Analysis of the optimal operation frequency with lowest time-delay jitter for an electrically triggered field-distortion spark gap

This work was stimulated by the assumption that for a gas-filled spark gap closing switch operating at a high repetition frequency, there is an optimal frequency range in which the time-delay jitter reaches a minimum value. The experiments to test this assumption use an electrically triggered, field-distortion spark gap filled with the SF6/N2 gas mixture. The results show that indeed, the time-delay jitter decreases for a range of frequencies for which the filling gas can substantially restore the interelectrode insulation before increasing at a higher operation frequency. The experimental results demonstrate the correctness of the abovepresented assumption: the time-delay jitter of the field-distortion spark gap has its minimum when the unit operates in the repetition frequency range between 20 and 30 Hz. Since the recovery time depends on the gas species and the gap distance, the optimum operation frequency range should also vary depending on the spark-gap distance and the filling gas properties

Electrode erosion and lifetime performance of a compact and repetitively triggered field distortion spark gap switch

© 1973-2012 IEEE. The electrode erosion and lifetime performance of a compact and repetitively triggered field distortion spark gap switch were studied at a repetitive frequency rate of 30 Hz, a peak current of 8.5 kA, and a working voltage of ±35 kV when the switch was filled with a gas mixture of 30% SF6 and 70% N2 at a pressure of 0.3 MPa. The variations of the time-delay jitter and the self-breakdown voltage were both studied for the whole service lifetime of the spark gap switch. The morphology of both the electrodes and the plate insulator, before and after the service lifetime tests, is also analyzed. The results show that during these tests, the time-delay jitter is basically synchronized with the self-breakdown voltage jitter, and both undergo firstly a process of rapidly decreasing their values, then remaining stable, and finally and gradually increasing after 70 000 pulses. The change in the electrode surface roughness (i.e., surface profile) is caused by erosion and chemical deposits in the switch cavity, which are mainly the two factors that affect the time-delay jitter of the switch. Tip protrusions on the electrode surface, due to electrode erosion, contribute to reducing the time-delay jitter. However, due to chemical reactions, fluorides and sulfides are deposited on the switch components, as well as metal particles caused by electrode erosion sputtering. Slowly, after a large number of shots, all these phenomena affect the self-breakdown performance resulting in an increased self-breakdown voltage jitter, which also causes the time-delay jitter to increase. Although there are a number of reasons that contribute to the deterioration of the performance of the switch, it is fortunate that if a switch suffering a degraded performance is reassembled, with the electrodes mechanically polished and all the components cleaned, the optimal performance of the switch can be restored. If maintenance work is carried out regularly to preserve the condition of the switch's inner components, the service lifetime of the switch can be prolonged

誘導性エネルギー蓄積に基づくパルスパワー発生に関する研究

国立大学法人長岡技術科学大

Faculty Publications and Creative Works 2004

Faculty Publications & Creative Works is an annual compendium of scholarly and creative activities of University of New Mexico faculty during the noted calendar year. Published by the Office of the Vice President for Research and Economic Development, it serves to illustrate the robust and active intellectual pursuits conducted by the faculty in support of teaching and research at UNM

A study of Direct Current Corona Discharges in Gases and Liquids for Thin Film Deposition

The applicability of DC corona discharges with their lower temperatures and uniformity was investigated for the deposition of thin films. The deposition was done at atmospheric pressure and room temperature, which lowers the facility cost as no vacuum or low pressure facilities are required and also enables continuous processing rather than batch processing. The operating regimes and the structures of DC negative corona discharges for a point to plate electrode configuration for thin film deposition were studied. Traditionally DC coronas have been operated at extremely low currents. By modifying the circuit, the DC corona was operated at higher currents without spark breakdown. The DC negative corona discharge was operated in a new regime where a stable and diffuse glow was observed near the anode surface. This diffuse glow was observed in air and methane discharges. The discharge was characterized by voltage-current diagnostics. Optical emission spectroscopy (OES) was used to obtain spatially resolved temperature measurements and electric field measurements. The DC negative corona discharge was also observed to deposit films on the anode surface. The deposition of films and particles on the anode surface has introduced the possibility of using corona discharges as a novel method of materials deposition or surface modification at atmospheric pressure. The study of electrical breakdown in both conducting and dielectric liquids has gained interest due to various applications. These discharges in liquids are unsuitable for many applications due to their thermal nature. Non-thermal discharges in liquids are relatively unexplored. DC plasma discharges in liquids for a negative pin-to-plate electrode configuration were also investigated. The discharge was characterized by voltage-current characteristics and visualization. The corona discharge is observed to deposit films on the anode surface when operated in tetraethyl orthosilicate (TEOS). Deposition on the anode surface by the proposed method has introduced the possibility of using corona discharges as a method of materials deposition or surface modification directly in liquid phase. The proposed plasma enhanced liquid deposition (PELD) technique is encouraging because it is both simple and effective in depositing films without damaging the substrate material.M.S., Mechanical Engineering -- Drexel University, 200

Ceramic dielectrics for high energy density capacity application

The objective of this dissertation is to investigate the relationship between the processing parameters, microstructural development, defect chemistry and electrical properties of titanium oxide (TiO₂) dielectrics for high energy density capacitor applications. The effects of aliovalent dopants on the dielectric properties of TiO₂ ceramics were investigated, aiming to further improve the desired dielectric properties especially at elevated temperatures (up to 200°C). Due to the segregation of acceptor type impurities in the starting powders, space charge polarization took place in TiO₂ ceramics with relative large grain size (\u3e̲500nm), leading to high dielectric loss and low energy storage efficiency. Increased ratio of grain boundary resistivity to bulk grain resistivity resulted in lower breakdown strength, as larger electric field was applied on the grain boundaries as they became the most resistive part. Donor doping (e.g phosphorus or vanadium) can effectively remove the space charge layer due to charge neutralization of positively charged defects created by donors and negatively charged defects created by acceptors. Large area, crack free tapes were fabricated by tape-casting method using nano-sized (~40nm) TiO₂ powders. An energy density of ~14 J/cm³ was demonstrated by testing of TiO₂ thick films (~100µm). Studies on dielectric materials were extended to BaTiO₃/SrTiO₃ (BST) ceramics which were processed by lamination of BaTiO₃ and SrTiO₃ green tapes with a 2-2 spatial configuration. Preliminary results showed that BST ceramics are promising dielectrics for energy storage applications and offer compositional flexibility to achieve maximum energy density under specified electric fields --Abstract, page iv

Gas-solid interfaces stressed with HV impulses : surface flashover behaviour and control

In pulsed power engineering, solid spacers are used to insulate high voltage parts from extraneous metal parts, providing electrical insulation as well as mechanical support. The breakdown/flashover voltage, at which a discharge process initiates across the gas-solid interface, is important in the design process, as it informs designers of specific threshold ‘failure’ voltages of the insulation system. In this thesis, a method to potentially increase the failure voltage, tested under multiple environmental conditions, without increasing the length of the solid spacer, was investigated. Three dielectric materials: High-Density Polyethylene (HDPE), Polyetherimide (Ultem) and Polyoxymethylene (Delrin), were tested under 100/700 ns impulse voltages. Cylindrical spacers made of these materials were located in the centre of a plane-parallel electrode arrangement in air, which provided a quasi-uniform field distribution. Breakdown and flashover tests were performed in a sealed container at air pressures of −0.5, 0 and 0.5 bar gauge, with varying relative humidity (RH) level of 90%. The materials were tested under both, negative and positive, polarity impulses. Additionally, the surfaces of a set of solid spacers were subjected to a ‘knurled’ finish, where ~0.5 mm indentations are added to the surface of the materials, prior to testing, to allow comparison with the breakdown voltages for samples with ‘smooth’ (machined) surface finishes. The results show that the flashover voltage is controlled by the physical insulation system and environmental parameters, where the multiple test conditions yielded results where the V50 breakdown voltage for samples with a smooth surface finish was higher than for knurled, by up to ~55 kV; where there were similar V50 breakdown voltages for each type of surface finish; and where the knurled spacer resulted in a higher (by up to ~66 kV) hold-off voltage than the corresponding smooth spacer. Each of these results is discussed herein, particularly in terms of the location of the discharge channel at breakdown, where changing the physical and environmental test parameters was shown to affect the discharge path, and therefore the flashover voltage of the insulation system. The results and discussion will inform designers and operators of outdoor pulsed power systems on the design of air-solid insulation systems, and the control of the flashover characteristics, under varying environmental conditions.In pulsed power engineering, solid spacers are used to insulate high voltage parts from extraneous metal parts, providing electrical insulation as well as mechanical support. The breakdown/flashover voltage, at which a discharge process initiates across the gas-solid interface, is important in the design process, as it informs designers of specific threshold ‘failure’ voltages of the insulation system. In this thesis, a method to potentially increase the failure voltage, tested under multiple environmental conditions, without increasing the length of the solid spacer, was investigated. Three dielectric materials: High-Density Polyethylene (HDPE), Polyetherimide (Ultem) and Polyoxymethylene (Delrin), were tested under 100/700 ns impulse voltages. Cylindrical spacers made of these materials were located in the centre of a plane-parallel electrode arrangement in air, which provided a quasi-uniform field distribution. Breakdown and flashover tests were performed in a sealed container at air pressures of −0.5, 0 and 0.5 bar gauge, with varying relative humidity (RH) level of 90%. The materials were tested under both, negative and positive, polarity impulses. Additionally, the surfaces of a set of solid spacers were subjected to a ‘knurled’ finish, where ~0.5 mm indentations are added to the surface of the materials, prior to testing, to allow comparison with the breakdown voltages for samples with ‘smooth’ (machined) surface finishes. The results show that the flashover voltage is controlled by the physical insulation system and environmental parameters, where the multiple test conditions yielded results where the V50 breakdown voltage for samples with a smooth surface finish was higher than for knurled, by up to ~55 kV; where there were similar V50 breakdown voltages for each type of surface finish; and where the knurled spacer resulted in a higher (by up to ~66 kV) hold-off voltage than the corresponding smooth spacer. Each of these results is discussed herein, particularly in terms of the location of the discharge channel at breakdown, where changing the physical and environmental test parameters was shown to affect the discharge path, and therefore the flashover voltage of the insulation system. The results and discussion will inform designers and operators of outdoor pulsed power systems on the design of air-solid insulation systems, and the control of the flashover characteristics, under varying environmental conditions

Gas Phase Switching for Pulsed Power Applications

This dissertation serves to increase the understanding of applied pulsed plasma. Pulsed plasmas are experimentally studied in three contexts 1) fundamentally as switches, 2) applied in a dense plasma focus (DPF), and 3) applied as flow actuators. In these contexts the systems were studied with voltage, repetition frequency, energy, and pulse duration, ranges from 10 – 100 kV, 1 to 20 kHz, 1 mJ to 1 J, and 5 to 100 ns respectively depending on the requirements of ultimate application. These high voltages at high frequency push the current limits of spark switches. Attaining desired conditions required an understanding of the plasma switching characteristics, electrical coupling with the load, and the ultimate application. In the first experimental study plasma pulsing limitation were determined. In these experiments a DC pulsed plasma is pushed to its limits (within constraints) to determine maximum pulsing frequency while maintaining 10 kV available to drive novel applications. In these experiments 137 mJ of energy were pulsed at a frequency of 20 kHz with full-width half-max of 8 ns. Similar pulsing at 42 kHz was observed while maintaining roughly 5 kV. Operating performance was governed by electrode material, discharge gas/flow, chamber pressure, and circuit elements, both intentional and parasitic. In the second experiment, the dense plasma focus (DPF) compresses stored energy through dynamic plasma processes to initiate fusion reactions. This requires controlled short duration pulsing. The DPF in this work is, at the time of this writing, the smallest of its kind to show evidence of pinching based on ns resolution image analysis. The reduction in size was made possible by introducing Knudsen scaling to DPF design criteria. The motivation for investigating microscale DPFs is that neutron production efficiency may scale as a^-3, where a is the DPF anode radius. Smaller sized systems are also more amenable to portability. Because these devices can fuse, they are capable of generating 15 MeV neutrons and other high energy particles, and they otherwise make for convenient observation of complex plasma dynamics. The plasma actuator for flow control was used for the delay of separation. Short duration plasma pulses were required to produce high velocity synthetic jets. Geometrically and electrically varied sets of individual actuators were computationally and experimentally investigated, compared and characterized. Also a 93 kV, 700 A peak current, 100 ns pulse duration linear array of 23 pulsed plasma actuators in series was designed and tested on a 58 cm span airfoil at Re = 400,000. At a pulsing frequency of 40 Hz and 11° stall was prevented and a drag reduction of 12% was measured. This study supplements current literature on individual actuators and is unique in reporting on full span actuated airfoils. All of the aforementioned studies show both the capabilities and limitations of plasma-pulsed pulsed-plasmas. But, also the necessary understanding of coupling between the pulsing mechanism and its applications. A better understanding of breakdown processes, specifically charged particle generation and diffusion, both in the switch and the load will advance capabilities of such pulsed plasma applications

Gas Phase Switching for Pulsed Power Applications

This dissertation serves to increase the understanding of applied pulsed plasma. Pulsed plasmas are experimentally studied in three contexts 1) fundamentally as switches, 2) applied in a dense plasma focus (DPF), and 3) applied as flow actuators. In these contexts the systems were studied with voltage, repetition frequency, energy, and pulse duration, ranges from 10 – 100 kV, 1 to 20 kHz, 1 mJ to 1 J, and 5 to 100 ns respectively depending on the requirements of ultimate application. These high voltages at high frequency push the current limits of spark switches. Attaining desired conditions required an understanding of the plasma switching characteristics, electrical coupling with the load, and the ultimate application. In the first experimental study plasma pulsing limitation were determined. In these experiments a DC pulsed plasma is pushed to its limits (within constraints) to determine maximum pulsing frequency while maintaining 10 kV available to drive novel applications. In these experiments 137 mJ of energy were pulsed at a frequency of 20 kHz with full-width half-max of 8 ns. Similar pulsing at 42 kHz was observed while maintaining roughly 5 kV. Operating performance was governed by electrode material, discharge gas/flow, chamber pressure, and circuit elements, both intentional and parasitic. In the second experiment, the dense plasma focus (DPF) compresses stored energy through dynamic plasma processes to initiate fusion reactions. This requires controlled short duration pulsing. The DPF in this work is, at the time of this writing, the smallest of its kind to show evidence of pinching based on ns resolution image analysis. The reduction in size was made possible by introducing Knudsen scaling to DPF design criteria. The motivation for investigating microscale DPFs is that neutron production efficiency may scale as a^-3, where a is the DPF anode radius. Smaller sized systems are also more amenable to portability. Because these devices can fuse, they are capable of generating 15 MeV neutrons and other high energy particles, and they otherwise make for convenient observation of complex plasma dynamics. The plasma actuator for flow control was used for the delay of separation. Short duration plasma pulses were required to produce high velocity synthetic jets. Geometrically and electrically varied sets of individual actuators were computationally and experimentally investigated, compared and characterized. Also a 93 kV, 700 A peak current, 100 ns pulse duration linear array of 23 pulsed plasma actuators in series was designed and tested on a 58 cm span airfoil at Re = 400,000. At a pulsing frequency of 40 Hz and 11° stall was prevented and a drag reduction of 12% was measured. This study supplements current literature on individual actuators and is unique in reporting on full span actuated airfoils. All of the aforementioned studies show both the capabilities and limitations of plasma-pulsed pulsed-plasmas. But, also the necessary understanding of coupling between the pulsing mechanism and its applications. A better understanding of breakdown processes, specifically charged particle generation and diffusion, both in the switch and the load will advance capabilities of such pulsed plasma applications