Showing papers in "High Voltage Engineering in 2009"

Natural Pollution Test of Composite and Porcelain Insulators Under AC and DC Stress

Abstract: A natural pollution was tested to study the pollution and self cleaning characteristics of composite insulators and porcelain insulators (type: XP-70,XWP-70) energized with AC and DC voltage. Under the station’s condition,pollution differences between different insulators and different stresses mainly appeared on the insulators’ under-surfaces. During the main pollution period,upper-surface pollution accumulation rate of composite insulators was slightly higher than porcelain insulators’,while the under-surface pollution accumulation rate of composite insulators was 2 times as much as porcelain insulators’,under AC stress. The under-surface pollution ratio between DC stressed and AC stressed composite insulators was more than 5. For porcelain insulators,this ratio was 10. Pollution composition of insulators under DC and AC stress was analyzed. Two kinds of insulator cleaning processes by rain were observed in high and low precipitation. Self cleaning of composite insulators' under-surface was slightly hindered by hydrophobicity. The upper-surface pollution ratio between 3-year exposed and 1-year exposed composite insulators was about 1,while this ratio for under-surface under DC and AC stress were 2.2 and 1.4,respectively.

Dielectric Barrier Discharge and Its Applications

Abstract: In order to comprehensively understand DBD,we reviewed the investigations of dielectric barrier discharge(DBD) by focusing on the physics related to the uniform discharge at atmospheric pressure.It is suggested that the best way to distinguish a uniform discharge from a filamentary one is to take a picture with an exposure time of about 10 ns.Even for a real uniform discharge,it is important to further distinguish a glow discharge from a Townsend discharge.The only way to get a uniform discharge at atmospheric pressure is to make the discharge at a lower electric field by increasing the seed electrons initiating the discharge.Recently,the uniform discharges at atmospheric pressure have been obtained in helium and nitrogen,i.e.,subnormal glow discharge in helium and Townsend discharge in nitrogen.Moreover,we briefly introduced three industrial applications of DBD plasmas,including the advanced ozone generator,continuous double-sided treatment of foil surface,plasma display panel.

Thermal Model for Hot Spot Temperature Calculation in Oil-immersed Transformers

Abstract: Oil-immersed transformers are key components in power systems.The inordinate temperature rise in oil-immersed transformers is featured by hot spot temperature(HST).HST is an important parameter to determine the optimum load ability of transformers.A procedure to calculate HST is recommended by GB/T 15164-94 as an easy approach,yet it is not accurate in predicting the HST in the transient state and overload state.We put forward an equivalent bottom oil temperature(BOT)thermal circuit model based on the IEEE Std C57.91 Annex G that improves the transient state and overload state prediction.The model is composed of three thermal circuits revealing the relationship between HST and featured oil temperatures.The model is proved to be effective by comparing the calculation results of the thermal model and measured data obtained from heat run tests of an ONAN,100kVA/5kV test transformer.Finally,the results from this model are comfared with GB/T 15164-1994 loading guide method results.The comparison proves the model presented is adequate and the method of using bottom oil temperature in thermal circuit is effective.

Envelope Analysis and Defects Identification of Partial Discharge UHF Signals in GIS

Abstract: In order to detect and identify the defects in GIS,the ultra-high frequency(UHF)envelope detection circuit and high-speed data acquisition system was designed,and the tests of five typical defects in GIS were made in the laboratory and the envelope signal was acquired based on ultra-high frequency envelop detection circuit.A large number of experiments show that time-domain characteristics of partial discharge signals generated by the same defect model are similar,and envelopes are nearly identical.The time-domain characteristics of partial discharge signals generated by different defect models are different,and their envelope shapes are different.A new method of pattern recognition was proposed to analyze the characteristic parameters of the envelope signal at time-domain with BP neural network.PD pattern recognition results of testing data in lab indicate that the method is effective.

Comparative Analysis Between LLS and Observation of Artificial-triggered Lightning

Abstract: Lightning location system(LLS) plays a key role in lightning forecast and protection. Performance index of LLS is not based on the practical test but the theoretical analysis. For the validation of the truth of lightning location results,detection efficiency and detection precision for artificial-triggered flashes and return strokes are comprehensively analyzed based on the close Optical-Electrical observation of Rocket-triggered lightning and the LLS records of Guangdong power network. The results show that the flash detection efficiency and stroke detection efficiency are 93%(13/14) and 42% (26/62)for rocket-triggered lightning,there are 24 LLS records achieved by more than 3 detection stations,21 of which are ground-triggered strokes and the normalized space location error is 760 meters(sample size:21). The relative errors of lightning current amplitude are normalized to be 14%(sample size:9).

Passive Interference to Radio Station Caused by UHV AC Transmission Line in Shortwave Frequency

Abstract: The scattering of transmission lines will affect the propagation of the electromagnetic wave,so the distance between transmission lines and the shortwave radio station should be assigned in order to assure the communication quality. Therefore,the radio interference of the 1000 kV UHV AC transmission lines,overhead ground line and power tower on the nearby radio station,which was resulted from the scattering of the incidence electromagnetic wave,was analyzed. By using the method of moment simulator NEC (Numerical Electromagnetic Codes),based on the calculation of the electromagnetic field from the wire antenna,the radio interference level from the UHV transmission line of different type was investigated,and corresponding protective distance was obtained. The resultant protective distance was validated by the measurement on the UHV transmission line ratio model. With the possible effect of other factors taken into account as well,the protective distance of the 1000 kV UHV AC transmission line for different radio station within shortwave frequency band was proposed from viewpoints of the environment protection and reliability. The protective distances are 2000 m,1000 m and 500 m respectively for the station of the first,second and third levels.

Theoretical Calculation and Experimental Research on Thermal Time Constant of Single-core Cables

Abstract: Cable conductor temperature in operation is the key factor influencing insulation life,and cable operation state can be monitored through conductor temperature.Not only the value of temperature rise but also the change rate of conductor temperature is concerned.Generally the change rate of cable conductor temperature is represented by its thermal time constant.Consequently,the thermal time constant of single-core cable was introduced,transient thermal circuit models of cable body and its ambient medium were established,and the simplified equivalent ones were given.Moreover,thermal time constants of single-core cable buried in soil and in air were calculated,the on-site temperature rise test under step current was carried out,then the actual thermal time constants were obtained by fitting of the conductor temperature detected in tests.The validity of theoretical calculation was verified by test results.Thermal time constant of cables can be used to roughly estimate the transient response of conductor temperature and to determine the needed time of achieving highest allowable conductor temperature of cables when step current is applied,which provides theoretical support for cable condition monitoring and fault early warming in cable operation.

Differentiation Technology and Strategy of Lightning Protection for Transmission Lines

Abstract: In order to improve the evaluation and rebuilding levels of lightning protection for transmission lines,we proposed a differentiation technology and strategy by analyzing the differences of lightning activities,terrains and topographic features,line's structures and insulation configurations,analysis methods,and lightning protection measures of transmission linesThis technology and strategy are presented in detail with two relevant examplesFirstly,the lightning distribution and parameters along the line are obtained based on the long-term lightning data detected by the lightning location systemSecondly,combined with the line's parameters,the lightning protection performance and security level of each tower are evaluated with the right analysis methodAnd the grade as well as its determination factors of each tower is obtainedThirdly,the rebuilding principle is proposed,and the applicable protection measures are chosen considering their different characteristicsMoreover,several rebuilding schemes are established,and the technology-economy rate of each scheme is estimatedFinally,the optimal scheme is determined according to the rebuilding objective and managing demand of the lineAnd the relationship between the cost and expected effects of the rebuilding project is definitely givenThe differentiation technology and strategy would provide a technical support for the differentiation design and rebuilding of lightning protection for transmission lines and also for realizing the meticulous lightning protection in the management of transmission lines

Simplified Analysis and Calculation on Circulating Current and Power Loss in Enclosure of GIS and GIL

Abstract: There are very large circulating current and some power loss generated in the enclosure of GIS and GILBy the principle of electro-magnetic current transformer and error calculation equation,we analyzed the physical phenomenon of the circulating current in the enclosure of GIS and GIL,and simply calculated the circulating current and its power loss in the enclosureMeanwhile,we discussed the influences of the circulating current and its power loss on the operation of GIS,GIL and earth wire

Boost-based Two-level Grid-connected Photovoltaic Inverter System

Abstract: In grid-connected photovoltaic (PV) system,maximum power point tracking (MPPT) for PV modules must be executed to achieve higher efficiency. For grid connecting,the dc voltage of the inverter must be higher than the amplitude of grid voltage which restricts the output voltage of PV modules. Consequently,a grid-connected photovoltaic inverter system is researched. The inverter system is composed of a Boost DC/DC chopper in series with an inverter. The boost chopper changes the output voltage of the PV array by adjusting the duty cycle,by which the MPPT was achieved. The controller for the inverter system contains inner current loop and external voltage loop. The external loop stabilizes the voltage of the capacitor of the inverter,while the inner current loop controls the grid-connecting current. The MPPT and the control of the grid-connected inverter are independent from each other which make the PV system more flexible and reliable. The design of main component's parameters and the control strategy for the inverter system is also presented. The simulation in MatlabR2007a/Simulink confirms the effectiveness of the inverter system.

Experimental Research on Partial Discharge Localization in GIS Using Ultrasonic Associated with Electromagnetic Wave Method

Abstract: After analyzing the partial discharge(PD)locating methods of GIS which are widely used currently,a PD localization method based on ultrasonic associated with electromagnetic wave(EM-wave)techniques was proposed.As the ultrasonic and EM-wave signals of PD are detected synchronously,this PD localization method can exclude the interference signal and confirm PD signal more effectively.In this PD localization method,PD source is located using UHF time of flight method firstly to confirm PD source position roughly,which always include one or two spacers.In the second step,PD source position is located further by the ultrasonic and UHF united method.For the advantage of precise locating function of ultrasonic,the PD signal can be detected effectively and localized precisely.Especially when insulation defect is near insulator,this PD localization method can improve the equipment maintenance efficiency effectively by confirming the GIS spacer of PD source and locating the concrete position of PD source accurately.The experimental results show that the PD localization method based on ultrasonic associated with EM-wave techniques can locate floating electrode defect and free metal particle in GIS very precisely.The field application experience also shows that this PD localization method can be used in online GIS PD localization effectively and conveniently,and the PD source position of localization result is accurate and precise.

Detecting AC Corona Discharges with the UVTRONR2862-Type Ultraviolet Sensor

Abstract: Current sensors have been widely used to detect corona discharges,but electromagnetic field may interferes the detection.UV light is observed when discharge occurs.Therefore the phenomenon of the discharge can be detected by using UV sensors.We used the UVTRONR2868 UV-light sensor,which had a narrow spectrum sensitivity of 185～260 nm and was insensitive to visible light,to measure discharge signal.The typical needle-plane electrode model was tested.The factors affecting the results were investigated.Under the same atmosphere and power frequency voltage,the ultraviolet image instrument,the pulse current sensor and UV sensor were simutaneously used to detect the corona discharge.The measured sensitivities of three methods were compared,the number of pulse and quantity of discharge were counted,and the optimum detecting distance was determined based on the tests;The results indicate that the number of pulse corresponds with the intensity of the corona discharge,and The UV sensor method has a higher sensitivity than the normal sensor method.

Evaluation Method of the Time-space-difference of Lightning Protection Performance of Transmission Lines

Abstract: Lightning activity causes the different lightning impacts to transmission lines varying with the time and region,accordingly,the lightning protection performance has a great difference in time and space.In order to completely master the lightning protection performance of transmission lines,we presented an evaluation method which takes the time-space-difference lightning protection performance of transmission lines into account especially.On the basis of the long-term lightning data detected by lightning location system,we adopted the grid statistical method of lightning parameters to carry out the lightning parameter analysis along the transmission line corridor in the appointed time period.With the obtained lightning parameters including ground flash density and cumulative probability distribution of lightning current,the lightning trip-out rate of transmission line as well as each line section were calculated in the appointed time period.Compared with the evaluation grade determined from the designed value,defined value or operating value of the lightning trip-out rate of the line,the time-space-difference of lightning protection performance of the transmission line was evaluated with detailed grades.The evaluation results can be used in taking more appropriate and selective lightning protection measures to improve the lightning protection performance of transmission lines.

Application of Statistic Parameters in Recognition of Partial Discharge in Transformers

Abstract: The pattern recognition for partial discharge(PD)is helpful for estimating PD type and level,which will provide a scientific basis for failure diagnosis and maintenance.We used Weibull statistic distribution parameters in the pattern recognition for PD,and adopted the simulation and model test to prove that the PD height distribution(PDHD)fits well with 2-parameter Weibull distribution.The simulation data were generated by the Monte-Carlo method and 8 typical PD models were designed for test.In the period of each test,the pulse amplitude and phase information of each PD pulse in 10 seconds were recorded.Meanwhile,the discharge amplitude was normalized during calculation of the PDHD.In order to eliminate the influence of random pulse interference,the amplitude whose cumulative probability is 99% was used as the normalization factor.Six characteristic parameters,including the shape parameter of Weibull distribution,the center of discharge amplitude and the center of discharge phase in positive half period and negative half period of power cycle,were adopted to characterize fault pattern.The artificial neuron network was used as classifier to get at least 85% recognition rate for PD types.The results show that excellent characterization capability is obtained using a few of characteristic parameters,and different types of PD can be accurately identified using the artificial neuron network.

Lightning Protection Study of Transmission Line,Part III:Protection Measures

Abstract: The lightning accidents threaten the safe operation of power system.We comprehensively analyzed the developing states,the existed problems in analysis methods and measures of transmission line lightning protection,and discussed the key issues of transmission line lightning protection in China that should be studied.The lightning protection measures are divided into back-up type and leading-type methods,so-called back-up type method is used in lightning protection of transmission line in China,which complicates lightning protection;but the so-called leading-type method is used in other countries,which simplifies lightning protection.The lightning protection measures for different sections of transmission lines should be comprehensively estimated and proposed by considering the micro-topographical feature and the regional performances of lightning parameters along transmission line.The lightning protection should be fully considered in transmission line design,reducing shielding angle of overhead wire,decreasing grounding resistances of tower footings,and suitably installing line surge arresters are fundamental methods of lightning protection of new transmission line.

Distribution Network Fault Line Detection Using the Full Waveband Complex Relative Entropy of Wavelet Energy

Abstract: It is difficult to detect fault line in resonance grounding system;especially the fault line of resonance grounding system with cable-overhead hybrid line,which is hotspot problem in field of fault line detection.When single-phase earth fault happened in cable-overhead hybrid lines of resonance grounding system,the distribution of wavelet energy is different in each feeder.Therefore,we put forward a new conception of complex relative entropy of integrated wavelet energy and a fault line detection method,which utilizes the complex relative entropy of integrated wavelet energy.It makes wavelet decomposition with initial half-wave of zero-sequence current,and reconstructs wavelet decomposition coefficients in single branch,then makes use of decomposition coefficients to calculate the wavelet energy in each frequency band.Combine with the great signal recognition ability of relative entropy.The wavelet energy relative entropy of every feeder in each frequency band is calculated to obtain the relative entropy of integrated wavelet energy in every feeder.The fault line is selected after the size comparison with the relative entropy of integrated wavelet energy.Theoretical analysis and simulation results show that such method effectively avoids the impact of saturated dead angle to line detection.With regard to cable-line hybrid lines,pure cable lines and pure overhead lines,this method is all applicable.

Calculation and Experiment of Transient Temperatures of Single-core Cables on Jacket Temperature Monitoring

Abstract: The real time measurement or calculation of conductor temperature is necessary;whereas it is hard to measure for technical difficulties,calculation is another option. The conductor temperature is associated with the temperature and thermal resistivity of material surrounded (e.g. soil),which is diverse with season and its water content and make the calculation complicated and inaccurate. Consequently,based on its jacket temperature monitoring,the transient thermal circuit model is established. Recurrence formulas of transient temperature rise of its conductor only considering current change and only considering jacket temperature change are both derived to obtain the integrated superposition formula of calculating transient temperature of single-core cables. The classical fourth-order Runge-Kutta method is used to solve differential equations of conductor temperature on the basis of the temperature of its jacket detected,temperatures of conductor and metal sheath can be calculated by software programmed. To verify the thermal model and the calculation,the emergency and cyclic current is tested. The calculation results are compared with the data of transient temperature rise tests,and it is shown that the calculation of transient temperature based on Runge-Kutta method is accurate. This method can be applied to the conductor temperature monitoring,control and prediction in the practical operation of single-core cables.

Design of Grading Rings for 1000kV AC Composite Insulator

Abstract: The electric field strength along the composite insulators should be restricted to maintain at a reasonable range. We adopted the finite element method to calculate the electric field and potential distribution along composite insulators as well as design the grading rings for the 1000 kV UHVAC transmission lines by the domain decomposition method according to the features of the composite insulator. The three-dimensional (3D) model of 1000 kV transmission lines with tower configuration and conductors were established by using the ANSOFT software. The effect of the corona ring for improving the electric field distribution on the composite insulator was investigated by changing the parameters of the corona ring,such as the ring radius,radius of the ring tube,and the position of the ring in its vertical plane. The approved parameters of the corona ring were gained in terms of controlling the electric field to be acceptable,and the optimized parameters of the grading ring were verified in the 3D model.The results indicate that the maximum electric field around the sheath,metal fitting and the grading ring are controlled to be satisfactory,and the potential distribution along the insulator becomes more uniform. The corona and RIV tests show the corona inception voltage and radio interference voltage of the fittings and corona rings can well meet the national standards.

Transducer Firing Method for Multi-pole Array Acoustic Logging Tool

Abstract: Multi-pole array acoustic logging tool includes monopole mode operation,dipole mode operation and quadrupole mode operationThe transmitter mandrel consists of monopole transducer,dipole transducer and quadrupole transducer,and all of the transducers are excited by high voltage firing pulses from transmitter electronicsParameters of firing pulses are various in different modes,which require that transmitter circuits can be easy to control and realizeComplex programmable logic device acts as firing controllerHigh voltage firing source is composed of power supply circuit,tank circuit,drive circuit,high voltage firing circuit and pulse transformersReal working parameters can be optimized by experimentations in various conditionsIf high voltage energy is fixed,triggering pulse widths of monopole and quadrupole are 30 μs,and that of dipole is 160 μs,then high Signal Noise Ratio wave signals can be received from receiving transducers,and wave features are clearHigh temperature test and field test indicate that acoustic logging tool based on the transmitter source is fully satisfied with application demands of petroleum downhole environment

Fault Location for Distribution Network by Improved Genetic Algorithm

Abstract: In order to overcome the limitation of standard genetic algorithm such as premature convergence and low local convergence speed,an improved genetic algorithm was proposed.In this algorithm,a help-operator is used to help the individuals of population according to the given probability.The genetic individuals are separated into male individuals and female individuals,and the consanguinity is fused into individuals.Two individuals with opposite sex can reproduce the next generation if they are distant consanguinity individual.So,the negative degeneration of offspring individual performance is avoided,and the ability of algorithm to search the global optimal is enhanced greatly.The improved genetic algorithm is used in fault location of distribution network.Firstly,the entire distribution network is divided into a main branch and a number of independent regions by making use of the radiation-like characteristic of distribution network and adopting the thought of stage treatment.Then,the improved genetic algorithm is used to locate faults for all independent regions and search for the global optimal.So,the dimension of feasible solution can be reduced largely and the location speed can be enhanced.In the simulation experiments of fault location by this method for a distribution network system with 20 nodes,the number of feasible solutions is reduced from 220 to 144.The experimental results show that the location method is fast and accurate to locate faults.It is especially effectual in fault location for complicated distribution network.

Dynamic Characteristics of Magnetic Core Under Micro-second Pulse Excitation

Abstract: A one-stage magnetic pulse compression(MPC) system without external remagnetization circuits was designed and manufactured so as to test the dynamic characteristics of magnetic core under micro-second pulse excitation.Three pieces of magnetic core samples represent Fe-based noncrystal,Ni-Zn and Mn-Zn soft magnetic materials respectively.B-H curves of the magnetic cores were derived from the measured voltage and current waveforms.Variation characteristics of the three materials under micro-second pulse excitation can be figured out from the B-H curves.Through detailed analysis and comparison,it can be concluded that Fe-based noncrystal magnetic core has the largest jump of magnetic flow,so that the volume of magnetic core needed is minimal with the same volt-second product and the same number of windings;however,Mn-Zn ferrite magnetic core bears the minimal energy loss,which makes it suitable for applications under high repetitive frequency;Ni-Zn ferrite magnetic core,which owns the lowest relative permeability while saturation,is seemly in MPC circuits with relative high compression gain.

Measurement and Analysis of Partial Discharge on Typical Defects in GIS

Abstract: In order to study the partial discharge(PD)characteristics of the typical defects in GIS,a 220 kV GIS bus bar cavity was taken as an object to design four PD physical models,and then the PD signals on different defects were detected by the pulse current method.The effects of the applied voltage on the center-phase distribution and average amplitude of the discharge pulses were investigated,as well as the signal discharge waveform and energy distribution were researched.The experimental results indicate that PD has the high stability and repeatability of the discharge on the identical defect model under the same condition.The phase-resolved PD(PRPD)patterns,the time domain waveforms,average amplitude and central phase changing of PD signals had very similar distribution characteristics and those of different defect had different ones.So the conclusion provides a test basis for the recognition of PD types and a deeper study of the mechanism of PD.

Pulse Interferences Elimination and Classification of On-line UHF PD Signals

Abstract: In order to eliminate pulse type interference signals in transformer partial discharge signals,an inside-outside signal antithesis method and inter-phase antithesis method were proposed to exclude external pulse type interferences,and were used to on-line UHF PD monitoring system of a 500 kV three-phase split type power transformer. The characteristic parameters including pulse initial phase,average pulse amplitude,maximum pulse amplitude,pulse number from the UHF enveloped signal in power frequency period were extracted. Data after interference eliminated were classified with fuzzy clustering and gray clustering method,and other interference signals were eliminated. The classified PD signals were statistically analyzed with PRPD and the diagnosis assessment on PD activities was made. The analysis shows that the proposed method is effective for interference signal elimination and partial discharge fault information extraction.

Application of Ultrasonic Flaw Detector to Internal Defects in Composite Insulators

Abstract: In order to eliminate the danger for the safe operation of composite insulator,this paper presented one method to detect the flaw of the bonding between sheath and rod by using the ultrasonic flaw detector.This method determines the flaw on the base of the echo quality of the ultrasonic wave with 0.5~10 MHz in different material.Much research indicated that the method of radio frequency detection was better than the methods of full detection,positive detection and negative detection.Test results for three materials of piezoelectric chip,Sound-Transparent-layer and silicone rubber sheath demonstrate that full transmission was occur by the matching of the acoustic impedance when the thickness of the Sound-Transparent-layer is one quarter of the wave.The method of the radio frequency wave amplitude was used to detect the large area bonding between housing and core.The other method by the echo of the radio frequency was used to detect the bubble and the dregs in the insulation material.It is an effective non-destructive technology for detecting the inner defects of composite insulator.

Fault Diagnosis of Transformer Based on Particle Swarm Optimization-based Support Vector Machine

Abstract: In order to solve the problem of over-fitting, local optimal solution and low convergence rate existed in artificial neural networks(ANN), the proposed PSO-SVM model is applied to fault diagnosis of power transformer in the paper. Among which particle swarm optimization(PSO) is used to determine free parameters of support vector machine. PSO is an intelligent swarm optimization method, which derives from the research for behaviour of bird flocking. The method not only has strong global search capability, but also is very easy to implement. Thus, PSO is suitable to determine free parameters of support vector machine(SVM). Finally, fault diagnosis examples are used to illustrate the performance of proposed PSO-SVM model. The experimental results indicate that the PSO-SVM method can achieve higher diagnostic accuracy than IEC three ratios, normal SVM classifier, artificial neural network. Consequently, the PSO-SVM model is a proper alternative for fault diagnosis of power transformer.

Corona Aging Tests and Lifetime Evaluation of RTV Silicone Rubber Through FTIR

Abstract: Corona is one of the main factors that lead to the aging of room temperature vulcanized silicone rubber(RTV).Corona aging tests of RTV were carried out,the aging performances were analyzed and evaluated by FTIR,and the mechanisms of anti-aging were discussed.The results show that nano-materials can improve the corona aging performance of RTV coatings.Moreover,the lifetime of RTV coatings was evaluated by the electrical aging lifetime equation for polymers based on trap theory and the FTIR spectra before and after corona aging.The lifetime evaluation results show that nano-materials can elongate the corona aging lifetime of RTV by a factor of 3~4.9.This research provides a method of lifetime prediction for organic insulation materials.

Influence Scope of AC Network by DC Grounding Electrode Rated ±800 kV

Abstract: The working current of ±800 kV Ultra High Voltage Direct Current transmission project(UHVDC) is over 4000 A.This high current will cause great influence to the AC Network around the grounding electrode when the UHVDC trnsmission operates under monopolar mode,especially in Sichuan Province where its AC and DC systems are being developed so fast.So it is important to evaluate the environmental influence brought about by the earth current effectively to the AC system.Based on the running ±500 kV direct current projects in China and the concrete data of electrode site and assumed model of AC network,the scope of influence brought about by the grounding electrode to the AC system has been calculated by image and numerical methods.The results show that 1) the DC current which is lowing into the AC network is not only related to the geographical position and linear distance between substations,but also correlative to the network connection and parameters of the AC power system.2) it is best to evaluate the environmental influence of DC grounding electrode rated ±800 kV within the scope radius of 20 km while the electricity of the electrode is 4000 A.As to the sites of newly built converter stations or AC transformer stations rated 110 kV and above,they are best to be chose at 60 km away from the DC grounding electrode.

DC Component Time Constant and Zero Offset Phenomena of Breaking Current for 1000 kV Circuit Breaker

Abstract: In order to determine DC component of rated short-circuit current break for UHV circuit breaker, the factors that influence DC component time constant and current zero offset are studied with EMTP simulation calculation. The simulation is based on 1000 kV Jindongnan-Nanyang-Jingmen pilot project in 2009 and in the future time 2015 when national UHV network interconnect to pilot project. This paper presents a formula to covert DC component time constant calculated by simulation into UHV circuit breaker test time constant. The statistic calculated longest 3 phase short circuit DC component time constant converted by the formula is 112 ms, so that it is suggested that UHV circuit breaker DC component time constant can select 120 ms and this suggestion is accepted by pilot project. In the four cases, which are 2 or 3 phases ground fault, energizing transmission line, single phase ground fault before transmission line connecting grid and transformer energizing, the current zero offset could occur during breaking time of UHV circuit breaker. The 4 cases do not damage the UHV breaker and no preventive measures should be taken,such as breaker with opening resistance.

Analysis of Discharge Based on Toroidal Field Coils of EAST

Abstract: As a fusion device,the rating charge energy of toroidal field(TF) coils of EAST is about 300 MJ,so it is very important for EAST to adopt a credible quench protection system to avoid damage to TF coils.In order to satisfy the requirements of joule integral of TF coils,a suitable discharge circuit for the huge energy must be found.Consequently,we focus on some kinds of schemes for discharge and the interlocking control for switches particularly.The double discharge is also chosen to solve the difficulty of breaker being disconnected for DC and to prolong the use life for breaker,which can be achieved at a lower arc voltage compared with the single discharge.The interlocking control scheme can both improve the reliability for protection and reduce the price for project,importantly,can set an accurate delay time,at which the backup breaker can not be disconnected in case the main breaker has been disconnected.Some analysis and experiments confirm that the chosen scheme can not only ensure the safety of TF coils,but also protect TF power supply timely.The results provide some references for the superconducting charge devices and the inductance loads.

Analysis of One-stage Magnetic Pulse Compression System

Abstract: A magnetic pulse compression system is presented which does not contain external remagnetization circuits that are commonly used in magnetic compressors.Principle of operation of the compressor is described.A thorough theoretical analysis of the circuit topology is presented.Equivalent circuits for two consecutive operation stages of the compressor accounting for nonlinear processes in magnetic switches are analyzed.Simulation results illustrate how inductance L2 affects the system.The experimental results obtained with a resistive load are well in agreement with the circuit simulation.To improve the matching,L2 is replaced with fast-recovering HV diode.The simulation and experiment show that the pulse voltage reverse amplitude and damped oscillation duration are reduced drastically.