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
A method for locating partial discharge in a transformer.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Venkatasami Athikkan of Condition Monitoring & Diagnostic Centre, Global R&D, Crompton Greaves Ltd, Kanjur Marg; Mumbai, Maharashtra, India, an 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
The present invention relates to a method of detecting and locating partial discharge in transformer winding.
BACKGROUND OF THE INVENTION
Transformers are vital components in a power system. When the insulation of a transformer is poor, electrical discharges of very short durations of much less than a microsecond called as Partial Discharge (PD) occur within the transformer winding. Partial discharge (PD) essentially, is a short release of current due to electric field intensity within a finite region, in transformers partial discharges can be symptomatic of problems within the device such as floating components and insulation flaws. Partial discharges in transformers can also lead to corrosion of solid insulating materials and thus cause a breakdown of the concerned operating component over a period of time. PD can also lead to decomposition and pollution of the insulating oil as a result of which the insulation properties of the oil can de-generate. Over a period of time partial discharges (PD) contribute towards de-grading of the rated electrical parameters for which the transformer was designed to operate. It is therefore important to locate a PD so as to investigate the cause that lead to it. Detection of a PD can also be used the quality of manufacture and to monitor the health of a transformer.
PDs can be detected and located by the measuring and analyzing the acoustic noise that accompanies them. Multiple acoustic sensors are placed outside a transformer tank to allow for detection of the acoustic noise caused by a PD using the well known time of arrival

(TOA) algorithm or the time difference of arrival (TDOA) algorithm. The acoustic sensors need to be placed outside the transformer as they cannot sustain the interior environment of a transformer tank and at the same time be electrically and chemically neutral. The path between a PD and the acoustic sensors include the wall of the tank, and other parts of the therefore the multipath interference can severely limit the accuracy of the positioning system. The interference is caused by the differing acoustic velocity of the wave in the transformer tank. As the acoustic pulse travels away from the source it encounters the tank wall at different times and is recorded by the exterior sensor. Such multiple reflections of the acoustic wave render such a system of detecting the position of a PD inaccurate. Additionally, determining the location of the PD using Time of Arrival (TOA) or Time difference of Arrival (TDOA) algorithms necessarily require multiple sensors placed at multiple locations to obtain feedback from various incident and reflected surfaces thus making such methods expensive,
To overcome all the drawbacks as mentioned above a need arises to improve upon the reliability of locating of partial discharges in a less expensive manner.

OBJECTS OF THE INVENTION
An object of the invention is to provide a method for locating partial discharge in transformers using a single ultra high voltage sensor (UHF).
An another object of the invention is to provide a method for location partial discharge of a transformer by using frequency domain correlations of UHF signals collected from UHF sensor.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a method to locate a partial discharge in a transformer. The method comprises the steps of:
a) simulating partial discharges at pre-determined locations within the transformer winding and obtaining multiple frequency responses for the electromagnetic noise caused by simulated partial discharges from a UHF antennae located at a pre-determined position.
b) creating a database for the multiple frequency responses and the corresponding pre-determined location of the simulated partial discharges.
c) receiving a frequency response on an occurrence of a real time partial discharge from the UHF antennae.

d) performing a statistical co-relation between the frequency response of the real time partial discharge and each of the frequency responses obtained from simulated partial discharges using nearest neighborhood algorithm or co-relation coefficient or orthogonal transformation algorithm.
e) identifying the frequency response of a simulated partial discharge that gives a maximum co-relation with the frequency response of the real time partial discharge and determining from the database the location of the real time partial discharge as the pre-determined location of the simulated partial discharge that gives the maximum co-relation.
Several aspects of the invention are described below with reference to examples for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details, or with other methods, etc. In other instances, well known structures or operations are not shown in detail to avoid obscuring the features of the invention.
The following is a detailed description of the invention with reference to the accompanying drawings, in which;
Figure 1 is a flow chart describing the method of locating partial discharges according to the present invention.

Figure 2 illustrates a database structure used to store the frequency responses for simulated partial discharges according to the present invention.
Figure 3 illustrates a database structure used to store the co-relation figures for the frequency responses of the simulated partial discharges according to the present invention.
Figure 1 represents a flow chart describing the method of locating the PD according to the invention.
In stepl 1, a database is obtained for frequency responses of simulated partial discharges and their locations within the transformer winding. As is well known a partial discharge can be simulated by introducing high voltages in known locations between the taps of the transformer winding. The high voltage is applied in such a manner so as to get a single controlled discharge across the winding section. Such a partial discharge can be obtained for different intensities of voltage and current and time durations. The electromagnetic noise as caused by the simulated partial discharge is measured by a UHF antennae placed in a known location and a frequency response is obtained for it. The frequency response as obtained for a simulated partial discharge is unique and is characteristic of the transfer function that models the mathematical behavior of the environment between the simulated partial discharge

location and the UHF antennae. The details of an exemplary database are given in Figure 1. The database of Figure 1 stores the frequency response and location of each simulated partial discharge. Row 21 of the database represents the co-ordinates of the location of the simulated partial discharge X1,Y1,Z1 and the frequency response F1(X1,Y1,Z1) of the electromagnetic noise of the simulated partial discharge. Similarly row 22 represents the location co-ordinates of simulated partial discharge at X2,Y2,Z2 and the frequency response F2(X2,Y2,Z2). Row 30 represents a simulated partial discharge of a different intensity at position X|,Y],Z| and has a frequency response F10(X1,Y1,Z1).
In step 12, the frequency response of a real time partial discharge is obtained by a UHF antenna which is placed in the same position as was used to prepare the database of the step 11. The placement of the UHF in the same position is important to replicate the same set up and the transfer function as was used to create the database of step 11.
In step 13, a statistical co-relation is performed between the frequency response of the real-time partial discharge FR and each of the frequency responses of the simulated partial iischarges to obtain a co-relation figure corresponding to each of the frequency responses. A ligher co-relation figure indicates a high correspondence between the frequency responses. The statistical co-relation can be performed in a known manner using popular algorithms such as Nearest Neighborhood algorithm or Co-relation coefficient algorithm or Orthogonal ransformation.

In step !4, the co-relation figures as obtained for each of the statistical co-relations are populated in the database. Figure 3 shows a exemplary database in which the co-relation figures are stored. Row 21 of the database represents a co-relation figure C1 for the statistical co-relation done for the frequency response F1(X1,Y1,Z1) and FR, Similarly row 22 represents a co-relation figure C2 for the statistical co-relation done for the frequency response F2(X2,Y2,Z2) and FR . With reasonable approximation one can infer the origin of the real time partial discharge close to a simulated partial discharge for which the co-relation figure is the highest. For e.g. if C2 > C1 the real time partial discharge could have originated closer to X2,Y2,Z2 One skilled in the relevant art can readily appreciate that the accuracy of such a method to determine the location of a real time partial discharge depends on the database of frequency responses for simulated partial discharges at pre-determined locations.

We Claim,
1. A method of locating a partial discharge in a transformer, the method comprising the steps of:
a) simulating partial discharges at pre-determined locations within the transformer winding and obtaining a plurality of frequency responses from a sensory device in a pre-determined position in respect of the simulated partial discharges; and
b) creating a database for the plurality of frequency response and the corresponding pre-determined location in respect of the simulated partial discharges; and
c) receiving a frequency response on an occurrence of a real time partial discharge from the sensory device placed in the pre-determined position; and
d) performing a statistical co-relation between the frequency response of the real time partial discharge and each of the plurality of frequency responses corresponding to the simulated partial discharges: and
e) identifying the frequency response of a simulated partial discharge that gives a maximum co-relation with the frequency response of the real time partial discharge and determining from the database the location of the real time partial discharge as the pre-determined location of the simulated partial discharge that gives the maximum co-relation.
2. A method of claim 1, wherein the sensory device provides the frequency response for an electromagnetic noise caused by the partial discharge.

3. A method of claim 1, wherein the sensory device is a UHF antenna.
4. A method of claim 1, wherein the simulating partial discharges involves applying voltages having high frequency components to the transformer winding at the pre-determined locations.
5. A method of a claim 1, wherein the statistical co-relation can be performed using nearest neighborhood algorithm.
6. A method of a claim1, wherein the statistical co-relation can be performed using co-relation coefficient algorithm.
7. A method of a claim 1, wherein the statistical co-relation can be performed using orthogonal transformation algorithm.