H. Heo

Experiments with a radial multichannel pseudospark switch for extremely high Coulomb transfer

Radial multichannel pseudospark switches for extremely high-charge transfer were designed, constructed, and tested. The characteristics of the switches were measured for different electrode geometries and materials in hydrogen and helium as function of gas pressure. The switches were operated in a 100 kJ capacitor bank and conducted an effective charge up to 31 C. A sealed-off radial multichannel pseudospark switch was also manufactured and tested with a 300 kJ capacitor bank. The switch was successfully tested up to 105 kA peak current and 78 C charge transfer. The experimental results demonstrated that a radial multichannel pseudospark switch with SiC electrodes and triggered by a high dielectric trigger has the capability of extremely high charge transfer under pulsed operation.

Development of Air Core Type 500 kV HV Pulse Transformer

Cylindrical type air core pulse transformers capable of passing high voltage and energy pulse waveforms with high efficiency and low distortion require a much more delicate design balance of physical dimensions and electrical parameters than iron or ferrite core units. The structure of an air core high voltage pulse transformer is relatively simple, but considerable attention is needed to prevent breakdown between transformer windings. Since the thickness of the windings in spiral type is on the order of sub-millimeter, field enhancement at the edge of the windings is very high. It is, therefore, important to find proper electrical insulation parameter to make the system compact. Several shapes of the winding are considered for air core pulse transformer development. Requirements of the transformer are 170 nH inductance at primary side, 500 kV. In this paper, we will describe a design procedure, parameters, measurement and experiment results of air core type 500 kV HV pulse transformer.

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It is our endeavor to develop switching technology for the breakdown reliability and reproducibility at extremely high voltages above 1 MV. One of the key objectives of the endeavor is to derive precise breakdown criteria for use in high-voltage applications. We have developed empirical criteria by which the breakdown field strength of a high-pressure SF_6-filled spark gap can be computed. The validity of the computed result has been verified with several experimental data from different investigators. The computed result has shown good agreement in an extended range of pd (pressure times gap distance) and field enhancement factor of the spark gap geometry. Furthermore, a spark gap has been designed and constructed with particular intention of generating a high-pulsed-power source in Pohang Accelerator Laboratory. In parallel, field modeling has been performed to verify the appropriate shape of the highly stressed insulator and electrode design in the spark gap and to evaluate their field enhancements. A series of breakdown voltage tests has demonstrated the function of the spark gap switch as intended up to 9 bars of SF_6. Aside from this, the limitation of the switching behavior has been examined with an aim of operating the designed spark gap to its maximum capability.

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An air-core strip-type high-voltage pulse transformer (HVPT) features a relatively simple structure in terms of design and fabrication. However, this HVPT requires considerable attention to prevent dielectric breakdown between the conductor windings. Because each spiral winding must be very thin, the field enhancement at the edges of the windings is very high. Therefore, it is important to develop proper methods to reduce the field enhancement factor and to prevent the dielectric breakdown at the winding edges. In this paper, in order to minimize the field enhancement, the proposed HVPT winding edges were folded, and each winding width was designed to decrease gradually to form a reverse trapezoid. These windings were insulated by multilayer insulators arranged in a specific manner. The requirement specifications are a maximum input voltage of 50 kV and an output voltage of 400 kV. This paper describes a design process and an electric field analysis to reduce the field enhancement. The simulation and experimental results confirmed the validity of the fabricated HVPT. The dielectric breakdown strength was tested up to 467 kV.

-Gas-Filled Spark Gap Switch for High-Voltage Application

We designed a fuse opening switch for the purpose of generation of high voltage pulses. The fuse opening switch was made with copper foil. The fuse opening switch was tested at a capacitor powered circuit discharged by a high current triggered vacuum switch. The experimental results were compared with simple numerical calculations. We measured several electrical parameters for a circuit composed of the fuse opening switch, a pulse transformer, and a peaking switch.

Minimized Field Enhancement Cylindrical Air-Core High-Voltage Pulse Transformer

We developed sealed-off type pseudospark switches for high current applications over 100 kA, with long pulse duration of several ms. We investigated the characteristics of sealed-off pseudospark switches, such as trigger delay times, hold-off voltages, peak currents, and effective charge transfer energy losses, recovery times. Effects of the electrode material and structure, power level of the switch reservoir, and vacuum conditioning of virgin electrodes as a method of electrode pretreatment are considered in this investigation. We also discuss the fabrication process of the high current sealed-off type pesudospark switches at the Pohang Accelerator Laboratory (PAL).

High Voltage Power Conditioning using a Fuse Opening Switch

To drive cathode of Magnetron Injection Gun (MIG), long pulse high voltage power supply (HVPS) is needed. HVPS have to be few seconds continuously -40 kV, 280 kW with rise and fall time less then 1 ms, and Included ripple stability of HV output is less than 1%. In order to develop HVPS, eight HVPSs are parallel operated by each power supply phase shifted PI control. HV pulse generation is performed by method ON and OFF of all HVPS gate drive pulse, simultaneity. Maximum output voltage and current of unit HVPS are -40kV and 1.2 A. In this paper, we will discuss topology, simulation and test results of HVPS.

Development status of the PAL sealed-off pseudospark switches

A multi-gap multi-channel (MGMC) switch of 500 kV has been developed at Pohang Accelerator Laboratory (PAL). It consists of ten of gaps to increase self-discharge voltage by filling up the gas. A structure of a multi-gap switch can increase its inductances. Thus, in order to solve those problems its structure made by multi-channels had been designed to decrease the inductance effects. The fabricated switch tested using marx generator of 500 kV. The design concept and its characteristics will be discussed.

Few seconds and −40kV compact high voltage pulse power supply

Summary form only given, as follows. We investigated a radial multi-channel pseudospark as a switch for pulsed power that has pulse durations of 1 ms and peak currents of 100 kA using 20 kJ, 100 kJ, and 300 kJ capacitor banks. The anode and the cathode were made of stainless steel, but the upper part of anode was made of SiC or CrCu for the purpose of reducing electrode erosion owing to low-pressure arc discharges. The hydrogen gas filled switch was triggered by a high dielectric trigger, which was explored by using optical and electrical measurements of the discharges for the development of a seal-off type switch with hydrogen reservoirs. The uniformity of discharges on each channel and the delay time or jitter were dependant on the gas pressure and the trigger biasing method. We discussed the switch characteristics and the arc dynamics between the upper parts of the electrodes.

Developments of 500 kV Multi-Channel Multi-Gap Self Breakdown

Summary form only given, as follows. An intense pulsed electron beam produced by a pseudospark discharge has been used for material processing. Such intense electron beams can be produced with high efficiency by a pulse charge mode pseudospark discharge. In this work, we experimentally investigated a pulse charge mode to generate enhanced pulsed electron beam from a 10-gap pseudospark device.