In order to investigate the injection current uniformity around the induction cell bores, two fully electromagnetic （EM） models are respectively established for a single-stage induction cell and an induction voltage...In order to investigate the injection current uniformity around the induction cell bores, two fully electromagnetic （EM） models are respectively established for a single-stage induction cell and an induction voltage adder （IVA） with three cells stacked in series, without considering electron emission. By means of these two models, some factors affecting the injection current uni- formity are simulated and analyzed, such as the impedances of adders and loads, cell locations, and feed timing of parallel driving pulses. Simulation results indicate that higher impedances of adder and loads are slightly beneficial to improve injection current uniformity. As the impedances of adder and loads increase from 5 Ω to 30Ω, the asymmetric coefficient of feed currents decreases from 10.3% to 6.6%. The current non-uniformity within the first cell is a little worse than that in other downstream cells. Simulation results also show that the feed timing would greatly affect current waveforms, and consequently cause some distortion in pulse fronts of cell output voltages. For a given driving pulse with duration time of 70-80 ns, the feed timing with a time deviation of less than 20 ns is acceptable for the three-cell IVAs, just causing the rise time of output voltages to increase about 5 ns at most and making the peak voltage decrease by 3.5%.展开更多
To address the lack of voltage ratio standards for accuracy testing of low-frequency voltage transformers,it is necessary to develop a 3 kV low-frequency induction voltage divider.Firstly,based on the analysis of the ...To address the lack of voltage ratio standards for accuracy testing of low-frequency voltage transformers,it is necessary to develop a 3 kV low-frequency induction voltage divider.Firstly,based on the analysis of the error sources of the induction voltage divider,a method was proposed to calculate the excitation impedance of the induction voltage divider using complex magnetic permeability.A measurement circuit based on the lock-in principle was set up to measure the complex magnetic permeability of grained-oriented silicon steel 30P100 and permalloy 1J85 at different frequencies.Secondly,a 3 kV low-frequency induction voltage divider with a two-stage excitation and a series-wound ra-tio winding in 10 sections was designed.The errors of the two stages of the instrument transformers were calculated at 20 and 50 Hz,respectively.Finally,the divider's errors were calibrated at 20 and 50 Hz using the reference potential method.The results showed that,compared to 50 Hz,the excitation impedance of the two stages decreased and the errors increased at 20 Hz,with the overall error of the induction voltage divider being better at 50 Hz than at 20 Hz.Experimental measurements indicated that at 20 Hz,the ratio error and phase error of the 3 kV two-stage excitation induction voltage divider were better than 110-5,whereas at 50 Hz,the errors were better than 110-6.This study provides support for the accuracy testing of voltage transformers used in low-frequency flexible AC transmission projects.展开更多
Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based o...Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based on the transient mea- surement and can distinguish the fault of one phase connecting ground. The method has been proved to be in correspondence with the simulation results by Matlab and LabVIEW in practice, The method has merits of simplicity, accuracy and ease of USe.展开更多
The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as describ...The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.展开更多
The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as describ...The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.展开更多
The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electrom...The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.展开更多
Excitation transformer is an important component of the power plant transformer group equipment. Its reliable operation is an important factor to ensure the stable safety of the unit. In recent years, due to the failu...Excitation transformer is an important component of the power plant transformer group equipment. Its reliable operation is an important factor to ensure the stable safety of the unit. In recent years, due to the failure of excitation transformer, some power plants have not stop, which has a great impact on the safety of equipment and power supply stability. Combined with the several failures of excitation transformer in a power generation enterprise in recent years, this paper sorts out the problems of excitation transformer in power plant caused by failure one by one, analyzes the causes in depth, and puts forward countermeasures.展开更多
基金supported by National Natural Science Foundation of China(No.51307141)partly by the State Key Laboratory of Intense Pulsed Radiation Simulation(Northwest Institute of Nuclear Technology)under Contract SKLIPR 1206
文摘In order to investigate the injection current uniformity around the induction cell bores, two fully electromagnetic （EM） models are respectively established for a single-stage induction cell and an induction voltage adder （IVA） with three cells stacked in series, without considering electron emission. By means of these two models, some factors affecting the injection current uni- formity are simulated and analyzed, such as the impedances of adders and loads, cell locations, and feed timing of parallel driving pulses. Simulation results indicate that higher impedances of adder and loads are slightly beneficial to improve injection current uniformity. As the impedances of adder and loads increase from 5 Ω to 30Ω, the asymmetric coefficient of feed currents decreases from 10.3% to 6.6%. The current non-uniformity within the first cell is a little worse than that in other downstream cells. Simulation results also show that the feed timing would greatly affect current waveforms, and consequently cause some distortion in pulse fronts of cell output voltages. For a given driving pulse with duration time of 70-80 ns, the feed timing with a time deviation of less than 20 ns is acceptable for the three-cell IVAs, just causing the rise time of output voltages to increase about 5 ns at most and making the peak voltage decrease by 3.5%.
基金The Innovation Fund Project of China Electric Power Research Institute:Research on accuracy test method of voltage transformer for low-frequency transmission and development of test system,Grant/Award Number:GY83-22-005。
文摘To address the lack of voltage ratio standards for accuracy testing of low-frequency voltage transformers,it is necessary to develop a 3 kV low-frequency induction voltage divider.Firstly,based on the analysis of the error sources of the induction voltage divider,a method was proposed to calculate the excitation impedance of the induction voltage divider using complex magnetic permeability.A measurement circuit based on the lock-in principle was set up to measure the complex magnetic permeability of grained-oriented silicon steel 30P100 and permalloy 1J85 at different frequencies.Secondly,a 3 kV low-frequency induction voltage divider with a two-stage excitation and a series-wound ra-tio winding in 10 sections was designed.The errors of the two stages of the instrument transformers were calculated at 20 and 50 Hz,respectively.Finally,the divider's errors were calibrated at 20 and 50 Hz using the reference potential method.The results showed that,compared to 50 Hz,the excitation impedance of the two stages decreased and the errors increased at 20 Hz,with the overall error of the induction voltage divider being better at 50 Hz than at 20 Hz.Experimental measurements indicated that at 20 Hz,the ratio error and phase error of the 3 kV two-stage excitation induction voltage divider were better than 110-5,whereas at 50 Hz,the errors were better than 110-6.This study provides support for the accuracy testing of voltage transformers used in low-frequency flexible AC transmission projects.
文摘Open phase in three phase induction motors is a common fault that can occur as a result of a fuse blowing or a pro- tective device failing on one phase of the motor. This paper introduces a new method,which is based on the transient mea- surement and can distinguish the fault of one phase connecting ground. The method has been proved to be in correspondence with the simulation results by Matlab and LabVIEW in practice, The method has merits of simplicity, accuracy and ease of USe.
文摘The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.
文摘The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.
基金This work was supported in part by the National Key Research and Development Program of China under Grant 2017YFB0902904,in part by the Natural Science Foundation of Hubei Province under Grant 2016CFB448,and in part by the Shenzhen City Science and Technology Innovation Plan under Grant JCYJ20170306170937861,and in part by Wuhan City Science and Technology Program under Grant 2016070204020165.
文摘The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.
文摘Excitation transformer is an important component of the power plant transformer group equipment. Its reliable operation is an important factor to ensure the stable safety of the unit. In recent years, due to the failure of excitation transformer, some power plants have not stop, which has a great impact on the safety of equipment and power supply stability. Combined with the several failures of excitation transformer in a power generation enterprise in recent years, this paper sorts out the problems of excitation transformer in power plant caused by failure one by one, analyzes the causes in depth, and puts forward countermeasures.
