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
Ultra high frequency sensor for sensing partial discharges in oil filled transformer
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Mithun Muthiah Sakthivel, Dwaraka, Thathampally P O, Alappuzha 688013, Kerala,
India and Lobo Anthony Marcel, BEST Rajhansa CHS, B6\4, Ghatkopar East, Mumbai 400075, 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 an ultra high frequency sensor for sensing partial discharges in oil filled transformer
BACKGROUND OF THE INVENTION
Partial discharges occur in a oil filled transformer due to defects or failure of the electrical insulation within the transformer. Intensity of partial discharges is indicative of quality of insulation in the transformer and health of the transformer. The higher the intensity of partial discharges, the poorer the insulation. Monitoring of partial discharges in the transformer is, therefore, of utmost importance. An ultra high frequency sensor is generally used for sensing partial discharges in an oil filled transformer. The ultra high frequency sensor mainly comprises a metallic, usually stainless steel, tubular housing having an antenna located within the sensing end thereof and a handle at the tail end thereof. The sensor also comprises a probe terminal provided at the tail end of the tubular housing and electrically connected to the antenna by a cable extending through the tubular housing. The tubular housing extends into the transformer tank through the drain valve of the transformer and is fitted to the drain valve body. Because of the sensing end of the sensor being conductive, extreme care should be taken to maintain electrical clearance between the sensing end and live parts of the transformer under transformer oil to prevent flashovers. While installing the sensor within the transformer extreme care also has to be taken to prevent the sensing end striking or hitting parts of the

transformer and causing flashovers and damaging them. Besides, there should be effective sealing arrangement between the tubular housing and the drain valve to prevent leakage during working of the transformer.
OBJECTS OF THE INVENTION
An object of the invention is to provide an ultra high frequency sensor for sensing partial discharges in oil filled transformer which sensor does not suffer from any constraints of electrical clearance between the sensing end thereof and life parts of the transformer under transformer oil and which sensor can be safely inserted into the transformer without causing flashovers and damages to the components of the transformer even under working conditions of the transformer and which transformer can be retracted from the transformer for repairs or inspection without shutting down the transformer and draining the transformer oil.
Another object of the invention is to provide an ultra high frequency sensor for sensing partial discharges in oil filled transformer which sensor ensures a positive and effective leak tight joint with the drain valve body so as to prevent leakage of transformer oil.
Another object of the invention is to provide an ultra high frequency sensor for sensing partial discharges in oil filled transformer which sensor is simple in construction and easy and convenient to operate and which sensor restricts its linear movement by itself and is versatile.

DETAILED DESCRIPTION OF THE INVENTION
According to the present invention there is provided an ultra high frequency sensor for sensing partial discharges in oil filled transformer, the sensor comprising a tubular housing extending into the transformer through the drain valve thereof and mounted to the drain valve body leak tight, the sensor comprising a sensing end made of an electrically insulating material and having an antenna located therein and further having a first stopper made of electrically insulating material at the tip of the sensing end, the sensor further comprising a probe terminal located at the tail end thereof and connected to the antenna by a cable extending through the tubular housing, the tail end further having a handle and a second stopper.
The following is a detailed description of the invention with reference to the accompanying drawings, in which:
Fig 1 is an isometric view of the ultra high frequency sensor for sensing partial discharges in oil filled transformer according to an embodiment of the invention; and
Fig 2 is a crossectional view of the sensor of Fig 1 inserted in the transformer tank through the drain valve thereof.

The ultra high frequency sensor 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a tubular housing 2 comprising a sensing end 3 made of an electrically insulating material selected from, for instance, fibre reinforced plastics and a tail end 4 made of a mechanically strong material selected from for instance, stainless steel. 5 is an antenna, preferably a conical monopole antenna, located within the sensing end of the sensor. 6 is a stopper fitted at the tip of the sensing end of the sensor. The stopper 6 is made of an electrically insulating material selected from, for instance, fibre reinforced plastics. The tail end of the sensor is fitted with a probe terminal 7 which is connected to the antenna by cable 8 extending through the tubular housing. The tail end of the sensor is also provided with a handle 9. The tail end of the sensor is further provided with an adjustable stopper 10 comprising ring 10a fitted onto the tail end of the sensor by grub screws 11. The ring position along the tail end of the sensor can be adjusted by loosening the grub screws, shifting the ring and refitting the ring on the tail end of the sensor by tightening the grub screws. The tubular housing extends into the tank 12 of an oil filled transformer (not shown) through the drain valve 13 and drain pipe 14 of the tank. 15 and 16 are drain pipe flange and valve flange, respectively fitted together with bolts (not shown) tightened in the bolt holes 17 and 18 in flanges 15 and 16 respectively with a sealing gasket 19 between the flanges 15 and 16. 20 is sealing sleeve located over the tail end of the sensor and having a mounting flange 21 fitted to a corresponding flange 22 of the drain valve by bolts (not shown) passing through bolt holes 23 and 24 in the sleeve flange 21 and the flange 22 of the valve, respectively. 25 is a sealing gasket provided between the flanges 21 and 22. A plurality of sealing rings 26 are provided between the sealing sleeve and tail end of the sensor. 27 is a sealing plug

at the distal end of the sealing sleeve. The sealing sleeve is made of a mechanically strong material selected from, for instance, stainless steel material. The plug is also made of a mechanically strong material selected from, for instance, stainless steel material. The tubular housing is slidable back and forth within the sealing sleeve. Because of the openings 28, 29 and 30 in flanges 15, 16 and 22 respectively being longer, the sensing end of the sensor with stopper 6 can move back and forth therethrough. Because of the spacing between the distal end of the sealing sleeve and stopper 10 the forward sliding movement of the tubular housing of the sensor can be adjusted or controlled in that the adjustable stopper abuts and restricts the forward movement of the tubular housing of the sensor. Similarly the stopper 6 abuts the mounting flange 21 of the sealing sleeve and restricts the backward movement of the tubular housing of the sensor. During operation of the sensor, the probe terminal is connected to a probe (not shown) and the intensity of the partial discharges in the transformer is monitored online or otherwise measured so as to keep a watch on the health and performance efficiency of the transformer.
The sensor of the invention can be inserted in the transformer tank either before transformer oil is filled in the transformer tank or during working condition of the transformer. In order to insert the sensor in the transformer tank in the working condition of the transformer the gate 31 of the drain valve is closed to prevent leakage of transformer oil. The tubular housing of the sensor is retracted to the extreme backward position and the mounting flange 21 of the sealing sleeve 20 is bolted onto the mounting flange 22 of the drain valve and the gate of the drain valve is opened. Leakage of oil will not take place because of the effective and positive sealing provided by the sealing sleeve

20 and sealing rings 26 and mounting flange 21 of the sealing sleeve and the mounting flange 22 of the drain valve with the sealing gasket 25 therebetween. The tubular housing of the sensor is pushed forward and inserted into the tank of the transformer by holding the handle. The adjustable stopper abuts against the distal end of the sealing sleeve and restricts the forward movement of the tubular housing. Installation of the sensor in the transformer tank without oil is also carried out by opening the gate of the drain valve and bolting the mounting flange 21 of the sealing sleeve to the mounting flange 22 of the drain valve. The stopper 6 at the tip of the sensing end of the sensor abuts against the mounting flange 21 of the sealing sleeve to restrict the backward movement of the tubular housing. Since the sensing end 3 and stopper 6 are made of electrically insulating material constraints of electrical clearance between the sensing end of the sensor and live parts of the transformer has been eliminated. As a result chances of flashover have been eliminated. As the forward and backward movement of the tubular housing of the sensor are restricted, possibility of the sensing end of the sensor striking parts of the transformer and causing flashovers and damage to the parts of the transformer also have been eliminated. The adjustable stopper provides flexibility to extend the tubular housing of the sensor to different lengths in the transformer and also use the same sensor in transformer tanks of different sizes. The sealing sleeve with the sealing rings and the plug 27 provide a very effective and positive sealing between the tubular housing of the sensor and the drain valve body so as to prevent leakage.
The above embodiment is by way of example and should not be construed and understood to be limitative of the scope of the invention. The stopper 6 and the sensing

end of the transformer and the sealing sleeve and the sealing plug can be made of different materials. The adjustable stopper and the stopper 6 can be of different construction. The adjustable stopper need not be adjustable. Embodiments of the invention comprising such variations of the invention are obvious to a person skilled in the art and are to be construed and understood to be within the scope of the invention.

We Claim:
1. An ultra high frequency sensor for sensing partial discharges in oil filled transformer, the sensor comprising a tubular housing Extending into the transformer through the drain valve thereof and mounted to the drain valve body leak tight, the sensor comprising a sensing end made of an electrically insulating material and having an antenna located therein and further having a first stopper made of electrically insulating material at the tip of the sensing end, the sensor further comprising a probe terminal located at the tail end thereof and connected to the antenna by a cable extending through the tubular housing, the tail end further having a handle and a second stopper.
2. The sensor as claimed in claim 1, wherein the tubular housing is leak tight mounted to the drain valve body by a sealing sleeve located over the tail end of the tubular housing leak tight defining a spacing with the second stopper, the sealing sleeve having a mounting flange fitted to a corresponding flange of the drain valve body leak tight and the tubular housing being slidable back and forth within the sealing sleeve.
3. The sensor as claimed in claim 2, wherein the sealing sleeve is made of stainless steel material and a plurality of sealing rings are provided between the sealing sleeve and the tail end of the sensor in longitudinally spaced apart relationship and the distal end of the sealing sleeve is provided with a sealing plug.

4. The sensor as claimed in anyone of claims 1 to3, wherein the sensing end of the tubular housing and the first stopper are made of fibre reinforced plastics
5. The sensor as claimed in claim 1 to 4, wherein the second stopper is an adjustable stopper and comprises a ring fitted on the tail end of the sensor with grub screws.
6. The sensor claimed in claim 1 to 5, wherein the antenna is a conical monopole antenna.
Dated this 18lh day of February 2009