DL/T 911-2016 PDF English
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Frequency response analysis on winding deformation of power transformers
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| DL/T 911-2004 | English | 70 |
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DL/T 911-2016: PDF in English (DLT 911-2016) DL/T 911-2016
DL
ELECTRICITY INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 27.100
F 24
Filing No.: 53992-2016
Replacing DL/T 911-2004
Frequency response analysis on winding deformation of
power transformers
ISSUED ON: FEBRUARY 05, 2016
IMPLEMENTED ON: JULY 01, 2016
Issued by: National Energy Administration
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Detection principle ... 6
5 Requirements for detection instruments ... 8
6 Detection method ... 9
7 Analysis and judgment of winding deformation ... 11
Appendix A (Informative) Basic requirements for transformer winding deformation
tester ... 14
Appendix B (Informative) Data export format of frequency response characteristic
curve ... 16
Appendix C (Normative) Use the correlation coefficient R to assist in determining the
deformation of transformer windings ... 18
Appendix D (Informative) Example of using the longitudinal comparison method to
determine the deformation of transformer windings ... 20
Appendix E (Informative) Example of using lateral comparison method to judge
transformer winding deformation ... 21
Appendix F (Informative) Example of using comprehensive analysis method to judge
transformer winding deformation ... 22
Appendix G (Informative) Example of typical interference waveform when the
transformer winding is deformed ... 24
Appendix H (Informative) Process for determining transformer winding deformation
using frequency response analysis method ... 27
Appendix I (Informative) Typical amplitude-frequency response characteristic curves
when transformer windings are deformed ... 29
Frequency response analysis on winding deformation of
power transformers
1 Scope
This standard specifies the basic requirements for detecting transformer winding
deformation by frequency response analysis.
This standard applies to power transformers with voltage levels of 66kV and above and
other transformers for special purposes.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
DL/T 1093 Guide for reactance method to detect and diagnose winding deformation
of power transformer
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Winding deformation
Refers to the axial or radial dimensional changes of power transformer windings
under the action of electric or mechanical forces, when they are subjected to short-
circuit current shock or collision during transportation; it is usually manifested as
local twisting, bulging or displacement of windings.
3.2
Bilateral network
Refers to a network with a pair of input ports and a pair of output ports. If the
network is composed of linear resistors, inductors (including mutual inductance),
capacitors, meanwhile it does not contain any independent power supply inside, it
H(f) - Modulus |H(jω)| of transfer function at frequency f;
U2(f), U1(f) - Peak or effective value of voltage |U₂(jω)| and |U₁(jω)| at response end
and excitation end at frequency f.
5 Requirements for detection instruments
5.1 Basic requirements for detection instruments
For the basic requirements of transformer winding deformation tester, please refer to
Appendix A.
5.2 Sweep frequency detection range
The sweep frequency detection range shall include the frequency band of 1kHz ~
1000kHz.
5.3 Sweep frequency detection method
It should adopt linear distribution frequency sweep detection method; repeat detection
of single frequency point can be performed.
5.4 Sweep frequency accuracy
The frequency accuracy of the sine wave signal output by the signal source shall not
exceed 0.01%.
5.5 Scanning frequency interval
The scanning frequency interval should be 1kHz.
5.6 Impedance matching method
The output impedance RS of the sine wave signal output source US of the detection
instrument shall be 50Ω; the input impedance of the two signal detection terminals U1
and U2 shall not be lower than 1MΩ; a 50Ω matching resistor R shall be installed
between the signal response terminal and the common terminal (see Figure 1).
The length of the coaxial cable should be within 15m ~ 20m; the cable used shall be a
RF cable with an impedance of 50Ω.
5.7 Detection accuracy
The detection instrument shall have a dynamic detection range of -100dB ~ 20dB; the
absolute error of detection within the range of -80dB ~ 20dB shall be less than 1dB.
5.8 Frequency selection and filtering characteristics
The detection instrument shall have a frequency selection and filtering function; its 6dB
bandwidth shall be less than 2% of the scanning frequency.
5.9 Data export format
For the data export format of the frequency response characteristic curve, see Appendix
B.
5.10 Data query function
The search function can be used to query the historical data of the same model, the same
manufacturer and the transformer.
5.11 Data display method
The frequency coordinates of the amplitude-frequency response characteristic curve
should be displayed in logarithmic coordinates.
6 Detection method
6.1 Detection condition requirements
6.1.1 Detection shall not be carried out in thunderstorms, rain, snow and other weather.
The detection shall strictly implement the requirements of the power safety work
regulations; it shall strictly implement the organizational and technical measures to
ensure safety. The test personnel shall be trained and have the ability to conduct on-site
tests.
6.1.2 Transformer winding deformation detection shall be carried out before all DC test
items or after the winding is fully discharged; demagnetization treatment shall be
carried out if necessary. According to the wiring requirements and wiring methods, each
winding of the transformer shall be tested one by one; the amplitude-frequency response
characteristic curve shall be recorded separately.
6.1.3 Before testing, all leads connected to the end of the transformer bushing shall be
removed; the removed leads shall be as far away from the tested transformer bushing
as possible.
6.1.4 The amplitude-frequency response characteristics of the transformer winding are
related to the position of the tap changer. It should test at the maximum tap position, or
ensure that the tap changer is in the same tap position each time the test is performed.
6.1.5 The test site shall provide AC220V power supply. When the site interference is
serious, the test equipment should be powered by an isolated power supply.
6.2 Wiring requirements
end; detect the amplitude-frequency response characteristics of the three-phase
windings of each voltage level of the transformer one by one.
7 Analysis and judgment of winding deformation
7.1 Analysis and judgment principle
The frequency response analysis method is used to judge the deformation of transformer
windings. The frequency response data curves of three-phase windings of the same
voltage level are mainly compared longitudinally, laterally, comprehensively; the
changes in the amplitude-frequency characteristics of the transformer windings are
judged by the correlation coefficient.
The method of using the correlation coefficient R to assist in judging the deformation
of transformer windings is shown in Appendix C.
7.2 Longitudinal comparison method
The longitudinal comparison method refers to comparing the amplitude-frequency
response characteristics of the same transformer, the same winding, the same tap
position, the different periods; judging the deformation of the transformer winding
according to the changes in the amplitude-frequency response characteristics. This
method has high detection sensitivity and judgment accuracy; however, it is necessary
to obtain the original amplitude-frequency response characteristics of the transformer
in advance, meanwhile the influence caused by changes in detection conditions and
detection methods shall be excluded.
For an example of using the longitudinal comparison method to judge the deformation
of transformer windings, see Appendix D.
7.3 Lateral comparison method
The lateral comparison method refers to comparing the amplitude-frequency response
characteristics of three-phase windings of the same voltage level of the transformer. If
necessary, the amplitude-frequency response characteristics of the same model
transformer manufactured by the same manufacturer at the same time are used to judge
whether the transformer winding is deformed. This method does not require the original
amplitude-frequency response characteristics of the transformer; it is relatively
convenient for field application. However, the possibility that the three-phase windings
of the transformer are deformed to a similar degree or that the amplitude-frequency
response characteristics of the three-phase windings of the normal transformer are
different shall be excluded.
See Appendix E for an example of using the lateral comparison method to judge the
deformation of the transformer winding.
7.4 Comprehensive analysis method
The comprehensive analysis method mainly compares the three-phase frequency
response fingerprints of the transformer laterally and longitudinally; makes a judgment
based on the differences in the three-phase frequency response fingerprints.
See Appendix F for an example of using the comprehensive comparison method to
judge the deformation of the transformer winding.
7.5 Analysis process
7.5.1 When conducting a transformer winding deformation test on site, the normal
measured frequency response data curve shall be continuous and smooth; however, in
a more complex field environment, the measured frequency response characteristic data
will sometimes be interfered, which will affect the effect of the test data; the validity of
the test data needs to be analyzed. See Appendix G for an example of a typical
interference waveform when the transformer winding is deformed.
7.5.2 When testing and analyzing the deformation of three-phase windings of the same
voltage level of the transformer, a certain process can be followed; if necessary, it can
combined with other test results such as transformer operating conditions and short-
circuit impedance. See Appendix H for the process of judging transformer winding
deformation using frequency response analysis.
7.6 Winding deformation analysis
7.6.1 The typical amplitude-frequency response characteristic curve of transformer
winding usually contains multiple obvious peaks and troughs. The changes in the
distribution position and number of peaks or troughs are important bases for analyzing
transformer winding deformation. See Appendix I for the typical amplitude-frequency
response characteristic curve of transformer winding deformation.
7.6.2 The peak or trough position of the low-frequency band (1kHz ~ 100kHz) of the
amplitude-frequency response characteristic curve changes significantly, which usually
indicates that the inductance of the winding changes; there may be a short circuit
between turns or between turns. When the frequency is low, the capacitive reactance
formed by the ground capacitance and inter-panel capacitance of the winding is large,
while the inductive reactance is small. If the inductance of the winding changes, the
peak or trough position of the low-frequency part of its frequency response
characteristic curve will move significantly. For most transformers, the amplitude-
frequency response characteristic curve of the three-phase winding in the low-
frequency band shall be very similar. If there is a difference, the cause shall be found
out in time.
7.6.3 The peak or trough position of the mid-frequency band (100kHz ~ 600kHz) of the
amplitude-frequency response characteristic curve changes significantly, which usually
Appendix B
(Informative)
Data export format of frequency response characteristic curve
B.1 Naming method of data file
The data file name shall contain the information of excitation end, response end,
measurement number, all of which is represented by 2 characters. Among them, the
characters representing the winding voltage level are H (high voltage), M (medium
voltage), L (low voltage), the characters representing the winding terminal name are A,
B, C and X, Y, Z. Other letters can also be used to represent it; the characters
representing the measurement number are two decimal numbers.
Example: The file name "HOHA03.csv" means that the excitation end is the neutral point O
end of the high voltage (H) winding, the response end is the A phase of the high voltage (H)
winding, the file is the data of the 03rd measurement.
B.2 Storage directory of data file
The frequency response characteristic test data of each winding of the same transformer
shall be saved in the same file directory; the name of the directory shall be named with
the operation number or factory number of the transformer.
B.3 Recording content of data file
a) The first column of the first row is the frequency unit "kHz"; the second column
is the amplitude unit "dB"; the third column is the starting frequency value of the
sweep frequency measurement; the fourth column is the ending frequency value;
the fifth column is the number of frequency points of the sweep frequency
measurement.
b) The third column of the second row is used to record the model and version of the
test instrument, which starts with ";".
c) The third row to the Nth row (N=number of frequency points + 3) is used to record
the test data, where the first column is the frequency (in kHz) and the second
column is the amplitude (in dB).
d) The third column of the (N+1)th row records the name information of the
transformer, which starts with ";".
e) The third column of the (N+2)th row records the test number, which starts with
";". For example, "; 01" means the first test.
f) The third column of the (N+3)th row records the gear information of the
Appendix G
(Informative)
Example of typical interference waveform when the transformer winding is
deformed
When analyzing the measured transformer winding frequency response characteristic
curve, the validity of the test data shall be identified first. Under normal circumstances,
the frequency response characteristic data curve of the transformer winding shall be
continuous and smooth; its amplitude is mostly distributed in the range of -70dB ~ 0dB,
only some may exceed 0dB or be lower than -70dB.
If the measured data curve is found to have burrs, spikes, overall translation or reversal,
the cause shall be found out first and then retested after solving the problem until valid
test data is obtained.
The following are several typical interference waveforms and their processing methods.
a) Burrs.
If the measured frequency response characteristic curve contains burrs as shown
in Figure G.1, the following inspections and processing shall usually be
performed:
1) It is caused by poor contact of the test circuit (such as unstable contact
resistance). On the one hand, the test lead can be checked and replaced; on the
other hand, confirm whether the contact of the sleeve end is good or the
grounding is reliable.
2) Whether there are electric tools such as electric drills, electric welders, cutting
machines around the test site; if necessary, the operation of such equipment
can be suspended, then the wiring can be reconnected for measurement.
3) Whether the working status of the tester itself is normal; self-checking can be
performed through the configured calibration unit.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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