Title of Invention	A DIAGNOSTIC METHOD FOR DETERMINING DEFORMATIONS IN A TRANSFORMER WINDING
Abstract	A diagnostic method for determining deformations in a transformer winding comprising the steps of representing the winding as a lumped parameter circuit and dividing the winding into at least two sections; generating a first set of fingerprint values based on capacitive values of the winding; the first set of finger print values indicating the location and extent of radial deformation in the winding; generating a second set of fingerprint values based on capacitive values of the winding; the second set of finger prints indicating the location and extent of axial deformation in the winding and determining the location and extent of radial or axial deformation or combination of both radial and axial deformation in the winding by comparing the measured values with the first set and second set of finger print values.

Title of Invention

A DIAGNOSTIC METHOD FOR DETERMINING DEFORMATIONS IN A TRANSFORMER WINDING

Abstract

A diagnostic method for determining deformations in a transformer winding comprising the steps of representing the winding as a lumped parameter circuit and dividing the winding into at least two sections; generating a first set of fingerprint values based on capacitive values of the winding; the first set of finger print values indicating the location and extent of radial deformation in the winding; generating a second set of fingerprint values based on capacitive values of the winding; the second set of finger prints indicating the location and extent of axial deformation in the winding and determining the location and extent of radial or axial deformation or combination of both radial and axial deformation in the winding by comparing the measured values with the first set and second set of finger print values.

Full Text	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 PROVISIONAL SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION A diagnostic method for determining deformations in a transformer or reactor winding INVENTORS Joshi Prasad Madhukar, Systems and Control Engineering Department, Indian Institute of Technology Bombay, Powai, Mumbai-400076, Maharashtra, India and Dr Kulkarni Shrikrishna Vyankatesh, Electrical Engineering Department, Indian Institute of Technology Bombay, Powai, Mumbai-400076, Maharashtra, India, both Indian nationals APPLICANTS Indian Institute of Technology, Bombay, an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961, Powai, Mumbai 400076, Maharashtra, India PREAMBLE TO THE DESCRIPTION The following specification describes the invention: FIELD OF INVENTION This invention relates to a diagnostic method for determining deformations in a transformer or reactor winding. BACKGROUND OF INVENTION Transformers are one of the important components of a power system and are used to step up or step down voltage levels in the power system. Deformations in the transformer winding will cause malfunctioning of the transformer and may even lead to explosion of the transformer thereby giving rise to damages to the other components of the power system and accidents. Therefore, it is essential to detect and determine deformations in the transformer winding to ensure normal operation of the transformer and power system, obtain expected operational life of the transformer and to prevent accidents. Deformations in the winding may be axial or radial in nature depending upon the displacement of the transformer windings with respect to the transformer core in the axial or radial direction. Frequency Response Analysis (FRA) is widely used for detection of deformations in the transformer winding. The FRA method comprises generation of a reference set or fingerprint values of transfer functions by applying a voltage (V) at different frequencies to the line end of the winding with the neutral end of the winding grounded and measuring the transfer function (In/V, in which In is the current flowing into the neutral end of the winding) for each frequency. These transfer function values are plotted to form a finger-print graph. At the time of detection of deformations in the winding, similar measurements for the winding are made and similar graph is plotted using the measured transfer function. The graph representing the subsequent measurements is superimposed on the finger-print graph and the differences, if any, between the curves of the two graphs are examined visually for deformations. Visual examination and analysis of the differences between the two graphs is subjective and may vary from person to person and may not provide a proper and accurate evaluation of the deformations. Several hundreds of measurements at various frequencies are required for plotting both the graphs. This is quite inconvenient and cumbersome to carryout. Although comparison of the two graphs indicates presence of deformation, if any, it does not indicate the location, nature and extent of the deformation. OBJECTS OF INVENTION An object of the invention is to provide a diagnostic method for determining deformations in a transformer or reactor winding, which method indicates the location of deformation in a winding and whether the deformation in the winding is radial or axial and the extent of deformation. Another object of the invention is to provide a diagnostic method for determining deformations in a transformer or reactor winding, which method is simple and easy to carry out. DETAILED DESCRIPTION OF THE INVENTION A transformer winding is represented as a lumped parameter circuit divided into discrete sections, each section having elements like series capacitance (Cs), self inductance (Z„), mutual inductance (Ly) and ground capacitance (Cg) as illustrated in Fig. 1 of the accompanying drawings. Each section of the winding is represented by a pi (11) model as illustrated in Fig 2 of the accompanying drawings, in which two legs are given by Cg/2. Such a lumped parameter circuit is used by researchers for transformer analysis. It is known that at high frequencies, movements of the transformer winding in the axial and radial direction can be closely related to the corresponding changes in sectional series capacitance (Cs) and sectional ground capacitance (Cg), respectively. According to the invention there is provided a diagnostic method for determining deformations in a transformer or reactor winding which comprises the following steps: A. Generation of finger print values Al. Generate a first set of fingerprint values based on capacitive values of the winding, which is indicative of the deformed section and extent of radial deformation in the deformed section of the winding, as follows: (i) Measure the terminal capacitance CI between one end (1) of the winding (W) and one ground terminal (T) in Fig 1 at a high frequency beyond which the terminal impedance of the winding remains capacitive, while keeping the other end (2) of the winding and the other ground terminal (2') disconnected. Measure the terminal capacitance C2 between other end (2) of the winding and the other ground terminal (2') in Fig 1 at the same high frequency, while keeping the one end (1) of the winding and the one ground terminal (1') disconnected. Measure the capacitance C3 across the two ends (1,2) of the winding at the same high frequency. Measure the terminal capacitance C4 between one end (1) of the winding and one ground terminal (!') or other end (2) of the winding and the other ground terminal (2') at a low frequency at which the terminal impedance of the winding is predominantly capacitive in nature, while keeping disconnected the winding end and ground terminal, at which the measurement is not taken. The selected high and low frequencies depend on winding characteristics and would generally lie between 1 MHz - 10 MHz and 50 Hz - 100 Hz respectively. (ii) Calculate the sectional series capacitance (Cs) and the sectional ground capacitance (Q) of each of the different sections S of the winding using the values of C3 and C4 obtained in step Al (i) as follows : Cg = C4/(number of sections) and Cs is calculated by known network reduction technique. Typically for 8 uniform sections of the winding, Cg and C, are calculated as follows : Cg = C4 / 8 and Cs, = k Cg, (iii) Simulate a range of deformations in each of the sections of the winding by changing the sectional ground capacitance Cg obtained in step Al(ii) by predetermined percentages and generate simulated terminal capacitance values CI', C2' and C4' under the same conditions and procedures corresponding lo CI, C2 and C4, respectively in step Al(i) for each change of the sectional ground capacitance; (iv) Calculate deformation coefficient which is a non-limiting function of (Cl-C1')/(C2-C2') for each of the sections of the winding for each change of the sectional ground capacitance Cg made in step Al(iii). Typically deformation coefficient can be calculated as log10 [(C1-C1')/(C2-C2')]. The deformation coefficients form the first set of fingerprints which are indicative of the location of the radially deformed section of the winding; (v) Calculate the difference between C4 in step Al(i) and C4' obtained in step Al(iii). A difference in the values is indicative of the extent of radial deformation in the winding. A2. Generate a second set of fingerprint values based on capacitive values of the winding, which is indicative of the deformed section and extent of axial deformation in the deformed section of the winding as follows: (vi) Simulate a range of deformations in each of the sections of the winding by changing the sectional series capacitance Cs obtained in step Al(ii) by predetermined percentages and generate simulated terminal capacitance values CI" and C2" and capacitance value C3" under the same conditions and procedures corresponding to CI, C2 and C3, respectively in step Al(i) for each of the said range of deformation percentages; (vii) Calculate deformation coefficient which is a non-limiting function of (Cl-C1 ")/(C2-C2") for each of the sections of the winding for each change of the sectional series capacitance C,. made in step A2(vi). Typically deformation coefficient can be calculated as log10 [(C1-C1")/(C2-C2")]. The deformation coefficients form one part of second set of fingerprints which are indicative of the location of the axially deformed section of the winding; (viii) Calculate the difference between C3 obtained in step Al(i) and C3" obtained in step A2(vi) for each section of the winding for each change of the sectional series capacitance in step A2(vi). The differences form the second part of the second set of fingerprints which are indicative of the extent of the axial deformation in the deformed section of the winding. B. Generation of diagnostic values At the time of determining whether deformations have occurred in the winding, diagnostic values are generated as follows: (1) Measure the terminal capacitance values CI"', C2'", C4'" and capacitance value C3'" as explained in step Al(i); (2) Compare the values of CI with CI'" and C2 with C2'". No difference in the values indicates that the winding has not been deformed. If there is a difference between the values the following steps 3-5 are carried out to locate the deformed section of the winding and to determine whether the deformation is radial or axial and its extent. (3) Compare the values of C4 with C4"'. A difference in the values indicates a radial deformation in the winding and its extent. To identify the section of the winding which has been radially deformed, deformation coefficient is calculated using the equation: Log10 [(C1-C1””)/(C2-C2””) The calculated deformation coefficient is compared with the fingerprints of deformation coefficients obtained in step Al(iv) to locate the section of the winding which has been radially deformed. (4) No difference between the values of C4 and C4'" indicates that a section of the winding has been axially deformed. To identify the axially deformed section, deformation coefficient calculated in B(3) is compared with the fingerprints of deformation coefficients obtained in step A2(vii) to locate the section of the winding which has been axially deformed. (5) To know the extent of axial deformation, C3"' is compared with C3. The difference is compared with the fingerprints of the differences in step A2(viii). It is to be understood that the method of the invention can be effectively used for determining deformations in any current carrying coil besides transformer or reactor winding. According to the method of the invention location of deformation in a winding and whether the deformation in the winding is radial or axial and its extent can be easily determined. The method is simple and easy to carryout, since only four capacitance measurements (CI, C2, C3 and C4) are required for generation of the fingerprints. Therefore, any deformations in the winding can be easily detected and timely remedial action can be taken to prevent malfunctioning of the transformer. Damages to the other components of the power system and accidents due to malfunctioning of the transformer can be prevented.

Full Text

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
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A diagnostic method for determining deformations in a transformer or reactor winding
INVENTORS
Joshi Prasad Madhukar, Systems and Control Engineering Department, Indian Institute of Technology Bombay, Powai, Mumbai-400076, Maharashtra, India and Dr Kulkarni Shrikrishna Vyankatesh, Electrical Engineering Department, Indian Institute of Technology Bombay, Powai, Mumbai-400076, Maharashtra, India, both Indian nationals
APPLICANTS
Indian Institute of Technology, Bombay, an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961, Powai, Mumbai 400076, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention:

FIELD OF INVENTION
This invention relates to a diagnostic method for determining deformations in a transformer or reactor winding.
BACKGROUND OF INVENTION
Transformers are one of the important components of a power system and are used to step up or step down voltage levels in the power system. Deformations in the transformer winding will cause malfunctioning of the transformer and may even lead to explosion of the transformer thereby giving rise to damages to the other components of the power system and accidents. Therefore, it is essential to detect and determine deformations in the transformer winding to ensure normal operation of the transformer and power system, obtain expected operational life of the transformer and to prevent accidents. Deformations in the winding may be axial or radial in nature depending upon the displacement of the transformer windings with respect to the transformer core in the axial or radial direction. Frequency Response Analysis (FRA) is widely used for detection of deformations in the transformer winding. The FRA method comprises generation of a reference set or fingerprint values of transfer functions by applying a voltage (V) at different frequencies to the line end of the winding with the neutral end of the winding grounded and measuring the transfer function (In/V, in which In is the current flowing into the neutral end of the winding) for each frequency. These transfer function values are plotted to form a finger-print graph. At the time of detection of deformations in the winding, similar measurements for the winding are made and similar graph is plotted using the measured transfer function. The graph representing the subsequent measurements is superimposed on the finger-print graph and the differences, if any, between the curves of the two graphs are examined visually for deformations. Visual examination and analysis of the differences between the two graphs is subjective and may vary from person to person and may not provide a proper and accurate evaluation of the deformations. Several hundreds of measurements at various frequencies are required for plotting both the graphs. This is quite inconvenient and cumbersome to carryout. Although comparison of the two graphs indicates presence of deformation, if any, it does not indicate the location, nature and extent of the deformation.

OBJECTS OF INVENTION
An object of the invention is to provide a diagnostic method for determining deformations in a transformer or reactor winding, which method indicates the location of deformation in a winding and whether the deformation in the winding is radial or axial and the extent of deformation.
Another object of the invention is to provide a diagnostic method for determining deformations in a transformer or reactor winding, which method is simple and easy to carry out.
DETAILED DESCRIPTION OF THE INVENTION
A transformer winding is represented as a lumped parameter circuit divided into discrete sections, each section having elements like series capacitance (Cs), self inductance (Z„), mutual inductance (Ly) and ground capacitance (Cg) as illustrated in Fig. 1 of the accompanying drawings. Each section of the winding is represented by a pi (11) model as illustrated in Fig 2 of the accompanying drawings, in which two legs are given by Cg/2. Such a lumped parameter circuit is used by researchers for transformer analysis. It is known that at high frequencies, movements of the transformer winding in the axial and radial direction can be closely related to the corresponding changes in sectional series capacitance (Cs) and sectional ground capacitance (Cg), respectively.
According to the invention there is provided a diagnostic method for determining deformations in a transformer or reactor winding which comprises the following steps:

A. Generation of finger print values
Al. Generate a first set of fingerprint values based on capacitive values of the winding, which is indicative of the deformed section and extent of radial deformation in the deformed section of the winding, as follows:
(i) Measure the terminal capacitance CI between one end (1) of the winding (W) and one ground terminal (T) in Fig 1 at a high frequency beyond which the terminal impedance of the winding remains capacitive, while keeping the other end (2) of the winding and the other ground terminal (2') disconnected. Measure the terminal capacitance C2 between other end (2) of the winding and the other ground terminal (2') in Fig 1 at the same high frequency, while keeping the one end (1) of the winding and the one ground terminal (1') disconnected. Measure the capacitance C3 across the two ends (1,2) of the winding at the same high frequency. Measure the terminal capacitance C4 between one end (1) of the winding and one ground terminal (!') or other end (2) of the winding and the other ground terminal (2') at a low frequency at which the terminal impedance of the winding is predominantly capacitive in nature, while keeping disconnected the winding end and ground terminal, at which the measurement is not taken. The selected high and low frequencies depend on winding characteristics and would generally lie between 1 MHz - 10 MHz and 50 Hz - 100 Hz respectively.
(ii) Calculate the sectional series capacitance (Cs) and the sectional ground capacitance (Q) of each of the different sections S of the winding using the values of C3 and C4 obtained in step Al (i) as follows :
Cg = C4/(number of sections) and Cs is calculated by known network reduction technique. Typically for 8 uniform sections of the winding, Cg
and C, are calculated as follows :

Cg = C4 / 8 and
Cs, = k Cg,

(iii) Simulate a range of deformations in each of the sections of the winding by changing the sectional ground capacitance Cg obtained in step Al(ii) by predetermined percentages and generate simulated terminal capacitance values CI', C2' and C4' under the same conditions and procedures corresponding lo CI, C2 and C4, respectively in step Al(i) for each change of the sectional ground capacitance;
(iv) Calculate deformation coefficient which is a non-limiting function of (Cl-C1')/(C2-C2') for each of the sections of the winding for each change of the sectional ground capacitance Cg made in step Al(iii). Typically deformation coefficient can be calculated as log10 [(C1-C1')/(C2-C2')]. The deformation coefficients form the first set of fingerprints which are indicative of the location of the radially deformed section of the winding;
(v) Calculate the difference between C4 in step Al(i) and C4' obtained in step Al(iii). A difference in the values is indicative of the extent of radial deformation in the winding.
A2. Generate a second set of fingerprint values based on capacitive values of
the winding, which is indicative of the deformed section and extent of axial deformation in the deformed section of the winding as follows:

(vi) Simulate a range of deformations in each of the sections of the winding by changing the sectional series capacitance Cs obtained in step Al(ii) by predetermined percentages and generate simulated terminal capacitance values CI" and C2" and capacitance value C3" under the same conditions and procedures corresponding to CI, C2 and C3, respectively in step Al(i) for each of the said range of deformation percentages;
(vii) Calculate deformation coefficient which is a non-limiting function of (Cl-C1 ")/(C2-C2") for each of the sections of the winding for each change of the sectional series capacitance C,. made in step A2(vi). Typically deformation coefficient can be calculated as log10 [(C1-C1")/(C2-C2")]. The deformation coefficients form one part of second set of fingerprints which are indicative of the location of the axially deformed section of the winding;
(viii) Calculate the difference between C3 obtained in step Al(i) and C3" obtained in step A2(vi) for each section of the winding for each change of the sectional series capacitance in step A2(vi). The differences form the second part of the second set of fingerprints which are indicative of the extent of the axial deformation in the deformed section of the winding.
B. Generation of diagnostic values
At the time of determining whether deformations have occurred in the winding, diagnostic values are generated as follows:
(1) Measure the terminal capacitance values CI"', C2'", C4'" and capacitance value C3'" as explained in step Al(i);
(2) Compare the values of CI with CI'" and C2 with C2'". No difference in the values indicates that the winding has not been deformed. If there is a difference between the values the following steps 3-5 are carried out to

locate the deformed section of the winding and to determine whether the
deformation is radial or axial and its extent.
(3) Compare the values of C4 with C4"'. A difference in the values indicates a
radial deformation in the winding and its extent. To identify the section of
the winding which has been radially deformed, deformation coefficient is
calculated using the equation:
Log10 [(C1-C1””)/(C2-C2””)
The calculated deformation coefficient is compared with the fingerprints of deformation coefficients obtained in step Al(iv) to locate the section of the winding which has been radially deformed.
(4) No difference between the values of C4 and C4'" indicates that a section of the winding has been axially deformed. To identify the axially deformed section, deformation coefficient calculated in B(3) is compared with the fingerprints of deformation coefficients obtained in step A2(vii) to locate the section of the winding which has been axially deformed.
(5) To know the extent of axial deformation, C3"' is compared with C3. The difference is compared with the fingerprints of the differences in step
A2(viii).
It is to be understood that the method of the invention can be effectively used for determining deformations in any current carrying coil besides transformer or reactor winding.
According to the method of the invention location of deformation in a winding and whether the deformation in the winding is radial or axial and its extent can be easily determined. The method is simple and easy to carryout, since only four capacitance

measurements (CI, C2, C3 and C4) are required for generation of the fingerprints. Therefore, any deformations in the winding can be easily detected and timely remedial action can be taken to prevent malfunctioning of the transformer. Damages to the other components of the power system and accidents due to malfunctioning of the transformer can be prevented.

Documents:

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Patent Number

269859

Indian Patent Application Number

1893/MUM/2007

PG Journal Number

47/2015

Publication Date

20-Nov-2015

Grant Date

12-Nov-2015

Date of Filing

27-Sep-2007

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY

Applicant Address

POWAI, MUMBAI

Inventors:

#	Inventor's Name	Inventor's Address
1	JOSHI PRASAD MADHUKAR	SYSTEM AND CONTROL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY BOMBAY, POWAI, MUMBAI-400076.
2	KULKARNI SHRIKRISHNA VYANKATESH	ELECTRICAL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY BOMBAY, POWAI, MUMBAI-400076

PCT International Classification Number

H01F27/32

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA