Creeping discharges over insulator surfaces have been related to the presence of triple junctions in compressed gas insulated systems. The performance of dielectric materials frequently utilised in gaseous insulating high voltage applications, stressed under triple junction conditions, has been an interesting topic approached through many different physical perspectives. Presented research outcomes have contributed to the understanding of the mechanisms behind the related phenomena, macroscopically and microscopically. This paper deals with the electrical detection of creeping discharges over disc-shaped insulator samples of different dielectric materials (polytetrafluoroethylene (PTFE), epoxy resin and silicone rubber) using atmospheric gases (dry air, N₂ and CO₂) as insulation medium in a point-plane electrode arrangement and under AC voltage application. The entire approach implementation is described in detail, from the initial numerical field simulations of the electrode configuration to the sensing and recording devices specifications and applications. The obtained results demonstrate the dependence of the generated discharge activity on the geometrical and material properties of the dielectric and the solid/atmospheric gas interface. The current work will be further extended as part of a future extensive research programme.

Negative and positive partial discharge inception voltages and breakdown measurements are reported in a needle-plane electrode system as a function of pressure under AC voltage for natural gases (N₂, CO₂, and O₂/CO₂), pure Novec^TM gases (C₄F₇N and C₅F₁₀O) and Novec^TM in different natural gas admixtures. For compressed 4% C₄F₇N–96% CO₂ and 6% C₅F₁₀O–12% O₂–82% CO₂ gas mixtures, the positive-streamer mode is identified as the breakdown mechanism. Breakdown and negative partial discharge inception voltages of 6% C₅F₁₀O–12% O₂–82% CO₂ are higher than those of 4% C₄F₇N–96% CO₂. At 8.8 bar abs, the breakdown voltage of 6% C₅F₁₀O–12% O₂–82% CO₂ is equal to that of 12.77% O₂–87.23% CO₂ (buffer gas). Synergism in negative partial discharge inception voltage/electric field fits with the mean value and the sum of each partial pressure individually component for a 20% C₄F₇N–80% CO₂ and 6% C₅F₁₀O–12% O₂–82% CO₂, respectively. In 9% C₄F₇N–91% CO₂, the comparison of partial discharge inception electric fields is E_max (CO₂) = E_max(C₄F₇N), and E_max (12.77% O₂–87.23% CO₂) = E_max(C₅F₁₀O) in 19% C₅F₁₀O–81%(12.77% O₂–87.23% CO₂). Polarity reversal occurs under AC voltage when the breakdown polarity changes from negative to positive cycle. Polarity reversal electric field E_PR was quantified. Fitting results show that E_PR (CO₂) = E_PR(9% C₄F₇N–91% CO₂) and E_PR(SF₆) = E_PR (22% C₄F₇N–78% CO₂). E_PR (4% C₄F₇N–96% CO₂) = E_PR (12.77% O₂–87.23% CO₂) and E_PR (6% C₅F₁₀O–12% O₂–82% CO₂) < E_PR (4% C₄F₇N–96% CO₂) < E_PR (CO₂).

This paper presents an improved temporal pulse sequence analysis (PSA) method for diagnosing partial discharge (PD) phenomena. The proposed method enables simultaneous high-resolution PD recognition across electrical sensors and ultra-high frequency antennae, facilitating the differentiation of defect types and the quantification of PD severity, as well as, their unique characteristics. This is achieved by utilizing advanced discrete-time integration techniques within two sensor measurement systems. Each PD event is time-stamped in post-processing, with a particular focus on analyzing charge-to-charge and ultra high frequency (UHF) energy-to-energy sequences analysis. The improved temporal PSA merits the advantages of a wide bandwidth of high-frequency current transformers and antennae to improve accuracy and efficiency. To conduct this method, a dual-sensor PD measurement circuit was set up to examine the protrusion on the ground side, the floating electrode, and the free-moving particle defects, which are potentially present in gas-insulated switchgear. Obtained results present dynamic PD variations in both time differences and magnitudes, establishing correlational PD patterns between sensors in a distinct manner. The application of the proposed method can serve as a reliable diagnostics approach for PD detection in gas-insulated switchgear and offer insights into underscoring PD phenomena itself.

This study examines the Partial Discharge (PD) performance of aircraft cables using a specially designed test electrode. Electrode positioning was precisely controlled within an atmospheric chamber to replicate coaxial geometries. Long exposure imaging reveals useful insights that enhance our understanding of PD behaviour at varying atmospheric pressure. The research compares the experimental data with existing mathematical models based on the Paschen and Halleck equations revealing notable inconsistencies, particularly at higher pressures. This work contributes valuable insights into the complexities of PD phenomena in aircraft cables and proposes a new model by enhancing an existing predictive model and incorporating the influence of an insulation barrier.

In this article, investigations of surface discharges using an ultraviolet (UV) intensified high-speed camera system are presented, accompanied by high-frequency response and resolution current recordings. A needle-plane electrode configuration is employed for the generation of a strongly nonuniform electric field on the surface of disk-shaped insulator samples made of polytetrafluoroethylene (PTFE) or epoxy resin. The electrode arrangement is further insulated by a gaseous medium of either technical air (21% O ₂ /79% N ₂ ), nitrogen (N ₂ ), or carbon dioxide (CO ₂ ). An alternating (ac) voltage waveform at power frequency (50 Hz) is maintained at levels sufficiently below the flashover voltage corresponding to each presented case. Detailed descriptions of the technical specifications of the utilized equipment are provided for both optical and electrical measurements in the experimental setup. The obtained results demonstrate the discharge propagation during the ac-cycle and its dependence on the insulator type and gaseous insulating medium. Individual surface discharges are captured in the microsecond range to describe the discharge morphology based on the generated current pulse and instantaneous applied voltage level. Back-discharges on the insulating disk are also discussed, and relevant image capture is presented.

Implementing pilot SF₆-free DC gas insulated switchgear connected to the rectifier station poses challenges due to the combination of discharge severity metrics, harmonic control, and gas characteristics. This paper examines the impact of DC harmonic voltages produced by line-commutated converters rectification on corona discharge phenomena in gas insulated switchgear. With a focus on the various types of harmonic distortions that present electric field fluctuations, this study evaluates corona discharge behaviour in C₄F₇N mixture, CO₂ and technical air under overstressing ripple voltages. Comprehensive descriptions of the methodology encompass: (i) reproducing representative DC terminal voltages of a generic line-commutated converter in a laboratory setting, and (ii) correlating the harmonics impact of these harmonics with discharge analytics using updated time-resolved analysis. Compared with pure DC voltage, it is found that the line-commutated converter harmonic discharge results demonstrate a non-monotonic increase in discharge inception voltage with increasing firing angles under fixed overlap angles. A strong correlation between voltage rate of change and discharge pulse sequence patterns is seen for the three gases. The concepts derived from pulse-pulse correlation are explored as indicators of the influence of commutation control logic in discharge generation, emphasising their utility in diagnosing DC gas insulated switchgear in rectifier stations.