Significantly enhanced flashover voltage of epoxy in vacuum by graded surface roughness modification

The flashover strength of epoxy(EP)insulations in the High voltage direct current applications of future energy grids can be improved by tailoring their surface condition.This work aims to improve the DC surface flashover characteristics of EP after being treated with sandpaper of different gradings.Samples with virgin EP and homogenously modified EP considering varying surface roughness(R_(a)=0.54,3.16,5.24,and 8.35μm)are prepared.Different experimental characterisations,such as water contact angle,surface intrinsic conductivity,surface voltages,flashover strength,and trap distributions are conducted and evaluated to analyse the difference between virgin and treated EP.Moreover,based on the obtained experimental results of homogenously treated EP and theoretical analysis,the concept of surface functionally graded materials(SFGMs)is put forward.The flashover voltages of homogenously treated EP are augmented significantly compared to virgin EP regardless of the voltage polarity and enhanced by enhancing the surface roughness.The sample T_(Model‐C) with SFGM design shows a 45.02%and 43.75%improvement in the negative and positive flashover voltages than that of the virgin EP.In the end,COMSOL simulations are conducted to justify the experimental findings and to analyse the difference between virgin and modified samples in terms of electric field distribution.

Accelerated ultraviolet weathering investigation on micro-/nano-SiO_(2)filled silicone rubber composites

This study attempts to elucidate whether the addition of micro and/or nano-silica(SiO_(2))particles can enhance the resistance of pure polydimethylsiloxane against synergistic effects of UV,temperature and high-voltage stress.Four types of composites(U-SR,M-SR,MN-SR and N-SR)are fabricated by adding micro and/or nano-silica particles and then subjected to multi-stress degradation in a test chamber.Results show that there is an apparent surface discoloration in the form of yellowish pale tint and a significant resistance to hydrophobicity reduction is offered by N-SR and MN-SR followed by M-SR and U-SR.Scanning electron microscopy and surface roughness findings proclaimed that N-SR and MN-SR offer excellent resistance against filler exposure and an increase in surface roughness.There is a minor reduction in absorbance level of Si(CH_(3))_(2) and Si-O-Si functional groups of composites but interestingly,hydrophilic hydroxyl group absorbance level is found higher in the U-SR comparatively.Furthermore,dielectric response measurements indicate considerable sensitivity to weathering with N-SR and MN-SR giving the lowest dielectric loss.Results indicate that the addition of nano-silica to pure and micro-silica filled SR can enhance its UV weathering resistance considerably by building an effective UV shielding layer.

Tracking,erosion and thermal distribution of micro-AlN+nano-SiO_(2) co-filled silicone rubber for high-voltage outdoor insulation

Thermal depolymerisation induced tracking and erosion of polymeric insulators is one of the key insulation failure modes and this process adversely affects the reliability of power delivery networks.This study reports the tracking,erosion and thermal distribution of micron-AlN and micron-AlN+nano-SiO_(2)co-filled silicone rubber composites.A tracking-erosion model is presented to explain how the co-filled set of particles directly affects such mechanisms.Aluminium nitride(AlN:5-10μm)and silica(SiO_(2):20 nm)particles were procured for fabricating test samples.The inclined plane test according to IEC 60587 was carried out using tracking voltage method 2 with an initial applied voltage of 3 kV and a ramping rate of 0.25 kV/h over the duration of 240 min.Measurement results show co-filled composites exhibit significantly lower physical tracking and erosion as compared to micron-AlN filled composites.Thermal accumulation and average leakage current in co-filled composites are found noticeably lower than micron-filled counterparts.Moreover,the increased surface area of the combined co-filled particles in the composites provides better scattering and reduce secondary electron collision.This may impede the release of high energy causing thermal degradation.

Improving the polarisation and depolarisation current measuring method to avoid ground wire interference

The ground wire is significantly interfered by the current above 1μA in the industrial field during the traditional polarisation and depolarisation current(PDC)measurement.This paper explains a method to test PDC from high-voltage wire using a principle of equipotential picoammeter,which is completely isolated from the ground wire and connected in series with the high voltage wire.In this method,a device is designed with a multi-range automatic switching function.The device can automatically switch the test range current from 1 pA to 10 mA with a resolution of 1 pA.To demonstrate the device and effectiveness of this new method,the traditional and the proposed new device are used to test the PDC of cable samples in the laboratory as well as in an industrial environment.It is worth noting that there is almost no interference on the Earth wire in the laboratory environment but massive interference in the industrial environment using a traditional method of PDC measurement from ground or Earth wire.The new method of high-voltage testing can efficiently eliminate the interference and accurately measure PDC in a strong industrial interference environment.Furthermore,the wiring of this new method and device is relatively simple,which is convenient for industrial applications.