Sima Wenxia

Fault location for transmission line based on traveling waves using correlation analysis method

This paper described the principle of transmission line fault location based on traveling waves. The principle and of correlation analysis is introduced, then the method using correlation analysis in fault location is given. Transmission line model is established with EMTP-ATP. Basing on the model, some kinds of fault are simulated. The feasibility of this algorithm is proved based on simulation results. By comparing with the classical wavelet analysis, this paper gave the advantages of this algorithm in two cases: noise influence suppression and accuracy of near distance fault location.

AC flashover performance and voltage correction of 27.5 and 110 kV iced composite insulator at 4000/spl sim/5500 m high altitude districts

Based on the test results carried out in the multi-function artificial climate chamber of Chongqing University (China) on two types of composite insulator, this paper discusses the effects of atmospheric pressures or altitudes, contamination level and ice amount secreted on the minimum AC flashover voltages of composite insulators, and analyzes the flashover performance of the composite insulator in icing, contaminating and low pressure conditions. The authors therefore put forward a correction method of flashover voltages.

Study on calculation model of the lightning protection performance of shielding failure for 500 kV double circuit transmission line

Using double-circuit transmission line is the developing trend for 500 kV main configuration to reduce the line holding ground, So analyzing its lightning protection performance is significative to extend double-circuit transmission line in Ultra high voltage network. When analyzing the lightning protection performance of shielding failure for 500 kV double-circuit transmission line, the EGM is improved by considering the effect of wind speed and the calculation model is built in this paper. Furthermore, the results that more accord with the practical condition are got by using program to calculate it.

Study of flashover performance and voltage correction of DC insulator in icing districts of altitude of 2500 m and below

Based on the results of the DC flashover tests of iced XZP-160, XZP-300 and XWP4-160 insulators carried out in the artificial climate chamber in the High Voltage Laboratory of Chongqing University, China, this paper analyses the effects of altitude and ice on the DC flashover voltage of the three types of insulator. The relations between the DC flashover voltage of iced insulators at high altitude or low atmospheric pressure and the ice amount accreted, as well as the effect of voltage polarity on flashover voltage have been obtained. A voltage correction formula for iced insulators in low atmospheric pressure is also put forward.

Local electron mean energy profile of positive primary streamer discharge with pin-plate electrodes in oxygen?nitrogen mixtures

Local electron mean energy (LEME) has a direct effect on the rates of collisional ionization of molecules and atoms by electrons. Electron-impact ionization plays an important role and is the main process for the production of charged particles in a primary streamer discharge. Detailed research on the LEME profile in a primary streamer discharge is extremely important for a comprehensive understanding of the local physical mechanism of a streamer. In this study, the LEME profile of the primary streamer discharge in oxygen-nitrogen mixtures with a pin-plate gap of 0.5 cm under an impulse voltage is investigated using a fluid model. The fluid model includes the electron mean energy density equation, as well as continuity equations for electrons and ions and Poissons electric field equation. The study finds that, except in the initial stage of the primary streamer, the LEME in the primary streamer tip tends to increase as the oxygen-nitrogen mole ratio increases and the pressure decreases. When the primary streamer bridges the gap, the LEME in the primary streamer channel is smaller than the first ionization energies of oxygen and nitrogen. The LEME in the primary streamer channel then decreases as the oxygen-nitrogen mole ratio increases and the pressure increases. The LEME in the primary streamer tip is primarily dependent on the reduced electric field with mole ratios of oxygen-nitrogen given in the oxygen-nitrogen mixtures.

Identification of induced lightning and direct striking based on wavelet transform

Based on the different discharge processes of lightning striking, lightning overvoltage can be divided into two types: induced lightning overvoltage and direct lightning striking overvoltage (including back-flash and shielding failure). The characteristics of these overvoltages are investigated in this paper and it is concluded that induced lightning overvoltage exists simultaneously in three phases of the transmission line and similarity of its inter-phase is more significant than that of direct striking lightning overvoltage. Therefore the energy matrix similarity dependent method with the implement of wavelet transform can be applied to identify them. Mass simulation with consideration for many different fault conditions has been computed to prove its effectiveness based on ATP.

Identifying the Overvoltage in Distribution Networks Based on Support Vector Machine

The internal and external overvoltage in distribution networks are the main reasons of accidents. Based on overvoltage data in distribution network recorded by overvoltage on-line monitoring system, this paper analyzes the characteristics of zero sequence voltage waveform. The maximum amplitude and RMS value of zero sequence voltage, the minimum RMS of low frequency component of three phase voltage in stable range and other five parameters are selected as characteristic parameters to identify internal and external overvoltage. According to the operation data and record, all overvoltage data record by on-line monitoring system were labeled as internal or external overvoltage and the discrimination function is constructed by support vector machine method. The test results of field acquired overvoltage data indicate that the identification parameters and method base on the zero sequence voltage and SVM are correct and effective.

Analysis on Shielding Effect of the Grounding Electrodes under Impulse-Current

Generally, the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors. In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode, the experiments that had carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity. However, in practical conditions, most of the grounding systems are constructed of grounding electrodes with branches in different directions. In this paper, basing on the principle of dimensional similarity, impulse simulation experiments are performed on the common ground electrodes with conductor branches. We focus on analyzing the impulse current dispersal regularity of different branches when injecting at one point. Comparing with the leakage current distribution of a single ground electrode, it is found that the leakage currents along the branches increase with the distance to the current feed point, and the more conductors near the injection point, the more uneven the leakage current distribution is. This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.

Lightning back-flash performance of 220kV AC quadruple-circuit transmission lines on the same tower

In this paper, an insulation flashover criterion model, in which the change of multi-conductor system coupling coefficient induced by impulsive corona is considered, is constructed by the electromagnetic transient analysis software ATP-EMTP. The model proposed, having taken the effect of the impulsive corona into account, is able to present the influence of conductor corona characteristics on potential difference of two ends of the insulator when an impulse flashover on insulator string occurs. A model of 220kV multi-circuit transmission line, which adopts insulation tower model with multi-wave impedance, is constructed as well. Thereby, it is feasible to study lightning back-flash proof levels (LBPL) and its influencing factors. The simulation result shows that the tower height plays a predominant role in deciding the performance of the counterattack lightning level of transmission lines. Moreover, the back-flash level of quadruple-circuit lines is remarkably lower than that of double and single circuit lines. It is suggested that, firstly the tower should be much lower if it is permitted; secondly the conductors at different heights in tower should adopt different insulation levels.

Ferroresonance overvoltage features extraction using nonlinear analytical technique

Ferroresonance is complicated phenomenon for its various modes. In this paper, two nonlinear features are extracted based on nonlinear analytical Technique. The features can be used to analyze the motion characteristics of the ferroresonance system of the overvoltage time series. The study on overvoltage acquired from a power substation shows that the feature is very useful for ferroresonance mode identification, especially for the quasi-periodical ferroresonance and chaotic ferroresonance.