FORM 2 THE PATENTS ACT, 1970
(39 of 1970) As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF INVENTION
Method and device for making oil impregnated paper insulation transformer
INVENTORS
Dr Raghavan Venkatesh, Dhasal Anil and Wakode Deelip, all Indian nationals and all of Crompton Greaves Ltd, Switchgear-6 & Power Quality Business, D2, MIDC, Waluj, Aurangabad 431136, Maharashtra, India
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, Dr Annie Besant Road, Worli Mumbai 400025, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to method and device for making oil impregnated paper insulation transformer.
BACKGROUND OF INVENTION
An oil impregnated paper insulation transformer such as current or voltage transformer, power transformer or distribution transformer generally comprises a core coil assembly located in a leak tight metallic tank filled with oil. The coil comprises a plurality of conductor windings and electric insulation paper layers interposed between the conductor windings. The method of making the transformer includes the steps of drying the insulation paper layers and impregnating them with oil prior to filling the tank with oil. A typical device for drying and oil impregnating the transformer comprises a top loading type metallic chamber which is externally thermally insulated and provided with a heating system, a vacuum system and an oil impregnation system. The heating system comprises a heat exchanger for heating a thermic fluid and an arrangement for introducing the vapours into the chamber and collecting the condensate formed due to heat transfer. The vacuum system includes a vacuum pump connected to the chamber. The method of drying and oil impregnating the transformer comprises the following steps:
(i) loading the transformer in the chamber from the top of the chamber; (ii) heating the transformer with thermic fluid at 100 - 110°C for a predetermined period of time, typically 18 to 20 hrs;
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(iii) heating the transformer with thermic fluid at 100 -110°C under vacuum of 60
mbar to 50 mbar for a predetermined period of time, typically 6 to 8 hrs;
(iv) heating the transformer with thermic fluid at 100-110°C for a predetermined
period of time, typically 6 to 8 hours; (v) heating the transformer with thermic fluid under vacuum of 50 mbar to 25
mbar for a predetermined period of time, typically 6 to 8 hours; (vi) heating the transformer with thermic fluid at 100-110°C under vacuum of
0.08 mbar to 0.05 mbar for a predetermined period of time, typically 24 to 26
hrs; (vii) cooling the transformer with thermic fluid to 50 to 60°C under a vacuum of
0.08 mbar to 0.05 mbar; (viii) oil impregnating the transformer under a vacuum of 1.2 mbar to 1.0 mbar; (ix) allowing the transformer to cool down to ambient termperature; and (x) unloading the transformer from the top of the chamber.
Generally the chamber is large to accommodate a plurality of transformers. This increases the size of the chamber considerably and makes it bulky and heavy besides increasing the material cost of the chamber. The size and capacity of the heating system, vacuum system and oil impregnation system and their cost and energy requirements are also correspondingly increased. The transformers to be dried and oil impregnated are loaded in the chamber by lifting and lowering them into the chamber one by one through the top using a crane or the like. Similarly unloading of the dried and oil impregnated transformers is carried out through the top by lifting them one by one using a crane or the
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like. Loading and unloading of the transformer is, therefore, time consuming,
troublesome and inconvenient and requires additional labour, Because of the use of the
thermic fluid undergoing the cycles of heating, evaporation and condensation, drying time is considerably increased and productivity is reduced. As the chamber inside is exposed to the heating fluid vapours, thermal insulation, if provided, internally will absorb the vapours and hamper evacuation. Therefore, the chamber is required to be externally insulated with very thick insulation thereby increasing the cost of the chamber. While carrying out the method, the entire chamber ie a large area is evacuated. This further increases the capacity of the vacuum pump and its energy requirement. As the chamber has to withstand high vacuum, it is required to be made of increased material thickness which increases the material cost of the chamber. The thermic fluid is required to be replenished periodically thereby furthering increasing the cost.
OBJECTS OF INVENTION
An object of the invention is to provide a method for making an oil impregnated paper
insulation transformer, which method reduces the drying time considerably and increases
productivity.
Another object of the invention is to provide a method for making an oil impregnated paper insulation transformer, which method reduces cost and energy requirements and is simple to carry out.
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Another object of the invention is to provide a device for making an oil impregnated paper insulation transformer, which device reduces the drying time considerably and increases productivity.
Another object of the invention is to provide a device for making an oil impregnated paper insulation transformer, which device is compact and simple in construction and reduces cost and energy consumption.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a method for making an oil impregnated paper insulation transformer, the method comprising the steps of:
(a) loading the transformer in a metallic chamber from the front of the chamber which is thermally internally insulated;
(b) heating the transformer with air at 100-110°C recirculated in the chamber for a predetermined period of time;
(c) heating the transformer with air at 100 - 110°C recirculated in the chamber under vacuum of 60 mbar to 50 mbar applied within the transformer for a predetermined period time;
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(d) heating the transformer with air at 100 -110°C recirculated in the chamber for a predetermined period of time;
(e) heating the transformer with air at 100 - 110°C recirculated in the chamber under vacuum of 50 mbar to 25 mbar applied within the transformer for a predetermined time;
(f) heating the transformer with air at 100 - 110°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer for a predetermined time;
(g) cooling the transformer with air at 50 to 60°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer;
(h) oil impregnating the transformer under a vacuum of 1.2 mbar to 1.0 mbar applied within the transformer;
(i) allowing the transformer to cool down to ambient temperature; and
(j) unloading the transformer from the chamber from the front thereof.
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The heating time in steps (b), (c), (d), (e) and (f) will depend upon factors like the sizes of
the chamber and transformer, moisture content in the insulation paper layers between the windings of the coil or the like. Preferably, the transformer is heated in steps (b), (c), (d), (e) and (f) for 5 to 6 hrs, 6 to 8 hrs, 6 to 8 hrs, 6 to 8 hrs and 6 to 8 hrs, respectively.
According to the invention there is also provided a device for making an oil impregnated paper insulation transformer, the device comprising a metallic chamber provided with thermal insulation internally and a front door, the chamber being further provided with hot and cold air recirculation system connected to the chamber, a vacuum system comprising a vacuum pump adapted to be connected to the transformer and provided with a moisture collector, an oil impregnation system adapted to be connected to the transformer and a control panel for controlling the operations of the air recirculation system, vacuum pump and oil impregnation system, the chamber being further provided with a support for the transformer.
The following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 is a schematic view of the device of the invention according to an embodiment thereof. The equipment 1 as illustrated in Fig 1 comprises a metallic chamber 2 which is provided with thermal insulation 3 internally and a front door 4. The chamber is preferably made of metals such as mild steel or stainless steel. 5 is a blower whose suction line 6a and discharge line 6b are connected
to the chamber. 7 is an electric heater provided in the discharge line of the blower. 8 is a
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thermostat provided in the chamber. 9 is a vacuum pump connected to a transformer 10
through conduit 11. The transformer is loaded in the chamber through the front aoor and
located on a stand 12 provided in the chamber. 13 is a moisture collector provided with the conduit 11. 14 is an oil impregnation system connected to the transformer through a conduit 15. 16 is a control panel connected to the blower, electric heater, thermostat, vacuum pump and oil impregnation system for controlling the operations thereof. During drying of the transformer, hot air is produced by heating the air with the heater and is blown onto the transformer by the blower. The control panel senses the temperature in the chamber through the thermostat and controls the temperature at 100-110°C in the chamber. During cooling of the transformer, the heater is switched off and air is blown onto the transformer by operating the blower. After drying and cooling of the transformer oil impregnation is carried out with the oil impregnation system. The dried and oil impregnated transformer is unloaded from the chamber through the front door thereof.
The following experimental example is illustrative of the invention but not limitative of the scope thereof.
Example 1 Eight 145kV current transformers were simultaneously dried and oil impregnated as per the conventional method. The total time periods of the method were as shown in the following Table 1.
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Table 1

Eight 145 kV current transformers were dried and oil impregnated in the equipment of Fig 1 according to the method of the invention one after the other. The total time periods of the method were as shown in the following Table 2
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Table 2
It is seen from the Tables 1 and 2 that the drying time according to the invention is considerably reduced.
According to the invention the heat exchanger and associated arrangement for introduction of vapours into the chamber and collection of the condensate from the chamber have been eliminated. Instead, the transformer is directly heated and cooled with air blown onto it. Therefore, drying time of the transformer is considerably
reduced. Energy requirement for drying is also reduced. During heating and cooling, vacuum is applied only within the transformer ie within a reduced area. Consequently
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only vacuum pump of reduced capacity is required. Energy requirement of the vacuum pump is also reduced. As vacuum is applied only within the transformer, the chamber is
not subjected to vacuum pressure. Therefore, the material thickness of the chamber can be reduced thereby reducing the material cost of the chamber. As air is used for heating and cooling, the chamber can be thermally insulated internally and that too with reduced insulation thickness. This further reduces the cost of the chamber. Because of front loading and unloading of the transformer in the device of the invention, loading and unloading time are also considerably reduced. The heating and cooling system used according to the invention can be a simple blower and heater. The device of the invention is simplified in construction with considerable cost benefit.
The device of the invention is advantageously designed to handle one transformer at a time so as to reduce the size and material requirement of the chamber and also capacity and size of the air circulation system, vacuum system and oil impregnation system of the device of the invention. The overall device cost and energy requirement are thus reduced still with the benefits like reduced drying time and increased productivity. It is, however, possible to have a larger device capable of handling simultaneously more than one transformer and at the same time realizing the other benefits of the invention like reduced drying time and increased productivity. The cost and energy requirement of the device also will still be reduced because air is directly blown onto the transformer so as to dry and cool it faster and vacuum is directly applied within the transformer. The chamber can be thermally insulated externally instead of being internally insulated. The chamber can also be made of thermal insulation material. Front loading and unloading of
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the transformer is only a preference. The transformer can be loaded and unloaded from the top in which case also the drying time will still be reduced as can be seen from the Table 2. Handling of more than one transformer for drying and oil impregnation at a time and loading and unloading of the transformer from top are thus within the scope of the invention and the scope of the invention should be construed and understood accordingly. Variations in the configuration and construction of the air recirculation system, vacuum system and oil impregnation system are also to be construed and understood to be within the scope of the invention.
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We claim:
1. A method for making an oil impregnated paper insulation transformer, the method comprising the steps of:
(a) loading the transformer in a metallic chamber from the front of the chamber which is thermally internally insulated;
(b) heating the transformer with air at 100-110°C recirculated in the chamber for a predetermined period of time;
(c) heating the transformer with air at 100 - 110°C recirculated in the chamber under vacuum of 60 mbar to 50 mbar applied within the transformer for a predetermined period time;
(d) heating the transformer with air at 100-110°C recirculated in the chamber for a predetermined period of time;
(e) heating the transformer with air at 100 - 110°C recirculated in the chamber under vacuum of 50 mbar to 25 mbar applied within the transformer for a predetermined time;
(f) heating the transformer with air at 100-110°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer for a
predetermined time;
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(g) cooling the transformer with air at 50 to 60°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer;
(h) oil impregnating the transformer under a vacuum of 1.2 mbar to 1.0 mbar applied within the transformer;
(i) allowing the transformer to cool down to ambient temperature; and
(j) unloading the transformer from the chamber from the front thereof.
2 A method as claimed in claim 1, wherein the transformer is heated in steps (b),
(c), (d), (e) and (f) for 5 to 6 hrs, 6 to 8 hrs, 6 to 8 hrs, 6 to 8 hrs and 40 to 42 hrs,
respectively.
3. A device for making an oil impregnated paper insulation transformer, the device comprising a metallic chamber provided with thermal insulation internally and a front door, the chamber being further provided with hot and cold air recirculation system connected to the chamber, a vacuum system comprising a vacuum pump adapted to be connected to the transformer and provided with a moisture collector, an oil impregnation system adapted to be connected to the transformer and a control panel for controlling the operations of the air recirculation system, vacuum pump and oil impregnation system, the chamber being further provided with a support for the transformer.
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4. A device as claimed in claim 3, wherein the air recirculation system comprises a
blower connected to the control panel, the suction line and discharge line of the blower being connected to the chamber, a heater provided in the discharge line of the blower and connected to the control panel and a temperature sensor provided in the chamber and connected to the control panel.
5. A device as claimed in claim 4, wherein the heater is an electric heater and the temperature sensor is a thermostat.
6. A device as claimed in claim 3, wherein the support for the transformer comprises a stand.
7. A device as claimed in anyone of claims 3 to 6, which is provided with a front
door.
Dated this 2nd day of January 2007

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ABSTRACT
A method for making an oil impregnated paper insulation transformer. The transformer is loaded in a metallic chamber (2) from the front of the chamber which is
thermally internally insulated and heated with air at 100 -110°C recirculated in the
chamber for a predetermined period of time. The transformer is further heated with air at 100-110°C recirculated in the chamber under vacuum of 60 mbar to 50 mbar applied within the transformer for a predetermined period time followed by air at 100 - 110°C recirculated in the chamber for a predetermined period of time. The transformer is further heated with air at 100 - 110°C recirculated in the chamber under vacuum of 50 mbar to 25 mbar applied within the transformer for a predetermined time followed by air at 100-110°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer for a predetermined time. The transformer is cooled with air at 50 to 60°C recirculated in the chamber under vacuum of 0.08 mbar to 0.05 mbar applied within the transformer and oil impregnated under a vacuum of 1.2 mbar to 1.0 mbar applied within the transformer. The transformer is cooled down to ambient temperature and unloaded from the chamber from the front thereof. Also a device for making an oil impregnated paper insulation transformer. The device (1) comprises a metallic chamber (2) provided with thermal insulation (3) internally and a front door (4). The chamber is further provided with hot and cold air recirculation system (5,7) connected to the chamber. A vacuum system comprising a vacuum pump (9) is adapted to be connected to the transformer (10) and is provided with a moisture collector (13). The device also comprises an oil impregnation system (14) adapted to be connected to the transformer and a control panel (lib) for controlling the operations of the air recirculation system, vacuum pump and oil impregnation system. (Fig 1).