Discharge and mass transfer characteristics of atmospheric pressure gas-solid two-phase gliding arc

In this work,a gas-solid two-phase gliding arc discharge(GS-GAD)reactor was built.Gliding arc was formed in the gap between the blade electrodes,and solid powder was deposited on the sieve plate positioned beneath the blade electrodes.A range of experimental parameters,including the inter-electrode spacing,gas flow rate,applied voltage,and the type of the powder,were systematically varied to elucidate the influence of solid powder matter on the dynamics of gliding arc discharge(GAD).The discharge images were captured by ICCD and digital camera to investigate the mass transfer characteristics of GS-GAD,and the electrical parameters,such as the effective values of voltage,current,and discharge power were record to reveal the discharge characteristics of GS-GAD.The results demonstrate that powder undergoes spontaneous movement towards the upper region of the gliding arc due to the influence of electric field force.Increasing the discharge voltage,decreasing relative dielectric constant of the powder and reducing the electrode-to-sieve-plate distance all contribute to a greater involvement of powder in the GAD process,subsequently resulting in an enhanced powder concentration within the GAD region.Additionally,powder located beneath the gliding arc experiences downward resistance caused by the opposing gas flow and arc.Excessive gas flow rate notably hampers the powder concentration within the discharge region,and the velocity of powder motion in the upper part of the GAD region is reduced.Under the condition of electrode-to-sieve-plate distance of 30 mm,gas flow rate of 1.5 L/min,and peak-to-peak voltage of 31 kV,the best combination of arc gliding and powder spark discharge phenomena can be achieved with the addition of Al_(2)O_(3) powder.

Influence of high-voltage pulse parameters on the propagation of a plasma synthetic jet

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 m J per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s-1 and 100 m s-1,respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s-1 to 93 m s-1. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies(XJ-15, NPG-18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s-1 is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s-1 is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.

Characteristics of the propagation of partial discharge ultrasonic signals on a transformer wall based on Sagnac interference

The acoustic emission(AE)method has been widely recognized for the detection of incipient insulation fault phenomenon(partial discharge,PD)in power transfomiers,nevertheless,the installation and placement of AE sensors should be taken into full consideration.In this manuscript,a three-dimensional multiphysics model was established and simulated to research the characteristics of the propagation in the transformer wall.Furthermore,a piezoelectric transducer was used to detect PD ultrasonic signals and verify the simulation results in the laboratory.To ensure the accuracy of the detection,an optical fiber sensor based on the Sagnac interference principle was designed and adopted.The variation of the amplitude of the ultrasonic signal with distance reveals the characteristics of the ultrasonic signal propagating in the transformer wall.The distribution of sound pressure on the upper and lower surfaces of the simulation model proved that ultrasonic waves propagate in the form of symmetrical Lamb waves in the transformer wall.Moreover,the amplitude of the AE attenuates due to absorption and refraction loss,and local fluctuations on account of acoustic interference.Thus,a stable signal detected by an AE sensor does not represent the absence of PD in a transfomier.To improve the reliability of AE detection,it is proposed in this manuscript that repeated movement of the AE sensor is necessary to obtain a suitable measurement position.Similarly,it is necessary to adjust the position of the AE sensor in order to locate the PD source well.In addition,this study is expected to provide a theoretical analysis and a fiber sensor to address the problem of sensor placement in AE detection.

Numerical study on the modulation of THz wave propagation by collisional microplasma photonic crystal

In order to demonstrate the modulation of terahertz wave propagation in atmospheric pressure microplasmas,in this work,the band structure and the transmission characteristics of a onedimensional collisional microplasma photonic crystal are investigated,using the transfer matrix method.For a lattice constant of 150μm and a plasma width of 100μm,three stopbands of microplasma photonic crystal are observed,in a frequency range of 0.1-5 THz.Firstly,an increase in gas pressure leads to a decrease in the central frequency of the stopband.When the gas pressure increases from 50.5 k Pa to 202 k Pa,the transmission coefficient of the THz wave first increases and then decreases at high frequency,where the wave frequency is much greater than both the plasma frequency and the collision frequency.Secondly,it is interesting to find that the central frequency and the bandwidth of the first THz stopband remain almost unchanged for electron densities of less than 10^15 cm^-3,increasing significantly when the electron density increases up to 10^16 cm^-3.A central frequency shift of 110 GHz,and a bandgap broadening of 200 GHz in the first stopband are observed.In addition,an atmospheric pressure microplasma with the electron density of 1×10^15-6×10^15 cm^-3 is recommended for the modulation of THz wave propagation by plasma photonic crystals.

Hysteresis characteristics of the initiating and extinguishing boundaries in a nanosecond pulsed DBD

The dielectric barrier discharge(DBD)is presently used in many fields,in eluding plasma medicine,surface modification,and ozone synthesis;the influe nee of airflow on the DBD is a widely investigated topic.In this work,a hysteresis characteristic on the initiating and extinguishing boundaries is observed in a nanosecond pulsed DBD,which is sensitive to the variation in the airflow velocities and pulse repetition frequencies(PRFs).It is found that,at a certain airflow velocity,the initiating PRF is higher than the extinguishing PRF.This differenee between the initiating PRF and the extinguishing PRF leads to a hysteresis phenomenon on the initiating and extinguishing boun daries.When the airflow velocity is in creased,both the initiating and extinguishing PRFs are increased and the differenee between the initiating PRF and the extinguishing PRF also increased.The hysteresis width between the initiating and extinguishing boundaries is enhanced.To explain these results,the physical processes involved with the seed particles and the mechanisms of forming discharge channels are discussed.

Plasma propagation in single-particle packed dielectric barrier discharges:joint effects of particle shape and discharge gap

In this work,a single Al_(2)O_(3) particle packed dielectric barrier discharge(DBD)reactor with adjustable discharge gap is built,and the influences of the particle shape(ball and column)and the residual gap between the top electrode and particle on the electrical and optical characteristics of plasma are studied.Our research confirms that streamer discharge and surface discharge are the two main discharge patterns in the single-particle packed DBD reactor.The strong electric field distortion at the top of the ball or column caused by the dielectric polarization effect is an important reason for the formation of streamer discharge.The length of streamer discharge is proportional to the size of the residual gap,but the number of discharge times of a single voltage cycle shows an opposite trend.Compared to the column,a smooth spherical surface is more conducive to the formation of large and uniform surface discharges.The surface discharge area and the discharge intensity reach a maximum when the gap is equal to the diameter of the ball.All in all,the results of this study will provide important theoretical support for the establishment of the synergistic characteristics of discharge and catalysis in plasma catalysis.

Investigation on the characteristics of an atmospheric-pressure microplasma plume confined inside a long capillary tube

An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discharge （DBD）, the ignition voltage of the microplasma decreases from 40 kV to 23.6 kV. Second, although the current density reaches as high as （1.2-7.6）× 10 4A cm-2, comparable to the current density in transient spark discharge, the microplasma plume is nonthermal. Third, it is interesting to observe that the amplitude of the discharge current in a positive cycle of applied voltage is much lower than that in a negative cycle of applied voltage. Fourth, the electron density measured by the Stark broadening of Ar spectral line 696.5 nm reaches as high as 3× 10 16 cm-3, which yields a conductivity of the microplasma column of around 48 S m-1. In addition, the propagation velocity of the microplasma plume, obtained from light signals at different axial positions, ranges from 1 × 10 5 m s-1 to 5× 10 5m s-1. A detailed analysis reveals that the surface charges deposited on the inner wall exert significant influence on the discharge behavior of the microplasma.

Experimental investigation on upstream and downstream discharges in airflows

Dielectric barrier discharge has widely used in airflow control, ignition and combustion, and other applications; the influence of airflow on dielectric barrier discharge is of extensive concern. Previous studies demonstrate that the discharge becomes more uniform and the discharge intensity decreases with increasing of airflow velocity. In this study, we adopt a discharge cell construction with upstream and downstream structure and study the discharge states and intensities. The experimental results demonstrate that within a specific range of airflow speed, the upstream discharge intensity is decreased, and the downstream discharge intensity is enhanced. The physical basis for this phenomenon is proposed as follows： Within a pulse interval time, some particles, such as charged and metastable particles produced by the upstream discharge, could be transported to the downstream region. The concentration of particles in the downstream region is increased, and these particles play a pre-ionization role in the downstream discharge, the intensity of the downstream discharge is enhanced. Further, factors such as the pulse frequency and the distance between electrodes are discussed in detail, along with the conditions for enhancing downstream discharge intensity.

A review on insulation challenges towards electrification of aircraft

Compared to the traditional aircraft,electrification of power system in aircraft has potential to revolutionise the aviation industry.Typically,more-electric aircraft(MEA),even all-electric aircraft has been developed and delivered to decrease the greenhouse gas emission and increase the energy efficiency.The next generation of MEA will operate at high voltage to facilitate the transfer of significant levels of electrical power in an electrified aircraft.However,the higher voltage inevitably leads to an increased risk to the insulation of the electrical components and power system.This study aims to provide a critical overview of the insulation challenges from the perspective of electrified aircraft,typically MEA application.The development of MEA and the special working conditions are explained at the beginning.Then the insulation challenges of power modules,electric machines,aeronautical cables etc.are discussed in detail.Finally,the existing technical barriers and future prospects of insulation for electrified aircraft are summarised.It provides a reference for the future design and test in power system of next generation MEA and related electrified air transportations.

Detection of DC series arc in more electric aircraft power system based on optical spectrometry

Series arcing faults have been recognised as a hazardous phenomenon in the power system of more electric aircraft(MEA),especially with the increasing voltage level and power supply.Instead of the electrical method,the optical method can be used as an approach to detect arc fault with the advantages of fast response and immunity to electromagnetic interference.It is the basis of optical arc detection to determine the distribution spectrum range of direct current(DC)arc fault.Aiming at series arc optical detection in the MEA DC system,a DC series arc test platform was established to measure the series arc spectrum.The spectrum was disassembled though empirical mode decomposition to extract characteristic wavelengths of arc light and denoised by means of wavelet decomposition and reconstruction(wavelet transformation)to reduce equipment noise.To resolve the baseline drift,the baseline of the arc spectrum measured was calculated and corrected based on Savitzky−Golay.The experimental results indicate that there are several series arc characteristic spectra of the MEA DC system,including 309.3 and 324.5 nm in the ultraviolet range.Moreover,the arc spectrum with different metals,copper and aluminium,were contrasted,indicating the arc spectral behaviour is related to the melting/boiling point and chemical properties of the anode material.The measurement of the series arc spectrum makes it more effective to apply optical detection in the MEA discharging faults diagnosis.

Fault diagnosis of the bushing infrared images based on mask R‐CNN and improved PCNN joint algorithm

Bushings are served as an important component of the power transformers;it's of great significance to keep the bushings in good insulation condition.The infrared images of the bushing are proposed to diagnose the fault with the combination of image segmentation and deep learning,including object detection,fault region extraction,and fault diagnosis.By building an object detection system with the frame of Mask Region convolutional neural network(CNN),the bushing frame can be exactly extracted.To distinguish the fault region of bushings and the background,a simple linear iterative clustering‐based pulse coupled neural network is proposed to improve the fault region segmentation performance.Then,two infrared image feature parameters,the relative position and area,are explored to classify fault type effectively based on the K‐means cluster technique.With the proposed joint algorithm on bushing infrared images,the accuracy reaches 98%,compared with 44%by the conventional CNN classification method.The integrated algorithm provides a feasible and advantageous solution for the field application of bushing image‐based diagnosis.

Propagation and localisation of partial discharge in transformer bushing based on ultra-high frequency technique

As an essential component of power transformers,the detection and diagnosis of incipient partial discharge(PD)activities of bushings are of great significance.A 35-kV oil-impregnated paper(OIP)bushing is investigated.The bushing is modelled by coaxial theory and electromagnetic(EM)simulation.As the paths of PD-induced ultra-high frequency(UHF)signal propagating in the bushing are OIPs and oil gap,small attenuation during signal propagation is seen.Since OIP is composed of het-erogeneous media compared with pure oil,there will be relatively less UHF signal leakage from OIPs,whereas more leakage from the oil gap.This leakage provides the possibility of non-contact detection outside the bushing by UHF method.PD mea-surements with UHF method are carried out on the bushing.Then,the minimum energy method is used to extract time-difference-of-arrival(TDOA),and Chan al-gorithm is adopted to locate points of UHF signal radiation.High accuracy locating with a small error of 15 cm has been achieved.The contactless UHF method-based tests have demonstrated the effectiveness of online monitoring and locating of bushing PD.

Physical-data Fusion Modeling Method for Energy Consumption Analysis of Smart Building

The energy consumption of buildings accounts for approximately 40%of total energy consumption.An accurate energy consumption analysis of buildings can not only promise significant energy savings but also help estimate the demand response potential more accurately,and consequently brings benefits to the upstream power grid.This paper proposes a novel physical-data fusion modeling(PFM)method for modeling smart buildings that can accurately assess energy consumption.First,a thermal process model of buildings and an electrical load model that focus on building heating,ventilation,and air conditioning(HVAC)systems are presented to analyze the thermal-electrical conversion process of energy consumption of buildings.Second,the PFM method is used to improve the accuracy of the energy consumption analysis model for buildings by modifying the parameters that are difficult to measure in the physical model(i.e.,it effectively modifies the electrical load model based on the proposed PFM method).Finally,case studies involving a real-world dataset recorded in a high-tech park in Changzhou,China,demonstrate that the proposed method exhibits superior performance with respect to the traditional physical modeling(TPM)method and data-driven modeling(DDM)method in terms of the achieved accuracy.