FORM 2
THE PATENTS ACT, 1970
(39 of 1970) As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A transformer with dual high-voltage (star-delta) windings with multiple voltage low-voltage windings.
APPLICANTS :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Mejari Kedar and Kulkarni Shubhangi both of Crompton Greaves Limited Transformer (Tl) Division, Kanjur Marg (East) Mumbai - 400 042, 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 the field of electronic and electrical equipment.
Particularly, this invention relates to transformers.
More particularly, this invention relates to multipurpose transformers.
Specifically, this invention relates to a transformer with dual high-voltage (star -delta) windings with multiple voltage low-voltage windings.
BACKGROUND OF THE INVENTION:
A Transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling without any moving parts. It works on the Principle of Faradays Law of Electromagnetic Induction together with other laws of electricity. When a magnetic flux linked with an electric circuit varies, an electro motive force (voltage) is generated in the electric circuit, proportional to the rate of variation of flux with time.
The basic functional components of the transformer are a core made of magnetic material, a primary winding, and a secondary winding. The primary winding is connected to a source of an alternating current and the secondary winding is connected to the output. As the alternating current flows through the primary winding, the change in current in the primary windings creates a time-varying magnetic flux in the core, which induces a voltage in the secondary windings.

There is insulation medium between the windings and the windings and core of the transformer which forms the core coil assembly of the transformer. This insulation is oil.
According to the prior art, High Voltage (HV) winding was either in star connection or delta connection. There was a need for upgrading of voltages or changed vector group which was not previously met.
Hence, same transformer could not be used in various vector groups.
There was a need for a transformer to obviate the limitations of the prior art.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a transformer which can be used in different vector groups.
Another object of the invention is to provide a transformer which can be used in star connection or delta connection.
Yet another object of the invention is to provide a transformer with High Voltage (HV) winding such that it can be used in star connection or delta connection without changing Volt / Turn ratio.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a transformer with dual high-voltage

(star - delta) windings with multiple voltage low-voltage windings, said transformer comprises:
a. at least two high voltage windings, per phase, said two high voltage
windings being a first high voltage winding and a second high voltage
winding;
b. at least two low voltage windings, per phase, said two low voltage windings
being a first low voltage winding and a second low voltage winding;
c. switch adapted to selectively connect or disconnect said second high voltage
winding;
d. a tap, per phase, for high voltage windings in order to select a certain
number of turns of windings; and
e. high voltage star-delta change-over switch adapted to selectively operate
said transformer in star connection mode or delta connection mode.
Typically, said transformer comprises a first tap related to said first high voltage winding.
Typically, said transformer comprises two high voltage star-delta change-over switch windings adapted to be disconnected from said at least two high voltage windings during star connection.
Typically, said transformer comprises two high voltage star-delta change-over switch windings adapted to be connected in parallel with each other adapted to be connected in series with said at least two high voltage windings during delta connection.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a schematic of the transformer windings and assembly of this invention; and
Figure 2 illustrates another connection-level schematic of the transformer windings and assembly of this invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a transformer with dual high-voltage (star - delta) windings with multiple voltage low-voltage windings.
Figure 1 illustrates a schematic of the transformer windings and assembly of this invention.
Figure 2 illustrates another connection-level schematic of the transformer windings and assembly of this invention.
In accordance with an embodiment of this invention, there are provided at least two high voltage windings (FTVl, HV2), per phase. The two high voltage windings include a first high voltage winding (FTVl) and a second high voltage winding (HV2).

In accordance with another embodiment of this invention, there are provided at least two low voltage windings (LV1, LV2), per phase. The two low voltage windings include a first low voltage winding (LV1) and a second low voltage winding (LV2).
In accordance with yet another embodiment of this invention, there is provided a switch (SW) adapted to selectively connect or disconnect the second High Voltage winding (HV2).
In accordance with still another embodiment of this invention, there is provided tap windings (Tl, T2) for the high voltage windings in order to select a certain number of turns of the windings.
According to one exemplary embodiment, illustrated herein, below, tap winding Tl and T2 each have voltage rating of 8.4kV.
Tap winding Tl and T2 are connected in parallel. Tl and T2 both form a single tap winding. HV1 and HV2 windings are connected in series. Tap winding provide variation for HV1+ HV2 winding during star connection. Tap winding provide variation for HV1+ HV2 + SW-SD winding during delta connection. Two SW-SD windings are connected in parallel with each other and during delta connection SW-SD windings connected in series with HV1 and HV2 windings.
In accordance with an additional embodiment of this invention, there is provided a high voltage star-delta change-over switch (SD-SW) adapted to selectively operate the transformer in star connection mode or delta connection mode.

According to one exemplary embodiment,
HV1 rating = 38KV
HV2 ratings 38KV
LV1 rating = 20KV
LV2 rating = 14.5KV
Tl rating = 8.4KV
T2 rating = 8.4KV
SD-SW rating = 8KV
Therefore, rating of transformer, of this invention, in Star connection mode = 131.6KV..
Therefore, rating of transformer, of this invention, in Delta connection mode = 84KV.
HV winding is designed for 131.6KV star connection. In order to obtain 84KV delta HV winding, HV winding is designed 131.6/^3= 76KV (during star connection). Additional 8KVis added in HV during Delta connection 76 + 8 = 84KV
Dual HV winding Transformer operates with High voltage winding either in star or delta connection. Volts per turns' ratio remain same when HV is operated as a star or delta. Consider HV winding voltage rating is 131.6kV for star connection and 84kV for delta connection. HV winding turns are calculated with phase voltage i.e. 131.6kV/ V3 = 76kV. For delta winding phase voltage required 84kV, thus 8kV winding is added in series with 76kV winding during delta connection. Thus HV delta winding can be design for equal to or greater than star winding phase voltage. LV winding is design with multiple voltage ratings. Current density, Bushing and

OLTC should be selected by considering maximum current value either in star or delta connection.
With reference to Figure 2 of the accompanying drawings, for achieving High Voltage star connection, connect terminal 21 to 31 in the switch (SW) and further connect terminal 51 to 61 in the star-delta change-over switch (SD-SW).
With reference to Figure 2 of the accompanying drawings, for achieving High Voltage delta connection, connect terminal 21 to 41 in the switch (SW) and further connect terminal 51 to 71 in the star-delta change-over switch (SD-SW).
The technical advancement of this invention lies in provisioning a transformer to be operated in different vector groups and at different voltage levels. The inventive step involves an arrangement of star and delta connection on HV side such that it can be selectively used in two vector groups i.e. YNdl and DdO.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A transformer with dual high-voltage (star - delta) windings with multiple voltage low-voltage windings, said transformer comprising:
a. at least two high voltage windings, per phase, said two high voltage
windings being a first high voltage winding and a second high voltage
winding;
b. at least two low voltage windings, per phase, said two low voltage
windings being a first low voltage winding and a second low voltage
winding;
c. switch adapted to selectively connect or disconnect said second high
voltage winding;
d. a tap, per phase, for high voltage windings in order to select a certain
number of turns of windings; and
e. high voltage star-delta change-over switch adapted to selectively operate
said transformer in star connection mode or delta connection mode.
2. The transformer as claimed in claim 1, wherein said transformer comprising two high voltage star-delta change-over switch windings adapted to be disconnected from said at least two high voltage windings during star connection.
3. The transformer as claimed in claim 1, wherein said transformer comprising two high voltage star-delta change-over switch windings connected in parallel with each other adapted to be connected in series with said at least two high voltage windings during delta connection.