This paper discusses the current state of the art of diagnostics at power transformers. A special focus is set on the UHF-PD-measurement （ultra-high-frequency partial discharge measurement） because at power transfor...This paper discusses the current state of the art of diagnostics at power transformers. A special focus is set on the UHF-PD-measurement （ultra-high-frequency partial discharge measurement） because at power transformers, this diagnostic method has become more important in recent years. The current state, basics and principles of operations, proceedings as well as advantages of PD-measurement methods are covered. Furthermore problems and proposed solutions are discussed. Bushings and tap changers are not discussed in detail. In many cases, one single diagnostic method does not have the ability to sufficiently evaluate a power transformer. Therefore, a variety of diagnostic methods came up over times, which are commonly used by now. To expand the evaluation opportunities of power transformers, science strives to develop new diagnostic methods as well as to improve the existing ones. Furthermore, environmentally friendly and hardly inflammable ester liquids are examined for the use at power transformers and PD-measurement at HVDC （high voltage direct current） converter transformers as well. Potential diagnostic options and respectively current developments and findings in the field of oil-paper-insulation systems are outlined conclusively.展开更多
In this paper, a self-mode-locked Nd:YVO_4 picosecond vortex laser is demonstrated, which can operate on the different Laguerre-Gaussian(LG) modes at 1 064 nm. A π/2 mode converter is utilized to realize the picoseco...In this paper, a self-mode-locked Nd:YVO_4 picosecond vortex laser is demonstrated, which can operate on the different Laguerre-Gaussian(LG) modes at 1 064 nm. A π/2 mode converter is utilized to realize the picosecond vortex laser with LG mode transformed from the high-order Hermite-Gaussian(HG) mode. For the proposed laser, the mode-locked pulse repetition rate is 1.81 GHz. The average output powers of LG_(12) mode and LG_(02) mode are 1.241 W and 1.27 W, respectively, and their slope efficiencies are 23.2% and 24%, respectively.展开更多
For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electr...For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.展开更多
This paper concentrates on compensating the power quality issues which have been increased in day-to-day life due to the enormous usage of loads with power electronic control.One such solution is compensating devices ...This paper concentrates on compensating the power quality issues which have been increased in day-to-day life due to the enormous usage of loads with power electronic control.One such solution is compensating devices like Pension Protection Fund(PPF),Active power filter(APF),hybrid power filter(HPF),etc.,which are used to overcome Power Quality(PQ)issues.The proposed method used here is an active compensator called unified power quality condi-tioner(UPQC)which is a combination of shunt and series type active filter con-nected via a common DC link.The primary objective is to investigate the behavior of the compensators in the distribution networks.The performance of two configurations of UPQC,Right Shunt UPQC(RS-UPQC)and Left Shunt UPQC(LS-UPQC)are tested in the distribution networks under various load con-ditions by connecting them at the source side of harmonic generation using a spe-cially constructed transformer called inductively filtered converter transformer which adopts special wiring scheme at the secondary side.PSCAD(Power Sys-tems Computer Aided Design)/EMTDC(Electromagnetic Transients with DC Analysis)software is used to model the compensators connected to the nonlinear load.Both RS-UPQC and LS-UPQC are tested at the distribution side of the sup-ply system with Hysteresis current controller for shunt and Sinusoidal pulse with modulation controller for series at various locations of power system network and their results are compared.展开更多
The internal component structure of the converter transformer plays an extremely important role in the generation and propagation of vibration noise.In order to comprehensively reveal the influence of the component st...The internal component structure of the converter transformer plays an extremely important role in the generation and propagation of vibration noise.In order to comprehensively reveal the influence of the component structure on the vibration and noise of converter transformers,this paper conducted vibration and noise experiments on different combinations of three iron core structures,four winding structures,two oil tank structures,two foot insulation structures and three positioning structures under different frequency harmonic excitations in a semi-anechoic chamber environment.The results show that the optimal configuration for minimising noise in converter transformers comprises the following components:an entanglement internal screen winding within the coil assembly,a 7.2 mm six-step-123 iron core,a cross-shaped reinforced oil tank,bottom foot insulation,an upper eccentric circle design and lower pouring positioning.展开更多
Digital twin(DT)modelling is a prerequisite for the successful application of DT technology in the power industry.However,traditional scene modelling methods are costly,time-consuming,focus on overall features and lac...Digital twin(DT)modelling is a prerequisite for the successful application of DT technology in the power industry.However,traditional scene modelling methods are costly,time-consuming,focus on overall features and lack real-time updates,hindering the interaction between DT models and physical power equipment scenes.Therefore,a scene DT modelling technique focusing on local features in risk areas and real-time updates is urgently needed.Herein,real-time modelling of the±800 kV converter transformer is achieved by improving the neural radiation field based on a hybrid attention mechanism and multiresolution hash encoding.Compared to traditional methods,modelling time is reduced from hours to 1 min without professional equipment or manual intervention.The model quality is more concerned with local features of risk areas in transformers while ensuring the overall scene,and the accuracy is improved by about 6%,realising the real-time modelling of transformers and the DT of scenes.展开更多
The partial discharge occurring in the weak part of the insulation of a converter transformer results in the formation of a large number of bubbles in the insulating oil.The migration,deformation,and other dynamic beh...The partial discharge occurring in the weak part of the insulation of a converter transformer results in the formation of a large number of bubbles in the insulating oil.The migration,deformation,and other dynamic behaviors of bubbles in the region of a strong electric field can cause them to easily accumulate into“small bridges”of impurities that can lead to breakdown of the oil gap.The authors of this study experimentally investigate and discuss the mechanisms of migration and deformation of bubbles in oil during partial discharge under composite AC/DC voltage to clarify their dynamic behaviors.The influence of the initial position of the bubbles on their trajectory of migration and velocity as well as the morphological changes occurring in them are analyzed using numerical simulations.The results show that the bubbles move away from the strong electric field due to the action of the dielectrophoretic force.The interface of the bubbles is longitudinally stretched under the action of the electrostrictive force and the vertical component of the drag force and gradually recovers to assume a spherical shape under the influence of surface tension and the horizontal component of the drag force.展开更多
The studied sending-terminal’s UHVDC converter transformer with the UHVAC grid is currently one of the largest-capacity converter transformers,which is characterized by strong support for the large-scale grid power d...The studied sending-terminal’s UHVDC converter transformer with the UHVAC grid is currently one of the largest-capacity converter transformers,which is characterized by strong support for the large-scale grid power delivering out,strengthening grid’s fault tolerance and backup capability,improving grid operation’s flexibility and security,lowering the short-circuit currents.The proposed single-active-part converter transformer structure is well-designed,including the single-phase five-leg iron core,the special winding arrangement,the special structure of the spacers and angle rings,and so on,which is a smaller footprint,easier to install and test on site,but is more challenging in the structural design due to the critical railway transportation limitations on aspects of both size and weight.The feasibility of the proposed structure schema is verified by a series of tests,concerning the wave process,the short circuit force,the temperature field,the main insulation,and so on.Among them,the main insulation’s electric fields at the import positions are verified to be reasonable,including the AC impressed voltage test,the DC impressed voltage test,and the polarity reversal test.It shows that the proposed single-active-part design scheme is practicable and conductive to manufacture and application for the UHV large-capacity converter transformers.展开更多
To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using...To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using the finite element method and model experiments.This paper quantifies the influence of different DC contents on the magnetic flux density,force,and displacement distribution characteristics of the iron core and winding and analyzes the internal relationship between various indicators.The inflection point of the DC bias coefficient on the vibration is obtained and the contribution mechanism of the different responses of the iron core and winding to this inflection point is explained.The value of the DC bias coefficient for changing the main vibration frequency is determined.When the DC bias coefficient is 1.0 and 1.5,the main frequency of vibration moves to the right to 250 Hz and 350 Hz.Based on the principle of similarity,a DC bias vibration experimental platform for converter transformers is developed,and DC bias magnetic experiments are conducted to verify the reliability of the simulation results.展开更多
Converter transformers are the core components of ultra-high voltage(UHV)transmission systems.The main cause of faults in converter transformers is irreversible deterioration of oil-pressboard insulation under combine...Converter transformers are the core components of ultra-high voltage(UHV)transmission systems.The main cause of faults in converter transformers is irreversible deterioration of oil-pressboard insulation under combined electrical-thermal-mechanical stress over long operating times.In this paper,the chemical characteristics of oil-pressboard insulation samples subjected to electrical-thermal-mechanical ageing for different times are studied.An image processing algorithm is used to analyse the discharge propagation characteristics of the samples under combined alternating current(AC)-direct current(DC)voltage,and the current pulse curves and phase resolved partial discharge spectrogram corresponding to the discharge images are analysed.An improved wavelet packet algorithm is used to denoise the discharge current pulse.Finally,the influence of electrical-thermal-mechanical ageing on discharge characteristics is analysed using radar charts.The condition of oil-pressboard insulation is one of the main factors determining the life expectancy of converter transformers.The results obtained here therefore have practical significance for understanding the process of insulation failure caused by accelerated ageing of oil-pressboard insulation.展开更多
Converter transformers are the core device in ultrahigh voltage direct current(UHVDC)transmission systems,and the oil-paper insulation at its rectifying valve side deals with the composite AC-DC voltage.A detailed inv...Converter transformers are the core device in ultrahigh voltage direct current(UHVDC)transmission systems,and the oil-paper insulation at its rectifying valve side deals with the composite AC-DC voltage.A detailed investigation of the partial discharge(PD)mechanism in the oil-paper insulation under the composite AC-DC voltage is,therefore,very important.The oilpaper insulated needle plate electrode simulation model for the electric field and charge distribution can be established using hydrodynamic drift-diffusion theory and bipolar charge carrier theory,and the simulation results can reflect the morphological changes of PD.The development characteristics of PD under composite AC-DC voltage are researched.In addition,the effects of simulation time,the AC-DC component proportion,and model parameters on PD are also explored.Results indicate that differences in applied voltage,interface charge,and geometry structure can cause changes in the electric field strength,which consequently influences the PD process in the simulation model.Oil-immersed paperboard is a type of liquid-immersed dielectric(LID).When the LID is arranged in perpendicular,only the positive streamers have narrow channels oriented toward the LID.When the LID is arranged in parallel,the PDs are in the form of creeping discharges and the negative streamers are more dispersed.The development characteristics of PD and its influencing factors reported here may provide theoretical and simulation support to explain the physical mechanism of PD at the rectifying valve side of the converter transformer.展开更多
文摘This paper discusses the current state of the art of diagnostics at power transformers. A special focus is set on the UHF-PD-measurement （ultra-high-frequency partial discharge measurement） because at power transformers, this diagnostic method has become more important in recent years. The current state, basics and principles of operations, proceedings as well as advantages of PD-measurement methods are covered. Furthermore problems and proposed solutions are discussed. Bushings and tap changers are not discussed in detail. In many cases, one single diagnostic method does not have the ability to sufficiently evaluate a power transformer. Therefore, a variety of diagnostic methods came up over times, which are commonly used by now. To expand the evaluation opportunities of power transformers, science strives to develop new diagnostic methods as well as to improve the existing ones. Furthermore, environmentally friendly and hardly inflammable ester liquids are examined for the use at power transformers and PD-measurement at HVDC （high voltage direct current） converter transformers as well. Potential diagnostic options and respectively current developments and findings in the field of oil-paper-insulation systems are outlined conclusively.
基金supported by the National Natural Science Foundation of China(No.61108021)the Fundamental Research Funds for the Central Universities(Nos.2013JBM091 and S16JB00010)
文摘In this paper, a self-mode-locked Nd:YVO_4 picosecond vortex laser is demonstrated, which can operate on the different Laguerre-Gaussian(LG) modes at 1 064 nm. A π/2 mode converter is utilized to realize the picosecond vortex laser with LG mode transformed from the high-order Hermite-Gaussian(HG) mode. For the proposed laser, the mode-locked pulse repetition rate is 1.81 GHz. The average output powers of LG_(12) mode and LG_(02) mode are 1.241 W and 1.27 W, respectively, and their slope efficiencies are 23.2% and 24%, respectively.
文摘For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.
文摘This paper concentrates on compensating the power quality issues which have been increased in day-to-day life due to the enormous usage of loads with power electronic control.One such solution is compensating devices like Pension Protection Fund(PPF),Active power filter(APF),hybrid power filter(HPF),etc.,which are used to overcome Power Quality(PQ)issues.The proposed method used here is an active compensator called unified power quality condi-tioner(UPQC)which is a combination of shunt and series type active filter con-nected via a common DC link.The primary objective is to investigate the behavior of the compensators in the distribution networks.The performance of two configurations of UPQC,Right Shunt UPQC(RS-UPQC)and Left Shunt UPQC(LS-UPQC)are tested in the distribution networks under various load con-ditions by connecting them at the source side of harmonic generation using a spe-cially constructed transformer called inductively filtered converter transformer which adopts special wiring scheme at the secondary side.PSCAD(Power Sys-tems Computer Aided Design)/EMTDC(Electromagnetic Transients with DC Analysis)software is used to model the compensators connected to the nonlinear load.Both RS-UPQC and LS-UPQC are tested at the distribution side of the sup-ply system with Hysteresis current controller for shunt and Sinusoidal pulse with modulation controller for series at various locations of power system network and their results are compared.
基金supported by the Key R&D Program of Shandong Province(2021CXGC010210).
文摘The internal component structure of the converter transformer plays an extremely important role in the generation and propagation of vibration noise.In order to comprehensively reveal the influence of the component structure on the vibration and noise of converter transformers,this paper conducted vibration and noise experiments on different combinations of three iron core structures,four winding structures,two oil tank structures,two foot insulation structures and three positioning structures under different frequency harmonic excitations in a semi-anechoic chamber environment.The results show that the optimal configuration for minimising noise in converter transformers comprises the following components:an entanglement internal screen winding within the coil assembly,a 7.2 mm six-step-123 iron core,a cross-shaped reinforced oil tank,bottom foot insulation,an upper eccentric circle design and lower pouring positioning.
基金National Key Research and Development Program of China,Grant/Award Number:2021YFB2401700。
文摘Digital twin(DT)modelling is a prerequisite for the successful application of DT technology in the power industry.However,traditional scene modelling methods are costly,time-consuming,focus on overall features and lack real-time updates,hindering the interaction between DT models and physical power equipment scenes.Therefore,a scene DT modelling technique focusing on local features in risk areas and real-time updates is urgently needed.Herein,real-time modelling of the±800 kV converter transformer is achieved by improving the neural radiation field based on a hybrid attention mechanism and multiresolution hash encoding.Compared to traditional methods,modelling time is reduced from hours to 1 min without professional equipment or manual intervention.The model quality is more concerned with local features of risk areas in transformers while ensuring the overall scene,and the accuracy is improved by about 6%,realising the real-time modelling of transformers and the DT of scenes.
基金supported by the National Natural Science Foundation of China(No.U1966209)the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources(NCEPU,LAPS22001).
文摘The partial discharge occurring in the weak part of the insulation of a converter transformer results in the formation of a large number of bubbles in the insulating oil.The migration,deformation,and other dynamic behaviors of bubbles in the region of a strong electric field can cause them to easily accumulate into“small bridges”of impurities that can lead to breakdown of the oil gap.The authors of this study experimentally investigate and discuss the mechanisms of migration and deformation of bubbles in oil during partial discharge under composite AC/DC voltage to clarify their dynamic behaviors.The influence of the initial position of the bubbles on their trajectory of migration and velocity as well as the morphological changes occurring in them are analyzed using numerical simulations.The results show that the bubbles move away from the strong electric field due to the action of the dielectrophoretic force.The interface of the bubbles is longitudinally stretched under the action of the electrostrictive force and the vertical component of the drag force and gradually recovers to assume a spherical shape under the influence of surface tension and the horizontal component of the drag force.
文摘The studied sending-terminal’s UHVDC converter transformer with the UHVAC grid is currently one of the largest-capacity converter transformers,which is characterized by strong support for the large-scale grid power delivering out,strengthening grid’s fault tolerance and backup capability,improving grid operation’s flexibility and security,lowering the short-circuit currents.The proposed single-active-part converter transformer structure is well-designed,including the single-phase five-leg iron core,the special winding arrangement,the special structure of the spacers and angle rings,and so on,which is a smaller footprint,easier to install and test on site,but is more challenging in the structural design due to the critical railway transportation limitations on aspects of both size and weight.The feasibility of the proposed structure schema is verified by a series of tests,concerning the wave process,the short circuit force,the temperature field,the main insulation,and so on.Among them,the main insulation’s electric fields at the import positions are verified to be reasonable,including the AC impressed voltage test,the DC impressed voltage test,and the polarity reversal test.It shows that the proposed single-active-part design scheme is practicable and conductive to manufacture and application for the UHV large-capacity converter transformers.
基金supported by the Key R&D Program of Shandong Province(No.2021CXGC010210).
文摘To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using the finite element method and model experiments.This paper quantifies the influence of different DC contents on the magnetic flux density,force,and displacement distribution characteristics of the iron core and winding and analyzes the internal relationship between various indicators.The inflection point of the DC bias coefficient on the vibration is obtained and the contribution mechanism of the different responses of the iron core and winding to this inflection point is explained.The value of the DC bias coefficient for changing the main vibration frequency is determined.When the DC bias coefficient is 1.0 and 1.5,the main frequency of vibration moves to the right to 250 Hz and 350 Hz.Based on the principle of similarity,a DC bias vibration experimental platform for converter transformers is developed,and DC bias magnetic experiments are conducted to verify the reliability of the simulation results.
基金supported by the Central Guided Local Science and Technology Development Project(Grant YDZX2022001).
文摘Converter transformers are the core components of ultra-high voltage(UHV)transmission systems.The main cause of faults in converter transformers is irreversible deterioration of oil-pressboard insulation under combined electrical-thermal-mechanical stress over long operating times.In this paper,the chemical characteristics of oil-pressboard insulation samples subjected to electrical-thermal-mechanical ageing for different times are studied.An image processing algorithm is used to analyse the discharge propagation characteristics of the samples under combined alternating current(AC)-direct current(DC)voltage,and the current pulse curves and phase resolved partial discharge spectrogram corresponding to the discharge images are analysed.An improved wavelet packet algorithm is used to denoise the discharge current pulse.Finally,the influence of electrical-thermal-mechanical ageing on discharge characteristics is analysed using radar charts.The condition of oil-pressboard insulation is one of the main factors determining the life expectancy of converter transformers.The results obtained here therefore have practical significance for understanding the process of insulation failure caused by accelerated ageing of oil-pressboard insulation.
基金This work was supported in part by the Science and Technology Project of State Grid Corporation of China(No.52060020002P).
文摘Converter transformers are the core device in ultrahigh voltage direct current(UHVDC)transmission systems,and the oil-paper insulation at its rectifying valve side deals with the composite AC-DC voltage.A detailed investigation of the partial discharge(PD)mechanism in the oil-paper insulation under the composite AC-DC voltage is,therefore,very important.The oilpaper insulated needle plate electrode simulation model for the electric field and charge distribution can be established using hydrodynamic drift-diffusion theory and bipolar charge carrier theory,and the simulation results can reflect the morphological changes of PD.The development characteristics of PD under composite AC-DC voltage are researched.In addition,the effects of simulation time,the AC-DC component proportion,and model parameters on PD are also explored.Results indicate that differences in applied voltage,interface charge,and geometry structure can cause changes in the electric field strength,which consequently influences the PD process in the simulation model.Oil-immersed paperboard is a type of liquid-immersed dielectric(LID).When the LID is arranged in perpendicular,only the positive streamers have narrow channels oriented toward the LID.When the LID is arranged in parallel,the PDs are in the form of creeping discharges and the negative streamers are more dispersed.The development characteristics of PD and its influencing factors reported here may provide theoretical and simulation support to explain the physical mechanism of PD at the rectifying valve side of the converter transformer.
