Understanding DC Partial Discharge:Recent Progress,Challenges,and Outlooks

As a non-destructive local gas breakdown phenomenon within a surface or bulk cavity surrounded by insulation,partial discharge(PD)contains important information which can be used to evaluate and diagnose electrical insulation systems.In this paper,distinctive characteristics of PD for DC versus AC are reviewed.A summary of experimental studies on DC PD in different insulation coordinations is presented,including PD in gaseous insulating media,PD in solid insulating media and PD in liquid insulating media.Conclusions and some thoughts based on existing studies are provided,and challenges and suggestions for future studies are given.This paper can serve as a guide reference for readers to learn the background and state-of-the-art of DC PD studies.More importantly,it is hopeful that this study can inspire novel ideas for further advancing fundamental research of DC PD mechanisms and PD mitigation methods.

Gas–solid interface charge characterisation techniques for HVDC GIS/GIL insulators

Surface charge accumulation on the spacers is one of the key issues restraining the development of HVDC GIS/GIL.The precise measurement of surface charge properties provides the basis for further study of the surface charge transport mechanism as well as the charge-induced flashover mechanism under DC voltage.In this study,the authors discuss their perspective on the current status,development needs and potential developing orientation of surface charge characterisation techniques.Different surface potential measurement methods and charge inversion algorithms are reviewed regarding the previous studies and future research needs.Drawbacks and outlooks of surface charge measurement techniques are also discussed with the background of laboratory experiment results and on-site measurements.It is hopefully that this study can serve as a useful guide reference for researchers within the same research field.More importantly,it is authors’hope that this study can inspire some novel ideas for readers into developing of more accurate and scientific interface charge characterisation techniques.

Feasibility of C_(3)F_(7)CN/CO_(2)gas mixtures in high-voltage DC GIL:a review on recent advances

With the rise of renewable energy resources,especially offshore wind power plant,the DC transmission concept has attracted more and more attention.The selection of eco-friendly insulating gas,as most critical insulating part of gas-insulated equipment is top priority for developing highly reliable system.Moreover,it is acknowledged that eco-friendly C_(3)F_(7)CN/CO_(2) gas mixtures have become a potential alternative to SF_(6) gas due to its excellent performance.This study reviews the basic physical properties of C_(3)F_(7)CN gas/gas mixtures and insulation properties including the gas gap breakdown and surface flashover performance at DC,as well as lightning impulse voltage.Investigation about the gas stability is presented,including the compatibility of gas with solid materials in gas-insulated transmission line(GIL),and the decomposition characteristics under long-term electrical and thermal stresses.The important progress on the charge accumulation characteristics of gas-solid interface in the novel gas environment under DC voltage stress is analysed.Finally,the key issues that need to be paid attention to and further followed through regarding the application of this novel gas in GIL are summarised and put forward.This study hopefully can provide a complete reference for the development of eco-friendly DC gas insulation equipment with C_(3)F_(7)CN/CO_(2) gas mixtures.

Significant enhancement in the electrical conductance properties of ethylene propylene diene monomer using the nano‐SiO_(2) particles

To study the effect of nano‐silica particles on the conductivity characteristics of ethylene propylene diene monomer(EPDM)insulation,EPDM nanocomposites with different mass fractions of nano silica were prepared via the melt‐blending method.Scanning electron microscopy was used to analyze the dispersion of nanoparticles in EPDM.Based on the Fourier‐transform infrared spectrum,the bonding properties between the nanoparticles and EPDM were analyzed.The steady‐state current at 30-100°C and 1-20 kV/mm was measured.Moreover,the conductivity characteristic was analyzed.The experimental results show that as the content of nano‐silica increases,the electrical conductivity of EPDM nanocomposite as well as the threshold field strength gradually decreases.Samples with a small number of nanoparticles will increase the activation energy of the carrier conductivity,and the interface region effect introduced by nanoparticles will reduce the carrier mobility and concentration,resulting in a lower conductivity.Comparing the calculated value of the dielectric constant with the measured value can conclude that the high‐field conductance process is a combination of the electrode effect and the body effect,which in this case,Schottky effect dominates.

Temperature-dependent partial discharge characteristics of high temperature materials at DC voltage for hybrid propulsion systems

The safe and reliable operation of insulation material used in key high voltage compo-nents under extreme environmental conditions represents the major concerns for man-ufacturers and operators of More Electric Aircrafts(MEA).Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life,especially at high-temperature conditions.Here,the surface discharge behaviour of two commonly used high-temperature insulation materials,ethylene-tetrafluoroethylene(ETFE)and polyetheretherketone(PEEK)is studied at different temperatures under ramp and DC voltages.Extracted partial discharge(PD)features are presented and the impact of voltage polarity on surface discharge propagation is discussed.Our studies reveal that,while both materials exhibit non-linear PD behaviour with respect to their electrical conductivity,ETFE generally shows PDs with higher in-tensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity.Overall,the PD mechanism in high-temperature,DC voltage applications is explored,and a basis for the selection of high-temperature PD suppressing materials is developed.