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 INVENTION
An electric arc furnace transformer and method of making the same
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Vishwanathan Shivakumar, Operations, Transformer Division (T3), Crompton Greaves Ltd., New Industrial Area No. 1, Mandideep - 462 046, Madhya Pradesh and Devadoss Jeya Bhaskaran Jude, Transformer Division (T3), Crompton Greaves Ltd., New Industrial Area No. 1, Mandideep - 462 046, Madhya Pradesh, 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 INVENTION
This invention relates to an electric arc furnace transformer and a method of
making the same.
BACKGROUND ART
Electric arc furnaces are generally used for melting of metals and are powered by a furnace transformer. The furnace transformer is located in an enclosure external to the electric arc furnace and comprises a main transformer connected to a booster transformer. The main transformer comprises a low voltage winding (LV), a tap winding and a high voltage winding (HV) and the booster transformer also comprises a low voltage (LV) winding and high voltage (HV) winding. The various windings of the main transformer and booster transformer are wound manually separately into the required number of turns using separate conductors usually on a mandrel. The wound windings of the main transformer and booster transformer are located or mounted on the limbs of the respective E shaped cores one above another. As the rating of a furnace transformer is very high normally in the order of 40 kA, the conductors forming the LV windings of the main transformer and booster transformer are large in number. Therefore, the LV windings of the main transformer and booster transformer each is wound in discrete multiple sections or parts. The furnace transformer is made by locating the cores of the main transformer and booster transformer parallel to each other at a distance and inter connecting the various windings of the main transformer and booster transformer. The tap winding of the main transformer is connected to the HV winding of the booster transformer in parallel. The tap winding of the
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main transformer ensures that a constant current is given to the LV winding of the main transformer and LV winding of the booster transformer. The connection between the tap winding and the HV winding of the booster transformer is carried out outside the transformer by taking lead wires from the HV winding and tap winding and connecting the lead wires by crimping using copper ferrules. Due to the large number of discrete sections of the LV windings of the main transformer and booster transformer, connections between the LV windings using lead wires as in the case of HV winding of the booster transformer and tap winding is difficult and cumbersome. Therefore, the various sections of the LV winding of the main transformer are directly connected to the corresponding sections of the LV winding of the booster transformer by keeping the cores face to face with each other and by the crimping operation using copper ferrules. In order to connect the various sections of the LV winding of the main transformer directly to the corresponding sections of the LV winding of the booster transformer, the distance between the cores of the main transformer and booster transformer should be such that the person(s) carrying out the connections should be able to stand between the two cores. This increases the size of the furnace transformer and correspondingly the size of the enclosure in which the furnace transformer is located. As there are multiple sections of the LV windings to be interconnected, inter connections of the LV windings is time consuming and tedious. If the crimping operation is not carried out properly and correctly there are chances of the windings getting disconnected during the operation of the furnace transformer thereby leading to failure of the furnace transformer. In the event of failure of the furnace transformer due to disconnection of the windings it becomes difficult to locate the connection which has failed as there are large number of connections. As a result the
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reliability of the furnace transformer is reduced. Due to the large number of sections of the LV windings of the main transformer and booster transformer, the number of copper ferrules required for connection also increases thereby increasing the cost of the furnace transformer.
OBJECTS OF INVENTION
An object of the invention is to provide a method of making an electric arc furnace transformer, which method reduces the number of connections to be carried out manually and the assembly time and increases productivity.
Another object of the invention is to provide a method of making an electric arc furnace transformer, which method renders the furnace transformer compact and economical.
Another object of the invention is to provide a method of making an electric arc furnace transformer, which method reduces the chances of failure of the furnace transformer and increases the reliability of the transformer.
Another object of the invention is to provide a method of making an electric arc furnace transformer, which method is simple and easy to carry out.
Another object of the invention is to provide an electric arc furnace transformer, which is compact and economical.
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Another object of the invention is to provide an electric arc furnace transformer, which is reliable and simple in construction.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a method for making an electric arc furnace transformer comprising the steps of forming the high voltage winding of each of the main transformer and booster transformer separately by winding conductors into the required number of turns; forming the tap winding of the main transformer separately by winding conductors into the required number of turns and forming each pair of sections of the low voltage windings of the main transformer and booster transformer together by winding the same conductors continuously into the required number of turns of each of the low voltage windings of each of the main transformer and booster transformer, mounting the various windings of the main transformer and booster transformer on the cores of the main transformer and booster transformer and connecting the tap winding of the main transformer to the high voltage winding of the booster transformer in parallel.
According to the invention there is also provided a furnace transformer comprising a main transformer and a booster transformer, the main transformer and booster transformer each comprising a high voltage winding formed separately by winding conductors into the required number of turns, the main transformer further comprising a tap winding formed separately by winding conductors into the required number of turns and the main transformer and booster transformer further comprising multiple sections of
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the LV winding, each pair of sections of the low voltage windings of the main transformer and booster transformer being formed together by winding the same conductors continuously into the required number of turns of each of the low voltage windings of each of the main transformer and booster transformer, the various windings of the main transformer and booster transformer being mounted on the cores of the main transformer and booster transformer and the tap winding of the main transformer being connected to the high voltage winding of the booster transformer in parallel.
According to the invention, the HV winding of the main transformer of the furnace transformer is formed by winding a set of conductors around a mandrel into the required number of turns. The HV winding of the booster transformer is also made in the same manner as the HV winding of the main transformer by winding a different set of conductors separately around a mandrel but having the same characteristics of the conductors used to form the HV winding of the main transformer. The tap winding is also separately formed by winding a set of conductors around a mandrel into the required number of turns. The wound HV windings and the tap winding are located or mounted on the E shaped cores of the main transformer and booster transformer in known manner and the tap winding is connected to the HV winding of the booster transformer by crimping using copper furnaces. Each pair of sections of the low voltage windings of the main transformer and booster transformer is formed together by winding a same set of conductors continuously into the required number of turns of each of the low voltage winding of each of the main transformer and booster transformer around two mandrels rotatably held parallely in a spaced apart relationship. The outer end of one wound section of each pair of sections
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formed on one mandrel is taken to the other mandrel and continuously wound on the other mandrel to form the other wound section of each pair of sections. Multiple sections of the LV windings of the main transformer and booster transformer so formed are mounted on the limbs of the E shaped cores of the main transformer and booster transformer in known manner.
According to the invention the interconnections between the corresponding sections of each pair of sections of the LV windings of the main transformer and booster transformer manually by crimping using copper ferrules have been eliminated as the interconnections have already been made during winding of the windings itself. This reduces the number of connections to be carried out manually after the wound windings are mounted on the cores thereby reducing the time required for making the furnace transformer and increasing productivity. As the LV windings are not connected after the same are mounted onto the limbs of the cores, the distance required to be maintained between the cores for enabling person(s) to stand between the cores and carry out the connections is reduced. This renders the furnace transformer compact thereby reducing the size of the enclosure in which the furnace transformer is located. Reduction in the size of the enclosure further reduces the cost of the furnace transformer. Since the LV windings are not interconnected by crimping using copper ferrules chances of failure of the furnace transformer due to disconnection of the LV windings during the working of the furnace transformer is reduced thereby increasing the reliability of the furnace transformer.
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We Claim
1. A method for making an electric arc furnace transformer comprising the steps of forming the high voltage winding of each of the main transformer and booster transformer separately by winding conductors into the required number of turns; forming the tap winding of the main transformer separately by winding conductors into the required number of turns and forming each pair of sections of the low voltage windings of the main transformer and booster transformer together by winding the same conductors continuously into the required number of turns of each of the low voltage windings of each of the main transformer and booster transformer, mounting the various windings of the main transformer and booster transformer on the cores of the main transformer and booster transformer and connecting the tap winding of the main transformer to the high voltage winding of the booster transformer in parallel.
2. A furnace transformer comprising a main transformer and a booster transformer, the main transformer and booster transformer each comprising a high voltage winding formed separately by winding conductors into the required number of turns, the main transformer further comprising a tap winding formed separately by winding conductors into the required number of turns and the main transformer and booster transformer further comprising multiple sections of the LV winding, each pair of sections of the low voltage windings of the main transformer and booster transformer being formed together by winding the same conductors continuously into the required number of turns of each of the low voltage windings of each of the main transformer and booster transformer, the various windings of the main
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transformer and booster transformer being mounted on the cores of the main transformer and booster transformer and the tap winding of the main transformer being connected to the high voltage winding of the booster transformer in parallel.
Dated this 27th day of April 2007

(Prita Madan)
Agent for the Applicants
Of Khaitan &Co
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ABSTRACT
A method for making an electric arc furnace transformer comprising forming the high voltage winding of each of the main transformer and booster transformer separately by winding conductors into the required number of turns. The tap winding of the main transformer is formed separately by winding conductors into the required number of turns. Each pair of sections of the low voltage windings of the main transformer and booster transformer is formed together by winding the same conductors continuously into the required number of turns of each of the low voltage windings of each of the main transformer and booster transformer. The various windings of the main transformer and booster transformer are mounted on the cores of the main transformer and booster transformer and the tap winding of the main transformer is connected to the high voltage winding of the booster transformer in parallel.