Gas Insulated Research Articles

Multi-source partial discharge diagnosis in gas-insulated switchgear via zero-shot learning

Partial discharge (PD) diagnosis in gas insulation switchgear (GIS) has been continuously studied as a hot issue. The diagnostic model developed at this stage requires the possible combination of all single PDs, and each combination has sufficient data. However, the demand for the number of multi-source PD samples increases in the form of an index due to the accidental and concurrency of different types of PD, where it is unrealistic to collect sufficient PD samples. To this end, we proposed zero-shot learning (ZL) to diagnose multi-source PD. The ZL diagnosis multi-source PD only required single PD for training. Specifically, an attention residual network was introduced for feature extraction. Then, a novel semantic descriptor was proposed to obtain the semantic attributes, and the semantic embedded features were mapped to the visual space with a full connection network. Finally, the relationship network adopted the similarity between the visual features and semantic embedded features, and the multi-source PD diagnosis was realized. In addition, the multi-source PD experiment in GIS was constructed to verify the proposed ZL. The experimental results demonstrated that the ZL could achieve 90.25 % accuracy when only single PD participated in the training. It provided novel solutions for the diagnosis of multi-source PD in GIS.

Multi-pass Differential Photoacoustic Sensor for Real-Time Measurement of SF6Decomposition Component H2S at the ppb Level

We designed and implemented a photoacoustic (PA) sensor for H2S detection in SF6 background gas based on a multi-pass differential photoacoustic cell (MDPC) and a near-infrared distributed feedback (DFB) laser. In the MDPC apparatus, two resonators with identical geometric parameters were vertically and symmetrically embedded. The differential processing algorithm of two phase-reversed signals realized the effective enhancement of the PA signal and suppressed the flow noise in the dynamic sampling process. In addition, the λ/4 buffer chamber in the MDPC was utilized as a muffler to further reduce the flow noise and realize the dynamic detection of H2S. The collimated excitation light was reflected 30 times in a multi-pass structure constituted of two gold-plated concave mirrors, and an absorption path length of 4.92 m was achieved. Due to the high gas density of SF6, the relationship between the signal-to-noise ratio (SNR) and the gas flow was different between SF6 and N2 background gases. The maximum flow rate of the characteristic gas components detected in the SF6 background is 150 standard cubic centimeters per minute (SCCM), which is lower than 350 SCCM in N2. The linearity property was analyzed, and the results show that the sensitivity of the sensor to H2S in the SF6 background was 27.3 μV/ppm. With the structure, parameters, temperature, gas flow, and natural frequency of the MDPC been optimized, a minimum detection limit (MDL) of 11 ppb was reached with an averaging time of 1000 s, which furnished an effective preventive implement for the safe operation of gas insulation equipment.

A semi-empirical algorithm for determining the impulse characteristics of gas-insulated two-electrode systems in the vicinity of Paschen minimum with and without taking into account the spark channel thermoionization time

The impulse characteristic represents the response of the gas insulation to the impulse load. There is no rational way to determine it, since it must include all pulse shapes and all probability quantiles of a random breakdown event. Near Paschen minimum is the operating point of gas surge arresters. For this reason, the results presented in this paper are important for the coordination of insulation at the low-voltage level. The semi-empirical algorithm derived in this paper is simple and allows obtaining impulse characteristics based on a small number of measurements. The paper presents two variants of the derived algorithm. One with and one without taking into account the thermoionization time of the streamer channel. Both variants were experimentally verified in well-controlled laboratory conditions and good results were obtained from the point of view of engineering practice. Of course, the algorithm which includes the thermoionization time of the spark channel gave more exact results. However, even in that case, an improvement can be made by observing the thermoionization process as a stochastic phenomenon. In this sense, suggestions for further improvement of the proposed algorithm are given.

Particle-Triggered Corona Discharge Characteristics in Air Insulation Under DC Voltage

Under a dc stress, a wire particle within gas insulation will exhibit complex motion behavior, leading to more challenges to detect its existence. Therefore, this work deals with an investigation of corona discharge characteristics generated from a wire particle with different particle positions in an air gap. Three different wire particles are prepared in this investigation. The particle is placed between parallel-plane electrodes with a fixed gap of 20 mm. Five different positions are evaluated to study the partial discharge (PD) behavior generated from the wire particle. The exponential probability distribution is used to evaluate the pulse occurrences from different positions. Pulse sequence analysis (PSA) technique is employed, and an interpretation algorithm is introduced to understand the discharge pattern. The results show that each of the particle positions creates a unique pattern, which discharge mechanism behind the pattern is explained. From the pattern observation, a wire particle has single cluster of corona type as attached to the electrode while multiclusters are found when it is floating in the gap. Moreover, it is also found that different particle lengths are also affecting the discharge pattern characteristic.

Assessment on the Application Feasibility of C4F7N/CO2 for Eco-Friendly Gas Insulated Transformer

Sulfur hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) gas insulated transformers (GIT) have been widely used in power transmission and distribution system due to the advantages of incombustible, explosion-proof, maintenance-free. However, SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is listed as the strongest greenhouse gas with the global warming potential of 23500. Recently, perfluoroisobutyronitrile (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N) gas mixture has attracted wide attention as eco-friendly gas insulating medium. Herein, we evaluated the application feasibility of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture for GIT considering the insulation, thermal conductivity and materials compatibility. The AC breakdown, partial discharge, heat dissipation and gas compatibility with typical materials in GIT were systematically investigated. We found that 15% C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N / 85% CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture demonstrated superior dielectric strength and self-recovery performance. The metal protrusion and PET surface partial discharge caused the decomposition of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N to mainly produce CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> . The thermal conductivity of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is lower than that of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , resulting in an average temperature rise of 63.7 K ~ 86.9 K under 100% load. Besides, the gas is compatible with most typical materials used in GIT. This work can provide guidance for the development of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture based GIT.

Theoretical Analysis of External Insulation of Typical Electric Equipment under Impulse Voltage and Research on Design and Verification Method of Margin

Lightning impulse voltage, one of the typical characteristic working conditions for assessing high-voltage power equipment, can be divided into two forms, namely full wave, and chopped wave. The external structure size of the power equipment directly depends on the lightning impulse voltage, but how lightning impulse voltage relates to the external structure size of the power equipment needs to be carefully studied. Firstly, the theoretical analytical expressions of full wave and chopped wave lightning waveforms are given from the perspective of theoretical formulas. And the lightning waveform is considered to be a polynomial superposition of exponential functions. Based on this, the discussion is divided into two typical insulation structure scenarios: 1) the verification and analysis of the space net distance of a 10 m class super long composite insulator; 2) the analysis of the relationship between the breakdown electric field strength of 5 mm tiny oil gap and oil gap spacing. Further, the lightning impulse voltage test was conducted for large hardware structures, and the corona layer mathematical model was obtained through the precise observation of the structure with the ultraviolet imager. The research shows that the lightning impulse voltage mainly checks the external insulation performance of large insulation structures such as bushings and post-insulators. For the internal oil gap duct structure of the large converter transformer, the lightning impulse voltage mainly checks the micro gap insulation strength. Lightning impulse voltage also has a breakdown effect on SF6 insulation gas, but its internal gas decomposition mechanism needs theoretical and experimental analysis urgently. The research content of this paper has certain theoretical and practical guiding value for the optimization design of large insulation structures under lightning impulse voltage.

Multi-dimensional functionally graded insulator for HVDC compact gas insulated apparatus

Gas insulated switchgear may be exposed to AC-DC mixed voltages in bipolar high voltage direct current (HVDC) systems. To improve the insulation performance of the epoxy insulator, this paper develops the multi-dimensional functionally graded materials (MFGM), which combines the bulk permittivity graded materials (ϵ-FGM) and the surface nonlinear conductivity materials (SNCM). The ϵ-FGM bulk and the SNCM layer of the MFGM insulator were prepared by the layer-by-layer pouring method and the air spraying technology. Results show that the electric field strength of the MFGM insulator around the HV triple junction is reduced by over 37% and 39% under AC and DC voltages. Compared with the uniform insulator, the AC and the DC flashover voltages of the MFGM insulator are raised by 17.5% and 27.5%, respectively. The MFGM insulator can adapt to both stationary and transient conditions, and thus has a promising application in HVDC compact gas-insulated apparatuses.

An investigation of the flow structure beneath solitary waves with constant vorticity on a conducting fluid under normal electric fields

The motion of an interface separating two fluids under the effect of electric fields is a subject that has picked the attention of researchers from different areas. While there is an abundance of studies investigating the free surface wave properties, very few works have examined the associated velocity field within the bulk of the fluid. Therefore, in this paper, we investigate numerically the flow structure beneath solitary waves with constant vorticity on an inviscid conducting fluid bounded above by a dielectric gas under normal electric fields in the framework of a weakly nonlinear theory. Elevation and depression solitary waves with constant vorticity are computed by a pseudo-spectral method, and a parameter sweep on the intensity of the electric field is carried out to study its role in the appearance of stagnation points. We find that for elevation solitary waves, the location of stagnation points does not change significantly with a variation of the electric field. For depression solitary waves, on the other hand, the electric field acts as a catalyzer that makes possible the appearance of stagnation points. In the sense that in its absence, there are no stagnation points.

Prediction models of the ionization coefficient and ionization cross-section based on multi-layer molecular parameters

Prediction models were proposed to estimate the reduced Townsend ionization coefficient and ionization cross-section. A shape function of the reduced Townsend ionization coefficient curves was derived from the ionization collision probability model. The function had three parameters: the first ionization potential energy, A α , and B α . A α and B α were related to the molecule symmetry and size. The polarization of molecules could characterize the molecule symmetry. The multi-layer molecular cross-section (MMCS) was proposed to describe the contributions of electrons and molecule radius on different molecule surfaces to collisions. A prediction model of the ionization cross-section was also proposed based on A α . The molecule parameters were calculated by the Becke3–Lee–Yang–Parr (B3LYP) method and the 6–311G** basis set. We used available data of 30 and 23 gases, respectively, to build the prediction models of reduced Townsend ionization coefficients and ionization cross-sections. The relationships between the molecular parameters A α and B α and the ionization cross-section were built up via nonlinear fittings. The determination coefficients R 2 of A α , B α , and the ionization cross-section were 0.877, 0.887, and 0.838, respectively. The results showed that the accuracy of models was positively correlated with the molecule symmetry and reduced electric field. This was mainly related to the accuracy of the MMCS model in predicting A α . The MMCS model needed to be improved to describe the collision direction selectivity caused by the molecule asymmetry. Under a high reduced electric field, that error of A α had less influence on the prediction results. However, the prediction results for single atoms with high symmetry were poor. This may be due to the absolute error of the model close to single atoms’ reduced Townsend ionization coefficients. The models could provide the basis for gas insulation prediction and discharge calculations, especially for symmetric molecules under a high electric field.

Penilaian Kualitas Gas SF6 Pada GISTET 500/150 kV

The number of Gas Insulated Switchgear (GIS) in operation is increasing in Indonesia. GIS failure requires expensive costs andextensive blackouts. Asset reliability management such as SF6 is needed to ensure GIS performance. Several studies have tested thequality of SF6 gas to assess the feasibility and operation of the GIS. However, a complete GIS feasibility study based on SF6 gas qualityparameters has not found. In this study, a condition assessment of the GISTET Kembangan 500/150 kV was carried out based on applicableinternational standards. There is an interesting phenomenon in the form of dew point anomaly and moisture content in severalcompartments, indicating that the gas is moist. The results of this study indicate the operational feasibility of the GISTET Kembangan500/150 kV , the effect of high humidity on GIS operations, and maintenance recommendations.

Studi Kelayakan Gas Insulated Switchgear di PT. Paiton Operation &amp; Maintenance Indonesia Unit 8

Protection systems are a collection of components that have the same purpose to protect or secure. One of the existing protection systems in the generator is switchgear. At PT. Paiton Operation &amp; Maintenance Indonesia Unit 8 using a switchgear insulated with SF6 gas is called gas insulated switchgear. Gas Insulated Switchgear is the newest of the Switchyard innovations. Innovations that have been developed from air isolation into gas insulation have fewer land use advantages and a better level of density. In determining the feasibility of gas insulated switchgear PT. Paiton Operation &amp; Maintenance Indonesia performs tests consisting of insulation resistance measurements, resistance measurements, gas leakage checks, polarity checking, gas density detectors, testing duration closure and circuit breaker opening. Each test has a pre-defined value limit. Gas Insulated switchgear is said to be feasible to operate when it meets the specified value limits on each test.

Transient thermal analysis of gas insulated switchgear modules using thermal network approach

Abstract Thermal analysis of Gas Insulated Switchgear (GIS) modules is of utmost important to optimize their dimensions for higher current ratings. Temperature rise test simulation has to be carried out on GIS modules to ensure that the temperature rise of modules shall not exceed the allowable temperature limits. The analyses also help to estimate the time duration required for GIS modules to reach steady state temperature as per IEC 62271-102 and IEC 61869-2. In the present study, to conduct transient thermal analysis, a novel Thermal Network Model (TNM) has been proposed for gas insulated switchgear equipment of two important modules i.e., disconnector switch (DS) and current transformer (CT). GISmodules.m program is developed in the study to analyze effect of various parameters like type of material being used for HT conductor and enclosure, rated voltage, rated current and enclosure current on time varying behavior of temperature rise of conductor and enclosure. Finally, the temperature rise test has also been carried out on 245 kV and 420 kV GIS modules at rated current ranging from 3150 A to 4000 A. When the transient temperature measurements conducted on 420 kV DS and compared with the results obtained through proposed TNM based analyses, it is clear that temperatures are within difference of 3.3 °C for conductor and 1.2 °C for enclosure. Further, it is evident that the time taken for conductor and enclosure to reach steady state temperature is about 8–10 h depending on enclosure current magnitude and GIS configuration.

Dielectric Withstand of a Mixture of Fluoroketone C5F10O and Air When Cooling Below its Dew Point

We investigate the temperature dependence of the dielectric withstand of a specific gas mixture consisting of a C5-fluoroketone (C5-FK) and air below its dew point. Both lightning impulse (LI) and ac dielectric withstand are investigated. Using standard testing techniques, it is found that the ac withstand stays constant until the dew point of the mixture and then decreases following the predicted withstand for the concentration of fluoroketone at the given temperature. On the contrary, when measuring the LI withstand using a common dielectric testing approach, one does not find a decrease but instead, in certain cases, an increase of the dielectric performance. We attribute this behavior to the charging droplets of the condensate fluoroketone after each dielectric breakdown event. Flipping the polarization of the LI after every breakdown event reestablishes the behavior seen with the ac stress application. Overall, these results confirm that the dielectric behavior of this alternative insulation gas for electrical devices is well understood and that the dielectric withstand at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 40\,\,^{\circ }\text{C}$ </tex-math></inline-formula> of a mixture specified for medium-voltage applications down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 25\,\,^{\circ }\text{C}$ </tex-math></inline-formula> still shows 80% of the dielectric withstand measured at the dew point.

Strength Analysis of Tubular Oil to Oil Cable Box Power Transformer GIS 60 MVA in the Case of Voltage Arc Energy Using the Finite Element Analysis Method

The power transformer is an essential part of the electrical distribution system because it must be reliable and safe from fire and explosions, one of which is brought on by internal oil arching that results in overheating. In general, on the high voltage side of the transformer, there are power transformers fitted with tubular oil to oil cable boxes for the demands of the client. The tubular oil to oil cable box is installed to reduce space in substations with limited space as well as to boost safety against weather and pollution at the high voltage terminal section of power transformers. The goal of this investigation is to determine the cause of an explosion that occurred in a tubular oil-to-oil cable box on the high voltage side of a Gas Insulation System (GIS) type power transformer with a power of 60 MVA and a voltage rating of 150/20 kV. For all parties involved, this incident will serve as a lesson about what to avoid doing in the future with similar power transformers. In this study, we will use a qualitative method with Finite Element Analysis (FEA), which takes samples and data of a Gas Insulation System (GIS) power transformer on the high voltage side, especially in the analysis of tubular strength. This power transformer has a voltage rating of 150/20 kV and a power of 60 MVA. Applying normal pressure to a pressure that could harm the tubular oil to oil cable box can prevent damage. The tubular oil to oil cable box is built of SS400 material and has an 8mm thickness so that it can be determined how robust it is.

Study of Polarization Sensitivity of UHF Sensor for Partial Discharge Detection in Gas Insulated Switchgear

Polarization sensitivity of ultrahigh-frequency (UHF) sensor for detecting partial discharge (PD) activity in gas insulated switchgear (GIS) is studied using a tapered planar spiral (TPS) antenna. The TPS antenna with coplanar broadband microstrip line balun was optimized for circular polarization (CP) over 0.5–3.5 GHz. The fabricated TPS antenna with protective cover and cavity backing has a unidirectional radiation pattern, a −10 dB bandwidth (BW) of 0.5–3.5 GHz, and an axial ratio (AR) < 3 dB over 0.57–3.5 GHz. The polarization sensitivity of TPS to detect PDs was studied for Corona and particle movement (PM)-induced PDs in L Section of a metal encapsulated GIS setup. PD induced UHF measurements of circularly polarized TPS for 0°, 90°, and 180° orientations inside L-GIS gathered before and after L bend were compared with a linearly polarized (LP) UHF antenna with comparable gain and receive pattern. PD measurements gathered after L bend show nearly twofold enhancement in signal amplitude for the TPS compared to the LP sensor. The reduction in the ratio of UHF sensor amplitude after and before L bend between 0° and 90° sensor orientations was less than 8% for the TPS compared to 19%–27% observed for the LP sensor. It is concluded that UHF sensor with broadband CP is desirable for PD sensing in GIS.

Time-Optimal Trajectory Planning of Flexible Manipulator Moving along Multi-Constraint Continuous Path and Avoiding Obstacles

To solve the trajectory planning problem of the flexible manipulator under various constraints such as end-camera attitude, drive space, and obstacles during video inspection along a continuous path in narrow three-dimensional space, this paper proposes a time-optimal trajectory planning method from the initial configuration to the final configuration. The trajectory planning problem is transformed into a multi-constraint optimization problem. First, to realize continuous video inspection in an unstructured complex environment, by analyzing the geometric model of the two-segment flexible manipulator with a camera at the end, the pose constraints between the camera and the shooting surface are formulated by the space vector method, the driving constraints are formulated based on kinematics, and the obstacle constraints are formulated by space mapping. Then, a multi-constraint optimization model is constructed to generate the smooth trajectory of the drive cable of the flexible manipulator by minimizing the total time of continuous path motion. Compared with the conventional point-to-point collision avoidance planning solution method, this paper starts from the global perspective and investigates the less considered continuous path trajectory planning problem; also, the swarm intelligence algorithm artificial jellyfish search algorithm (JS) is employed to optimize the solution and find the minimum time trajectory conforming to a variety of complex constraints. Finally, a simulation is conducted with CoppeliaSim, and the continuous path video inspection experiment is carried out in the 500KV GIS (Gas Insulated Switchgear) equipment, the simulation and experimental results indicate that the planned drive cable trajectory is smooth and effective. In addition, each path point is tracked and obstacles are avoided safely. When the flexible manipulator moves along the whole path, the pose of the camera satisfies the relaxed attitude constrain The proposed method can guide the two-segment flexible manipulator to complete the continuous video inspection task of the GIS cavity wall and conductive column surface.

Mechanistic and Kinetic Investigations on Decomposition of Trifluoromethanesulfonyl Fluoride in the Presence of Water Vapor and Electric Field

As a potential insulation gas to replace sulfur hexafluoride (SF6) due to environmental concerns, trifluoromethanesulonyl fluoride (CF3SO2F) has attracted great interests in various high-voltage electric applications. Thermal stability of CF3SO2F plays an important role in the rational design of the gas-insulated electric equipment. Unimolecular decomposition of CF3SO2F was investigated using high-level ab initio methods including the explicitly correlated RCCSD(T)-F12, the composite ROCBS-QB3, and the multireference RS2 extrapolated to complete basis set limit on the basis of M06-2X-, B2PLYPD3-, and CCSD-optimized geometrical parameters. Rate coefficients and decomposition temperatures were simulated using master equations. CF3SO2F decomposes predominantly via a simple C-S bond cleavage to form CF3 and SO2F, accompanied by a roaming induced F-abstraction detour to release CF4 and SO2, or isomerizes via CF3 migration to the more stable CF3OSFO followed by the production of CF2O and SOF2. Various characteristic decomposition products (e.g., CF4, C2F6, CF2O, SO2, SOF2, SO2F2, CF3H, and so on.) have been identified theoretically through secondary reactions and hydrolysis of CF3SO2F in the presence of water vapor. Electronic structures and stability of CF3SO2F could be affected significantly by the external electric field orientated along the S-C bond. The field-dependent electron-molecule capture rates support that CF3SO2F is superior to SF6 in dielectric strength. The present computational findings shed light on the practical use of CF3SO2F as the replacement gas for SF6.

Development of HVDC Gas-Insulated Components for the Power Supply of Neutral Beam Injectors

The development of High Voltage Direct Current Gas-Insulated components that will be employed for the power supply of Neutral Beam Injectors, requires specific numerical tools to analyze the electric field distribution, with the purpose of supporting the engineering and operational phases.The tools must comply with the nonlinearity of the material properties of solid insulators and the transport mechanisms in the dielectric gas. Despite its high Global Warming Potential, SF6 will be considered as the baseline dielectric gas for the development of HVDC gas-insulated components to be used for the Acceleration Grid Power Supply of Neutral Beam Injectors. Attention especially to the mechanisms driving to an increase of leakage current flowing in the gas, thus giving rise to possible discharge phenomena is here placed, mainly focusing on radiation and injection regimes. The described methodologies are adopted for the numerical modeling of the 500 kV DC gas-insulated components that will be used for the power supply of the Neutral Beam Injector of the Divertor Tokamak Test facility. In particular, a conceptual design of the SF6 Transmission Line and the SF6-air bushing is conceived.

A Field High Resolution Measurement Method for Irregular Surface Electrostatic Potential

Characterized by noninvasiveness and high sensitivity, the noncontact electrostatic testing technology has been widely used in scientific research and engineering practices such as electrostatic charge imaging, high-voltage insulator analysis, biological sensing, and gas—solid two-phase flow parameter measurement. However, in many practical applications, scanning electric potential microscope (SEPM) technologies focusing on high spatial resolution cannot meet the testing requirements of charged objects with irregular 3-D structures and flexible activities. Based on the principle of direct inductive electrostatic potential measurement and a six-axis robot arm, a 3-D scanning method for noncontact electrostatic potential measurement is proposed in this article. A low-noise electrostatic potential sensor with both high sensitivity and high accuracy was designed via positive feedback circuit technology. A calibration system was built, which has an adjustable excitation signal, progressive spatial accuracy, and variable 3-D attitude. The experimental data verify the effectiveness of this method. The correlation between the signal characteristics and the physical size of the calibration device was statistically analyzed. The effects of parameters such as the amplitude and frequency of the excitation signal, speed, and normal distance of the robot arm scanning on the resolution of the test results were investigated. The testing results show that the 3-D spatial resolution of dc and low-frequency ac potential distribution reached 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> .

Effect of Working Coefficient on Induced Breakdown Characteristics of Plasma-Triggered-Based Gas Gap Switch in Fast Bypass Conditions

Gas gap switch (GGS) has obvious advantages in fast bypass operation, quick response, simple structure, and strong controllability. The working coefficient (i.e., the ratio of the main gap working voltage to the steady-state breakdown voltage) of GGS is mainly affected by the working voltage, the main gap distance, the type of trigger gas, and the pressure. However, the research mostly focuses on the influence of the above single factors on the trigger performance of GGS. There is a lack of studies on the induced breakdown characteristics of GGS considering the variation of the working coefficient under different factors. In this article, a research platform about the induced breakdown of GGS is established. It is shown that the working process of the GGS trigger cavity is divided into the high voltage pulse prebreakdown stage in the first cavity, the discharge ablation stage in the first cavity, and the discharge ablation stage in the second cavity. With the increase of the working voltage, the critical trigger capacitor voltage is lower, and the plasma jet characteristic parameters are decreased gradually during the critical conduction. The conduction time delay and time delay jitter are decreased rapidly, the triggering stability is significantly improved. Changing the main gap distance, the discharge channel shape is a significant difference at the moment of GGS-induced breakdown. And the electric characteristics of plasma jets are varied obviously. The high trigger gas pressure hinders the development of the plasma jet and causes a greater trigger jitter. With the increase of SF6 content in the trigger environment, the characteristic parameters of GGS decrease obviously. The strong insulation and electronegative gas seriously constrain the plasma jet capability. The research results can provide theoretical guidance for the improvement of trigger stability and the selection of trigger condition parameters of plasma-triggered-based gas switches used in fast bypass conditions.