E.J.M. van Heesch

A fast pulsed power source applied to treatment of conducting liquids and air

Two pilot pulsed power sources were developed for fundamental investigations and industrial demonstrations of treatment of conducting liquids. The developed heavy-duty power sources have an output voltage of 100 kV (rise time 10 ns, pulse duration 150 ns, pulse repetition rate maximum 1000 pps). A pulse energy of 0.5-3 J/pulse and an average pulse power of 1.5 kW have been achieved with an efficiency of about 80%. In addition, adequate electromagnetic compatibility is achieved between the high-voltage pulse sources and the surrounding equipment. Various applications, such as the use of pulsed electric fields (PEFs) or pulsed corona discharges for inactivation of microorganisms in liquids or air, have been tested in the laboratory. For PEF treatment, homogeneous electric fields in the liquid of up to 70 kV/cm at a pulse repetition rate of 10-400 pps could be achieved. The inactivation is found to be 85 kJ/L per log reduction for Pseudomonas fluorescens and 500 kJ/L per log reduction for spores of Bacillus cereus. Corona directly applied to the liquid is found to be more efficient than PEF. With direct corona we achieve 25 kJ/L per log reduction for both Gram positive and Gram negative bacteria. For air disinfection using our corona pulse source, the measured efficiencies are excellent: 2 J/L per log reduction.

X-ray emission in streamer-corona plasma

X-ray emission has been detected occasionally during the streamer-corona propagation in a wire-plate corona reactor open to ambient air. A 65 kV pulse with 15 ns rise time is applied to the wire anode superimposed on a 20 kV dc bias. The duration of the driving voltage pulse (110 ns) is less than 2.5 times the primary streamer transit time. Under this condition no arc discharge occurs between the wire and the cathode plates separated by 6 cm air. The onset of x-ray emission coincides with the initiation of the primary streamers near the wire anode. No x-rays were detected later, during or after the primary or secondary streamer development. X-ray energies ranged between 10 and 42 keV, as detected by a LaBr3 (Ce) scintillator–photomultiplier combination. Time resolved imaging of the streamer propagation highlights the different stages in the streamer discharge process. The energetic electrons originate near the anode, at the moment of streamer initialization.

A 10 kW high-voltage pulse generator for corona plasma generation

In this article we discuss a 10 kW high-voltage pulse generator for producing corona-induced plasma. The generator mainly consists of a three-step resonant charging circuit switched by thyristors, a transmission line transformer, and a triggered spark-gap switch. Voltage pulses of 30–100 kV with a rise time of about 20 ns, a pulse duration of 50–250 ns, pulse repetition rate of 1–900 pulses per second, energy of up to 12 J/pulse, and an average power of up to 10 kW have been achieved with a total energy transfer efficiency of about 80%–90%. At each frequency, the deviation of the energy per pulse is around 1.0%. Moreover, the generator has been tested for more than 100 h for both industrial demonstrations and laboratory investigations at an average output power of 1–10 kW.

A novel circuit topology for pulsed power generation

This paper presents novel circuit topologies based on multiple switches and transmission line transformers (TLTs). The proposed pulsed power circuit topologies produce high levels of pulsed power either at higher voltages or at higher currents. The TLTs are used for impedance matching and synchronization of multiple switches. This paper also presents our first experimental results to verify the circuit topologies.

Pulsed corona for gas and water treatment

The successful introduction of pulsed corona for industrial processes very much depends on the reliability of high-voltage and pulsed power technology and on the efficiency of energy transfer. In addition, it is crucial that adequate electromagnetic compatibility (EMC) is achieved between the high-voltage pulse source and surrounding equipment. Pulsed corona (1.5 kW) is generated in a pilot unit that produces narrow 50 MW pulses at 1000 pps. The pilot unit can run continuously for use in industrial applications: cleaning of gases (100 m/sup 3//h) or fluids (e.g. waste water). Various chemical processes, such as toluene removal from an air flow are tested. To examine the processes in the reactor, the authors use current and voltage sensors and a fast CCD camera. They also developed a model to analyze the VOC conversion. Incorporated EMC techniques are based on the successful concept of constructing a low transfer impedance between common mode currents induced by pulsed power and differential mode voltages in signal lines and external mains AC.

Transmission line transformers for up to 100 kW pulsed power generation

Transmission line transformers (TLTs) are usually used for impedance match. In this paper, we present a novel circuit topology based on multiple switches and TLTs for both the impedance match and synchronization of multiple switches. In contrast to the Marx pulse generator, our proposed pulsed power systems produce high levels of pulsed power not only at higher voltages but also at higher currents.

Experimental program of the pulsed corona tar cracker

We are concentrating on the development of pulsed corona discharges to crack heavy tar components (hydrocarbons) into lighter ones. The method has the advantage that it can operate at a high temperature, and be retrofitted to existing installations. The corona discharge is energized by 100-150 ns wide voltage pulses (100 kV) at a continuous repetition rate of 600-1000 pulses per second. The power dissipated by the corona discharges is 1.5 kW average and 50 MW peak in each pulse. To be cracked by discharges, the hydrocarbons of the tar mixture need to be gaseous and therefore, the corona reactor must operate at a high temperature. In the first phase of the experiments the reactor will run at a modest temperature of 150/spl deg/C. The reactor is a 1-3 m long stainless steel cylinder, 0.25 m diameter with a corona wire along the axis. The pressure will be 1 atmosphere.

On-site voltage measurement with capacitive sensors on high voltage systems

In Extra/High-Voltage (EHV/HV) power systems, over-voltages occur e.g. due to transients or resonances. At places where no conventional voltage measurement devices can be installed, on-site measurement of these occurrences requires preferably non intrusive sensors, which can be installed with little effort under all circumstances. This paper presents three methods, which involve different algorithms based on a capacitive measuring system using simple design and easy-to-install sensors which couple with air-capacitors to the lines. Each capacitive sensor couples in principle to all phases. The presented methods differ in the pre-assumptions needed to determine the coupling matrix to reconstruct the phase-voltages, either power frequency, transient or resonant over-voltage on each of the three phases. The feasibility and the performance of the methods are discussed.

Repetitive pulsed power to serve nanotechnology, sustainability and hydrogen production

Repetitive pulsed-power has enormous enabling potential for a wide range of unconventional processes, such as nanotechnology, hydrogen production, gas and water processing and direct pulse interactions. The technology focuses on multiple switch concepts, a multiple pulsed plasma torch for thermal and nonthermal plasma and the combination of a near zero-erosion spark gap or an opening switch with a transmission line transformer.

A 2.0 kW pulsed corona system for inducing chemical reactions

This paper discusses a voltage pulse generator for producing streamer corona plasma. The generator consists of three resonant charging circuits, a transmission line transformer (TLT), and a self-triggered spark-gap switch. Voltage pulses in the order of 100 kV, rise time of 20-50 ns, pulse duration of 100-200 ns, pulse repetition rate of 1-1000 pps, corona energy of 0.5-3.0 J/pulse, and the average corona power of 2.0 kW have been achieved with total energy conversion efficiency of 65-85%. Detailed discussions on elements of the system are presented in this paper.