Half-wavelength transmission can transmit large-scale renewable energy over very long distances.This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering ...Half-wavelength transmission can transmit large-scale renewable energy over very long distances.This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering largescale wind-power transmission.First,the unique voltage characteristics of half-wavelength lines are deduced based on the distributed parameter model.In the secondary voltage-control level,reactive power-transmission limits of half-wavelength lines are introduced as another control objective except for tracing the pilot bus voltage reference.Considering the uncertainty and fluctuation of wind power,the overvoltage risk-assessment method of half-wavelength lines is presented to determine specific voltage-control strategies.Simulation results demonstrate that the proposed voltage-control method delivers superior tracking performance according to a voltage reference value and prevents the overvoltage risk of halfwavelength lines effectively in different wind-power penetrations.展开更多
The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced...The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.展开更多
Telegraph equations are derived from the equations of transmission line theory. They describe the relationships between the currents and voltages on a portion of an electric line as a function of the linear constants ...Telegraph equations are derived from the equations of transmission line theory. They describe the relationships between the currents and voltages on a portion of an electric line as a function of the linear constants of the conductor (resistance, conductance, inductance, capacitance). Their resolution makes it possible to determine the variation of the current and the voltage as a function of time at each point of the line. By adopting a general sinusoidal form, we propose a new exact solution to the telegraphers’ partial differential equations. Different simulations have been carried out considering the parameter of the 12/20 (24) kV Medium Voltage Cable NF C 33,220. The curves of the obtained solution better fit the real voltage curves observed in the electrical networks in operation.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
In this paper we analyze plane wave coupling to transmission lines rotating randomly over an infinite and perfectly conducting ground and present an efficient method to calculate average voltage. Under the assumption ...In this paper we analyze plane wave coupling to transmission lines rotating randomly over an infinite and perfectly conducting ground and present an efficient method to calculate average voltage. Under the assumption of small rotation quantity, the factors affecting the induced voltage and their effects are analyzed and then an efficient method to calculate the average voltage is presented when the distribution of the random rotation angles is uniform in [-π, π]. The results show that voltage variation is mainly due to the change of the source term. The effects of the source term increase linearly with the magnitude of the incident wave, change periodically with the rotation angle, and are larger in the high frequency range than in the low frequency range. The results show that the average voltages obtained by the proposed method agree well with those via the Monte Carlo method and the proposed method is much more efficient. The results also imply that the effect of random rotation is more important than that of random translation.展开更多
This paper proposes a hybrid submodule modular multilevel converter(MMC)topology which is suitable for multi terminal direct current(MTDC)transmission systems.Each arm of the proposed MMC topology consists of a half-b...This paper proposes a hybrid submodule modular multilevel converter(MMC)topology which is suitable for multi terminal direct current(MTDC)transmission systems.Each arm of the proposed MMC topology consists of a half-bridge submodule(HBSM)branch and two parallel full-bridge submodule(FBSM)branches.Comparing with the conventional MTDC transmission system,the proposed topology can selectively block the DC fault current and isolate the corresponding fault line without expensive DC circuit breakers(DCCBs).Thus,the influence range of the DC fault can be reduced and the reliability of the power supply can be improved as well.The corresponding modulation and voltage balancing strategies are developed for the proposed hybrid MMC topology.The feasibility of the proposed topology and control strategy is verified in the MATLAB/Simulink simulation.展开更多
Melanosomes, isolated by centrifugal separation from culture broth of B16 melanoma cells derived from mouse, were observed by scanning electron microscopy (SEM), and by transmission electron microscopy (TEM). Some int...Melanosomes, isolated by centrifugal separation from culture broth of B16 melanoma cells derived from mouse, were observed by scanning electron microscopy (SEM), and by transmission electron microscopy (TEM). Some interesting structural features were found inside and outside of the melanosomes. By SEM observation, the melanosomes were ellipsoid shape, their surface was not smooth and was covered with rough substructure, 10 to 20 nm particles. By TEM, uneven structure and micro particles were observed in the melanosomes. Furthermore, three-dimensional analysis was tried by using the ultra-high voltage electron microscopy(UHVEM). Micrographs of the melanosomes were taken at various tilted angles by UHVEM, after preparing 500 nm thickness specimens stained with lead citrate. From the micrographs collected, the three-dimensional structures were reconstructed by using i-mode software. Melanin stained by lead and non stained parts was clearly observed in the reconstructed structure. Non stained parts were round, regular size, and distributed widely in the melanosomes.展开更多
A novel dual direction silicon-controlled rectifier(DDSCR)with an additional P-type doping and gate(APGDDSCR)is proposed and demonstrated.Compared with the conventional low-voltage trigger DDSCR(LVTDDSCR)that has posi...A novel dual direction silicon-controlled rectifier(DDSCR)with an additional P-type doping and gate(APGDDSCR)is proposed and demonstrated.Compared with the conventional low-voltage trigger DDSCR(LVTDDSCR)that has positive and negative holding voltages of 13.371 V and 14.038 V,respectively,the new DDSCR has high positive and negative holding voltages of 18.781 V and 18.912 V in a single finger device,respectively,and it exhibits suitable enough positive and negative holding voltages of 14.60 V and 14.319 V in a four-finger device for±12-V application.The failure current of APGDDSCR is almost the same as that of LVT-DDSCR in the single finger device,and the four-finger APGDDSCR can achieve positive and negative human-body model(HBM)protection capabilities of 22.281 kV and 23.45 kV,respectively,under 40-V voltage of core circuit failure,benefitting from the additional structure.The new structure can generate a snapback voltage on gate A to increase the current gain of the parasitic PNP in holding voltage.Thus,a sufficiently high holding voltage increased by the structure can ensure that a multi-finger device can also reach a sufficient holding voltage,it is equivalent to solving the non-uniform triggering problem of multi-finger device.The operating mechanism and the gate voltage are both discussed and verified in two-dimensional(2D)simulation and experiemnt.展开更多
Using composite field arithmetic in Galois field can result in the compact Rijndael S-Box. However, the power con- sumption of this solution is too large to be used in resource-limited embedded systems. A full-custom ...Using composite field arithmetic in Galois field can result in the compact Rijndael S-Box. However, the power con- sumption of this solution is too large to be used in resource-limited embedded systems. A full-custom hardware implementation of composite field S-Box is proposed for these targeted domains in this paper. The minimization of power consumption is implemented by optimizing the architecture of the composite field S-Box and using the pass transmission gate (PTG) to realize the logic functions of S-Box. Power simulations were performed using the netlist extracted from the layout. HSPICE simulation results indicated that the proposed S-Box achieves low power consumption of about 130 μW at 10 MHz using 0.25 μm/2.5 V technology, while the consumptions of the positive polarity reed-muller (PPRM) based S-Box and composite field S-Box based on the conventional CMOS logic style are about 240 μW and 420 μW, respectively. The simulations also showed that the presented S-Box obtains better low-voltage operating property, which is clearly relevant for applications like sensor nodes, smart cards and radio frequency identification (RFID) tags.展开更多
In view of the imbalanced distribution of power load and resources, including the status of “electric shortage” in some cities in our country, the article discusses the long-distance transmission technology. It main...In view of the imbalanced distribution of power load and resources, including the status of “electric shortage” in some cities in our country, the article discusses the long-distance transmission technology. It mainly analyzed two ways of the long-distance transmission: UHV AC transmission and UHV DC transmission. The fractional frequency transmission technology and half wavelength AC transmission technology of AC transmission are introduced. Some key technologies of long-distance transmission are described. It has a guess for long-distance transmission future direction.展开更多
An optimal load shedding strategy for power systems with optimum location and quantity of load to be shed is presented in this paper. The problem of load shedding for avoiding the existence of voltage instability in p...An optimal load shedding strategy for power systems with optimum location and quantity of load to be shed is presented in this paper. The problem of load shedding for avoiding the existence of voltage instability in power systems is taken as a remedial action during emergency state in transmission and distribution sector.Optimum location of loads to be shed is found together with their optimum required quantity. L-Indicator index is in used for this purpose with a modified new technique. Applications to be standard 6 bus Ward-Hale test system and IEEE – 14 bus system are presented to validate the applicability of the proposed technique to any system of any size.展开更多
Long span ultra-high voltage(UHV) transmission lines have serious aeolian vibration problems. To control these vibrations,we improved the energy balance method in the following aspects:the wind power input,the conduct...Long span ultra-high voltage(UHV) transmission lines have serious aeolian vibration problems. To control these vibrations,we improved the energy balance method in the following aspects:the wind power input,the conductor self-damping,and the damper dissipated power. Meanwhile,we built a theoretical mechanical model of β wire dampers and derived energy dissipation calculation formulae. This permits the vibration energy dissipated by β wire dampers can be considered in the energy balance method. Then,we developed a computer program based on the improved energy balance method using Matlab,and analyzed UHV long span ground wires of the Han River long span project in P. R. China. The results show that the combination of β wire dampers and Stockbridge dampers can reduce vibration of UHV long span transmission lines,which provides a reference for research and construction of UHV engineering projects.展开更多
The impact of 500 kV transmission lines of Anqing power plant across the lake wetland reserve along the Yangtze River on the safety of the ecosystem was taken as the researched object.The power frequency electric fiel...The impact of 500 kV transmission lines of Anqing power plant across the lake wetland reserve along the Yangtze River on the safety of the ecosystem was taken as the researched object.The power frequency electric field intensity(PFEFI),power frequency magnetic field intensity(PFMFI),radio interference,construction noise,vegetation destruction and the influence on water quality were investigated and monitored,and the influences of PFEFI,PFMFI,radio interference and construction noise on wild animals,especially the habitats and migration of birds were mainly researched.The direct and indirect influences on the surrounding environment as well as plants and animals in sensitive areas were analyzed and predicted.The results firstly showed there existed a 182 400m^3 stereo-space(PFEFI>4kV/m)which made flying birds unsafe under the lowest height 11 mof the lines,which fills the gap in the research of this field.Finally,some operational protection countermeasures were put forward at the current technical level to achieve the win-win goal of economic development and natural protection.展开更多
In recent years,several failures of double circuit transmission line on the same tower due to lightning were happened in Beijing power grid.Although it can be reclosed successful,the lightning strike caused a grave th...In recent years,several failures of double circuit transmission line on the same tower due to lightning were happened in Beijing power grid.Although it can be reclosed successful,the lightning strike caused a grave threat to the power grid security.The cause of the accident and the accident process were studied for the sake of further understanding of the impact of lightning on power grid.As an example,110 kV double circuit transmission line(Xilong-line) was analyzed.At first,the system topology was given.Through the analysis on relay protection actions and the fault recorder data,over voltage on the insulator strings was calculated.Based on the analysis and the calculation,accident cause and the process were presented respectively.Secondly,it comes to the conclusion that the lightning failure was caused by counterattack.The wave of the lightning over voltage would spread to the not grounded neutral point of the transformers,and make the neutral protective gap breakdown,then cause freewheeling with the frequency of 50 Hz.As results of the relay protection,the double circuit transmission line all tripped out.Finally,the causes of the accident were proposed that included terrain features,large corner towers,strong thunderstorm weather and poor grounded contact of the tower.展开更多
This paper uses CT to gain the energy directly from the high-voltage transmission line, to address the problem of power supply for monitoring system in high voltage side of transmission line. The draw-out power coil c...This paper uses CT to gain the energy directly from the high-voltage transmission line, to address the problem of power supply for monitoring system in high voltage side of transmission line. The draw-out power coil can induce voltage from the transmission line, using single-chip microcomputer to analog and output PMW wave to control the charging module, provides a stable 3.4 V DC voltage to the load, and solve the problem of easy saturating of core. The power supply based on this kind of draw-out power coil has undergone the overall testing, and it is verified-showing that it can properly work in a non-saturated status within the current range of 50 - 1000 A, and provide a stable output. The equipment also design protection circuit to improve the reliability to avid the impacts of the impulse current or short-circuit current. It effectively solves the problem of power supply for On-line Monitoring System of Transmission.展开更多
基金supported by State Grid Corporation of China,Projects under Grant 520626200031National Natural Science Foundation of China,No.51877200。
文摘Half-wavelength transmission can transmit large-scale renewable energy over very long distances.This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering largescale wind-power transmission.First,the unique voltage characteristics of half-wavelength lines are deduced based on the distributed parameter model.In the secondary voltage-control level,reactive power-transmission limits of half-wavelength lines are introduced as another control objective except for tracing the pilot bus voltage reference.Considering the uncertainty and fluctuation of wind power,the overvoltage risk-assessment method of half-wavelength lines is presented to determine specific voltage-control strategies.Simulation results demonstrate that the proposed voltage-control method delivers superior tracking performance according to a voltage reference value and prevents the overvoltage risk of halfwavelength lines effectively in different wind-power penetrations.
文摘The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.
文摘Telegraph equations are derived from the equations of transmission line theory. They describe the relationships between the currents and voltages on a portion of an electric line as a function of the linear constants of the conductor (resistance, conductance, inductance, capacitance). Their resolution makes it possible to determine the variation of the current and the voltage as a function of time at each point of the line. By adopting a general sinusoidal form, we propose a new exact solution to the telegraphers’ partial differential equations. Different simulations have been carried out considering the parameter of the 12/20 (24) kV Medium Voltage Cable NF C 33,220. The curves of the obtained solution better fit the real voltage curves observed in the electrical networks in operation.
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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61231003 and 61201090)
文摘In this paper we analyze plane wave coupling to transmission lines rotating randomly over an infinite and perfectly conducting ground and present an efficient method to calculate average voltage. Under the assumption of small rotation quantity, the factors affecting the induced voltage and their effects are analyzed and then an efficient method to calculate the average voltage is presented when the distribution of the random rotation angles is uniform in [-π, π]. The results show that voltage variation is mainly due to the change of the source term. The effects of the source term increase linearly with the magnitude of the incident wave, change periodically with the rotation angle, and are larger in the high frequency range than in the low frequency range. The results show that the average voltages obtained by the proposed method agree well with those via the Monte Carlo method and the proposed method is much more efficient. The results also imply that the effect of random rotation is more important than that of random translation.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51637007in part by the Science and Technology Projects of State Grid Corporation of China under project SG-TYHT/16-JS-198.
文摘This paper proposes a hybrid submodule modular multilevel converter(MMC)topology which is suitable for multi terminal direct current(MTDC)transmission systems.Each arm of the proposed MMC topology consists of a half-bridge submodule(HBSM)branch and two parallel full-bridge submodule(FBSM)branches.Comparing with the conventional MTDC transmission system,the proposed topology can selectively block the DC fault current and isolate the corresponding fault line without expensive DC circuit breakers(DCCBs).Thus,the influence range of the DC fault can be reduced and the reliability of the power supply can be improved as well.The corresponding modulation and voltage balancing strategies are developed for the proposed hybrid MMC topology.The feasibility of the proposed topology and control strategy is verified in the MATLAB/Simulink simulation.
文摘Melanosomes, isolated by centrifugal separation from culture broth of B16 melanoma cells derived from mouse, were observed by scanning electron microscopy (SEM), and by transmission electron microscopy (TEM). Some interesting structural features were found inside and outside of the melanosomes. By SEM observation, the melanosomes were ellipsoid shape, their surface was not smooth and was covered with rough substructure, 10 to 20 nm particles. By TEM, uneven structure and micro particles were observed in the melanosomes. Furthermore, three-dimensional analysis was tried by using the ultra-high voltage electron microscopy(UHVEM). Micrographs of the melanosomes were taken at various tilted angles by UHVEM, after preparing 500 nm thickness specimens stained with lead citrate. From the micrographs collected, the three-dimensional structures were reconstructed by using i-mode software. Melanin stained by lead and non stained parts was clearly observed in the reconstructed structure. Non stained parts were round, regular size, and distributed widely in the melanosomes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61774129,61827812,and 61704145)the Huxiang High-level Talent Gathering Project from the Hunan Science and Technology Department,China(Grant No.2019RS1037)the Changsha Science and Technology Plan Key Projects,China(Grant Nos.kq1801035 and kq1703001).
文摘A novel dual direction silicon-controlled rectifier(DDSCR)with an additional P-type doping and gate(APGDDSCR)is proposed and demonstrated.Compared with the conventional low-voltage trigger DDSCR(LVTDDSCR)that has positive and negative holding voltages of 13.371 V and 14.038 V,respectively,the new DDSCR has high positive and negative holding voltages of 18.781 V and 18.912 V in a single finger device,respectively,and it exhibits suitable enough positive and negative holding voltages of 14.60 V and 14.319 V in a four-finger device for±12-V application.The failure current of APGDDSCR is almost the same as that of LVT-DDSCR in the single finger device,and the four-finger APGDDSCR can achieve positive and negative human-body model(HBM)protection capabilities of 22.281 kV and 23.45 kV,respectively,under 40-V voltage of core circuit failure,benefitting from the additional structure.The new structure can generate a snapback voltage on gate A to increase the current gain of the parasitic PNP in holding voltage.Thus,a sufficiently high holding voltage increased by the structure can ensure that a multi-finger device can also reach a sufficient holding voltage,it is equivalent to solving the non-uniform triggering problem of multi-finger device.The operating mechanism and the gate voltage are both discussed and verified in two-dimensional(2D)simulation and experiemnt.
基金Project supported by the Hi-Tech Research and Development Program (863) of China (No. 2006AA01Z226)the Scientific Research Foundation of Huazhong University of Science and Technol-ogy (No. 2006Z001B), China
文摘Using composite field arithmetic in Galois field can result in the compact Rijndael S-Box. However, the power con- sumption of this solution is too large to be used in resource-limited embedded systems. A full-custom hardware implementation of composite field S-Box is proposed for these targeted domains in this paper. The minimization of power consumption is implemented by optimizing the architecture of the composite field S-Box and using the pass transmission gate (PTG) to realize the logic functions of S-Box. Power simulations were performed using the netlist extracted from the layout. HSPICE simulation results indicated that the proposed S-Box achieves low power consumption of about 130 μW at 10 MHz using 0.25 μm/2.5 V technology, while the consumptions of the positive polarity reed-muller (PPRM) based S-Box and composite field S-Box based on the conventional CMOS logic style are about 240 μW and 420 μW, respectively. The simulations also showed that the presented S-Box obtains better low-voltage operating property, which is clearly relevant for applications like sensor nodes, smart cards and radio frequency identification (RFID) tags.
文摘In view of the imbalanced distribution of power load and resources, including the status of “electric shortage” in some cities in our country, the article discusses the long-distance transmission technology. It mainly analyzed two ways of the long-distance transmission: UHV AC transmission and UHV DC transmission. The fractional frequency transmission technology and half wavelength AC transmission technology of AC transmission are introduced. Some key technologies of long-distance transmission are described. It has a guess for long-distance transmission future direction.
文摘An optimal load shedding strategy for power systems with optimum location and quantity of load to be shed is presented in this paper. The problem of load shedding for avoiding the existence of voltage instability in power systems is taken as a remedial action during emergency state in transmission and distribution sector.Optimum location of loads to be shed is found together with their optimum required quantity. L-Indicator index is in used for this purpose with a modified new technique. Applications to be standard 6 bus Ward-Hale test system and IEEE – 14 bus system are presented to validate the applicability of the proposed technique to any system of any size.
基金Funded by the Natural Science Foundation of China (No. 50878093).
文摘Long span ultra-high voltage(UHV) transmission lines have serious aeolian vibration problems. To control these vibrations,we improved the energy balance method in the following aspects:the wind power input,the conductor self-damping,and the damper dissipated power. Meanwhile,we built a theoretical mechanical model of β wire dampers and derived energy dissipation calculation formulae. This permits the vibration energy dissipated by β wire dampers can be considered in the energy balance method. Then,we developed a computer program based on the improved energy balance method using Matlab,and analyzed UHV long span ground wires of the Han River long span project in P. R. China. The results show that the combination of β wire dampers and Stockbridge dampers can reduce vibration of UHV long span transmission lines,which provides a reference for research and construction of UHV engineering projects.
基金Supported by the Provincial Governmental Foundation for Forestry of Anhui Province in 2013(2136203)
文摘The impact of 500 kV transmission lines of Anqing power plant across the lake wetland reserve along the Yangtze River on the safety of the ecosystem was taken as the researched object.The power frequency electric field intensity(PFEFI),power frequency magnetic field intensity(PFMFI),radio interference,construction noise,vegetation destruction and the influence on water quality were investigated and monitored,and the influences of PFEFI,PFMFI,radio interference and construction noise on wild animals,especially the habitats and migration of birds were mainly researched.The direct and indirect influences on the surrounding environment as well as plants and animals in sensitive areas were analyzed and predicted.The results firstly showed there existed a 182 400m^3 stereo-space(PFEFI>4kV/m)which made flying birds unsafe under the lowest height 11 mof the lines,which fills the gap in the research of this field.Finally,some operational protection countermeasures were put forward at the current technical level to achieve the win-win goal of economic development and natural protection.
文摘In recent years,several failures of double circuit transmission line on the same tower due to lightning were happened in Beijing power grid.Although it can be reclosed successful,the lightning strike caused a grave threat to the power grid security.The cause of the accident and the accident process were studied for the sake of further understanding of the impact of lightning on power grid.As an example,110 kV double circuit transmission line(Xilong-line) was analyzed.At first,the system topology was given.Through the analysis on relay protection actions and the fault recorder data,over voltage on the insulator strings was calculated.Based on the analysis and the calculation,accident cause and the process were presented respectively.Secondly,it comes to the conclusion that the lightning failure was caused by counterattack.The wave of the lightning over voltage would spread to the not grounded neutral point of the transformers,and make the neutral protective gap breakdown,then cause freewheeling with the frequency of 50 Hz.As results of the relay protection,the double circuit transmission line all tripped out.Finally,the causes of the accident were proposed that included terrain features,large corner towers,strong thunderstorm weather and poor grounded contact of the tower.
文摘This paper uses CT to gain the energy directly from the high-voltage transmission line, to address the problem of power supply for monitoring system in high voltage side of transmission line. The draw-out power coil can induce voltage from the transmission line, using single-chip microcomputer to analog and output PMW wave to control the charging module, provides a stable 3.4 V DC voltage to the load, and solve the problem of easy saturating of core. The power supply based on this kind of draw-out power coil has undergone the overall testing, and it is verified-showing that it can properly work in a non-saturated status within the current range of 50 - 1000 A, and provide a stable output. The equipment also design protection circuit to improve the reliability to avid the impacts of the impulse current or short-circuit current. It effectively solves the problem of power supply for On-line Monitoring System of Transmission.