Analysis and Study on GNSS Data under EHV Transmission Environment by Using TEQC

At present, the EHV transmission system in China has entered a new stage of large-scale construction, which is different from the general EHV transmission lines. The distributed current in the EHV transmission lines has increased substantially. To realize the overall balance of long-distance transmission in the power grid, a differential protection method for EHV transmission lines based on current traveling wave prediction is proposed. The fault current traveling wave of the EHV transmission line is predicted. The fault current traveling wave section is distinguished, and different schemes are selected to realize the traveling wave differential protection for internal and external faults. The simulation results show that the proposed method is reliable and sensitive for the protection of UHV transmission lines, and has certain practical value for ensuring the stable operation of the smart grid.

Lightning is main reason that endangers safety and reliability of transmission line, but existing models of estimating shielding failure flashover rate can not be in agreement with field experience at present. This paper deals with shielding failure flashover rate of EHV transmission lines with many parameters by improved electric-geometry model. The parameters consist of phase wires, shield wires, and ground angle. In improved model, strike is calculated with expression recommended by IEEE, the striking distance factor is introduced to describe difference of electric intensity between lightning stroke on transmission line and ground, and uncovered is adopted to calculate shielding failure flashover rate for ultra high voltage transmission line. Taking 500 kV transmission line as example, improved electric-geometry model gets result in agreement with field experience. Compared with order of method, it is more accurately. At same time, paper analyzes influence of shielding angle, height of wire, grounding obliquity on shielding failure flashover rate. The results of studies show that shielding failure flashover rate is a function of shielding angle, ground angle and height of tower. It will increase with increase of grounding obliquity, protection angle and height of tower. The simulation calculation shows that when shielding angle is -6.24 degrees, shielding failure flashover rate reduces from 0.2135 to 0 in this paper. It will help designers in making correct economic judgment.

The purpose of the research is differentiation of recent geodynamic processes within the Carpathian Mountains on the basis of freely available GNSS data. Methodology. The methodology included GNSS data collection, processing and analysis. An algorithm for processing was proposed, which consisted of 5 main stages: transformation of data into an internal format, verification of time series for compliance with requirements, determination of horizontal velocities, division of the GNSS network into triangles, and determination of deformation parameters. Results. This study presents a comprehensive analysis of recent geodynamic processes based on GNSS data freely available from the Nevada Geological Survey. Taking into account the requirements for time series, 50 GNSS stations were selected and processed. In general, absolute and regional velocities were obtained and analysed during 2000–2023. Regional velocities of horizontal movements were used to calculate the deformation tensor and deformation parameters. The results of the study are consistent and correlate well with the studies of other scientists. The obtained results confirm the presence of active geodynamic processes within the Carpathians. Originality. The proposed approach made it possible to estimate the main deformation parameters (value and direction of deformation axes, total shear and dilation) within the Carpathian Mountains. This makes it possible to analyse and predict recent geodynamic processes in the region. Practical significance. On the basis of the calculated values, maps of the distribution of vectors of absolute and regional horizontal velocities, total shear rates, dilatation rates, and rotation rates were constructed.

A study is made of the steady-state short circuit current Is.c., and open circuit voltage, Vo.c., to ground for conducting objects under E.H.V. transmission lines. This is carried out in a computer program and on a scaled down laboratory model of a transmission line. In addition, tests are conducted at the American Electric Power Service Corporation and Westinghouse Electric Corporation E.H.V. test site at Apple Grove, West Virginia[1]. The Apple Grove results are used for comparison with the other two approaches. Values of Is.c. within a few percent of the field data and of Vo.c. within about 30 percent are predicted by the computer program. For the transmission line model, the measured values of Is.c. are within a few percent of the Apple Grove measurements and the values of Vo.c. are within approximately 15 percent.

Digital Current Differential Carrier Relaying System for EHV Transmission Line

In this study, we investigate the impact of GNSS antenna calibration models and multi-GNSS observations on the quality of the tropospheric estimates. The accuracy and homogeneity of the Zenith Total Delay (ZTD) time series estimated from ground-based GNSS data strongly depend on the processing strategy. These factors significantly imply the GNSS solution performance; however, their impact on the quality of the derived ZTD series used for climate applications has not been comprehensively investigated.We analyzed three years of ZTD time series obtained from GNSS data processing and afterward converted integrated water vapor (IWV). Nine different processing strategies distinguished into three groups were employed: the 1st group of solutions was obtained by applying the International GNSS Service (IGS) type mean Phase Center Correction (PCC) models (IGS14); in the 2nd group, PCC models from individual field robot calibration were used; in the 3rd group of solutions, an anechoic chamber calibration was applied. Each group of solutions was processed three times using different GNSS constellations, namely GPS-only, Galileo-only, or combined GPS+Galileo.The results reveal that the impact of employed GNSS constellations on the accuracy of the ZTD time series is more pronounced than the impact of antenna calibration models. However, the latter factor is also noticeable and thus cannot be neglected. Moreover, validation against climate reanalysis data confirms that all approaches provide high-quality tropospheric delays.The outcomes also indicate that ZTD estimates obtained with robotic and IGS14 calibrations are closer to that of ERA5 reanalysis than estimates derived when using calibrations in an anechoic chamber. In addition, multi-GNSS-derived tropospheric parameters are more comparable to the benchmark ones from ERA5 than those provided by single-system solutions. The results also depend, among others, on the stations' equipment (receiver and antenna). 

Lightning stroke is the main cause of trip-outs of EHV and UHV transmission lines in China Southern Power Grid (CSG). In order to improving the lightning performance of overhead transmission lines, the lightning activities of CSG in 2006 to 2014 was analyzed. It indicates that the coastal Guangdong and Guangxi province are suffered more ground flashes, where the average ground flash density is over 7.98 flashes/km2/year. 306 lightning flashover incidents of 500kV AC, ± 500kV HVDC and ± 800kV UHVDC transmission lines were investigated. It is inferred that about 84% lightning flashover incidents was caused by lightning shielding failure. The corresponding ground wire protection angle for 81% incidents is larger than 5°, and with protection angle decreases, lightning trip-out failures are significantly reduced. Based on the guidelines proposed by IEEE and CIGRE working group, CSG has developed their own lightning risk estimation tool named LPTL. The predication result of six 500kV AC transmission lines was compared to field experience which validates the IEEE recommended method for 500kV AC transmission lines. Further works should be done to revisit the validity of existing risk estimation method for HVDC transmission lines.

Most transmission line protective schemes are based on deterministic computations on a well defined model of the system to be protected. This results in difficulty because of the complexity of the system model, the lack of knowledge of its parameters, the great number of information to be processed, and the difficulty in taking into consideration any system variation as the rules are fixed. The application of fuzzy logic for exploring complex, nonlinear systems, diagnosis systems and other expert systems, particularly when there is no simple mathematical model to be performed, provides a very powerful and attractive solution to classification problems. In this paper, a feasibility study on the application of different fuzzy reasoning mechanisms to power system relaying algorithms is conducted. Those mechanisms are namely, Mamdani's mechanism, Larsen's mechanism, Takagi-Sugeno's mechanism, and Tsukamoto mechanism. A comparative analysis on the application of these fuzzy inference mechanisms to a novel fault detection and phase selection technique on EHV transmission lines is reported. The proposed scheme utilises only the phase angle between two line currents for the decision making part of the scheme. A sample three-phase power system was simulated using the EMTP software. An online wavelet-based preprocessor stage is used with data window of 10 samples (based on 4.5 kHz sampling rate and 50 Hz power frequency). The performance of the proposed model was extensively tested in each case of fuzzy inference mechanism using the MATLAB software. The advantages and disadvantages of each mechanism are reported and compared together. Some of the test results are included in this paper.

High impedance faults (HIFs) are difficult to be detected by overcurrent protection relays. This paper presents an ATP/EMTP fault simulations studies based algorithm for high impedance fault detection in extra high voltage transmission line. The scheme recognizes the distortion of the voltage waveforms caused by the arcs usually associated with HIF. The discrete wavelet transform (DWT) based analysis, yields three phase voltage in the high frequency range which are fed to a classifier for pattern recognition. The classifier is based on an algorithm that uses recursive method to sum the absolute values of the high frequency signal generated over one cycle and shifting one sample. A HIF model of distribution is modified for EHV transmission lines. Characteristics of the proposed fault detection scheme are analyzed by extensive simulation studies that clearly reveal that the proposed method can accurately detect HIFs in the EHV transmission lines.

The accurately mathematical models, simulation models and protection algorithms of high impedance fault (HIF) on transmission lines are difficult problems. Based on the measured data and physical phenomena, a new mathematical model of HIF was presented by numerical analysis methods and MAYR’s equation. Using EMTP, the model of HIF includes a group of nonlinear time-varying resistances and a dynamic arc resistance. Based on the features of HIF under different frequency bands, this paper presents HIF comprehensive detection algorithms containing four algorithms, and analyzes the logic between each algorithm. Finally, the models and algorithms are simulated.

Non-unit transient based boundary protection for UHV transmission lines

A technique is described for approximating the effect of various factors on the radio noise level, due to conductor corona, on EHV transmission lines. The technique is essentially one of comparison. Relations are given in the Appendix for calculating the conductor gradients and results are presented in curve form. The application is intended only for comparison of radio noise generated by conductor corona on ac lines, with conductors ranging only from 0.3 to 1.3 inches radius (1.5 to 3.3 cm) and for the frequency range from about 0.2 to 1.6 MHz. If an existing line has been evaluated statistically the technique can be used to approximate the radio noise level of another line. A relation is also given for obtaining curves of 3-phase voltage to conductor radius for the same radio noise generation. Because of possible conductor surface differences and environmental differences, which cannot be too accurately evaluated, care is necessary in any final estimation of the average radio noise level.

This work is concerned with describing the development and subsequent field experience with an adaptive autoreclose technique, based on artificial neural networks (ANNs), as applied to circuit breaker control on EHV transmission lines. This technique, developed at the University of Bath in conjunction with a major manufacturer of protection and control equipment in the UK, can recognise when it is 'safe to reclose' and when it is 'unsafe to reclose' transmission line circuit breakers. This is a radical transgression from the present philosophy whereby conventional autoreclosing relays reclose to restore the power system, following initial circuit breaker opening after a fault. With this advanced adaptive technique, the primary requirement remains to protect the power system by reducing damaging shocks and voltage dips with a concomitant concern to maintain the continuity of supply.

GMV is developing FocusPOD, a suite of tools for POD and geodesy, powered by GMV MAORI, a new GMV in-house Flight Dynamics & Geodesy library, written from scratch in modern C++ and python. FocusPOD supports several projects led by GMV, including the operational provision of Precise Orbit Determination (POD) products of the Copernicus Sentinel satellites in the frame of the CPOD Service, the simulation of tracking data for Galileo 2nd Generation (G2G) System Test Bed, and other space debris and flight dynamics activities.FocusPOD is currently capable of processing GNSS data, with a focus on on-board receivers to support POD, and Satellite Laser Ranging (SLR), mostly used in CPOD as an external orbit validation source. Capabilities to process DORIS have been recently added, also targeting POD applications as a first step. GMV’s roadmap for FocusPOD include processing VLBI in addition to these 3 techniques, with the target of becoming a reference software for the geodesy community.This contribution intends to present FocusPOD roadmap to incorporate VLBI processing capabilities, describing the modelling challenges that have been identified and the various steps that will be taken to finally be able to process VLBI and provide VLBI-based ITRF products. As part of this roadmap, other parallel activities to tie together the rest of the techniques will also be undertaken and described, mostly related to the ground-based processing of GNSS, SLR and DORIS data.

The insulation of transmission lines phase-ground and phase-phase air gaps decrease significantly under forest fire condition, which causing transmission lines trip and threatening the operation safety of EHV and UHV transmission lines. In order to attain a simulation method to test the gaps discharge characteristics under forest fire condition, wooden cribs were applied to study the flame heights and discharge characteristics under different scale of cribs and also the leakage currents and discharge voltages of gaps under typical vegetation fire conditions were tested. Test results show that the flame of different scale of wooden cribs were stability and flame heights were separately 62 cm, 90 cm and 140 cm, the flame temperature was between 810 ~ 900 °C.The breakdown voltage gradient under three scale wooden cribs flames were in the range of 81.7 ~ 87.8 kV/m, and breakdown voltage gradient under the flames of typical vegetation were respectively 30 kV/m, 38 kV/m and 60 kV/m, which were far less than the breakdown voltage levels under the condition of wood crib fires. Besides flame temperature, flame conductivity and flying ash particles has important effect on breakdown voltage of gap clearance. So, the simulation gap discharge test under forest fire condition must consider the flame conductivity, temperature and flying ash particles effects on the discharge under forest fire condition.