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DL/T 345-2019: Application guidelines of UV diagnostic technology for live electrical equipment
DL/T 345-2019
DL
ELECTRICAL INDUSTRY STANDARD
OF THE PEOPLE?€?S REPUBLIC OF CHINA
ICS 29.240.20
F 23
Replacing DL/T 345-2010
Application guidelines of UV diagnostic technology for live
electrical equipment
ISSUED ON: NOVEMBER 04, 2019
IMPLEMENTED ON: MAY 01, 2020
Issued by: National Energy Administration
Table of Contents
Foreword ... 4
1 Scope ... 6
2 Normative references ... 6
3 Terms and definitions ... 6
4 On-site detection requirements ... 7
4.1 Personnel requirements ... 7
4.2 Safety requirements ... 8
4.3 Requirements for detection environmental conditions ... 8
4.4 Instrument requirements ... 8
5 Detection methods ... 9
5.1 General detection ... 9
5.2 Accurate detection ... 9
5.3 Main influencing factors of UV detection ... 10
6 Determination of discharge defect type and detection result diagnosis ... 10
6.1 The main reasons for the discharge of defective equipment ... 10
6.2 Judgment method for discharge of defective equipment ... 11
6.3 Diagnosis of discharge detection results of defective equipment ... 11
7 Classification and handling of defect severity ... 11
8 Detection period ... 12
9 Imager management ... 12
10 Detection data management ... 13
Appendix A (Informative) Identification of wind class and wind speed ... 14
Appendix B (Normative) Diagnosis of detection result of discharge from defective
equipment ... 15
Appendix C (Informative) Normalization principle for 10 m photon number ... 19
Appendix D (Informative) The main reasons for the discharge of defective equipment
... 21
Appendix E (Informative) Ultraviolet test report for live electrical equipment ... 22
Appendix F (Informative) Typical diagram of corona discharge for power transmission
and transformation equipment and generators ... 23
Application guidelines of UV diagnostic technology for live
electrical equipment
1 Scope
This standard specifies the on-site detection requirements, detection methods,
determination of discharge defect types and detection results diagnosis, defect severity's
classification and handling, detection cycle, instrument and data management
requirements, for the application of ultraviolet imaging technology, to the diagnosis of
corona discharge of live electrical equipment.
This standard applies to the corona discharge detection and defect diagnosis, for high-
voltage live electrical equipment (mainly including equipment conductors and insulator
surfaces), which is caused by various reasons, using an ultraviolet imager.
2 Normative references
The following documents are essential for the application of this document. For dated
references, only the dated version applies to this document. For undated references, the
latest edition (including all amendments) applies to this document.
GB 26859 Safety code of electric power industry - Part of electric lines
GB 26860 Safety code of electric power industry - Electric part of power plants and
transformer substations
DL/T 298 Guide for detection and evaluation of corona defects on stator winding
overhangs of generator
DL/T 1779 Specification of ultraviolet imager for corona discharge detection in high
voltage electrical equipments
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Gain
and work site.
4.2 Safety requirements
The safety requirements are as follows:
- It shall strictly comply with GB 26859 and GB 26860;
- It shall strictly abide by the patrol requirements of the power plant, substation
(converter station), line;
- There shall be a special person for monitoring.
4.3 Requirements for detection environmental conditions
4.3.1 General detection requirements
The general detection requirements are as follows:
- The equipment to be tested is a live electrical equipment; it shall avoid the
obstructions that affect the detection, as much as possible;
- Detection shall not be performed under severe weather and environmental
conditions (such as lightning, heavy rain, etc.);
- The wind class should not be higher than class 4. Please refer to Appendix A, for
the identification of wind class and wind speed.
4.3.2 Requirements for accurate detection
In addition to meeting the general detection requirements, the following requirements
shall also be met:
- The wind class should not be higher than class 3;
- Try to eliminate or reduce the influence of electromagnetic interference or other
factors, on the measurement of the instrument.
4.4 Instrument requirements
Meet the requirements of DL/T 1779 standard.
5 Detection methods
5.1 General detection
Turn on the UV imager. Set the appropriate gain, to make the image clear and stable.
Then start to conduct a large-area patrol inspection of the equipment and corona
discharge, to find out the equipment, parts and the intensity of the discharge.
5.2 Accurate detection
Accurately locate the discharge site. Obtain the visible light photos and discharge
characteristics of the discharge equipment, including the number of discharge photons,
discharge form, frequency and corona discharge intensity on the surface of the insulator,
etc. The requirements are as follows:
a) General requirements:
1) Within the range allowed by the safety distance, when the image content is
complete, the UV imager should be as close as possible to the detected
equipment, to maximize the corona discharge area of the detected equipment,
within the field of view; measure and record the distance from the UV imager
to the corona discharge area;
2) In the positioning of the discharge position, the UV imager shall select the
appropriate detection direction and angle, for the observation of the corona
discharge part, to avoid other equipment blocking and discharge interference;
3) Make judgement of discharge characteristics in combination with Appendix B;
4) During the detection process, it shall record the parameters, such as instrument
gain, ambient temperature/humidity, detection distance, focus state.
b) Recording of discharge pattern and frequency:
1) Adjust parameters such as instrument gain, to make the visual image clear. The
video recording time shall be able to fully describe the discharge process; the
recording time of the discharge phenomenon, at each point, shall not be less
than 5 s;
2) In the process of detecting the length form discharge, by detecting the range of
repeated occurrence of corona discharge on the outer insulation surface of the
equipment, estimate and record the remaining dry arc distance or the number
of insulator sheets and sheds;
6.2 Judgment method for discharge of defective equipment
6.2.1 Average photon number method
Under the normalization principle of the number of 10 m photons, according to the
average number of photons, the discharge intensity is divided into three ranges: high-
intensity discharge, medium-intensity discharge, low-intensity discharge.
6.2.2 Image observation method
Judgment and defect classification are mainly based on the corona state, characteristic
attribute, occurrence location, severity of the live electrical equipment in the image.
6.2.3 Same type comparison method
Evaluate the corona discharge status of live electrical equipment, by horizontally
comparing the ultraviolet images of the corona discharge of the corresponding parts of
the same model or the same type of live electrical equipment (which can include
archival images of different periods, different weather, environments) OR the number
of ultraviolet photons.
6.2.4 Comprehensive light image comparison method
Through the comparison with the infrared thermal image and visible light image of the
equipment, which is corresponding to the corona discharge position, carry out the
diagnosis and evaluation of the defects of the live electrical equipment.
6.3 Diagnosis of discharge detection results of defective equipment
See Appendix B for the diagnosis method of the discharge detection results of the main
defective equipment.
7 Classification and handling of defect severity
According to the impact of corona discharge defects on the operation of live electrical
equipment or power grid, it proposes different severity and treatment methods, for three
categories of defects:
- Category 1: The equipment has low-intensity discharge, which does not affect the
normal operation of the live electrical equipment. It will be observed later.
- Category 2: The equipment has medium-intensity discharge, which may affect the
normal operation of the live electrical equipment. It shall increase the frequency of
detection; carry out the maintenance, during the planned power outage.
- Category 3: The equipment has high-intensity discharge, which obviously affects
the normal operation of the live electrical equipment; OR the diagnosis and
evaluation of equipment defects indicate that it may cause equipment or power grid
accidents in the short term, so it shall arrange power outage for maintenance or
replacement, as soon as possible.
8 Detection period
The UV detection period for running live electrical equipment shall be comprehensively
determined, according to factors, such as the importance of the live electrical equipment,
voltage level, environmental conditions.
Under normal circumstances, for the patrol detection of live electrical equipment at a
voltage level of 500 kV (330 kV) and above, that is, general detection, it should not be
less than once a year. For important substations, converter stations, lines, at 500 kV
(330 kV) and above voltage level, which have bad operating environment or serious
aging equipment, it may shorten the detection period, appropriately.
For live electrical equipment, which has a voltage level of 220 kV and below, UV
detection should be carried out every 1 year ~ 3 years.
For important newly-built, renovated, expanded, overhauled live electrical equipment,
it shall be detected within 1 month, after being put into operation.
Under special circumstances, such as abnormal corona discharge sound in live electrical
equipment, ice and snow weather (especially freezing rain), serious pollution and
atmospheric humidity greater than 90%, THEN, it shall be detected in time.
Accurate detection is mainly used as follow-up detection of general detection; the
detection period is no longer specified. However, if necessary (such as the categories 2
and 3 defective equipment of concern), it may carry out accurate detection directly, at
any time.
9 Imager management
UV imager management shall meet the following requirements:
- There shall be a special person in charge of UV imager; keep it properly; regularly
check the power-on and operation functions, to ensure that the instrument and
accessories are in good condition.
- The instrument files are complete and available; have exit-factory certificate,
instruction for use, warranty letter, analysis software, operation manual, etc.
- The storage and use environmental conditions of the UV imager, as well as the
Appendix C
(Informative)
Normalization principle for 10 m photon number
Different models of solar-blind UV imagers have different on-screen photons, when
measured for the same corona in counting mode. Therefore, under standard laboratory
conditions, it shall use the relationship formula of "photon number-detection distance",
at a standard distance of 10 m, for conversion; use the revised coefficient between
different ultraviolet imagers for conversion, that is, the normalized photon number shall
be obtained. At this time, the photon number of each model is the same value.
C.1 Calibration of photon number of UV imager
In the dark room, select a standard light source (it may select the deep ultraviolet LED
ultraviolet laser, mercury lamp and other classic ultraviolet light sources), which pass
through the integrating sphere and diaphragm (aperture of the diaphragm shall not be
greater than 1 mm), to form a point light source. A metrologically verified ultraviolet
radiometer is set up beyond 1 m, to measure the ultraviolet irradiance value, W.
A metrologically verified solar-blind ultraviolet attenuation system is added, between
the light source and the integrating sphere. Its attenuation coefficient is ??. The
theoretical irradiance value, ??W, of the attenuated point light source, at a distance of 1
m, shall be in the order of 10-14 W/cm2 ~ 10-15 W/cm2.
Place the instrument to be calibrated, at 10 m in front of the attenuated point light source.
Adjust the instrument, so that the light source image is centered on the instrument image.
Adjust the instrument to counting mode. Record multiple times (at least 10 times), to
obtain the average photon number N1;
Add a metrologically verified solar-blind UV attenuator, in front of the light source.
The attenuation coefficient is 0.1 Record multiple times (at least 10 times), to obtain
the average photon number N2;
The photon number's correction coefficients, k and b, of the instrument are calculated
as follows:
Where:
E - Ultraviolet photon energy, which is 7.645 x 10-19 J, when selecting 260 nm for
calculation;
n - Standard calibration factor, which is 0.001.
The values of k and b can be obtained by solving the above system of equations:
Appendix D
(Informative)
The main reasons for the discharge of defective equipment
D.1 Equipment classification
Power transmission and transformation equipment, in which discharge occurs, can be
roughly divided into two categories: Conductors and insulators.
D.2 Abnormal discharge on conductor surface
The abnormal discharge on the surface of the conductor has the following situations:
a) Sharp angles, sharp points, rough surfaces, which are formed due to installation
or maintenance, etc.;
b) Broken strands (or loose strands) and scratches of the wires during operation
(auxiliary means such as telescopes can be used to help judgement);
c) Improper voltage equalization and shielding measures OR no voltage equalization
measures;
d) The gap between the condu...