T. Reess

Very Fast Rise-Time Short-Pulse High-Voltage Generator

This paper relates to the development of an ultrafast compact system readily applicable to the field of ultrawideband microwave applications such as transient radar or laser drivers. The design, production, and experimental results of a short-pulse generation system are presented in this paper. The coaxial generator technology based on the principle of a line discharge by means of a high-pressure gas switch in a simple transmission line arrangement is described. In the first stage of the process, the coaxial generator was charged by a high-voltage direct current source. Interesting results were obtained, but due to the jitter of the discharge formative time, the reproducibility of the output pulses was not sufficient. To improve the performance, a pulsed source was developed in order to apply an overvoltage to the gap switch and thus reduce the jitter of the discharge formative time. The characteristics of the pulsed source are defined. A thyristor Marx generator and a pulse transformer using magnetic properties of ferrite cores were combined in order to produce this pulsed source. The main performances of this source are a pulse amplitude of 60 kV, a rise time of 250 ns, and a maximum frequency of 900 Hz from a 1-kV dc supply. Finally, the complete generation system is able to generate pulses with 25-kV amplitude and 70-ps rise time through a 50-Omega impedance from the single shot mode up to 900 Hz. The output pulses reproducibility obtained is better than plusmn5%

High Pulsed Power Sources for Broadband Radiation

This paper explains the design and production of two autonomous ultrawideband (UWB) radiation sources. These sources consist of a high-gain broadband antenna that is driven by one of two subnanosecond pulsed power sources. Each source is made up of a Marx generator and a pulse-forming device based on the use of a gaseous spark gap. The first source combines a four-stage 200-kV/34-J Marx generator with a coaxial pulse-forming line. Its main characteristics are an output voltage of 100 kV, a 250-ps rise time, a subnanosecond pulse duration, and a repetition rate of about 40 Hz. The second pulsed source is a ten-stage subnanosecond Marx generator that delivers pulses in the 250-kV/1.5-J range, with a 300-ps rise time and a subnanosecond pulse duration at a pulse repetition rate of 350 Hz. Probes were produced based on capacitive line dividers to measure both the temporal characteristics and the high-voltage (HV) amplitude of the pulses delivered by the pulsed power sources. The antenna, combined with these two pulsed sources, is a traveling-wave antenna called the Valentine antenna. Some mechanical modifications were made to the antenna to improve its dielectric strength. First, a 3-D model of the antenna was created on time-domain electromagnetic software to study the influence of these modifications on its main radiating characteristics. Its high gain and its capability to radiate short pulses without dispersion allow us to achieve a high measured figure of merit (the maximum value of far-field peak-to-peak electric field strength multiplied by the distance). A new method called the Instantaneous Electromagnetic Field Measurement by Signature of a Neutral Object (MICHELSON) method is used to measure the very intense electromagnetic fields that are radiated. The incident field is diffracted by a special small-dimension target. The diffracted field is measured by a conventional low-power UWB antenna. The target that is used has small dimensions, and no cables are used in the field region; thus, the electromagnetic interference that is generated and undergone by the measurement device is considerably limited. The figure of merit that is measured is 436 kV.

Optimizing the operation of an electrostatic precipitator by developing a multipoint electrode supplied by a hybrid generator

The authors investigated and improved the filtration efficiency of an electrostatic precipitator (ESP). A laboratory-scale pilot unit was developed to allow experimentation under conditions approaching those of the industrial ESPs used by the CEA at Marcoule (France). After elucidating the electrical phenomena and optically analysing the physical processes occurring inside the precipitator, a specific electrode was developed for use with a hybrid power supply. The experiments were based on analysing the variation over time of the electric charge injected into the particle separator, the particle mass collected at the ground electrode and the charges quantity measured on a grid in the airstream after the electrode unit. Photos were also taken under different electrical discharge conditions. The results show that combining a multipoint electrode and a hybrid generator (30 kV dc and 30 kV, 1 kHz) improves the process efficiency and significantly extends the time frame (more than 10 h) during which the process operates at optimum efficiency.

Experimental demonstration of the effectiveness of an early streamer emission air terminal versus a franklin rod

This paper is devoted to a detailed presentation of all aspects involved in a novel experimental technique to prove the effectiveness of an early streamer emission air terminal (ESEAT) versus a traditional Franklin rod in a laboratory. Firstly, a theoretical basis for the equivalent-circuit analysis of an ESEAT model is presented. It is shown that the dynamic electric field intensity on the active ESE rod is higher (theoretically even twice as high) than the static field intensity of the conventional Franklin lightning rod. Then, an experimental test using a method and associated with an electrostatic simulation demonstrates the effectiveness of an ESEAT (Pix3-60 from Piorteh Company) versus a conventional Franklin rod in the SIAME laboratory of the University of Pau in France. This method consists in locating both the ESE terminal and the Franklin rod together in the same configuration in accordance with the French Standard NFC 17-102 (09/2011). During the tests, all discharges were recorded on the ESEAT manufactured by Piorteh Company when its rod was active. This experimental test could be used on any kind of lightning protection device.

Electrohydraulic shock wave generation as a mean to increase intrinsic permeability of concrete

The objective of this article is to present an experimental study of Pulsed Arc Electrohydraulic Discharges (PAED) in water. The aim is to produce dynamic shock waves in order to increase the intrinsic permeability of mortar specimens which are immersed in water.

A Semiempirical Model for the Prebreakdown-Heating Process in the Underwater Discharge Acoustic Source

The breakdown of water in underwater discharge acoustic source (UDAS) is usually in the mode of electrothermal breakdown. The prominent characteristic of the electrothermal breakdown is the existence of prebreakdown-heating phase. In our experiment, the influences of salt concentration and water temperature on breakdown are tested. Three phenomena are observed: 1) The breakdown time obeys a “double peak” stochastic distribution; 2) the higher salt concentration in water leads to higher probability of nonbreakdown; and 3) the higher temperature of salty water also results in higher probability of nonbreakdown. In this paper, the mechanism of electrothermal breakdown is theoretically analyzed, and two conditions to realize electrothermal breakdown are concluded: 1) enough energy deposited to the gap to ensure “border boiling” and 2) enough remaining voltage on the gap at the moment of “border boiling.” Focused on the water temperature and gap voltage, a semiempirical model for prebreakdown-heating process is proposed. When two heating effects of both ionic current and radiation from the initial arc are taken into account, this semiempirical model provides preliminary explanations to the three phenomena observed in our experiment. Based on this model, a simulation code (CPH ) is developed which can numerically simulate the evolution of the gap voltage in prebreakdown-heating phase. The simulation reproduces the experimental phenomena under the same initial conditions.

Improvement of polyphenols extraction from grape pomace using Pulsed Arc Electro-hydraulic Discharges

This work aims at producing high dynamic shock waves by Pulsed Arc Electro-hydraulic Discharges (PAED) in a water based mixture in order to increase polyphenols extraction from grape pomace. Grape pomace is the main winemaking by-product composed of skins, seeds and stems. They contained valuable compounds like polyphenols. These molecules have attracted interest for their antioxidant activity. A triggered air-gap switch was used to discharge capacitors into the mixture containing grape pomace and water. The gap switch breakdown (40 kV maximum pulse voltage) produced a high dynamic shock wave in the liquid. The pulse energies were set to 160 J and 4 kJ with a pulse repetition frequency of 0.5 Hz. The contents of total solutes and total polyphenols of extracts were obtained by the values of degree Brix and absorbance at 280 nm respectively. Results point out the intensification of the extraction of total solutes and total polyphenols from grape pomace after PAED treatment. However, maintaining constant the ratio of energy to product mass (in our case, it was equal to 0.53 J/g) was not enough to obtain similar results for laboratory and semi-pilot experiments. Other parameters should be taken into account (treatment chamber design, pressure wave distribution ...). For example, a treatment of 53 kJ/kg at the laboratory scale gives similar results as a treatment of 160 kJ/kg at the pilot scale. In these conditions, the content of polyphenols in extracts is approximately 300 mg/L and the degree Brix is 1.2%.

Measurement of the Treatment Efficiency on Soot Particles Flowing into a Wire/Cylinder Filter Energized by a Repetitive Impulse Voltage Generator

The electrostatic filtration is a process that has been studied for more than one century. Its applications are very various : one of the most recent applications is the Diesel exhaust gas after treatment. In a more specific way, car manufacturers are very interested in using corona discharges to remove the soot particles from the exhaust gas. The aim of this paper is to investigate the effects of repetitive voltage impulses on the treatment efficiency on soot particles and to compare results with those achieved when a DC supply is used. Experiments have been performed on a motor test bench where temperature and flow velocity of the exhaust gas are perfectly controlled. Several configurations of power supply have been tested at four engine revolution speeds. This study showed that the combination of direct voltage (- 7 kV) and pulsed voltage (-14 kV, 3 kHz) yields very interesting results. The voltage generator that has been used to provide these voltage waveforms is a thyristors-based switch.

Discussion on "Experimental demonstration of the effectiveness of an early streamer emission air terminal versus a Franklin Rod" [and Reply]

The paper [1] reports on comparative experiments on a triggered-gap electrode used as an early streamer emission air terminal, with some equivalent circuit analysis of the triggering circuit and simplified electric field calculations.

Experimental comparison of the performance of an early streamer emission air terminal versus a Franklin rod in laboratory using a novel methodology

This paper is devoted to a detailed presentation of all aspects involved in a novel experimental technique to prove the effectiveness of an early streamer emission air terminal (ESEAT) versus a traditional Franklin rod. An experimental test using a novel method and associated with electrostatic simulation demonstrates the effectiveness of an ESEAT (Pix3-60 from Piorteh Company) versus a conventional Franklin rod in the SIAME laboratory of the University of Pau in France. This method consists of locating both the ESEAT and the Franklin rod together in the same configuration in accordance with the French Standard NFC 17-102 (09/2011). During tests, all discharges are recorded on the ESEAT from Piorteh Company when its rod is active.