Alex Pokryvailo

A high-power pulsed corona source for pollution control applications

The system comprises an all solid-state compact nanosecond pulser and a plasma reactor. The pulser makes use of magnetic compression techniques. Owing to a fast switching at the feed of the HV transformer provided by an ABB GCT switch, one compression stage suffices for the forming of 45-kV, 100-ns pulses across a 120-/spl Omega/ resistive load at a PRF of up to 1 kHz; the risetime is 15 ns. Plasma reactor is capable of handling both gases and liquids by adding small amounts of atomized water to the gas discharge, in the case of gas, or atomizing polluted liquid itself. In both cases, the treatment is conducted in heterogeneous media. Circuit analysis of compressor and charging system accounting for nonlinear processes in magnetic switches and numerous parasitic parameters is presented. Mechanical and electrical designs are detailed. Typical voltage and current waveforms, volt-ampere characteristics, corona discharge appearance, and light emission characteristics are presented. At operation on a resistive load, the compressor efficiency was found to be approximately 80%, which allowed for air cooling. The experimental results obtained with a resistive load are in fair agreement with the circuit simulation. A novel magnetic compressor circuit improving the coupling to PC discharge is proposed and evaluated.

High-power short-pulsed corona: investigation of electrical performance, SO/sub 2/ removal, and ozone generation

Visual appearance, electrical performance, and chemical activity of a 50-MW 100-kV 22-ns pulsed corona were studied in simulated air-SO/sub 2/ gas mixture in a coaxial reactor. Infrared and mass spectrometers and electrochemical sensors were used for gas diagnostics; solid byproducts were identified using X-ray fluorescent spectrometry. Electrochemical sensors were employed for the measurement of initial concentration, before the discharge commencement. The removal efficiency of SO/sub 2/ in dry and humid air-SO/sub 2/ mixtures was studied. The removal efficiency of SO/sub 2/ decreased at lower pollutant concentration and higher frequency, while the pulse energy was kept invariant. Removal efficiency in dry mixtures was 25 g/kWh; in humid air, it was several times greater, which is attributed to the influence of OH radicals. In dry mixtures, the removal efficiency was much higher at positive polarity. Traces of many compounds were found and identified in treated gas. Ozone was produced in large concentrations both in dry and humid mixtures. Dependence of its formation rate on the pulsed power, and on the voltage polarity was studied. The precipitation of a yellowish powder identified as sulfur was observed. It is ascribed to cleavage of bonds of the SO/sub 2/ molecule by energetic species and confirmed by experiments with dry N/sub 2/-SO/sub 2/ and Ar-SO/sub 2/ mixtures.

A 1 KW pulsed corona system for pollution control applications

The system comprises an all-solid state compact nanosecond pulser and a plasma reactor. The pulser makes use of magnetic compression techniques. Owing to a fast switching at the feed of the HV transformer provided by an ABB A-Z switch, one compression stage suffices for the forming of 45 kV, 100 ns pulses across a 120 /spl Omega/ load; the risetime is 20 ns. Plasma reactor is capable of handling both gases and liquids by adding small amounts of atomized water to the gas discharge, in the case of gas, or atomizing polluted liquid itself. In both cases, treatment is conducted in heterogeneous media, which proved high removal efficiency. Circuit analysis of compressor and charging system accounting for nonlinear processes in magnetic switches and numerous parasitic parameters is presented. Mechanical and electrical designs are detailed. Typical voltage and current waveforms and the corona discharge appearance are presented. The compressor efficiency was found to be approximately 65%, which allowed for air cooling. The experimental results obtained with a dummy resistive load are in fair agreement with the circuit simulation.

A compact source of subgigawatt subnanosecond pulses

The system comprises a nanosecond solid-state opening switch (SOS) generator that charges resonantly a short pulse-forming line (PFL) through a decoupling inductor, one or two pulse-compression stages based on high-pressure gas spark gaps (SGs), a matched load and several built-in voltage and current probes. Weighing less than 50 kg, the pulser provides up to 160-kV subnanosecond pulses at a 37.5-/spl Omega/ load at a repetition rate of up to 300 Hz. The pulsewidth can be regulated from 2 ns down to 300 ps without SG depressurization. The rise- and fall times are 180 and 100 ps, respectively. Alternatively, unipolar or bipolar output can be provided. The latter was formed by a synchronous operation of SGs located at the beginning and at the end of a PFL; thus, an active conversion of unipolar to bipolar output was realized. The load peak-to-peak voltage was almost two times as high as the amplitude of the unipolar pulse. In the active converter, a virtually identical electrical field stress across the switching SGs was achieved, which alone provided its stable operation. Circuit analysis accounting for distributed character of the components and numerous parasitic parameters is presented. Voltage and current measurement means were developed and time-domain calibrated. Waveforms probed at different locations of the pulser system, from the SOS generator to the load, are presented. The experimental results are in fair agreement with PSpice simulations used for the hardware design. Life test of a one-stage compressor with two types of electrode systems was performed, and the results are reported. The pulser was tested with a TEM horn antenna. The effective potential (field multiplied by distance) of this radiation source is 640 kV in far field.

Comparative testing of simple terminations of high-voltage cables

This section describes the layout of the test setup, the design of the tested cables, and the experimental routines. Six different types of 2124 cable shield termination were tested for leakage current and dielectric strength. The main results can be summarized as follows: (1) Shrink sleeve strongly affects ionization phenomena, effectively suppressing corona discharge. (2) Flush cutting a shield leaves loose short strands, which increase the probability of main insulation damage. (3) Folding the shield back over an O-ring decreases the electric field strength, leaves no loose strands, and decreases the probability of main insulation damage. This is recommended for dc applications. (4) Stress-grading tapes reduce (and greatly stabilize) leakage currents, at a level around 1 nA at 100 kV and room temperature. They also increase the breakdown voltage to approximately 130 kV for a 15-cm length of insulation. They are recommended for pulsed operation and critical DC applications.

Modeling of a Streamer Plasma Reactor Energized by a Pulse Compression Modulator

This paper presents a semi-empirical model for a wire-wire corona reactor driven by a capacitive storage solid-state pulse generator. The reactor electrode system is configured as a checker mesh of potential and grounded threaded electrodes, and the pulse generator is based on a modern magnetic pulse compression topology. This presentation considers the effect of the geometrical parameters of the reactor (the total length of the high-voltage electrode surrounded by its grounded counterparts and the gap between the high-voltage and grounded electrodes) on the operation of the atmospheric pressure streamer plasma system. The model analyzes the discharge processes in the reactor by distinguishing between four phases, each being represented by an equivalent circuit: before the streamer generation, during the primary streamer propagation, after the primary streamers have crossed the interelectrode gaps, and after the plasma conductivity quenching. The new reactor model is realized on the PSpice platform, and the simulations are done using an improved pulse modulator model. The simulation results are compared with the experimental data, showing the model validity. Based on the simulated model, a better matching between the wire-to-wire reactor load to the pulse generator may be achieved.

Development of short pulsed corona on two-wire transmission line

Propagation of short high-voltage pulses along a 6-m-long twin line was studied in the presence of corona discharge. The experimental setup included a twin-line arrangement, a 100-kV, 5-ns pulse generator, voltage and current probes, and photomultipliers. The dependencies on line geometry and wire conductivity and on pulse voltage and polarity have been studied. PSpice and electrostatic simulations are presented; the latter are compared to still photos of corona discharge. Of most interest was the finding that the discharge was very much asymmetric when one of the pulsers terminals was grounded, even when the line height was much greater than the distance between the wires. This effect will be pronounced to heights of hundreds of meters. Pulsed corona study on NiCr resistive wires revealed intense pulse decay: only 1% of the launched energy reaches the end.

Hazardous waste treatment and recovery of valuable products with a thermal pulsed-plasma technology

Material decomposition is an essential process in chemical industries. A new, efficient and environmentally friendly technique that can be used in a closed-loop process for the treatment and recovery of materials is described. The idea is to decompose a material using a high-energy pulsed-plasma jet. The plasma specific features enable an efficient radiative heat transfer to the treated material bed. Therefore, enhanced energy transfer to selected chemical bonds is achieved. The process can be defined as a highly efficient photolysis. Proof-of-concept tests were carried out on 1,2-dichloroethane (DCE) fed in batches of a few grams each. A total decomposition of the DCE was achieved with less than 60% of the energy consumption required in a conventional treatment. In the current project, a modular transportable laboratory has been constructed. It comprises a 30 kW pulsed power supply featuring an all-solid state power switching system, confined plasma injector, reactor and gas handling and monitoring systems. The expected treatment capacity is 10 kg/h of fluid waste with expected lifetime of the plasma injector of 10/sup 5/ pulses. Simulations and experimental characterization of major components are presented. It is expected that the proposed method will be the Best Available Technology (BAT-as defined by the European Union regulations) for many fluid wastes.

Accurate Measurement of on-State Losses of Power Semiconductors

For safe design, the junction temperature should be kept within the specified range. Three methods are used most often for determining the power losses: 1. Calorimetric method; 2. Using calibrated heatsinks; 3. Electrical measurements of the device voltage and current, and finding the losses by integrating these variables. The paper concentrates on the third method with the emphasis given to the accurate measurement of the on-state voltage. The techniques of using non-linear dividers with deep voltage clamping are discussed. Novel circuits allowing faithful measurements of the on-state voltage along with good timing resolution of the switching transitions are proposed. Results of circuit simulations are borne out by extensive testing. Examples of measurement of the on-state voltage of large IGBT modules and free wheeling diodes (FWD) are presented. The obtained results are applicable for characterizing various power switches, e.g., gas discharge devices.

Comparative Testing of Shield Terminations of High Voltage Cables

In HV systems, cable terminations are one of the weakest links. They are especially stressed by the electric field in free space connections. In this light, several termination types for polyethylene HV cables were tested for dielectric strength and leakage current, down to a pico-ampere level. The tested terminations ranged from simple flush cut to graded insulation using non-linear insulation materials. Procedures and results of the testing are described. The dependencies of leakage current on the applied voltage for different terminations are presented. Visual patterns of breakdown are investigated. The major results are summarized as follows. (1) Flush cut shield may have loose strands and presents a danger of the main insulation denting. (2) Shrink sleeve dominates the ionization phenomena, effectively suppressing the corona discharge. Its influence is much greater at positive polarity of the shield terminus. (3) Shield folded back over an O-ring decreases the electric field, leaves no loose strands and decreases probability of the main insulation damage. It can be recommended for DC applications. (4) Stress grading tapes reduce and greatly stabilize leakage current at a level of 1 nA at 100 kV at room temperature, at positive polarity. They are less effective in leakage suppression at negative polarity. They also increase the breakdown voltage that reaches 130 kV at a 15-cm insulation length, at both polarities.