Impact of the Foucault Current and Its Vibration Noise Reduction on Bracket Features for AMDT

This manuscript explores the influences of the Foucault current on bracket vibration. Noise measurements are obtained in conditions that the coils are enclosed by the bracket, and exposed to the air for confirming the impact of Foucault current on bracket vibration. The outcomes illustrate that the bracket increases the primary noise to 21 d B. Throughout investigational modal computation, ordinary frequencies of the coils stay afar from the exciting frequency of 100 Hz but the ordinary frequency 72.924 Hz of the bracket stands near to 100 Hz, which similarly explicates the upsurge of the noise level. To do the computations on bracket vibrations instigated by the Foucault current, a finite-element method(FEM) has been utilized for evaluating the eddy current density, electromagnetic forces(EMF), coupled with bracket response in frequency domain. The calculations displayed a proper approval by mean of theoretic investigations, and the simulations analyzed effectively the bracket vibration produced by Eddy current, and the electromagnetic force(EMF). Referring to the simulation, the primary vibration characteristics, and noise level, the method by applying weights(stress) on the top bracket of transformer is proposed to lessen the vibration amplitude, and noise level. To indorse the utility, and application of the suggested technique, the experiment results are obtained, analyzed, and compared with those of simulations, primary vibration characteristics, and noise level.

Investigation on Vibration Characteristics of Amorphous Metal Alloy Core Dry-type Distribution Transformer

Large power transformers have severe vibration and noise problems. Thus, as the source of noise, it is vitally important to have accurate core vibration calculations. The calculation of the vibration is incredibly difficult to consider the complex propagation pathway of the vibration in the clamp and the Amorphous Metal Alloy Core Distribution Transformer(AMACDT). To understand the vibration characteristics of AMACDT, this manuscript provides a different approach on investigation of the vibration characteristics of an SCBH15-200/10 type. Based on the vibration characteristics calculation and displacement of an Amorphous Metal Alloy Core Distribution Transformer(AMACDT), they are obtained and solved using Finite Element Analysis software(FEA). Conferring to the outcomes of the vibration analysis, the method by adding bar-reinforcements on the upper clamp of transformer is proposed to lessen the vibration amplitude. To verify the usefulness and application of the suggested approach, the analytical results are obtained. The suggested approach is analyzed with those of experimental.

Dynamic interactive characteristics between icicle growth and corona discharge on HVDC outdoor insulators during icing accretion

In order to improve the stability and reliability of high voltage direct current(HVDC)transmission lines in cold regions,this article investigated the corona discharges and the icicle growth characteristics on outdoor insulators under DC voltages.The experiments were conducted at CIGELE laboratory at University of Quebec.The simulation model of corona discharges and the theoretical model of icicle growth were established.The dynamic process and interactive characteristics between the icicle growth and corona discharges under different HVDC voltages were obtained.The results showed that the discharge activity was strong and the cooling effect of ionic air was weak under negative DC voltage,resulting in a large number of bubbles inside the icicle.More negative ions were produced under negative DC voltage,which enhanced the polarisation of water droplets,leading to a greater density of ice beads outside the icicles.In addition,the longest icicles of each insulator under high humidity could bridge the shed gap.The accumulated charge and leakage current were higher under negative DC voltage,as well as the corona discharge at the top of the icicles lasted longer.Therefore,the negative DC corona discharge more significantly inhibited the growth of the icicle,resulting in a slower growth rate of the icicles.

Electric field control by permittivity functionally graded and superficially non-linear conductivity materials for DC-GIS spacer

This paper offers a simulation study on the application of a novel approach to control the electric field around a basin-type spacer by combining permittivity functionally graded materials(ε-FGM)and superficially non-linear conductivity materials(SNCM),namely multi-dimensional functional materials(MDFM).The permittivity distribution of theε-FGM spacer is designed by the iteration optimization algorithm,and the epoxy/SiC composites with 30 and 60 phr doping contents are assigned as the coating materials of two SNCM spacers,namely SNCM30 and SNCM60.The MDFM spacer combinesε-FGM in its bulk and SNCM60 on its surface.The electric field regulation effect of each functional spacer is investigated under variable conditions,that is,DC steady state(DC-steady),DC turn-on state(DC-on),DC polarity reversal(DC-PR),and DC superimposed with switching impulse voltage(DC-SI).Results show that the applicability ofε-FGM and SNCM is limited to transient and stationary conditions,respectively.The MDFM spacer combines the advantages ofε-FGM and SNCM for adaptively relaxing the electric field under all the above conditions.It is hoped that this research will be beneficial to the development and application of spacers for the direct current gas-insulated switchgear(DC-GIS).

Dynamic formation mechanism of water droplet and induced surface discharges on silicone rubber composites

Wettability has become one of the most important factors influencing power equipment insulation system in coastal power grid,which can seriously threaten the safety of power grid.This paper aimed at numerical simulation and experimental investigation on dynamic formation mechanism of water droplet and induced surface discharges on silicone rubber composites under different AC voltages,considering the factors of surface tension and droplet volume.Obtained results reveal that the spreading coefficient increases with increasing the electric field intensity from 1 to 5 kV/cm and with increasing the droplet volume from 10 to 50μL.The spreading coefficient shows a decreasing tendency when the surface tension increases from 29.3 to 61.0 mN/m.Moreover,the maximum of surface electric field shows an increasing tendency under the condition of increasing both the droplet volume and the surface tension.On the basis of the physical model of droplet deformation,the electric field force and the surface tension play a significant role in the process of droplet deformation.Meanwhile,the experimental results are consistent with the simulation analysis,reflecting that the droplet deformation and the induced surface discharges mainly depend on two parameters:the droplet volume and the magnitude of applied voltage.

Study on non-uniformity and dynamic fracture characteristics of GIL tri-post insulators considering Al_(2)O_(3) sedimentation

Tri-post insulators in gas-insulated transmission line(GIL)are usually fabricated with high mass fraction of micron aluminum oxide(Al_(2)O_(3)),which will unavoidably settle under the action of gravity during the preparation process and seriously affect the uniformity.A model of filler sedimentation in epoxy resin composite materials was proposed based on the particle size analysis and Stokes'Law.Some scaled tri-post insulators were prepared and tested by slicing.It is determined that the position of density concentration is the lower side of the two lower posts and the upper interface between the insulator and the conductor.The density ranges from 2.144 to 2.346 g/cm^(3).The dynamic fracture simulation model of insulator was established and it is found that the insulator fracture occurs at the interface of upper post/insert under radial load,which is verified by experiments.By comparing the influence of sprue position on the density distribution,it is found that the uniformity of insulators is increased by 13.7% by forward pouring compared with reverse pouring.This research develops an accurate method for simulating the filler sedimentation and the fracture process in epoxy-based insulators,which is helpful for the improvement of mechanical reliability of GIL.

Crystallisation regulation of long‐chain branched polypropylene on dielectric performance and energy density for metallised film capacitors

The degradation of dielectric properties of polypropylene(PP)at high temperature affects the operational stability of metallised film capacitors.This study presents a method to improve the high‐temperature dielectric performance of PP through long‐chain branching modification and regulating the crystalline properties.Different amounts of nucleating agents were added to long‐chain branched polypropylene(LCBPP)to study the effect of crystallisation on electrical properties.The results show that the long‐chain branches improve thermal stability by enhancing the chain entanglement,and also increase the number of crystals due to heterogeneous nucleation.The addition of nucleating agents promotes the crystallisation of LCBPP,which increases the nucleation density and improves the crystallinity.The regulation of the microstructure of PP suppresses the relaxation of the chains and limits the charge transport.The dielectric constant of the modified films with long‐chain branching is slightly increased,and the doping of nucleating agents has little effect on the dielectric constant and loss of LCBPP.At 125°C,the conductivity of the modified LCBPP films with the addition of 0.05 wt%nucleating agent decreased by 2 orders of magnitude and the breakdown strength increased by 26.3%.This study has implications for improving the dielectric properties of PP films.

Effects of nanofiller and voltage stabilizer on partial discharge resistance of polypropylene/elastomer blends:A comparison study

This paper reports on the individual and synergistic influence mechanisms of nano-silica(SiO_(2))and voltage stabilizers on partial discharge(PD)resistance of polypropylene blended with ethylene-octene copolymer elastomer.The SiO_(2)nanoparticles and three types of voltage stabilizers,that is,benzoin,4,40-dimethoxybenzil,and 3-aminobenzoic acid are selected as fillers to prepare samples.PD is initiated in a rod-to-plane electrode system with an alternating current voltage of 5 kVrms.PD characteristics are captured with multi-sensors,and the erosion profile of the test sample is measured using a three-dimensional(3D)optical profilometer.Carrier trap distribution is extracted with isothermal surface potential decay measurement to assist the analysis of PD eroding material.Fourier transform infrared spectrum,scanning electron microscopy,X-ray diffraction spectrum,and differential scanning calorimetry analysis are performed to reveal the change in material structures caused by the fillers.Test results indicate that the PD resistance of the blend can be improved by the addition of nano-SiO_(2)and voltage stabilizers individually and synergistically.The PD resistance of PO is increased by 71.2%at most in the sample with 3 wt%nano-SiO_(2)addition.The sample filled with SiO_(2)exhibits better PD resistance than that with the voltage stabilizer or co-added,which should be ascribed to the introduction of deep traps,the formation of the packaged layer,the suppression of oxygen diffusion of the nanofillers,and the good compatibility between additives and the polymer matrix.

Mechanical stress distribution and risk assessment of 110 kV GIS insulator considering Al_(2)O_(3)settlement

The growing application of gas insulated switchgear(GIS)in electric power system asks for higher reliability of epoxy(EP)insulators,thus it is important to seek effective methods to improve the operating reliability of GIS insulators.On the basis of the 110 kV GIS insulator,this study studied the aluminium oxide(Al_(2)O_(3))settlement in the curing process and the stress distribution of the horizontally laid GIS.Besides,the risk coefficient was defined to evaluate the operating reliability of insulators laid by different methods(I-V).Some conclusions are shown below:the Al_(2)O_(3)settlement in the curing process causes the insulator density to have a large variation from 2.13 to 2.32 g/cm^(3).The Al_(2)O_(3)content has a great influence on the mechanical performances of EP/Al_(2)O_(3)system.The first principle stress is localised on the upper interface between the insulator and the conductor,which is the main threat to the mechanical damage of insulator.The laying method V appears to be optimal with a pretty low risk coefficient of 31.5.In actual application,for the horizontally laid GIS,the insulator should be laid with the mould gate downward to improve its mechanical reliability.

Promising functional graded materials for compact gaseous insulated switchgears/pipelines

The electric field distributions along gas-solid interfaces determine the reliability,lifetimes and sizes of gaseous insulated switchgears/pipelines(GIS/GIL),which also affect the reliability of power systems.In this study,the characteristics of steady and transient electric field distributions were first introduced,followed by the concept of functionally graded materials(FGMs).The development histories of FGM applied in electrical engineering and the related optimisation methods were described in detail.The field regulation effect and fabrication technology of different FGM insulators were also compared.To overcome the limitations of traditional FGM insulators,the design of surface FGM(SFGM)was proposed,together with their preparation methods and electrical performance.Furthermore,the future development prospects of FGM and SFGM insulators for compact GIS/GIL were summarised.

Electrical tree degradation in high-voltage cable insulation:progress and challenges

High-voltage direct current(HVDC)and high-voltage alternating current(HVAC)cables are the most important equipment for high-voltage,large-capacity and long-distance power transmission.Electrical tree is a pre-breakdown phenomenon leading to failure of insulation materials,and it is the major issue that threatens the safe and stable operation of HVDC and HVAC cable systems.This study summarises and analyses the achievements in the research of electrical tree for HVDC and HVAC cables.The initiation mechanisms of the electrical tree,including Maxwell electro-mechanical stress,charge injection-extraction,charge trapping and electroluminescence theories,are elaborated for fully understanding the electrical degradation process in insulation materials.Then,the influences of the high electric field,high temperature and mechanical stress on electrical tree behaviours are discussed,and the relationship between charge transport and the electrical tree is analysed and illustrated.The suppression methods of the electrical tree are put forward by introducing inorganic and organic additives into insulation materials,and the suppression mechanisms are presented from the viewpoints of the structure-property and microscale-macroscale relationships.Recently,the electrical tree research studies are focused on the high-precision of initiation models,high-dependence of multi-physical fields and high-efficiency of suppression methods.The achievements provide theoretical support for improving the electrical performance of insulation materials,while it is a practical problem to explore their application feasibility in HVDC and HVAC cable.

Effect of chemical corrosion on charge transport behaviour in epoxy/Al_(2)O_(3)nanocomposite irradiated by gamma ray

Chemical corrosion and gamma‐ray irradiation appeared with the loss of coolant accident may seriously threaten the safe operation of a nuclear power plant,where epoxy resin(ER)‐based materials are widely used.It is urgent to study the effects of the corrosion and the irradiation on the electrical performance in an ER‐based nanocomposite.In this work,ER/Al_(2)O_(3)nanocomposite samples with 0,1,3,5‐wt%nano Al2O3 filler content were prepared at the thickness of 2 mm,and the total gamma irradiation dose was 0,500,and 1000 kGy.The samples were chemically corroded in a boric acid solution(pH=4.7)and a trisodium phosphate alkaline solution(pH=11)at 60℃and 100℃for 48 h.Charge transport behaviour in the samples was derived from the surface potential decay method.In addition,the sample structures were characterised to analyse the corrosion mechanism in the solutions.The results indicated that the depth and the density of the trap showed a temperature‐dependent manner associated with the corrosion.With the addition of appropriate content of the filler,the trap centre was deepened and the carrier mobility was limited even after the corrosion.It is found that the appearance of hydroxyl and carboxyl groups during corrosion,the interaction between the nanoparticle and the matrix and the crosslinking reaction caused by the irradiation are responsible for the variation in charge transport behaviour.

Evaluation of high-voltage AC cable grounding systems based on the real-time monitoring and theoretical calculation of grounding currents

For high-voltage(HV)AC cable transmission systems,the metal sheaths of three separate single-core cables are cross-bonded at each end of the cable section,to suppress the induced voltages in sheaths.The status of HV cable grounding systems is,therefore,an important consideration for power utilities.This study presents the status evaluations of 93 cable grounding systems in Beijing,obtained using the standards established by State Grid Corporation of China.As a result,13 of these systems were classified as abnormal or defective.Additionally,a theoretical calculation of grounding currents was proposed and these 13 systems are re-evaluated by comparing the calculated and measured values of certain parameters.Based on this work,the authors propose a modified evaluation standards.It is indicated that the absolute value of grounding current(|I|)during a given 24-hr period has no relationship with the status of grounding system,and the ratio of grounding current to load current(K)at the time of maximum load current could be used as a status indicator instead of K at some other time,in order to avoid possible incorrect evaluations due to light load conditions.

Temperature‐dependent electric field distribution in±800 kV valve‐side bushing insulation for a converter transformer

The electric field distribution is determined for the design and long‐term performance of bushing yet gets complicated when coupled with temperature due to the highly tem-perature‐dependent conductivity of insulation.An electrothermal coupling model is established based on a�800 kV converter transformer valve‐side bushing.The measured temperature‐dependent conductivity of insulation is adopted and fitted.The electric field distribution inside a condenser core under the influence of temperature was investigated,and the related mechanism was analysed,considering the different voltage forms,loading currents,and changeable ambient conditions.The temperature gradient within the condenser core is verified,and the electric field migration is observed.It is indicated that the electric field strength shows a strong dependence on temperature and increases along the radial direction.The maximum field strength appears at the outmost shield layer under the operating voltage and the load current 4500 A,which is higher than that under the DC long‐term withstand voltage of 1455 kV without thermal stress.The increased load current,decreased oil temperature,and enhanced valve hall temperature will lead to more serious electric field distortion,and unacceptable dielectric stress may occur.More attention should be paid to the design and operation of bushing for DC applications.

Molecule diffusion behaviours of waterproof sealants into silicone rubber insulation for submarine cable joint based on molecular dynamics simulations

The repair joints of high-voltage cables play a significant role in the urgent cable main-tenance,by recovering cable conductor,insulation,shielding layer and waterproof layer especially for submarine cables.However,the molecule diffusion and permeation pro-cesses from waterproof sealant into the cable joint insulation occur,leading to the insulation ageing and deterioration.In this article,the molecule diffusion behaviours of six typical molecules from the asphalt-based and polyurethane-based waterproof sealants into silicone rubber insulation are investigated.The results show that the order of diffusion coefficients is as follows,phenanthrene>fluoranthene>pyrene>benzo[k]fluoranthene>indeno[1,2,3-cd]pyrene>polyurethane(PU).The relative molecular mass and binding energy are pivotal factors affecting the diffusion behaviour,while there is a linear relationship between the logarithm of the diffusion coefficient and the ratio of binding energy to relative molecular mass.Besides,the rising ambient temperature in-creases the fraction of free volume of silicone rubber and decreases the binding energy,thus resulting in a higher diffusion coefficient and an enhanced permeation process of the asphalt-based sealant.In summary,the PU-based waterproof sealant,with a much lower permeability than the asphalt-based material,has a potential application in the waterproof layer for high-voltage submarine cable repair joints.

Effects of ZnO magnetron sputtering on surface charge and flashover voltage of oilimpregnated paper

With the aim of exploring an alternative method of nano-doping in cellulose paper and improving flashover strength of oil-impregnated paper,radio frequency(RF)magnetron sputtering method is introduced into the structural modification of insulating paper for converter transformers.In this experiment,insulating paper was treated with ZnO sputtering for 0,7.5,15 and 30 min,respectively.The surface morphology of dry paper was observed with a scanning electron microscope.The bonding mode of sputtered ZnO particles with cellulose matrix was investigated via attenuated total reflection infrared(ATR-IR)spectroscopy and mechanical property of the sputtered samples were studied.Surface and volume conductivities of the oilimpregnated sputtered paper were measured.Moreover,the charge dissipation characteristics of sputtered insulating paper was investigated by means of surface potential decay.In addition,trap distribution and carrier mobility of specimen were further obtained.Finally,the DC flashover strength were tested.The results showed that ZnO magnetron sputtering had a distinct influence on the structure of the insulating paper,resulting in the formation of hydrogen bond and chemical bond and an increase of the surface and volume conductivities.ZnO sputtering was found to decrease the initial potential and accelerate charge decay.Moreover,appropriate sputtering enhanced the surface flashover strength.

Charge transport behavior in gamma‐ray irradiated poly(ethylene terephthalate)estimated by surface potential decay

This study reports on the variation in charge transport behaviour of poly(ethylene terephthalate)(PET)caused by gamma‐ray irradiation estimated by means of surface potential decay(SPD)measurement.The 100μm‐thick PET specimens were exposed to 60Co gamma rays to a maximum total dose of 1000 kGy.The SPD test was carried out to obtain charge transport related parameters via various models,and the effect of gamma‐ray on the transport behaviour was examined.Furthermore,Fourier trans-form infrared spectrum,gel content,ultraviolet‐visible spectroscopy,X‐ray photo-electron spectroscopy,differential scanning calorimetry and polarized optical microscope were employed to characterize the change in material structure induced by the irradiation.The test results indicated that with the growth in the total dose,the deep trap centre was basically unchanged,whereas the shallow trap centre became shallower.In addition,the trap density tended to decrease.The carrier mobility in PET increased with the total dose,and the charge transport manner conformed well to the hopping model.It is suggested that the formation of oxygen‐based groups from the irradiation induced oxidation reaction tends to encourage the charge transport,while the decrease of amorphous region gives rise to the reduction in trap density.

Improved space charge transport model in bilayer dielectrics—considering carrier dynamic equilibrium

The Maxwell–Wagner model and bipolar charge transport model both aim at describing the charge transport behaviours in dielectrics.The Maxwell–Wagner model performs well in calculating the polarisation current and electric field distribution,but it is too macroscopic to describe the microscopic behaviours of space charges.The bipolar charge transport model can well simulate the space charge accumulation,but it cannot quantitatively relate the microscopic transport behaviours with the macroscopic conductivities of dielectrics.Considering the shortages of the above two models,an improved charge transport model,named carrier dynamic equilibrium model,was proposed in this study to simulate the polarisation process of the low-density polyethylene/ethylene propylene diene monomer bi-layer dielectric by introducing a source term of carrier dynamic equilibrium.Effects of carrier mobility and non-equilibrium carrier lifetime on the simulation results were explored,and a comparison among the results of measurement and different models was also made.Compared with the Maxwell–Wagner model and bipolar charge transport model,the improved model has the best coincidence with measurements,which can provide an accurate reference for the design of high-voltage direct current insulation systems.