On-line partial discharge monitoring system for distribution networks
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Abstract:
Partial discharges (PD) occur as a result of dielectric breakdown in electrical insulation under high voltage stress. PD activity, once initiated, causes chemical and physical degradation of insulating material and can lead to catastrophic failure. Early warning of PD activity and localisation is considered essential to ensure the reliable operation over the long term of high voltage equipment including cables, cable accessories and switchgear. PD detection in high voltage cable and cable accessories is usually carried out with test objects offline, requiring potentially significant interruption of service. An online detection system is preferable but difficult to calibrate apparent charge magnitudes due to changes in real distribution network loading and topologies. An online PD detection system with continuous calibration has been developed to determine the apparent charge magnitudes of PD activity and locations in a section of in-service distribution network with high monitoring frequency and no requirement to take cables off line. Results of the on-line PD monitoring system in a typical urban distribution network in Spain are presented. System components including the online calibration pulse injector, capacitive sensors for high frequency PD pulse detection, and data acquisition, processing and communication components at each monitoring site are presented.Keywords:
Switchgear
High Voltage
Condition Monitoring
Ultra-High Frequency (UHF) method is one of the most effective methods, which is widely applied for partial discharge (PD) detection of HV switchgear owning to its high sensitivity and strong resistance to external interference. Despite of these advantages, it is still uneasy to realize the accurate identification of the fault types of HV switchgear because of the lack of a systematic research and analysis on the partial discharge characteristics of different defects in switchgear. In this paper, three typical partial discharge defect models, including needle discharge, suspended discharge, and internal discharge were designed. Then the ϕ-q-n patterns of different partial discharges were obtained by application of UHF method. The results demonstrated based on the characteristics of ϕ-q-n patterns of various PD and differences among them, the type of single or combined PD could be effectively recognized by extracting the characteristic variables of the ϕ-q-n patterns. Moreover, the accuracy of locating PD in switchgear could be improved by use of iterative least square method. Therefore, UHF provides an effective way to evaluate and predict the defect type and position of PD of HV switchgear.
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Partial discharge technology has been applied to medium voltage rotating machines for many years. This technology can now be applied to support on-line diagnostics of medium voltage switchgear assemblies. Partial discharge sensors have been developed, with calibration both in the factory-test floor environment, as well as in the field under normal operating conditions. The application of partial discharge measurement technology to MV switchgear will be presented, with actual examples of pending failures, which were identified by on-line partial discharge measurements. This application of partial discharge technology can greatly aid in the day-to-day reliability and life-extension of the medium voltage electrical power substation assemblies
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Gas-Insulated Switchgear(GIS) has very high reliability compared to Air-Insulated Switchgear (AIS), But any fault in it may once occur, the impacts due to it for modern society is vast and serious. The needs of predictive maintenance for GIS is on the rise, especially development of partial discharge sensor is strongly requested. We have been developed the GIS partial discharge locating system whose advantages are simple construction, the least number of sensors, easy maintenance, and high reliability. This paper describes about the basic experiment to develop the system, the principle of location of partial discharge source, application to the actual switching stations, Chubu Electric Power Co., Inc. TOYONE SW/S and consideration about the field data. We used the external type par-tial discharge sensor. The location of partial discharge can be calculated from the travel time differences between the partial discharge source and sensors. The data obtained in the SW/S shows the suggested algorithm for partial discharge judgment and location of partial discharge source is useful and function of external noise reduction effectively acts as we expected.
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Abstract Partial discharge detection is an effective method to find potential insulation defects in switchgear. At present, the switchgear is mainly composed of busbars, circuit breakers, grounding knives, cables and other components, which leads to multiple faults and simultaneous discharges in the partial discharge detection process of the switchgear. In order to realize the partial discharge detection and rapid location of the switchgear, based on the introduction of the detection methods and location principles of ultrasonic, transient ground voltage and UHF partial discharge, this paper proposes to use ultrasonic, transient ground voltage and UHF detection technology to diagnose and analyse the multi-source partial discharge of the switchgear and realize the detection of partial discharge; the multi-source partial discharge of the switchgear is realized by the rapid localization method combining the UHF time difference method and the flat surface method. Through partial discharge detection and localization analysis of a 35kV switchgear, the feasibility of multi-source partial discharge diagnosis and rapid localization method is verified, which provides a basis for on-site inspection personnel to realize multi-source partial discharge detection and localization of switchgear.
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Transient (computer programming)
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Application of online partial discharge detection of switchgear based on ultra-high frequency method
Ultra-High Frequency (UHF) method is one of the most effective methods for partial discharge (PD) detection of HV switchgear, due to its high sensitivity and strong resistance to external interference. Despite of these advantages, it is still uneasy to realize the accurate identification of the fault types and discharge stages of HV switchgear owning to the lack of a systematic research and analysis on the partial discharge characteristics of different defects in switchgear. In this paper, three typical partial discharge defect models, including needle discharge, suspended discharge, and internal discharge were designed. The PRPD spectra of different discharge defect models at various discharge stages were obtained by application of UHF method. The results demonstrated that based on the characteristics of the PRPD spectra of various discharge defect model, the type of PD could be effectively recognized by analyzing the characteristic variables of the PRPD spectra. Moreover, the discharge stages could also be roughly inferred from the diversity of different PRPD spectra. Therefore, UHF provides an effective way to evaluate the defect type and stage of PD in HV switchgear.
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There exists many reasons for the partial discharge in switchgear such as the insulation defect, insulation aging, and bad contact and so on, so the judgment of partial discharge type is important for the evaluation of switchgear operation status. The types and causes of switchgear are analyzed, discuss the advantages and disadvantages of transient earth voltage detection method, ultrasonic detection method and ultra high frequency detection method. The applicability of different detection methods are summarized under the different insulation defects and partial discharge types according to the partial discharge detection data for the heavy duty area and pivotal substation. The location methods are analyzed for partial discharge source. Base on the four typical defects in switchgear, as for the employed detection method, the amplitude, types and reason of partial discharge are discussed. It can provide a practical application basis for condition based maintenance and technical guarantee for tester.
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Transient (computer programming)
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There are many reasons for the partial discharge in switchgear, so to achieve the safety and reliability operation of switchgear is more important. The internal partial discharge of wall bushing in switchgear are researched by employing the transient earth voltage detection method, ultrasonic detection method and ultra high frequency detection method based on the partial discharge case. Based on the related testing data, the amplitude, type and reason of partial discharge are discussed, and the location of partial discharge are accomplished by using the method of the acoustic-electric location method. The signal of partial discharge of wall bushing disappears after the treatment. The study shows that it can provide a reference basis for the practical measurement and accurate location for the internal partial discharge fault of wall bushing in the switchgear.
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Partial discharge (PD) online monitoring of MV switchgear was implemented in several large industrial plants beginning in 1998. A switchgear manufacturer completed offline testing and calibration to determine the type and location of sensors for measuring the effective sensitivity of partial discharge activity. This paper also presents actual pending failures, which were identified and prevented by online PD monitoring. The pending failures include bus corona damage, CT corona damage and failing insulation due to surface tracking. An update of new continuous online partial discharge monitors for MV switchgear is also included.
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Gas-insulated switchgear (GIS) is one of the important equipment in power system. Using UHF partial discharge detection method to find and diagnose internal insulation defects in time is an important means during the operation and maintenance of GIS equipment. Different discharge types in GIS show different partial discharge characteristics. This paper proposes a diagnosis and positioning method of discharge faults in GIS equipment through experiments. Firstly, UHF partial discharge signals of different typical discharge models in GIS are obtained by UHF sensor, and then 3D GIS PRPS patterns are drawn. After that, PRPS patterns are transformed into 3 decomposition patterns through Gabor transform, and the texture and shape features of these decomposition patterns are extracted. Based on extracted characteristics, different kinds of machine learning algorithms are applied to identify the discharge type. The results show that the recognition accuracy of three typical discharge types by different machine learning algorithms is high. The characteristics extracted from decomposition patterns obtained by Gabor transform well reflect the discharge type and has high discrimination. Combined with relevant positioning algorithms of GIS, the fault location can be better realized when the rough location of defects is known when accurate identification of partial discharge defects is obtained. This diagnosis method can provide a reliable reference basis for the early warning and accurate location of GIS faults.
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Industry has been exposed to partial discharge technology, related to generators, for many years. A switchgear manufacturer has invested in the advancement of partial discharge technologies related to the on-line analysis of insulation systems for MV switchgear. Partial discharge testing has been completed on both new MV switchgear in the factory setting, as well as several older field installations. The results clearly indicate that partial discharge analysis of MV switchgear is an excellent on-line predictive maintenance tool. It has also been found that older MV switchgear designs are prone to internal corona activity. The majority of existing plants contain MV switchgear of a very old design, therefore the use of on-line PD analysis can identify areas of immediate concern. This paper reviews the applications to MV switchgear. Actual examples of pending failures, which were identified by on-line partial discharge measurements, are presented. This new application of partial discharge technology can greatly aid in the day-to-day reliability and life-extension of MV electrical equipment.
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