The paper reports results of investigation on the harmonic detection technique of a complicated power supply system such as an AC excited generation system, which has a variable fundamental frequency and low order har...The paper reports results of investigation on the harmonic detection technique of a complicated power supply system such as an AC excited generation system, which has a variable fundamental frequency and low order harmonics with rich sub-harmonics whose frequencies are lower than the fundamental one. The in-phase correlation filtering technique, based on the frequency shifting principle, is proposed in this paper.Theoretical analysis and experimental results validate the effectiveness of this technique for the harmonic detections of AC excited generation systems.展开更多
Plasma’s conductive and dielectric properties have been well known for decades. Plasma antenna is a general terms representing using plasma as a conductive medium to transmit or reflect signals. It has unique propert...Plasma’s conductive and dielectric properties have been well known for decades. Plasma antenna is a general terms representing using plasma as a conductive medium to transmit or reflect signals. It has unique properties like low RCS (radar cross section), variable impedance and instant on-off capability. Previous plasma antenna uses RF power to generate the plasma column. We developed AC-biased (alternating current) plasma antenna, which has larger operation frequency scale and lower sustaining power. Signals propagated are coupled into the plasma antenna via capacitive coupling. Impedance of the plasma shifts slightly with the AC current. Radiation pattern of the plasma antenna is less uniform than metal antenna and its gain is related to AC power, from the measuring results of AC-biased plasma antenna we found its advantages compare to the plasma antenna excited by the surface wave.展开更多
For developing ultra-high voltage(UHV) AC power transmission systems,it is important to precisely estimate and to limit the radio interference(RI) level of power lines.Based on the stochastic characteristics in amplit...For developing ultra-high voltage(UHV) AC power transmission systems,it is important to precisely estimate and to limit the radio interference(RI) level of power lines.Based on the stochastic characteristics in amplitude and repetition rate of induced corona current,by using the probability theory and mathematical statistics,we establish a stochastic model for the wide-sense stationary random process of corona discharges.Then combining the stochastic model with model-propagation-analysis method,the RI levels under three-phase UHV AC transmission lines are calculated.The results of the calculation based on stochastic model method and International Council on Large Electric Systems(CIGRE) excitation function are compared with that based on semi-empirical method and some other excitation functions.The stochastic model based on different excitation functions is also adopted to simulate the RI levels under finite test lines with two opened terminations.The results indicate that with the same average maximum gradient on conductor surface and the same conductor type,the number of corona discharge per unit length is one of the main reasons that causes the difference between different excitation functions.It is also concluded that for a long test line,the effect of standing wave on RI field strength is negligible in the middle of the line,but obvious near both terminations: for a 10-km line,the maximum difference in RI field strength is 2.78 dB,between the peak value of the standing wave near the ends and the steady value near the middle of the line.展开更多
文摘The paper reports results of investigation on the harmonic detection technique of a complicated power supply system such as an AC excited generation system, which has a variable fundamental frequency and low order harmonics with rich sub-harmonics whose frequencies are lower than the fundamental one. The in-phase correlation filtering technique, based on the frequency shifting principle, is proposed in this paper.Theoretical analysis and experimental results validate the effectiveness of this technique for the harmonic detections of AC excited generation systems.
文摘Plasma’s conductive and dielectric properties have been well known for decades. Plasma antenna is a general terms representing using plasma as a conductive medium to transmit or reflect signals. It has unique properties like low RCS (radar cross section), variable impedance and instant on-off capability. Previous plasma antenna uses RF power to generate the plasma column. We developed AC-biased (alternating current) plasma antenna, which has larger operation frequency scale and lower sustaining power. Signals propagated are coupled into the plasma antenna via capacitive coupling. Impedance of the plasma shifts slightly with the AC current. Radiation pattern of the plasma antenna is less uniform than metal antenna and its gain is related to AC power, from the measuring results of AC-biased plasma antenna we found its advantages compare to the plasma antenna excited by the surface wave.
基金supported by Science and Technology Project of SGCC(SG1021)
文摘For developing ultra-high voltage(UHV) AC power transmission systems,it is important to precisely estimate and to limit the radio interference(RI) level of power lines.Based on the stochastic characteristics in amplitude and repetition rate of induced corona current,by using the probability theory and mathematical statistics,we establish a stochastic model for the wide-sense stationary random process of corona discharges.Then combining the stochastic model with model-propagation-analysis method,the RI levels under three-phase UHV AC transmission lines are calculated.The results of the calculation based on stochastic model method and International Council on Large Electric Systems(CIGRE) excitation function are compared with that based on semi-empirical method and some other excitation functions.The stochastic model based on different excitation functions is also adopted to simulate the RI levels under finite test lines with two opened terminations.The results indicate that with the same average maximum gradient on conductor surface and the same conductor type,the number of corona discharge per unit length is one of the main reasons that causes the difference between different excitation functions.It is also concluded that for a long test line,the effect of standing wave on RI field strength is negligible in the middle of the line,but obvious near both terminations: for a 10-km line,the maximum difference in RI field strength is 2.78 dB,between the peak value of the standing wave near the ends and the steady value near the middle of the line.
