Average Discharge Current Research Articles

Investigation of the Effect of Magnetic Field and Propellant on Hall Thruster’s Stability via a 0D Model

Hall thrusters are plasma-based devices that have established themselves as one of the most attractive and mature electric propulsion technologies for space applications. These devices often operate in a regime characterized by low frequency, large amplitude oscillations of the discharge current, which is commonly referred to as the ‘breathing mode’. The intensity of these oscillations depends on the thruster’s design and operating conditions and can reach values of the order of the average discharge current, posing issues for the thruster’s performance and for coupling with the driving electronics. A 0D model of the thruster discharge was developed to investigate the core physical mechanisms leading to the onset and sustenance of the breathing mode. The model was found to be capable of reproducing oscillations with characteristics in line with those observed in the breathing mode. In this work, we extend the use of the 0D model to investigate the effect of the magnetic field intensity and of different propellants on the system stability.

Close accord on partial discharge diagnosis during voltage harmonics in electric motors fed by variable frequency drives

AbstractPartial discharge (PD) diagnostics test is a reliable solution for estimating insulation health conditions in power system components. During laboratory PD diagnostics, the effect of harmonic components in the voltage waveform generated by variable frequency drives (VFD) fed electric motors (EMs) is often overlooked. As VFD‐fed EMs operate at low speeds, the harmonic concentration in the voltage increases. It has been found that PD activity in VFD‐fed EM is significantly affected by the addition of harmonic components in the voltage, thus making it necessary to consider their impact when performing true PD diagnostics. This paper investigates the influence of voltage harmonic distortion produced in VFD‐fed EM on PD severity and the subsequent insulation degradation. Eight VFD‐fed EM are used to study the PD behaviour under different levels of harmonic pollution. The PD characteristics, such as inception voltage, pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate, are determined. Using probability distribution functions, PD activity and severity at various voltage harmonic levels are estimated. The proposed technique can be used to plan the maintenance activities that ensure the reliability for industrial applications dealing with the voltage harmonic distortion.

Investigating the progression of insulation degradation in power cable based on partial discharge measurements

Assessments of aging and insulation degradation in power components are important to observe and track their condition during operation. Partial discharge (PD) diagnostics is an efficient method for health estimation of the components’ insulation. PD is initiated when the dielectric strength of localized insulation part is decreased. The intensity of PD increases with time, which may lead to insulation failure. This paper investigates the influence of the electrical stresses on the behavior of PD activity in medium voltage (MV) cable containing insulation defects. For this purpose, insulation defects such as internal, surface, and corona are developed in the MV cable environment under laboratory conditions. PD behavior is studied in these defects at gradually increased voltage levels by observing different PD characteristic features including PD inception voltage (PDIV), pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. The Tobit regression model is developed for these progressing defects to identify the trends and to predict the behavior based on PD characteristic features. The presented work proposes a framework for the evaluation of the progression of insulation degradation due to increased electrical stress. The study is carried out on XLPE cables, however, the developed approach can be equally implemented on other types of dielectrics and components.

Negative DC corona patterns for different wire particle geometries in air insulation

This work deals with an investigation of negative corona discharge generated from standing wire particles in air insulation. Eight samples from different particle lengths and diameters were studied to understand the effect of particle geometries on discharge characteristics. The particle was stood artificially on the ground inside parallel plane electrodes and was energized with a positive HVDC generator. Pulse sequence analysis (PSA) technique was used to evaluate the corona discharge patterns and behaviors. Under the same applied voltage, it is concluded that an increase in particle length causes a rising trend on the average discharge current and pulse magnitude, as well as the pulses appear more frequent and fluctuate. Meanwhile, variation of the particle diameter shows that a larger particle size generates fewer pulses and a lower average discharge current. However, the pulse magnitude is higher and appears randomly with larger particle diameter. A simulation model based on Finite Element Method (FEM) was also established to explain the behaviors better. It is found that the pulse repetition rate is related to the electric field distribution and negative ions movement, while the pulse magnitude is related to ionization rate and positive ions velocity.

Investigation of flexible electrochemical storage with Li+/PVdF-HFP/PEO blend

ABSTRACT Design and development of lithium ion batteries with flexible solid polymer electrolyte along with high ionic conductivity is crucial and challenging so as to protect from electrical short circuits within electrochemical devices. The present research work describes the fabrication of lithium based solid polymer electrolytes (LSPEs) using polymer blends of poly (vinylidene fluoride- hexafluoropropylene) (PVdF-HFP), poly (ethylene oxide) (PEO) with selective weight ratios of lithium trifluoromethanesulfonate (LiCF3SO3) salt by using solution-cast approach. The scanning electron microscopy (SEM) exposed morphology of LSPE membranes depicts crosslinking of polymer network with salt elevates strong dissociation behavior of LiCF3SO3. The amorphous behavior of LSPEs explored using X-ray diffraction (XRD) crystallographs clearly accommodates reduction of average crystallite size from 10─6 m to 10─9 m. The complexation studies, bond length and force constants calculations, interaction of ions, ionic pairs and aggregates of LiCF3SO3 in LSPE films were briefly analyzed using Fourier transform infrared spectroscopy (FTIR). IR modes correspond to [δs (SO3)], [υas (SO3)], [υas (CF3)], and amorphous phase of PVdF-HFP results in complexation, whereas IR modes correspond to [δas (SO3)], [δs (CF3)], [δas (CF3)], [υs (SO3)], C=O and β-phase of PVdF-HFP attributes ionic pairs and aggregation phenomena. The [υs (SO3)] mode contribution toward ionic conductivity was detailed. The ionic conductivity (σionic) values were estimated using Electrochemical impedance spectroscopy (EIS). The σionic values were enhanced from 10─7 S/cm to 10─4 S/cm as salt concentration increases. Charge accumulation, ionic strength, and transference number analysis of LSPE membranes were investigated using Chronoamperometry and Cyclic Voltammetry. Further, we have fabricated flexible electrochemical storage device (FESD) which are accentuating carriers of smart electronics technology (SET) in terms of foldable and stretchable electronic devices. We have explored discharge characteristics of our FESD with an average discharge current of 3 mA for 25 hours and denoted using 0.04C rating.

Characterization of hexamethyldisiloxane plasma polymerization in a DC glow discharge in an argon flow

This work aims to study hexamethyldisiloxane (HMDSO) plasma polymerization in a low-pressure glow discharge in a gas flow. HMDSO was activated in a plasma-chemical reactor with a DC glow discharge in an argon flow. The argon flow (the mass flow rate was 230 mg/min) was injected in the direction of the anode from the cathode. HMDSO vapors were injected into the plasma-chemical reactor either through the hollow cathode or through the inlet located between the cathode and the anode. Polymer coatings were deposited on the substrates located in a vacuum chamber. Plasma polymerization was characterized based on the mass of coatings deposited under varying external conditions: the HMDSO mass flow rate (1–10 mg/min), the average discharge current (6–60 mA), and the discharge power (6–30 W). The operation modes of the plasma-chemical system were determined. The chemical structure of the coatings was analyzed using the infrared spectroscopy. The processes occurring in different regions of the glow discharge and at the interface near the substrate surface are proposed. A DC glow discharge in a gas flow can be used for local deposition of polymer coatings on the surface of dielectric or conductive materials.

Influence of Voltage Harmonics on Partial Discharge Diagnostics in Electric Motors Fed by Variable-Frequency Drives

Typically, in partial discharges (PD) diagnostics tests carried out in a laboratory, harmonic content in a voltage waveform is ignored. However, during the operation of variable-frequency drives (VFD)-fed electric motors, the distorted voltage waveform is produced due to the addition of harmonics components in the sinusoidal voltage waveform. The distortion level increases when the VFD is operated at a lower speed ratio. The additional spectral components in the applied voltage waveform can have a significant impact on the PD behavior in the insulation of the electric motor. Therefore, during online PD monitoring, overlooking the harmonic regime in the applied voltage may lead to a false interpretation of PD data. This article investigates the influence of voltage harmonics distortion produced during the variable-speed operation of VFD on PD characteristics. For this purpose, online PD measurements have been carried out by performing a series of experiments on eight VFD-fed motors under variable operating conditions. The PD severity at different harmonic compositions is experimentally investigated by determining various PD characteristic parameters including PD inception voltage, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. Also, two terms Gaussian models have been mathematically developed using 288 data samples to quantify the variations in PD characteristic parameters against distortion parameters. The article proposes a framework for properly evaluating harmonics impact in PD for electric motors and correctly estimating stator insulation degradation.

Design and application of electromechanical flywheel hybrid device for electric vehicle

The electromechanical flywheel hybrid power device has the dual attributes of energy supply and power output, which can provide more design space for the optimization of vehicle energy utilization efficiency. It involves two key problems of device parameters design and energy management. Therefore, the optimization design of electromechanical flywheel device’s parameters and the energy management strategy are the main research objects in this paper. Firstly, based on the working principle of planetary gear mechanism, the dynamic characteristics of electromechanical flywheel device under different topological structure schemes are analyzed, and the design schemes of speed regulating motor connecting to the sun gear, flywheel connecting to the ring gear and output end connecting to the planet carrier are determined. Then, according to the dynamic characteristics of the vehicle, the parameters of flywheel, speed regulating motor and planetary gear mechanism were designed. Furthermore, considering the state of energy (SOE) of the electromechanical flywheel device, 15 working modes of the vehicle were designed, and the corresponding energy management strategies were proposed. Finally, a vehicle test platform was constructed to analyze the dynamic and economic performances of the electromechanical flywheel hybrid electric vehicle. Results show that, compared with the original vehicle driven by a single motor of the front axle, owing to the power intervention of the electromechanical flywheel hybrid device, the average acceleration from 0 km/h to 100 km/h is increased by 22.32% and the acceleration time is reduced by 18.25%, which effectively improves the vehicle dynamic performance. Moreover, the new hybrid system designed is conducive to the miniaturization design of the drive motor, increasing the load rate of the motor and improving the efficiency of powertrain system. With the advantage of short-term energy supply of electromechanical flywheel, the average discharge current of lithium battery can be reduced to improve its efficiency. Under J1015, NEDC and HWFET cycles, the average operating efficiencies of the powertrain system are increased by 8.2%, 5.6% and 4.3% respectively; the efficiency improvements of lithium battery also reach 6.7%, 4.2% and 4.1% respectively. The research of this paper is devoted to applying electromechanical flywheel to electric vehicles to help improve the performance of vehicles and promoting the development of hybrid electric vehicles in the future.

Effect of discharge current boost on ignition and combustion under cross flow conditions

A strong electric spark can effectively create a high-quality ignition and hence, a stable initial flame kernel for spark ignition engines under severe operating conditions, such as ultra-lean combustion and excessive exhaust gas recirculation (EGR) dilution. Cyclic variation of the ignition process is influenced by the complex in-cylinder flow environment and the stochastic the plasma state, which can result in significant combustion fluctuations, eventually deteriorating the engine performance. In this study, with a customized, unique spark ignition system, the effect of discharge current setting on ignition and combustion is thoroughly studied under cross-flow conditions similar to a spark ignition direct injection (SIDI) engine. The discharge voltage and current, as well as high-speed images of plasma channel were recorded simultaneously for the spark discharge event. A boosted discharge voltage yields a higher discharge current, a prolonged spark channel length and an enlarged plasma area, and therefore, can resist high-velocity cross-flows. Results of the lean combustion investigation in a constant volume combustion chamber demonstrate that the increased average discharge current can effectively improve the initial flame kernel size by generating a larger plasma size, thereby accelerating the early flame propagation in presence of a cross-flow. But an insufficient average discharge current leads to a misfire. Combustion in an optical engine further validated the effectiveness of increasing average discharge current in enhancing combustion stability. Even though the actual in-cylinder flow near the top dead center (TDC) is highly transient, strong and complex, with high in-cylinder pressure, increasing average discharge current can still improve the consistency and stability of ignition. The study indicates that the discharge current of the electric spark can be an effective criterion for evaluating the ignition performance.

Experiment and simulation of the characteristics and mechanisms of self-oscillations in parallel-plate glow discharges

This paper presents experimental results of the characteristics appearance and the mechanism of self-oscillation in a parallel-plate glow discharge with argon as the discharge gas at 266 Pa. The cathode and anode are molybdenum plates with a diameter of 3 cm. The distance between the electrodes is 1 cm. Discharge average voltage and current vary between 300 V and 500 μA, respectively. Light emission from the electrode gap is measured by a charge coupled device camera and argon spectra are recorded of emission lines at 650–800 nm. Results show that self-oscillations exist in the negative differential resistance region in the static V–I curve. An obvious negative differential resistance also can be observed in the dynamic of the V–I curve for the self-oscillations. The appearance and disappearance of the self-oscillating phenomenon are companied with an obvious change in all of the discharge current, discharge images, and electron excited temperature. It can be determined that the self-oscillation is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. The frequency range of self-oscillations starts with 0.4 k Hz up to 24 k Hz in dependence of the average discharge current and the external capacitors. When the self-oscillation disappears, the luminescence shows a significant radial contraction, the electron excitation temperature rise obviously. The frequency of oscillations exhibits a substantial linear increase with the average discharge current and decreases with the increase in the external capacitance from 0 pF up to 250 pF. A resistance–capacitance circuit model is used to simulate the self-oscillation discharge in this experimental glow discharge. Results show that the waveforms simulated by this circuit model are well consistent with those obtained experimentally at different average discharge currents and external parallel capacitances. The equivalent plasma resistance decreases with an increase in the average discharge current. The theory of charge and discharge of a capacitor provides good insights into the characteristics and mechanism of self-oscillations in parallel-plate discharges.

Effects of Environmental Factors on Partial Discharge Activity and Estimation of Insulation Lifetime in Electrical Machines

Partial discharges (PD) are produced in the stator insulation of electrical machines while energized. The sources of PD are internal voids, crack, and manufacturing defects, which keep on extending with its normal operation, leading to the complete failure of insulation. The intensity of PD is considerably influenced by the environmental factors, including surrounding temperature, pressure, humidity, and contamination. This paper investigates the influence of these factors on the PD activity in electrical machines and estimates the lifetime of insulation. The PD measurements were conducted by placing the motors in a climate-controlled chamber. The PD trend under varying environmental stresses was investigated over time. Accordingly, PD inception voltage and various discharge characteristic parameters such as accumulated apparent charge, cumulative energy function, average discharge current, discharge power, and quadratic rate have been determined. The combined effect of various environmental stresses on the PD activity was also investigated. The mathematical relationships were developed to estimate the discharge characteristics as the functions of pressure and temperature using the Gaussian model and the Exponential model. Finally, the endurance of insulation was estimated under different environmental conditions based on the average discharge current to differentiate between correct and incorrect PD measurements and to develop a right maintenance schedule for motors in service.

Study of Battery Performance Analysis with Regenerative Braking Methods using SIMULINK

The purpose of this study is to find the most eligible battery capacity for ultra-compact electric vehicle. Lithium-Ion batteries configuration is designed and examined for the research. Physical characteristics of the vehicle and motor assign battery capacity. The battery must be able to attain certain length of track and to utilize regenerative braking method. Designed battery will be examined by adjusting loading variations and regenerative braking method with specified track length. The performance of the battery is analyzed with and without controller used during certain experiments. The obtained results emphasize the designed battery performances throughout variations of loading and regenerative braking method applied. During performance test in the field, the battery shows that the average discharge current is inversed to the average voltage during constant and varied velocity tests. Moreover, the battery velocity rises when the regenerative braking method is applied. The throughout experiment will be compared and analyzed using SIMULINK.

Electrical Characteristics of Atmospheric Air Corona Plasma by Multi-pin Electrodes

Recently, non-thermal plasma has been widely applied in many fields related to plasma advanced chemical reaction. However, large-scale production of non-thermal plasma is difficult to be achieved in the atmospheric environment. Among other plasma models, corona discharge generated by multi-pin electrodes is one of the good candidates for a massive atmospheric non-thermal plasma production. This paper reports an experimental study on the electrical characteristics of non-thermal atmospheric multi-pin air corona discharges. A plasmamodel composed of multi-pin anodes with 1, 5, 15, and 64 pins, and a planar counter electrodehas been developed. The gap between the electrodes has been 12 mm. Stable streamer glow corona plasma has been generated and observed at the dc-supplied voltage of 14–18 kV. The influences of the electrode number and the supplied voltage on the electrical characteristics of the plasma have been investigated and discussed. The plasma has been found out to be in a self-pulsing discharge mode under every examined experimental condition. The pulsing frequency has increased when the supplied source voltage increased. However, non-periodical pulsing could be observed in the multi-pin electrode cases owing to the multi-discharges from each pin anode. At the same supplied voltage, a greater number of pin electrodes could be sustained with the lower voltage in order to obtain a larger average discharge current. Moreover, more uniform plasma could be achieved, and the transition from glow to arc discharge could be extended due to an interaction of electric field and equipotential lines between the adjacent pin electrodes.

Influence of Gas Flow on Partial Discharge Behaviors in Air and Nitrogen

Gas flow is an unavoidable factor to influence partial discharge (PD) behavior of insulators, e.g., in the cases of strong wind and high-speed train. In this paper, the surface charge distribution of PD sequences was obtained by the PD measurement system based on Pockels effect in different gas flows. Both phase-resolved PD (PRPD) and pulse sequence analysis method (dV-dV pattern) were employed to study the PDs behavior. We found that the air flow could homogenize the distribution of surface charge spots and influence the inception voltage, discharge number, as well as average discharge current. The discharge number increased with the airflow velocity until reaching its maximum at the threshold of 4 L/min. Although in nitrogen, with increasing the nitrogen flow velocity, the surface charge distribution became more uniform and the discharge number decreased together with its corresponding PDs pattern varying at the same time. This difference of PD behaviors in air and nitrogen was attributed to the presence of oxygen molecules in gas.

Analysis of the production mechanism of H2O2 in water treated by helium DC plasma jets

In this paper, helium plasma jets are used for water activation to explore the production mechanism of H2O2 in the water. Either positive or negative DC voltage is used for the plasma excitation. It is found that the concentration of aqueous H2O2 induced by the positive plasma jet is ~4 times larger than that by the negative plasma jet with similar average discharge current. Three production pathways of aqueous H2O2 are considered important in literature, including the electrolysis, the dissolution of gaseous H2O2, and the combination of aqueous OH. However, the first two pathways are found to have similar contributions on H2O2 production for the positive and negative plasma jets. It is deduced that the OH combination in the surface layer of the plasma-activated water is most responsible for the concentration difference of aqueous H2O2 between the two plasma jets.

Electrical Characteristics of a Glow Discharge in Air over the Surface of Aluminum Sulfate Aqueous Solution

The paper presents the current−voltage characteristics, the magnitudes of cathode potential drop, the dependences of the total and specific glow discharge power which is injected into the plasma from the discharge current, as well as the density of electrons in the glow discharge in air at atmospheric pressure with the cathode based on 1−10% solutions of aluminum sulfate in distilled water. The distance between the electrolytic liquid cathode and the metal anode is varied from 1 to 10 mm at an average discharge current of 8−36 mA. The discharge is promising for the synthesis of nanostructures of aluminum and aluminum oxide which are formed when processing the solutions with a glow discharge.

DC negative corona discharge characteristics in air flowing transversely and longitudinally through a needle-plate electrode gap

The electrical characteristics of a steady-state DC negative corona discharge in air flowing transversely or longitudinally in relation to the needle-to-plate (or mesh) electrode axis were experimentally investigated. The velocity of air flowing into the corona discharge chamber was limited to a range from 0 to 6 m/s, typical of electrostatic precipitators, gas ionisation sensors and EHD pumps. The investigations showed that in this airflow velocity range three discharge current modes of the DC negative corona could exist: the Trichel-pulse corona mode, the ‘Trichel pulses superimposed on the steady current (or DC) component’ mode and the steady glow (the steady current or DC) corona mode, regardless of the airflow direction. The average corona discharge current, which is a macroscopic corona discharge parameter, was almost not affected by the airflow. However, both microscopic corona discharge parameters: the electric charge and the repetition frequency of Trichel pulses were influenced by the airflow. The transverse airflow caused an increase in the electric charge and a decrease in the repetition rate of Trichel pulses, the both by about 25% at a velocity of 6 m/s. In the case of longitudinal airflow the average corona current slightly increased when the airflow was directed towards the mesh and decreased when the airflow was directed towards the needle tip. Similarly as in the case of transverse airflow, the electric charge and the repetition frequency of Trichel pulses were affected by the longitudinal airflow. The electric charge and the repetition frequency of Trichel pulses increased and decreased, respectively, with growing airflow in the direction towards the needle electrode. The airflow growing in the direction towards the mesh electrode produced the opposite effect - the electric charge and the repetition frequency of Trichel pulses decreased and increased, respectively. The opposite behaviours of the electric charge and the repetition frequency of Trichel pulses with growing airflow velocity could explain the weak dependence of the negative corona average current on transverse or longitudinal airflow. Therefore, the independence of the negative corona average current of the airflow cannot be considered as sufficient proof that the airflow (up to 6 m/s) does not affect the negative corona parameters.

Design and evaluation of a unipolar aerosol particle charger with built-in electrostatic precipitator

ABSTRACTA new unipolar charger of aerosol particle has been designed and evaluated. The free ion and particle trajectories have been simulated. Four parameters, including electrical characteristics, particle loss, charging efficiency and the average charges, were varied to evaluate the charger. The experimental results show that the average discharge current was stable at 5 µA with 2.6 kV applied on the needle. The standard deviation is 0.0016 when clean air is entered in the discharging zone, as compared to the deviation of 0.024 with unfiltered ambient air which indicates that discharge current is more stable when clean air is entered. The electrostatic loss, diffusion loss and total particle loss were below about 4, 7 and 9% for all particles (sizes of 20–1000 nm), respectively. The intrinsic and extrinsic charging efficiency increased with the particle diameter. The intrinsic efficiency is practically 100% for particle diameters above 50 nm. Compared to the intrinsic efficiency, the extrinsic charging efficiency decreased by 5% given the fact that some of particles may be deposited inside the charger. As for the average particle charge number, the maximum relative error between the results of experiment and theory was less than 15%.

Effect of metal-hydride hydrogen activation on longitudinal yield of negative ions from PIG

We present the results of the study of activated hydrogen, desorbed from a metal hydride cathode, effect on a PIG ability to emit negative hydrogen ions H− in the longitudinal direction. It becomes possible due to a change in the discharge properties with the further output of negatively charged particles together with positive ions along the magnetic field. The separation of negative ions from an extracted flow of charged particles was carried out by an electromagnetic filter. The efficiency of the filter was investigated and the optimal external parameters for H− ions separation were determined. The beam current of H− ions has been obtained at the level of 5 mkA at an average discharge current 2 mA and a discharge voltage 5 kV.

Characteristics of cold atmospheric plasma source based on low-current pulsed discharge with coaxial electrodes

This work investigates the characteristics of the gas discharge system used to create an atmospheric pressure plasma flow. The plasma jet design with a cylindrical graphite cathode and an anode rod located on the axis of the system allows to realize regularly reproducible spark breakdowns mode with a frequency ∼ 5 kHz and a duration ∼ 40 μs. The device generates a cold atmospheric plasma flame with 1 cm in diameter in the flow of various plasma forming gases including nitrogen and air at about 100 mA average discharge current. In the described construction the cathode spots of individual spark channels randomly move along the inner surface of the graphite electrode creating the secondary plasma stream time-average distributed throughout the whole exit aperture area after the decay of numerous filamentary discharge channels. The results of the spectral diagnostics of plasma in the discharge gap and in the stream coming out of the source are presented. Despite the low temperature of atoms and molecules in plasma stream the cathode spots operation with temperature of ∼ 4000 °C at a graphite electrode inside a discharge system enables to saturate the plasma by CN-radicals and atomic carbon in the case of using nitrogen as the working gas.