The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments wi...The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.展开更多
This contribution describes the use of chromatic techniques for quantifying signatures of partial discharges(PD).A brief description of the basis of chromatic monitoring is given along with explanations of how the app...This contribution describes the use of chromatic techniques for quantifying signatures of partial discharges(PD).A brief description of the basis of chromatic monitoring is given along with explanations of how the approach may be applied for addressing signals produced by PDs.Laboratory test data from several sources for different types of PDs,operating conditions and geometries have been subjected to the chromatic procedures.These include a point-plane gap,a sphere in a liquid and treeing in a cable.Chromatic changes in PD signals have been investigated as a function of the amplitude of the alternating voltage producing the PD,the time duration before full electrical breakdown and for different forms of PDs.Results of the chromatic processing of these data are presented in the form of a number of chromatic maps relating to different quarter cycles of the alternating voltage producing the PDs.The results show the potential of the chromatic techniques for indicating the likelihood of full electrical breakdown and for distinguishing between certain forms of PDs.A summary of the chromatic processing procedures is presented for producing chromatic maps and for adaptation in further exploring PD signal features.展开更多
On-line partial discharge(PD)detection still remains a very challenging task because of the strong electromagnetic interferences.In this paper,a new method of de-noising,using complex Daubechies wavelet(CDW)transform,...On-line partial discharge(PD)detection still remains a very challenging task because of the strong electromagnetic interferences.In this paper,a new method of de-noising,using complex Daubechies wavelet(CDW)transform,has been proposed.It is a relatively recent enhancement to the real-valued wavelet transform because of tow important properties,which are nearly shift-invariant and availability of phase information.Those properties give CDW transform superiority over other real-valued wavelet transform,and then the construction algorithm of CDW is introduced in detail.Secondly,based on the real threshold algorithm of real-valued wavelet transform,complex threshold algorithm is devised.This algorithm take the different characteristics of real part and imaginary part of complex wavelet coefficients into account,it modifies the real and imaginary parts of complex wavelet coefficients respectively.Thirdly,to obtain a real de-noised signal,new combined information series is devised.By applying different combination of real part and imaginary part of de-noised complex signal,a real de-noised signal can be restored with higher peak signal-to-noise ratio(PSNR)and less distortion of original signals.Finally,On-site applications of extracting PD signals from noisy background by the optimal de-noising scheme based on CDW are illustrated.The on-site experimental results show that the optimal de-noising scheme is an effective way to suppress white noise in PD measurement.展开更多
Direct current (DC) partial discharge (PD) test has drawn extensive attention from world-wide electric power research institutes in recent years. However, presently, no DC PD detection device on the market has the sta...Direct current (DC) partial discharge (PD) test has drawn extensive attention from world-wide electric power research institutes in recent years. However, presently, no DC PD detection device on the market has the statistical function. Thus, we developed a test system for PD detection under DC voltage, which is characterized by strong anti-jamming capability, continuous high-speed real-time data acquisi- tion and effective, complete detection of DC PD signals. The DC PD mechanism, as well as the measuring principles, software system, and hardware design of the test equipment were introduced. Adopting typical electrode pairs, we tested the statistical spectrum of PD under DC voltage. The main difference in statistical spectrums between parallel plate electrodes and needle-plate electrodes was that the time interval between two consecutive discharges for needle-plate electrodes has obviously larger variation range than that for parallel plate electrodes, which could be the convincing proof for distinguishing the type of electrodes under DC PD. Practical results indicate that the proposed sys- tem can measure time domain signals of DC PD of oil-paper insulation effectively and promptly, and it can be used to determine and detect defects in DC power transmission equipment.展开更多
To investigate the partial discharge (PD) online monitoring of transformers by ultra-high-frequency (UHF) approaches,high-qualified UHF antennas are focused on as one key technique. The size of UHF sensor used for PD ...To investigate the partial discharge (PD) online monitoring of transformers by ultra-high-frequency (UHF) approaches,high-qualified UHF antennas are focused on as one key technique. The size of UHF sensor used for PD UHF online monitoring in transformer is excessively large,therefore,it is not convenient for internal installation of transformer. Two types of compact UHF antennas with small sizes,a Hilbert fractal antenna and a small loop antenna are presented. PD experiments of three typically artificial insulation defects are executed and both antennas are used for PD measurement. The spectra of power via frequency of detected PD signals are analyzed and compared. The experimental results show that the Hilbert fractal antenna and small loop antenna are qualified for PD online UHF monitoring.展开更多
Detection of gas decomposition products is widely used for condition diagnosis of SF6-insulated equipment because of its an- ti-electromagnetic-interference ability and high sensitivity. Previous investigations show t...Detection of gas decomposition products is widely used for condition diagnosis of SF6-insulated equipment because of its an- ti-electromagnetic-interference ability and high sensitivity. Previous investigations show that the volume of gas chamber influences the types and concentrations of SF6 decomposition products. Therefore using a newly developed dual gas chromatography (GC) detection sys- tem we investigated the discharge and decomposition of SF6 in a discharge chamber with its volume close to that of the real chambers in GIS. Tests in the chamber were performed with different applied voltage, different electrode arrangements, and different defect types. For discharge between needle-to-plane electrodes, the typical gas decomposition products are SO2F2, SO2 and S2OF10. A near linear growth with the increase of voltage duration is found in the concentration of SO2F2, whereas the growth rates of SO2 and S2OF10 concentration decrease with time. Concentrations of SO2F2, SO2 and S2OF10 at the same voltage duration decrease with the decrease of the voltage amplitude and the increase of the needle-to-plane distance. Change of the gas chamber volume affects the generation rates of SO2F2 and SO2, however not S2OF10. For insulator surface defects, the typical gas decomposition products are CF4, CS2 and SO2. Among which, the concentrations of CF4 and SO2 increase with the voltage duration almost linearly. Moreover, a new parameter that represents the degree of SF6 degradation, the SF6 deterioration ratio, is proposed. In the needle-to-plane case, SF6 deterioration ratio is positively correlated to the fitting value of an averaged discharge capacity. However, the maximum value of SF6 deterioration ratio varies with the defect type.展开更多
Numerous equivalent circuits for cavity discharges have been developed, yet most of these models cannot provide simulated sig- nals that precisely reveal the variability of the discharge’s characteristic parameters, ...Numerous equivalent circuits for cavity discharges have been developed, yet most of these models cannot provide simulated sig- nals that precisely reveal the variability of the discharge’s characteristic parameters, such as repetition rate, magnitude and phase of discharges, which makes them not suitable for intensive studies of discharge process. Therefore, using Simulink code, we theoretically ana- lyzed and studied the classical equivalent circuits of cavity discharges, as well as the influence of circuit components on simulation results, and then proposed a novel equivalent circuit, the key parameters of which were determined according to the physical behavior of cavity discharges. In the novel equivalent circuit, the repetition rate can be changed by discharge resistance, inception and residual voltages; meanwhile the phase of discharge can be controlled by adjusting the parameters of shunt resistance. Furthermore, a controlled current source as a function of space charge is introduced in the equivalent circuit. Compared with the former ones, the simulated signals obtained by this novel model are better approximation of real signals. This work could be referred by latter studies of the characteristics and the me- chanisms of cavity discharge in oil-paper insulation.展开更多
基金supported by National High-tech Research and Development Program of China（863 Program）（2009AA04Z416） National Science Foundation of China（51021005） Scientific Innovation of Colleges and Universities（Project v-200704）
基金Project supported by National Basic Research Program of China(973 Program) (2011CB 209400)Program of State Key Laboratory of Power Systems for ±1 100 kV UHVDC Technology(SKLD10M09)
文摘The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.
文摘This contribution describes the use of chromatic techniques for quantifying signatures of partial discharges(PD).A brief description of the basis of chromatic monitoring is given along with explanations of how the approach may be applied for addressing signals produced by PDs.Laboratory test data from several sources for different types of PDs,operating conditions and geometries have been subjected to the chromatic procedures.These include a point-plane gap,a sphere in a liquid and treeing in a cable.Chromatic changes in PD signals have been investigated as a function of the amplitude of the alternating voltage producing the PD,the time duration before full electrical breakdown and for different forms of PDs.Results of the chromatic processing of these data are presented in the form of a number of chromatic maps relating to different quarter cycles of the alternating voltage producing the PDs.The results show the potential of the chromatic techniques for indicating the likelihood of full electrical breakdown and for distinguishing between certain forms of PDs.A summary of the chromatic processing procedures is presented for producing chromatic maps and for adaptation in further exploring PD signal features.
基金Project Supported by National Natural Science Foundation China（50577069）, National Grid Company （2004-SGKJ）.
文摘On-line partial discharge(PD)detection still remains a very challenging task because of the strong electromagnetic interferences.In this paper,a new method of de-noising,using complex Daubechies wavelet(CDW)transform,has been proposed.It is a relatively recent enhancement to the real-valued wavelet transform because of tow important properties,which are nearly shift-invariant and availability of phase information.Those properties give CDW transform superiority over other real-valued wavelet transform,and then the construction algorithm of CDW is introduced in detail.Secondly,based on the real threshold algorithm of real-valued wavelet transform,complex threshold algorithm is devised.This algorithm take the different characteristics of real part and imaginary part of complex wavelet coefficients into account,it modifies the real and imaginary parts of complex wavelet coefficients respectively.Thirdly,to obtain a real de-noised signal,new combined information series is devised.By applying different combination of real part and imaginary part of de-noised complex signal,a real de-noised signal can be restored with higher peak signal-to-noise ratio(PSNR)and less distortion of original signals.Finally,On-site applications of extracting PD signals from noisy background by the optimal de-noising scheme based on CDW are illustrated.The on-site experimental results show that the optimal de-noising scheme is an effective way to suppress white noise in PD measurement.
基金supported by National High-tech Research and Development Program of China（863 Program）（2009AA04Z416） National Science Foundation of China（51021005） Scientific Innovation of Colleges and Universities（200704）
基金Project supported by National Basic Research Program of China (973 Program) (2011CB 209400)State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments (SKLD10M09)Program for ±1 100 kV UHVDC Technology
文摘Direct current (DC) partial discharge (PD) test has drawn extensive attention from world-wide electric power research institutes in recent years. However, presently, no DC PD detection device on the market has the statistical function. Thus, we developed a test system for PD detection under DC voltage, which is characterized by strong anti-jamming capability, continuous high-speed real-time data acquisi- tion and effective, complete detection of DC PD signals. The DC PD mechanism, as well as the measuring principles, software system, and hardware design of the test equipment were introduced. Adopting typical electrode pairs, we tested the statistical spectrum of PD under DC voltage. The main difference in statistical spectrums between parallel plate electrodes and needle-plate electrodes was that the time interval between two consecutive discharges for needle-plate electrodes has obviously larger variation range than that for parallel plate electrodes, which could be the convincing proof for distinguishing the type of electrodes under DC PD. Practical results indicate that the proposed sys- tem can measure time domain signals of DC PD of oil-paper insulation effectively and promptly, and it can be used to determine and detect defects in DC power transmission equipment.
基金Project Supported by New Century ExcellentTalents of the Ministry of Education (NCET-06-0763)the Foundation of the Key Project of the Science and Technology Depart ment inChongqing (CSTC2005AA6003)
文摘To investigate the partial discharge (PD) online monitoring of transformers by ultra-high-frequency (UHF) approaches,high-qualified UHF antennas are focused on as one key technique. The size of UHF sensor used for PD UHF online monitoring in transformer is excessively large,therefore,it is not convenient for internal installation of transformer. Two types of compact UHF antennas with small sizes,a Hilbert fractal antenna and a small loop antenna are presented. PD experiments of three typically artificial insulation defects are executed and both antennas are used for PD measurement. The spectra of power via frequency of detected PD signals are analyzed and compared. The experimental results show that the Hilbert fractal antenna and small loop antenna are qualified for PD online UHF monitoring.
基金Project supported by International Cooperation Project in Shaanxi Province of China (2012KW-01)
文摘Detection of gas decomposition products is widely used for condition diagnosis of SF6-insulated equipment because of its an- ti-electromagnetic-interference ability and high sensitivity. Previous investigations show that the volume of gas chamber influences the types and concentrations of SF6 decomposition products. Therefore using a newly developed dual gas chromatography (GC) detection sys- tem we investigated the discharge and decomposition of SF6 in a discharge chamber with its volume close to that of the real chambers in GIS. Tests in the chamber were performed with different applied voltage, different electrode arrangements, and different defect types. For discharge between needle-to-plane electrodes, the typical gas decomposition products are SO2F2, SO2 and S2OF10. A near linear growth with the increase of voltage duration is found in the concentration of SO2F2, whereas the growth rates of SO2 and S2OF10 concentration decrease with time. Concentrations of SO2F2, SO2 and S2OF10 at the same voltage duration decrease with the decrease of the voltage amplitude and the increase of the needle-to-plane distance. Change of the gas chamber volume affects the generation rates of SO2F2 and SO2, however not S2OF10. For insulator surface defects, the typical gas decomposition products are CF4, CS2 and SO2. Among which, the concentrations of CF4 and SO2 increase with the voltage duration almost linearly. Moreover, a new parameter that represents the degree of SF6 degradation, the SF6 deterioration ratio, is proposed. In the needle-to-plane case, SF6 deterioration ratio is positively correlated to the fitting value of an averaged discharge capacity. However, the maximum value of SF6 deterioration ratio varies with the defect type.
基金Project supported by National Basic Research Program of China(973 Program) (2012CB215205)Fund for Innovative Research Groups of China (51021005)
文摘Numerous equivalent circuits for cavity discharges have been developed, yet most of these models cannot provide simulated sig- nals that precisely reveal the variability of the discharge’s characteristic parameters, such as repetition rate, magnitude and phase of discharges, which makes them not suitable for intensive studies of discharge process. Therefore, using Simulink code, we theoretically ana- lyzed and studied the classical equivalent circuits of cavity discharges, as well as the influence of circuit components on simulation results, and then proposed a novel equivalent circuit, the key parameters of which were determined according to the physical behavior of cavity discharges. In the novel equivalent circuit, the repetition rate can be changed by discharge resistance, inception and residual voltages; meanwhile the phase of discharge can be controlled by adjusting the parameters of shunt resistance. Furthermore, a controlled current source as a function of space charge is introduced in the equivalent circuit. Compared with the former ones, the simulated signals obtained by this novel model are better approximation of real signals. This work could be referred by latter studies of the characteristics and the me- chanisms of cavity discharge in oil-paper insulation.
