Yanpeng Hao

Development of Optical Fiber Sensors Based on Brillouin Scattering and FBG for On-Line Monitoring in Overhead Transmission Lines

A distributed on-line temperature and strain fiber sensing system based on the combined Brillouin optical time domain reflectometry (BOTDR) and fiber Bragg grating (FBG) technology is presented and investigated experimentally for monitoring the overhead transmission lines. The BOTDR sensing system can be used to measure the temperature of transmission lines (Optical Phase Conductor, OPPC or Optical Power Ground Wire, OPGW) which is helpful for monitoring the dynamic ampacity and icing forecasting. In order to effectively monitor the distortion of transmission line induced by the climatic fluctuation and natural disaster, e.g., ice coating and hurricane wind, a quasi-distributed FBG strain sensing system is connected in series with the insulator, integrated into the BOTDR system. The results showed the proposed system was effective and reliable for the monitoring of overhead transmission lines.

Transition from symmetric discharge to asymmetric discharge in a short gap helium dielectric barrier discharge

The discharge dynamics of a 2.08 mm gap helium dielectric barrier discharge (DBD) are studied with a one-dimensional fluid model. By increasing the amplitude of a sinusoidal voltage source, it is observed that the discharge is symmetric at first and abruptly turns into an asymmetric state after passing a certain critical value. Compared with former publications dealing with relatively larger gap-distance DBD, our simulation results indicate some new discoveries. First, in both the symmetric and asymmetric states, every discharge event is fully developed from Townsend discharge to glow discharge, and the discharge current appears as a steep narrow pulse. Second, the residual positive column is always completely dissipated before the next break down; therefore, its influence on the symmetric-to-asymmetric transition can be eliminated. It is further revealed that the symmetric-to-asymmetric transition in the short-gap DBD is more delicate. A subtle phase shift is observed before the transition process. When ...

Two-dimensional simulation of spatiotemporal generation of dielectric barrier columnar discharges in atmospheric helium

A two-dimensional (2D) fluid model is presented to investigate the spatiotemporal generation and dynamic mechanics of dielectric barrier columnar discharges in atmospheric helium. The model was examined with discharge currents measured in experiments and images taken by an intensified charge couple device camera. Based on the model, a columnar discharge was simulated for several cycles after being ignited. The discharge could be regarded as an initial unstable stage for the first three and a half cycles, then a steady state for the following cycles. In the initial stage, the discharge evolves from a uniform pattern into a columnar one. The calculated equipotential lines, 2D radial electric field, and electron density distributions at the edge of uniform discharges show the radial electric field accounts for the shrinking discharge area and the formation of discharge columns in the end. The columnar glow discharges and the Townsend discharges beyond the columns could coexist in the initial stage, and a Townsend discharge might develop into a new glow column in the next half-cycle. The radial electric field surrounding a glow discharge column has an inhibiting effect on the ionization in the peripheral area.

Influence of lightning flashover criterion on the calculated lightning withstand level of ±800 kV UHVDC transmission lines at high altitude

The operation experiences of power transmission lines show the lightning outage is still the main part of the total outage rate. So it is very important to calculate the lightning overvoltage across the insulators precisely and evaluate the lightning outage of the transmission lines correctly. Lightning flashover criterion of the insulator/gap is one of the most important factors that influence the precise calculation results of the lightning withstand level of transmission lines. In China, several ±800 kV ultra high voltage direct current (UHVDC) power transmission projects have been set up in recent years, and the altitude of the regions that the transmission lines across ranges from 0-3650 m. The paper mainly analyzed the influence of the modelling methods of insulator/gap on the lightning withstand level of ±800 kV UHVDC transmission lines by PSCAD/EMTDC program. The compared lightning flashover criteria of insulator/gap include the leader propagation model recommended by CIGRE, the volt/time curve recommended by IEEE and an improved leader propagation model, which is proposed based on the lightning flashover experiments of the ±800 kV UHVDC line insulators carried out at an altitude of 2100 m. Meanwhile, the influences of lightning current waveform and insulator structure were also considered and compared. The simulation results show that the calculated back-flashover lightning withstand level is much lower when using the improved leader propagation than that using other flashover criterions in the paper, it is lower under the 2.6/50 μs double exponential lightning current than that under the 2.0/50 μs Heidler function lightning current, and it is higher when using V-string than that using I-string insulator. Besides, the influences of the lightning current waveform and the insulator structure on the calculation of shielding failure lightning withstand level are little, but the flashover criterion has obvious influences on the shielding failure lightning withstand level.

Combined influence of the impurities and radial electric field on dielectric barrier discharges in atmospheric helium

The combined influence of nitrogen impurities and radial electric field on dielectric barrier discharges in atmospheric helium is investigated using a two-dimensional (2D) fluid simulation. Discharge current waveforms, 2D electron densities, distributions of surface charge, and radial and axial components of the electric field at the electrode edge are calculated for different impurity levels varying from 0 to 30 ppm. It is observed that the discharge presents the characteristic of a column in pure helium, and it gradually becomes a relatively uniform glow discharge as the impurity level is increased to 20 ppm; for the higher impurity level of 30 ppm, the discharge adopts a concentric-ring pattern discharge. Our result shows that the radial electric field at the electrode edge is approximately 0.6–1.2 kV/cm during the discharge. This radial electric field has an effect that leads to a non-uniform discharge. After doping a low level of impurities, the Penning ionizations caused by the impurities can inhibi...

Recognition of natural ice types on in-service glass insulators based on texture feature descriptor

For in-service transmission lines, insulator icing condition depends on analysis of images collected by cameras installed on towers, and ice type analysis is mostly completed by human beings, which is infeasible to monitor a large area. Although image processing is successfully applied to segmentation of insulators from aerial images, there are few literatures on automatically determining ice types on insulators via image processing. In this paper, a recognition method of ice types on in-service glass insulators is established based on a texture feature description operator. Uniform Local Binary Patterns (ULBP) and Improved Uniform Local Binary Patterns (IULBP) were adopted for texture feature extraction of typical images of six ice types including glaze ice, heavy rime, medium rime, light rime, partial rime and snow. The six ice types are concluded based on icing insulator images and corresponding meteorological data from China Southern Power Grid Transmission Line (Icing) Online Monitoring System. Ice types are recognized by correlation coefficient calculation of texture histograms. The experiment results show that IULBP obtains better results for recognition of the six ice types as each ice type has distinguished texture features.

Dynamic Characteristics of Dielectric Barrier Columnar Discharge During Its Decay

This paper pays particular attention to the dynamic characteristics of dielectric barrier columnar discharge after it starts to decay based on a 2-D fluid model. Waveforms of the gas gap voltage, discharge current, and 2-D distributions of the electron density and the equipotential lines were calculated for the steady state of dielectric barrier columnar discharges in atmospheric helium. The evolution process of the discharge during its decay can be divided into four phases: phase (i), in which new discharges occur at nondischarge-column locations after the extinction of the discharge columns; phase (ii), in which the new discharges are extinguished; phase (iii), in which the axial electric field begins to reverse in the gap; and phase (iv), in which Townsend discharges occur at the discharge column locations before entering into the next columnar discharges. Via an analysis of the time evolution of the axial electron density, we show that new discharges occurred at nondischarge-column locations are Townsend discharges. An in-depth study of the reversion process of the axial electric fields at different locations shows that nonuniform accumulated surface charges play a key role in determining the spatiotemporal discharge characteristics. These results contribute toward gaining a comprehensive understanding of columnar discharges.

Evaluation of wetting condition and its effects on pollution flashover voltage of aerodynamic insulators

The flashover performance of insulators is significantly affected by the degrees and ways of wetting the pollution layer. However, there have only been a few reports on the wetting condition and its effects on the flashover characteristics of pollution on insulators to date. In this paper, a phase-angle difference-based method is proposed to test the wetting conditions of the pollution layer on insulators. A corresponding measuring device is also developed. The wetting process of the pollution layer on aerodynamic-type glass insulators is studied in an artificial climate chamber using the developed device. The related flashover performance is studied via the even-rising voltage method. Test results show that the phase-angle difference (PAD) curve accurately reflects the entire wetting process of the pollution layer from the initial stage, through the saturated stage to the oversaturated and washing away stages. Over the wetting process, the PAD curve initially drops sharply, and then remains stable for a few minutes before eventually rising slowly to the initial value. The PAD curve has its lowest value when the pollution layer is wetted to saturation, which occurs after approximately 5 min in our experiments. The flashover voltage characteristics of insulators are also significantly affected by the wetting conditions of the pollution layer. The flashover voltage in the saturated stage is shown to be lower than that in the other stages. Therefore, to improve the accuracy of the artificial pollution tests, quantitative methods (including PAD) should be used to obtain the exact time of wetting to saturation.

Leader propagation models of ultrahigh-voltage insulator strings based on voltage/time curves under negative lightning impulses at high altitude

Lightning protection analysis is the foundation of estimating the lightning protection behaviors of transmission lines. The lightning flashover criteria of insulators/gaps are an important part of such analysis. One lightning flashover criterion of an insulator/gap is the leader propagation model recommended by CIGRE; however, this model does not consider altitude or longer gaps/insulators (>5 m). In this paper, the 50% disruptive-discharge voltage U50% and 50% voltage/time curve for an air gap of 7.1 m configured by a composite V-string and composite I-string of 7.1 m were measured under negative lightning impulses at the National Engineering Laboratory for Ultrahigh-Voltage Engineering Technology (Kunming), at an altitude of about 2100 m. The insulator types and configurations are similar to those used in the +800kV Ultrahigh-voltage Direct Current (UHVDC) power transmission project. The experimental result shows that the 50% disruptive voltage U50% of the V-string is 7% higher than that of the I-string, and the best-fitting constants of the new leader propagation model of the V-string are different from those of the I-string. The two 50% voltage/time curves were compared with the voltage/time curves predicted by the leader propagation model recommended by CIGRE. The best-fitting constants in leader propagation models are proposed to be used for long air gaps of the V-string insulator and longer I-string composite insulator at high altitude. The new models are verified for a 1.9 m air gap in parallel with a 2.04 m composite insulator and 2.04 m I-string composite insulator.

Shed parameters optimization of composite post insulators for UHV DC flashover voltages at high altitudes

DC artificial pollution tests were carried out on 26 insulators with various shed parameters in high altitude areas to investigate the influence of shed parameters on the flashover performance of composite post insulators. The parameters tested included shed overhang, shed spacing and the core diameter for type A insulators with alternating single large and small sheds and type B insulators with alternating single large and dual small sheds. Ultraviolet photons emitted during partial discharge phenomena in the tests were characterized with an ultraviolet camera, and the arc development paths along the insulator surfaces were observed using a high-speed camera. The results show that the partial discharge phenomena become increasingly intense and arc bridging between the sheds becomes more serious with increasing shed overhang, but these phenomena become weaker with increasing shed spacing. The flashover voltage decreases with increasing core diameter, but increases initially and then decreases with increasing average shed overhang or large shed spacing. An optimal value for the ratio of large shed overhang to large shed spacing must therefore exist and is recommended based on the test results.