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
AN EFFICIENT LOW VOLTAGE TRANSFORMERS
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Goyal Neeraj of Crompton Greaves Ltd, Transformer (T2) Division , Plot No. Tl & T2, MPAKVN Industrial. Area, Malanapur, Distt. Bhind, Madhaya Pradesh, India; Indian National
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 efficient low voltage transformers.
Particularly, this invention relates to turns/ taps in low voltage transformers. Still particularly, this invention relates to central tap for transformers.
Background of the Invention:
A transformer is an electrical device which transfers currents from one circuit to another, without any moving parts. It comprises a first set of windings called primary windings, of metal. It further comprises a secondary set of windings called secondary windings, of metal. The transformer works on the principle of Faraday's Law of Electromagnetic Induction together with other laws of electricity. A magnetic flux linked with an electric circuit varies, and an electro motive force (voltage) is generated in the electric circuit, which electric circuit is proportional to the rate of variation of flux with time. Input power supply is connected to the primary windings. The secondary windings are connected to the output. Typically, the input power supply is an Alternating Current. The changes in the Alternating Current, as it flows through the primary windings, induces magnetic flux which changes with time, and subsequently 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.
However, there is a need for improving the efficiency of low voltage transformer, to provide an increased output.
It is known that distribution transformers are required with tappings which are taken out from the winding at pre-determined intervals. The commonly used

voltages for windings required with tapping are 11, 22, 33 kV. The tapping voltage per step of 2.5% is most commonly used.
Apart from the standard voltages, some transformers are required with voltages as low as 433 V on HV side. In such cases, with a tapping step of 2.5%, the voltage per step becomes very low and accordingly the turns per tap become too less & pose difficulty in winding.
Objects of the Invention:
An object of the invention is to increase the efficiency of low voltage transformers.
Another object of the invention is to increase the efficiency of low voltage transformers, without substantial increase in costs incurred.
Another object of the invention is to provide the efficiency of low voltage transformers which having mechanically stronger windings resulting in better short circuit strength
Another object of the invention is to the efficiency of low voltage transformers where Taps are taken out neatly and increase higher productivity

Summary of the Invention:
According to this invention, there is provided a central tap adapted to be placed between primary windings and secondary windings of a transformer for controlling the output efficiency of said transformer, characterized in that, said central tap being a metallic open-ended ring.
Preferably, said metallic ring is a copper ring.
Typically, said central tap includes a fixing / hooking means to attach the ring to the windings, in a firm manner.
According to an embodiment of this invention, there is provided a transformer with a central tap between its primary windings and secondary windings, wherein said central tap is an open ended ring. Preferably, said said central tap is an open ended metallic ring. Still preferably, said central tap is an open ended copper ring.
According to an alternative embodiment of this invention, there is provided a transformer with a central tap between its primary windings and secondary windings, wherein said central tap is a series of open ended rings connected together.

Typically, said central tap is an open ended ring with a hooking means adapted to hook aid central tap with said primary windings and said secondary windings.
Brief Description of the Accompanying Drawings:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates an isometric view of transformer with primary windings, secondary windings, and central tap;
Figure 2a illustrates an isometric view of central tap; Figure 2b illustrates a front view of central tap; Figure 2c illustrates a side view of central tap; and
Figure 3 illustrates a top view of transformer with primary windings, secondary windings, and central tap.
Detailed Description of the Accompanying Drawings:
According to this invention, there is provided a central tap (10) which is a metallic ring adapted to be inserted in between primary windings (12) of a transformer and secondary windings (14) of said transformer.

Figure 1 illustrates an isometric view of transformer with primary windings, secondary windings, and central tap.
Figure 2a illustrates an isometric view of central tap. Figure 2b illustrates a front view of central tap. Figure 2c illustrates a side view of central tap.
Figure 3 illustrates a top view of transformer with primary windings, secondary windings, and central tap.
Typically, said metallic ring is a copper ring. The insertion of said copper ring aims at, typically, achieving 1 turn / tap per copper ring attached. This will improve productivity of output power, thus increasing efficiency. The use of this metallic ring avoids breaking / use of mechanical winding styles of the primary and / or secondary windings. By selecting the number of such rings to be used, the output may proportionally be increased.
The copper ring is, typically, an open ring, forming almost a full circle. Typically, one of the ends of the ring has fixing / hooking means (16) to attach the ring to the windings, in a firm manner.

According to another embodiment, a plurality of rings may be envisaged to be fitted in series. Thus, subsequent proportional rise in output and efficiency may be achieved, without tampering with windings.
In accordance to the invention, the turns per step are required as 1 which are not possible to be done with conventional disc winding. Since disc windings are supposed to be mechanical the strongest compared to helical or layer windings, it is some times preferred to have disc winding. But since taking out tappings was possible with disc windings with such low turns per tap, layer windings are resorted to be designers which pose problems in manufacturing and also not mechanically strong. With the idea of insertion of copper discs between normal discs, it is possible to achieve the tapping turns as 1 & at the same time use the disc winding.

We claim,
1. A central tap adapted to be placed between primary windings and secondary windings of a transformer for controlling the output efficiency of said transformer, characterized in that, said central tap being a metallic open-ended ring.
2. A central tap as claimed in claim 1 wherein, said metallic ring is a copper ring.
3. A central tap as claimed in claim 1 wherein, said central tap includes a fixing / hooking means to attach the ring to the windings, in a firm manner.
4. A transformer with a central tap between its primary windings and secondary windings, wherein said central tap is an open ended ring.
5. A transformer with a central tap between its primary windings and secondary windings, wherein said central tap is an open ended metallic ring.
6. A transformer with a central tap between its primary windings and secondary windings, wherein said central tap is an open ended copper ring.

7. A transformer with a central tap between its primary windings and secondary windings, wherein said central tap is a series of open ended rings connected together.
8. A transformer with central tap between its primary windings and secondary windings, wherein said central tap is an open ended ring with a hooking means adapted to hook aid central tap with said primary windings and said secondary windings.