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 THE INVENTION
Method for drying and oil impregnating instrument transformer without autoclave
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Delip C Wakode, Anil R Dhasal and Uday S Sanvastsarkar, all of Crompton Greaves Ltd , Switchgear-6 & Power Quality Business, D2, MIDC, Waluj, Aurangabad, Maharashtra, India, all Indian Nationals
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 for drying and oil impregnating instrument transformer.
BACKGROUND OF INVENTION
An instrument transformer 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 insulation paper layers are dried and impregnated with oil. Prior to filling the tank with oil. A typical equipment for drying and oil impregnating an instrument transformer comprises a metallic chamber which is externally thermally insulated and provided with a heating and cooling system, a vacuum system and an oil impregnation system. The heating and cooling system comprises a heat exchanger comprising an endless tube containing a thermic fluid, a recirculation pump for recirculation of the thermic fluid in the endless tube of the heat exchanger and an electric heater for heating the thermic fluid. Part of the endless tube of the heat exchanger is located within the chamber. The vacuum system includes a vacuum pump connected to the chamber through a moisture collector. The method of drying and oil impregnating the instrument transformer comprises the following steps:
(i) Loading the instrument transformer in to the chamber.
(ii) Heating the instrument transformer indirectly at 90 to 115 ° C with hot thermic fluid circulated through the endless tube of the heat exchanger for a predetermined period of time, typically 3 to 8 hrs, after reaching approximate at 100 °C.


(iii) Heating the instrument transformer indirectly at 90 to 120° C with hot thermic fluid circulated through the endless tube of the heat exchanger under vacuum of 100 mbar to 20 mbar for a predetermined period of time typically 4 to 12 hrs;
(iv) Heating the instrument transformer indirectly at 90 to 120°C with hot thermic fluid circulated through the endless tube of the heat exchanger for a predetermined period of time, typically 4 to 12 hours;
(v) Heating the instrument transformer indirectly at 90 tol20°C with hot thermic fluid circulated through the endless tube of the heat exchanger under vacuum of 100 mbar to 20 mbar for a predetermined period of time, typically 4 to 12 hours;
(vi) Heating the instrument transformer indirectly at 90 to 120° C with hot thermic fluid circulated through the endless tube of the heat exchanger under vacuum of 0.10 mbar to 0.02 mbar for a predetermined period of time, typically 52 to 62 hrs;
(vii) Cooling the instrument transformer indirectly to 50 to 60°C with cold thermic fluid circulated through the endless tube of the heat exchanger under a vacuum of 0.10 mbar to 0.02 mbar;
(viii) Oil impregnating the instrument transformer under a vacuum of 1.4 mbar to 0.8 mbar.
(ix) Allowing the instrument transformer to cool down to ambient temperature; and
(x) Unloading the instrument transformer from the chamber.
The cooling step (vii) is carried out by stopping heating of the thermic fluid. Allowing the thermic fluid to be cooled by the coolant flowing through the shell side of the heat exchanger and circulating the cold thermeric fluid through the endless tube of the heat exchanger. Generally the chamber is large enough to accommodate a plurality of instrument


transformers approximate 4 to 24 Nos. 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 and cooling system, vacuum system and oil impregnation system and their energy requirements are also correspondingly increased. The instrument 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 opening using a crane or the like. Similarly unloading of the dried and oil impregnated instrument transformers is carried out through the opening by lifting them one by one using a crane or the like. Loading and unloading of the instrument transformer is, therefore, time consuming, troublesome and inconvenient and requires additional labor. Due to indirect heating and cooling of the instrument transformer, drying time is considerably increased and productivity is reduced. As the chamber is exposed to vacuum it essentially need higher thickness to take care of Hookes stresses. Unlike to this in invention the chamber need not to exposed to vacuum, it does not required high thickness & hence cost effective. Insulation thickness required is high thereby further increasing the cost of the chamber. While carrying out the method, the entire chamber i.e. a large volume 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. These further increases the material cost of the chamber. The heat exchanger requires an endless leak-tight tube for recirculation of the thermic fluid. Besides, the tehrmic fluid is required to be replenished periodically. Cost is increased because of all this also.


OBJECTS OF INVENTION
An object of the invention is to provide a method for drying and oil impregnating an
instrument transformer, which method reduces the drying time considerably and increases
productivity.
Another object of the invention is to provide a method for drying and oil impregnating an instrument transformer, which method reduces cost and energy requirements and is simple to carry out.
Another object of the invention is to provide equipment for drying and oil impregnating an instrument transformer, which equipment reduces the drying time considerably and increases productivity.
Another object of the invention is to provide equipment for drying and oil impregnating an instrument transformer, which equipment is compact and simple in construction and reduces cost and energy consumption.
Another object of the invention is to provide flexibility heating, evacuating & oil impregnation system for manufacturing of oil impregnated instrument transformers.


DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a method for drying and oil impregnating an
instrument transformer, the method comprising the steps of:
(a) Enclosing the tank portion of instrument transformer in a flexible non metallic encloser in which air heaters are embedded to heat gut portion.
(b) Enclosing of porcelain insulator portion with metallic or non metallic enclosure in which heat insulating paint is applied from inside. Before putting enclosure, wrapping of air heater to porcelain to heat lower portion of instrument transformer
(c) Thus heating the instrument transformer at 80 to 120°C directly with electric air heater wrapped around tank portion & porcelain portion along with the enclosure for a predetermined period of time;
(d) Heating the instrument transformer at 80 to 120°C directly by same process that of (c) under vacuum of 100 mbar to 40 mbar applied within the instrument transformer for a predetermined period time.
(e) heating the instrument transformer at 80 to 120°C directly by same process that of (c) for a predetermined period of time;
(f) heating the instrument transformer at 80 to 120°C directly under vacuum of 60 mbar to 20 mbar applied within the instrument transformer for a predetermined time;


(g) heating the instrument transformer at 80 to 120° C directly by same process that of (c) under vacuum of 1.0 mbar to 0.03. mbar applied within the instrument transformer for a predetermined time; (h) cooling the instrument transformer to 50° C to 60° C by putting all heating source off under vacuum of 1.0 mbar to 0.03 mbar applied within the instrument transformer; (i) Impregnating the oil into the instrument transformer under a vacuum of .2 mbar
to 0.5 mbar applied within the instrument transformer; (j) allowing the instrument transformer to cool down to ambient temperature; and (k) Take out the instrument transformer for the further operation.. The heating time in steps (c), (d), (e), (f) and (g) will depend upon factors like size of 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 to 6 hrs, 4 to 10 hrs, 4 10 hrs, 4 to 10 hrs and 30 to 42 hrs, respectively.
Embodiment 1: Only External Heating According to this embodiment of the invention,
There is also provided equipment for drying and oil impregnating an instrument transformer. The equipment comprising a non-metallic or metallic enclosure provided with thermal insulation internally for tank portion. The instrument transformer is being further provided with a metallic or non metallic enclosure for insulator area to retain the heat generated by electrical heaters wrapped around the tank & insulating portion. Heat is generated to reduce the time of heating. A vacuum system comprising a vacuum pump, adaptor to be connected to the top cover of the instrument transformer and provided with


a moisture trap A oil impregnation system adaptor to be connected to the oil inlet of the instrument transformer. A control panel for controlling the operations of the heating system, vacuum pump and oil impregnation system.
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 equipment & heating system of the invention according to an embodiment The equipment 1 as illustrated in Fig 1 comprises a metallic or non metallic flexible enclosure 3 with electric heater 4 embodied & metallic or non metallic enclosure 5 which is provided with thermal insulation internally and equipped with rope heater 6 fitted there in . The encloser is preferably made of metals such as mild steel or stainless steel or non metal. 14 is a vacuum tight adaptor to be connected to the top cover of a instrument transformer 2 through conduit 15. 16 is a moisture collector provided with the conduit 18. This is connected to vacuum pump 19. 8 is an oil impregnation system adaptor to be connected to the oil inlet of the instrument transformer. 17 is a control panel connected to the electric heaters, thermocouples, vacuum pump and oil impregnation system for controlling the operations. During drying of the instrument transformer, heat is produced by heating the instrument transformer body as well winding with the heaters provided. The control panel senses the temperature in the chamber through the thermocouples 10, 11,13 and controls the temperature in the instrument transformer. During cooling of the instrument transformer, the heater is switched off & it allowed cooling by natural air. Oil impregnation after drying and cooling of the instrument transformer is carried out with the oil impregnation system.


Embodiment 2: Internal heating (using method a, b, or a & b) According to another embodiment of the invention,
There is also provided equipment for drying and oil impregnating an instrument transformer. The equipment comprising a metallic or non-metallic enclosure provided with thermal insulation internally for tank portion. The instrument transformer is also being further provided with a metallic or non metallic enclosure for insulator area to retain the heat generated by internal heating system. The internal heating system essentially comprises of A.C. current source connected to the secondary of instrument transformer & a high voltage source is connected across secondary terminals & primary terminals with special electric circuit (a, b) simultaneously. At the same time primary terminal P1& P2 are linked with conductor to ensure close circuit between PI & P2 while performing internal heat up cycle.
Above described combination of internal heating either a, b or a&b result into less heat up time. A vacuum system comprising a vacuum pump adaptor to be connected to the top cover of the instrument transformer and provided with a moisture trap and a oil impregnation system adaptor to be connected to the top cover of the instrument transformer and a control panel for controlling the operations of the heating system, vacuum pump and oil impregnation system.
According to this embodiment the following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 2 is a schematic view of the equipment & heating system of the invention.


The equipment 2 as illustrated in Fig 2 comprises 2 is a instrument transformer & 3 a non metallic flexible enclosures for tank area & which is provided with thermal insulation internally. Enclosure 5 is preferably made of metals such as mild steel or stainless steel or non metal for porcelain area .4 is a conductor used to connect primary terminals PI & P2. 7 is high voltage source provided to generate dielectric heat within capacitor network. 8 is current source provided to enhance internal heating speed by ohmic heating when primary end are in shorted condition 14 is an adaptor to be connected to the top cover of a instrument transformer 2 through conduit 15.. 16 is a moisture collector provided with the conduit 18 connected to vacuum pump 19. 20 is an oil impregnation system adaptor to be connected to the oil inlet of the instrument transformer through a conduit. 17 is a control panel connected to the high voltage source, current source, thermocouples, vacuum pump and oil impregnation system for controlling the operations. 6, 9, 10, 11, 12, &13, are the connections. During drying of the instrument transformer, heat is produced by heating the instrument transformer winding & capacitor network with high current source & voltage source respectively. The control panel senses the temperature in the instrument transformer through the thermocouples and controls the temperature in the instrument transformer chamber. During cooling of the instrument transformer, the power supply is switched off & it allowed cooling by natural air. Oil impregnation after drying and cooling of the instrument transformer is carried out with the oil impregnation system.
Embodiment 3 (Internal & external heating )
According to another embodiment of the invention, there is also provided equipment for
drying and oil impregnating an instrument transformer. The equipment comprising a


metallic or non metallic enclosure provided with thermal insulation internally for tank area & the transformer is also being further provided with a metallic or non metallic enclosure for insulator area to retain the heat generated by internal heating system. The internal heating system essentially consists of A. C. current source connected to the secondary of transformer & high voltage source is connected across secondary terminals & primary terminals with special electric circuit ( a, b ) simultaneously. At the same time primary terminals P1& P2 are linked with conductor to ensure close circuit between PI & P2 while performing internal heating cycle. The internal heating is performed either by a, b or a&b circuits.( Ohmic & dielectric heating)
Above described combination of external & internal heating results into less heat up time. A vacuum system comprising a adaptor to be connected to the top cover of the transformer and provided with a moisture trap which is connected to vacuum pump. A oil impregnation system adaptor to be connected to the oil inlet of the transformer and a control panel for controlling the operations of the heating system, vacuum pump and oil impregnation system.
According to this embodiment the following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 3 is a schematic view of the equipment & heating system of the invention.
The equipment 3 as illustrated in Fig 3 comprises 2 is a transformer & 3 a non metallic flexible enclosures for tank area & which is provided with thermal insulation internally. Enclosure 6 is preferably made of metals such as mild steel or stainless steel or non metal


for porcelain area. 4 & 7 are flexible heaters. 5 is a link used for short circuiting primary terminals PI & P2. Where as 8 is high voltage source provided to generate heat within winding. 12 is current source provided to enhance internal heating speed when primary end are in shorted condition 20 is a vacuum pump adaptor to be connected to the top cover of a transformer 2 through conduit 21... 22 is a moisture collector provided with the conduit 24 connected to vacuum pump 25. 27 is an oil impregnation system adaptor to be connected to the oil inlet of the transformer through a conduit. 23 is a control panel connected to the high voltage source, current source, rope heaters, thermocouples, vacuum pump and oil impregnation system for controlling the operations. Where as 9,10,11,13,14,15,16,17,18,19 & 26 are connections. During drying of the transformer, heat is produced by activating the rope heater provided around the instrument transformer & heating the instrument transformer winding with high voltage source & current source respectively. The control panel senses the temperature in the instrument transformer through the thermocouples and controls the temperature in the instrument transformer chamber. During cooling of the instrument transformer, the power supply is switched off & it allowed cooling by natural air. Oil impregnation after drying and cooling of the instrument transformer is carried out with the oil impregnation system.
According to the invention the instrument transformer is directly heated by generating heat internally as well as externally by using special electric circuits ( a, b, a &b ) and cooled by natural ventilation. 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 instrument transformer i.e. within a reduced area. Consequently only vacuum pump of reduced capacity is required. Energy requirement of


the vacuum pump is also reduced. As vacuum is applied only within the instrument transformer, no chamber is required. Therefore, it reduces the material cost of the equipment substantially. As heat is directly applied to the instrument transformer, heat energy required to heat the chamber is avoided. Because of easy loading and unloading of the instrument transformer in the equipment of the invention, loading and unloading time are considerably reduced. The invention eliminates heat exchanger and the use of thermic fluid which requires a leak tight closed loop of tube for recirculation. The heating and cooling system used according to the invention can be a simple heater & natural ventilation. The equipment of the invention is simplified in construction with considerable cost benefit.
The equipment of the invention is advantageously designed to handle one instrument transformer at a time so as to eliminate material requirement of the chamber and also capacity and size of the hot and cold air circulation system, vacuum system and oil impregnation system of the equipment of the invention. The overall equipment 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 equipment capable of handling simultaneously more than one instrument transformer and at the same time realizing the other benefits of the invention like reduced drying time and increased productivity. The equipment cost and energy requirement also will still be reduced because the heat is generated from internally from the instrument transformer so as to dry and cool it faster and vacuum is directly applied within the instrument transformer. The enclosures can be thermally insulated externally instead of being internally insulated. The instrument transformer loading and unloading is totally eliminated to reduce work


content. Handling of more than one instrument transformer for drying and oil impregnation at a time are thus within the scope of the invention and the scope of the invention should be construed and understood accordingly. Variations in the method of generation of heat ohmic & dielectric (internally) or externally is under scope of invention. Vacuum system and oil impregnation system are also to be construed and understood to be within the scope of the invention.


We claim:
1. A method for drying and oil impregnating an instrument transformer, the method
comprising the steps of:
(a) Enclosing the instrument transformer externally with insulated metallic or non metallic enclosure, covering the transformer with rope heaters.
(b) Heating the instrument transformer at 90°C to 115° C directly with rope heaters & high voltage source with current source to generate heat in the instrument transformer either by ohmic heating or dielectric heating or both for a predetermined period of time;
(c) Heating the instrument transformer at 90°C to 115° C directly with rope heaters & high voltage source with current source to generate heat in the instrument transformer either by ohmic heating or dielectric heating or both under vacuum of 100 mbar to 20 mbar applied within the instrument transformer for a predetermined period time;
(d) Heating the instrument transformer at 90°C to 115° C directly with rope heaters & high voltage source with current source to generate heat in the instrument transformer either by ohmic heating or dielectric heating or both under vacuum of 100 mbar to 20 mbar applied within the transformer for a predetermined time;
(e) Heating the instrument transformer at 90°C to 115° C directly with rope heaters &
high voltage source with current source to generate heat in the instrument transformer
under vacuum of 0.1 mbar to 0.02 .mbar applied within the instrument transformer for
a predetermined time;


(g) Cooling the instrument transformer to 50 to 60°C directly with natural air circulated under vacuum of 0.1 mbar to 0.02 mbar applied within the transformer;
(h) Oil impregnating the instrument transformer under a vacuum of 1.2 mbar tol.Ombar applied within the instrument transformer;
(i) Allowing the instrument transformer to cool down to ambient temperature; and
2 A method as claimed in claim 1, wherein the transformer is heated in steps (b), (c),
(d), (e) and (f) for 1 to 2 hrs, 4 to 8 hrs, 4 to 8 .hrs, 4 to 8 .hrs and 3 to 32 hrs, respectively.
3. An equipment for drying and oil impregnating an instrument transformer, the
equipment comprising a metallic or non metallic enclosure provided with thermal insulation
internally and the rope heaters all around the instrument transformer, a vacuum system
comprising a vacuum pump adaptor to be connected to the top cover of the instrument
transformer and provided with a moisture collector and a oil impregnation system adaptor to
be connected to the oil inlet of the instrument transformer and a control panel for controlling
the operations of the heating system, vacuum pump and oil impregnation system,
4. An equipment as claimed in claim 3, wherein the heating system comprises the rope heater
& ohmic heating & dielectric heating. A temperature sensor provided in the instrument
transformer chamber and connected to the control panel.


5. An equipment as claimed in claim 4, wherein the heater is an electric heater and the temperature sensor is thermocouples.
Dated this 31st day of March 2008