of oil it is essential to maintain the oil moisture content at the acceptable level continuously during service of transformer. The second important factor is to keep a check on the sludge content in the oil. When the oil is exposed to air, the oxygen present in the air oxidizes the hydrocarbons in oil and creates heavy compounds that settle in the form of sludge in the transformer and restrict heat dissipation leading to over-heating and failure of the transformer. The third factor in oil-filled transformers to be taken care is that during its service, the transformer gets heated up when transformer has to cater for higher loads. During this period the oil also becomes hot and on heating it expands. To allow for oil expansion without causing build-up of pressure that may damage the transformer tank, transformers are provided with oil expansion chamber called conservator. The conservator is half filled with oil and the other half is kept empty, only filled with air. When the transformer is catering to higher loads the oil also heats up and expands. The expanded oil rises from the transformer oil tank and goes into the conservator. Similarly, when the load is not there, the transformer cools down, cooling the oil. Now on cooling, the oil contracts and the extra oil form the conservator goes into the transformer tank. To facilitate smooth exchange of oil, conservator is provided with a small outlet that allows the air to go from the conservator into the atmosphere, when oil heats up and expands, and lets air into the conservator when oil contracts on cooling down. The air is passed through a moisture removing device, called silica gel breather, so that only dry air goes in the conservator and moisturized air is prevented to come into contact with oil. But, this requires lot of maintenance of air-drying silica gel breather which is a cumbersome task. Even with best of efforts and practices many times moist air still comes into contact with oil due to the above arrangement and it has been always felt that the best way is to avoid contact of air with oil completely for better life of the transformer. Prior Art And Background:- At present, for sealed type of transformers, the folloWing arrangements are being used: 1. USPatent No. 5,736,915 dated April 7th, 1998 from Goedde et al. describes a hermetically sealed non-venting electrical apparatus with dielectric fluid. However, in this invention for the expansion of the dielectric fluid, expandable chamber with flexible walls is required. The practical problem faced in provision of expandable chamber with flexible walls is that the life of the expandable chamber is limited. Many times the flexible walls develop leaks and overall arrangement is costly. Whereas in the presently proposed method the metal conservator with extra space provides for simple and cost effective long term solution with none of the above problems. 2. USPatent No 6,233,198 dated February 1, 1966 from Roger F Schrader et al. describes a Hermetically sealed distribution transformer with the transformer being totally filled with dielectric fluid and sealed, allowing no extra space for expansion of dielectric fluid. This arrangement is possible only for very small ratings of transformers in the range of 100-200 VA and low voltage application of 120V 240 V since, for any larger rating the fluid volume will be such that containing the same in completely sealed chamber without any space for allowance of thermal expansion of fluid will not be feasible as it will lead to bursting of the sealed chamber. In the present proposed arrangement the transformers rated in the range of 500KVAand high voltage class of 66KV are possible. 3. US Patent No 3,544,938 dated June 12, 1969 from Elmer G Bergmann et al. describes sealed power transformers with the space for expansion of fluid in the same tank without extra conservator. In this type of transformer design the problem is that proper protection for detection of gas in case of internal transformer fault cannot be provided. Any type of fault inside a liquid a liquid filled transformer results in generation of gas and early detection of gas using gas detection relays prOVideseffective protection of transformers by early fault detection and safety from catastrophic failure of transformer that may lead to serious accident. Also, for llKV class and above the design has got limitations as the HV bushing ends inside the tank are exposed to air leading to reqUirement of expensive bushings with higher creepage. 4. In other practices, the oil filled transformers are prOVidedwith conservator and a rubber or plastic bag, filled with air, is prOVidedinside the conservator on top of the oil. The air bag then expands and contracts to take care of the change in volume of transformer fluid due to thermal expansion. However, this has a problem that the arrangement is expensive and frequently the rubber bags develop leakage due to continuous contact with hot oil and number of cycles of expansion and contraction experienced over the long service life of the transformer. This requires continuous maintenance and checking of expansion bags or membranes inside the conservators. The arrangement is more suitable for larger transformer where the fixing of air bag inside the large conservator can be made easily. But, for smaller transformer with small size of conservator, the arrangement is difficult and maintenance of rubber membrane bags is cumbersome. This problem is eliminated in the proposed arrangement where the air spaceabove the oil inside the conservator provides for expansion of oil. S. In yet another practice the transformer tank walls are made of thin steel corrugated sheet having continuous fin-like structure. The corrugations in the steel sheets are flexible so that the fins, created by the sheet corrugations are flexible and can expand and contract as the oil expands or contracts. The expansion and contraction of the corrugated sheets take care of the change in the volume of fluid during service. These type of transformers are not provided with conservator and the tank is completely sealed. But, the shortcoming in this arrangement is that the tank walls are very thin, only 1.0 to 1.2 mm, and are prone to easy damage during transportation and storage. Another problem is that during service there is a slow permanent set in the steel corrugations which requires frequent oil topping up. The thin steel walls are also not suitable for sufficient vacuum and pressure required for drying up of transformers in case of any problem at site when the transformer fault needs to be attended by opening the transformer. Further problem is that expensive differential oil and gas protection relay is required for protection, instead of simple standard buchholz relay. In the present proposed arrangement the transformer tank is made with standard sturdy steel walls which are rugged and suitable for long service in the most strenuous conditions. There is no permanent set in the extra space provided for the oil expansion in the conservator which gives trouble free operation and the transformer is fully suited to take the desired vacuum level and pressure required for processing in case any repair is required at site. Thus this present arrangement leads to a very simple and cost effective sealed transformer arrangement which gives maintenance free unattended and safe long service life to the transformer. The present invention overcomes the above mentioned drawbacks of the prior art. Objects Of The Invention:- It is therefore, an object of the present invention to prOVidea sealed oil filled transformer which does not have an expandable chamber. Another object of the invention is to provided a sealed oil filled transformer which has a long service life. A further object of the invention is to provided sealed oil filled transformer with conservator but without an air bag. A still further object of the invention is to prOVidea sealed oil filled transformer without thin walled corrugated steel sheets. Yet another object of the invention is to provide a sealed oil filled transformer which allows normal oil and gas relay protection for the transformer. Another object of the invention is to provide sealed oil transformers which have capacity of up to 1000 KVA. grief Description Of The Accompanying Drawing:- Fig. 1 shows the front view and side view of the sealed oil transformer according to the invention. The invention will now be described in an exemplary embodiment as depicted in the accompanying drawing. However, then can be other embodiments of the same inventions, all of which are deemed covered by this description. Description Of The Invention:- In the proposed invention of a sealed type of transformer (A), the arrangement is shown in the figure-1. As per the figure, the main transformer tank (01) is made in the similar fashion as the conventional oil tank with steel walls of sufficient thickness as required for suitable vacuum and pressure levels. Additional stiffeners (12), wherever reqUired, are provided. Rollers(03) and HV/LV bushings (04) are prOVIDEdon the side or top of the tank, as required. The conservator (06) is made bigger than the usual conventional conservator used in the oil filled transformers. The volume of the oil in the conservator is kept same as that required in conventional transformer, to cater for the oil expansion and contraction during the service but, the total volume of the conservator is increased. The increased volume of conservator is kept for the space for air expansion and contraction during service. The complete volume of the conservator is calculated considering the total service temperature range, the expected maximum ambient air temperature variation and the maximum change in volume of oil expected during the service under the worst of circumstances. The total conservator volume and its size is thus increased so that the pressure inside the transformer can rise only up to a pre-determined value when the oil expands on heating, due to normal loading or overload conditions. During service, when oil temperature rises, the oil expands. The air, being a gas, gets compressed and when the oil temperature falls, the oil contracts and the air in the conservator expands. The increased volume of the conservator is calculated such that during the worst of load condition also the expansion of oil gives rise to the pre-determined maximum air pressure. The air inside the larger conservator acts as a cushion and continuous exchange of air with raw atmospheric air is avoided. The conservator is connected to the tank through standard gas and oil protection relay, the buchholz relay (07). All other fittings and accessoriesare also standard and maintained as in any conventional oil filled transformer for case in maintenance/replacement. In the accompanied figure the transformer is shown with pressure relief valve, part no. 08 of figure-1, but, the same arrangement can be used with pressure relief vent also. The list of components given below gives the main components of the transformer. The empty portion of the transformer conservator is filled with dry air or with dry nitrogen after filling the transformer with oil, and then sealed to have a trouble free and Virtually maintenance free long service life. The breather or air bag inside the conservator is not required and the conservator is totally sealed. The magnetic oil level gauge (09), is SUitably fixed in the lower half of the conservator instead of in the center to monitor the oil level in conservator. we Claim: 1. A sealed oil filled transformer (A) comprising: - main transformer tank (01), - conservator (06) - rollers (03) and HV/LV bushings (04), - Buchholz relay (07) - additional stiffness (02), - pressure relief valve/vent (08) and - magnetic oil level gange (09), characterized in that the empty portion of the conservator (06) is filled with dry air or nitrogen after filling the transformer with oil and then sealed to achieve a trouble-free and maintenance free long service life. 2. A sealed oil filled transformer as claimed in claim 1, wherein said additional stiffners are provided so that the main tank (01) can withstand required vacuum pressure. 3. A sealed oil filled transformer as claimed in claim 1, wherein the magnetic oil level gange (09) is fixed in the lower half of the conservator (06) instead of at its centre to monitor the oil level in conservator. 4. A sealed oil filled transformer as claimed in claim 1, wherein the main transformer tank (01) is made with standard shut steel, eliminating thin corrugated short steel.

Full Text

Field Of The Inyeotign:
The present invention relates to sealed oil filled transformers and a method of
making the same. These transformers are used for conversion of electric energy
from one level to another for various purpose, and are of sealed construction to
eliminate ingress of atmospheric moisture.
Background Qt The Inventign:-
For distribution and transmission of electricity from generating station to various
utilities transformer is a Vital device. The transformers are generally oil filled and
the oil in the transformers acts as a cooling and dielectric agent to cater to the
requirement of the transformer for working at high voltages. For good service life
it is required to continuously maintain the oil quality so that it carries out both
the required functions effectively throughout the long service life of the
transformer.
The dielectric capacity of the transformer oil is dependent on the moisture
content of the oil. Presence of even minute traces of moisture, above a certain
level, lowers the oil dielectric property drastically even so much so that if moisture content is higher, even in parts per millions, it becomes a reason for
failure of the transformer. Hence, to ensure good dielectric property of oil it is
essential to maintain the oil moisture content at the acceptable level continuously
during service of transformer.
The second important factor is to keep a check on the sludge content in the oil.
When the oil is exposed to air, the oxygen present in the air oxidizes the hydrocarbons
in oil and creates heavy compounds that settle in the form of sludge in
the transformer and restrict heat dissipation leading to over-heating and failure
of the transformer.
The third factor in oil-filled transformers to be taken care is that during its
service, the transformer gets heated up when transformer has to cater for higher
loads. During this period the oil also becomes hot and on heating it expands. To
allow for oil expansion without causing build-up of pressure that may damage
the transformer tank, transformers are provided with oil expansion chamber
called conservator. The conservator is half filled with oil and the other half is
kept empty, only filled with air. When the transformer is catering to higher loads
the oil also heats up and expands. The expanded oil rises from the transformer
oil tank and goes into the conservator. Similarly, when the load is not there, the
transformer cools down, cooling the oil. Now on cooling, the oil contracts and the extra oil form the conservator goes into the transformer tank. To facilitate
smooth exchange of oil, conservator is provided with a small outlet that allows
the air to go from the conservator into the atmosphere, when oil heats up and
expands, and lets air into the conservator when oil contracts on cooling down.
The air is passed through a moisture removing device, called silica gel breather,
so that only dry air goes in the conservator and moisturized air is prevented to
come into contact with oil. But, this requires lot of maintenance of air-drying
silica gel breather which is a cumbersome task. Even with best of efforts and
practices many times moist air still comes into contact with oil due to the above
arrangement and it has been always felt that the best way is to avoid contact of
air with oil completely for better life of the transformer.
Prior Art And Background:-
At present, for sealed type of transformers, the folloWing arrangements are
being used:
1. USPatent No. 5,736,915 dated April 7th, 1998 from Goedde et al. describes a
hermetically sealed non-venting electrical apparatus with dielectric fluid.
However, in this invention for the expansion of the dielectric fluid, expandable
chamber with flexible walls is required. The practical problem faced in provision
of expandable chamber with flexible walls is that the life of the expandable chamber is limited. Many times the flexible walls develop leaks and overall
arrangement is costly. Whereas in the presently proposed method the metal
conservator with extra space provides for simple and cost effective long term
solution with none of the above problems.
2. USPatent No 6,233,198 dated February 1, 1966 from Roger F Schrader et al.
describes a Hermetically sealed distribution transformer with the transformer
being totally filled with dielectric fluid and sealed, allowing no extra space for
expansion of dielectric fluid. This arrangement is possible only for very small
ratings of transformers in the range of 100-200 VA and low voltage application of
120V 240 V since, for any larger rating the fluid volume will be such that
containing the same in completely sealed chamber without any space for
allowance of thermal expansion of fluid will not be feasible as it will lead to
bursting of the sealed chamber. In the present proposed arrangement the
transformers rated in the range of 500KVAand high voltage class of 66KV are
possible.
3. US Patent No 3,544,938 dated June 12, 1969 from Elmer G Bergmann et al.
describes sealed power transformers with the space for expansion of fluid in the
same tank without extra conservator. In this type of transformer design the
problem is that proper protection for detection of gas in case of internal transformer fault cannot be provided. Any type of fault inside a liquid a liquid
filled transformer results in generation of gas and early detection of gas using
gas detection relays prOVideseffective protection of transformers by early fault
detection and safety from catastrophic failure of transformer that may lead to
serious accident. Also, for llKV class and above the design has got limitations as
the HV bushing ends inside the tank are exposed to air leading to reqUirement of
expensive bushings with higher creepage.
4. In other practices, the oil filled transformers are prOVidedwith conservator
and a rubber or plastic bag, filled with air, is prOVidedinside the conservator on
top of the oil. The air bag then expands and contracts to take care of the change
in volume of transformer fluid due to thermal expansion. However, this has a
problem that the arrangement is expensive and frequently the rubber bags
develop leakage due to continuous contact with hot oil and number of cycles of
expansion and contraction experienced over the long service life of the
transformer. This requires continuous maintenance and checking of expansion
bags or membranes inside the conservators. The arrangement is more suitable
for larger transformer where the fixing of air bag inside the large conservator can
be made easily. But, for smaller transformer with small size of conservator, the
arrangement is difficult and maintenance of rubber membrane bags is cumbersome. This problem is eliminated in the proposed arrangement where the
air spaceabove the oil inside the conservator provides for expansion of oil.
S. In yet another practice the transformer tank walls are made of thin steel
corrugated sheet having continuous fin-like structure. The corrugations in the
steel sheets are flexible so that the fins, created by the sheet corrugations are
flexible and can expand and contract as the oil expands or contracts. The
expansion and contraction of the corrugated sheets take care of the change in
the volume of fluid during service. These type of transformers are not provided
with conservator and the tank is completely sealed. But, the shortcoming in this
arrangement is that the tank walls are very thin, only 1.0 to 1.2 mm, and are
prone to easy damage during transportation and storage. Another problem is
that during service there is a slow permanent set in the steel corrugations which
requires frequent oil topping up. The thin steel walls are also not suitable for
sufficient vacuum and pressure required for drying up of transformers in case of
any problem at site when the transformer fault needs to be attended by opening
the transformer. Further problem is that expensive differential oil and gas
protection relay is required for protection, instead of simple standard buchholz
relay. In the present proposed arrangement the transformer tank is made with
standard sturdy steel walls which are rugged and suitable for long service in the
most strenuous conditions. There is no permanent set in the extra space provided for the oil expansion in the conservator which gives trouble free
operation and the transformer is fully suited to take the desired vacuum level
and pressure required for processing in case any repair is required at site. Thus
this present arrangement leads to a very simple and cost effective sealed
transformer arrangement which gives maintenance free unattended and safe
long service life to the transformer.
The present invention overcomes the above mentioned drawbacks of the prior
art.
Objects Of The Invention:-
It is therefore, an object of the present invention to prOVidea sealed oil filled
transformer which does not have an expandable chamber.
Another object of the invention is to provided a sealed oil filled transformer
which has a long service life.
A further object of the invention is to provided sealed oil filled transformer with
conservator but without an air bag.
A still further object of the invention is to prOVidea sealed oil filled transformer
without thin walled corrugated steel sheets.
Yet another object of the invention is to provide a sealed oil filled transformer
which allows normal oil and gas relay protection for the transformer. Another object of the invention is to provide sealed oil transformers which have
capacity of up to 1000 KVA.
grief Description Of The Accompanying Drawing:-
Fig. 1 shows the front view and side view of the sealed oil transformer according
to the invention.
The invention will now be described in an exemplary embodiment as depicted in
the accompanying drawing. However, then can be other embodiments of the
same inventions, all of which are deemed covered by this description.
Description Of The Invention:-
In the proposed invention of a sealed type of transformer (A), the arrangement
is shown in the figure-1. As per the figure, the main transformer tank (01) is
made in the similar fashion as the conventional oil tank with steel walls of
sufficient thickness as required for suitable vacuum and pressure levels.
Additional stiffeners (12), wherever reqUired, are provided.
Rollers(03) and HV/LV bushings (04) are prOVIDEdon the side or top of the tank,
as required. The conservator (06) is made bigger than the usual conventional conservator
used in the oil filled transformers. The volume of the oil in the conservator is
kept same as that required in conventional transformer, to cater for the oil
expansion and contraction during the service but, the total volume of the
conservator is increased. The increased volume of conservator is kept for the
space for air expansion and contraction during service. The complete volume of
the conservator is calculated considering the total service temperature range, the
expected maximum ambient air temperature variation and the maximum change
in volume of oil expected during the service under the worst of circumstances.
The total conservator volume and its size is thus increased so that the pressure
inside the transformer can rise only up to a pre-determined value when the oil
expands on heating, due to normal loading or overload conditions.
During service, when oil temperature rises, the oil expands. The air, being a gas,
gets compressed and when the oil temperature falls, the oil contracts and the air
in the conservator expands. The increased volume of the conservator is
calculated such that during the worst of load condition also the expansion of oil
gives rise to the pre-determined maximum air pressure. The air inside the larger
conservator acts as a cushion and continuous exchange of air with raw
atmospheric air is avoided. The conservator is connected to the tank through
standard gas and oil protection relay, the buchholz relay (07). All other fittings
and accessoriesare also standard and maintained as in any conventional oil filled transformer for case in maintenance/replacement. In the accompanied figure the
transformer is shown with pressure relief valve, part no. 08 of figure-1, but, the
same arrangement can be used with pressure relief vent also. The list of
components given below gives the main components of the transformer.
The empty portion of the transformer conservator is filled with dry air or with dry
nitrogen after filling the transformer with oil, and then sealed to have a trouble
free and Virtually maintenance free long service life. The breather or air bag
inside the conservator is not required and the conservator is totally sealed. The
magnetic oil level gauge (09), is SUitably fixed in the lower half of the
conservator instead of in the center to monitor the oil level in conservator.
we Claim:
1. A sealed oil filled transformer (A) comprising:
- main transformer tank (01),
- conservator (06)
- rollers (03) and HV/LV bushings (04),
- Buchholz relay (07)
- additional stiffness (02),
- pressure relief valve/vent (08) and
- magnetic oil level gange (09),
characterized in that the empty portion of the conservator (06) is filled with dry
air or nitrogen after filling the transformer with oil and then sealed to achieve a
trouble-free and maintenance free long service life.
2. A sealed oil filled transformer as claimed in claim 1, wherein said additional
stiffners are provided so that the main tank (01) can withstand required vacuum
pressure.
3. A sealed oil filled transformer as claimed in claim 1, wherein the magnetic oil
level gange (09) is fixed in the lower half of the conservator (06) instead of at its
centre to monitor the oil level in conservator.
4. A sealed oil filled transformer as claimed in claim 1, wherein the main
transformer tank (01) is made with standard shut steel, eliminating thin
corrugated short steel.

Documents:

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Patent Number

272263

Indian Patent Application Number

539/KOL/2009

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

25-Mar-2016

Date of Filing

26-Mar-2009

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OFFICES AT REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	MR. RAJEEV AGARWAL	TRE, BHEL, JHANSI
2	MR. NEERAJ VARSHNEY	TRE, BHEL, JHANSI
3	MR. ANAND KUMAR SONI	TRE, BHEL, JHANSI
4	MR. BIRANCHI NAIK	TRE, BHEL, JHANSI

PCT International Classification Number

H01F27/06

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA