High-voltage Direct Current Source Research Articles

Low-current gliding DC discharge in high-speed flows

Abstract A low-current gliding discharge (current range 1–5 A) in high-speed air flows of 100–250 m s−1 was experimentally studied. A high-voltage direct current source with a maximum voltage of 4.5 kV was used to create the discharge. The average electron concentration n e ∼ 1014 cm−3 and the plasma ionization degree were determined by measuring the Stark broadening of the hydrogen H β line (λ Hβ = 486.1 nm). The estimates of the electric field (E ∼ 100 V cm −1 ÷ 600 V cm−1) in the discharge positive column were found using time-synchronized high-speed video recordings and oscillograms. The gas rotational temperature T g = 7000–9500 K and the vibrational temperature T v = 7000–11 000 K were estimated using optical emission spectroscopy. Time-resolved spectroscopy is used to investigate the effective plasma channel spatial regions from which the N, NH, N2 +, O and OH molecules radiate. The difference of the obtained radii indicates the presence of a radial temperature gradient and inhomogeneous plasma composition in the discharge cross section. The possibility of using of gliding discharge to ignite hydrocarbon-air mixtures in the ramjet engines combustors has been experimentally demonstrated.

REVIEW OF WAYS TO IMPROVE THE MAGNETIC PROPERTIES OF WEAKLY MAGNETIC IRON ORES

The issues of using hardly enriched weakly magnetic iron ore raw materials, which should be widely involved in production in connection with the depletion of reserves of the richest and most accessible iron ore deposits, are considered. A literature and patent review of ways to improve the magnetic properties of weakly magnetic iron ores has been carried out. Magnetizing roasting of ores, which is widely used to convert weakly magnetic minerals into highly magnetic ones, as well as methods based on heating the ore with a concentrated energy flow in the form of laser radiation irradiating the ore with plasma, and treating the ore with ultrasound are considered. The advantages and disadvantages of these methods for increasing the magnetic properties of weakly magnetic iron ores are analyzed. Information about the method of magnetic enrichment of iron ore material developed at the Novotroitsk branch of the National University of Science and Technology “MISIS” is presented. The method includes preparation of iron ore material, crushing and grinding to open ore grains, transportation to a magnetic separator and separation into magnetic and non-magnetic parts. At the same time, the transportation of iron ore material is carried out through a solenoid coil connected to an adjustable high voltage direct current source. The necessity of studying the regimes of magnetic influence on minerals by this method and the prospects of its use for increasing the magnetic properties of hardly enriched weakly magnetic iron ore.

A barrierless pulse discharge cell

A barrierless plasmachemical ozone generator, operating on the corona discharge, is studied. A high-voltage pulse power source and a discharge chamber are its basic elements. For obtaining high-voltage pulses with duration of several tens nanoseconds, a rotating discharger is connected to the output of a highvoltage direct-current source. The studied barrierless discharge chamber is characterized by a high efficiency of ozone synthesis, design simplicity, and minimal sizes. As compared to discharge chambers of other types, its advantage is that a corona discharge virtually fully fills its volume. Due to this fact, ozone is synthesized almost in the whole volume of the discharge chamber, resulting in attaining its high concentration at the chamber output. A productivity equal to 30 g/m3 and higher was reached in the experiments.

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%

Solid state Marx Generator using series-connected IGBTs

This paper describes a newly developed novel repetitive impulse voltage generator using a boost converter array. To solve problems such as short life time, low operating frequency, and the fixed pulse width of conventional generators, the proposed generator is designed with a boost converter array that employs series-connected capacitors and insulated gate bipolar transistors. The circuit can easily obtain a high-voltage pulse without any high-voltage direct current source and pulse transformer. Thus, the proposed circuit not only allows elimination of the expensive high-frequency transformer but also allows operation at a frequency up to several kilohertz with high reliability and longer life span. To validate the proposed circuit, two pulse generators rated at 1.8 kV, 40 A and 20 kV, 300 A are implemented and tested.

Design and simulation of a high-voltage direct-current source

This paper presents the design and simulation results of a 70 kV, 60 A, high-voltage direct-current source. The proposed solution consists of 96 three-phase bridges connected in series in a 36-pulse arrangement and fed by a cascade of three dry-type transformers. Simulation results obtained using the EMTP software (Electro Magnetic Transient Program) confirm the feasibility of the design and the theoretical estimates of the dc voltage ripple and the ac line current harmonics.