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, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A tap changer enabled compensation transformer with main transformer.
APPLICANT(S)
Crompton Greaves Limited, CG House, 6l Floor, Dr. Annie Besant Road, Worli, Mumbai - 400030, Maharashtra, India, an Indian Company
INVENTOR(S)
Saha Raja, Hassan Hafiz Imtiaz and Wachasundar Shripad; all of Crompton Greaves Limited, CG Global R&D, Aryabhatta Building, Kanjur Marg (East), 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 the field of electrical and electronics engineering.
Particularly, this invention relates to the field of transformers.
More particularly, this invention relates to tap changers for transformers.
Specifically, this invention relates to a tap changer enabled compensation transformer with main transformer.
BACKGROUND OF THE INVENTION
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 load. 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.
The formula for working of an ideal transformer is:

Vp/Vs = Np/Ns where, Vp is the voltage in the primary side, Vs is the voltage in the secondary side, Np is the number of turns of winding on the primary side, Ns is the number of turns on the secondary side.
Upon varying, the number of turns on any side, subsequent changes of voltages occurs. Thus, it is possible to have a step-up transformer, wherein the formula executes an output power which is higher than the input power. Conversely, it is possible to have a step-down transformer, wherein the formula executes an input power which is higher than the output power.
This selection of turns may be automated by the provisioning of a central tap. Both the primary and secondary windings on power transformers may have external connections, called taps, to intermediate points on the winding to allow selection of the voltage ratio.
For many power transformer applications, a supply interruption during a tap change is unacceptable, and the transformer is often fitted with a more expensive and complex on-load tap-changing (OLTC) mechanism. On-load tap changers may be generally classified as mechanical, electronically assisted, or fully electronic.
The on-load tap changing (OLTC) regulators have been widely used since the introduction of electric energy. They ensure a good regulation of the output voltage in presence of large variations of the input voltage with typical response time from 100 ms to several seconds. The continuous growth of power semiconductor devices, such as the insulated gate bipolar transistor (IGBT), allows the development of fast OLTC regulators being able to fix other problems in the ac mains, like sags and flicker.

The common practice in Transformer industry for voltage regulation is by using an OLTC (on load tap changer). Taps can be taken out either from primary (High voltage side) or secondary (Low voltage) side. By changing the taps output voltage of the transformer can be regulated.
With the advent of fast semiconductor devices and fast control techniques, Electronics Tap changers are gaining more popularity over mechanical ones. The prime advantageous of electronics based OLTC over mechanical ones are fast response time, arc-less operation, being maintenance free and unlimited number of operation.
The obvious practice is to use tapping either in primary or in secondary side of the main transformer. The main problems of using the electronics switching in primary side are requirement of switching of high PIV (peak inverse voltage), their isolation and insulation. Whereas in other case, i.e. tapping from secondary, would require switches of high current rating, which will introduce extra losses in the system.
PRIOR ART
US3560843 relates to autotransformer voltage regulator. Voltage regulation can be achieved by compensating transformer of the two-winding type having a predetermined turns ratio, the compensating transformer being connected at its secondary side in series with the circuit of the tertiary winding and at its primary side with an operating tap winding of the autotransformer to be energized thereby. But problem with this kind of circuit arrangement is that, every time, when tapping is needed a new winding should be inserted which will impact the existing transformer design.

CN201063441 relates to a power saving controller. The controller has a power saving optimizing software built in a main controller for sending commands to a tap control switching circuit according to detected signals. The switching circuit receives the commands sent from the main controller, and controls tapping action of a compensation transformer group which changes the output voltage. The output potential of the compensation transformer group is outputted after adding the potential of an autotransformer group. A protection circuit controls a working mode of a power saving controller. Problem with this particular arrangement is that it needs extra winding whenever tap changing is required. This will impact the complete design of transformer.
CN201266329 relates to compensating alternating current stabilizer. It has multi-tap voltage-regulating transformer whose primary winding ends are connected with controllable switch parts to control positive and negative connection of primary winding. The stabilizer realizes the regulation of ascending level of output of the voltage-regulating transformer, and has simple technique and reliable operation. This invention uses extra winding whenever tapping is necessary. This will impact the complete design of transformer.
Non patent literature "Analysis, Design, and Implementation of a Fast On-Load Tap Changing Regulator" relates to OLTC regulation, in which compensating transformer is placed at primary or secondary winding for tapping. Even though it employs compensating transformer tapping is made from the main winding of transformer. This particular arrangement disturbs the main winding of transformer which is not efficient.

To cope with these problems, the common practice is to use a compensation transformer in series with secondary side, which will reduce the current stress on the devices. However, the extraction of tapping from secondary is quite difficult in a step-down transformer, as the numbers of turns are very less compared to primary.
OBJECTS OF THE INVENTION
An object of the invention is to provide tap changer to a transformer without disturbing primary windings or secondary windings.
Another object of the invention is to provide tap changer to a transformer without introducing tertiary windings in the transformer.
Another object of the invention is to provide a plug and play compensator transformer to a main transformer with the ability to control tap changes to the main transformer.
Yet another object of the invention is to eliminate changes in main transformers, thereby enabling retro-fitting of compensation transformer and / or tap changers, thereof.
Still another object of the invention is to provide for extraction of tapping from a step-down, as the numbers of turns are very less compared to primary.
SUMMARY OF THE INVENTION
According to this invention, there is provided a tap changer enabled compensation

transformer with main transformer (comprising at least primary windings and at least secondary windings) comprising: i. at least a compensation transformer adapted to be connected in series to said main transformer, said at least a compensation transformer comprising at least primary windings and at least secondary windings; and ii. at least a tap changer located in correlation with said compensation transformer.
Typically, said at least a tap changer located in correlation with said compensation transformer is connected to said at least secondary windings of said compensation transformer for a step-down transformer.
Typically, said at least a tap changer located in correlation with said compensation transformer is connected to said at least primary windings of said compensation transformer for a step-up transformer.
Typically, said at least a tap changer comprises multiple tap in series at said secondary windings of said compensation transformer for a step-down transformer.
Typically, said at least a tap changer comprises multiple tap in series at said primary windings of said compensation transformer for a step-up transformer.
Typically, said at least a tap changer comprises a mechanical contactor adapted to change polarity of voltage which will be added in series with main secondary voltage for a step-down transformer.

Typically, said at least a tap changer comprises switches corresponding to each tap in order to decide number of turns.
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 network diagram of a compensation transformer in series with a main transformer, the compensation transformer being provided with a tap changer at its secondary side;
Figure 2 illustrates configuration of mechanical contactor such that there is no compensation;
Figure 3 illustrates configuration of mechanical contactor such that there is positive compensation; and
Figure 4 illustrates configuration of mechanical contactor such that there is negative compensation. Here, when contactor Ml and M2 is at position C2 and C4 respectively, negative compensation is provided by the transformer.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to this invention, there is provided a tap changer enabled compensation transformer with main transformer.

Figure 1 illustrates a schematic network diagram of a compensation transformer in series with a main transformer, the compensation transformer being provided with a tap changer at its secondary side.
In accordance with an embodiment of this invention, there is provided a compensation transformer (CPT) adapted to be connected in series to a main transformer (MT). Reference numeral P1 refers to primary windings of the main transformer. Reference numeral S1 refers to secondary windings of the main transformer. Reference numeral L refers to load.
In accordance with another embodiment of this invention, there is provided a tap changer (TC) located in correlation with the compensation transformer (CPT). For a step down transformer, the tap changer is connected to the secondary windings of the compensation transformer, as the secondary windings' side has relatively lesser current. Reference numeral P2 refers to primary windings of the compensation transformer. Reference numeral S2 refers to secondary windings of the compensation transformer. It is easy to extract tapping from the compensation transformer due to high number of turns in primary side of compensation transformer. Reference numerals Tapl, Tap2, Tap3, and Tap4 disclose taps of the tap changer (TC). There may be more or less taps depending upon the design and requirement. Reference numerals SW1, SW2, SW3, and SW4 refer to switches which correspond with the taps Tapl, Tap2, Tap3, and Tap4 in order to decide the number of turns which should be provided at the secondary side of the compensation transformer (CPT), thereby affecting the function of the main transformer (MT).
In accordance with yet another embodiment of this invention, there is provided a mechanical contactor (MC) adapted to be connected to the tap changer (TC).The

mechanical contactor is used to change polarity of voltage which will be added in series with main secondary voltage. The mechanical contactor is depicted by reference numerals C1, C2, C3, C4, Ml, M2 - which represent contacts. Contacts Ml and M2 are connected to taps in a pre-defined manner. Contacts C1, C2, C3, and C4 are connected to load (L). Depending on how Ml and M2 connect with C1, C2, C3, and C4 - the polarity of voltage to load is decided.
Whenever there is a variation in primary side voltage of the main transformer (MT), compensation transformer (CPT) will come into the picture to adjust the secondary output voltage of the main transformer as desired by the user.
Figure 2 illustrates configuration of mechanical contactor such that there is no compensation. Here, when contactor Ml and M2 is at position CI and C4 respectively, no compensation is provided by the transformer.
Figure 3 illustrates configuration of mechanical contactor such that there is positive compensation. Here, when contactor Ml and M2 is at position C1 and C3 respectively, positive compensation is provided by the transformer.
Figure 4 illustrates configuration of mechanical contactor such that there is negative compensation. Here, when contactor Ml and M2 is at position C2 and C4 respectively, negative compensation is provided by the transformer.
According to a non-limiting exemplary embodiment shown in the accompanying figures, four tappings (in secondary side of compensation transformer) in compensation is equally spaced, hence each winding has n (let say 230) turns. In primary side of compensation transformer number of turns is n/10(23).

According to another non-limiting exemplary embodiment, assume secondary output voltage is dropped to 210V. To achieve 230 V, there is a need to add 20V. For this, contactor Ml is connected to C1 and contactor M2 is connected to C3; hence compensating transformer will see 210V across the secondary terminal. SCR SW4 is closed, so effective turn ratio is {secondary to primary} n: (n/10). Primary voltage becomes 21V. Hence total output voltage is 210V + 21V (compensation) = 231V.
The INVENTIVE STEP of the current invention lies in the electrical configuration of the tap changing mechanism for the compensation transformer which allows it to provide a tap changer to control output without affecting the windings of either the main transformer or the compensation transformer. The windings of the main transformer are neither altered nor touched. Even, at the compensation transformer, the windings are neither altered nor touched. The location of the OLTC at the compensation transformer makes it easy to extract tappings due to high number of turns in its primary side.
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 tap changer enabled compensation transformer with main transformer
(comprising at least primary windings and at least secondary windings)
comprising:
i. at least a compensation transformer adapted to be connected in series to said main transformer, said at least a compensation transformer comprising at least primary windings and at least secondary windings; and
ii. at least a tap changer located in correlation with said compensation transformer.
2. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer located in correlation with said compensation transformer being connected to said at least secondary windings of said compensation transformer for a step-down transformer.
3. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer located in correlation with said compensation transformer being connected to said at least primary windings of said compensation transformer for a step-up transformer.
4. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer comprising multiple tap in series at said secondary windings of said compensation transformer for a step-down transformer.
5. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer comprising multiple tap

in series at said primary windings of said compensation transformer for a step-up transformer.
6. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer comprising a mechanical contactor adapted to change polarity of voltage which will be added in series with main secondary voltage for a step-down transformer.
7. The tap changer enabled compensation transformer with main transformer as claimed in claim 1, wherein said at least a tap changer comprising switches corresponding to each tap in order to decide number of turns.