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
A method of manufacturing an oil filled internally clamped transformer
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030,
Maharashtra, India, an Indian Company
INVENTORS
Vaidya Sameer Sharadchandra, Joshi Vikrant Shashikant and Vanage Manish Madhukar , all of Crompton Greaves Limited. Transformer Division (Tl), Kanjurmarg (E), Mumbai 400042 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 THE INVENTION
This invention relates to a method of manufacturing an oil filled internally clamped
transformer.
BACKGROUND OF THE INVENTION
An oil filled transformer is single phase or multiphase. Each phase includes a coil mounted over a limb of a magnetic material core and comprising a high voltage winding and a low voltage winding. Each of the windings comprises a plurality of turns of conductor layers electrically insulated with dielectric material layers. The core coil assembly is located within a transformer tank and the coil is clamped in position prior to filling the tank with transformer. The coil is clamped in position internally or externally of the tank. During manufacture of an internally clamped transformer, the core coil assembly is dried to remove moisture and then mounted in the transformer tank. After the core coil assembly is mounted in the transformer tank, the coil is compressed in the vertical place to the design pressure and clamped in position with clamping members, usually clamping screws tightened against a clamping ring located against the top of the coil. The transformer tank is filled with transformer oil and closed with a closure. The transformer is then tested and dispatched to site or customer for installation. It is well known to those in the transformer technology that over a period of time, the coil shrinks in service due to absorption of the transformer oil by the dielectric insulation and probably because of the oil density being low and because of the insulation material being under constant application of force. As a result, deformation of the coil takes place and a gap develops between the tips of the clamping members and the clamping ring. This may lead to
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development of short circuits and malfunctioning of the transformer and the transformer may even fail. The reliability and life of the transformer are thus reduced.
OBJECTS OF THE INVENTION
An object of the invention is to provide a method of manufacturing an oil filled internally
clamped transformer which is reliable and which has increased life.
Another object of the invention is to provide an oil filled internally clamped transformer having improved reliability and life.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a method of manufacturing an oil filled internally clamped transformer, which method comprises mounting a dried core coil assembly in a transformer tank, clamping the coil by compressing the coil in the vertical plane to the design pressure by tightening clamping members against a clamping ring located on top of the coil, saturating the core coil assembly with transformer oil over a predetermined period of time followed by draining the transformer oil from the transformer tank and reclamping the coil by compressing the coil in the vertical plane to the design pressure by tightening the clamping members against the clamping ring followed by filling the transformer tank with transformer oil.
Preferably the core coil assembly is saturated with transformer oil by allowing the core coil assembly to remain immersed in transformer oil in the tank for atleast two days. The tank is
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closed with a closure after it is filled with oil. Following this, the transformer is tested and dispatched to site or customer for installation. Saturation of the core coil assembly with transformer oil prior to filling the tank with transformer oil helps to allow the coil to shrink and deform. Therefore, on reclamping the coil and filling the tank with oil, further shrinking and deformation of the coil does not take place. As a result, the clamping members remain in contact with the clamping ring without developing any gap with the tips of the clamping members. This helps to prevent development of short circuits and ensure stability of transformer even under very high forces due to short circuit and also ensure proper and trouble free functioning of the transformer for a long period of time. Thus the reliability and life of the transformer are improved. It is obvious to those skilled in the art that the core coil assembly can be compressed and compacted and saturated with transformer oil prior to mounting the same in the transformer tank and the reclamping of the coil can be carried in the transformer tank. Such a variation of the invention is to be construed and understood to be within the scope of the invention.
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We claim :
1. A method of manufacturing an oil filled internally clamped transformer, which method comprises mounting a dried core coil assembly in a transformer tank, clamping the coil by compressing the coil in the vertical plane to the design pressure by tightening clamping members against a clamping ring located on top of the coil, saturating the core coil assembly with transformer oil over a predetermined period of time followed by draining the transformer oil from the transformer tank and reclamping the coil by compressing the coil in the vertical plane to the design pressure by tightening the clamping members against the clamping ring followed by filling the transformer tank with transformer oil.
2. The method as claimed in claim 1, wherein the core coil assembly is saturated with transformer oil by allowing the core coil assembly to remain immersed in transformer oil in the tank for atleast two days.
3) An oil filled internally clamped transformer manufactured by the method as claimed in claim 1 or 2.
Dated this 25th day of March 2009

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