Search Results (112)

Sulfur hexafluoride (SF₆), an extraordinary gas insulation medium, must be replaced by environmentally friendly gas in electric equipment because of its high global warming potential (GWP). In this research work, the DC breakdown properties of R404a gas and its mixtures with N₂ and CO₂ are studied under a sphere–sphere electrode configuration and uniform field conditions. The GWP of R404a is 16% of SF₆ and its liquefaction temperature is also in the suitable range for practical applications. Nitrogen and carbon dioxide are mixed with R404a to reduce its boiling point and GWP. Other important parameters such as the self-recoverability, liquefaction temperature, GWP, and synergistic effect of R404a/CO₂ and R404a/N₂ were also studied to complement the insulation performance and the results are comparable to other gas mixtures. As a result, it was found that both the mixtures containing 80% R404a and 20% N₂ or 20% CO₂ possess a breakdown strength of 0.83 times that of SF₆. Mixtures containing an 80% concentration of R404a possess a GWP equal to only 15% of SF₆. These properties make gaseous mixtures containing 80% R404a and 20% N₂ or CO₂ a suitable alternative to SF₆ in medium-voltage gas-insulated equipment. Full article

To address the impact of insulation medium degradation in the arc quenching chambers of ultra-high-voltage SF₆ circuit breakers on phase-controlled switching accuracy caused by multiple operations throughout the service life, this paper proposes an adaptive switching algorithm. First, a modified formula for the breakdown voltage of mixed gases is derived based on the synergistic effect. Considering the influence of contact gap on electric field distortion, an adaptive switching strategy is designed to quantify the dynamic relationship among operation times, insulation strength degradation, and electric field distortion. Then, multi-round switching-on and switching-off tests are carried out under the condition of fixed single-arc ablation amount, and the laws of voltage–current, gas decomposition products, and pre-breakdown time are obtained. The test data are processed by the least squares method, adaptive switching algorithm, and machine learning method. The results show that the coincidence degree of the pre-breakdown time obtained by the adaptive switching algorithm and the test value reaches 90%. Compared with the least squares fitting, this algorithm achieves a reasonable balance between goodness of fit and complexity, with prediction deviations tending to be randomly distributed, no obvious systematic offset, and low dispersion degree. It can also explain the physical mechanism of the decay of insulation degradation rate with the number of operations. Compared with the machine learning method, this algorithm has stronger generalization ability, effectively overcoming the defects of difficult interpretation of physical causes and the poor engineering adaptability of the black box model. Full article

The plasma reactor and cylindrical-type electrostatic precipitator (PRESP), combined operation in one device, made in the metallic chimney of low-thermal power boilers (up to 50 kW) that burn wood, can be used in home applications. The discharge electrode is stretched and supported by two groups of medium-voltage insulators. The sensitive elements of PRESP are medium-voltage insulators. This article analyses the design, use, and effect of dirty gases on the medium-voltage insulators that support the discharge electrode under real operating conditions for a PRESP installed in a 20 kW thermal power boiler that burns wood (there are no studies on the performance of PRESP). The electrical properties of the medium-voltage insulators (isolation resistance, dielectric absorption ratio, and polarisation index) and the chemical analysis of the dust layer deposited on the medium-voltage insulators are analysed. Of the two types of insulators analysed, a longer length of the electrical insulators determines a safer and better operation of PRESP. After a period of operation of the PRESP, the insulation resistance decreases by more than 10 times. The polarisation index (values greater than 1.1–1.2) provides better information (compared to the dielectric absorption ratio) on the insulation quality. Full article

Flat panel displays for large applications (monitors and TVs) have structural weaknesses in improving the yield of mass-produced products due to large panels: the yield is defined by ratio of output quantity to input into panel fabrication process. From a panel manufacturing point of view, low-cost production should be achieved through improved yield of mass production (Samsung Display’s quantum dot display backplane panel). So, we set the target yield at an extreme value, over the golden yield (90%) at the beginning of new mass products. The main factors contributing to the yield loss were “lifted insulator and etched active pattern defects”. To reach the target yield, we focused on these two main defects. The root causes of these defects (delta coefficient of thermal expansion and galvanic corrosion) are explained, and a defect generation mechanism is proposed (the size of the separated large power line in relation to the defect rate). The power lines are defined based on an Electroluminescent Voltage at the Drain (ELVDD) and Electroluminescent Voltage at the Source (ELVSS). We developed a separated large power line design to reduce defect rates. This design plays a role in preventing these two defects during the mass production of medium to large display panels for use in TVs by ensuring that the large power line area is less than the optimum value (<0.44 cm²). Full article

In this study, we analyzed the electrical characteristics of metal–insulator–metal (MIM) capacitors fabricated with reference to insulator (Si_xN_y) thickness and deposition condition. Si_xN_y thicknesses of 650 Å, 500 Å, and 400 Å were used with four different conditions designated as MIM (N content 1.49), NEWMIM (N content 28.1), DAMANIT (N content 1.43), and NIT (N content 0.30), deposited by controlling gas flow and RF power as a function of N content. Capacitor characteristics were evaluated mainly in terms of the relationship between leakage current and breakdown voltage (BV). Current–voltage (I–V) characterizations revealed that a higher N–H/Si–H ratio effectively suppressed trap-assisted leakage conduction and enhanced dielectric robustness under high-field stress. Among the tested conditions, the NEWMIM process demonstrated the most favorable electrical performance with highest N contents. The MIM and NEWMIM conditions proved most effective among the evaluated processes, achieving sufficient BV values (>20 V) for reliable MIM capacitor operation and proposing a process optimization framework for integrating medium-density Si_xN_y–based MIM capacitors (2 fF/µm²) with sufficiently high BV values in the future. Full article

Ensuring the fire resistance and thermal stability of power cables is crucial for their reliable performance in fire environments, essential for sustainable power distribution, and allowing for more time to extinguish fires and for evacuation. This study utilises numerical simulation to analyse the thermal behaviour of fire-resistant medium-voltage cable, focusing on the impact of conductor radius and material properties under external heat flux. A heat transfer model of cables with conductor radii of 3 mm, 5 mm, and 7 mm under a localised external heat flux of 750 °C was developed. The results show that smaller conductors stabilise faster (reaching the steady state at 45 min for 3 mm vs. 79 min for 7 mm) but experience higher thermal stress, with conductor temperatures peaking at 692.5 °C. Larger conductors enhance axial heat conduction, reduce steady-state temperature by up to 25%, and improve heat dissipation by over 360%. The 5 mm conductor radius provided balanced performance, lowering the temperature by 65 °C compared to 3 mm, although it remained 20.1% hotter than the 7 mm. The ceramic layer played a crucial role in reducing heat flux in the heat source section. Optimised polyethylene insulation and ceramic material improved heat retention and surface temperature control in non-heat source sections. Also, thermal resistance analysis decreased from 1.00 K/W (3 mm) to 0.65 K/W (7 mm). Among material properties, increasing ceramic thermal conductivity had a more significant impact on reducing core temperature than improving insulation. These findings provide practical recommendations for optimising conductor geometry and material properties for more fire-resistant cables. Full article

A cable accessory is a critical component in constructing high-voltage direct current (HVDC) power grids, and it is typically composed of multiple materials. Due to the discontinuity of the insulation medium, it is prone to failure. This study focuses on a two-layered composite insulation medium simplified from HVDC cable accessories, and its surface potential decay (SPD) characteristics are related to the space charge transport characteristics. Previous studies on surface charge migration have been limited and primarily focused on single-layered insulation materials. However, the actual insulation structure is mostly composite. Therefore, it is of great practical significance to explore the surface charge migration characteristics of two-layered structures. This study presents a bipolar charge transport model after pre-depositing surface charges to investigate the surface charge migration characteristics of an ethylene–propylene–diene monomer (EPDM)/polyethylene (PE) two-layered polymer film. The effects of charge injection and trap related to nano-doping, local defects, and thermal aging on the surface potential decay (SPD) and space charge distribution in EPDM/PE were analyzed. The results show that the increase in the electron injection barrier slows surface charge dissipation and inhibits charge accumulation at the interface. An increase in the trapping coefficient leads to a higher surface potential in the stable state and a greater space charge density. During the early depolarization stage, the SPD rate is weakly dependent on the trap depth, with charge migration primarily governed by the external electric field. Full article

Medium-voltage cables in hydropower plants are typically arranged in multi-circuit configurations to ensure reliability, yet their exposure to harsh operational conditions accelerates insulation degradation and increases partial discharge risks. Traditional fault localization methods, such as the traveling wave method using wavelet transform to process fault signals, suffer from wavefront distortion due to inter-line reflections and noise interference in multi-circuit systems, because wavelet-based techniques are limited by preset basis functions and environmental noise. To address these challenges, a fault localization method for multi-circuit parallel cables based on the Teager–Kaiser Energy Operator (TKEO) is proposed in this paper. First, the fault signal is decoupled using Clarke transformation to suppress common-mode interference, obtaining the α component. Subsequently, the α component is subjected to wavelet transform to obtain the high-frequency components, which are then optimized using the TKEO. The TKEO is applied to optimize the wavelet-transformed signal, enhancing transient energy variations to precisely identify the arrival time of the fault wavefront at measurement points, thereby enabling accurate fault localization. The results of the four types of fault experiments indicate that the use of the TKEO to optimize the wavelet transform of the traveling wave method improved the accuracy of fault localization. Full article

The study of incipient faults due to insulation defects in cables is crucial for preventing electrical fires and ensuring personal safety. However, research on incipient faults in low-voltage cables remains relatively underexplored compared to that on medium-voltage cables. This paper focuses on low-voltage cross-linked polyethylene (XLPE) cables and investigates the changes in voltage and current caused by insulation defects in different wet conditions. The main findings are that the voltage applied to the cable with defective insulation shows sub-cycle disturbances that become more frequent. The current in the cable conductor shows a pulsed shape, coincident with the voltage disturbances. Over time, the sub-cycle disturbances gradually disappear, instead, the steady-state leakage current emerges. The wet conditions affect waveforms of the voltage/current disturbance and the frequency of occurrence. The findings provide detailed and unique characteristics of the voltage and current during the cable incipient fault, which are different from those of the incipient fault in the medium-voltage cables. The simulation and analysis support the experimental results. Based on the experimental results, a model is developed for further research on LV-cable incipient fault detection and protection. Full article

Propylene carbonate (PC) has several advantages, including a high dielectric constant, high resistivity, and excellent environmental adaptability, making it a promising candidate as a novel energy storage medium for pulse forming lines (PFL). In this study, an experimental platform for liquid insulation that is capable of delivering a maximum output voltage of 700 kV and a pulse rise time of approximately 100 ns is employed to examine the breakdown characteristics of PC under different electrode gaps. For comparison, the breakdown characteristics of deionized (DI) water are also investigated. The experiment utilizes a sphere-to-plate electrode configuration with a hemispherical electrode diameter of 5 cm, plate electrode diameter of 9 cm, and an adjustable electrode gap ranging from 0 to 1.5 cm. The results indicate that the breakdown voltages of both PC and DI water increase almost linearly with the electrode gap, whereas the average breakdown field strength decreases exponentially as the electrode gap widens. Unlike DI water, PC does not exhibit polarity effects under the test conditions. However, the insulation performance exhibits a measurable decline after the first breakdown. These findings highlight the advantages and limitations of PC as an energy storage medium and offer valuable insights into its potential applications in related fields. Full article

Solid-State Transformers (SSTs) enable significant improvements in size and functionality compared to conventional power transformers. However, one of the key challenges in Solid-State Transformer design is achieving reliable insulation between the high-voltage and low-voltage sections. This proposal presents the design and optimization of a high-insulation Medium-Frequency Transformer (MFT) for 66 kV grids operating at 50 kHz and delivering up to 75 kW for SST applications using Inductive Power Transfer (IPT) technology. A fixed 50 mm gap between the primary and secondary windings is filled with dielectric oil to enhance insulation. The proposed IPT system employs a double-D coil design developed through iterative 2D and 3D finite element method simulations to optimize the magnetic circuit, thereby significantly reducing stray flux and losses. Notably, the double-D configuration reduces enclosure losses from 269.6 W, observed in a rectangular coil design, to 4.38 W, resulting in an overall system loss reduction of 42.4% while maintaining the electrical parameters required for zero-voltage switching operation. These advancements address the critical limitations in conventional Medium-Frequency Transformers by providing enhanced insulation and improved thermal management. The proposed IPT-based design offers a low-loss solution with easy thermal management for solid-state transformer applications in high-voltage grids. Full article

This paper comprehensively presents an approach for modeling form wound coils of a motor driven by an inverter, with focus on the electric stresses on the coil insulation. A 10 kV SiC testbed for medium voltage form wound coils was developed to support and validate the modeling techniques discussed. A finite element analysis (FEA) model of the motor coil is presented using COMSOL 6.1. The FEA model was used to determine parameters for an electrical model based on the multi-conductor transmission line theory. The linking of these models allows for a rapid analysis of the electrical stresses the insulation can be exposed to. An experimental method for model validation using the empirical transfer function estimation (ETFE) approach to find the impedance response of the testbed for comparison to the proposed electrical model is presented and employed. The paper also uses the model to analyze the impact of insulation delamination and voids and to demonstrate the implementation of a metric called insulation state of health monitoring for both healthy and damaged coils. Full article

This study proposes an electrohydrodynamic multiphysics modeling and finite element analysis technique to accurately simulate corona-streamer discharges in a two-phase flow medium. The discharge phenomenon is modeled as a multiphysics system, coupling the Poisson equation for the electric field with a charge dynamics model based on fluid methods and a thermofluid field for temperature effects. To optimize the numerical simulation, the tip-flat plate electrode model was simplified to two-dimensional axisymmetry, and an unordered lattice network was used to reduce computational time while maintaining high resolution in the region of interest. A high DC voltage was applied to the model to generate a local non-uniform electric field exceeding 10 MV/m, allowing the numerical simulations of ionization, recombination, and charge attachment in the streamer channel. The numerical results were compared with voltage and current measurements from full-scale experiments under identical geometry and initial conditions to verify the effectiveness of the proposed method. The results of this study enhance the understanding of the multiphysical mechanisms behind electrical discharge phenomena and can enable the prediction of insulation failure through simple simulations, eliminating insulation experiments on devices. Full article

As the integration of renewable energy sources into the grid increases, the insulation systems of grid components such as transformers and switchgear encounter significant challenges due to the transients and harmonics generated by power-electronic-based converters. A test generator capable of replicating these component stresses is essential to accurately evaluate these insulation systems under real-grid conditions. This paper proposes a modular cascaded H-bridge-based high-voltage arbitrary waveform generator, prototyped with three stages to generate customized waveforms (triangular, sawtooth, pulse, and complex) up to 8 kV. The H-bridge modules are designed using Si MOSFETs with a maximum blocking voltage of 4.5 kV. The input to the HV H-bridge module is provided by a 10 kV medium-frequency transformer, whose design is described with a focus on the insulation system and winding configuration. This transformer is driven by a zero-voltage switching driver. This arbitrary waveform generator excels in several aspects, including a straightforward design procedure, compact size, high voltage capability, ease of integration, and cost. Full article

The reliability of components of industrial electrical assets fed by power electronics might be at risk due to the type and extent of electrothermal stresses. The move of power electronics toward higher levels of voltage, switching frequency, slew rate, and specific power increases the risk of partial discharge inception and thus of accelerated extrinsic aging and premature failure. The reaction to this challenge is to embrace the concept of partial discharge-free (PD-free) design and operation. This paper presents a PD-free approach to the design of laminated busbars, considering both AC and DC insulation subsystems, and focusing on surface insulation. The availability of a recently proposed model to estimate the inception field is a key tool. The model is validated through PD measurements performed on a laminated busbar, using new automatic software that can identify the type of source generating PD. Combined with electric field calculations, the model provides estimates of the PD inception voltage which are almost coincident with the measurement results. Inception voltages in the order of 10 kV and 20 kV have been observed for AC and DC excitation, respectively. In the case of DC supply, tests at different ambient temperatures, 25 °C and 60 °C, indicate that the inception voltage does not change significantly with temperature. Disposability, scalability to any voltage/power, and capability to work, potentially, for any other type of insulation system, are interesting features of the proposed approach, which are discussed in the paper. Full article