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
A compact single phase variable flux autotransformer with neutral end taps
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Joshi Vikrant and Vora Shekhar, both of Transformer Division, Crompton Greaves Limited, Kanjur (East), 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 compact single phase variable flux autotransformer with neutral end taps.
BACKGROUND OF THE INVENTION
Single phase constant flux autotransformers and single phase variable flux autotransformers with neutral ends are generally used for interconnecting power grids in power transmission and distribution lines. A constant flux autotransformer comprises a series winding (high voltage winding), a common winding and a tertiary winding (low voltage winding) wound concentrically in radially spaced apart relationship with one another and mounted on the middle limb of a three limb magnetic material core. A constant flux autotransformer further comprises a tapping winding and an exciting winding wound concentrically in radially spaced apart relationship with each other and mounted on one end limb of the core. The series winding and tapping winding are connected in series with each other and further connected in series with the common winding and exciting winding which are connected parallel to each other. The free end of the series winding and the junction between the tapping winding and common winding are connected to a power supply and the junction of the common winding and exciting winding is earthed. The tertiary winding is connected to a power supply. The moving end of the tapping winding is earthed. A single phase variable flux autotransformer with neutral end taps comprises a tertiary winding, a tapping winding, a common winding and a series winding all wound concentrically in radially spaced apart relationship with one another and mounted on the middle limb of a three limb magnetic material core. The series winding, common winding and tapping winding are connected in series with one
3 0 MAR 2009
2

another. The free end of the series winding and junction between the common winding and tapping winding are connected to a power supply. The moving end of the tapping winding is earthed and the tertiary winding is connected across a power supply. In order to ensure healthy and efficient performance of power grid systems in which a single phase autotransformer is used, it is important that the percentage of leaking impedance of the transformer is controlled within permissible limits typically in the range 8 to 17% for a power transformer or generator transformer. A problem encountered in any transformer is that when the voltage and current ratings of the transformer are increased, the percentage of leakage impedance of the transformer increases. Normally the percentage of leakage impedance of the transformer is controlled by increasing the height of the transformer. Because of the size increase, transportation of the transformer becomes difficult. Space requirement for installing the transformer also increases. In the case of a variable flux autotransformer with neutral end taps where all the windings are concentrated on the middle limb, it is normally necessary to increase height of the transformer in order to increase voltage and current ratings of the transformer. There is, therefore, need for a single phase variable flux autotransformer with neutral end taps whose height does not increase with increase in the voltage and current ratings of the transformer.
OBJECTS OF THE INVENTION
An object of the invention is to provide a compact single phase variable flux autotransformer with neutral end taps wherein the height of the transformer does not increase with voltage and current ratings of the transformer.

3

Another object of the invention is to provide a compact single phase variable flux
autotransformer with neutral end taps, which transformer is easy to transport and
requires reduced space for installation.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a compact single phase variable flux autotransformer with neutral end taps, the autotransformer comprising a tertiary winding, a common winding and a series winding wound concentrically in radially spaced apart relationship with one another and mounted on the middle limb of a three limb magnetic material core and a tapping winding and an exciting winding wound concentrically in radially spaced apart relationship with each other and mounted on one end limb of the transformer, the series winding, common winding and tapping winding being connected in series with one another, the free end of the series winding and the junction between the series winding and common winding being connected to a power supply, the moving end of the tapping winding being earthed and the tertiary winding and exciting winding being connected to each other parallelly and to a power supply.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a cross-sectional view of the compact single phase variable flux autotransformer with neutral end taps according to an embodiment of the invention; and
3 0 MAR 2009
4

Fig 2 is an electrical diagram of the transformer of Fig 1.
The compact transformer 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a tertiary winding 2, a common winding 3 and a series winding 4 wound concentrically in radially spaced apart relationship with one another and mounted on the middle limb 5 of a three limb magnetic material core 6. The end limbs of the core are marked 7 and 8. The transformer also comprises a tapping winding 9 and an exciting winding 10 wound concentrically in radially spaced apart relationship with each other and mounted on end limb 8 of the transformer. The series winding, common winding and tapping winding are connected in series with one another. The free end of the series winding and the junction between the series winding and common winding are connected to a power supply. The moving end 11 of the tapping winding is earthed. The tertiary winding and exciting winding are connected to each other parallelly and to a power supply. Normally for increased voltage and current ratings of the transformer radial dimensions of each winding are to be increased. And as the percentage impedance is the direct function of square of the radial dimensions it increases rapidly with increment of radial dimensions. According to the invention the tap winding 9 is mounted on the side limb 8. This will create space between common winding 3 and tertiary winding 2. As a result, radial dimensions are reduced and the percentage impedance is also reduced. In order to counterbalance the magneto motive force generated by tapping winding 9 in side limb 8, the exciter winding 10 is used.
According to the invention it is possible to control the percentage of leakage impedance with increase in voltage and current ratings of the transformer by distributing the windings on the limbs of the transformer and electrically connecting
3 0 MAR
5

the windings as illustrated in the drawings. As the percentage of leakage impedance is controlled without increasing the height of the transformer, the transformer is compact and its transportation is easy. Space requirement for installation of the transformer is reduced.
3 0 MAR 2009

We claim :
1. A compact single phase variable flux autotransformer with neutral end taps, the autotransformer comprising a tertiary winding, a common winding and a series winding wound concentrically in radially spaced apart relationship with one another and mounted on the middle limb of a three limb magnetic material core and a tapping winding and an exciting winding wound concentrically in radially spaced apart relationship with each other and mounted on one end limb of the transformer, the series winding, common winding and tapping winding being connected in series with one another, the free end of the series winding and the junction between the series winding and common winding being connected to a power supply, the moving end of the tapping winding being earthed and the tertiary winding and exciting winding being connected to each other parallelly and to a power supply. Dated this 30th day of March 2009
(Jose M A)
Of Khaitan&Co
Agent for the Applicants
3 0 MAR 2009
7