The gap-type controllable metal oxide arrester (CMOA, shortly), a type of CMOA, refers to a CMOA where the controlled component is connected to a gap. Under steady-state operating voltage and power frequency overvoltage, the gap is in an open state, and both the fixed and controlled components of the MOA body are fully operational, resulting in a low charge rate and high reliability. Under switching overvoltage and lightning one, the voltage sustained by the gap exceeds its breakdown voltage, triggering the gap to conduct, short-circuiting the controlled component of the MOA body and only allowing the fixed component to operate, resulting in a low residual voltage and deep suppression of overvoltage. Under steady-state operating voltage, the gap is open, and the capacitance between the gap contacts and the stray capacitance of the contacts to ground affect the voltage distribution across the controlled component of the MOA body and even the MOA body itself. The relative position and distance between the gap and the MOA body vary, affecting the degree of influence. It is necessary to simulate the steady-state voltage distribution of the gap-type CMOA. If the voltage distribution does not meet the requirements, the grading capacitor configuration of the lightning arrester body can be adjusted in a timely manner, and the grading ring structure can be optimized. This paper presents the structure of the gap-type CMOA, and calculates the steady-state voltage distribution of the gap-type CMOA using a field-circuit coupling method. It identifies the influencing factors on the steady-state voltage distribution of the gap-type CMOA. The research results serve as a basis for determining the structural type and prototype development of UHV AC gap-type CMOA.

Moisture exchange in oil-paper insulation under temperature-varying conditions exhibits significant complexity, particularly with interfacial moisture accumulation readily occurring during cooling-a phenomenon that critically compromises transformer insulation integrity, yet consensus remains elusive regarding key parameters and formation mechanisms of such accumulation under thermal cycling. To address this, a computational model for moisture diffusion and exchange in oil-paper insulation is developed. Through experimental measurements of spatiotemporal moisture distribution in oil-impregnated pressboard and oil moisture content evolution, temperature-dependent relationships for the diffusion coefficient D and interfacial moisture exchange coefficient α are established. Subsequent temperature-varying experiments reveal interfacial exchange hysteresis relative to temperature changes, with hysteresis loop areas expanding with increasing temperature variation rates, temperature ranges, and initial moisture content. Integrated model-experimental analysis demonstrates that interfacial moisture exchange exhibits higher activation energy than the diffusion process, establishing it as the rate-limiting step. Furthermore, moisture accumulation fundamentally stems from coupled interfacial kinetic hysteresis induced by high activation and abrupt solubility changes, where sluggish interfacial exchange during cooling fails to match rapidly escalating oil supersaturation levels. These findings provide theoretical foundations for dynamic moisture prediction in transformer insulation systems and operational load management strategies.

Accurate analysis of power quality disturbances (PQDs) is essential for fault diagnosis, equipment assessment, and pollution control. As disturbances in renewable-integrated power systems become increasingly complex and diverse, existing frequency methods show limited adaptability and flexibility. To address this issue, this paper proposes a Component-Adaptive Segmented S-Transform (CASST). CASST adaptively partitions the frequency axis according to the distribution of dominant frequency components, achieving segmentation at the component level, and employs a composite objective function to optimize Gaussian window parameters in each segment. This enables dynamic adjustment of time-frequency resolution tailored to the characteristics of individual components. Comparative studies on composite disturbances show that CASST effectively avoids spectral overlap and reduces amplitude envelope tracking error and transient onset detection error relative to the standard S-transform and its variants. Specifically, CASST achieves an average event onset/offset localization error of only 2.81%, and reduces the transient-oscillation onset localization error by up to 10.10% compared with the benchmark methods. Furthermore, in application scenarios such as wind-speed disturbance scenario and field-measured resonant overvoltage, CASST provides a clearer depiction of disturbance evolution and reveals key time-frequency features that other methods fail to capture, demonstrating strong engineering applicability.

Trace hydrogen monitoring in nitrogen-purged gas lines and inert process chambers is important for maintaining stable and contamination-controlled semiconductor manufacturing conditions. For palladium thin film resistive hydrogen sensors, rapid and accurate detection of ppm-level trace hydrogen in nitrogen on a minute timescale remains challenging. This study proposes a surface modification strategy based on pulsed hollow cathode discharge plasma treatment, which constructs high-amplitude nanoscale protrusions on the film surface to mitigate the adsorption-kinetics-limited process governing the sensor response to trace hydrogen and thereby markedly shorten the response time. Specifically, the response times to 200 and 50 ppm H2 decreased to 41.5 and 67.4 s, respectively, which are approximately one-half and less than one-third of those of the untreated sensor. Owing to the bimodal-energy-distribution and low-density plasma characteristics, neither sensitivity nor baseline stability is degraded after modification. The proposed strategy endows the modified Pd thin film hydrogen sensor with the capability for rapid and reliable minute-scale detection of trace hydrogen down to 1 ppm. Furthermore, plasma energy diagnostics indicated that effective surface modification requires a plasma with a high proportion of high-energy ions. Mechanistic analysis suggests that the proposed surface modification strategy enhances the hydrogen adsorption flux under trace-hydrogen conditions by increasing the effective adsorption area, providing additional diffusion pathways, and inducing near-wall flow perturbations, thereby significantly reducing the sensor response time to trace hydrogen.

The influence of air pressure on positive leader inception in long spark discharges is unclear, as some key parameters are still unknown. Positive long air gap discharge experiments were conducted at different altitudes: specifically, in Tibet (4300 m) and Anhui (37 m), with the same applied voltage waveform. The positive leader discharge process was observed, with synchronous measurements of discharge voltage, current, and optical morphology. Under low-pressure conditions, the first corona inception voltage was found to be significantly lower, while the associated charge quantity was substantially higher. In contrast, the duration of the dark period remained almost unchanged. Consequently, the leader inception voltage was markedly reduced under low-pressure conditions. That indicates that a positive leader is easier to start at low pressure. The duration of the dark period depends on the amount of charge produced by the first corona, regardless of the air pressure. Furthermore, the parameter used in the self-consistent leader inception and propagation model for calculating the charge generated by the first corona was analyzed. This study provides theoretical support for numerical models that consider the influence of atmospheric pressure.

In positive leader discharge, the channel evolution process during pause period significantly impacts the subsequent discharge behavior accompanied by sudden elongation and intense reillumination of the discharge channel. The discontinuous discharge phenomenon is widely observed in the intermittent positive leader of natural lightning and laboratory positive long air gap discharge. In this study, direct optical photography and schlieren observation system were designed to acquire the time-resolved morphology images of optical and thermal plasma channel during pause period of positive leader discharge. The synchronized propagation of luminous and thermal channels within pause duration is experimentally characterized. Besides, it is confirmed that the secondary streamer triggering leader inception bursts in front of the residual channel within pause duration and further reactivates the discharge channel, providing insight into the stepped propagation mode of positive leader discharges in nature lightning and restrike phenomenon.

The series-connected insulated gate bipolar transistors (IGBTs) always endure a secondary voltage imbalance introduced by the difference of tail current. The state-of-the-art models often oversimplify or neglect key physical processes, such as carrier transport and recombination, leading to inaccurate descriptions of the tail current and complicating the characterization of secondary voltage imbalance. To address this issue, a physics-based model of IGBT is analytically established, which could accurately describe the tail-current characteristics. First, this article introduces an improved carrier transport formulation that incorporates the description of space-charge generation current and the characterization of nonlinear carrier distribution. Furthermore, an equivalent carrier lifetime expression is developed to describe the recombination effect more comprehensively by incorporating the recombination mechanism under the low carrier concentration conditions. Based on this IGBT model, a circuit composed of series-connected IGBTs is constructed to investigate the mechanism of secondary voltage imbalance. Finally, the accuracy and superiority of the proposed model were validated through comparative experiments and simulations. Compared with the conventional models, the proposed model achieves a 42.66% improvement in accuracy in describing the voltage imbalance between series-connected IGBTs. Furthermore, the proposed model provides valuable references and theoretical support for the design of voltage-balancing strategies and circuit parameters in series-connected IGBT equipment.

The partial discharge occurring in the weak part of the insulation of a converter transformer results in the formation of a large number of bubbles in the insulating oil. The migration, deformation, and other dynamic behaviors of bubbles in the region of a strong electric field can cause them to easily accumulate into "small bridges" of impurities that can lead to breakdown of the oil gap. The authors of this study experimentally investigate and discuss the mechanisms of migration and deformation of bubbles in oil during partial discharge under composite AC/DC voltage to clarify their dynamic behaviors. The influence of the initial position of the bubbles on their trajectory of migration and velocity as well as the morphological changes occurring in them are analyzed using numerical simulations. The results show that the bubbles move away from the strong electric field due to the action of the dielectrophoretic force. The interface of the bubbles is longitudinally stretched under the action of the electrostrictive force and the vertical component of the drag force and gradually recovers to assume a spherical shape under the influence of surface tension and the horizontal component of the drag force.

Frequent overvoltage, thermal cycling, and vibration accelerate arrester aging and threaten power system’s reliability. This paper reviews “electro‑thermal‑mechanical” aging mechanisms of ZnO arresters, along with experimental methods, modeling approaches, and performance enhancing strategies. Degradation characteristics and interactions among electrical, thermal, and mechanical aging are summarized; testing indices, standards, and condition monitoring techniques are compared; macro-/micro-scale equivalent-circuit and physical models are reviewed. Material and structural optimization strategies are analyzed, and future research directions are proposed.

Arc discharges in transformer oil under internal short-circuit conditions decompose the insulating oil, producing gases that accumulate in the sealed, oil-filled tank, thereby raising the internal pressure and potentially triggering explosion accidents. In recent years, multiple incidents of large oil-immersed power transformers experiencing internal short-circuit-induced explosions have been reported, highlighting the urgent need for accurate pressure calculations under arc conditions to support explosion-proof design. The pressure rise inside the tank involves coupled interactions among gas, liquid, and solid phases. Although previous studies have performed gas–liquid–solid coupled simulations, they did not account for the segmented characteristics of the pressure waveform and failed to elucidate the underlying coupling mechanism. This study investigates the formation mechanism of segmented pressure waveforms resulting from arc discharges in transformer oil within sealed tanks. By analyzing the distinct generation mechanisms across different pressure stages, the gas–liquid–solid coupling mechanism of the pressure rise is clarified, and a segmented coupling calculation method is proposed. The computed waveforms achieve over 90% similarity with experimental results. This work provides both a practical tool for calculating arc-induced pressure inside transformers and theoretical support for explosion-proof design.

The electric arc caused by insulation failure inside a transformer oil tank can lead to the decomposition of insulating oil, resulting in the generation of gas and an increase in internal pressure, which may trigger an explosive combustion accident. To prevent excessive pressure rising in the tank, pressure relief valves (PRV), rupture disc, and other devices are typically installed on the tank for pressure release. However, the coupling mechanism between the pressure generation during arc discharge and the release devices remains inadequately assessed in a quantitative manner, making it challenging to perform effective explosion-proof design for the pressure relief device (PRD). This paper explores the coupling relationship between the release flow rate of devices such as the conservator tank, PRV, rupture disc and pressure generation process, using the flow rate as a coupling variable. A coupling algorithm is developed to describe the interaction between pressure generation and release. The coupling algorithm was validated using both two interconnected tanks experiment and the 1/16-scale Ultra-High-Voltage（UHV）transformer tank experiments. Finally, the discharge performance of PRVs with different flow capacities was evaluated for application in UHV transformer tanks. This study provides tools for the explosion-proof pressure relief design of transformer oil tanks.

Optical emission spectroscopy (OES) is one of the most practical methods for quantitative analysis in lightning research. Although the method has been widely used in studies of return strokes, laboratory discharges, and negative lightning leaders, the spectra of continuously propagating positive leader channels have not yet been recorded due to their faint luminance. In this paper, we report 14 events of spatiotemporal resolution emission spectra of continuously propagating positive leader channels obtained using a slit-less high-speed spectrograph consisting of a grating mounted in front of a high-speed camera. These spectra showed that the OI 777 nm triplet exhibited the strongest intensity, observed during the continuous and stable development stage of the propagating positive leaders. We analyzed the temporal and spatial evolution of the OI 777 nm triplet intensity and estimated the electron density based on the Stark broadening of the OI 777.41 nm subline, which belongs to the same triplet. The results of these estimations show that the electron density calculated from the OI 777 nm triplet can be a powerful tool for understanding the physical characteristics of positive lightning leaders.

Determining the coupling matrix is crucial for reconstructing transient voltages on overhead transmission lines using non-contact measurement techniques. However, existing methods often fail to account for the effects of asymmetrical sensor placement and the presence of multiple adjacent conductors in substations. This paper proposes an optimization-based approach to estimate the coupling matrix elements, aiming to minimize the transient voltage reconstruction error, with the measured power frequency voltage imposed as a constraint. The influence of adjacent conductors on the measured electric field is assumed to have a waveform similar to that of the measured conductors, as ensured by the electrically small condition during switching transients. The method is applied to reconstruct the closing and opening transient voltage waveforms of a 500 kV overhead transmission line. The estimated coupling matrix coefficients exhibit consistent performance across 11 tests, with maximum estimation errors of 6.2% and 2.5% for the opening and closing transient voltages, respectively. Moreover, the results indicate that the low-frequency response characteristics of capacitive voltage transformers (CVTs) are insufficient for capturing the opening transient voltages on transmission lines. By leveraging the full waveform of the measured transient electric field signal, the proposed method eliminates the need for symmetrical sensors and ensures robust field performance.

The mechanism of positive leader discharge is a key issue in the insulation design of extra-high voltage systems and in plasma-based industrial processes, yet the role of channel thermodynamic state remains insufficiently resolved. In this work, positive leader discharges in a 3.0 m rod-plane air gap are experimentally investigated using a high-resolution quantitative schlieren system to capture the spatiotemporal evolution of channel temperature. A hybrid reconstruction approach integrating convolutional neural networks with physics-informed neural networks is proposed to suppress measurement noise and improve stability under long-gap conditions, enabling reliable inversion of temperature fields from schlieren data. The spatiotemporal distributions of channel temperature near the electrode region under both breakdown and withstand modes were revealed under identical experimental conditions. Furthermore, it is found that continuously developing leaders maintain an axial average temperature above similar to 3000 K, which sustains thermal ionization against strong convective loss associated with restrike currents, thereby enabling persistent propagation and eventual breakdown. By contrast, in relaxation regimes, restrike-induced expansion intensifies energy loss, causing the axial temperature to fall below the thermal ionization-sustaining threshold and leading to propagation failure. These findings demonstrate that the spatiotemporal evolution of channel temperature governs development mode, providing direct experimental insight into the discharge behavior of positive leader in long air gap.

In recent years, short-circuit explosion accidents in ultra-high voltage oil-filled equipment have occurred frequently, causing significant economic losses. Internal short-circuit faults in oil-filled equipment can trigger arc discharge, leading to the vaporization and decomposition of oil, which generates significant relative pressure and may cause explosion and fire accidents. The typical waveform of relative pressure includes four stages: shock wave, fluctuating pressure, quasi-static pressure, and steady-state pressure. Among the components of relative pressure, static pressure is the dominant factor. However, existing methods for calculating static pressure have ignored two main factors: the influence of free gas on static pressure and the time-varying temperature of discharge-induced gas, causing deviations in the calculation results. This paper addresses the two aspects through theoretical analysis and experimental research. A time-varying static pressure calculation method is proposed, which significantly improves the accuracy of calculations when considering the free gas within the tank. Additionally, the relative significance of each factor influencing the static pressure is analyzed. This research provides a reference for calculating the static pressure generated by arc discharge inside transformer tanks.

The detection of lightning electromagnetic radiation signals is fundamental to both lightning physics research and lightning location systems. Antenna plays an important role in accurately detecting lightning electromagnetic radiation signals. This paper proposes a differential-based parallel-plate antenna. By establishing a 2D axisymmetric electrostatic field model, we compared the transfer factor of grounded parallel-plate antenna (GPPA) and the differentialbased parallel-plate antenna (DPPA). Simulation results demonstrate that, unlike the GPPA, the DPPA maintains a constant transfer factor when installation height changes, thereby eliminating the need for the height-specific calibration required by the GPPAs. Furthermore, an equivalent capacitive network model representing mutual couplings among the lightning cloud, ground, and antenna was developed. Based on this model and the design of the DPPA, a differential-based broad-band lightning electric field sensor is designed using the DPPA as the antenna. Experimental tests with a signal generator and power amplifier verified the sensor's frequency response and sensitivity. The proposed sensor exhibits a -3 dB bandwidth spanning 1 kHz to 3 MHz and maintains a stable sensitivity.

Gas discharge tube (GDT) often breaks down and discharges due to surge overvoltage in long-term use. When the discharge continues to accumulate for a certain number of times, the breakdown voltage and insulation resistance of GDT change significantly, resulting in performance degradation, threatening the safety of the protected equipment. In order to explore the degradation process, this article establishes a cumulative discharge experimental platform to conduct cumulative discharge experiments throughout the life cycle of GDT. The changes and relationships of four characteristic parameters in the process of GDT degradation are studied: electrical characteristics, electrode surface morphology and its element composition, and electrode mass transfer. The results show that the following characteristics are presented with the increase of discharge times. The breakdown voltage first increases and then decreases, and the value at the end stage is only about 60% of the initial value. The insulation resistance value continues to decrease, and at the end of the stage, the value drops sharply, and finally, it is less than 1 M Omega . The electron powder coverage of the electrode surface decreases gradually, and the erosion degree of the grid edge increases gradually until it is combined with the inside of the grid. The total content of Fe and Ni in the electrode material increased from 60.03% to 98.37%, and the content of relevant elements in the electronic powder decreased from 39.97% to 1.63%. Finally, the reasons for the above deterioration phenomena and results are discussed, and the relationship between the results is analyzed.

Switching operations of disconnectors emit electromagnetic fields (EMF) to the external environment via gas-to-air bushing, posing a threat to the secondary equipment in gas-insulated substations (GIS) and potentially causing telecommunications outages in nearby residential areas. In this paper, a comprehensive method for EMF simulation is introduced. This method encompasses the entire process, from arc breakdown to very fast transient currents (VFTCs) and EMF generation, while considering radiation loss. A frequency-domain algorithm is proposed to address the complex, frequency-dependent problems encountered during simulation. The simulation of the 1000 kV Wuhu substation reveals that overlooking radiation losses leads to an overestimation of the high-frequency component of the EMF. The study further analyzes the EMF characteristics in relay protection rooms, control rooms, and residential areas under different operating conditions. Based on these EMF characteristics and in accordance with IEC 61000-4-10, this paper proposes immunity requirements for equipment located both within 1000 kV substations and in adjacent residential areas. This research makes a substantial contribution to assessing the transient electromagnetic environment caused by switching operations in GIS substations.