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 Voltage detection sensor for detecting voltage at a transformer winding
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road. Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
Inventors
Deepak Krishna Remje and Venkatasami Athikkan of Crompton Greaves Ltd, Condition Monitoring and Research Centre, Kanjur Marg (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
The present invention relates to a voltage detection sensor for detecting voltage at a transformer winding. More particularly, the present invention relates to a voltage detection sensor for detecting voltage at a transformer winding without contacting its conductor portion.
BACKGROUND OF THE INVENTION
As a transformer ages, the insulation material applied to windings of the transformer tends to shrink, thereby reducing the overall winding clamping pressure and allowing the windings to move. Any movement, looseness, deformation or distortion in transformer windings can lead to undesirable voltages across the transformer windings and malfunctioning thereof. An early and reliable detection of such conditions may be carried out by regularly testing voltage surges (if any) at transformer windings.
A typical transformer winding comprises a conductor coated with an insulating material. To measure the voltage at a transformer winding, the insulating material has to be pricked with a probe in order to make contact with the conductor portion. The insulating layer is repaired when the testing is completed, however, frequent pricking of the insulating layer damages it and therefore, it is not preferable to prick the insulating layer every time the voltage at the corresponding transformer winding have to be measured.
Alternatively, voltages can be measured at those transformer windings which are provided with a tap. A transformer tap is an external connection point along a transformer winding at which the voltage across the winding can be measured.

However, there is no provision for measuring the voltage at a tap-less transformer winding without pricking the insulating layer of the corresponding winding.
Therefore, there is a need for efficiently detecting voltage at a transformer winding, without pricking/removing the insulating layer of winding. The voltage at a transformer winding should be measured without contacting its conductor portion.
OBJECTS OF THE INVENTION
An object of the present invention is to facilitate detection of voltage at a transformer winding, without pricking/removing the insulating layer of the winding.
Another object of the present invention is to measure voltage at a transformer winding without contacting its conductor portion.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided a voltage detection sensor for detecting voltage at a transformer winding without contacting conductor portion of the transformer winding, the voltage detection sensor comprising a conductor, an insulating layer surrounding said conductor, and a metal layer disposed over said insulating layer, the voltage detection sensor being adapted to be detachably attached around the transformer winding as a test winding, wherein alternating conducting and insulating portions of the transformer and test windings form a capacitive voltage divider thereof.
Preferably, the capacitive voltage divider is a series combination of at least two capacitors, each of which being formed by a pair of conducting portions and an insulating portion therebetween.

Preferably, the voltage at the transformer winding is measured based on voltage at the test winding and capacitances of capacitors of the capacitive voltage divider.
Preferably, the voltage detection sensor is detachably attached around the transformer winding through fasteners like cable ties.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is schematic view of a transformer illustrating a voltage detection sensor and a plurality of windings in accordance with an embodiment of the present invention:
Fig 2 illustrates an exploded view of the voltage detection sensor of Fig.l in accordance with an embodiment of the present invention;
Fig 3 illustrates detachable attachment of the voltage detection sensor to a transformer winding in accordance with an embodiment of the present invention; and
Fig.4 is a cross section of the transformer winding and the voltage detection sensor of the Fig.3, illustrating formation of a capacitive voltage divider.
With reference to Figs. 1-3, a voltage detection sensor 1 is described which is used for detecting voltage at a transformer winding 2 of a transformer 100 without contacting conductor portion 3 of the winding 2. The transformer 100 includes Low Voltage (LV) winding 4 and High Voltage (HV) winding 5. The HV winding 5 include a plurality of discs 6, 7, 8 and 9 of the HV winding 5, each of which includes a plurality of concentric transformer windings. For example, the disc 6 includes concentric transformer windings 2, 10, 11, 12, 13, and 14.

Each of the transformer windings 10, 11, 12. 13, 14 and 2 comprise a conductor surrounded by an insulator. For example, the transformer winding comprises the conductor 3 and the insulator 15.
The voltage detection sensor 1 comprises a conductor 20, an insulating layer 21 surrounding said conductor 20, and a metal layer 22 disposed over said insulating layer 21. The metal layer 22 may either be a metal coating over the insulating layer 21 or either a metal foil wrapped over the insulating layer 21. In an embodiment of the present invention, the detection sensor 1 is made with the same conductor and insulation used in the transformer winding 2. The voltage detection sensor 1 can also be referred to as a dummy conductor with metalized insulation.
The voltage detection sensor 1 is adapted to be detachably attached around the transformer winding 2 through fasteners such as cable ties 30 as a test winding. The alternating conducting and insulating portions of the test winding 1 and the transformer winding 2 form a capacitive voltage divider thereof.
Fig.4 is a cross-section of the detachably attached voltage detection sensor 1 and the transformer winding 2. The insulator 15 and conductor 3 of the transformer winding 2, and the metal layers 22, insulating layers 21 and the conductor 20 of the test winding 1 are illustrated herein. It may be noted that the pair of conducting portions 3 and 22 and an insulating layer 15 therebetween form a capacitor, whereas the pair of conducting portions 22 and 20 and insulating layer 21 therebetween form a

capacitor. Said capacitors are connected in series and therefore form a capacitive voltage divider,
The capacitances of said capacitors are calculated based on the area of overlap of respective conducting portions, distance between the conducting portions and type of insulating portion therebetween.
Based on the voltage at the test winding 1 and capacitances of the capacitive voltage divider, the voltage at the transformer winding 2 is measured.
Thus, the voltage at the transformer winding 2 is measured without contacting conducting portion 3 of the transformer winding 2.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
1. A voltage detection sensor for detecting voltage at a transformer winding without
contacting conductor portion of the transformer winding, the voltage detection sensor
comprising a conductor, an insulating layer surrounding said conductor, and a metal
layer disposed over said insulating layer, the voltage detection sensor being adapted to
be detachably attached around the transformer winding as a test winding, wherein
alternating conducting and insulating portions of the transformer and test windings
form a capacitive voltage divider thereof.
2. The voltage detection sensor as claimed in claim 1, wherein the capacitive voltage divider is a series combination of at least two capacitors, each of which being formed by a pair of conducting portions and an insulating portion therebetween.
3. The voltage detection sensor as claimed in claim 2, wherein voltage at the transformer winding is measured based on voltage at the test winding and capacitances of capacitors of the capacitive voltage divider.
4. The voltage detection sensor as claimed in claim 1, wherein the voltage detection sensor is detachably attached around the transformer winding through fasteners like cable ties.