Research on Magnetically Coupled Resonant Detection Method for Breakpoint of Four Mesh Grounding Grid

Magnetically coupled resonant technology is a novel method for solving the breakpoint locating of power grounding grid.But the method can only detect breakpoints of a single mesh grounding grid at present.In this paper,a magnetically coupled resonant detection method for four-hole grounding grid breakpoint is proposed.Firstly,the equivalent circuit model of the four mesh grounding grid with two types of breakpoints,namely edge branch and intermediate branch,is established.The input impedance and phase angle of the system are obtained by analyzing the equivalent capacitance and equivalent resistance in the model.Secondly,the magnetically coupled resonant physical process of grounding grid faults is solved via HFSS software.The magnetic field intensity and phase frequency characteristic curves of four mesh holes with different branches and positions of breakpoints and different corrosion degrees are studied,and an experimental system is built to verify the feasibility.The results show that under the condition of grounding grid buried depth of 0.5 m and input frequency of 1~15MHz,and there is an inverse relationship between equivalent capacitance and distortion frequency,the phase angle is positively correlated with the degree of corrosion of grounding grid,and the error of signal distortion frequency can be positioned at 5%.This paper provides some ideas for the application of magnetic coupling grounding grid detection technology.

Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power systemtomaintain reliable operation.With equal conductor spacing grounding grid design,the distribution of the current in the grid is not uniform.Hence,unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing.This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors:the least-square curve fitting technique and the compression ratio techniquewith equal grid configuration for both square and rectangular grids.Particle Swarm Optimization(PSO)is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids.Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration.Simulation results are obtained by theMATLAB software developed.Percentage of improvement in ground potential rise,step voltage,touch voltage,and grid resistancewith variation in compression ratios are plotted.

An Improved Algorithm of Grounding Grids Corrosion Diagnosis Based on Total Least Square Method

A new model considering corrosion property for grounding grids diagnosis is proposed,which provides reference solutions of ambiguous branches.The constraint total least square method based on singular value decomposition is adopted to improve the effectiveness of grounding grids' diagnosis algorithm.The improvement can weaken the influence of the model's error,which results from the differences between design paper and actual grid.Its influence on touch and step voltages caused by the interior resistance of conductors is taken into account.Simulation results show the validity of this approach.

Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed （C 1 steel）, and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy- dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C 1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.

A magnetic detecting and evaluation method of substation’s grounding grids with break and corrosion

The grounding grid buried in the earth will become a hidden danger to the safety of substations due to some faults of breaks or thinner conductors in corrosion.A novel method to get accurate status of grounding grid was proposed based on measuring magnetic induction intensity.The basic structure of grounding grid without working drawing was concluded,and the positions and the status of faults were diagnosed by this method.The completed detecting system,including hardware device of data measurement,diagnosis,and analysis software,was introduced concisely.The results of simulations and applications show that this method is simple and effective in the practical engineering.

Study on Lightning Transient Ground Potential in the Chaoyang Mountain Wind Farm

In order to get the distribution characteristics of lightning transient ground potential of 100 MW wind farm in the Chaoyang Mountain,Jinzhai County,the characteristics of lightning parameters within 5 km of the wind farm were analyzed based on the lightning monitoring data from 2006 to 2020 provided by Anhui Meteorological Bureau.According to the on-site geological investigation,a double-ring ground network model was established to simulate the three-dimensional transient contact voltage and step voltage distribution of a typical wind fan was obtained through simulation.The results show that the average lightning current amplitude around the wind farm was 44 kA,instead of 10 kA in the current traditional simulation research,which is used as the excitation source for the subsequent simulation of lightning transient ground potential.The peak value of lightning transient contact voltage of the single wind turbine is 2158.35 V,and the peak value of lightning transient step voltage is 441.75 V.The simulation results can provide certain reference for subsequent lightning risk assessment,lightning scheme design and ground grid construction of wind farms.

Investigation on corrosion of yttrium-doped magnesium-based sacrificial anode in ground grid protection

In the simulated DC and AC discharge circuit in ground grid protection of substation,corrosion and potential of magnesium anode with yttrium addition were studied by potential measurement and scanning electron microscopy.The results showed that potential of anode increased with increasing current density in DC simulation,potential increase of anode with 0.1% yttrium addition was the smallest,and the affordable current density of the anode reached 1.85 A/cm2,which was two times that of the anode without yttrium addition.In AC simulation,addition of yttrium had less effect on its potential.Grains of magnesium alloy sacrificial anode without yttrium addition were the equiaxed grains of magnesium grains coated with β-Mg17Al12,while the anode with yttrium was α-Mg phase with dispersed β phase.The corroded magnesium anode with 0.1% yttrium addition showed the most uniform and the smallest pit on its surface.

Innovative Compensation Methods for Large Voltage Drop Effects in Very Long HVDC Transmission Systems

This paper discusses the impacts of large voltage drops on very long HVDC transmission lines,especially when operating in a monopolar mode.The effect of using dedicated metallic return(DMR)conductors is discussed.The main focus is on the potential rise at the neutral point of the converters and the need for an increased range for the converter transformer tap changers.Two grounding schemes for multiterminals transnational HVDC systems are presented:single point low impedance grounding and high impedance multi-point grounding.The advantages of the high impedance scheme are discussed.An innovative compensation method for voltage drop effects using a series HVDC converter is presented along with simulation results.The novel series converter can address both issues of neutral voltage rise and the impractical tap changer range.To put the ideas into the perspective,a realistic example of a transnational HVDC connecting China,central Asia,Russia and West Europe is presented.