The characteristics of negative corona discharge and radio interference at different altitudes based on coaxial wire-cylinder gap

The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes. The radio interference caused thereby is a key factor to be considered when designing transmission lines. To study the influence of altitude on negative corona characteristics, an experimental platform comprising a movable small corona cage was established: experiments were conducted at four altitudes in the range of 1120-4320 m, and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected. The experimental results show that the average amplitude, repetition frequency and average current of the corona current pulse increase with increasing altitude. The dispersion of pulse amplitude increases with increase in altitude, while the randomness of the pulse interval decreases continuously. Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained. The result of this research has some significance for understanding the corona discharge characteristics of ultra-highvoltage lines.

Preparation and Properties of Epoxy Piezoelectric Vibration Reduction Composites

The epoxy resin (E-51) was used as polymer matrix,conductive carbon black (CB) as conductive filler,and PZT was used to prepare a composite by curing.The effects of PZT and CB content on the properties of PZT/ CB/ EP piezoelectric composite were studied.When the PZT content reaches 40 wt%,the optimized vibration attenuation properties of PZT/CB/EP materials could be achieved with a loss factor of 0.9 from room temperature to 60 ℃.With the increase of PZT content,the bending strength of PZT/CB/EP piezoelectric composite vibration reduction material firstly increased from 45 MPa to 65 MPa and then decreased to 38 MPa.At room temperature,the dielectric constant increased from 7 to 50,and the dielectric loss increased from 0.1 to 0.5.

A New Method for the Aging Evaluation of Oil-Paper Insulation Using η-Butanol and Methanol

To improve the accuracy and efficiency of the aging life prediction and assessment of transformer oil-paper insulation,and to make up for the deficiencies of traditional characterizers,such as 2-furfural,carbon monoxide,and carbon dioxide,a method for the simultaneous determination of methanol,ethanol,n−propanol,and η-butanol in oil with a single injection is established by headspace-gas chromatography-mass spectrometry.The measured results show that the determination limits of the four alcohol characterizers can be controlled to 10μg/kg level.Based on this method,the change patterns of the above four alcohols with thermal aging time and degree of polymerization are obtained through thermal aging experimental research.Ethanol,η-propanol,and η-butanol in oil indicate nearly linear correlations with thermal aging time and degree of polymerization,similar to that of methanol.By analyzing 52 sets of measured data of 500 kV EHV transformers in operation,η-butanol is found to have excellent performance,and a new method to evaluate the aging state of oil-paper insulation employing η-butanol and methanol is proposed along with the aging attention value model.The measured data of 500 kV EHV transformers in operation indicate that the combination of η-butanol and methanol as the preferred characterizers can effectively compensate for the shortcoming of traditional characterizers in the early stages of aging,and the feasibility of the method is verified.Two possible pathways for the generation of η-butanol by cellulose cleavage during the aging of oil-paper are proposed from the chemical structure of cellulose.

Shape optimisation of basin insulator for DC gas insulated switchgear/gas insulated transmission lines based on artificial bee colony algorithm

The surface charge accumulation on the basin insulator is a particular problem in high-voltage direct current(HVDC)gas insulated switchgears(GIS)and gas insulated trans-mission lines(GIL),which restricts the development and application of extra/ultra high-voltage(EHV/UHV)technology.The surface charge distribution and anti-flashover performance are closely related to the insulator shape.To obtain the optimal basin insulator,a shape optimisation model based on artificial bee colony algorithm was established,and the minimisation objective functions based on capacitive(initial)electric field distribution and resistive(steady-state)electric field distribution were respectively constructed.The optimisation results of the two objective functions were calculated,and the electric field and charge distribution on the surface of the insulator before and after optimisation were evaluated and compared using the simulation model.The results indicated that the optimisation based on the capacitive electric field can significantly inhibit the surface charge accumulation,and the optimised insulator can significantly reduce the surface normal electric field and make the distribution of the tangential electric field more uniform,and the maximum tangential electric field can be reduced by 10%;the optimisation based on resistive electric field can achieve similar results,but requires more computational resources.Based on the results,the‘anti-charge’basin insulator structure suitable for the DC field was given.

Editorial:The development of eco-friendly insulating gases and SF6-free equipment for‘net-zero’

Developing low-carbon gas insulated transmission and distribution equipment is essential to achieve the‘carbon peak,carbon neutralisation’or‘net-zero’in the power industry.Scholars have carried out various research on the eco-friendly insulating gas(such as C4F7N,C5F10O)and next-generation SF6-free equipment to gradually reduce the utilisation of strong greenhouse gas SF6.

Assessment on gas-polyethylene terephthalate solid interface partial discharge properties of C4F7N/CO_(2)gas mixture for eco-friendly gas insulating transformer

The eco-friendly insulating gas perfluoroisobutyronitrile(C_(4)F_(7)N)is potentially used in gas-insulated transformers(GIT)to replace sulphur hexafluoride(SF_(6)).However,evaluation of the long-term insulation reliability and gas–solid interface discharge decomposition characteristics of the gas–solid film insulation structure in GIT is indispensable.The authors simulated the gas–solid film insulation structure in GIT and explored the interface partial discharge(PD)characteristics of C4F7N/CO_(2)gas mixture with polyethylene terephthalate(PET).The effect of gas pressure,mixing ratio on gas–solid interface gas decomposition,PET degradation was investigated,and the interaction mechanism was analysed.It is found that the interface PD generated three degradation regions on a PET film.The gas–solid interface reaction in the electrode contact region and the discharge development trace was significantly higher than that of halation region.The content of gas decomposition products decreases with the increase of gas pressure and the PD intensity of SF6-PET is inferior to that of C_(4)F_(7)N/CO_(2)under the same condition.Relevant results provide reference for the development and application of C_(4)F_(7)N/CO_(2)based GIT.

Audible Noise Performance of High Voltage AC Conductor Bundles at an Altitude of 226lm

Extra or ultra-high voltage transmission lines can exhibit strong corona discharge and generate severe audible noise(AN)at high altitudes,which has become a critical limiting factor for power lines construction.However,the AN data of bundle conductors at high altitudes are very rare,which cannot adequately support the power utilities to make reasonable conductor selections.In this paper,a sound pressure level(SPL)of 14 types of bundle conductors is investigated by using an ultra-high-voltage(UHV)corona cage(8 m×8 m×35 m)at an altitude of 2216 m,where the bundle numbers between 4 and 12 and the conductor types are used in 500 kV,750 kV or 1000 kV power transmission projects.Then a large number of valuable AN data are obtained;the influences of bundle numbers and sub-conductor diameters on an acoustic power density level(LPWL)are analyzed;and an A-weighted LPWL calculation method is proposed.In addition,by comparing the AN data obtained from the low-altitude area(altitude:23 m),the AN altitude correction factor is concluded,and the influences of conductor parameters and the surface electric field strength on correction factors are discussed.The results obtained in this paper can provide important data for the construction of high-altitude AC power lines.

Diversity of wave structures to the conformable fractional dynamical model

This manuscript examines the recently developed conformable three-dimensional Wazwaz-Benjamin-Bona-Mahony(3D-WBBM)equation’s dynamical behavior in terms of its spatial and temporal variables.The governing equation is stretch for the Korteweg-de-Vries equation that represents the unidirectional propagation of small amplitude long waves on the surface of hydro magnetic and acoustic waves in a channel,especially for shallow water.Solitary wave solutions of various types,such as kink and shock,as well as singleton,combined solitons,and complex solitons,are all retrieved.Additionally,solutions to hyperbolic,exponential,and trigonometric functions are obtained through the use of recently developed methods,namely the Kudryashov method(KM),the modified Kudryashov method(MKM),and the new extended direct algebraic method(NEDAM).The study conducts a comparison of our findings to well-known findings,and concludes that the solutions reached here are novel.Additionally,the earned results are sketched in different shapes to demonstrate their dynamics as a function of parameter selection.We can assert from the obtained results that the applied techniques are simple,vibrant,and quite well,and will be helpful tool for addressing more highly nonlinear issues in various of fields,especially in ocean and coastal engineering.Furthermore,our findings are first step toward understanding the structure and physical behavior of complicated structures.We anticipate that our results will be highly valuable in bet-ter understanding the waves that occur in the ocean.We feel that this work is timely and will be of interest to a wide spectrum of experts working on ocean engineering models.

Analysis of Conducted Disturbance via Current Transformer Due to Switch Operation of GIS Disconnector in UHV Substation

The characteristics of conducted disturbances via current transformer(CT)caused by switch operations in 1000 kV UHV substations are studied in this paper.Since the broadband circuit models might have limitations on the stability and accuracy for CT conducted disturbance simulation,a frequencydomain simulation method without circuit synthesis is proposed based on VFTC spectrum and CT transfer characteristics.To improve VFTC simulation accuracy,both the bushing radiation loss and frequency-dependent earth impedance are taken into consideration.Transfer characteristics of three types of windings for the 1000 kV GIS CT are ingeniously measured from a combination of fast and slow impulse tests.Through conducted disturbances simulations in UHV Wuhu substation,bushing radiation loss is found to have a suppression effect on the highfrequency response but the effect of frequency-dependent earth impedance can be ignored.As a result,the maximum amplitude of 84.5 A for the conducted disturbance is obtained,thus a fast damped oscillatory wave immunity test with no lower than Level 4 from IEC standard is suggested to test the anti-interference performance of the secondary equipment in UHV substation.

Hygrothermal ageing performance of high temperature vulcanised silicone rubber and its degradation mechanism

High temperature vulcanised silicone rubber(SR)has excellent hydrophobicity and thus is widely applied both in indoor and outdoor insulation.According to the analysis of different experimental ageing tests and field investigation of SR,temperature and humidity are considered to be the fundamental factors during degradation.Hygrothermal ageing was proposed in this study to simulate the chalking state of the SR,finally leading to the irreversible degradation far below the thermal decomposition temperature.The variation of morphology,hardness and polydimethylsiloxane(PDMS)content was quantified during the yearlong hygrothermal ageing test.It is implied that the gradual process of whitening and hardening are accompanied by the decline of the PDMS content.Finally,ageing delamination in SR and its degradation mechanism were proposed.

Dispersion characteristics of switching transients from large‐scale experiments in a 1100 kV gas insulated switchgear circuit

The switching operation of gas insulated switchgear(GIS)disconnector will produce multiple random spark discharges between the gas gaps of the disconnector.Each spark discharge can be affected by various random factors,such as trapped charge on the load side,the initial operating phase,gap distance and operating speed of the disconnector,leading to dispersion characteristics.At present,some studies have mentioned this dispersion,but its impact is still unclear due to the lack of experimental data,resulting in a deviation between the simulation results and the measured results.In this study,thousands of switching operations were carried out based on the 1100 kV full‐scale GIS circuit in Wuhan ultra‐high voltage alternating current Test Base.The maximal information coeffi-cient analysis,linear regression fitting and other statistical methods were used to discuss the dispersion characteristics of very fast transient overvoltage(VFTO)and transient enclosure voltage(TEV)from large‐scale experimental data.The results show that the dispersion of VFTO and TEV in amplitude aspects both increase gradually as the breakdown voltage increases,with the maximum difference of five times of TEV amplitude at normalised breakdown voltage.In terms of frequency characteristics,the dispersion of different fre-quency components in TEV is always greater than that of VFTO,especially for the high‐frequency components.Moreover,by comparing the frequency characteristics of TEV at different positions,we notice that the dispersion is almost independent of the spatial po-sition but only determined by the randomness of spark discharges.These discoveries reveal the importance of the dispersion in switching transients and make up for the lack of theoretical understanding of the correlation among them.

On the interaction phenomena to the nonlinear generalized Hietarinta-type equation

In this paper,we describe the nonlinear behavior of a generalized fourth-order Hietarinta-type equa-tion for dispersive waves in(2+1)dimension.The various wave formations are retrieved by using Hirota’s bilinear method(HBM)and various test function perspectives.The Hirota method is a widely used and robust mathematical tool for finding soliton solutions of nonlinear partial differential equa-tions(NLPDEs)in a variety of disciplines like mathematical physics,nonlinear dynamics,oceanography,engineering sciences,and others requires bilinearization of nonlinear PDEs.The different wave structures in the forms of new breather,lump-periodic,rogue waves,and two-wave solutions are recovered.In addi-tion,the physical behavior of the acquired solutions is illustrated in three-dimensional,two-dimensional,density,and contour profiles by the assistance of suitable parameters.Based on the obtained results,we can assert that the employed methodology is straightforward,dynamic,highly efficient,and will serve as a valuable tool for discussing complex issues in a diversity of domains specifically ocean and coastal engineering.We have also made an important first step in understanding the structure and physical be-havior of complex structures with our findings here.We believe this research is timely and relevant to a wide range of engineering modelers.The results obtained are useful for comprehending the fundamental scenarios of nonlinear sciences.

Review of the decomposition characteristics of eco-friendly insulation gas

As one of the major concerns of climate change,identifying a proper eco‐friendly insulation gas for replacing sulphur hexafluoride(SF_(6))becomes a prominent research topic in recent years.c-C_(4)F_(8),CF_(3)I,C_(5)F_(10O),C_(6)F_(12O)and C4F7N are some potential al-ternatives that are proved to have excellent characteristics,including high insulation strengths and low Global Warming Potentials(GWPs).Beyond these key factors,the decomposition products of these alternatives are closely related to the gases'insulation performance,as well as the safety of operators and the compatibility with other materials.In addition,the type and content of decomposition products can be used for fault diagnosis.Therefore,a number of studies were carried out to reveal the decomposition mechanism of these alternative gases,and then to explore the gases'application feasibility and strategy.The recent advances obtained in these studies,including theoretical calcu-lation methods,detection of gas decomposition products,decomposition mechanism are reviewed,and some perspectives for future works are proposed.It is concluded that the phenomenon of solid matter precipitation in c-C_(4)F_(8)and CF_(3)I gas decomposition cannot be ignored and that more research is needed to reveal the influence of buffer gases,micro‐aerobic,micro‐water and other impurities on the gas decomposition process.

Simulations and experiments of the generation apparatus of the DC electric field with the space charge

To make accurate measurements,field mills must be calibrated in a known DC electric field space charge in which the quantities can be control1ed.A simulation model of the generation apparatus of the electric field with a space charge has been built.Based on the combination of the electric field and the transfer of a dilute substances model,the in-fluence of openings in the metal screen was calculated.Simulation results showed that the opening size of the high‐voltage electrode has a great influence on the distribution of the electric field and ion density at the calibration zone.Next,a generation apparatus was designed and developed and ion mobility was researched.The experimental results showed that ion mobility decreased with an increase in electric field strength.However,ion mobility tends to be saturated when the electric field reaches a certain critical value.Two fitting formulas of ion mobility of positive and negative charge are proposed that can be used to predicate ion mobility in a high electric field.

Influence of micro-water on AC breakdown characteristics of C_(4)F_(7)N/CO_(2)gas mixture under non-uniform electric field

The application of eco-friendly C_(4)F_(7)N/CO_(2)gas mixture has become a hot topic in the power industry.To obtain the influence law of micro-water on the AC insulation characteristics of C_(4)F_(7)N/CO_(2)gas mixture,breakdown tests were carried out under different non-uniform electric fields and micro-water volume fractions.With the gap distance of 1 mm and the electric field non-uniform coefficient less than 4.42,the breakdown voltage is positively correlated with gas pressure.With the gap distance of 6 mm and the electric field non-uniform coefficient of 9.28,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.With the gap distance of 9 mm and the electric field non-uniform coefficient up to 16.45,the breakdown voltage shows a typical N-type change trend with the increase of gas pressure.Micro-water has a negative effect on breakdown voltage under different electric fields,meanwhile the breakdown voltage of slightly non-uniform electric field is greatly affected by micro-water,and the influence of micro-water on breakdown voltage is different under different gas pressures.Therefore,the influence of operating gas pressure and slightly non-uniform electric field should be considered when the micro-water control index of C_(4)F_(7)N/CO_(2)gas mixture insulated equipment is formulated.

Prediction of radio interference from HVDC transmission lines based on corona discharge characteristics

Many research works have proved that it is viable to predict the radio interference (RI) of high-voltage alternating current transmission lines by corona cage test. However, it is uncertain whether the same method can be adopted for RI prediction of high-voltage direct current (HVDC) transmission lines, since the corona performance of HVDC lines is obviously affected by the widely distributed space charge. In this study, the detailed corona current characteristics, such as the current pulse amplitude, rise time, half-wave time, and repetition frequency are systematically studied by the reduced-scale experiment and the relationship between the average corona current and the RI excitation current is confirmed. Furthermore, based on the experimental study, a method for predicting the RI level of HVDC transmission lines by the corona cage test is proposed. The RI level of a ±800 kV bipolar HVDC transmission line is predicted and compared with the measured result, which verifies the validity of the proposed method.

Ion-acoustic wave structures in the fluid ions modeled by higher dimensional generalized Korteweg-de Vries-Zakharov-Kuznetsov equation

In this paper,the higher dimensional generalized Korteweg-de-Varies-Zakharov-Kuznetsov(gKdV-ZK)equation is under investigation.This model is used in the field of plasma physics which describes the effects of magnetic field on the weak ion-acoustic wave.We have applied two techniques,called asφ^(6)-model expansion method and the Hirota bilinear method(HBM)to explore the diversity of wave struc-tures.The solutions are expressed in the form of hyperbolic,periodic and Jacobi elliptic function(JEF)solutions.Moreover,the solitary wave solutions are also extracted.A comparison of our results to well-known results is made,and the study concludes that the solutions achieved here are novel.Additionally,3-dimensional and contour profiles of achieved outcomes are drawn in order to study their dynamics as a function of parameter selection.On the basis of the obtained results,we can assert that the pro-posed computational methods are straightforward,dynamic,and well-organized,and will be useful for solving more complicated nonlinear problems in a variety of fields,particularly in nonlinear sciences,in conjunction with symbolic computations.Additionally,our discoveries provide an important milestone in comprehending the structure and physical behavior of complex structures.We hope that our findings will contribute significantly to our understanding of ocean waves.This study,we hope,is appropriate and will be of significance to a broad range of experts involved in ocean engineering models.