Enhancing flashover performance of alumina/epoxy spacers by adaptive surface charge regulation using graded conductivity coating

Abstract

Surface flashover properties of alumina/epoxy spacers, involving a surface charge accumulation process, are critical for the safe and reliable operation of a high-voltage direct-current (HVDC) gas-insulated transmission line (GIL). This study reports surface charging behavior and flashover performance of alumina/epoxy spacers with different surface conductivity graded coating (SCGC) schemes in SF 6 /N 2 mixtures under DC stress. Four kinds of SCGC schemes, i.e. localized coating near high voltage (HV-coating), near grounded electrode (GND-coating), at the middle of spacer surface (SPM-coating) and near both high voltage and grounded electrode (HV-GND-coating), are designed by partially spraying SiC/epoxy composites on the spacer surface. Surface charge distribution patterns exhibit varied features with different SCGC schemes. The HV-coating and GND-coating schemes lead to aggravated homo-charge and hetero-charge accumulation respectively, whereas in the SPM-coating scheme surface charge shows a multi-tier distribution pattern with alternating polarity. A transition of the dominant surface charge mechanism from bulk conductivity to surface conductivity with increasing conductivity on the coated area is found. Flashover performance differs a lot with different SCGC schemes: the HV-coating and HV-GND-coating schemes increase the flashover voltage while the SPM-coating and GND-coating schemes degrade it. The optimal surface insulation strength is achieved in the HV-coating scheme with a coating width of about 10 mm. The impact of different SCGC schemes on flashover performance is revealed based on the electric field analysis by considering the effect of surface charges.

Nonsacrificial Nitrile Additive for Armoring High‐Voltage LiNi0.83Co0.07Mn0.1O2 Cathode with Reliable Electrode–Electrolyte Interface toward Durable Battery

“…In order to solve these problems, many efforts have been attempted such as ion doping, [ 11 ] surface coating, [ 12 ] and electrolyte modification. [ 13 ] Based on the perspective of cost and procedures, regulation of the CEI layer by adding small amounts of functional additives is a promising approach.…”

“…In addition, at a high charging voltage (> 4.0 V, Li + /Li), Ni 4+ will migrate to the NCM83 surface, and further react with the electrolyte, resulting in the mixed arrangement of nickel and lithium sites and the continuous side reactions of electrode and electrolyte. [10] In order to solve these problems, many efforts have been attempted such as ion doping, [11] surface coating, [12] and electrolyte modification. [13] Based on the perspective of cost and procedures, regulation of the CEI layer by adding small amounts of functional additives is a promising approach.…”

Gas–solid interface charge tailoring techniques: what we grasped and where to go

“…Flashover voltage in 0.1MPa 20% SF6/N2 mixtures increases gradually with decrease of SiC particle size. Then they proposed surface conductivity graded coating scheme to overcome the drawbacks of entire coating manner [9]. Four kinds of surface graded coating schemes are considered, as shown in Figure 31.…”

“…In recent years, due to the urgent requirement of HVDC GIL driven by the expansion of HVDC projects, especially offshore projects, the problem of surface charge accumulation has become tremendously pronounced [11][12][13][14]. As a consequence, extensive research studies regarding surface charge behavior has become a focus which is a specific challenge [7][8][9][10]. However, suitable surface charge tailoring methods still remain to be a difficult problem which captures the interests of researchers.…”

Progress in Gas/Solid Interface Charging Phenomena

“…Despite the extensive studies and output during the past few years, charge behaviors such as charge generation, transport, and relaxation in dielectrics should be studied, as these fields of research have still not been fully understood [17]. Regarding the above-mentioned problems, related studies have been performed, including charge measurement techniques, charge transport mechanisms, charge related DC surface flashover mechanisms, and charge control methods.…”