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 single phase traction transformer
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli,
Mumbai 400 030, Maharashtra, India, an Indian Company
Inventors
Bhatia Anilkumar Brijlal and Tomar Abhishek Singh of Crompton Greaves Ltd, Tl division, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India, both 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 single phase traction transformer. BACKGROUND OF THE INVENTION -
A single phase traction transformer comprises of a core and coil assembly disposed in a protective tank. The core usually comprises of three vertically spaced apart limbs made up of magnetic material laminations and held between a top and bottom yoke. The coil comprises of an auxiliary winding wound concentrically around one of the limbs electrically insulated therefrom and a regulatory winding wound concentrically around the auxiliary winding electrically insulated therefrom. Further, the coil comprises of secondary windings wound around each of the remaining two limbs electrically insulated therefrom and primary windings wound concentrically around the secondary windings and electrically insulated therefrom. In order to increase the auxiliary load carrying capacity of the transformer, cross-sectional area of the auxiliary windings is required to be increased. Increased winding is among the other major factors responsible for increase in the leakage reactance or impedance of the transformer which is detrimental to voltage regulation and dynamic response of the transformer. Therefore, boosting the auxiliary load carrying capacity of the transformer by a significant amount leads to an unacceptable level of increased impedance in the transformer. Moreover, increasing the cross-sectional area of the auxiliary windings, which is generally made up of copper or aluminum strips, requires increasing the size of the protective tank in which core and coil assembly is held.

OBJECTS OF THE INVENTION
An object of the invention is to provide a single phase traction transformer with increased auxiliary load carrying capacity without increasing the impedance thereof.
Another object of the invention is to provide a single phase traction transformer with increased auxiliary load carrying capacity without increasing the size of the protective tank.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided a single phase traction transformer comprising a core and coil assembly disposed in a protective tank, the core comprising three vertically spaced apart limbs held between a bottom yoke and a top yoke, all made of magnetic material laminations, the coil comprising an auxiliary winding and a regulatory winding wound concentrically electrically insulated from each other and inserted over one core limb and electrically insulated therefrom and a primary winding and a secondary winding wound concentrically electrically insulated from each other and inserted over each of the remaining two core limbs and electrically insulated therefrom wherein the regulatory winding comprises a pair of sub-windings connected in series and the auxiliary winding is sandwiched between the sub-windings.
Preferably, the secondary windings in each of the two limbs comprises of a pair of sub-winding wound concentrically over each other and electrically insulated from each other. Copper foils are used as auxiliary and secondary windings. The windings and core limbs are insulated from one another with a high thermal and electrical insulation grade material.

These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is an isometric view of a single phase traction transformer.
Fig 2 is a top view of a single phase traction transformer.
Fig 3 is a cross-sectional view of a single phase traction transformer.
Referring to the drawings, the single phase traction transformer comprises of a core and coil assembly. The core comprises of three vertically spaced apart limbs 1,2 - & 3 made up of magnetic material laminations. The limbs 1, 2 & 3 are held adjacently to each other in a spaced relationship between a bottom 4 and top 5 yoke. The coil assembly comprises of an auxiliary winding 6, regulatory winding having a pair of sub-windings 7a & 7b connected in series, two secondary windings each having a pair of sub-windings 8a & 8b and 9a & 9b respectively; and two primary windings 10 & 11. Auxiliary 6 and secondary 8a & 8b and 9a & 9b windings are made up of copper foil whereas regulatory 7a & 7b and primary windings 10& 11 are made up of normal strip conductors. One of the regulatory sub-winding 7a is wound concentrically around the one of the three limbs 1 and electrically insulated therefrom with an electric grade insulating material tube (not shown in the figure) disposed therebetween. Thereafter, the auxiliary winding 6 is wound concentrically around the first regulatory sub-winding 7a and electrically insulated therefrom with a high thermal electrical insulation grade material, such as of Nomex (a registered trademark of E.I. du Pont de Nemours and Company) provided therebetween. Lastly, the other regulatory sub-winding 7b connected in series with sub-winding 7a is wound concentrically around the auxiliary winding 6 and electrically insulated therefrom with a high thermal electrical insulation grade material provided therebetween thereby

sandwiching the auxiliary winding 6 between the pair of regulatory sub-windings 7a & 7b. Tap changers (not shown in the fig) are provided on the regulatory windings 7a & 7b in a known way. Formation of windings on the other two limbs 2 & 3 is identical. One of the each secondary sub-winding 8a & 9a is wound concentrically around each of the remaining two limbs 2 & 3 respectively and electrically insulated therefrom with an electric grade insulating material tube disposed therebetween. Thereafter, the other secondary sub-windings 8b & 9b is wound concentrically around the respective first secondary sub-windings 8a & 9a in both the limbs 2 & 3 and electrically insulated therefrom with a high, thermal electrical insulation grade material provided therebetween. Lastly, the primary windings 10 & 11 are wound concentrically around the respective second secondary sub-windings 8b & 9b in both the limbs 2 & 3 and electrically insulated therefrom with a high thermal electrical insulation grade material provided therebetween. Electrical connections between the windings are made in a known manner. The core and coil assembly are disposed in the protective tank (not shown in the fig) and held therein in by means of components such as clamps etc. Similarly, other known components of the transformer for normal functioning thereof such as suction pump, blower, bushings etc are installed therein and not being described here for the reasons of relevancy.
In the transformer, the regulatory windings 7a and 7b receives an external power supply from a catenary and variably distributes it to the primary windings 10 and 11 of the other two limbs 2 & 3 through the tap changers. Voltage in the primary windings 10 & 11 induces voltage in the respective secondary windings 8a, 8b, 9a & 9b which is used for supplying power to the traction motors. Also, voltage in the regulatory windings 7a & 7b induces voltage in the auxiliary winding 6 which is used to power other devices in a locomotive apart from the traction motors.

Experimentally, it was found that the impedance in a transformer designed in the above manner, wherein the auxiliary winding is sandwiched between regulatory windings, was limited to 3-5 % as against the limit of 15-20% in a conventional transformer when the capacity of the auxiliary windings is boosted to 1000-1500 kVa (Kilo Voltage Ampere) from 200-300 kVa. On account of the auxiliary winding being sandwiched between the regulatory sub-windings, the leakage magnetomotive flux distribution becomes negative which in turn limits the impedance of the transformer which otherwise would have shot to 15-20%. Usage of copper foils instead of copper and/or aluminum strips contributes to limiting the size of the core coil assembly thereby not requiring any increase in the protective tank dimensions. The high thermal electrical grade insulating material provides better insulation properties and hence better transformer efficiency.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
1. A single phase traction transformer comprising a core and coil assembly
disposed in a protective tank, the core comprising three vertically spaced
apart limbs held between a bottom yoke and a top yoke, all made of magnetic
material laminations, and the coil comprising
a. an auxiliary winding and a regulatory winding wound concentrically
electrically insulated from each other and inserted over one core limb
and electrically insulated therefrom and
b. a primary. winding and a secondary winding wound concentrically
electrically insulated from each other and inserted over each of the
remaining two core limbs and electrically insulated therefrom wherein
the regulatory winding comprises a pair of sub-windings connected in
series and the auxiliary winding is sandwiched between the sub-
windings,
2. The traction transformer as claimed in claim 1, wherein the secondary winding is wound concentrically electrically insulated over the said remaining two core limbs and the primary winding is wound concentrically electrically insulated over the secondary winding.
3. The traction transformer as claimed in claim 1, wherein the secondary winding comprises of a plurality of sub-windings wound concentrically electrically insulated from each other.
4. The traction transformer as claimed in claim 1 to 3, wherein copper foils are used as auxiliary and secondary windings.

5. The traction transformer as claimed in anyone of claims 1 to 4, wherein the windings and core limbs are insulated from one another with high thermal and electrical insulation grade material.
Dated this 16th day of February 2010
—-JM^nModi)
of Khaitan & Co
Agent for the Applicants
RegNoIN/PA-1586